Showing papers in "The Journal of Physiology in 1973"

Long-lasting potentiation of synaptic transmission in the dentate area of the anaesthetized rabbit following stimulation of the perforant path.

Abstract: 1. The after-effects of repetitive stimulation of the perforant path fibres to the dentate area of the hippocampal formation have been examined with extracellular micro-electrodes in rabbits anaesthetized with urethane.2. In fifteen out of eighteen rabbits the population response recorded from granule cells in the dentate area to single perforant path volleys was potentiated for periods ranging from 30 min to 10 hr after one or more conditioning trains at 10-20/sec for 10-15 sec, or 100/sec for 3-4 sec.3. The population response was analysed in terms of three parameters: the amplitude of the population excitatory post-synaptic potential (e.p.s.p.), signalling the depolarization of the granule cells, and the amplitude and latency of the population spike, signalling the discharge of the granule cells.4. All three parameters were potentiated in 29% of the experiments; in other experiments in which long term changes occurred, potentiation was confined to one or two of the three parameters. A reduction in the latency of the population spike was the commonest sign of potentiation, occurring in 57% of all experiments. The amplitude of the population e.p.s.p. was increased in 43%, and of the population spike in 40%, of all experiments.5. During conditioning at 10-20/sec there was massive potentiation of the population spike (;frequency potentiation'). The spike was suppressed during stimulation at 100/sec. Both frequencies produced long-term potentiation.6. The results suggest that two independent mechanisms are responsible for long-lasting potentiation: (a) an increase in the efficiency of synaptic transmission at the perforant path synapses; (b) an increase in the excitability of the granule cell population.

Physiological types and histochemical profiles in motor units of the cat gastrocnemius.

Abstract: 1. A variety of physiological properties of single motor units have been studied in the gastrocnemius muscle (primarily in the medial head) of pentobarbitone-anaesthetized cats. Intracellular stimulation of individual motoneurones ensured functional isolation of the muscle units innervated by them. 2. A system for muscle unit classification was developed using a combination of two physiological properties. Almost all of the units studied could be classified into one of three major types, including two groups with relatively short twitch contraction times (types FF and FR, which were differentiable from one another on the basis of sensitivity to fatigue) and one group with relatively long contraction times (type S, which were extremely resistant to fatigue and were differentiable from FF and FR units on the basis of the shape of unfused tetani). Post-tetanic potentiation of twitch responses was observed in all three muscle unit types. The distributions of axonal conduction velocities for motoneurones innervating FF and FR muscle units were essentially the same, while conduction velocities for motoneurones innervating type S units were, in general, slower. 3. Histochemical profiles of muscle units representative of each of the physiological classes present in the gastrocnemius pool were determined using a method of glycogen depletion for muscle unit identification. Each of the physiological categories of muscle units exhibited a corresponding unique set of muscle fibre staining reactions, or histochemical profile. Within each physiological type, all of the units examined had the same histochemical profile. The results generally support the hypothesis that the histochemical characteristics of muscle fibres are meaningfully related to the physiological properties of the same fibres. However, certain limitations in the detailed application of the hypothesis were also apparent. 4. Systematic assessment of the histochemical profiles of relatively large numbers of fibres belonging to single muscle units provided strong support for the hypothesis that all of the muscle fibres innervated by a single α-motoneurone are histochemically identical.

Voltage clamp analysis of acetylcholine produced end-plate current fluctuations at frog neuromuscular junction

Abstract: 1. Acetylcholine produced end-plate current (e.p.c.) noise is shown to be the results of statistical fluctuations in the ionic conductance of voltage clamped end-plates of Rana pipiens. 2. These e.p.c. fluctuations are characterized by their e.p.c. spectra which conform to a relation predicted from a simple model of end-plate channel gating behaviour. 3. The rate constant of channel closing α is determined from e.p.c. spectra and is found to depend on membrane potential V according to the relation α = BeAV (B = 0·17 msec−1±0·04 S.E., A = 0·0058 mV−1±0·0009 S.E. at 8° C) and to vary with temperature T with a Q10 = 2·77, at −70 mV. A and B in this expression both vary with T and therefore produce a membrane potential dependent Q10 for α. 4. Nerve-evoked e.p.c.s and spontaneous miniature e.p.c.s decay exponentially in time with a rate constant which depends exponentially on V. The magnitude and voltage dependence of this decay constant is exactly that found from e.p.c. spectra for the channel closing rate α. 5. The conductance γ of a single open end-plate channel has been estimated from e.p.c. spectra and is found not to be detectibly dependent on membrane potential, temperature and mean end-plate current. γ = 0·32±0·0045 ( S.E.) × 10−10 mhos. Some variation in values for γ occurs from muscle to muscle. 6. It is concluded that the relaxation kinetics of open ACh sensitive ionic channels is the rate limiting step in the decay of synaptic current and that this channel closing has a single time constant. The relaxation rate is independent of how it is estimated (ACh produced e.p.c. fluctuations, e.p.c., m.e.p.c.), and is consistent with the hypothesis that individual ionic channels open rapidly to a specific conductance which remains constant for an exponentially distributed duration. 7. The voltage and temperature dependence of the channel closing rate constant agree with the predictions of a simple dipole-conformation change model.

