Horseradish peroxidase-positive neurons of nonspecific thalamic nuclei projecting to the primary somatosensory cortex in cats

The morphology and topography of neurons whose axons form the nonspecific thalamic input in the primary somatosensory area were studied in the cat forebrain by the retrograde axonal horseradish peroxidase transport method. Stained cells were found in the dorsolateral part of the nucleus ventralis anterior, and were diffusely distributed in the nucleus centralis, lateralis, the lateral part of the nucleus dorsalis medialis, and the dorsal part of the centrum medianum. In the nucleus paracentralis only solitary, palely stained neurons were detected. Cells stained with horse-radish peroxidase were multipolar, triangular, or fusiform. The results are evidence that besides the ventrobasal complex, the nonspecific nuclei of the diencephalon also project into the somatosensory cortex. This indicates the existence of multiple afferent thalamic inputs into the somatic cortex.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 11, No. 5, pp. 435–440, September–October, 1979.     

Connections of thalamic nucleus lateralis posterior with suprasylvian cortex in cats

Cats were immobilized with D-tubocurarine. Responses of 231 neurons of the thalamic nucleus lateralis posterior to cortical stimulation in areas 5b and 21 of the suprasylvian gyrus were studied. Responses of 34 neurons were antidromic, indicating the existence of a direct projection of this nucleus to the cortical areas studied. This projection was most extensive in area 5b. The long latencies (up to 60 msec) of the antidromic responses of some neurons indicate that axons of certain neurons of thalamic nucleus lateralis posterior conduct excitation very slowly (0.3 m/sec). Orthodromic responses with latencies of 2–3 msec to cortical stimulation point to the presence of direct pathways from cortex to nucleus. The flow of afferent impulses into the nucleus from area 5b is stronger than from area 21. Convergence of impulses from these areas was observed on 44% of neurons of the nucleus. Cortical stimulation of areas 5b and 21 evoked postsynaptic inhibition in most neurons of the nucleus. It is concluded that two-way direct connections exist between nucleus lateralis posterior of the thalamus and the suprasylvian cortex.     

Neuronal responses of the reticular and anterior ventral thalamic nuclei to stimulation of the thalamic ventrolateral nucleus and motor cortex

Responses of 137 neurons of the rostral pole of the reticular and anterior ventral thalamic nuclei to electrical stimulation of the ventrolateral nucleus and motor cortex were studied in 17 cats immobilized with D-tubocurarine. The number of neurons responding antidromically to stimulation of the ventrolateral nucleus was 10.5% of all cells tested (latent period of response 0.7–3.0 msec), whereas to stimulation of the motor cortex it was 11.0% (latent period of response 0.4–4.0 msec). Neurons with a dividing axon, one branch of which terminated in the thalamic ventrolateral nuclei, the other in the motor cortex, were found. Orthodromic excitation was observed in 78.9% of neurons tested during stimulation of the ventrolateral nucleus and in 52.5% of neurons during stimulation of the motor cortex. Altogether 55.6% of cells responded to stimulation of the ventrolateral nucleus with a discharge of 3 to 20 action potentials with a frequency of 130–350 Hz. Similar discharges in response to stimulation of the motor cortex were observed in 30.5% of neurons tested. An inhibitory response was recorded in only 6.8% of cells. Convergence of influences from the thalamic ventrolateral nucleus and motor cortex was observed in 55.7% of neurons. The corticofugal influence of the motor cortex on responses arising in these cells to testing stimulation of the ventrolateral nucleus could be either inhibitory or facilitatory.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 10, No. 5, pp. 460–468, September–October, 1978.     

Unit responses of the thalamic and ventral anterior thalamic nuclei to electrical stimulation of thalamic relay nuclei in cats

Responses of 92 neurons of the reticular (R) and 105 neurons of the ventral anterior (VA) thalamic nuclei to stimulation of the ventrobasal complex (VB) and the lateral (GL) and medial (GM) geniculate bodies were investigated in cats immobilized with D-tobocurarine. Altogether 72.2% of R neurons and 76.2% of VA neurons responded to stimulation of VB whereas only 15.0% of R neurons and 27.1% of VA neurons responded to stimulation of GM and 10.2% of R neurons and 19.6% of VA neurons responded to stimulation of GL. The response of the R and VA neurons to stimulation of the relay nuclei as a rule was expressed as excitation. A primary inhibitory response was observed for only two R and three VA neurons. Two types of excitable neurons were distinguished: The first respond to afferent stimulation by a discharge consisting of 5–15 spikes with a frequency of 250–300/sec; the second respond by single action potentials. Neurons of the first type closely resemble inhibitory interneurons in the character of the response. Antidromic responses were recorded from 2.2% of R neurons and 7.8% of VA neurons during stimulation of the relay nuclei. Among the R and VA neurons there are some which respond to stimulation not only of one, but of two or even three relay nuclei. If stimulation of one relay nucleus is accompanied by a response of a R or VA neuron, preceding stimulation of another nucleus leads to inhibition of the response to the testing stimulus if the interval between conditioning and testing stimuli is less than 30–50 msec.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 8, No. 6, pp. 597–605, November–December, 1976.     

