Showing papers in "The Journal of Physiology in 1971"

Voltage clamp studies of a transient outward membrane current in gastropod neural somata

Abstract: 1. Outward directed membrane currents have been studied in voltage clamp experiments on isolated neural somata of the marine gastropod Anisodoris. 2. Stepping the membrane potential from a hyperpolarized level to a value in the neighbourhood of resting potential (−35 to −50 mV at 5° C) results in an outward current transient, IA, which is apparently carried by potassium ions. 3. The peak amplitude of IA is dependent upon both the holding voltage level and the test step voltage while the time courses of development and decay are independent of, or only slightly dependent on, these parameters. 4. The developing and decaying phases of IA are approximated by exponentials, leading to time constants for development of 10–25 msec and for decay of 220–600 msec over the aggregate of cells studied (data at 5° C). Q10 for the processes is approximately 3. 5. It is concluded that the transport mechanism for IA is at least operationally distinct from the mechanism underlying delayed outward current, IK.

Sustained and transient neurones in the cat's retina and lateral geniculate nucleus.

Abstract: 1. Cat retinal ganglion cells may be subdivided into sustained and transient response-types by the application of a battery of simple tests based on responses to standing contrast, fine grating patterns, size and speed of contrasting targets, and on the presence or absence of the periphery effect. The classification is equivalent to the ;X'/;Y' (linear/nonlinear) subdivision of Enroth-Cugell & Robson which is thus confirmed and extended.2. The sustained/transient classification applied to both on-centre and off-centre cells.3. Lateral geniculate neurones may be similarly classified by the same tests. Occasional concentrically organized cells had a mixture of sustained and transient properties.4. A technique for simultaneous recording from a geniculate neurone and one or more retinal ganglion cells providing its excitatory input showed that the connexions were specific with respect to the sustained/transient classification as well as the on-centre/off-centre classification. Most geniculate neurones are excitatorily driven only by retinal ganglion cells of the same functional type. In a few cases the inputs were mixed but only with respect to the sustained/transient classification.5. Sustained retinal ganglion cells had slower-conducting axons than the transient type. The same was true for lateral geniculate neurones but in this case the distributions showed considerable overlap.6. The sustained/transient classification is the functional correlate for the well-known segregation of optic nerve fibres into two conduction groups.7. The pathways carrying sustained and transient information remain essentially separate from retina through the lateral geniculate nucleus to the striate cortex.

Receptive fields of cones in the retina of the turtle.

Abstract: 1. Intracellular recordings have been made of the responses to light of single cones in the retina of the turtle. The shape of the hyperpolarizing response to a flash depends on the pattern of retinal illumination as well as the stimulus intensity. 2. Although changes in the stimulus pattern can produce changes in the effective stimulus intensity, the responses to certain patterns cannot be matched by any adjustment of stimulus intensity. 3. The initial portion of responses to large or small stimulating spots is proportional to light intensity; this allows comparison of responses when the amount of light on a cone is kept constant but the light on surrounding cones is changed. For equal light intensity on the cone, the response to a spot 2 or 4 μ in radius is smaller than that to a spot 70 μ in radius. 4. Responses to spots 70 and 600 μ in radius coincide over their rising phases and peaks without any adjustment of stimulus intensity. The responses to the larger spot, however, contain a delayed depolarization not present with the smaller spot. 5. During steady illumination of a cone with a small central spot, the response to transient illumination superimposed on the same area is greatly reduced. Illumination of cones in the near surround, however, produces a hyperpolarizing response, and illumination of cones in the more distant surround generates a delayed depolarization. 6. The results described above suggested that synaptic signals might impinge on cones. This possibility was tested by electrically polarizing one retinal cell while recording from another. 7. Currents passed through a cone within 40 μ of another cone can change the membrane potential of the latter. Not all cones within this distance show the interaction, however, and it has never been detected at distances greater than 50 μ. 8. Hyperpolarization of a horizontal cell with applied current can produce a depolarization of a cone in the vicinity. During this depolarization, the response of the cone to a flash is reduced in size and altered in shape. 9. It is concluded that the response of a cone to light may be modified by synaptic mechanisms which are activated by peripheral illumination.

Prediction of repetitive firing behaviour from voltage clamp data on an isolated neurone soma

Abstract: 1. Membrane parameters of an isolated neural cell body have been determined by voltage clamp analysis. Data are expressed as membrane ion-specific conductances, leak conductance, and capacitance. 2. Three ionic currents are present: Inward, II; and two operationally distinct outward currents, IK and IA. Both outward currents are apparently carried by potassium ions. 3. Hodgkin—Huxley-like equations were solved for the discharge of two sequential action potentials in response to a constant stimulus current. The digital computer solutions are compared with action potential data recorded from the investigated cell. 4. The computed and experimentally measured relationships between firing frequency and stimulus current intensity are compared and are linear over the same portion of the total frequency range. 5. Cell behaviour in the latter part of the interspike interval is dominated by the conductance gA while gNa and gK largely determine the character of the action potential and the initial portion of the interspike interval. 6. Prehyperpolarization of the membrane activates gA and the membrane response to depolarizing current differs markedly from the response elicited when no prehyperpolarization is imposed.

The mechanism of excitation by acetylcholine in the cerebral cortex

Abstract: 1. The muscarinic depolarizing action of ACh on cortical neurones is associated with an increase in membrane resistance (mean DeltaV/DeltaR = 3.16 mV/MOmega).2. ACh also promotes repetitive firing by slowing repolarization after spikes.3. The depolarizing effect has a mean reversal level of -86.7 mV (with mean resting potential -56 mV).4. It is concluded that as a muscarinic excitatory agent, ACh probably acts by reducing the resting K(+) conductance of cortical neurones, and also the delayed K(+) current of the action potential.5. These results are discussed in relation to the possible role of ACh in cortical function.

Depolarization and calcium entry in squid giant axons.