The orderly recruitment of human motor units during voluntary isometric contractions

Abstract: 1. The contractile properties of human motor units from the first dorsal interosseus muscle of the hand were studied during voluntary isometric contractions using recently developed techniques. 2. The twitch tensions produced by motor units varied widely from about 0·1–10 g. The twitch tension of a motor unit varied nearly linearly as a function of the level of voluntary force at which it was recruited over the entire range of forces studied (0–2 kg). 3. The number of additional motor units recruited during a given increment in force declined sharply at high levels of voluntary force. This suggests that even though the high threshold units generate more tension, the contribution of recruitment to increases in voluntary force declines at higher force levels. 4. Contraction times for these motor units varied from 30 to 100 msec. Over 80% had contraction times less than 70 msec, and might be classed as fast twitch motor units. The larger motor units, which were recruited at higher threshold forces, tended to have shorter contraction times than the smaller units.

Psychophysical evidence for sustained and transient detectors in human vision

Abstract: 1. The sensitivity to temporally modulated sinusoidal gratings was determined. Two thresholds could be distinguished for the modulated gratings: the contrast at which flicker could be perceived and the contrast at which the spatial structure became distinct.2. The flicker detection thresholds and pattern recognition threshold varied independently as functions of the spatial and temporal frequencies, suggesting that the two thresholds represent the activity of two independent systems of channels.3. The channels detecting flicker prefer low and medium spatial frequencies. They have a pronounced decline in sensitivity at low temporal frequencies of sinusoidal modulation. They respond twice as well to gratings whose phase is alternated repetitively as to gratings turned on and off at the same rate.4. The channels responsible for the discrimination of spatial structure are most responsive at high and medium spatial frequencies. There is no decline in sensitivity at low temporal frequencies. These channels respond equally well to alternating and on/off gratings up to about 8 Hz.5. The temporal properties as revealed with sinusoidal modulation, suggest that the flicker-detecting channels would give transient responses to prolonged presentation of stimuli: the channels responsible for analysing the spatial structure would give sustained responses. The responses of the two types of channel to alternating and on/off gratings confirm this suggestion.

The binding of acetylcholine to receptors and its removal from the synaptic cleft

Abstract: 1. Acetylcholine (ACh) noise and miniature end-plate potentials were recorded with focal external micro-electrodes.2. The effect of prostigmine on the time course of the ;molecular' and ;quantal' transmitter actions was studied. Prostigmine (10(-6) g/ml.) has little or no effect on the duration of the molecular ;gating action', while it greatly prolongs the quantal conductance change.3. After inhibition of ACh hydrolysis, the removal of the transmitter from the synapse is generally too slow to be accounted for by free diffusion. It is suggested that diffusion is delayed by binding to post-synaptic receptors. This is consistent with the finding that receptor blockage by curare or alpha-bungarotoxin shortens as well as reduces quantal transmitter action.4. The correlated effects of the receptor-blocking agents, on size and time course of the miniature end-plate currents, were subjected to a simple analysis. Its result suggests that after inhibition of cholinesterase about two thrids of the quantal packet of ACh combines with post-synaptic receptors.5. During focal external recording the effect of prostigmine on the time course of miniature end-plate potentials can become exaggerated due to what appears to be a compression artifact which obstructs outward diffusion of the transmitter.

Changes in firing rate of human motor units during linearly changing voluntary contractions.

Abstract: 1. Human subjects generated approximately linearly increasing or decreasing voluntary, isometric contractions using the first dorsal interosseus muscle of the hand. 2. Single motor units began firing at 8·4±1·3 impulses/sec (mean ± S.D. of an observation) and increased their firing rate 1·4±0·6 impulses/sec for each change of 100 g in voluntary force. These values were independent of the threshold force for recruiting motor units. 3. At intermediate rates of increasing and decreasing voluntary force (one complete cycle every 10 sec) the firing rate of single motor units varied linearly with force over the entire range of forces studied. However, during slow increases in voluntary force, the firing rate tended to reach a plateau, while during rapid increases an initial train of impulses at a roughly constant rate was observed. 4. The relative importance of recruitment and increased firing rate, as mechanisms for increasing the force of voluntary contraction, was determined. Only at low levels of force is recuitment the major mechanism. Increased firing rate becomes the more important mechanism at intermediate force levels and contributes the large majority of force if the entire physiological range is considered.

The contractile properties of human motor units during voluntary isometric contractions

Abstract: 1. The electrical activity of single motor units has been recorded from the first dorsal interosseus muscle of normal human subjects during voluntary, isometric contractions, together with the force generated by the muscle.2. By averaging the force correlated with the impulses from a single motor unit, the contraction time and twitch tension generated by that motor unit could be measured. When the rate of discharge was limited, either voluntarily or by automatic selection of intervals for analysis, the time for the tension to decline to half its maximum value (half-relaxation time) could also be measured for some motor units.3. Under our experimental conditions the trains of impulses from different motor units in most subjects were generated quite independently as tested by (a) measuring the correlation between activity in single units and that in the whole muscle as recorded by the surface electromyogram (e.m.g.), (b) measuring the cross-correlations between pairs of single units and (c) comparing the tension generated by stimulating single motor units with the average tension correlated in time with voluntary activity of single units in the same location.4. In one normal subject evidence of synchronization between separate motor units was obtained. Cross-correlation studies suggested that the cause of the synchronization was the presence of substantial common excitation received by the various motor units in the muscle.5. The frequency response for the contractions of single motor units was well fitted by that for a linear, second-order system with nearly critical damping. However, when stimulation of a few motor units was superimposed on a voluntary contraction, underdamped (oscillatory) responses were seen which were probably of reflex origin.6. The significance of these results in relation to the normal postural tremor in hand muscles is discussed.

