Unit responses in the auditory cortex to stimulation of geniculocortical fibers

Extracellular and intracellular single unit responses of neurons of the auditory cortex to electrical stimulation of geniculocortical fibers (GCF) were recorded in experiments on cats immobilized with tubocurarine. The latent period of responses of 15% of neurons to GCF stimulation was 0.3–1.5 msec. It is postulated that they were excited anti-dromically. The latent period of spikes generated by neurons responding to GCF stimulation orthodromically varied from 1.6 to 12 msec. In 28.6% of neurons the latent period was 1.6–2.5 msec. It is postulated that these neurons were excited monosynaptically. Intracellular recording revealed primary IPSPs in response to GCF stimulation in 63.3% of neurons, a brief EPSP followed by a prolonged IPSP in 17.7%, an EPSP-spike-IPSP complex in 12.3%, and subthreshold EPSPs in 7% of neurons. The latent period of the primary IPSPs varied from 1.8 to 11 msec, being 1.8–3.7 in 72%, 3.8–5.7 in 20.0%, and 5.8–11 msec in 8.0% of neurons. The latent period of responses beginning with an EPSP was 1–4 msec (mean 1.8 msec). Orthodromic responses arising 3–10 msec after the antidromic response, and consisting of 3–5 spikes, were recorded in some antidromically excited neurons. Hypotheses regarding the functional organization of the auditory cortex and mechanisms of inhibition in its neurons are put forward on the basis of the results obtained.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 4, No. 3, pp. 227–235, May–June, 1972.     

Postsynaptic potentials of neurons of the cat auditory cortex

The electrical reactions of 294 neurons of the auditory cortex to a click were recorded in experiments on cats immobilized with tubocurarine (174 intra- and 120 extracellularly). The value of the membrane potential varied from 30 to 70 mV with intracellular leads. The following types of reactions were obtained (the number of neurons is given in parentheses): a peak without slow oscillations in the membrane potential (4), EPSP (3), EPSP-peak (6), EPSP-peak-IPSP (17), EPSP-IPSP (9), primary IPSP (114, including 23 with an after-discharge). Twenty one neurons did not react to a click. The amplitude of the sub-threshold EPSP was 1–1.5 mV, the duration of the ascending part was about 10 and of the descending part 20–30 msec. The peak potential on the ascending part of the EPSP developed at the critical level of 3–4 mV. The amplitude of the peaks varied from several millivolts to 50–60. In 17 neurons prolonged hyperpolarization having all the properties of an IPSP, developed after the peak. The amplitude of these IPSP varied in different neurons from 1 to 10 mV and the duration varied from 20 to 80 msec. IPSP without preceding excitation of the given neuron were the predominant types of reaction. The latent period of these primary IPSP varied from 7 to 20 msec and the amplitude from 1 to 15 msec with a duration of 30–200, more frequently 80–100 msec. It is suggested that two types of inhibition develop in neurons of the auditory cortex in response to a click: recurrent and afferent. The functional significance of the first consists in limiting the duration of the discharge in the reacting neurons, the second prevents the development of excitation in adjacent neurons, thereby limiting the area of neuronal activity.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSSR, Kiev. Translated from Neirofiziologiya, Vol. 3, No. 4, pp. 339–349, July–August, 1971.     