Abstract: 1. Changes in ionized calcium in giant axons were followed by recording the light produced by injected aequorin.2. From the effect of injecting calcium buffers the internal concentration of ionized calcium was found to be about the same as in a mixture of 45 Ca EGTA:55 free EGTA, i.e. about 0.3 muM.3. After an axon had been exposed to cyanide for 50-100 min the velocity of the aequorin reaction increased about 500 times. This effect, which could be reversed rapidly by removing cyanide, was probably brought about by release of calcium from an internal store.4. Injecting 30 mumole ATP per litre of axoplasm into a cyanide-poisoned axon caused a transient lowering of light intensity; oligomycin blocked the effect.5. Raising external calcium or replacing external sodium by choline or lithium reversibly increased the light produced by axons injected with aequorin.6. Stimulation at 50-200 impulses/sec in a solution containing 112 mM-Ca caused the light intensity to increase to a new steady level; after stimulation the light intensity returned to its original level with a time constant of 10-30 sec. Similar but smaller effects were seen in solutions containing less external calcium. The recovery after stimulation is probably due to uptake of calcium by the internal store.7. Injecting 3 m-mole EGTA per litre axoplasm lowered the resting glow and abolished the aequorin response to stimulation.8. There was no light response to stimulation immediately after an axial injection of aequorin and the effect increased to a ;steady' level with a half-time of about 5 min. The conclusion is that the rise in calcium concentration resulting from stimulation is confined to the peripheral part of the axon and that the diffusion coefficient of aequorin in axoplasm is about 4 x 10(-7) cm(2)/sec.9. The increment in light per impulse often increased markedly during the course of a long experiment and there was also considerable variation between axons.10. If the light response to stimulation was small it was proportional to the frequency of stimulation; if large to the square of the frequency.11. Voltage-clamp experiments showed that the calcium entry associated with a depolarizing pulse could be divided into an early component which was abolished by tetrodotoxin (TTX), and a late component which was unaffected by this inhibitor.12. The time relations of the early calcium entry were consistent with its being a leak of calcium ions through the sodium channel; the permeability of the sodium channel to calcium was about 1% of the permeability to sodium.13. The late entry of calcium was little changed by injecting enough tetraethylammonium (TEA) to block the outward potassium current; it was greatly reduced by external concentrations of manganese which had little effect on the maximum potassium conductance.14. The voltage-response curve for the late entry of calcium had a well defined maximum and was similar in shape to the curve relating calcium entry to depolarization at the presynaptic ending (Katz & Miledi, 1969, 1970).

Observations on the control of stepping and hopping movements in man

Abstract: 1. The presence of a form of stretch reflex, previously described in the arm by other authors, has been confirmed in the gastrocnemius muscle of the human leg. The electromyographic (e.m.g.) manifestation of this reflex occurred 120 msec (S.E. of mean = 3.5 msec) following a sharply applied, and maintained, dorsiflexing force to the foot. This form of response is referred to in this article as the Functional Stretch Reflex (FSR).2. To determine the contribution of the FSR to the control of normal leg movement, the e.m.g. activity in the above muscle was monitored during single downward steps of 12.7, 25.4 and 38.1 cm and during repetitive, rhythmic, hopping movements on one foot.3. It was found that e.m.g. activity associated with steps to the ground began 141 msec (S.E. of mean = 8.5 msec) before contact with the ground and ended 131 msec (S.E. of mean = 7.6 msec) after contact, when the e.m.g. usually became temporarily inactive.4. It is inferred from these results that the muscular deceleration associated with landing was brought about by the release of a pre-programmed pattern of neuromuscular activity which was inaccessible to reflex activity resulting from the mechanical event of landing, rather than by a stretch reflex.5. It was found that subjects chose their preferred frequency of hopping with great accuracy and consistency. The mean value obtained was 2.06 Hz (S.E. of mean = 0.02 Hz).6. At the preferred frequency, e.m.g. activity began 84 msec (S.E. of mean = 9.6 msec) before and terminated 263 msec (S.E. of mean = 10 msec) after contact with the ground.7. It is inferred that in rhythmical hopping and perhaps also in running, each landing is effected, as in single steps, by a predetermined pattern of neuromuscular activity. However, when hopping at the preferred frequency, the take-off phase of muscular activity is timed to make maximal use of the FSR, i.e. between 120 and 260 msec after initial contact.8. The results emphasize the importance of pre-programming complex muscular contractions suitable for opposing sudden passive stretching forces, and of initiating them prior to the onset of these forces.

The reflex nature of the pressor response to muscular exercise.

Abstract: 1. In anaesthetized cats tetanic contraction of the hind-limb muscles, elicited by stimulating the ventral roots L6-S1, caused a rise of arterial blood pressure, usually accompanied by small increases in heart rate and pulmonary ventilation: in decerebrate cats, all components of the response were much increased.2. With tetani of different strengths, obtained by stimulating with different intensities at the same frequency, the pressor response increased with increasing tension.3. When muscle contraction had been abolished by gallamine, or when dorsal roots L6-S1 had been sectioned, ventral root stimulation no longer caused a pressor response. The response is therefore a reflex, initiated in the exercising limb.4. The pressor response was not affected by section of all articular nerves to knee and ankle joints, or by section of the vagi. The stimulus therefore originates in the contracting muscles alone.5. The pressor response is potentiated by occluding the circulation through the working muscles. Reasons are discussed for concluding that the stimulus is chemical rather than mechanical, and that the ;metabolic receptors' for this exercise reflex are the free endings of group III and IV sensory nerve fibres located around the blood vessels.

