Showing papers in "Experimental Brain Research in 1969"

Distribution of readiness potential, pre-motion positivity, and motor potential of the human cerebral cortex preceding voluntary finger movements.

Abstract: Potentials recorded from the scalp of human subjects preceding voluntary finger movements may be devided into 3 components: 1. a slowly increasing surface negative readiness potential which starts about 850 msec before movement and is bilaterally symmetrical over the pre- and post-central region with a maximum at the vertex; 2. a pre-motion positivity which is also bilaterally symmetrical and starts about 86 msec before the onset of EMG; 3. a surface negative motor potential which starts about 56 msec before the onset of movement in the EMG and has its maximum over the contralateral precentral hand area.

The rubrospinal tract. II. Facilitation of interneuronal transmission in reflex paths to motoneurones

Abstract: Summary. 1. The effect of stimulation of the red nucleus on transmission of synaptie actions from different systems of primary afferents to alpha motoneurones has been invest/gated in cats, mainly with intracellular recording from motoneurones. 2. The dominating effect is facilitation, presumably caused by excitatory action exerted from the rubrospinal tract on interneurones of reflex arcs. The time course of facilitation suggests that the minimal linkage from the rubrospinal tract to these interneurones is monosynaptic. 3. Interneuronal transmission in reflex pathways from the following afferent systems is facilitated : a) Ia inhibitory between flexors and extensors, l~ubrospina] facilitation did not reveal Ia inhibitory pathways between adductors and abductors at the hip. b) Ib excitatory and inhibitory. There is marked facilitation of the reciprocal effects evoked by Ib afferents from extensors but also of other Ib pathways, for example inhibitory from extensors to flexor nuclei and from flexors to extensor nuclei and excitatory from flexors to extensor nuclei, e) Low threshold joint, inhibitory and excitatory, presumably from afferents with Ruffini endings. d) Low threshold cutaneous, excitatory and inhibitory. Since transmission from these afferents could be facilitated under conditions when there was no effect on transmission from high threshold muscle afferents it is postulated that the effect is exerted on pathways which are not part of the common pathways from the flexor reflex afferents, e) Flexor reflex afferents, excitatory and inhibitory. Facilitation of these pathways is not found regularly, in some eases there was no effect and in others inhibition. 4. The effeets are discussed in relation to the complex effects evoked from the rnbro spinal tract in motoneurones and to supraspinal regulation of proprioceptive reflexes. 5. It is postulated that in complex movements alternative Ib patterns may be mobilized, whereas flexion-extension movements are subserved by the Ib pattern found in the spinal eat. 6. Facilitation of the Ia inhibitory pathway is taken to indicate "a-y-linkage" in reciprocal inhibition. It is pointed out that convergence from Ia and descending impulses on a common inhibitory interneurone may play an important role in the regulation of a-y-linked flexion-extension movements.

Inhibitory and excitatory factors influencing the receptive fields of lamina 5 spinal cord cells.

Abstract: Examination of cutaneous receptive fields (RFs) of lamina 5 cells in the lumbar spinal cord of decerebrate cats shows them to have three distinct zones with respect to mechanical and electrical stimulation. The mean response rate to both mechanical and electrical stimulation in zone 1 increases steadily up to the highest strengths used; in zone 2, surrounding zone 1 mainly proximally, mild stimuli reduce the mean rate, stronger stimuli increase it; in zone 3, mainly proximal to zone 2, all stimuli reduce the rate.

Cerebellar monoamine nerve terminals, a new type of afferent fibers to the cortex cerebelli.

