Unit responses of the medial group of thalamic nuclei to stimulation of the frontobasal regions of the neocortex

In acute experiments on cats anesthetized with pentobarbital and chloralose, single-unit and focal responses of the medial group of thalamic nuclei (mediodorsal, central lateral, paracentral, central medianum, parafascicular) were studied to stimulation of the frontobasal regions of the cortex (proreal, posterior orbital, basal temporal regions). Depending on the number of neurons responding to cortical stimulation and on the length of the latent period of the responses three functionally heterogeneous subdividions of the medial nuclei were distinguished; the parvocellular and magnocellular portions of the mediodorsal nucleus and the intralaminar nuclei with the parafascicular complex. On the basis of responses of neurons activated antidromically by stimulation of the same cortical region and synaptically by stimulation of another region, the concept of the integrative function of nuclei of the medial group, integrating the frontobasal zones of the neocortex with the aid of neuron circuits in which the medial nuclei are included, is argued.M. Gor'kii Donetsk Medical Institute. Translated from Neirofiziologiya, Vol. 9, No. 1, pp. 11–18, January–February, 1977.     

Modulation of neuronal impulse activity of the anterior hypothalamus as a functional basis of the mechanisms underlying hypothalamic control

We examined the neuronal activity of hypothalamic neurons in acute experiments on cats under ketamine anesthesia. Using glass microelectrodes, we extracellularly recorded the impulse activity (IA) of neurons of the anterior hypothalamus in the absence of controlled influences (background IA, BIA) and after stimulation of evolutionary heterogeneous zones of the brain cortex projecting to the hypothalamus (hippocampal CA3 area, pyriform, cingular, and proreal gyri). Electrical 5-sec-long stimuli were applied with frequencies of 12, 30, or 100 sec⁻¹. In another experimental series, we recorded changes in the IA of hypothalamic neurons induced by visceral stimuli (heating or cooling by 7°C of the foot pad, cooling of the body of the animal, and infusions of 5% glucose, 0.2% NaCl, 3.0% NaCl, or phenylephrine in the carotid artery), modeling in such a way shifts of the constants of homeostasis within physiological limits. We also compared the parameters of neuronal BIA and stimulation-influenced IA in equal epochs of the analysis and classified the types of BIA. About 50% of the cells of the total studied sampling of hypothalamic neurons responded by a considerable modulation of their BIA with a significant change in the frequency in the course of and after stimulations of the above-mentioned modalities. In some neurons after cortical or visceral stimulation, a significant transformation of the temporal structure of the IA with no changes in the mean frequency occurred. We hypothesize that stimulation-induced transformation of the IA pattern with preservation of the mean discharge frequency can be one of the modes of encoding of information necessary for triggering of one efferent reaction or another, which are controlled by the hypothalamus. Examination of the BIA parameters of subcortical neurons, as well as comparison of the parameters of such an activity with the localization of cells and with the modality of stimulation that leads to modification of the IA, should allow one to reveal reasons for the formation and modification of the IA on neurons of the anterior hypothalamus. Since functional peculiarities of the neurons correlate with their BIA pattern, such data can provide an insight into the functional bases of the neurophysiological mechanisms underlying regulatory functions of the hypothalamus. Neirofiziologiya/Neurophysiology, Vol. 37, Nos. 5/6, pp. 463–474, September–December, 2005.     

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.