Responses of medial geniculate body neurons to auditory cortical stimulation

Extracellular and intracellular unit responses of thepars principalis of the medial geniculate body to stimulation of the first (AI), second (AII), and third (AIII) auditory cortical areas were studied in cats immobilized with D-tubocurarine. In response to auditory cortical stimulation both antidromic (45–50%) and orthodromic (50–55%) responses occurred in the geniculate neurons. The latent period of the antidromic responses was 0.3–2.5 msec and of the orthodromic 2.0–18.0 msec. Late responses had a latent period of 30–200 msec. Of all neurons responding antidromically to stimulation of AII, 63% responded antidromically to stimulation of AI also, confirming the hypothesis that many of the same neurons of the medial geniculate body have projections into both auditory areas. Orthodromic responses of geniculate neurons consisted either of 1 or 2 spikes or of volleys of 8–12 spikes with a frequency of 300–600/sec. It is suggested that the volleys of spikes were discharges of inhibitory neurons. Intracellular responses were recorded in the form of antidromic spikes, EPSPs, EPSP-spike, EPSP-spike-IPSP, EPSP-IPSP, and primary IPSP. Over 50% of primary IPSP had a latent period of 2.0–4.0 msec. It is suggested that they arose through the participation of inhibitory interneurons located in the medial geniculate body.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 8, No. 1, pp. 5–12, January–February, 1976.     

Excitatory postsynaptic potentials of hippocampal neurons and their extinction during repeated stimulation

A method of detecting "minimal" excitatory postsynaptic potentials (EPSP) in neurons of hippocampal area CA₃ of the unanesthetized rabbit during stimulation of the septo-fimbrial region and the dentate fascia is described. The method consists of presenting a strong (a current of up to 1 mA) conditioning stimulus, inducing a distinct inhibitory postsynaptic potential (IPSP), before a near-threshold (current of 0.03–0.35 mA) testing stimulus. The response to the testing stimulus, develoing after the previous conditioning IPSP, in most cases was purely depolarizing and, judging from the change in the latent period in some cases and the absence of correlation between its amplitude and that of the IPSP, it is a pure EPSP. If the testing stimuli are presented at low enough frequency (intervals of not less than 1 sec) the amplitude of the EPSP evoked by them gradually falls. This decrease exhibits some of the characteristic properties of extinction of behavioral responses (recovery after an interruption, a more rapid decrease during repeated series of stimuli, a slower decrease in amplitude during less frequent stimulation). The amplitude of the IPSP also fell or showed no significant change. The results are evidence in support of the hypothesis that extinction is based on a mechanism of homosynaptic depression.Brain Institute, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 10, No. 1, pp. 3–12, January–February, 1978.     

Corticofugal postsynaptic influences on red nucleus neurons

The responses of red nucleus neurons to stimulation of the sensorimotor cortex was studied on nembutal-anesthetized cats. Most of the rubrospinal neurons were identified according to their antidromic activation. Stimulation of the sensorimotor cortex was shown to evoke in the red nucleus neurons monosynaptic excitatory potentials with a latency of 1.85 msec, polysynaptic excitatory potentials (EPSP), and inhibitory postsynaptic potentials (IPSP) with a latency of 9–24 msec. The EPSP often produced spikes. The probability of generation of spreading excitation is greater with motor cortex stimulation. The monosynaptic EPSP are assumed to arise under the influence of the impulses arriving over the corticorubral neurons as a result of excitation of axodendritic synapses. The radial type of branching of red nucleus neurons facilitates the transition from electrotonically spreading local depolarization to an action potential triggered by the initial axonal segment. Polysynaptic EPSP and IPSP seem to be a result of activation of fast pyramidal neurons whose axon collaterals are connected via interneurons with the soma of the red nucleus neurons.L. A. Orbeli Institute of Physiology of the Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 3, No. 1, pp. 43–51, January–February, 1971.     

