After-effects of repetitive stimulation in spinal neurons

Spontaneous activity of interneurons before and after repetitive stimulation at 0.1–0.5/sec was recorded in acute experiments on spinal cats and kittens. Using the dynamic selective correlation method a search was made for areas of spontaneous activity with the same distribution of action potentials in time as in the averaged evoked response to a single stimulus. In the case of some neurons portions of the background which correlate reliably in structure with the evoked response repeated at an interval equal to or a multiple of the interval of stimulation. Reproduction of the rhythm of stimulation in the spontaneous activity is intensified with an increase in the total duration of preceding stimulation with the same input and shows positive correlation with the degree of posttetanic potentiation. The facts obtained are evidence of prolonged after-processes in spinal neurons.Institute of Experimental Medicine, Academy of Medical Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 5, No. 3, pp. 272–280, May–June, 1973.     

Role of different types of fibers of the infraorbital nerve in synaptic activation of masseter and digastric motoneurons

Postsynaptic potentials of motoneurons of the masseter and digastric muscles evoked by stimulation of the infraorbital nerve with a strength of between 1 and 10 thresholds were investigated in cats anesthetized with a mixture of chloralose and pentobarbital. Depending on their ability to be activated by low-threshold afferents of this nerve, motoneurons of the masseter were divided into two groups. Stimuli with a strength of 1.2–2.5 times above threshold for the most excitable fibers of the infraorbital nerve evoked short-latency EPSPs in the motoneurons of the first group; a further increase in stimulus strength (3–9 thresholds) led to the appearance of IPSPs with latent periods of 2.8–3.5 msec. Motoneurons of the second group responded to stimulation of the infraorbital nerve with a strength of 3–9 thresholds by IPSPs whose latent periods varied from 6 to 8 msec. Stimuli below 3 thresholds in strength evoked no responses in these motoneurons. Stimulation of the infraorbital nerve with pulses of between 1 and 2 thresholds in strength evoked EPSPs in digastric motoneurons, but an increase in the strength of stimulation led to action potential generation. The presence of many excitatory and inhibitory inputs formed by afferent fibers of different types evidently provides a basis for functional diversity of jaw-opening and jaw-closing reflexes.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 12, No. 6, pp. 596–603, November–December, 1980.     

Analysis of long-latency components of field potentials evoked by stimulation of the cerebral cortex and nerves in the cerebellar paramedian lobule

Field potentials evoked in the graunular layer of the cerebellar paramedian lobule of unanesthetized cats in response to stimulation of the sensomotor cortex and limb nerves contained slow negative waves, appearing after a long latent period, which were generated by granule cells. In the case of nerve stimulation this component was recorded both inside and outside the projection zone of the corresponding limb. Cortical stimulation by single stimuli or series of stimuli not more than 1.8–2.5 times above threshold strength led to the appearance of evoked potentials only inside the corresponding projection zone. The long-latency component of field potentials evoked by cerebral stimulation followed high frequencies of repetitive stimulation and was less sensitive to the action of barbital anesthesia than the analogous component of potentials evoked by nerve stimulation. In the case of combined cerebral and nerve stimulation the long-latency components underwent summation. It is concluded that mossy fibers of slowly-conducting spino- and cerebrocerebellar tracts innervate different granule cells in the cerebellar cortex.Institute of Problems in Information Transmission, Academy of Sciences of the USSR, Moscow. M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 14, No. 4, pp. 379–385, July–August, 1982.     