Abstract: The monoamine innervation of the cerebellum of the rat has been studied by both in vivo and in vitro techniques using the histochernical fluorescence method for the demonstration of catecholamines (CA) and certain tryptamines. By way of a pharmacological approach using inter alia protriptyline, which acts mainly by blocking the membrane pump of the noradrenaline (NA) neurons, evidence was obtained that CA nerve terminals in the cerebellum mainly represent NA nerve terminals. These were found to innervate practically all parts of the cerebellar cortex with a patchy innervation pattern and with an innervation of especially the anterior and posterior lobes. The terminals mainly seem to make axodendritic contacts in the molecular and granular layers without any strict localization of the terminal plexus to any special plane of the cerebellar folia. The fibers enter the cerebellum via the inferior cerebellar peduncle and run in the white matter of the cortex cerebelli. Incubation studies with 6-hydroxytryptamine indicate that there exists also a 5-hydroxytryptamine (5-HT) innervation of the cortex cerebelli, although not as pronounced as the NA innervation. The 5-HT nerve terminals are very fine, varicose fibers and innervate mainly the molecular layer, especially of the anterior lobe. The terminals run mainly in the transverse plane of the folium parallel to the surface. Thus, the pattern of innervation of these 5-HT afferents is different from that of the NA nerve terminals. In the uvula, structures which may represent the “rosettes” of the mossy fibers or golgi axon terminals in the granular layer take up and accumulate monoamines after incubation with amine in vitro. The exact nature of these structures remains to be elucidated.The cerebellar nuclei receive a very low to low degree of innervation of NA and 5-HT nerve terminals.

The regulation of heart rate during sleep.

Abstract: One group of the experiments was carried out on cats using encephale isole preparations, a second group was performed on cats with chronically implanted electrodes. Cortical EEG, electromyogram, ocular movements and electrocardiogram were recorded simultaneously.

Cortical inhibition and γ-aminobutyric acid

Abstract: 1. In cats under Dial, multiple micro-electrodes were used to analyze the changes in membrane potential and conductance of cortical neurones produced by inhibition (evoked by surface shocks) and by microiontophoretic applications of GABA. 2. IPSPs are associated with a marked but variable increase in membrane conductance. At the peak, the conductance may rise 3–4 fold. 52 estimates gave a mean increase of 54.0% (S.D. 77%). 3. The time course of the main increase in conductance coincides approximately with the time course of the IPSP and the period of reduced excitability. After an initial phase of very high conductance, the conductance diminishes exponentially with a time constant of about 50 msec. 4. GABA causes a very striking increase in membrane conductance and, in most cases, a negative shift in membrane potential. 5. Estimates of the reversal potential of the action of GABA (EGAB) agree well with estimates of the reversal potential for IPSPs (EI) obtained before or after the application of GABA. There was a strong positive correlation between values of EI and EGAB, and the slope of the line describing EI vs EGAB, did not differ significantly from 1.0 6. These observations therefore greatly reinforce previous evidence of a close identity between the actions of GABA and of the normal transmitter of cortical IPSPs. 7. The increase in conductance produced by GABA shows an initial peak (mean 17.1 n-mho/nA GABA current, S.E. 4.50, n=41) and then tends to fall, after 10–20 sec, to a relatively stable level (mean 9.31 n-mho/nA (S.E. 2.38, n=32)). This phenomenon is particularly evident with large doses of GABA. 8. A maintained application of GABA is usually associated with a change in EI towards greater positivity, probably owing to a large influx of Cl−.

The rubrospinal tract. I. Effects on alpha-motoneurones innervating hindlimb muscles in cats.

Abstract: 1. The effect of stimulation of the red nucleus on lumbosacral motoneurones was investigated in cats with conditioning of monosynaptic test reflexes and intracellular recording. 2. Experimental procedures were adopted to assure that the effect of stimulation was mediated by the rubrospinal tract. 3. Excitation of flexor and inhibition of extensor motoneurones is common but a mixture of EPSPs and IPSPs is found in many motoneurones. In some extensor (particularly toe extensor) motor nuclei there is dominating excitation. 4. Differential effects are found in motor nuclei innervating fast and slow muscles, excitation being more prevalent in the former and inhibition in the latter. 5. For both EPSPs and IPSPs the minimal synaptic linkage is disynaptic but in one exceptional case a monosynaptic EPSP was observed. 6. The results are discussed in relation to other findings regarding the interneuronal organization in the spinal cord.

