[Glucose-monitoring neurons of the medial ventrolateral prefrontal (orbitofrontal) cortex are involved in the maintenance of homeostasis]. / A medialis ventrolateralis praefrontalis (orbitofrontalis) kéreg glükózmonitorozó idegsejtjei szerepet játszanak a homeosztázis fenntartásában.

INTRODUCTION: The medial orbitofrontal cortex is involved in the regulation of feeding and metabolism. Little is known, however, about the role of local glucose-monitoring neurons in these processes, and our knowledge is also poor about characteristics of these cells. AIM: The functional significance of these chemosensory neurons was to be elucidated. METHOD: Electrophysiology, by the multibarreled microelectrophoretic technique, and metabolic investigations, after streptozotocin induced selective destruction of the chemosensory neurons, were employed. RESULTS: Fifteen percent of the neurons responded to glucose, and these chemosensory cells displayed differential neurotransmitter and taste sensitivities. In acute glucose tolerance test, at the 30th and 60th minutes, blood glucose level in the streptozotocin-treated rats was significantly higher than that in the controls. The plasma triglyceride concentrations were also higher in the streptozotocin-treated group. CONCLUSIONS: Glucose-monitoring neurons of the medial orbitofrontal cortex integrate internal and external environmental signals, and monitor metabolic processes, thus, are indispensable to maintain the healthy homeostasis. Orv Hetil. 2017; 158(18): 692-700.

Multiple functional attributes of glucose-monitoring neurons in the medial orbitofrontal (ventrolateral prefrontal) cortex.

Multiple functional attributes of glucose-monitoring neurons in the medial orbitofrontal (ventrolateral prefrontal) cortex. NEUROSCI BIOBEHAV REV 73(1) XXX-XXX, 2017.- Special chemosensory cells, the glucose-monitoring (GM) neurons, reportedly involved in the central feeding control, exist in the medial orbitofrontal (ventrolateral prefrontal) cortex (mVLPFC). Electrophysiological, metabolic and behavioral studies reveal complex functional attributes of these cells and raise their homeostatic significance. Single neuron recordings, by means of the multibarreled microelectrophoretic technique, elucidate differential sensitivities of limbic forebrain neurons in the rat and the rhesus monkey to glucose and other chemicals, whereas gustatory stimulations demonstrate their distinct taste responsiveness. Metabolic examinations provide evidence for alteration of blood glucose level in glucose tolerance test and elevation of plasma triglyceride concentration after destruction of the local GM cells by streptozotocin (STZ). In behavioral studies, STZ microinjection into the mVLPFC fails to interfere with the acquisition of saccharin conditioned taste avoidance, does cause, however, taste perception deficit in taste reactivity tests. Multiple functional attributes of GM neurons in the mVLPFC, within the frame of the hierarchically organized central GM neuronal network, appear to play important role in the maintenance of the homeostatic balance.

Noradrenaline and acetylcholine responsiveness of glucose-monitoring and glucose-insensitive neurons in the mediodorsal prefrontal cortex.

The mediodorsal prefrontal cortex (mdPFC), as part of the forebrain glucose-monitoring (GM) system, plays important role in several regulatory processes to control the internal state of the organism and to initiate behavioral outputs accordingly. Little is known, however, about the neurochemical sensitivity of neurons located in this area. Substantial evidence indicates that the locus ceruleus - noradrenaline (NA) projection system and the nucleus basalis magnocellularis - cholinergic projection system regulate behavioral state and state dependent processing of sensory information, various cognitive functions already associated with the mdPFC. The main goal of the present study was to examine noradrenergic and cholinergic responsiveness of glucose-monitoring and glucose-insensitive (GIS) neurons in the mediodorsal prefrontal cortex. One fifth of the neurons tested changed in firing rate to microelectrophoretically applied NA. Responsiveness of the GM cells to this catecholamine proved to be significantly higher than that of the GIS units. Microiontophoretic application of acetylcholine (Ach) resulted in activity changes (predominantly facilitation) of more than 40% of the mdPFC neurons. Proportion of Ach sensitive units among the GM and the GIS neurons was found to be similar. The glucose-monitoring neurons of the mdPFC and their distinct NA and remarkable Ach sensitivity are suggested to be of particular significance in prefrontal control of adaptive behaviors.