Corticofugal influences on the motoneurons of the trigeminal nucleus

We studied the postsynaptic potentials evoked from 76 trigeminal motoneurons by stimulation of the motor (MI) and somatosensory (SI) cortex in the ipsilateral and contralateral hemispheres of the cat. Stimulation of these cortical regions evoked primarily inhibitory postsynaptic potentials (PSP) in the motoneuron of the masseter muscle, but we also observed excitatory PSP and mixed reactions of the EPSP/IPSP type. The average IPSP latent period for the motoneurons of the masseter on stimulation of the ipsilateral cortex was 6.1±0.3 msec, while that on stimulation of the contralateral cortex was 5.2±0.4 msec; the corresponding figures for the EPSP were 7.6±0.5 and 4.5±0.3 msec respectively. Corticofugal impulses evoked only EPSP and action potentials in the motoneurons of the digastric muscle (m. digastricus). The latent period of the EPSP was 7.6 msec when evoked by afferent impulses from the ipsilateral cortex and 5.4 msec when evoked by pulses from the contralateral cortex. The duration of the PSP ranged from 25 to 30 msec. Postsynaptic potentials developed in the motoneurons studied when the cortex was stimulated with a single stimulus. An increase in the number of stimuli in the series led to a rise in the PSP amplitude and a reduction in the latent periods. When the cortex was stimulated with a series of pulses (lasting 1.0 msec), the IPSP were prolonged by appearance of a late slow component. We have hypothesized that activation of the trigeminal motoneurons by corticofugal impulsation is effected through a polysynaptic pathway; each functional group of motoneurons is activated in the same manner by the ipsilateral and contralateral cortex. The excitation of the digastric motoneurons and inhibition of the masseter motoneurons indicates reciprocal cortical control of their activity.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 3, No. 5, pp. 512–519, September–October, 1971.     

Unit responses in the cat auditory cortex to medial geniculate body stimulation

Responses of 98 auditory cortical neurons to electrical stimulation of the medial geniculate body (MGB) were recorded (45 extracellulary, 53 intracellularly) in experiments on cats immobilized with tubocurarine. Responses of the same neurons to clicks were recorded for comparison. Of the total number of neurons, 75 (76%) responded both to MGB stimulation and to clicks, and 23 (24%) to MGB stimulation only. The latent period of extracellularly recorded action potentials of auditory cortical neurons in response to clicks varied from 7 to 28 msec (late responses were disregarded), and that to MGB stimulation varied from 1.5 to 12.5 msec. For EPSPs these values were 8–13 and 1–4 msec respectively. The latent period of IPSPs arising in response to MGB stimulation varied from 2.2 to 6.5 msec; for 34% of neurons it did not exceed 3 msec. The difference between the latent periods of responses to clicks and to MGB stimulation varied for different neurons from 6 to 21 msec. Responses of 11% of neurons to MGB stimulation, recorded intracellularly, consisted of sub-threshold EPSPs, while responses of 23% of neurons began with an EPSP which was either followed by an action potential and subsequent IPSP or was at once cut off by an IPSP; 66% of neurons responded with primary IPSPs. Neurons responding to MGB stimulation by primary IPSPs are distributed irregularly in the depth of the cortex: there are very few in layers III and IV and many more at a depth of 1.6–2 mm. Conversely, excited neurons are predominant in layer III and IV, and they are few in number at a depth of 1.6–2 mm. It is concluded that the afferent volley reaching the auditory cortex induces excitation of some neurons therein and, at the same time, by the principle of reciprocity, induces inhibition of others. This afferent inhibition takes place with the participation of inhibitory interneurons, and in some cells the inhibition is recurrent. The existence of reciprocal relationships between neurons in different layers of the auditory cortex is postulated.A. A. Bogomolets' Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 4, No. 1, pp. 23–31, January–February, 1972.     

Connections of neurons of the cat somatosensory cortex with the thalamic relay nuclei

Of 103 neurons in the rostral part of the posterior sigmoid gyrus of the cat cortex 30 responded to stimulation of the ventro-posterolateral and ventrolateral nuclei of the thalamus (VPL and VL), 42 responded to stimulation of VL only, and 31 to stimulation of VPL only. It was shown by intracellular recording that stimulation of VPL induces a spike response with or without subsequent IPSPs in some neurons and an initial IPSP in others. The spike frequency of single neurons reached 60/sec, but the IPSP frequency never exceeded 10–20/sec. Stimulation of VL was accompanied by: a) antidromic spike responses; b) short-latency monosynaptic EPSPs and spikes capable of following a stimulation frequency of 100/sec; c) long-latency polysynaptic EPSPs and spikes appearing in response to stimulation at 4–8/sec; d) short-latency IPSPs; e) long-latency IPSPs increasing in intensity on repetition of infrequent stimuli. It is concluded that the afferent inputs from the relay nuclei to neurons of the somatosensory cortex are heterogeneous. An important role is postulated for recurrent inhibition in the genesis of the long-latency IPSPs arising in response to stimulation of VL, and for direct afferent inhibition during IPSPs evoked by stimulation of VPL. It is shown that the rostral part of the posterior sigmoid gyrus performs the role of somatic projection and motor cortex simultaneously.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 4, No. 3, pp. 245–255, May–June, 1972.     

