Modulation of neuronal impulse activity of the anterior hypothalamus as a functional basis of the mechanisms underlying hypothalamic control |
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Authors: | V N Kazakov L V Natrus |
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Institution: | (1) Ministry of Public Health of Ukraine, Donetsk State Medical University, Ukraine |
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Abstract: | 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. |
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Keywords: | hypothalamus homeostasis impulse activity frequency temporal structure |
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