Intracellular recording from the myenteric plexus of the guinea-pig ileum.

Abstract: 1. Ganglion cells of the myenteric plexus of the guinea-pig ileum have been studied with intracellular micro-electrodes.2. Three types of cell were distinguished. Type 1 cells had a high resistance (58 MOmega) and had properties similar to guinea-pig sympathetic ganglion cells. Type 2 cells were also excitable but had a lower resistance (21 MOmega) and showed accommodation to depolarizing current pulses. Type 3 cells were inexcitable.3. Point stimulation within 150 mum excited neurones either antidromically or orthodromically, sometimes both.4. Antidromic responses had a small all-or-nothing component which was subthreshold for the soma spike. Two or more such components sometimes occurred, and were probably due to stimulation of two or more cell processes.5. Excitatory post-synaptic potentials (e.p.s.p.s) were blocked by hexamethonium (400 muM). They progressively declined in amplitude when elicited at frequencies of 0.05 Hz or more, and this is discussed in relation to studies on acetylcholine (ACh) output.6. Many cells often showed a slow after-hyperpolarization following a direct or antidromic spike. Its mechanism and significance are discussed.7. Spontaneous e.p.s.p.s and spikes were occasionally seen.8. Intracellular injection of a fluorescent dye reveals that the neurones have one to seven processes, which usually arise from the poles of the oval soma.

Detection and resolution of visual stimuli by turtle photoreceptors.

Abstract: 1. Hyperpolarizing responses up to 30 mV in amplitude were recorded from cones and from certain cells believed to be rods in the isolated retina of the swamp turtle, Pseudemys scripta elegans.2. The responses evoked by weak flashes of light reach their maximum in 100-140 msec in red-sensitive cones, 140-180 msec in green-sensitive cones, and 300-600 msec in the rod-like cells (20 degrees C).3. The cone response evoked by weak flashes of light is linearly related to light intensity and obeys the superposition principle in that the response to a very weak step of light is the integral of the response to a very weak flash.4. On the basis of their spectral sensitivities cones can be divided into three distinct classes, namely red-sensitive cones whose relative quantum sensitivity is maximal at 630 nm, green-sensitive cones with a maximal sensitivity at 550 nm and blue-sensitive cones with a maximum at 460 nm.5. The difference between the spectral sensitivity of rods with a maximum at about 520 nm and green-sensitive cones (lambda(max) = 550 nm) is consistent with the view that both receptors contain a 518(2) retinal pigment as reported by Liebman & Granda, but that light is filtered by an orange oil droplet in green-sensitive cones.6. The spectral sensitivities of both red- and green-sensitive cones agree well amongst themselves at long wave-lengths but differ markedly in the extent of the reduction at short wave-lengths. This variation is attributed to differences in the extent to which light is filtered through the coloured oil droplets.7. There is a significant positive correlation between the absolute sensitivity of red- and green-sensitive cones and the reduction in sensitivity at short wave-lengths. This would be explained if a greater fraction of the light passes through the oil droplet in the most sensitive cells.8. The absolute flash sensitivities of the most sensitive receptors were about 250 muV photon(-1) mum(2) in red- and green-sensitive cones, 120 muV photon(-1) mum(2) in blue-sensitive cones, and 1300 muV photon(-1) mum(2) in rods.9. If the effective collecting area (which includes factors for absorption etc.) is taken as 10 mum(2) in a red-sensitive cone the peak hyperpolarization produced by 1 photon would average 25 muV.10. Provided that small spots of light are used, individual receptors obey the ;univariance principle' and the response produced by light of strength I', and wave-length lambda(1) can be matched by a light of strength kI' and wave-length lambda(2), where k is the same for all values of I'.11. A small proportion of cones behave like isolated units in that they have very sharp sensitivity-profiles and obey the univariance principle with respect to the position as well as to the wave-length of light.12. The majority of red and green cones have more diffuse sensitivity-profiles, sometimes with bumps on the descending limb, and behave as though cones with the same spectral sensitivity were electrically coupled to one another.13. The relation between the area of illumination and flash sensitivity agreed approximately with that calculated from the spatial profile.

