Analysis of evoked discharges in hypothalamic neurons to somatosensory,acoustic, and photic stimulation

Single unit activity in the supramammillary, mammillary, and anterior hypothalamic areas in response to acoustic, photic, and sciatic nerve stimulation was recorded in cats anesthetized with chloralose and immobilized with succinylcholine. In response to sensory stimulation the spontaneous firing rate was increased or decreased, and silent neurons were activated. Evoked potentials of the silent neurons had the shortest latent period to acoustic and somatosensory stimulation (15 msec), and rather longer to photic stimulation (30 msec); in some cases their latent period was 200 msec. Histograms of interspike interval distribution showed a maximum for intervals of up to 50 msec. Histograms of spike distribution relative to the beginning of stimulation showed maximal density between 100 and 200 msec. A high degree of convergence of excitation was found on units of the anterior as well as the posterior hypothalamus. Unit responses in the hypothalamus to sensory stimuli of all three modalities are regarded as being of secondary, nonspecific type.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 3, No. 6, pp. 592–598, November–December, 1971.     

Elementary transcallosal connections of the rabbit sensomotor cortex]

Antidromic responses of two callosal neurones to a local electrical stimulation of the rabbit sensorimotor cortex may be recorded simultaneously with one microelectrode in the homotopic cortical area. In such recording conditions the relative amplitude of extracellularly recorded action potentials of the two neurones is determined primarily by the distance between these neurones and the electrode's tip. In response to the stimulation of the symmetrical area transcallosal monosynaptic excitation of the callosal neurone may occur; two callosal neurones may exite monosynaptically one and the same recorded neurone. The results suggest the existence of clusters or columns, formed jointly by the bodies and terminals of callosal neurones; a functional interconnection between symmetrical clusters or columns may exist, in particular a positive feedback.     

Responses of secondary sensomotor cortical neurons to electrodermal and acoustic stimulation in waking cats

Unit responses in the second somatosensory cortical projection area (SII) to clicks and electric shocks applied to the contralateral limb were investigated in chronic experiments on cats. In response to specific stimulation for the cortical region studied the discharge frequency of 75% of neurons increased, spontaneous activity of 18% was reduced in frequency or the discharges ceased altogether, and 25% of cells did not respond. In response to "nonspecific" stimulation (clicks) 30% of neurons were activated; the discharge of 25% of cells was inhibited and 45% did not respond. The results of investigation of intersensory convergence of stimuli from different sensory systems showed that a high proportion (55%) of SII neurons give bimodal responses. Another 18% of neurons give a specific response to both adequate and inadequate stimulation. It is suggested that the presence of polysensory convergence of SII neurons and of short pathways for the conduction of sensory information, and also the ability of neurons to acquire polysensory properties during stimulus presentation are evidence of the important role of this cortical region in conditioning.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 9, No. 5, pp. 453–459, September–October, 1977.     

Organization of neurons responding to photic stimulation in the Clare-Bishop area in cats

Neuronal organization in the Clare-Bishop cortical association area was studied by consecutive vertical penetration of an electrode and analysis of unit responses to photic stimulation during each penetration. Activity of one or two neurons was recorded during 131 penetrations, and activity of over 3 neurons responding to photic stimulation (visually driven) during 55 penetrations. In 8 of the 55 penetrations all neurons discovered in each had identical characteristics; this type of organization corresponded most of all to the columnar organization of the cortical neurons. In 24 penetrations the neurons were arranged in groups: two or three neurons of one type intermingled with neurons of other types. In 18 penetrations considerable overlapping of the receptive fields of neurons in the same column was observed. A chaotic distribution of neurons with different characteristics was found in 5 penetrations. It is suggested that the organization of neurons in the Clare-Bishop area in columns as functional units of cortical structure is not the principal type of their organization.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 11, No. 4, pp. 297–302, July–August, 1979.     

Synaptic reactions of sensomotor cortex neurons to stimulation of emotionally significant brain structures

The study deals with synaptic and spike responses of neurones in the rat sensorimotor cortex to stimulation of the lateral and medial hypothalamus, locus coeruleus and raphe nuclei. The activity of 57 neurones was recorded, 41 of them intracellularly and quasi-intracellularly, in response to the stimulation of sites in these structures, which were previously identified as "emotionally/ significant. No considerable differences in the effects of the stimulation of different "emotiogenic" zones were found. The stimulation parameters, differing from the "behavioural" ones by a greater strength, elicited in the majority of neurones clear post-synaptic responses, often in the form of EPSP-IPSP. Latencies of the responses varied from 3 to 80 msec. The most stable and pronounced responses were obtained to the stimulation of the lateral hypothalamus. No significant correlations of the latencies of the responses to the stimulation of different "emotiogenic" structures were found.     

