Corticofugal influences on the neurons of different regions of the hypothalamus

Abstract

Responses of the neurons of the lateral and ventromedial hypothalamic regions (HL and Hvrn, respectively), as well as of the area of the dorsal hypothalamus (arid) and the projection region of the medial forelimb bundle (MFB), evoked by stimulation of the proreal cortex (field 8), cingular cortex (field 24), pyriform Iobula (periamigdalar cortex), and hippocampus (CA3) were studied in acute experiments on cats under ketamine anesthesia. Distributions of the latent periods of the responses recorded from hypothalamic neurons at stimulation of the above cortical structures were analyzed. The responses were classified into primary excitatory and primary inhibitory. Stimulation of the proreal gyrus evoked four times more excitatory responses than inhibitory responses. With stimulation of the cingular gyrus, the ratio of excitatory/inhibitory responses was 1.5:1. Stimulation of the pyriform cortex evoked activatory and inhibitory responses with a similar probability. With hippocampal stimulation, inhibitory responses appeared two times more frequently than excitatory reactions. The hypothalamus was found to be a zone of wide convergence: one-half of all responding neurons in the HL and Hvm responded to stimulations of two or more tested cortical zones. In 26~o of the cells, only excitatOry convergence was observed, while in 10~o only inhibitory convergence was found; 21 ~/~, of the cells revealed mixed convergence.

Corticofugal effects on the neuronal activity in the emotiogenic/motivational zones of the hypothalamus

“…We found that these are the hypothalamic regions with the maximum number of the neurons responding to stimulation of the neoarchipaleocortex. There are two main loci of convergence of the influences arriving at hypothalamic neurons [6,7 ]; one such focus is localized …”

“…The responses were evoked by single and repeated (serial, 6 to 300 sec 1) stimulations of the proreal (field 8) and cingular (field 24) cortices, pyriform lobe (periamygdalar cortex), and hippocampus (CA3). Surgical procedures and the course of experiment were described earlier [7] in more detail.…”

“…It should be emphasized that under conditions of single stimulations the neurons with mixed or excitatory responses prevailed in these regions [7], while repeated stimulation evoked here mostly inhibitory effects [61.…”

“…Neurophysiological characteristics of one or another brain structure are determined by the pattern of interaction of the excitatory and inhibitory processes in this structure and balance of these processes [2,6,7 ]. This statement can be fully applied to the mechanisms of cortical control of emotional/motivational behavior, I Donetsk State Medical University, Ministry of Public Health of Ukraine, Ukraine.…”

“…The latter can be considered a near ideal intrabrain model of functional and neurochemical heterogeneity. In spite of significant progress in the studies of the processes of central control of the autonomic sphere, in which the hypothalamus plays a key role [1, 3,[5][6][7][8][9], the mechanisms of relations between evolutionarily diverse regions of the brain cortex with the hypothalamic structures have been studied insufficiently.…”