The interaction of sodium and potassium with the sodium pump in red cells

Abstract: 1. At high internal K concentrations the efflux of Na from red cells increases with internal Na concentration following an S-shaped curve. As internal K is reduced the S-shaped region and the value of internal Na for which the Na efflux is half-maximal are both shifted progressively towards zero. 2. The effects of internal Na on the shape of the Na efflux curves can be quantitatively accounted for if it is assumed that the rate of Na efflux is linearly related to the number of pump units having three identical and non-interacting sites occupied by Na. 3. The effects of internal K on the shape of the Na efflux curves are fully explained if it is assumed that the inner sites for Na of the Na pump also behave as identical and non-interacting sites for internal K, being the K-carrier complexes unable to promote Na translocation. The apparent affinity of the Na pump for internal K is about 50 times less than for internal Na. 4. Internal K not only alters the apparent affinity of the Na pump for Na, but also affects its turnover rate. The turnover rate of Na: K exchange increases with internal K following a curve which saturates at about 30 m M internal K. The turnover rate for Na:Na exchange increases linearly with internal K. 5. The linear dependence of the rate of Na:Na exchange on internal K explains why, when internal Na is increased at the expense of internal K, the rate of Na:Na exchange progressively decreases after passing through a maximum. 6. The effects of external Na on the rate of Na:Na exchange can be satisfactorily explained assuming that they are due to the occupation by external Na of three identical and non-interacting sites on each pump unit. The apparent affinity of the Na pump for external Na is about 160 times less than the apparent affinity for internal Na. 7. Under all the experimental conditions tested, it was found that the relation between flux and cation concentration at one of the surfaces of the cell membrane is altered only by a constant factor by changes in the cation composition at the opposite surface of the cell membrane. This fact strongly suggests that there are no interactions between the inner and outer sites of the Na pump. 8. The effects of inner and outer cations on both the Na:K and the Na:Na exchanges catalysed by the Na pump suggest that cation fluxes are proportional to the number of pump units having its inner and outer sites simultaneously occupied by the relevant cations. It seems therefore that sequential models for ion transort do not provide an adequate description of the molecular mechanism of active transport in red cells.

Separate channels for the analysis of the shape and the movement of a moving visual stimulus

Abstract: 1. The effects of temporal modulation on the properties of spatial frequency channels have been investigated using adaptation. 2. Adapting to drifting sinusoidal gratings caused threshold elevation that was both spatial frequency and direction specific. Little systematic difference was found between the band widths of the elevation curves for drifting and stationary gratings. 3. It was confirmed that adaptation fails to reveal channels at low spatial frequencies when stationary gratings are used. However, channels were revealed at frequencies at least as low as 0·66 c/deg when the test gratings were made to move. These channels are adapted only a little by stationary gratings, confirming their dependence on movement. 4. The existence of movement-sensitive channels at low spatial frequencies explains the well known observation that temporal modulation greatly increases the sensitivity of the visual system to low spatial frequencies. 5. Temporal modulation was effective at revealing these channels only when the flicker or movement of the test patterns was apparent to the observer; only at low spatial frequencies did patterns, modulated at low rates, actually appear to be temporarily modulated at threshold. At higher spatial frequencies, they were indistinguishable from stationary patterns until the contrast was some way above the detection threshold. 6. It is suggested, therefore, that the movement-sensitive channels are responsible for signalling the occurrence of movement; the channels at higher spatial frequencies give no information about temporal changes. These two systems of channels are compared to the Y- and X-cells respectively of the cat.

Dependence on calcium concentration and stoichiometry of the calcium pump in human red cells.

Abstract: 1. In resealed human red cells loaded with Ca-EGTA buffer solutions it was found that the intracellular free Ca2+ concentration for half saturation of the Ca transport system (which pumps Ca out of the cell) is equal to or smaller than 4 × 10−6 M and thus closely agrees with the dissociation constant of the Ca + Mg activated membrane ATPase. 2. The maximal rate of Ca transport from resealed cells to medium was found to be 0·148 ± 0·009 μmole/ml. cells.min at 28° C. 3. The rate of Ca transport was unaffected by a variation of the extracellular Ca2+ concentration from 3·10−7 to 5·10−3 M. 4. Evidence is presented making it probable that the stoichiometric relation between Ca transported and ATP hydrolysed is 1:1 rather than 2:1. 5. As the Ca transport is quite rapid even at half saturation and the passive leak for Ca negligible in intact cells it can be predicted that the steady-state cellular Ca2+ concentration must be low, most probably less than 10−6 μmole/ml. cells. Transport from cells containing 5·10−7 μmole/ml. into blood plasma is thermodynamically compatible with the normal plasma Ca2+ concentration and the normal cellular ATP, ADP and Pi content. 6. Treatment with the mercurial PCMBS in the cold for 15 hr allows to load red cells with 1 μmole Ca/ml. cells without destroying their ability to transport Ca after removal of the mercurial. 7. It is shown that at high cellular Ca concentrations (0·1–3 μmole/ml. cells) about 50% of the total is free Ca2+ on account of binding mainly to dialysable cell constituents.

Changes in the statistics of transmitter release during facilitation

Abstract: 1. The statistical nature of transmitter release during facilitation was studied at single synaptic sites by recording extracellular excitatory junctional potentials from the claw opener muscle in crayfish. 2. At low temperatures, single quanta could be counted in the responses to nerve impulses. The distribution of the number of quanta observed (x) was most accurately described by assuming that x is a binomial random variable. 3. A quantitative estimate was made of the effects of errors in counting quanta due to the simultaneous release of quanta and the release of quanta which were not individually detectable above the noise of the recording system. Such errors of observation cannot account for the deviation of quantal release from a Poisson distribution. 4. Facilitated release occurred in the responses to the second of two closely following nerve impulses and in the responses to successive impulses in a tetanus. In both cases, the increase in the average number of quanta released (m) could be attributed entirely to an increase in the probability (p) that available quanta were released. 5. The results can be interpreted most easily in terms of a model in which the maximum number of releasable quanta is limited by a finite number of discrete release sites within recording distance of the microelectrode. In this model, the binomial parameter n is an estimate of the number of these sites, and the statistical parameter p is a compound probability depending on the rate of re-occupying sites after a nerve discharge and the probability that an impulse activates an occupied site.

Anatomy and innervation ratios in motor units of cat gastrocnemius.