The large synaptic complexes of the substantia gelatinosa

Abstract: A Golgi and electron microscope study, using also secondary degeneration after dorsal root transection and chronically isolated dorsal horn preparations, were undertaken with the objective to clarify the large (glomerulus-like) synaptic complexes in lamina II of the dorsal horn. The large sinusoid axon terminals forming the centers of these synaptic complexes are of intraspinal origin and are thought to arise from the hitherto unknown type of pyramid-shape nerve cells, situated at the border between laminae III and IV. The sinusoid axon terminals establish axo-dendritic synapses with substantia gelatinosa neurons and abundant axo-axonic synapses with smaller terminals that could be identified (at least partly) as endings of primary sensory afferents. The central sinuous axon terminals of the synaptic complexes are always presynaptic to the smaller axons and thus might be considered as a device for 1. presynaptic inhibition of impulse transmission from primary afferents to substantia gelatinosa neurons, and 2. as the anatomical basis for primary afferent depolarization.

Penetration of 14C-inulin and 14C-sucrose into brain, cerebrospinal fluid, and skeletal muscle of developing rats.

Abstract: 1. We studied the decrease in brain uptake of two substances, inulin and sucrose, during maturation of the brain. Concentration ratios of CSF/plasma and brain/plasma for 14C-labeled inulin and sucrose were calculated and time-uptake curves plotted for prenatal and postnatal rats. Comparisons of these ratios among the various ages showed a progressive decrease in the inulin ratios of both compartments with increasing age. Sucrose “spaces” were always larger than inulin “spaces,” suggesting possible sucrose penetration into cells. The brain/CSF concentration ratio for inulin, however, appears to reflect brain extracellular space in young rats, but not in older animals. Electrolyte concentration ratios of CSF and plasma suggested progressive maturation of transport mechanisms at the choroid plexus and increase of CSF flow. The degree of concentration of inulin in the developing brain and the CSF of the young rat probably reflects cellular maturation of both barrier and secretory mechanisms. 2. We also measured the inulin and sucrose space of skeletal muscle in rats of different age. In contrast to brain, the spaces measured by the two substances were the same and decreased with maturation of the animals.

Responses of spinocervical tract neurones to natural stimulation of identified cutaneous receptors.

Abstract: Microelectrode recordings were made from ascending fibres of the spinocervical tract in spinal, decerebrate and anaesthetized cats. Three types of unit were recognised in spinal cats on the basis of their response to mechanical stimulation; units excited by 1. hair movement; 2. hair movement and skin pressure; 3. pressure and pinch of the skin. Five types were recognised in decerebrate and anaesthetized cats; units excited by 1. movement of guard hairs and skin pressure; 2. movement of tylotrich hairs; 3. movement of all the hairs and skin pressure; 4. pressure and pinch of the skin; 5. units which could not be influenced from the periphery. The presence or absence of inhibitory fields and the mean rate of spontaneous discharges depended on the type of preparation and the type of unit. The differences between spinal and decerebrate or anaesthetized cats suggest that a descending neuronal system, intact in the decerebrate and anaesthetized animals, operates to control the input to the spinocervical tract.

The sense of flutter-vibration evoked by stimulation of the hairy skin of primates: Comparison of human sensory capacity with the responses of mechanoreceptive afferents innervating the hairy skin of monkeys

Abstract: We have studied the response properties of peripheral myelinated fibers ending in the hairy skin of the Rhesus monkey, activated by sinusoidal mechanical stimulation. In parallel experiments we measured thresholds of the sensations evoked in man by identical stimuli, delivered under similar conditions to corresponding areas of the hairy skin. We found that the sense of low frequency vibration (i. e., flutter) depends upon activity in rapidly adapting alpha fibers which end in or about the hair follicles. High frequency vibration is signalled by Pacinian afferents whose terminals lie deep to the skin itself. These two sets of fibers, by reason of their discharge patterns and differential sensitivities in different frequency ranges, are thought to provide the essential first order input for the human sense of vibration evoked by stimulation of the hairy skin. Rapidly adapting cutaneous afferents of the delta size and two classes of slowly adapting alpha fibers are also entrained by mechanical sinusoids, but are thought not to contribute to vibratory sensibility. Our findings support the proposition that the sensitivity of humans to oscillatory mechanical stimuli at different frequencies, and the quality of the sensations evoked by them, are determined in the first instance by the properties of two distinct sets of peripheral afferent fibers.