Posttetanic changes in hippocampal minimal evoked potentials

Changes in the EEG induced by a single spike were recorded in the hippocampus of an unanesthetized rabbit. Summation of focal electrical activity synchronous with spontaneous single unit discharges at the symmetrical point of contralateral hemisphere revealed no stable potentials which could reflect these changes. In two cases discharges identified as activity of Shaffer's collaterals were recorded in area CA₁. Summation of post-spike changes in evoked activity recorded by the same microelectrode showed stable negative waves with an amplitute of 40–60 µV, which could have been evoked by single spikes. The curve of amplitude of the averaged evoked potentials versus near-threshold current strength stimulating the intrahippocampal pathways was not smooth in most experiments but stepwise in character. It is suggested that the minimal evoked potential corresponding to the first step (amplitude 40–80 µV) reflects a response to stimulation of one fiber. After above-threshold tetanization prolonged posttetanic potentiation of the minimal evoked potentials did not arise in CA₁ in response to stimulation of Shaffer's collaterals. Minimal evoked potentials recorded in area CA₃ in response to stimulation of the dentate fascia showed clear potentiation. The results are in agreement with the hypothesis of the synaptic localization of the mechanisms responsible for prolonged posttetanic potentiation.Brain Institute, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 9, No. 2, pp. 124–134, March–April, 1977.     

Depression of evoked potentials in rat thalamic ventro-basal complex and somatosensory cortex after reticular stimulation

Experiments on unanesthetized rats immobilized with D-tubocurarine showed that electrical stimulation (100/sec) of the central gray matter and the mesencephalic and medullary reticular formation considerably depressed potentials in the somatic thalamic relay nucleus and somatosensory cortex evoked by stimulation of the forelimb or medial lemniscus. The mean threshold values of the current used for electrical stimulation of these structures did not differ significantly and were 70 (20–100), 100 (20–120), and 120 (50–200) µA, respectively. On comparison of the amplitude-temporal characteristics of inhibition of evoked potentials during electrical stimulation of the above-mentioned structures by a current of twice the threshold strength, no significant differences were found. Immediately after the end of electrical stimulation the amplitude of the cortical evolved potential and the post-synaptic components of the thalamic evoked potential was 50–60% (P<0.01) below the control values. The duration of this depression varied from 0.5 to 1 sec. An increase in the intensity of electrical stimulation of brain-stem structures to between three and five times the threshold led to depression of the presynaptic component of the thalamic evoked potential also. Depression of the evoked potential as described above was found with various ratios between the intensities of conditioning and testing stimuli.M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 8, No. 5, pp. 467–475, September–October, 1976.     

Synaptic potentials of motoneurons of the masseter muscle

Postsynaptic potentials of 93 motoneurons of the masseter muscle evoked by stimulation of different branches of the trigeminal nerve were studied. Stimulation of the most excitable afferent fibers of the motor nerve of the masseter muscle evoked monosynaptic EPSPs with a latent period of 1.2–2.0 msec, changing into action potentials when the strength of stimulation was increased. A further increase in the strength of stimulation produced an antidromic action potential in the motoneurons with a latent period of 0.9 msec. In some motoneurons polysynaptic EPSPs and action potentials developed following stimulation of the motor nerve to the masseter muscle. The ascending phase of synaptic and antidromic action potentials was subdivided into IS and SD components, while the descending phase ended with definite depolarization and hyperpolarization after-potentials. Stimulation of cutaneous branches of the trigeminal nerve, and also of the motor nerve of the antagonist muscle (digastric) evoked IPSPs with a latent period of 2.7–3.5 msec in motoneurons of the masseter muscle. These results indicate the existence of functional connections between motoneurons of the masseter muscle and its proprioceptive afferent fibers, and also with proprioceptive afferent fibers of the antagonist muscle and cutaneous afferent fibers.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 1, No. 3, pp. 262–268, November–December, 1969.     

Effect of local cooling of the cortex on evoked potentials in the reticular formation in response to somatosensory stimulation