Abstract: 1. Muscle fibres belonging to single motor units of identified type were studied in frozen sections of cat medial and lateral gastrocnemius muscles. Reconstruction of the distribution of fibres in individual units showed that the territories of all three physiological types present in the cat medial gastrocnemius were quite extensive. Within its territory, fibres belonging to the studied unit were distributed more or less uniformly without localized collections. The density of unit fibres suggests that, in cat medial gastrocnemius, a given region of the muscle may be shared by as many as fifty different muscle units.2. Direct determination of innervation ratios in identified muscle units required complete reconstruction of the three-dimensional distribution of unit fibres within the whole medial gastrocnemius. Satisfactory results were obtained with two type FF units and one type FR unit.3. Indirect estimates of the average innervation ratios expected for muscle units of different physiological type were obtained using counts of muscle fibres with characteristic histochemical profiles and data on relative frequencies of motor units of known type in the medial gastrocnemius unit pool. Such indirect estimates of innervation ratios agreed with the results of direct fibre counts in identified units for types FF and FR muscle units. Taken in sum, the available evidence suggests that an average muscle unit in the cat medial gastrocnemius contains between 400 and 800 muscle fibres, irrespective of physiological type.4. Tension production by single muscle units depends on a number of factors, including innervation ratio, the cross-sectional areas of unit fibres and the specific tension outputs of the unit fibres. The present results suggest that the specific tension output of gastrocnemius type S unit muscle fibres is considerably smaller (about 0.6 kg/cm(2)) than in either FF units (about 1.5-2.0 kg/cm(2)) or type FR units (2.6-2.9 kg/cm(2)).

Properties of sustained and transient ganglion cells in the cat retina

Abstract: 1. The functional basis for a sustained/transient classification of cat retinal ganglion cells has been strengthened by quantitative measurements of the sizes of the centre and surround components of receptive fields. Transient cells had larger surrounds than sustained; the distributions were non-overlapping. Although the distributions of centre sizes overlapped, the transient cells had very significantly larger centres on average. 2. There were characteristic differences in area-threshold and annulus-threshold curves and shapes of responses to brief and long flashes of light, and relative differences in the nature of surround adaptation and maintained discharge rates. 3. The distinction of sustained from transient units survived over a wide range of backgrounds including the two principle reorganizations of function: relative weakening of surround components at low background; Purkinjě shift at high. 4. Sustained and transient units were differentially distributed in the retina: there was an overwhelming preponderance of sustained units in the area centralis. 5. It is proposed that the transient units are the so-called multidendritedeep cells and the sustained units are the variously styled small ganglion cells.

Nervous activity of afferent cardiac sympathetic fibres with atrial and ventricular endings.

Abstract: 1. We recorded the electrical activity of single afferent cardiac fibres isolated from the third and fourth left thoracic sympathetic rami communicantes of anaesthetized cats. Their conduction velocities ranged from 12 to 32 m/sec.2. The endings of each fibre were localized to one cardiac chamber by mechanical probing of the opened heart performed at the end of the experiment.3. The impulse activity was spontaneous and, in fibres with atrial or ventricular endings, it was in phase with a particular atrial or ventricular event.4. This nervous activity increased during increases in pressure occurring in the chamber where the endings were located. Conversely, decreases in pressure were accompanied by decreased nervous discharge.5. In some experiments the left coronary artery was perfused at different flows and pressures. Brief decreases or increases in coronary flow and pressure decreased or increased, respectively, the discharge of fibres with atrial or ventricular endings. Fibres were excited by intracoronary injections of veratridine.6. Cessation of coronary pump flow increased the discharge of fibres with atrial or ventricular endings only when myocardial ischaemia was accompanied by signs of heart failure.7. These afferent cardiac sympathetic fibres which provide the spinal cord with continuous specific information on cardiac events are likely to contribute to the neural control of circulation.

Receptive fields of simple cells in the cat striate cortex

Abstract: 1. The excitatory and inhibitory components in the receptive fields of unimodal simple cells in the striate cortex of the cat anaesthetized with nitrous oxide have been described using slits of light and single light-dark edges as stimuli. 2. There is a small excitatory region (excitatory complex) centrally located in the receptive field that is made up of various combinations and spatial arrangements of subliminal excitatory and discharge subregions or centres. 3. The subliminal excitatory centres were revealed by a binocular facilitation technique. The excitability of the cell was raised by repeated stimulation via one eye while the neurone was tested with single edges via the other eye. 4. The subliminal excitatory and discharge centres are each specifically activated by only one type of edge, light-dark or dark-light, and then only in one direction of motion. All the subregions in the excitatory complex have the same optimal stimulus orientation. 5. Inhibitory components in the receptive field were identified by stimulating the cell with bars of light and single edges against an artificial background discharge produced by repeated stimulation separately applied either to the same eye (monocular conditioning) or to the other eye (binocular conditioning). There are powerful inhibitory sidebands to either side of the excitatory complex and these inhibitory regions merge to include the excitatory complex when stimulus orientation is angled away from the optimal. 6. Excitation is highly stimulus specific whereas inhibition is non-specific. 7. The organization of the two receptive fields of a binocularly discharged cell can be closely similar. 8. The attempt is made to translate the concept of subliminal excitatory and discharge centres into specific neural mechanisms involving both the geniculo-cortical input and various intracortical circuits. 9. These new developments call for only minor modifications to the model we have proposed for the organization of the receptive field.