Functional organization of the vestibular afferents to the cerebellar cortex of frog and cat.

Abstract: 1. Field and unitary potentials evoked in the vestibulo-cerebellum of frog and cat following vestibular nerve stimulation were recorded with microelectrodes and correlated with their site of origin in the various layers of the cerebellar cortex. 2. In the frog, primary vestibular fibers project both as mossy and as climbing fibers onto the cerebellar auricular lobe. Secondary vestibulo-cerebellar fibers seem to end exclusively as mossy fibers in the auriculum. As a consequence of this dual projection, extra- and intracellular recordings from Purkinje cells in the auricular lobe show two kinds of responses to vestibular nerve stimulation: a) graded, repetitive firing mediated through mossy fiber-granule cell-parallel fiber pathways, and b) all-or-none burst responses caused by monosynaptic impingement of vestibular climbing fibers on Purkinje cells. 3. The field and unitary potentials evoked in the cat nodulus, flocculus and uvula following vestibular nerve stimulation are shown to be generated by mossy fibers exclusively. Considerable convergence of the two labyrinthine mossy fiber inputs to a given cerebellar area was found. 4. Interaction of contralateral and ipsilateral mossy fiber input at the level of the flocculus suggests that Golgi cell inhibition might operate not only as a simple inhibitory feedback loop, but also as a complex gating operator at the granule layer. 5. No short latency climbing fiber activation of Purkinje cells was observed following VIIIth nerve stimulation. Stimulation of the contralateral inferior olive evoked short latency climbing fiber EPSPs in Purkinje cells of the vestibulo-cerebellum. Suggestions are made as to the possible role of mossy and climbing fiber inputs to this area of the cerebellum.

The temporal evolution of the distribution of dendritic spines in the visual cortex of normal and dark raised mice

Abstract: A set of equations which define the distribution of spines along the apical dendrites have been developed. They are satisfied by the distribution of spines and its evolution with the age in the apicals of the layer V pyramidal cells of the visual cortex in normal and dark raised mice. The principal equation describes the distribution of the spines with three coefficients IF, B and K whose values have a functional relation with the age T of the animal. This relation has been defined by three additional equations whose coefficients were calculated. The equations have been used to predict the distribution of dendritic spines corresponding to age-groups of mice not previously studied and to find out the age of mice from the data of their known spine distribution resolving the inverse equations of IF (T) and B(T).

Evoked response correlates of psychophysical magnitude estimates for tactile stimulation in man.

Abstract: Cortical responses evoked by transient sensory stimulation of the index and middle fingers were recorded from the scalp over the contralateral primary somatic projection area in man. Stimulus amplitude and locus were systematically varied. The relationship between stimulus intensity and the magnitude of the evoked response is adequately described by a power function. The exponent of the psychophysical function generated under similar stimulus conditions is of approximately the same size. A mathematical model is presented to describe and predict spatial summation. A complete isomorphism between psychological and neurophysiological events is obtained.

Natural and melatonin-induced sleep in young chickens--a behavioral and electrographic study.

Abstract: 1. Natural sleep and waking states of young chickens were studied by polygraphic recording (EEG, EOG, EMG and ECG) together with behavioral observation. Effects of melatonin were observed. 2. The sleep-wake periods of the chickens were analysed for three states: awake, slow wave sleep (SS) and paradoxical sleep (PS). Polygraphic characteristics of these 3 states were analogous to, though in several aspects different from, those in mammalians. 3. The sleep states alternated irregularly at short intervals. SS usually did not last longer than 6 min without being interrupted by an episode of arousal or PS. PS appeared at irregular intervals usually lasting only 6–8 sec. Total duration of PS was 7.3±1.8% of total sleep time. 4. Melatonin (0.01–0.06 mg/g) had a powerful sedative and hypnotic effect which appeared within 1–2 min after i. perit. injection and lasted for 30–60 min. Melatonin-induced sleep was characterized by slow EEG activity of high voltage similar to that in normal SS but with a higher incidence of 2–3 c/sec waves. 5. Melatonin besides activating SS, delayed the appearence of the first PS episode and decreased total PS time. 6. In melatonin sleep as in natural sleep the chickens were easily aroused by sensory stimuli both in behavior and electrographic pattern. 7. Possible mechanisms related to sleep-inducing effects of melatonin are discussed.

