The effect of neurotropic agents on evoked potentials of the association and projection regions of the cat neocortex]

Intensive non-specific inactivation of the cortex by means of its local cooling, in the cat anasthetized with nembutal, blocks in a similar way the early component of associative responses (ECAR) in the parietal area and the primary responses (PR) in the projection areas. In the case of local application of neurotropic drugs possessing specific and differentiated action on postsynaptic activity, the same ECAR changes require a somewhat higher concentration of the reagents as compared with the concentration that produces a similar PR transformation. The higher threshold of chemical sensitivity in ECAR than in the PR depends on the characteristics of the morpho-functional organization of the cortical formations. Dissimilar reactivity of the direct cortical response and of ECAR of the parietal area to the action of chemical drugs is related to the peculiarities of intracortical origin of these potentials which are due to the dissimilar nature of their generation in response to a direct and to a peripheral stimulation.     

Neurophysiologic analysis of the bilateral organization of the associative parietal regions of the neocortex in the cat

In cats under Nembutal anesthesia, impulses come to the parietal areas of both hemispheres, which, when evoked by unilateral stimulation of fore- and hind-paws, converge at the same cortical points forming early components of associative responses (ECAR). In responses to contralateral paws' stimulation, individual interhemispheric functional asymmetry is shown. The influence of the contralateral parietal area on the ipsilateral one is more strong than the reverse effect. In contrast to ECAR formation on the contralateral side as a result of the arrival of impulses of specific genesis along the "classical" lemniscal tract,--the signals of the same type participating in the initiation of ECAR in the ipsilateral hemisphere, on their way form a relay in the thalamus and the same zone of the opposite side via the interthalamic commissure and callosal body, correspondingly. It is suggested that along with the arrival of impulses through the mentioned crossed tracts, ECAR generation in the ipsilateral parietal cortex involves impulses, coming through the uncrossed channel of the extralemnisc tract.     

Origin of associative evoked potential of the orbital cortex

In acute experiments on cats evoked potentials (EP) of the orbital cortex were recorded and the electrogenesis and functional purpose of individual components of associative responses (AR) were investigated. It was concluded that the initial negative fluctuation of the AR arises as a consequence of the physical propagation of potentials from the projection somatosensory cortex and the second, positive, component and the following negative component are the result of arrival of an afferent volley into the orbital cortex via specific thalamic nuclei. These two components are due to activation of neurons of the orbital cortex. The afterdischarge, which appears sometimes, develops under the effect of impulses arriving from nonspecific thalamic nuclei. It is shown that during the second, positive, phase of the AR, primarily afferent neurons are activated, and during the negative phase, efferent neurons of the orbital cortex. The afterdischarge, which complicates the negative phase of the AR, is due to inhibition of afferent neurons.N. I. Pirogov Medical Institute, Vinnitsa. Translated from Neirofiziologiya, Vol. 2, No. 4, pp. 384–390, July–August, 1970.     

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.     

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.     

Field potentials in the lumbar ventral horn during combined extrapyramidal and cortical stimulation

Field potentials arising in the medial (Rexed's layer VIII) and lateral (region of the flexor motoneuronal nuclei) zones of the ventral horn during stimulation of the motor cortex or ventromedial funiculus in the cervical spinal cord were recorded in experiments on cats. Inhibition of the electrical response in the flexor nerve to stimulation of the contralateral cortex, an indicator of the cortical motor response, can be evoked by stimulation not only of the symmetrical point of the opposite cortex but also of the group of fibers of the ventromedial funiculus connected functionally with that point. In each experiment the fact that these fibers belonged functionally to the system conducting cortically evoked descending influences was verified in each experiment from a combination of specific criteria. Extrapyramidal inhibition of the cortical motor response is accompanied by the same changes in field potential in the medial and lateral zones of the ventral horn as cortical inhibition: by an increase in negativity in the first and by its suppression in the second. The differences between the two types of interaction are concerned chiefly with the temporal course of all the processes studied. The results are used as evidence of the extrapyramidal nature of cortical inhibition of the cortical motor response.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 4, No. 6, pp. 597–607, November–December, 1972.     