Evidence for central timing of rhythmical mastication

Abstract: 1. The origin of the co-ordination and rhythm of mastication provoked by electrical stimulation of the putamen and corticobulbar pathways was studied in the rabbit. 2. Bursts of activity were recorded from the mandibular and hypoglossal nerves and the hypoglossal nucleus, which were in phase with the observed masticatory movements. Discharges occurred alternately in nerves to jaw-opening and jaw-closing muscles. 3. The rate of burst discharges was not altered by paralysis, or by large variations in the stimulation frequency. 4. Regularly recurring bursts of activity continued to occur in the hypoglossal nucleus in response to random frequency stimulation after severing branchial nerves, cervical nerves and the spinal cord of paralysed rabbits. 5. Mechanical deformation of the brain of vascular or respiratory origin was discounted as the origin of the rhythm. 6. It is concluded that mastication is controlled by a brain-stem pattern generator which can be activated by adequate inputs from certain higher centres and, as concluded in other studies, from the oral cavity itself.

Micropuncture studies of the electrochemical aspects of fluid and electrolyte transport in individual seminiferous tubules, the epididymis and the vas deferens in rats.

Abstract: 1. Micropuncture and micro-analytical techniques were used to study some of the electrochemical aspects of fluid and electrolyte transport in single seminiferous tubules, the epididymis and vas deferens. 2. Seminiferous tubules contain a fluid that is slightly hypertonic to plasma, has a high potassium and chloride ion concentration, a lower sodium ion concentration and is slightly acidic relative to plasma. 3. The lumen of the seminiferous tubule is about 5 mV negative to a Ringers bathing solution. 4. Potassium and chloride ions enter the seminiferous tubule lumen against an electrochemical gradient, while the gradient for sodium ion favours its entry. This does not preclude possible active transport of sodium ion. 5. Between the seminiferous tubules and the beginning of the caput epididymis spermatocrit changes indicate that about 50% of the fluid leaving the testis is reabsorbed. Chloride ion and potassium ion are reabsorbed in concentrations greater than in lumen while sodium ion is reabsorbed in a concentration equal to that in the lumen. This region is also the site of intense hydrogen ion secretion. 6. The region between the seminiferous tubules and the caput is isopotential. Reabsorption of sodium and chloride ions are against electrochemical gradient. Potassium ion reabsorption is favoured by the electrochemical gradient. 7. Osmolar and electrical considerations indicate the probable secretion of organic acids between the seminiferous tubules and the caput epididymis. 8. Between the caput and the vas deferens 50% of the remaining fluid is reabsorbed. Sodium ion is reabsorbed in concentrations much greater than in lumen, potassium ion enters the lumen and the pH rises. Sodium reabsorption in this region is essentially independent of chloride reabsorption. 9. The corpus epididymis is 20 mV negative to a Ringers bathing medium while the beginning of the vas deferens is 27 mV negative. Reabsorption of sodium ion is against an electrochemical gradient as is potassium entry. Osmolality data and the concentration of sodium in the reabsorbate require further secretion of organic compounds in this region.

Recurrent inhibition of interneurones monosynaptically activated from group Ia afferents

Abstract: 1. Interneurones monosynaptically excited from large muscle spindle (Ia) afferents and inhibited from motor axon collaterals were searched for in the lumbar spinal cord of the cat. 2. Monosynaptic Ia excitation was found in sixty-seven of sixty-nine interneurones inhibited by antidromic volleys. These interneurones were excited from Ia afferents from one or a few muscles (mainly close synergists). Volleys in high threshold muscle and skin afferents (FRA) evoked polysynaptic excitation or inhibition. Weak inhibition from Ia afferents (from antagonists to those giving Ia excitation) was seen in a few cells. Monosynaptic excitation was evoked from the ventral quadrant of the spinal cord and polysynaptic excitation from the dorsal quadrant. 3. Inhibition from motor axon collaterals was evoked with a latency (1·2–2·0 msec) suggesting a disynaptic linkage and had the same time course as in motoneurones. It prevented synaptic activation of 60% of interneurones and decreased the firing index and delayed generation of spikes in the remaining. 4. The interneurones with convergence of monosynaptic Ia excitation and inhibition from motor axon collaterals were found in the ventral horn dorsomedial to motor nuclei. No inhibition by antidromic volleys could be detected in interneurones located in intermediate nucleus and activated monosynaptically from Ia, Ib, group I or cutaneous afferents. 5. It was concluded that the ventral Ia interneurones inhibited by volleys in recurrent motor axon collaterals mediate the reciprocal Ia inhibition to motoneurones.

Projection from low-threshold muscle afferents of hand and forearm to area 3a of baboon's cortex.

Abstract: 1. The precentral and postcentral banks of the Rolandic fissure of the arm area of the baboon's cortex have been probed to their depths with extracellular micro-electrodes under nitrous oxide and oxygen anaesthesia, supplemented by minimal intravenous pentobarbitone or chloralose. 2. Afferent volleys were sent in from the deep (motor) radial nerve and the deep palmar (motor) branch of the ulnar nerve. Their entry into the central nervous system was timed at the dorsal root entry zone. The nerves were stimulated in continuity and the effects of stimuli below threshold for the motor axons were investigated. 3. Area 3a, in the depths of the postcentral bank, which is cytoarchitectonically transitional between areas 3 and 4, is the receiving area for afferent impulses from muscle. 4. Evoked potential waves and unitary discharges began 4 msec, and the majority of units discharged between 5 and 10 msec, after the afferent volley reached the dorsal root entry zone. 5. Similar responses were elicited by a brief pull (70 μ in 1 msec) or brief vibration (50 μ at 250-400 Hz) applied to the tendons of m. extensor digitorum communis. 6. No potential waves were evoked in area 4, even in the depths adjacent to area 3a, by muscle afferent volleys.