Vestibular-evoked postsynaptic potentials in Deiters neurones

Abstract: Stimulation of the vestibular nerve induced EPSPs monosynaptically in 29% of cat's Deiters neurones sampled on the ipsilateral side. These EPSPs started with latencies of 0.6–1.0 msec, rose sharply with a summit time of 0.5 msec and decayed exponentially with a time constant of 0.9–1.7 msec. Then amplitudes were graded finely according to the intensity of the vestibular nerve stimulation, the maximal size being 5–10 mV. The unitary EPSPs, evoked by vestibular nerve stimulation at juxta-threshold intensity or appearing spontaneously, were as small as 0.2–0.3 mV in amplitude. Those neurones monosynaptically activated by vestibular nerve volleys were located in the ventral portion of the nucleus of Deiters, in agreement with histological data. The vestibular nerve impulses also produced delayed EPSPs with latencies of 1.0–1.8 msec, presumably disynaptically. They occurred in many Deiters neurones located not only ventrally but also dorsally. Even later EPSPs often were superposed on the monosynaptic EPSPs with latencies of 1.9–2.2 msec. There is evidence that they were caused by repetitive discharges in the vestibular nerve fibres which occur in response to single shock stimulation of the vestibular nerve. IPSPs were produced only polysynaptically in some Deiters neurones in association with the monosynaptic EPSPs.

Anionic permeability of cortical neurones

Abstract: 1. In cats under Dial, thirty different anions were injected into some 400 cerebral cortical neurones, by diffusion from micro-electrodes, while observing IPSPs evoked by surface stimulation. 2. The probability of stable intracellular recording was much enhanced when micro-electrodes were filled with an organic salt of K. 3. With the exception of I03−, all univalent anions tested were capable of producing a reversal of IPSPs in a substantial proportion of cases. IPSPs therefore appear to be associated with a high permeability to many univalent anions. 4. Apart from CrO4−, multivalent anions only rarely caused a reversal of an IPSP. 5. The probability of observing a reversal with inorganic anions was a very steep function of their relative mobility in water. The relative mobilities through the membrane, calculated on the assumption that the membrane pores have the same permeability at rest and during IPSPs. are consistent with the hypothesis that inorganic anions travel through pores whose equivalent diameter is about twice the diameter of hydrated Cl− and is appreciably greater than that of the corresponding pores in spinal motoneurones. 6. The probability of observing a reversal with organic univalent anions (mainly of aliphatic and aromatic acids) bore an approximately linear relation to their mobility in water. These anions have a much higher mobility through the membrane (during inhibition, and perhaps even at rest) than would be expected from their size if they travel through the same pores as the inorganic anions. 7. As in other membranes, the rate of diffusion of various ions is evidently determined not only by the ions' size relative to membrane pores, but also by their chemical structure and their ability to interact with membrane constituents.

Monosynaptic inhibition of neck motoneurons by the medial vestibular nucleus.

Abstract: Stimulation of the brain stem in cats anesthetized with pentobarbital evoked short-latency IPSPs in many neck motoneurons. From the segmental delay of these IPSPs, and from comparison of their latencies with those of monosynaptic EPSPs evoked in the same motoneuron population by stimulation of the brain stem, it is concluded that the IPSPs are monosynaptic and are produced by descending inhibitory fibers.

The inhibitory vestibular efferent system and its relation to the cerebellum in the frog