Responses of the neurons of the cortical secondary auditory area to acoustic and non-acoustic stimuli in cats

The responses of the cortical secondary auditory area (AII) to the non-acoustic stimuli (electrical stimulation of the skin in the vibrissae area and light flash) and their combination with acoustic stimulation (sound click or tone) were studied in experiments on cats anesthetized by kalipsol using extra- and intracellular recording. Of the total number of neurons, 69% of the units generating spike responses to the acoustic stimulation responded to the non-acoustic stimulation too. The responses to the modal-nonspecific stimulation, as a rule, were weak and variable; they were mostly represented by a tonic change in the neuronal discharge frequency. The nonspecific stimulation evoked primary excitatory and inhibitory postsynaptic potentials in 77% and 20% of the examined neurons, respectively. We found that synaptic effects of the nonspecific and specific stimulations interact with each other, ensuring considerable modulation of the latter (mostly a significant facilitation resulting from the EPSP summation and suppression of an inhibitory component of the response to acoustic stimulation). Possible participation of the midbrain reticular formation in the transmission of the modal-nonspecific influences to the cortical neurons is considered; stimulation of this structure evoked responses similar to those evoked by the modal-nonspecific sensory stimuli.Neirofiziologiya/Neurophhysiology, Vol. 26, No. 5, pp. 356–364, September–October, 1994.     

Synaptic effects induced in efferent neurons of the parietal associative cortex of the cat by stimulation of the cerebellar nuclei

Properties of EPSP, evoked in efferent neurons of the parietal associative cortex by stimulation of the cerebellar nuclei, were studied in acute experiments on anesthetized and immobilized cats; intracellular recording was used. The neurons were identified by their antidromic activation after stimulation of the motor cortex, pontinen.n. proprii, or red nucleus. The effects of stimulation of the cerebellar nuclei were of oligo- and polysynaptic nature. The latencies of cerebellofugal EPSP correlated with the latencies of antidromic activation, and correlations were significant both in the cases when the effects of stimulation of separate efferent projections (cortico-cortical, cortico-pontine, or cortico-rubral) and the effects of stimulation of separate cerebellar nuclei were analyzed. The functional role of the efferent systems of the parietal associative cortex and significance of functional parameters of the neurons constituting these systems are discussed.Neirofiziologiya/Neurophysiology, Vol. 27, No. 3, pp. 190–198, May–June, 1995.     

Role of cholinergic mechanisms in the genesis of some cortical responses

The dynamics of evoked potentials during blocking of cholinergic cortical structures was investigated in unanesthetized cats. Application of the anticholinergic drug benactyzine inhibits the negative phases of cortical responses to stimulation of the reticular formation and non-specific thalamic nuclei and also of responses to direct cortical stimulation. Direct cortical responses (DCRs), inverted by -aminobutyric acid, are also depressed, indicating the role of cholinergic mechanisms in the genesis of these responses. During blocking of cholinergic synapses, negative phases of the primary response (PR) and response to stimulation of the specific thalamic nucleus are facilitated. A tendency is then observed toward grouping of spontaneous unit discharges and abolition of inhibition of cortical neurons produced by high-frequency stimulation of the reticular formation. One cause of the increase in amplitude of the primary response (PR) to the action of anticholinergic drugs may be widening of the zone of cortical neurons involved in the response because of abolition of the localizing effect of inhibitory neurons.Institute of Physiology, Siberian Division, Academy of Sciences of the USSR, Novosibirsk. Translated from Neirofiziologiya, Vol. 2, No. 4, pp. 406–411, July–August, 1970.     

Activation of various areas of the ventral horn of lumbar segments during stimulation of the motor cortex

Focal potentials (FP) in segments L₆–L₇ of the ventral horn, evoked by stimulation of the motor cortex with series of stimuli of threshold magnitude for the flexor nerve response, were studied in acute experiments on cats. Appreciable differences were found to exist between the FP arising in the medial zone (layer VIII of Rexed) and those in the inner and outer parts of the lateral zone (layer IX). The FP of the medial zone appear earlier than in other zones (with a latency of 5–12 msec); they are multiphasic, negative components predominating over the positive ones. The FP from the inner part of layer IX possess the largest amplitude (up to 500 µV), a latency of 7–13 msec, a large first negative phase, and marked late positivity. Positive — negative FP (latency 9–15 msec) of small amplitude are recorded from the outermost portion of the ventral horn. The FP of the three zones mentioned above differ also with respect to other functional criteria. The FP of the medial zone are assumed to reflect the realization at the segmental level of the extrapyramidal component of descending cortical activity, the FP of both lateral zones reflecting reciprocal interrelations between postsynaptic processes in the motoneurons of flexor and extensor nuclei during implementation of a cortical motor reaction.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 3, No. 2, pp. 175–184, March–April, 1971.     