Receptive field organization of bipolar and amacrine cells in the goldfish retina

Abstract: 1. Intracellular recordings were made from bipolar and amacrine cells in the isolated goldfish retina. Cells were identified mainly from their response patterns to a spot and an annulus in reference to the knowledge obtained from the previous work of intracellular Procion Yellow injection. Using white light and monochromatic lights receptive field organization of recorded cells were analysed. 2. All bipolar cells had a centre-surround organization in their receptive fields. The field centre was estimated to be 100–200 μm in diameter, and the surround 1–1·5 mm. 3. Bipolar cells were classified into two types according to the response properties to monochromatic lights. Opponent colour cells received inputs from red and green cones, responding with red on-centre, red and green off-surround or vice versa. Cells without colour coding received input from red cones both in the field centre and the surround. In these cells the centre and the surround were well balanced. 4. Amacrine cells were also classified into two types, a sustained type and a transient type. The sustained type amacrine cells responded with a steady potential change and were colour coded. They were hyperpolarized by red and depolarized by green light. The transient type amacrine cells responded with transient depolarization at on and off of light flashes. They received input chiefly from red cones and were not colour coded. Both types of amacrine cells showed a large spatial summation in an area over 2·5 mm; centre-surround antagonism was not seen. 5. Comparing the size of the receptive field with anatomy, especially with the size of dendritic spread, the field centre of bipolar cells agreed in size with their dendritic spread. Bipolar cell surround clearly exceeded its dendritic field. Since the response properties of the bipolar cell surround was mimicked most closely by the receptive field of external horizontal cells, the input to the bipolar cell surround is thought to be mediated by external horizontal cells. 6. By comparing receptive field properties of various retinal cells it is suggested that both the opponent colour bipolar cells and the colour coded amacrine cells converge on to the double opponent ganglion cells.

Reconstruction of the action potential of frog sartorius muscle.

Abstract: 1. Propagated action potentials of striated muscle are calculated using an equivalent circuit that represents the transverse tubular system as a radial cable of sixteen elements. The membrane of the transverse tubules is assumed to have activatable ionic currents similar to those in the fibre surface.2. The configuration of the after-potential and the conduction velocity are best accounted for by postulating a resistance of about 150Omega cm(2) separating the extracellular fluid from the lumen of the transverse tubules at the edge of the fibre, and a density of sodium channels in the tubular wall about a twentieth of that in the fibre surface.3. Calculations with imposed voltage steps at the fibre surface suggest that the potential across the tubular membrane at the centre of the fibre is very far from clamped.4. Currents providing charge for the tubular capacity can give rise to substantial errors in estimating the zero-current potential of the ionic currents.

Effects of manganese and other agents on the calcium uptake that follows depolarization of squid axons.

Abstract: 1. The Ca-sensitive photoprotein aequorin was injected into squid axons and the light response to stimulation or depolarizing voltage clamp pulses recorded.2. The effects of Mn(2+), Co(2+), Ni(2+), La(3+) and of the organic Ca antagonists D-600 and iproveratril on the early tetrodotoxin-sensitive and late tetrodotoxin-insensitive components of the light response were studied.3. The late tetrodotoxin-insensitive component can be blocked, reversibly, by concentrations of Mn, Co and Ni that reduce but do not block the tetrodotoxin-sensitive component. The late component can also be blocked by La(3+) and the organic Ca antagonists D-600 and iproveratril.4. Mn(2+), Co(2+), Ni(2+) and the drug D-600 all reduce the Na currents, but have little effect on either outward or inward K currents. Tetraethylammonium blocks the outward K current but has no appreciable effect on the tetrodotoxin-insensitive entry of Ca.5. Concentrations of Mn between 5 and 50 mM substantially reduce the light output during a train of action potentials; they also slightly reduce the rate of rise of the action potential.6. On pharmacological grounds it is concluded that the tetrodotoxin-insensitive component of Ca entry does not represent Ca ions passing through the K permeability channels. There must exist a potential-dependent late Ca channel that is distinct from the well known Na and K channels of the action potential. A possible function for this late Ca channel in the coupling of excitation to secretion is discussed.

Stimulus—response functions of rapidly adapting mechanoreceptors in the human glabrous skin area

Abstract: 1. Single unit impulses were recorded from the ulnar and median nerves of awake human subjects with tungsten electrodes inserted percutaneously in the upper arm. 2. Forty-nine rapidly adapting mechanoreceptors with receptive fields in the glabrous skin area were studied. Thirty-nine units had small receptive fields with distinct borders (RA-receptors) while ten units had large fields with indistinct borders (PC-receptors). 3. The afferent response to stimuli of varying indentation amplitude and velocity of indentation, was analysed. 4. Amplitude thresholds varied from 0·05 to 1·65 mm for the RA-receptors. For the PC-receptors amplitude thresholds ranged from less than 0·05 to 1·95 mm. 5. Velocity thresholds varied for the RA-receptors from 0·4 to 39·3 mm/sec, and for the PC-receptors from 0·5 to 19·6 mm/sec. 6. The conduction velocities of the afferents were all in the A α—β range. For the RA-receptors the conduction velocities ranged from 26 to 91 m/sec (mean = 55·3 ± 3·4), and for PC-receptors the range was from 34 to 61 m/sec (mean = 46·9 ± 3·6). 7. The nerve impulse frequency as a function of indentation velocity was analysed for nineteen RA-receptors and four PC-receptors. A hyperbolic log tangent function of the type first introduced by Naka & Rushton (1966) in studies on S-potentials in the fish retina was found to be the best description of the stimulus—response function for sixteen RA-receptors and two PC-receptors. For the remaining units a pure logarithmic function was the best description. However, the logarithmic function may be, as found in the present study, a special case of the more general log tanh function.