Abstract: 1. In the frog, peripheral stimulation of the anterior and posterior branches of the VIIIth nerve evokes antidromic activation of Purkinje cells in the ipsilateral cerebellar auriculum. 2. The antidromic Purkinje cell invasion is followed by orthodromic action potentials due to the activation of direct and secondary vestibulo-cerebellar afferents. 3. In order to demonstrate the existence of vestibular efferent fibers at the level of the vestibular nerve, its anterior or posterior branches were electrically activated and a recording electrode placed proximally in the same nerve. Under these circumstances, efferent fiber action potentials with an average latency of 3 msec could be recorded, even after the peripheral vestibular organ had been removed. 4. Comparison of the latency for orthodromic activation of Purkinje cells at the auricular lobe with that of the action potentials recorded at the vestibular nerve level agrees very well, there being on the average a slight lead at the Purkinje cell level which can be explained by the conduction time (0.6 msec) from the cerebellum to the vestibular organ. 5. The vestibular efferent system could not be easily activated by moderate angular acceleration adequate for afferent fiber activation, or by tilting or vibratory stimulation. On some occasions, contralateral rotation evoked efferent discharge. 6. Activation of the vestibular efferent system following VIIIth nerve or auricular stimulation produces an inhibition on the spontaneous activity of saccular and utricular afferents for an average period of 15 msec. 7. It is therefore concluded that a direct cerebello-otolithic efferent system represented by axons of Purkinje cells is present in the frog. This cerebello-otolithic system, which is shown to be inhibitory, represents the first demonstration of cerebellar control of a sensory input.

Light and electron microscopical study of the relationships between the cerebellum and the vestibular organ of the frog.

Abstract: The relationships between the frog vestibular afferents and the cerebellum as well as the efferent vestibular system, have been studied by electron microscopy and Nauta degeneration technique The primary vestibular fibers were found to have synaptic boutons in both the granular and the molecular layers of the cerebellar marginal zone In the granular layer synaptic contacts are made with the granule cell dendrites while the molecular layer projection is directed to the main dendrites of the Purkinje cells in a manner similar to that of the climbing fibers As for the efferent system, the vestibular receptor cells of the macula saccularis are contacted by vesicle-filled boutons which terminate synaptically in relation to a submembranous sac within the cell The efferent fibers contain neurofilaments and a few neurotubules Following lesions at different sites, it was found that all the above fibers and boutons degenerated after a) vestibular nerve section, and that b) most of them were lost when the brain stem was hemisected above the vestibular nerve On the other hand, brain stem sectioning above the Vth nerve produced degeneration of 35% of these boutons while cerebellar undercutting produced 20% degeneration The Nauta technique shows that following cerebellar undercutting a small efferent bundle leaves the ventral caudal side of the nerve These findings demonstrate the existence of a cerebello-vestibular efferent system originating most possibly from the auricular lobe Purkinje cells

Electronmicroscopic observations on the structure of the pontine nuclei and the mode of termination of the corticopontine fibres. An experimental study in the cat.

Abstract: The electron microscopical changes occurring in the pontine nuclei following unilateral lesions of the primary sensorimotor cortex have been studied in 7 cats with a survival time from 2–23 days. A description is also given of the fine structure of the pontine regions in receipt of the fibres. These regions are shown in Fig. 1.

A comparison of the mode of termination of the hippocampal and hypothalamic afferents to the septal nuclei as revealed by electron microscopy of degeneration

Abstract: Previous studies with the Nauta technique have established that fibres which originate in two important areas — the hippocampus and the hypothalamus — converge upon the cells of the septal nuclear complex. The purpose of this study was to investigate the anatomical basis of how the septal cells could differentiate between fibres from the two sources. Differences in the mode of termination of these two systems have been studied quantitatively at the electron microscope level by using the orthograde degeneration of terminals after lesions of the fimbria and the medial forebrain bundle. In the medial septal nucleus, the hippocampal fibres account for 35% of the terminals, and in the lateral septal nucleus, 43% of the terminals on the same side and a further 13% on the opposite side. These terminals are at least 98% axodendritic and 91% of them contain predominantly clear synaptic vesicles of 500 A diameter. The hypothalamic fibres are the source of up to 19% of the axodendritic terminals in the medial septal nucleus, but considerably fewer in the lateral septal nucleus. In contrast to the hippocampal afferents, the hypothalamo-septal system has two characteristic features: firstly, the fibres give rise to up to 24% of the axosomatic terminals in the medial septal nucleus, and secondly, 63% of the terminals contain a population of vesicles with significantly higher proportions of dense centred vesicles of 800–1000 A diameter.

Microelectrophoretic studies concerning the spread of glutamic acid and GABA in brain tissue.

