Effect of sensory input on the levels of enzymes involved in energy metabolism

Abstract

Presentation of sensory stimuli of various modalities to rats immediately before their decapitation led to a significant increase in the level of succmate dehydrogenase in the hippocampus, the magnitude of the increase being dependent on the number of stimuli presented. In each individual case, this enzyme's activity was proportional to the amplitude of the population spike recorded in the hippocampus of the same rat. An inverse relationship was noted between the rate of plastic processes in the hippocampus upon rhythmic stimulation and succinate dehydrogenase activity.Key Words: sensory stimulation; hippocampus; succinate dehydrogenase; population spike; frequency facilitationThe regulation of cell-cell interactions is inextricably bound up with assimilation-dissimilation processes. It has been shown that a major part of the glutamate secreted from nerve terminals becomes involved in energy metabolism [10][11][12]14,15]. Most of the glutamate is taken up by astrocytes [13]. The oxidation of exogenous glutamate provides an external energy source for astrocytes during neuronal excitation [5]. The remaining glutamate is taken up by neurons [13].These findings have enabled a hypothesis to be formulated concerning astro-neuronal interactions during functional activity.A convenient structure for verifying the validity of this hypothesis is the hippocampus. The main pathways in the latter are known to be glutamatergic [8]. Presentation of sensory stimuli should be accompartied by an elevation of glutamate secretion in the hippocampus and, according to the above hypothesis, will lead to increased uptake of glutamate by astrocytes followed by its entry into the Krebs cycle. This is bound to activate enzymes for the subsequent reactions, ff so, then glutamate should be expected to influence primarily the level of succihate dehydrogenase (SDH). Indeed, as shown in several studies [1,3,5], glutamate has an activating effect on succinate oxidation, and such activation is usually explained by elimination of oxaloacetic acid, which inhibits SDH [1].The purpose of this study was to elucidate the possible reasons for alterations in the level of SDH in response to sensory stimulation of different types. MATERIALS AND METHODSFour groups of Wistar rats were used for the experiments. Control rats were decapitated without being exposed to any stimulation. The second group were presented 15 light flashes immediately before decapitation, the third group was exposed to 15 electrocutaneous stimuli, and the fourth group,

Dynamics of the activity of respiratory enzymes in neuronally isolated zones of the neocortex and symmetrical regions in rats

“…Our previous studies showed that with increasing brain excitability the level of SDH activity increased by on average 20% compared with the norm [4,6]. In the present study, the increase in SDH activity was observed in ICS after 21 days and later.…”

“…2). The data obtained in other experimental models indicate that the increase in SDH activity is primarily due to its activation in astroglial cells [4]. Therefore, decreased SDH activity in this period can be explained by redistribution of glial cells.…”

“…Increased activity of SDH and slightly lowered activity of NADH-DH are indicative of an increased excitability of brain tissue [1,4,6]. Our previous studies showed that with increasing brain excitability the level of SDH activity increased by on average 20% compared with the norm [4,6].…”

“…These structural changes result in considerable shifts in the functional state of isolated cortical strip (ICS) [8]. The most informative indices of the tissue conditions are the activities of the main redox enzymes succinate dehydrogenase (SDH) and NADH dehydrogenase (NADH-DH) and their balance [4][5][6]. In this work we investigated the dynamics of structural changes and energy metabolism in surviving ICS from the rat brain and in homotopic cortical zone of the contralateral hemisphere (HCZ).…”