Neurons of the thalamic ventrobasal complex,labeled with horseradish peroxidase,projecting to the primary somatosensory cortex in cats

The morphology and localization of neurons of the thalamic ventrobasal complex projecting to the primary somatosensory cortex were studied in cats by the retrograde axonal transport of exogenous horseradish peroxidase method. Different types of neurons were detected: triangular, round with symmetrical processes, oval with processes diverging asymmetrically, and fusiform. Tagged neurons were distributed as two large populations in the central region of the complex adjoining the boundaries of the two nuclei. Comparison with the somatotopic map showed that the tagged neurons were concentrated mainly in the projection area of the forelimb and head. Since microinjections of peroxidase into the somatosensory cortex also were given in the projection areas for the forelimb and head, the results confirm the neurophysiological concept of strict somatotopic organization of thalamocortical input.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. A. A. Ukhtomskii Physiological Institute, Leningrad. Translated from Neirofiziologiya, Vol. 11, No. 2, pp. 125–129, March–April, 1979.     

The correlations of the evoked activity of the auditory cortex and amygdala in cats during conditioned reflex activities]

By averaged summary activity of symmetric points of the cat auditory cortex and amygdala evoked by sound, the character of interaction (Spirman coefficient of correlation) was determined between the structures before, at elaboration, at extinction and restoration of instrumental food-procuring reflex and also at automatization of the reflex. Individual character of co-tuning of the cortex and amygdala was found at adaptation of the animal, changing into close interconnections at formation of the reflex and into disturbance of their correlation at its extinction. Stabilization of the reflex up to the stage of automatization was accompanied by the weakening of connections between the cortex and amygdala. The results testify to complex and dynamic character of interaction in the system cortex-amygdala in conditioned activity.     

Single units activities in ventral posterior and posterior group thalamic nuclei during nociceptive and non nociceptive stimulations in the cat.

The purpose of this study was to define, in hyperventilated and unanesthetized cats, the role of the posterior thalamic nuclei in pain mechanisms. Unit activities of these structures were compared to those of the ventro-posterior nucleus during non-noxious (touch, brushing) and noxious stimulations (pinches and intra-arterial injections of bradykinin into the limbs). 135 cells with somatic inputs and clear peripheral excitatory receptive field were studied. The cells driven by noxious stimulations were located in the posterior group nuclei as anatomically defined by Rinvik. These units, preferentially excited from contralateral receptive fields, were localized in POm, POl, suprageniculate nuclei, the magnocellular division of the medial geniculate body (Mgmc) and the ventral part of the lateral posterior nucleus. At this level two groups of units were found: those driven only by noxious stimulations and those driven by both noxious and non-noxious stimulations. On contrast, cells recorded at the levels of the VPm and VPl were not activated by noxious stimuli. These results emphasize the role of the posterior thalamic nuclei in pain processing.     

Neuronal responses of a chronically isolated slab of auditory cortex to intracortical stimulation during paroxysmal electrical activity in cats

Responses of 155 neurons 3 weeks after neuronal isolation of a slab of auditory cortex (area AI) to single intracortical stimulating pulses at the level of layer IV were studied in unanesthetized, curarized cats during paroxysmal electrical activity evoked by series of high-frequency (10–20 Hz) electrical stimulation by a current 2–5 times above threshold for the direct cortical response. In response to such stimulation a discharge of paroxysmal electrical activity, lasting from a few seconds to tens of seconds, appeared in the slab. As a rule it consisted of two phases — tonic and clonic. This indicates that cortical neurons can form both phases of paroxysmal cortical activity. Depending on behavior of the neurons during paroxysmal electrical activity and preservation of their ability to respond to intracortical stimulation at this time, all cells tested in the isolated slab were divided into four groups. Their distribution layer by layer and by duration of latent periods was studied. Two-thirds of the neurons tested were shown to generate spike activity during paroxysmal discharges whereas the rest exhibited no such activity. A special role of neurons in layer II in generation of paroxysmal activity in the isolated slab was noted. The view is expressed that at each moment functional neuronal circuits, independent of each other, exist in the slab and also, evidently in the intact cortex, which can interact with one another when conditions change.I. I. Mechnikov Odessa State University. Translated from Neirofiziologiya, Vol. 16, No. 1, pp. 3–11, January–February, 1984.     