Effect of bradykinin and morphine on rat sensomotor cortex neurons]

As revealed in acute experiments on rats bradykinin applied microiontophoretically produced neuronal activation in the sensory-motor region of the rat brain cortex. Morphine applied iontophoretically prevented bradykinin effect. It is suggested that bradykinin interacts with opiate receptors in the cortical neurones.     

Cortico-cortical connections between the auditory fields and the sensomotor area of the cortex]

In 18 cats by means of two methods--anterograde degeneration and retrograde transport of exogenic horseradish peroxidase--cortico-cortical connections of the auditory fields to the cortical sensomotor area have been studied. These connections have been stated to terminate in layers V-III of certain parts of the sensomotor area corresponding to the projections of the foreleg and the head. Initial neurons of the connections studied are pyramidal cells in layers III and II. They are situated in rostral and caudal parts of the fields AI and AII, but within these levels they occur in different areas of the auditory fields.     

Afferent inhibition and functional properties of neurons in the vibrissae projection area of the cat somatosensory cortex]

The aim of this study was to investigate the role of inhibitory processes in S-1 cortex of cats. The inhibition was evoked by "natural" afferent stimulation of the fascial vibrissae. For this purpose, two neighboring vibrissae were sequentially stimulated by mechanical deflection; single unit activity was recorded simultaneously from the cortex. Results showed that conditioning by afferent stimulation significantly influenced the directional sensitivity of cortical neurons. These data and analysis of spatial pattern of stimulated vibrissa indicate that detector neurons could be quickly modified during sensory processing.     

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.     

Effect of early photic deafferentation on the neuronal development of the parietal area of the rabbit cerebral cortex]

It has been shown interferometrically that the neurons of laminae III-V of the parietal area in the cortex of visual deprivated rabbits manifest features of morphochemical underdevelopment (decrease in size and protein content in the neurons) in comparision with the normal ones. These changes resemble those in the visual area, but are less pronounced being definitely specific for each lamina. The reaction of the neurons of the cortex parietal area of rodents on the light deafferentation is discussed.     

Response of parietal association cortex neurons to acoustic stimulation before and after auditory cortex blockage in the cat

The effect of auditory cortex blockade on response patterns of parietal association cortex neurons responding to different frequency tones was investigated in the cat. Blockade was produced by two methods: bilateral isolation and application of a 6% Nembutal solution to the auditory cortex surface. Frequency threshold curves were plotted for all test neurons. The majority of test neurons (84%) displayed one or two characteristic frequencies before blockade, as against only 63% of all neurons responding following blockade. Changes also affect the range of frequencies at which the cells could respond. Virtually all test neurons responded to application of a broad spectrum of frequencies under normal conditions. After blockade of the auditory cortex 69% of neurons no longer responded to tones above 8–10 kHz. This would suggest that mainly information on high frequency tones is transmitted via the auditory cortex. The question of where acoustic information for parietal association cortex neurons mostly originates is also discussed; association thalamic nuclei are thought to be the main source.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 18, No. 3, pp. 354–360, May–June, 1986.     

Reactions of neurons of orbitofrontal cortex to stimulation of limbic system formations

The reactions of 164 neurons of the orbitofrontal cortex (OFC) to stimulation of the mediodorsal nucleus of the thalamus (MD), the amygdaloid complex, and various sections of the hypothalamus, were investigated in acute experiments on cats. Stimulation of the MD led to the development in OFC neurons of reactions with a short (sometimes less than 6 msec) and stable latent period. Similar reactions were observed upon stimulation of the lateral amygdaloid nuclei. Stimulation of the basal and central nuclei of the amygdala evoked synchronization of the discharges in OFC neurons. Stable responses of OFC neurons developed from nuclei of the hypothalamus only in the lateral region. Stimulation of the other nuclei of the hypothalamus was accompanied by irregular responses or synchronization of the discharges. In an analysis of the material obtained, the functional characteristics of the connections between the structures investigated and OFC neurons were examined.State Medical Institute, Kemerovo. Translated from Neirofiziologiya, Vol. 3, No. 5, pp. 484–490, September–October, 1971.