Potentials evoked in nuclei of the reticular formation by electrodermal stimulation of the limbs were investigated in acute experiments on unanesthetized, immobilized rats during cooling of the somatosensory cortex in the area of representation of one forelimb. Evoked potentials in the reticular formation were found to depend on the degree of cold inhibition of the cortical primary response to the same stimulation. The peak time of the main negative wave increased from 40–50 to 60–80 msec with a simultaneous decrease in its amplitude or its total disappearance in the case of deep cooling of the cortex. Cooling of the cortex had a similar although weaker effect on the earlier wave of the evoked potential with a peak time of 14 msec, recorded in the ventral reticular nucleus. In parallel recordings of potentials evoked by stimulation of other limbs they remained unchanged at these same points of the reticular formation or were reduced in amplitude while preserving the same temporal parameters. Cooling of the cortex thus selectively delays the development and reduces the amplitude of the response to stimulation of the limb in whose area of representation transformation of the afferent signal into a corticofugal volley is blocked. Consequently the normal development of both late and early components of the potential evoked in the reticular formation by somatic stimulation requires an additional volley, descending from the cortex, and formed as a result of transformation of the same afferent signal in the corresponding point of the somatosensory cortex.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 13, No. 1, pp. 32–38, January–February, 1981.     

Inhibition in hippocampal pyramidal neurons during peripheral stimulation

Responses of hippocampal pyramidal neurons were investigated intracellularly in unanesthetized rabbits immobilized with tubocurarine. A single stimulus, applied to the sciatic nerve, evoked prolonged (up to 2.5 sec) hyperpolarization of the cell membrane, accompanied by inhibition of action potentials. The latent period of the evoked hyperpolarization was 48±16.4 msec, and its amplitude 2.5±1.9 mV. In some neurons the development of hyperpolarization potentials was preceded by excitation. The suggestion is made that hyperpolarization of the membrane of pyramidal cells during peripheral stimulation is manifested as an inhibitory postsynaptic potential (IPSP), generated with the participation of hippocampal interneurons. The possibility of prolonged tonic action of interneurons from outside as a cause of prolonged inhibition of the pyramidal neurons is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 1, No. 3, pp. 278–284, November–December, 1969.     

Spatial configuration of rabbit superior collicular evoked response to punctiform afferent stimulation

Evoked potentials arising in the rabbit superior colliculus in response to punctiform stimulation of the receptive field were studied. This response has only negative polarity at the focus of maximal activity and does not exhibit reversal of the potential which is a characteristic feature of the response to diffuse stimulation. The evoked potential was recorded at depths of between 0.1 and 0.9–1.0 mm from the collicular surface, corresponding to the stratum griseum superficiale. The response disappeared when the stimulating spot was shifted through 4–6° away from the optical position. It is suggested that evoked potentials to punctiform stimulation can give more complete information on the location of different synapses.A. N. Severtsov Institute of Evolutionary Morphology and Ecology of Animals, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 11, No. 5, pp. 441–450, September–October, 1979.     

Evoked potentials to electrical stimulation of the facial nerve in the carp tectum mesencephali

Tectal evoked potentials to stimulation of the facial nerve, containing afferent fibers of nonolfactory chemoreception, in the carp are positive evoked potentials with a latent period of 5 to 25 msec which show no phase shift as the microelectrode is advanced to a depth of 600 µ. Depending on the amplitude and latency of evoked potentials seven active zones differing in one or both parameters were distinguished in the ipsilateral tectum mesencephali. The role of impulses from the medulla in the mechanism of tectal evoked potentials to facial nerve stimulation is proved by differences in latent periods and disappearance of the tectal response (although it is preserved in the primary center) after severance of connections between the two parts of the brain. Descending influences from the tectum on the primary center were found: its extirpation disturbs evoked potential generation in several parts of the medullla, so that they either disappear completely or their parameters are modified.A. A. Zhdanov State University, Leningrad. Translated from Neirofiziologiya, Vol. 8, No. 1, pp. 39–46, January–February, 1976.     

Mechanisms of interaction between the parietal association and projection areas of the cat neocortex