Responses of neurons in the vibrissae projection area of the cat somatosensory cortex to afferent activation

Responses of 375 primary somatosensory cortical neurons located in the projection area of the vibrissae to electrical stimulation of the infraorbital nerve and also to adequate stimulation of the vibrissae were investigated in unanesthetized cats immobilized with tubocurarine. Stimulation of the nerve and vibrissae most frequently evoked synaptic responses in the neurons, in the form of a short EPSP followed by an IPSP or, less frequently, as a primary IPSP; during extracellular recordings corresponding changes were observed in spike activity. In response to stimulation of the vibrissae, initial inhibition was found more often than to stimulation of the nerve (in 45 and 16% of neurons respectively). The difference between the minimal values of latent periods of IPSP and EPSP evoked by stimulation of the infraorbital nerve was 0.8 msec in different neurons, and the difference between the mean values 1.4 msec. Directional sensitivity of the cortical neurons was demonstrated (to a change in the direction of deflection of the vibrissae). Neurons located close together could differ in the character of their directional sensitivity during stimulation of the same vibrissae. It is concluded that short-latency inhibition arising in the primary projection area of the cat somatosensory cortex is predominantly afferent and not recurrent. The probable mechanisms of directional sensitivity of the neurons studied are discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSSR, Kiev. Translated from Neirofiziologia, Vol. 11, No. 6, pp. 550–559, November, 1979.     

Aspects of excitation and inhibition produced in parietal association cortex neurons by stimulating thalamic association nuclei

Neuronal response to single stimuli applied to the thalamic dorsolateral and posterolateral nuclei (DLN and PLN resepctively) was investigated in the parietal association cortex. Primary IPSP following DLN and PLN stimulation was noted in 62.5% and 79.6% of instances respectively. Latencies of EPSP and IPSP when stimulating the two nuclei were longer for the DLN. The amplitude of EPSP evoked by stimulating association nuclei rose and declined smoothly, while that of IPSP showed a fast rise and a more steady decline. The EPSP appearing during the evolution of IPSP were of higher amplitude than control level of resting potential. Both amplitude and duration of IPSP induced in a single unit by stimulating different association nuclei were extremely similar, thus confirming the involvement in this operation of the same inhibitory cortical interneurons. Duration of IPSP was shorter than that of inhibitory background spike activity. It is postulated that the discrepancy in duration can largely be ascribed to properties of the neurons themselves.State University, Odessa. Translated from Neirofiziologiya, Vol. 23, No. 5, pp. 529–536, September–October, 1991.     

Intracellular responses of primary auditory cortical neurons to tones of different frequencies and to electrical stimulation of spiral ganglion fibers in cat

Experiments on cats anesthetized with pentobarbital showed that, depending on the intensity and frequency of acoustic stimulation, neurons in auditory area AI give responses of EPSP, EPSP-spike-IPSP, EPSP-IPSP, and IPSP type. Presentation of a tone of characteristic or near-characteristic frequency and above-threshold intensity, and also electrical stimulation of nerve fibers of the spiral ganglion, innervating the central zone of the receptive field of the neuron, evoke in most cases a response of EPSP-spike-IPSP type. Tone differing considerably in frequency from the characteristic, and electrical stimulation of peripheral zones of the receptive field, evoked responses of EPSP-IPSP or IPSP type. The range of frequencies of tones to which, at threshold intensity, an action potential is generated by the neuron is considerably narrower than the range of frequencies of tones evoking an EPSP and IPSP. Above the intensity of tone threshold IPSP is an invariable component of the response of most neurons in area AI. The appearance of an IPSP in the neuron is accompanied by depression of spontaneous activity and the neuronal response to testing stimulation. Two types of IPSP were distinguished: One type is a component of the EPSP-spike-IPSP response and arises during excitation of auditory receptors located in the central part of the receptive field of the neuron, the other arises during excitation of receptors located at the periphery of the field, and which project to neurons with other characteristic frequencies. The former arise after spike excitation of the neuron, the latter after EPSP or primarily.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 16, No. 1, pp. 123–131, January–February, 1984.     