The elastic constants of the human lens

Abstract: 1. When the lens is spun around its antero-posterior polar axis in an apparatus designed for the purpose, high speed photography can be used to record its changing profile. By this method a variable radial centrifugal force can be applied to the lens which mimics the pull of the zonule.2. If the lens is not stressed at its centre beyond 100 Nm(-2) it behaves as a truly elastic body. When stressed beyond this limit visco-elastic strain is produced at its poles.3. The human lens has isotropic elastic properties at the extremes of life, but at the other times Young's Modulus of Elasticity varies with the direction in which it is measured.4. Young's Modulus of Elasticity of the lens varies with age, polar elasticity and equatorial elasticity, at birth being 0.75 x 10(3) and 0.85 x 10(3) Nm(-2) respectively, while at 63 years of age both are equal to 3 x 10(3) Nm(-2).5. A comparison of Young's Modulus of the young human lens with that of the rabbit and cat shows that the polar elasticity of the lenses of these animals was 5 times greater in the young rabbit, and 21 times greater in the adult cat. Equatorial elasticities of the rabbit and human lens were equal, while in the cat the equatorial elasticity was four times greater.6. A mathematical model showing the lens substance possessing a nucleus of lower isotropic elasticity than that of the isotropic elastic cortex surrounding it, accounts for the difference between polar and equatorial elasticity of the intact adult lens.7. The implications of these findings are discussed in relation to:(i) accommodation and the rheological properties of the lens;(ii) possible differences in the physical state of the lenticular proteins in the cortex and nucleus which may account for the senile variations in Young's Modulus of Elasticity in these regions of the lens;(iii) the loss of accommodation due solely to an increase in Young's Modulus of Elasticity of the lens between the ages of 15 and 60. This would amount to 44% of the total observed in vivo.

Muscle spindle response at the onset of isometric voluntary contractions in man. Time difference between fusimotor and skeletomotor effects

Abstract: 1. Impulses in single muscle afferents were recorded from the median nerves of waking human subjects with percutaneously inserted tungsten needle electrodes. During isometric voluntary contractions, unitary discharges were analysed from muscle spindle endings in the wrist and finger flexor muscles and the electromyographic activity from these muscles was recorded simultaneously. 2. When the subject activated the muscle portion in which a spindle was located, the afferent discharge increased in spite of the mechanical unloading effects of the skeletomotor contraction indicating a concomitant fusimotor activation. This was valid for slowly rising contractions as well as small fast rising twitches. 3. The time of onset of spindle acceleration was determined in relation to the time of onset of the electromyographic activity for thirty-one units studied altogether in more than seven hundred contractions. It was found that spindle acceleration regularly occurred after the onset of the electromyographic activity. 4. There was a considerable variation from one test to the other, for the individual units, with regard to the exact time of onset of spindle acceleration, although spindle acceleration occurred mostly within 0·5 sec after the onset of the electromyographic activity in sustained contractions and within 0·1 sec in small fast rising twitches. It was not possible to assess to what extent this variation was accounted for by variations in the mechanical unloading effects of the skeletomotor contraction or variations in the timing of the fusimotor outflow. 5. For many units, spindle acceleration did not occur until 10–50 msec after the onset of the skeletomotor contraction. This time is of the same order of magnitude as the time difference in latency from the spinal cord to the recording points in the two systems, as estimated from reasonable assumptions. 6. It was concluded that the fusimotor system does not participate in the initiation of voluntary contractions in man, but that the skeletomotor activity is initiated by descending impulses from supraspinal structures and their effects on the neuronal organization within the spinal cord. 7. The fact that fusimotor activation occurs also in very small and short lasting twitches, when spindle acceleration must have a negligible influence on the skeletomotor outflow, suggests that the fusimotor and the skeletomotor systems are rigidly co-activated in voluntary contractions. 8. The finding that spindle acceleration does not occur until 10–50 msec after the onset of the electromyographic activity suggests that there is an approximately simultaneous onset of the fusimotor and the skeletomotor outflows from the spinal cord.

Electrical connexions between horizontal cells in the dogfish retina

Abstract: 1. In dogfish, studies were made of electrical connexions between pairs of cells giving S-potentials. After recording, the types and locations of the two cells were determined morphologically by electrophoretically injecting two different fluorescent dyes. 2. Hyperpolarizing S-potentials were observed in external and internal horizontal cells; depolarizing responses were seen in bipolar cells. All pairs of external horizontal cells examined were electrically coupled, i.e. intra-cellular polarization of one horizontal cell gave rise to polarization in its neighbour. Coupling was detected for cells separated by five other cells. The electrical coupling was non-rectifying. No coupling was found between external and internal horizontal cells or between external horizontal cells and bipolar cells. 3. Generally the smaller the distance between cells, the larger the coupling ratio, but some pairs of cells separated by similar distances showed widely different coupling ratios. 4. The coupling between cells was also demonstrated by the finding that Procion Yellow injected into one external horizontal cell diffused into one or two neighbouring external horizontal cells. It did not diffuse into internal horizontal cells or bipolar cells. 5. Close membrane apposition has been reported between neighbouring external horizontal cells, but not between these and either bipolar or internal horizontal cells. The distribution of electrical connexions observed in the present study agrees with these anatomical findings.

Effects on body temperature of prostaglandins of the A, E and F series on injection into the third ventricle of unanaesthetized cats and rabbits

Abstract: 1. Prostaglandins were injected into the third ventricle of unanaesthetized cats and rabbits whilst rectal temperature was recorded.2. In cats prostaglandin E(1) and E(2) (PGE(1) and PGE(2)) produced hyperthermia which mostly began within a minute of injection and lasted 1 or more hours. With PGE(1) the hyperthermia was shown to be dose dependent between 10 ng and 10 mug (2.8 x 10(-11) and 2.8 x 10(-8)M). The hyperthermia was associated with vigorous shivering, skin vasoconstriction and piloerection. In several experiments a secondary rise in temperature occurred a few hours after the injection but such an effect was sometimes observed with control injections of 0.9% NaCl solution as well.3. None of the other prostaglandins (A(1), F(1alpha), F(2alpha)) examined in cats had an immediate or strong effect on temperature comparable to the hyperthermia produced by PGE(1) and PGE(2).4. In rabbits PGE(1) (2 mug) also caused hyperthermia which began shortly after the injection and lasted for hours. PGF(2alpha) and PGA(1), did not affect temperature.5. In cats it was seen that an intraperitoneal injection of 4-acetamidophenol (paracetamol 50 mg/kg) did not affect the initial strong hyperthermia produced by PGE(1) and PGE(2) but abolished the secondary rise.6. The possibility is discussed that PGE(1) plays a role as a central transmitter or modulator in temperature regulation.