Determination of the frequency response of isometric soleus muscle in the cat using random nerve stimulation.

Abstract: 1. The frequency response of isometric soleus muscle was determined efficiently by analysis of the unfused tension generated during short periods of random stimulation of the divided ventral roots, in anaesthetized cats. 2. Despite the complexities of skeletal muscle, the frequency response of soleus, at moderate lengths and stimulation rates in the physiological range, is closely approximated by the frequency response function for a simple, linear, second-order system near critical damping. 3. The soleus muscle shows a uniformly high sensitivity to fluctuations in nerve activity over a range of frequencies similar to the range of frequencies of muscular activity observable during behaviour. The nerve-muscle preparation appears to be well suited for smooth and steady motor activity, since it is much less responsive to the higher frequency components contained in individual action potentials or generated in tremor. 4. The second-order parameters: low-frequency gain, natural frequency and damping ratio provide useful descriptions of the changes in the muscle's response caused by variations of muscle length, nerve stimulation rate or number of active motor units. 5. A reduction in tension incurred, for example, during fatigue can be compensated to some extent either by a lengthening of the loaded muscle or through an increase in neural spike repetition rate. However, both mechanisms produce concomitant increases in the `sluggishness' (increased damping and lower natural frequency) of the preparation. This sluggishness may arise out of limitations imposed by the mechanism for the re-uptake of calcium into the sarcotubular system. 6. One naturally occurring method of increasing tension, by recruitment of more active motoneurones, seems to be desirable because tension can be augmented in this way without an increase in sluggishness. This is presumably because recruitment increases the muscle's response without affecting excitation-contraction coupling in fibres already active.

The relationship between calcium exchange and enzyme secretion in the isolated rat pancreas

Abstract: 1. The role of extracellular and intracellular Ca(2+) in pancreatic enzyme secretion has been assessed by correlating the exchange of (45)Ca with amylase secretion in the isolated uncinate pancreas of baby rats.2. The rate coefficient of (45)Ca efflux from pre-loaded glands declined continually (indicating that (45)Ca is retained in several different pools) and probably reflects changes in the concentration of cytoplasmic free (45)Ca, which is determined by the rate at which (45)Ca is released from intracellular organelles into the cytoplasm.3. The rate coefficient of (45)Ca release was not influenced by extracellular Ca(2+) or Mg(2+) concentrations.4. Cholecystokinin-pancreozymin (CCK-PZ) and acetylcholine accelerated the release of both (45)Ca and amylase in a dose-dependent fashion, even when extracellular Ca(2+) was reduced to 0.1 mM, but did not affect the initial rate of (45)Ca uptake by the tissue.5. In Ca(2+)-free media (containing 0.5 mM-EGTA) basal amylase secretion slowly declined and stimulated secretion was virtually abolished, but the accelerated release of (45)Ca was maintained.6. These observations indicate that natural stimuli of pancreatic enzyme secretion alter (45)Ca distribution in the cell by a process which is independent of extracellular Ca(2+) and which is associated with amylase secretion provided that the plasma membrane has not been depleted of Ca(2+).7. Secretin, glucagon and insulin did not influence (45)Ca release. Secretin slightly increased amylase secretion, but this may have been a washout effect.8. Replacement of extracellular Na(+) by Li(+) increased the release of (45)Ca and amylase, but only in the presence of extracellular Ca(2+). Li(+)-substitution also increased (45)Ca uptake. Thus, under special conditions, secretion may be stimulated when increased amounts of Ca(2+) are made available from extracellular sources.9. Hyperosmolarity (known to increase (45)Ca release in muscle) also accelerated (45)Ca release and amylase secretion.10. 2,4-Dinitrophenol markedly accelerated (45)Ca efflux but did not stimulate amylase secretion, indicating that a rise in cytoplasmic Ca(2+) will not initiate secretion if energy metabolism is impaired.11. CCK-PZ slightly increased the rate coefficient of (42)K release, indicating a changed membrane permeability.12. The stimulatory effects of CCK-PZ and acetylcholine were suppressed during Na(+)-substitution by Li(+), suggesting that the Na(+) concentration gradient across the membrane is important in secretion.13. It is concluded that the primary action of CCK-PZ and acetylcholine may be to increase the influx of Na(+) into the cell by changing membrane permeability. This in turn is responsible for the release of Ca(2+) from intracellular stores (probably endoplasmic reticulum), leading to a rise in Ca(2+) concentration close to the structures involved in enzyme secretion. Secretion then follows provided that ATP is available and the plasma membrane is not depleted of Ca(2+).

The pharmacology and ionic dependency of amino acid responses in the frog spinal cord.