Parasympathetic discharges evoked in the pelvic nerve by stimulation of various structures in the amygdala

Parasympathetic discharges evoked by application of single and paired stimuli to central, corticomedial, and basolateral nuclei of the amygdala were recorded from the pelvic nerve (PN) in anesthetized and immobilized cats. The discharges were found to include three main negative waves (I, II, and III waves, appearing with the latencies of 16.0–17.8, 74–87, and 171–184 msec, respectively). The first two waves were seen most regularly. Sometimes the I wave was preceded by a super-early negative component of a low amplitude appearing with a latency of 8.5–10.7 msec. The discharges evoked by stimulation of various nuclei of the amygdala did not significantly differ from each other in their thresholds, time courses, and amplitudes, which suggests a relatively diffuse distribution of parasympathetic efferent structures in the amygdala. It was shown, using paired stimuli, that a response to the second stimulus needed a long-lasting period (a few tens of milliseconds) to be restored. The origin of the components of the amygdalofugal parasympathetic discharges recorded from the PN, as well as the corresponding pathways they spread through, are discussed. In addition, the possible origin of the positive components of the PN discharges are considered.Neirofiziologiya/Neurophysiology, Vol. 26, No. 5, pp. 326–333, September–October, 1994.     

Analysis of long cortical evoked potentials

Evoked potentials arising in the motor cortex in response to its direct stimulation (dendritic and slow negative potentials), to stimulation of the ventrolateral (primary response) and intralaminar (nonspecific response) thalamic nuclei, and to stimulation of the pyramidal tracts (antidromic response), and also postsynaptic responses of neurons corresponding to them were studied in acute experiments on curarized cats. Evoked potentials arising in response to direct cortical stimulation and also to stimulation of the specific and nonspecific thalamic nuclei and pyramidal tracts were recorded from the same point of the motor cortex, and the corresponding intracellular responses were recorded from the same neuron. Slow negative potentials arising under these conditions of stimulation and the IPSPs corresponding to them were shown to have an identical time course. The results show that slow negative potentials are a reflection of hyperpolarization of pyramidal neurons. It is suggested that the individual components of responses evoked by direct stimulation of the cortex and thalamic nuclei have a common genesis.I. S. Beritashvili Institute of Physiology, Academy of Sciences of the Georgian SSR, Tbilisi. Translated from Neirofiziologiya, Vol. 14, No. 2, pp. 115–121, March–April, 1982.     

Early positive component of the tectal evoked potential ofSqualus acanthias during electrical stimulation of the optical nerve

The evoked potential of the tectum opticum during electrical stimulation of the optic nerve was studied in acute experiments on the dogfishSqualus acanthias L. The negative phase of the "classical" negative-positive evoked potential of the contralateral hemisphere of the tectum opticum was shown to be a complex potential, including an early positive component. A similar potential also was recorded from the ipsilateral hemisphere. Enhancement of this positive potential on insertion of the recording electrode deep into the brain, its resistance to functional block on application of potassium chloride to the brain surface, and recording a similar potential from the surface of the floor of the third ventricle after extirpation of the tectum opticum are evidence of the nontectal location of the source of this evoked potential component. On the basis of existence of a focus of maximal activity in the rostral zones of the brain beneath the tectum opticum, and disappearance of the early positive component during functional block and extirpation of this brain region, it is concluded that a leading role in the generation of this component is played by thalamic nuclei.M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 16, No. 1, pp. 61–67, January–February, 1984.     

Responses of limbic cortical neurons to stimulation of splanchnic and sciatic nerves and of the mammillary bodies

Spontaneous and evoked unit activity in the anterior limbic cortex in response to stimulation of the splanchnic and sciatic nerves and of the mammillary region of the hypothalamus were recorded extracellularly in acute experiments on cats. The study of heterogeneous transsynaptic influence on limbic cortical neurons showed that in the presence of effective sensory viscerosomatic convergence, weak convergence of influences from the central hypothalamic and peripheral sources took place. Short-latency responses of limbic cortical neurons to stimulation of the mammillary bodies consisted of orthodromic and antidromic responses, evidence of the existence of short two-way connections between the anterior limbic cortex and mammillary nuclei of the hypothalamus.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 11, No. 5, pp. 419–426, September–October, 1979.     