Inward and delayed outward membrane currents in isolated neural somata under voltage clamp

Abstract: 1. Membrane current—voltage relationships were investigated under voltage clamp conditions in isolated neural somata of marine gastropods. 2. Step depolarizations from the resting potential produce an initial inward current followed by a delayed outward current. 3. Inward current appears to be carried by both sodium and calcium ions and displays time and voltage dependent properties similar to those of other excitable membranes. 4. Activation and deactivation of the delayed outward current follow a more complicated time course than that of a single exponential raised to a power but can be fitted by the product of two exponential functions. 5. Delayed outward current inactivation proceeds with a time constant which decreases as membrane voltage is made more positive. The steady-state levels of inactivation as a function of membrane voltage are related by an S-shaped curve similar to that for K inactivation in squid giant axon.

Chloride conductance in normal and myotonic muscle fibres and the action of monocarboxylic aromatic acids

Abstract: 1. Cable parameters, component conductances, excitability and membrane potentials in isolated external intercostal fibre bundles at 38° C from normal and myotonic goats were measured in normal and low-chloride Ringer, and in the presence of monocarboxylic aromatic acids that produce myotonic responses in mammalian muscle. 2. The mean resting chloride conductance in μmho/cm2 of myotonic fibres (range 0-147) was significantly less than that of normal fibres (range 376-951). The mean resting potassium conductance was higher in myotonic fibres (range 123-285) than in normal fibres (range 44-132). Potassium conductance increased about 10 μmho/cm2 per mV increase in absolute resting potential. 3. In normal fibres in normal Ringer 3-chloro-2,5,6-trimethylbenzoic acid; 5,6-dihydro-5,5-dimethyl-7-carboxybenz[c]acridine; phenanthrene-9-carboxylic acid; and anthracene-9-carboxylic acid at 10-5-10-4 M decreased membrane conductance without consistently changing diameter or capacitance. In low-chloride Ringer 3-chloro-2,5,6-trimethylbenzoic acid (5 × 10-5 M) increased potassium conductance in myotonic and normal fibres. It is concluded that these compounds block chloride conductance. 4. The carboxylic acids produced myotonia in normal fibres similar to that in untreated myotonic fibres. 5. Anthracene-9-carboxylic acid intravenously (8 mg/kg) in normal goats produced acutely a condition resembling myotonia congenita. The carboxylic acids produced no myotonic effects in frog muscle.

Muscular control of landing from unexpected falls in man.

Abstract: 1 It was previously shown that the controlled landing from single steps to the ground is typically brought about by accurately timed motor activity, commencing before the actual landing, and completed before time would permit the participation of a useful stretch reflex response2 To investigate further the validity of this conclusion, subjects were dropped from an electromagnetic suspension at unexpected moments Their gastrocnemius electromyographic (emg) responses and the forces applied to their feet were recorded throughout3 No useful contribution of a stretch reflex response was detected Indeed, it was shown that a functionally effective reflex resulting from the mechanical event of landing would occur far too late to contribute to the muscular deceleration of the fall4 It was also found that a consistent muscular response occurred, commencing 742 msec (SE of mean = 14 msec) after starting the fall, independent of height5 It is suggested that this response in the leg musculature is a reflex originating in the otolith apparatus In addition, a possible mechanism for the control of repetitive hopping, and perhaps running, movements, involving the above reflex, is suggested

The transformation of myosin in cross‐innervated rat muscles

Abstract: 1. The characteristics of isometric twitch and tetanic contractions have been determined for normal (N-EDL, N-SOL), self-innervated (S-EDL, S-SOL) and cross-innervated (X-EDL, X-SOL) extensor digitorum longus (EDL) and soleus (SOL) muscles of the rat at 35° C. The muscles were then used for biochemical analyses of properties of myosin and actomyosin. 2. The ATPase activities of myosin and actomyosin of X-EDL decreased to the level of those of N-SOL or S-SOL, and the ATPase activities of X-SOL approached those of N-EDL or S-EDL. Of the various ATPase activities, the actin- and Mg2+-activated ATPase activity of myosin and the Mg2+-activated ATPase activity of actomyosin showed the highest degree of correlation with the intrinsic speed of shortening of the muscles. 3. Myosin of normal, self-innervated, and cross-innervated muscles combined with F-actin superprecipitated at rates which were proportional to the speed of muscle contraction. 4. The pH profile curve and the ATP-induced dinitrophenylation reaction revealed that the structure of myosin of X-EDL was altered to that of N-SOL or S-SOL, and the structure of myosin of X-SOL was modified to that of N-EDL or S-EDL. 5. No differences were found in the yield of myosin of normal, self-innervated, and cross-innervated extensor digitorum longus and soleus muscles.

Correlation between nerve terminal size and transmitter release at the neuromuscular junction of the frog

Abstract: 1. End-plate potentials were recorded intracellularly at the frog neuromuscular junction bathed in a solution containing a low concentration of calcium and a high concentration of magnesium.2. The muscle was subsequently subjected to ;cholinesterase staining', and the area of the individual end-plates, studied with intracellular electrodes, was measured.3. A positive correlation was found between the end-plate area and the diameter of muscle fibres.4. The mean quantum content (m) showed a positive correlation with the size of end-plates.5. The frequency of spontaneous miniature end-plate potentials was positively correlated with m as well as with end-plate area.6. It is concluded that the amount of transmitter released following nerve stimulation is related to the size of nerve endings.

Recurrent inhibition from motor axon collaterals of transmission in the Ia inhibitory pathway to motoneurones.