Neuronal oscillations and multisensory interaction in primary auditory cortex

Recent anatomical, physiological, and neuroimaging findings indicate multisensory convergence at early, putatively unisensory stages of cortical processing. The objective of this study was to confirm somatosensory-auditory interaction in A1 and to define both its physiological mechanisms and its consequences for auditory information processing. Laminar current source density and multiunit activity sampled during multielectrode penetrations of primary auditory area A1 in awake macaques revealed clear somatosensory-auditory interactions, with a novel mechanism: somatosensory inputs appear to reset the phase of ongoing neuronal oscillations, so that accompanying auditory inputs arrive during an ideal, high-excitability phase, and produce amplified neuronal responses. In contrast, responses to auditory inputs arriving during the opposing low-excitability phase tend to be suppressed. Our findings underscore the instrumental role of neuronal oscillations in cortical operations. The timing and laminar profile of the multisensory interactions in A1 indicate that nonspecific thalamic systems may play a key role in the effect.     

Responses of auditory cortex neurons in unanesthetized cats to best-frequency tones

The characteristics of extra- and intracellular responses of neurons in the AI region were studied in experiments with unanesthetized cats. It was established that auditory cortex neurons with similar best frequencies showed different forms of responses to tones of the corresponding frequency. About 40% of the auditory cortex neurons generated on responses to tone presentation. On — off and off responses were found in 27% of the neurons. Cortical neurons (27%) in which stimulation or inhibition of impulse discharge persisted throughout tone action were assigned to the tonic type group of cells. Approximately 6% of neurons in the AI region did not respond to a tone. During intracellular recording about 85% of the neurons responded to the turning on and/or off of a tone by generating an action potential followed by an IPSI. In 96% of the cortical neurons studied the IPSPs were a constant component of the intracellular responses to a tone. It is concluded that the inhibition of the impulse activity of the given neurons is of primarily a postsynaptic origin. Neurons showing one or another form of response differ from one another in the relative intensity and time characteristics of excitatory and inhibitory processes interacting on their postsynaptic membranes. In neurons of the phasic type inhibitory processes are dominant over excitatory, while excitatory processes are predominant in neurons of the tonic type.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 17, No. 4, pp. 500–508, July–August, 1985.     

Reactions of neurons of the orbitofrontal cortex to stimulation of optic thalamic nuclei

The reactions of 288 neurons of the orbitofrontal cortex (OFC) to stimulation of the posteroventral (VP), ventral anterior (VA), and reticular (R) nuclei, as well as the median center (CM) of the thalamus, were investigated in acute experiments on cats. OFC neurons can be divided into four groups by their reactions to stimulation of thalamic nuclei: 1) those which respond with an increase in the frequency of the discharges to single and serial stimuli with a frequency of up to 20/sec; 2) those which respond doubtfully to single stimuli with a frequency of 4–12/sec; 3) those which respond with inhibition of the background impulses; 4) those which do not respond to stimulation of the nuclei. Stimulation of the thalamic nuclei evoked responses of OFC neurons with a large scatter of the latent period duration. The responses of neurons to stimulation of the VP (mean latent period 19.1±6.1 msec) had the shortest latent period (sometimes less than 3–4 msec). Reactions with a longer latent period developed upon stimulation of the VA (23.8±7.4 msec) and CM (42.8±12.8 msec). The uniqueness of the links of the OFC with the various optic thalamic nuclei is shown in an analysis of the material obtained and possible methods of the activation of the neurons of this region from thalamic structures are discussed.State Medical Institute, Kemerovo. Translated from Neirofiziologiya, Vol. 3, No. 4, pp. 350–358, July–August, 1971.     

Neuronal activity of the cerebral cortex in cats with conditioned inhibition

Unit activity of the somatosensory cortex was studied in chronic experiments on cats during alimentary instrumental conditioned reflex performance and elaboration of conditioned inhibition (CI). First presentations of the CI signal at the beginning of CI formation caused, due to orienting reaction to a new stimulus, a levelling of the response of the neurones to the positive conditioned signal included into the CI complex. At the stage of consolidated CI, this depression proceeded gradually during the development of conditioned inhibition caused by consecutive presentations of the nonreinforced CI combination. Two groups of neurones were involved in the process of the CI performance: one of them being the same which was activated also in response to positive stimulation during performance of the conditioned response, and the second one being areactive to the positive conditioned stimulus but reducing the frequency of the background activity.