Abstract: 1. The isolated frog spinal cord was used to study the action of amino acids and their antagonists on primary afferent terminals and motoneurones. The direct effects of these substances were observed by bathing the cord in 20 m M magnesium sulphate (thus blocking synaptic transmission) and recording the polarization level of the dorsal and ventral roots. 2. γ-Aminobutyric acid (GABA) and glutamic acid depolarized the dorsal root and reduced dorsal-root potentials, while glycine produced only weak and variable effects. Glutamic acid also depolarized the ventral root; GABA usually produced either a hyperpolarization or had little effect, while glycine caused variable effects. 3. Bicuculline and picrotoxin antagonized all the synaptic potentials recorded on the dorsal root, as well as the GABA responses on both dorsal and ventral roots. 4. All the synaptic potentials examined remained and were markedly prolonged in the absence of external chloride except the ventral root-dorsal root potential. Replacement of the physiologic complement of chloride during chloride-free perfusion restored the potentials to their original time courses. 5. Depolarizing amino acid responses remained in the absence of external chloride, while hyperpolarizing responses were reversed into depolarizations. Return to normal Ringer solution re-established the hyperpolarizations. 6. Removal of external sodium reversibly abolished the amino acid depolarizations but had little effect on the depolarizations in response to applications of high external potassium concentrations. 7. The results support the hypotheses (a) that GABA mediates presynaptic inhibition by depolarizing primary afferent terminals and (b) that the GABA-mediated depolarization is sodium dependent. 8. The results also indicate that GABA utilizes different ionic mechanisms to mediate presynaptic inhibition (sodium) and post-synaptic inhibition (chloride) in the amphibian (and presumably in the mammal).

Relationship between the velocity of rolling granulocytes and that of the blood flow in venules

Abstract: 1. The mean velocities at which granulocytes roll along the walls of small venules have been related to their mean blood flow velocities in preparations of hamster cheek pouch and mouse mesentery. In animals anaesthetized with Nembutal, 30-200 mum venules were observed microscopically and the movement of rolling granulocytes quantitated on films. Apparent mean blood flow velocity was determined from films of embolizing platelet thrombi.2. In four venules the velocity distribution of about 100 rolling cells was almost symmetrical about the mode, with a small proportion moving at up to three times the mode velocity. Therefore, the mean and mode velocities were very similar.3. In two mesenteric and two cheek-pouch venules, blood flow velocity was temporarily altered during and after gentle compression with a fine glass fibre; this was associated with proportional changes in mean cell velocities.4. In four different venules of a hamster cheek pouch, the mean velocity of rolling granulocytes increased in proportion to the mean blood flow velocity (r = 0.963).5. In thirty-six venules of ten mouse mesenteries, the velocities were proportional (r = 0.915) between blood velocities of about 300 and 1000 mum/sec. Above this the velocity of the cells did not increase further.6. The rolling of granulocytes is presumably governed by two forces, the shear force of the flowing blood and an adhesive force between the surfaces of granulocytes and vascular endothelium. Our results suggest that, within limits, the proportionality between the velocities of blood flow and rolling cells is due to shear force, the adhesive force being similar for all the cells. The results suggest that this adhesion force per granulocyte is of the order of 10(-5) dynes.

The action of cobalt ions on neuromuscular transmission in the frog

Abstract: 1. Cobalt ions, in concentrations of 0.05-2 mM, block neuromuscular transmission in the frog sartorius muscle.2. The reduction in the e.p.p. amplitude produced by Co(2+) is due to a decrease in the amount of transmitter released by a nerve impulse (mean quantum content). This reduction is associated with little change in the resting membrane potential of the muscle fibre or in the mean amplitude of spontaneous m.e.p.p.s.3. The reduction in evoked transmitter release produced by Co(2+) may be antagonized by elevation of the external Ca(2+) concentration. It is suggested that the antagonism between Co(2+) and Ca(2+) is competitive in nature.4. The mean dissociation constant for Co(2+) and its hypothetical membrane complex was found to be 0.18 mM. On this basis, it is concluded that Co(2+) is about 20 times more potent than Mg(2+) in suppressing evoked transmitter release.5. In contrast to the inhibitory action on evoked release, Co(2+) increases spontaneous transmitter release. However, concentrations of Co(2+) 20-60 times greater than those which decrease the e.p.p. amplitude are needed to produce a significant increase in m.e.p.p. frequency.

Effects of proteolytic enzymes on function and structure of frog neuromuscular junctions

Abstract: 1. Frog cutaneous pectoris nerve-muscle preparations were incubated with collagenase and protease and examined with electrophysiological and electron microscopic techniques. 2. The physiological properties and intracellular ultrastructural appearance of individual muscle and nerve cells were not affected by the enzyme treatment. However, neuromuscular transmission and the morphology of the nerve-muscle junction were altered. 3. Collagenase produced an irreversible loss of activity of end-plate cholinesterase and a partial loss of stainable ‘synaptic cleft material’. 4. Protease produced these changes and, in addition, the entire basement membrane was digested, which led to ‘synaptic disjunction’ of nerve terminals and muscle end-plates.

Blood volume determination in the mouse.

Abstract: 1. The blood volume of the mouse has been measured using (59)Fe-labelled red cells to determine the red cell volume and (131)I-labelled human serum albumin to determine the plasma volume.2. Values for the blood volume of 95.0 +/- 1.5, 96.3 +/- 2.7 and 84.7 +/- 1.2 ml./kg body wt. were found for CSI female, CBA female and CBA male mice respectively.3. A marked discrepancy was observed between the venous (cardiac) haematocrit and the whole body haematocrit.4. The blood volume of the mouse must be determined from the red cell volume and the plasma volume, measured using appropriate labels, and not from the red cell volume or the plasma volume using the venous haematocrit.