Abstract: 1. The effects of impulses in recurrent motor axon collaterals on reflex transmission from different types of primary afferents to motoneurones were investigated in the cat by conditioning of PSPs evoked in motoneurones. 2. IPSPs evoked by volleys in large muscle spindle (Ia) afferents were effectively decreased when preceded by an antidromic stimulation of ventral roots. Some IPSPs from group II muscle afferents and low threshold cutaneous afferents were also slightly depressed, while other PSPs were unaffected. 3. The depression of the IPSPs could be evoked by antidromic volleys, which produced neither conductance changes in the motoneurones nor depolarization of Ia afferent terminals. 4. The effect on the Ia IPSPs is most likely due to post-synaptic inhibition of the Ia inhibitory interneurones, evoked through α-motor axon collaterals and Renshaw cells. The depression of some IPSPs from flexor reflex afferents is explained by a convergence of excitatory effects from these afferents on the Ia inhibitory interneurones. 5. The results indicate a selective recurrent control from motor axon collaterals of the interneurones in the reciprocal Ia inhibitory pathway to motoneurones.

Relative contribution from different nerves to recurrent depression of Ia IPSPs in motoneurones

Abstract: 1. The pattern of depression of Ia IPSPs by volleys in recurrent motor axon collaterals was investigated in motoneurones supplying hind-limb muscles in the cat. The test IPSPs were evoked by stimulation of dorsal roots and the conditioning antidromic volleys by stimulation of motor fibres in different peripheral muscle nerves. 2. In all motor nuclei investigated the strongest depression of Ia IPSPs is evoked from motor fibres to muscles whose Ia afferents produce the IPSPs. For example, the Ia IPSP from the knee extensor recorded in motoneurones to a knee flexor is most effectively depressed by antidromic stimulation of motor fibres to the knee extensor. 3. The origin of recurrent inhibition of α-motoneurones and of Ia inhibitory interneurones with the same Ia input display a striking similarity. This suggests that the same population of Renshaw cells mediates effects to motoneurones and to Ia inhibitory interneurones. 4. The functional significance of impulses in motor axon collaterals was discussed and it was suggested that they have an important role in the control of the excitatory as well as inhibitory Ia actions to motoneurones. The recurrent inhibition may limit the Ia effects to excitation of homonymous motoneurones, which would provide optimal conditions for control of individual muscles via the γ-loop.

The orientation specificity of two visual after‐effects

Abstract: 1. Inspection of a high-contrast adapting grating produces two visual after-effects: (a) the contrast threshold is raised for test gratings of similar spatial frequency to that of the adapting pattern and (b) the apparent spatial frequency of test gratings shifts away from that of the adapting grating—higher frequencies seem higher and lower ones lower than they really are. 2. Both after-effects are orientation-specific. A horizontal adapting grating influences neither the threshold nor the apparent spatial frequency of vertical test gratings. 3. The magnitude of the two after-effects was measured with vertical test gratings as a function of (a) tilt of a high-contrast adapting grating and (b) contrast of a vertical adapting grating. 4. At all frequencies of the test grating, the decline of both after-effects produced by an increase in tilt of approximately 6¾° could be matched by a reduction in contrast by a factor of 2. 5. We take this as evidence for a common neural origin for these two visual phenomena.

Aberrant visual projections in the Siamese cat.

Abstract: 1. Guillery has recently shown that the Siamese cat has a grossly abnormal lateral geniculate body. His anatomical study suggested that certain fibres originating in the temporal retina of each eye cross in the chiasm instead of remaining uncrossed. They thus reach the wrong hemispheres, but in the geniculate they terminate in the regions that the missing fibres from the ipsilateral eye would normally have occupied. The result is that each hemisphere receives an input from parts of the ipsilateral field of vision, this input being entirely from the opposite eye. The purpose of the present work was to study the physiological consequences of this aberrant projection, in the lateral geniculate body and visual cortex.2. Single-cell recordings from the lateral geniculate body confirmed the presence of projections from the ipsilateral visual field of the contralateral eye. The part of layer A(1) receiving these projections was arranged so that the receptive fields of the cells were situated at about the same horizontal level and at the same distance from the vertical meridian as the fields of cells in the layers above and below (layers A and B), but were in the ipsilateral visual field instead of the contralateral. They thus occupied a region directly across the mid line from their normal position.3. In the cortex of all animals studied, we found a systematic representation of part of the ipsilateral visual field, inserted between the usual contralateral representations in areas 17 and 18. When the visual cortex was crossed from medial to lateral the corresponding region of visual field moved from the contralateral periphery to the mid line, and then into the ipsilateral field for 20 degrees . The movement then reversed, with a return to the mid line and a steady progression out into the contralateral field. The entire double representation was, with some possible exceptions, a continuous one. The point of reversal occurred at or near the 17-18 boundary, as judged histologically, and this boundary was in about the same position as in ordinary cats.4. Cells in the part of the cortex representing the ipsilateral fields had normal receptive fields, simple, complex, or hypercomplex. These fields tended to be larger than those in corresponding parts of the contralateral visual fields. Receptive-field size varied with distance from the area centralis, just as it does in the normal cat, so that cells with the smallest fields, in the area centralis projection, were situated some distance from the 17-18 border.5. Projections originating from the first 20 degrees from the midvertical in both visual half-fields had their origin entirely in the contralateral eye, as would be expected from the abnormal crossing at the chiasm. Beyond this visual-field region, and out as far as the temporal crescents, there were projections from both eyes, but we found no individual cells with input from the two eyes. The cells were aggregated, with some groups of cells driven by one eye and some by the other.6. From previous work it is known that ordinary cats raised with squint show a decline in the proportion of cells that can be driven binocularly, whereas animals raised with both eyes closed show little or no decline. A Siamese cat raised with both eyes closed had binocular cells in the regions of 17 and 18 subserving the peripheral visual fields, suggesting that the absence of binocular cells seen in the other Siamese cats was indeed secondary to the squint.7. In two Siamese cats there were suggestions of an entirely different projection pattern, superimposed upon that described above. In the parts of 17 and 18 otherwise entirely devoted to the contralateral visual field, we observed groups of cells with receptive fields in the ipsilateral field of vision. The electrode would pass from a region where cells were driven from some part of the contralateral visual field, to regions in which they were driven from a part of the ipsilateral field directly opposite, across the vertical mid line. The borders of these groups were not necessarily sharp, for in places there was mixing of the two groups of cells, and a few cells had input from two discrete regions located opposite one another on either side of the vertical mid line. The two receptive-field components of such cells were identical, in terms of orientation, optimum direction of movement, and complexity. Stimulation of the two regions gave a better response than was produced from either one alone, and the relative effectiveness of the two varied from cell to cell. These cells thus behaved in a way strikingly reminiscent of binocular cells in common cats.8. The apparent existence of two competing mechanisms for determining the projection of visual afferents to the cortex suggests that a number of factors may cooperate in guiding development. There seems, furthermore, not to be a detailed cell-to-cell specificity of geniculocortical connexions, but rather a tendency to topographic order and continuity, with one part of a given area such as 17 able to substitute for another. Whether or not these tentative interpretations are ultimately proved correct, it seems clear that this type of genetic anomaly has potential usefulness for understanding mechanisms of development of the nervous system.