Abstract: The spread of microelectrophoretically applied substances was investigated in the cortex and in the caudate nucleus by means of double-multi-barrelled electrodes with tip separations varying from 12–300 μ. Spike activity induced in non-spontaneously firing neurones by application of glutamate and inhibition of spontaneously firing neurones by GABA were interpreted as an effect of the substances diffusing into the immediate neighbourhood of the neurone. This interpretation seems to be acceptable, since in only a small number of tests could an indication for trans-neuronally induced firing be found.

Inhibition in the medial geniculate body of the cat.

Abstract: 1. Inhibitory activity in the cat medial geniculate body (MG) was examined by stimulating electrically and acoustically the input and output of the MG. 2. A longer and more profound depression of excitability occurs following a click-evoked potential in the MG than in the inferior colliculus (IC) in both anesthetized and unanesthetized states. Recovery is cyclic in the barbiturate MG preparation. 3. Electrical stimulation of the brachium of the inferior colliculus (BIG) evokes a field potential in the MG consisting of clearly distinguishable presynaptic and postsynaptic components. The presynaptic component recovers rapidly, while the postsynaptic component requires 100–200 msec for full recovery. This depression of excitability is localized within the MG since cortical ablation does not alter its occurrence. 4. Stimulation of the BIC mimics the effects of click stimulation on single units. Excitatory, inhibitory and reverberatory responses are evoked by the BIC shock. Suppression of single unit activity correlates with the depression of excitability following a BIC-evoked field response. 5. Cortical stimulation can evoke antidromic and trans-synaptic unit responses in the MG, as well as causing a variety of inhibitory effects and reverberation. In view of the fact that cortical ablation does not impair the recording of these responses to afferent stimuli, it is suggested that the cortical-evoked responses are at least partly mediated by antidromic conduction to MG. 6. Evidence is presented that inhibitory effects of both afferent and cortical stimulation are due to active inhibition of MG unit activity. Speculations are made as to the mechanisms producing inhibition and reverberation in the MG.

Defence, attack, and flight elicited by electrical stimulation of the hypothalamus of the cat.

Abstract: 1. Affective behaviour patterns produced by electrical stimulation of the hypothalamus were studied in unanaesthetized, freely-moving cats. Bipolar stimulation with coaxial electrodes and small cathode was used to elicit defence, attack or flight. The development of these responses was studied by varying stimulation strength. In some experiments a stuffed animal was introduced in order to study the reactions of the cat to changes in the environment during stimulation. 2. The following responses were evoked at threshold intensity: (i) growling reaction; (ii) hissing reaction; (iii) two types of flight — type a preceded by hastily looking to and fro as if in search of an exit, type b preceded by inspection of surroundings, in most cases associated with sniffing. 3. Increasing stimulation 1.5 times threshold often yielded combined patterns. At points yielding the growling reaction a defence response in which growls alternated with hisses was obtained. The points yielding flight type a sometimes yielded hissing followed by flight. Increasing stimulation at hissing points yielded either a defence reaction or the combined effect hissing-flight. 4. The growling reactions were obtained from the tuber region. The hissing responses were obtained from points above the tuber. The flight reactions, type a, were produced from the intermediate zone extending from the level of the preoptic area to the mamillary bodies and type b from the caudo-lateral hypothalamus. 5. The reactions of the cats to a dummy during stimulation varied depending on the type of response which had been evoked in the absence of the dummy. The defence reaction was converted into threatening and striking of the dummy, the combined effects into threatening, striking or biting, culminating in sudden flight. The dummy was ignored during stimulation of points yielding flight type a, but examined by sniffing during stimulation of points yielding flight type b.

The activity pattern of limb muscles in freely moving normal and deafferented newts.

Abstract: Bipolar silver electrodes were implanted into eight forelimb muscles of normal and deafferented newts In freely moving animals muscle potentials were recorded with the aid of a Hellige EEG apparatus combined with a set of transistorized preamplifiers of high input impedance The steps, as the animals lifted up and put down the limb, were electrically signalled The myograms revealed a delicate interaction of antagonistic muscle groups The normal activity pattern of muscles was maintained following deafferentation of one or both forelimbs, although irregularities in placing the deafferented limb were apparent It was concluded that the spinal cord is capable of securing the accurately timed activity of agonistic and antagonistic limb muscles without receiving afferent information from the moving limb

Demonstration of a somatotopical pattern in the cortico-olivary projection in the cat. An experimental-anatomical study.