Evoked Potentials of the Somatic Cortex and EMG Reactions of the Shoulder Muscles Elicited by Passive Extension of the Elbow Joint in Unanesthetized Cats

We recorded electromyographic (EMG) reactions from the flexors of the elbow joint and evoked potentials (EP) from the somatic cortex (fields 3, 4, and 6) of unanesthetized cats. These reactions were elicited by perturbation of an external extensor loading applied to the arm and evoking passive extension of the elbow joint. Perturbation of the loading was performed in two modes: (i) with different fixed force moments within a 0.04–0.2 N·m range, but with a constant rate of change in this moment (3.2 N·m·sec^–1), and (ii) with a constant force moment magnitude (0.2 N·m), but with different rates of change in this moment (from 0.1 to 6.4 N·m·sec^–1). When the elbow joint was passively extended, an EMG response was generated in the m. biceps brachii. The amplitude of this response correlated with the amplitude of perturbation of the external loading, and the time course of the response was rather close to that of the evoked passive moment. It was possible to differentiate several (up to seven) successive components in EP recorded from the three above-mentioned cortical fields; among them, the component N(50–60) was the most stable and clearly manifested. Its amplitude did not depend on the level of external loading and decreased with a decrease in the rate of loading perturbation. The time course of the N(50–60) changed insignificantly with variation of temporal parameters of the stimulus and of the evoked movement. We conclude that the spinal level and the cortical level responsible for formation of the stretch reflex differ significantly from each other in their functional roles. Reactions of the spinal level (which could be characterized by changes in EMG) are to a greater extent related to a change in the position of the limb link, while reactions of the cortical level (EP) are determined by the arrival of information about changes in the forces applied to the joint. Neurons of the somatic cortex, which are excited in the course of the stretch reflex, cannot be considered the main source responsible for generation of the M2 component of the myographic response. It is supposed that the cortical level predetermines the formation of non-reflex motor commands related to motor reflexes closed in the somatic brain cortex.     

Unit responses of the cat caudate nucleus to cortical stimulation before and after destruction of nonspecific thalamic nuclei

Responses of caudate neurons to stimulation of the anterior sigmoid and various parts of the suprasylvian gyrus were studied in acute experiments on cats. The experiments consisted of two series: on animals with an intact thalamus and on animals after preliminary destruction of the nonspecific thalamic nuclei. Stimulation of all cortical areas tested in intact animals evoked complex multicomponent responses in caudate neurons with (or without) initial excitation, followed by a phase of inhibition and late activation. The latent periods of the initial responses to stimulation of all parts of the cortex were long and averaged 14.5–25.5 msec. Quantitative and qualitative differences were established in responses of the caudate neurons to stimulation of different parts of the cortex. Considerable convergence of cortical influences on neurons of the caudate nucleus was found. After destruction of the nonspecific thalamic nuclei all components of the complex response of the caudate neurons to cortical stimulation were preserved, and only the time course of late activation was modified.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 12, No. 5, pp. 464–471, September–October, 1980.     

Spike train structure following application of nociceptive potassium chloride solutions to the cat saphenous nerve

The structure of the spike train coding the nociceptive signal was investigated by a cross-correlation method. The action of nociceptive solutions of potassium chloride (125–1000 mM) on the saphenous nerve caused excitation of both myelinated and nonmyelinated fibers. The density of the spike train increased during the action of the stimulus up to a threshold sufficient for the appearance of nociceptive reflexes. The maximum of these reflexes coincided with the appearance of synchronous pulsations of discharges in the group of unmyelinated fibers. The nociceptive signal evoked by direct action of highly concentrated potassium chloride solutions on the nerve is thus coded by a high density of the spike train generated by the nerve fibers. Synchronous pulsations may be present in the spike train under these circumstances.Research Institute of Applied Mathematics and Cybernetics, N. I. Lobachevski Gor'kii State University. Translated from Neirofiziologiya, Vol. 9, No. 6, pp. 598–605, November–December, 1977.     