The influence of wind resistance in running and walking and the mechanical efficiency of work against horizontal or vertical forces

Abstract: 1. O2 intakes were determined on subjects running and walking at various constant speeds, (a) against wind of up to 18·5 m/sec (37 knots) in velocity, and (b) on gradients ranging from 2 to 8%. 2. In running and walking against wind, O2 intakes increased as the square of wind velocity. 3. In running on gradients the relation of O2 intake and lifting work was linear and independent of speed. In walking on gradients the relation was linear at work rates above 300 kg m/min, but curvilinear at lower work rates. 4. In a 65 kg athlete running at 4·45 m/sec (marathon speed) VO2 increased from 3·0 l./min with minimal wind to 5·0 l./min at a wind velocity of 18·5 m/sec. The corresponding values for a 75 kg subject walking at 1·25 m/sec were 0·8 l./min with minimal wind and 3·1 l./min at a wind velocity of 18·5 m/sec. 5. Direct measurements of wind pressure on shapes of similar area to one of the subjects yielded higher values than those predicted from the relation of wind velocity and lifting work at equal O2 intakes. Horizontal work against wind was more efficient than vertical work against gravity. 6. The energy cost of overcoming air resistance in track running may be 7·5% of the total energy cost at middle distance speed and 13% at sprint speed. Running 1 m behind another runner virtually eliminated air resistance and reduced VO2 by 6·5% at middle distance speed.

The mechanism of acetylcholine release from parasympathetic nerves

Abstract: 1. The output of acetylcholine from the plexus of the guinea-pig ileum longitudinal strip has been used to study the mechanism of acetylcholine release. From the effects of hexamethonium and tetrodotoxin, it was inferred that 60% of the normal resting output is due to propagated activity in the plexus, and 40% to spontaneous release. Tetrodotoxin virtually abolishes the increase in output in response to electrical stimulation. 2. Resting acetylcholine output is increased when the bathing medium is changed in the following ways: (a) sodium replacement by sucrose, trometamol or lithium; (b) addition of ouabain or p-hydroxymercuribenzoate (PHMB), or withdrawal of potassium; (c) the combination of PHMB and partial sodium replacement; (d) addition of potassium; this increase in output becomes greater in the absence of sodium. 3. The resting output is virtually abolished by calcium withdrawal, and is restored by barium substitution for calcium. It is also reduced by raising the magnesium concentration. 4. The enhanced resting output in response to sodium withdrawal also occurs in the absence of calcium. 5. Cooling to 5° C greatly reduces both the resting output and the output in response to raised potassium concentration or to electrical stimulation. 6. The increase in resting output due to potassium excess is slight up to 25 m M [K+]o, but increases thereafter with about the fourth power of the potassium concentration; it is resistant to tetrodotoxin. 7. Synthesis of acetylcholine by the longitudinal strip is increased when output is enhanced by electrical stimulation, by potassium excess or by addition of barium, so that the acetylcholine content of the strip is maintained approximately normal. Synthesis is reduced, in relation to output, by potassium lack or by treatment with ouabain, and is virtually abolished by sodium withdrawal. 8. The theory is discussed that acetylcholine release depends on inhibition of the activity of a (Na+ + K+ + Mg2+)-activated ATPase at the axonal membrane.

The effect of calcium on the force-velocity relation of briefly glycerinated frog muscle fibres.

Abstract: 1. Twitch fibres were isolated from the semitendinosus muscles of frogs. The sarcolemma was made more permeable by a 30 min soak in a solution containing 47.3% glycerine (v/v), 2 mM-EGTA and 10 mM phosphate buffer, pH 7. This was followed by a 30-60 min soak in a solution containing the non-ionic detergent Lubrol-WX. The fibres were then placed in a relaxing medium containing (in mM): KCl, 100; MgCl(2), 1; ATP, 4; EGTA, 2; imidazole buffer, 10; pH 7.0.2. A piece of fibre about 1-2 mm long treated as described in (1) was attached to a servo apparatus. This apparatus made it possible either to hold fibre length constant giving isometric conditions, or alternatively to hold the force constant while measuring isotonic length changes. A special network made it possible to switch control from isometric to isotonic conditions so that afterloaded contractions with a shortening stop could be carried out.3. Contractions were induced at about 4 degrees C by lowering the pCa in the relaxing solution to various levels determined by the ratio of calcium and EGTA added. Contractions were never observed above pCa 7. The steady force generated reached a maximum over the range of pCa 6.09 to 5.49. The relationship between steady force generated and pCa is S-shaped and very steep, implying that multiple interacting binding sites for calcium are involved in the force generating process.4. The relative force-velocity relation is the same at pCa 6.09 and 5.49 where the steady force is at a maximum. The data points can be well fitted by a hyperbola in which the extrapolated value for V(max) is 2.39 muscle lengths/sec. The values obtained for the Hill parameters a/P(0) and b are within the range of those reported for living electrically excited frog muscle.5. The relative force-velocity points obtained at higher pCa values at which the steady force was on average 37% of that developed at pCa 5.49 can also be fitted by a hyperbola. However, the extrapolated value for V(max) is only 1.12 muscle lengths/sec. The value for a/P(0) is increased slightly and the value for b is markedly decreased.6. Evidence is presented against the possibility that an unrecognized fixed internal load is responsible for the change in the relative force-velocity relation obtained at high pCa.7. The relative force-velocity relation does not change appreciably over at least part of the range of sarcomere lengths in which the force generated varies linearly with overlap provided the pCa is held constant.8. The results support the view that lowering the pCa produces a mechanical state equivalent to that produced by tetanic electrical stimulation.9. Some models for calcium activation are discussed. It is concluded that a model based on calcium binding to troponin on the thin filaments is difficult to reconcile with all of the experimental evidence. There is additional evidence for believing that activating calcium may directly influence the cross-bridges.