Changes in evoked potentials in the first visual (VI), first somatic (SI), and parietal areas of the cortex during local cooling of each area were investigated under pentobarbital anesthesia. Two types of interaction were distinguished. Type I interaction was found in all areas in the early stages of local cooling and was reflected in a similar decrease in amplitude of evoked potentials in intact parts of the cortex. In the thalamic association nuclei — the pulvinar and posterolateral nucleus — somatic evoked potentials were unchanged but visual were transformed differently from those in the cortex. Type IIinteraction was found in the later stages of cooling and only between the association area and each of the projection areas. It was reflected in a greater change in amplitude of the evoked potentials and also in their configuration. In response to somatic stimulation in the early stage of type II interaction transformation of evoked potentials in the cortex took place sooner than in the nuclei; in the later stage it took place immediately after transformation of the "subcortical" evoked potentials. In response to photic stimulation transformations of cortical evoked potentials were always preceded by the corresponding transformations in the nuclei. It is suggested that type I interaction is formed by intercortical connections and type II by direct and subcortical relay connections. Differences in the role of the association area in interaction of types I and II when activated by stimuli of different modalities are discussed.Brain Institute, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 10, No. 6, pp. 573–581, November–December, 1978.     

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.     

Effect of injury to the lateral reticular nucleus and nuclei of the inferior olive on electrical responses of the cerebellar cortex evoked by vagus nerve stimulation in cats

The role of the lateral reticular nucleus and nuclei of the inferior olive in the formation of cerebellar cortical evoked potentials in response to vagus nerve stimulation was determined in experiments on 28 cats anesthetized with chloralose and pentobarbital. After electrolytic destruction of the lateral reticular nucleus, in response to vagus nerve stimulation, especially ipsilateral, lengthening of the latent period and a decrease in amplitude of evoked potentials were observed; after bilateral destruction of this nucleus, evoked potentials could be completely suppressed. It is concluded that the lateral reticular nucleus relays interoceptive impulses in the vagus nerve system on to the cerebellar cortex. Additional evidence was given by the appearance of spike responses of Purkinje cells, in the form of mainly simple discharges, to stimulation of the vagus nerve. After destruction of the nuclei of the inferior olive, the latent period and the number of components of evoked potentials in response to vagus nerve stimulation remained unchanged but their amplitude was reduced. The role of the nuclei of the inferior olive as a regulator of the intensity of the flow of interoceptive impulses to the cerebellum is discussed.N. I. Pirogov Medical Institute, Vinnitsa. Translated from Neirofiziologiya, Vol. 9, No. 3, pp. 290–299, May–June, 1977.     

Features of evoked potentials in the cerebellar cortex of rabbits

We investigated evoked responses of the cerebellar cortex of rabbits under Nembutal or chloralose anesthesia to stimulation of the sciatic, brachial, and vagus nerves. The parameters of evoked potentials (E Ps), together with features of their distribution throughout the cerebellar cortex, enabled us to divide them provisionally into three types. Evoked potentials of the first type have a latent period of 5–10 msec and a two-phase or more complex shape. Evoked potentials of the second type have a latent period of 10–23 msec and include from one to four components. Evoked potentials of the third type are discharges with long latent periods (20–50 msec) and consist of a series of slow sinusoidal oscillations. Appearance of an initial electronegative component is characteristic of EPs of the cerebellar cortex of rabbits, especially those of the second and third types. Evoked potentials of the first type are local.N. I. Pirogov Vinnitsa Medical Institute. Translated from Neirofiziologiya, Vol. 1, No. 1, pp. 73–80, July–August, 1969.     

Comparison of evoked potentials to tones and clicks recorded simulataneously by multiple electrodes from the auditory cortex in unanesthetized cats

Evoked potentials to tones and clicks were recorded simultaneously from seven points of the auditory cortex and one or two points of the somatosensory cortex in unanesthetized cats. Comparison of evoked potentials to tones of equal loudness in the 250–7000 Hz band showed no common pattern of cortical tonotopic distribution. However, an individual dependence of the components of the evoked potential on pitch and on localization of the recording point exists for each animal. With a change in stimulus intensity the absolute and relative values of these components of the evoked potential vary. The initial positive waves are the most variable; besides the two waves already known a third, intermediate wave, particulary sensitive to loudness, was discovered. The negative wave of the primary response increases proportionally to loudness. Evoked potentials to clicks are more uniform over the auditory cortex and more stable than those to tones. Responses appeared in the somatosensory cortex to loud stimuli, more regularly to clicks than to tones. It is concluded that the parameter of pitch is reflected in the cat cortex as a complex spatially-individual distribution of the amplitude and time parameters of the evoked potentials.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 7, No. 2, pp. 115–125, March–April, 1975.     