Inhibition of jaw opening reflexes by stimulation of the central gray matter and raphe nuclei in cats

The effect of stimulation of the mesencephalic central gray matter and raphe nuclei on jaw opening reflexes evoked by excitation of high-threshold (dental pulp) and low-threshold (A-alpha) fibers of the infraorbital nerve afferents was studied in cats anesthetized with chloralose and pentobarbital. The jaw opening reflex evoked by stimulation of the dental pulp was shown to be effectively suppressed by conditioning stimulation of the central gray matter and raphe nuclei. The reflex evoked by stimulation of low-threshold infraorbital nerve afferents also was depressed (but less deeply and for a shorter period than the reflex evoked by stimulation of the dental pulp) during stimulation of the raphe nuclei and caudal zone of the central gray matter, but was unchanged after stimulation of the points located in the rostral zone of the central gray matter. Application of single stimuli or bursts of five stimuli with a frequency of 100 Hz had no effect on the reflexes studied. Short-term stimulation with a burst of 10–20 stimuli with a following frequency of 200–400 Hz led to inhibition of the reflexes, which lasted 450–1000 msec. Long-term stimulation of the central gray matter and raphe nuclei for 30 sec with a frequency of 50 Hz caused inhibition of jaw opening reflexes evoked by stimulation of both high- and low-threshold afferents for 60 min. Impulses from the central gray matter and raphe nuclei thus have a mainly inhibitory action on the jaw opening reflex evoked by stimulation of high-threshold afferents, but they act less effectively on the reflex evoked by stimulation of low-thres-hold afferents. The duration of inhibition depends essentially on the parameters of stimulation.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 16, No. 3, pp. 374–387, May–June, 1984.     

Structural Transformations of the Associative Cortex As the Morphological Base of the Development of Human Cognitive Functions from Birth to 20 Years of Age

The microstructure of the temporo-parieto-occipital subregion and the frontal area of the brain from birth to 20 years of age was studied using computer morphometry. These brain zones are involved in the higher integrative mechanisms of cognitive functioning in children, adolescents and young adults. Structural transformations of the cortex represent a stage-by-stage process. Each stage in the frontal and occipital associative zones has specific temporal limits and is characterized by the quantitative and qualitative specificity of the morphological changes at each of the system levels considered: neuronal, modular, and stratification. The structural modifications from birth to early adulthood are primarily associated with the final development of micro and macroassembles and their structural components, primarily, neurons of various types. The growth and differentiation of neurons involves heterochrony with respect to the terms and developmental rates in the frontal and occipital associative cortex. The terms of the most active synchronous postnatal structural modifications, occurring during the first year of life, during the years 2–3, 6–7, 9–10, and 13–14 were analyzed. It was shown, that local specialization of cellular ensembles at various levels is a consequence of the functional specialization of microensembles, involved in cortical information processing, including cognitive activity and other higher psychophysiological functions of the human brain.     

Unit activity of the reticular and relay nuclei of the cat thalamus

Relations between neurons of the reticular and specific relay nuclei of the thalamus were studied in cats immobilized with tubocurarine. Under the influence of stimulation of the reticular nucleus (RN) unit activity in the thalamic relay nuclei was found to be considerably modulated. Cases of the appearance of IPSPs (possibly of monosynaptic nature), evoked by stimulation of RN, in neurons of the ventroposterolateral nucleus (VPLN) and lateral geniculate body (LGB) are described. During simultaneous recording of unit activity in RN and VPLN or LGB by means of two electrodes interaction of several types was found: inhibition of discharges of VPLN or LGB neurons accompanied by excitation of RN neurons: alternation of excitation-inhibition in neuron pairs in RN and VPLN or RN and LGB during low-frequency afferent or cortical stimulation (in this case excitation of RN neurons is associated with inhibition of VPLN or LGB neurons), and strengthening of the discharge of VPLN or LGB neurons during excitation of RN neurons. The possibility of the existence both of direct monosynaptic inhibition of activity of VPLN or LGB relay neurons under the influence of excitation of RN neurons and of their inhibition by activation of hypothetical interneurons of the relay nuclei themselves is accepted.I. S. Beritashvili Institute of Physiology, Academy of Sciences of the Georgian SSR, Tbilisi. Translated from Neirofiziologiya, Vol. 13, No. 1, pp. 24–31, January–February, 1981.