Rubrospinal synaptic influences on the lumbar motoneurons of the rat

Intracellular recording was employed in experiments on rats with the nervous system intact and after acute pyramidotomy to study the postsynaptic effects produced in the lumbar motoneurons on stimulation of the nucleus ruber. Stimulation of this nucleus with single stimuli and with a short series of stimuli caused excitatory and inhibitory postsynaptic potentials (EPSP and IPSP) to develop in the motoneurons. Most of the EPSP recorded were disynaptic, but response development involved a monosynaptic segmental delay in five of the 124 cells that exhibited EPSP. A capacity for high-frequency potentiation was a characteristic feature of the disynaptic excitatory and inhibitory effects. Transmembrane polarization of the motoneurons had a marked influence on the amplitude of the disynaptic EPSP and IPSP. The properties of the disynaptic rubrospinal influences were similar to those described for the cat.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 3, No. 3, pp. 266–273, May–June, 1971.     

Responses of bulbar neurons to stimulation of locomotor and inhibitory sites in the cat brainstem

Bulbar locomotor and inhibitory sites were located in the pons of mesencephalic decerebellate cats. Rhythmic stimulation of locomotor sites through microelectrodes at the rate of 60 Hz elicited stepping movements in the forelimbs which were halted when the inhibitory sites were rhythmically stimulated. Neuronal response was elicited by single or paired stimulation of locomotor sites at the rate of 1.5 Hz or by applying a series of 2–4 stimuli spaced 2 msec apart to the inhibitory site. Medial neurons generated synaptic responses (postsynaptic potentials or action potentials) to stimulation of the inhibitory site twice as frequently as when the locomotor site was stimulated. Responses in lateral neurons, however, occurred twice as frequently to stimulation of the locomotor site, while IPSP were only observed half as often as EPSP in neurons of both groups. In neurons excited by stimulation of the locomotor site, stimulation of the inhibitory site did not normally produce IPSP. Possible mechanisms underlying the halt of locomotion occurring in response to stimulation of the inhibitory site are discussed.Information Transmission Institute, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 18, No. 4, pp. 525–533, July–August, 1986.     

Unit responses of the pericruciate cortex to stimulation of the medial geniculate body

Responses of 239 neurons of the pericruciate cortex to stimulation of the medial geniculate body and pyramidal tract were investigated (189 extracellularly, 50 intracellularly) in cats anesthetized with thiopental and immobilized with D-tubocurarine. In response to stimulation of the medial geniculate body, the mean spontaneous firing rate of 63.6% of neurons in the pericruciate cortex increased by 10–25%, in 23.6% of neurons it decreased within the same limits, and mixed effects were observed in 5.5% of neurons. Phasic responses to single stimulation of the medial geniculate body were observed in 20% of neurons of the pericruciate cortex. Responses with a latent period of 0.3–1.0 msec (16%) were classed as antidromic, those with a latent period of 1.5–2.0 msec (20%) as orthodromic, monosynaptic, and those with a latent period of 2.5–4.0 msec or more (64%) as polysynaptic. With intracellular recording, excitatory responses of the EPSP, EPSP-AP, and AP type with latent periods of between 1.3 and 19.5 msec developed in 78.2% of cells. IPSPs, which were recorded in 21.8% of neurons, were usually found as components of mixed responses; primary IPSPs were found in only two cases. Monosynaptic connection of the medial geniculate body was shown to take place with neurons of the pericruciate cortex that did not belong to the pyramidal tract.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 11, No. 1, pp. 18–24, January–February, 1979.     