Evoked potentials in the parafascicular complex of the rabbit thalamus during peripheral noxious stimulation

Systematic research was conducted into the parafascicular complex of the nonspecific nociceptive system of the rabbit hypothalamus using a technique of evoked potentials. Two types of evoked response were recorded during electrocutaneous stimulation of the paw; a compound response consisting of early and late positive-negative potentials in the lateral region and a simple positive-negative evoked potential in the medial area. Evidence suggests a more complex organization of the thalamic parafascicular complex in leporines than previously supposed.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 18, No. 6, pp. 787–793, November–December, 1986.     

Contribution of specific and nonspecific afferent inputs to shaping evoked potentials produced in the cat brain by photic stimulation

Acute and chronic experiments on cats served to show that generation of evoked potentials continued in both the cortex and a number of subcortical structures and that these contained a component matching initial response (except in its reduced amplitude) even after cutting off specific pathways for visual impulse access. This involved severing the optic tract prior to its entry into the lateral geniculate body. Amplitude of primary response decreased less sharply after coagulating the lateral geniculate body, thus preserving a proportion of nonspecific impulse transmission (with pathways via the retino-collicular fibers persisting). Once a major proportion of the nonspecific visual pathways had been destroyed by severing the brachium of the superior colliculi, photic stimulation led to the formation of two-stage evoked potentials with a profile hardly differing from normal. It is presumed that genesis of evoked potentials depends on the quantity rather than the quality of incoming afferents.I. V. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 20, No. 1, pp. 3–7, January–February, 1988.     

Secondary hair cells and afferent neurones of the squid statocyst receive both inhibitory and excitatory efferent inputs

Summary Intracellular recordings were obtained from the hair cells and afferent neurones of the angular acceleration receptor system of the statocyst of the squid,Alloteuthis subulata. Electrical stimulation of the efferent fibres in the crista nerve (minor) evoked responses in all of the secondary hair cells recorded from (n=211). 48% of the secondary air cells responded with a small depolarization, 15% with a hyperpolarization, and 37% with a depolarization followed by a hyperpolarization. The depolarizations and hyperpolarizations had mean stimulus to response delays of 6.7 ms and 24 ms, and reversal potentials of about –1 mV and –64 mV, respectively. Both types of potential increased in amplitude, up to a point, when the stimulus shock was increased and facilitation and/or summation effects could be obtained by applying multiple shocks. These data, together with the fact that both responses could be blocked by bath application of cobalt or cadmium, indicate that the secondary hair cells receive both inhibitory and excitatory efferent inputs and that these are probably mediated via chemical synapses. No efferent responses were seen in the primary hair cells but both depolarizing and hyperpolarizing efferent responses were obtained from the afferent neurones.     

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.     

Hypothalamic evoked potentials to vagus and sciatic nerve stimulation

Hypothalamic evoked potentials to stimulation of the cervical portion of the vagus nerve and the sciatic nerve were recorded in experiments on cats anesthetized with chloralose and immobilized with succinylcholine. When both monopolar and bipolar recording techniques were used the focus of maximal activity of both "visceral" and "somatic" evoked potentials was located in the supramammillary and posterolateral region of the hypothalamus. Responses in the tuberal and anterior hypothalamus occurred in most experiments after a longer latent period, their amplitude was lower, and they were less stable. Evoked potentials in the focus of maximal activity of the posterior hypothalamus are similar in all parameters to responses of the mesencephalic reticular formation. Evoked potentials to stimulation of the visceral nerve have a higher threshold of generation and a lower amplitude than the "somatic" responses and they are inhibited more strongly when the frequency of stimulation is increased. Evoked potentials arising in the hypothalamus in response to stimulation of the vagus and sciatic nerves are regarded as nonspecific responses of reticular type.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 5, No. 3, pp. 253–260, May–June, 1973.