Evidence against adrenergic motor transmission in the guinea-pig vas deferens

Abstract: 1. Field stimulation of desheathed preparations of guinea-pig vas deferens, treated with a ganglion-blocking agent, has revealed the presence of two tetrodotoxin-susceptible components in the motor response, suggesting the existence of two sets of post-ganglionic motor nerve fibres of different excitability: one set responding maximally to pulses of 0·1–0·4 msec; the other, to pulses of 2 msec. No distinction could be made pharmacologically between the two components. 2. Cooling potentiated that component in the twitch-responses which was due to stimulation of the more excitable fibres. 3. The sensitivity of the longitudinal muscle to the motor action of noradrenaline was low and was subject to considerable animal variation. But normal responses to post-ganglionic field stimulation were elicited in noradrenaline-insensitive preparations, in which the twitches elicited by 5 pulses could not be matched with noradrenaline, even 100–125 μg/ml. 4. In some forty experiments, small doses of noradrenaline inhibited the twitch-responses evoked by either set of motor fibres. This inhibition differed from that produced by isoprenaline in two respects. Firstly, propranolol did not antagonize the noradrenaline inhibition, thus excluding an action on β-adrenoceptors; and secondly, noradrenaline did not depress contractions elicited by muscarine or by 5-methylfurmethide. 5. Phenoxybenzamine, 10−6 g/ml., produced a thousandfold reduction in the sensitivity of the muscle to the motor action of noradrenaline, without any decrease in the height of the twitches elicited by 0·1 or 1 msec pulses. 6. The twitch-responses were not affected by combined α + β adrenoceptor blockade with phentolamine and propranolol. 7. Tyramine, amphetamine, tranylcypromine and prostaglandin E2 inhibited the twitches but potentiated the contractile effect of noradrenaline. 8. The twitch-responses and their inhibition by noradrenaline were present in preparations taken from reserpinized animals. 9. Although the twitch-responses could be paralysed by bretylium or guanethidine, the foregoing results excluded adrenergic transmission at the motor endings. Cholinergic transmission was also excluded by negative findings with anticholinesterases, atropine, nicotine and (+)-tubocurarine. 10. Motor transmission by histamine, 5-hydroxytryptamine, γ-aminobutyric acid or ATP was also excluded.

Switching of the respiratory phases and evoked phrenic responses produced by rostral pontine electrical stimulation

Abstract: 1. In midcollicular-decerebrate, gallamine-paralysed, vagotomized cats, efferent phrenic discharge was recorded as an indicator of the central respiratory cycle. Electrical stimulation (50-250/sec) delivered in the rostral lateral pontine ;pneumotaxic centre' region (in and near nucleus parabrachialis), and set to occur at specified times in the cycle, produced powerful respiratory effects: (a) at dorsolateral points, inspiratory-facilitatory effects (increase of phrenic discharge, shortening of the expiratory phase); (b) at ventrolateral points, expiratory-facilitatory effects (decrease of phrenic discharge, shortening of the inspiratory phase, lengthening of the expiratory phase).2. At both inspiratory-facilitatory and expiratory-facilitatory points, a single stimulus delivered during the inspiratory phase produced a short-latency (4-7 msec) reduction of phrenic discharge, followed by a wave of increased activity. The short latency of the response indicates the existence of paucisynaptic descending inhibitory pathways. Succeeding stimuli in a high-frequency train produced alternating waves of evoked activity and depression; the form of the responses depended on stimulus frequency and on locus of stimulation.3. At inspiratory-facilitatory points, short stimulus trains (10-30 stimuli) of adequate strength delivered in the middle and late expiratory phase caused early termination of the phase (latency 100-300 msec) and switching to a complete inspiratory phase, in which the phrenic discharge pattern resembled that in a normal inspiratory phase. Similarly, adequate stimulus trains applied at expiratory-facilitatory points during the middle and late inspiratory phase caused early termination of the phase and switching to a complete expiratory phase.4. The threshold for occurrence of each type of phase-switching response depended on stimulus current, frequency, number of stimuli, and time of stimulus delivery. As stimulus trains were delivered later in the phase, the threshold for switching to the succeeding phase was progressively reduced. Moreover, the nature of the evoked effects was a non-linear function of stimulus characteristics: a small increase of stimulus efficacy changed the system's response from (a) moderate shortening of the phase or transient change in phrenic discharge, to (b) complete termination of the phase.5. These results indicate that, as each respiratory phase progresses, there is a steady increase of excitability in systems which promote the onset of the succeeding phase. Further, the existence of a relatively sharp threshold for switching of the respiratory phases suggests that the phase transitions occur when critical levels of excitation and inhibition are reached synchronously in populations of respiratory neurones.