Abstract: Following small lesions of the first sensorimotor (MSI) and second somatosensory (SII) cortical areas the ensuing degeneration in the inferior olives was studied with the Nauta method in 14 cats. No convincing signs of degeneration were found in the olives in cases with lesions restricted to the first and second somatosensory areas (SI and SII). Following lesions of the primary “motor” cortex (anterior sigmoid gyrus and rostral part of the coronal gyrus) degeneration was consistently found in the olive of both sides. The contralateral projection is somewhat more abundant than the ipsilateral, but both are modest. Degeneration is restricted to certain parts of the olivary complex (see Fig. 11). Lesions restricted to different somatotopical subdivisions of the primary “motor” cortex give rise to degeneration distributed in a somatotopical pattern in certain areas of the medial and dorsal accessory olives and the rostral part of the ventral lamella. Somatotopical patterns could not be established in the smaller projections to some other minor olivary regions. When the findings are correlated with the pattern of the olivocerebellar projection it can be concluded that there is a somatotopically organized direct corticoolivo-cerebellar pathway to the intermediate part of the anterior lobe, the posterior vermis and the crus II. Attempts to correlate the findings with physiological observations are difficult. It appears that the current view that climbing fibres arise only in the olive may need revision. The role of the pontine nuclei in mediating somatotopically localized cerebellocerebellar impulses appears to have been underestimated.

The action of glycine on cortical neurones.

Abstract: 1. Microiontophoretic applications on cortical neurones in the “cerveaux isoles” of cats show that glycine is only 1/4 as potent as GABA in blocking glutamate-evoked discharges. 2. Glycine produces only relatively slight changes in the membrane conductance of cortical neurones. Its action falls off rapidly during a prolonged application. 3. In most cases, glycine produces either no clear change in membrane potential or a small depolarization. Although there is a positive correlation between the IPSP reversal potential (EI) and the reversal potential for the effect of glycine (EGLY), EGLY is usually much more positive than EI. 4. Glycine causes no gross interference with the action of GABA or with cortical IPSPs. 5. It is concluded that glycine is unlikely to play a major role in cortical inhibition.

Correlation between cerebral blood volume and cerebral blood flow in the cat.

Abstract: Blood flow and blood volume were measured simultaneously in the same cerebral region in anaesthetized cats with controlled respiration. The measurements were made with the same scintillation-detector, using the freely diffusible indicator 133 Xenon for flow determinations and the intra-vascular indicator RISA (131I) for volume recordings. A very high correlation was found between volume and flow changes (r = .96, p < 0.001). This finding indicates that variations of regional cerebral blood volume are accompanied by proportional blood flow changes.

Electrophysiology of the intertectal commissures in the pigeon. II. Inhibitory interaction

Abstract: 1. In pigeons with one retina chronically removed, the tectal response to the stimulation of the contralateral eye was subjected to conditioning stimulation applied to the opposite tectum. The effect on evoked potentials and unitary responses was studied. 2. The response evoked by light flashes was depressed by the conditioning stimulation. In the response evoked by electrical stimulation of the optic nerve, the negative component of the slow wave was depressed by the conditioning stimulation. This depression was abolished by section of the tectal and posterior commissures. 3. Among 222 units activated by optic nerve stimulation, the conditioning tectal stimulation suppressed, delayed or reduced the discharge of 49 units (22%). The tectal stimulation did not evoke unitary discharge by itself nor had a facilitatory effect. The time course of the inhibition was from 5–70 msec with a maximal effect at 20–30 msec. The inhibited units had a latency longer than 4 msec and did not follow a stimulation frequency higher than I/sec. No unit could be inhibited in the superficial layers of the tectum, where the evoked response is negative, but 25% of the units were inhibited in the middle and deep layers, where the response is positive-negative or positive.