Connections of the second auditory cortical area with the medial geniculate body and the first auditory area

Extra — and intracellular unit responses in area AII to stimulation of geniculocortical fibers and of area AI were studied in cat immobilized with D-tubocurarine. In response to stimulation of geniculocortical fibers, antidromic mono-, di-, and polysynaptic spikes were generated by neurons in area AII. The number of antidromic responses in area AII was about half that found in area AI under the same conditions of stimulation. Most of the orthodromic responses were di- and polysynaptic. Intracellular responses also were recorded in the form of EPSPs, EPSP-IPSPs, and primary IPSPs. Stimulation of area AI evoked responses in the neurons of area AII with latent periods of 0.75–6.0, 6.1–16.0, 18.0–23.0, and 60–100 msec. Removal of the medial geniculate body led to a marked decrease in the number of responses with latent periods of 6.1–16.0 msec. Some neurons of area AII responded by spikes to stimulation of both the geniculocortical fibers and area AI. Comparison of the latent periods of responses to these two types of stimulation showed that impulses from area AI to area AII are directed both to input neurons for impulses from the medial geniculate body and to neurons at subsequent stages of the intracortical neuronal change. In response to stimulation of cortical area AI, disynaptic IPSPs appeared in many neurons of area AII. Only one IPSP with a latent period of 1.0 msec, regardable as monosynaptic, was recorded.     

Electrophysiological investigation of conduction of afferent impulses through the medial geniculate body

Extra- and intracellular reactions of 280 neurons of the pars principalis of the medial geniculate body (MGB) and of 408 auditory cortical neurons in area AI to stimulation of the inferior brachium of the midbrain and geniculocortical fibers were studied in cats immobilized with D-tubocurarine. Single electrical stimulation of the inferior brachium was shown to evoke a long and complex neuronal response in MGB in the form of excitation of some and inhibition of other neurons. The initial component of this response lasted 13 msec. Excitation of 72% of neurons participating in the response took place during the first 3 msec after the beginning of stimulation. In the same period 84% of IPSP arose. The inferior brachium was shown to contain a certain number of descending fibers. Some of them are axons of MGB neurons. Many fibers of the inferior brachium reach the auditory cortex without synaptic relay in MGB. Of all cells of MGB excited by stimulation of the inferior brachium monosynaptically, 76% are thalamocortical relay neurons; the rest are interneurons. Of the relay neurons of MGB 90% are excited monosynaptically, the rest by impulses passing through two or three synaptic relays in MGB. During stimulation of the inferior brachium, responses consisting of EPSP-IPSP and primary IPSP are recorded in many neurons of MGB. About 20% of primary IPSP arise monosynaptically, evidently in response to stimulation of inhibitory fibers of the inferior brachium. Most IPSP arise disynaptically, with the participation of an inhibitory interneuron located at the entrance to MGB. Inhibition observed in this case is direct afferent in nature.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 11, No. 6, pp. 515–523, November–December, 1979.     

Characteristics of unit responses of the cat cerebellar cortex to acoustic stimuli

Investigation of unit responses of the cerebellar cortex (lobules VI–VII of the vermis) to acoustic stimulation showed that the great majority of neurons responded by a discharge of one spike or a group of spikes with a latent period of 10–40 msec and with a low fluctuation value. Neurons identified as Purkinje cells responded to sound either by inhibition of spontaneous activity or by a "climbing fiber response" with a latent period of 40–60 msec and with a high fluctuation value. In 4 of 80 neurons a prolonged (lasting about 1 sec or more), variable response with a latent period of 225–580 msec was observed. The minimal thresholds of unit responses to acoustic stimuli were distributed within the range from –7 to 77 dB, with a mode from 20 to 50 dB. All the characteristics of the cerebellar unit responses studied were independent of the intensity, duration, and frequency of the sound, like neurons of short-latency type in the inferior colliculi. In certain properties — firing pattern, latent period, and threshold of response — the cerebellar neurons resemble neurons of higher levels of the auditory system: the medial geniculate body and auditory cortex.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 5, No. 1, pp. 3–12, January–February, 1973.     

Synaptic processes in the neurons of Clarke's column evoked by an antidromic volley from the dorsolateral column

In cats under nembutal-chloralose anaesthesia we investigated the response of neurons of Clarke's column to stimulation of axons ascending in the dorsal part of the lateral funiculus. Excitation of the descending fibers of the funiculus was prevented either by an ipsilateral hemisection of the thoracic cord carried out 7–10 days previously, which caused them to degenerate, or by stimulation of ascending axons in the region of the restiform bodies. It was found that with both kinds of stimulation records could be obtained from neurons in Clarke's column in which a descending volley causes not antidromic action potentials but primary excitatory postsynaptic potentials (EPSP). The length of the latent period of the EPSP (10–15 msec) suggests that they are monosynaptic. Such neurons may also be activated by low- or high-threshold afferents from various muscles; evidently they correspond to those described by Retheyi [14] as "edge" neurons on which terminate collaterals of axons ascending in the dorsal spinocerebellar tract (DSCT). In some of the neurons of the DSCT whose axons are distinguished by a low conduction velocity, stimulation of the dorsolateral funiculus caused not only antidromic spikes but also EPSP's following after them, and it would seem that the "edge" neurons were involved in their formation. We consider the possible functional role of a negative feed back loop formed by axon collaterals of neurons of the DSCT and by the "edge" neurons.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 2, No. 3, pp. 269–278, May–June, 1970.     

Conduction of excitation in the cat visual system

Unit responses in area 17 of the visual cortex to stimulation of the lateral geniculate body and optic tract were studied in experiments on unanesthetized cats immobilized with D-tubocurarine. Of the neurons tested, 53.6% responded to stimulation of the lateral geniculate body. In 92% of these cells the responses were orthodromic with latent periods of between 2 and 12.5 msec. Most cells responded with latent periods of 2.0–2.5, 3.0–3.5, and 4.0–4.5 msec, corresponding to latent periods of the components of the electropositive wave of the primary response. Antidromic responses to stimulation of the lateral geniculate body were given by 8% of neurons. The difference between the latent periods of responses of the same visual cortical neurons to stimulation of the optic tract and lateral geniculate body was 0.1–1.8 msec, but for most neurons (55.8%) it was 0.5–1 msec. The histograms of response latencies of visual cortical neurons to stimulation of the above-mentioned formations were found to be similar. It is concluded that the optic radiation contains three principal groups of fibers with conduction velocities of 28.5–16.6, 11.7–8.9, and 7.4–6.0 m/sec, respectively.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 7, No. 6, pp. 589–596, November–December, 1975.     

Suppression of "fast" IPSP,superposed on "slow", as a possible cause of priming in murine hippocampus

Intra- and extracellular response in area CA1 to stimulation of two independent afferent inputs, one a priming or conditioned and the other a test or primed input (C1 and C2, respectively) were recorded in surviving murine hippocampal slices. Duration and amplitude of test field potentials (FP) and of excitatory postsynaptic potentials (EPSP), were measured, as well as amplitude of "fast" and "slow" components of inhibitory postsynaptic potentials or stimulation varying between 0 and 1 sec. Conditioning brought about an increase in the duration of FP, in duration and amplitude of EPSP, and suppression of IPSP at intervals of between 50 and 500 msec peaking at 200 msec (i.e., priming effect). These changes correlated with level of IPSP_b in response to conditioned stimuli. The most pronounced effect could be seen in neurons manifesting hyperpolarizing IPSP in response to test stimuli. Suppression of test IPSP_a after superposition on IPSP_b is thought to bring about the increase in test FP and EPSP seen during priming.Institute for Brain Research, All-Union Mental Health Research Center, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 22, No. 6, pp. 730–739, November–December, 1990.