Sensitivity of nucleus tractus solitarius neurons to induced moderate hyperglycemia, with special reference to catecholaminergic regions.

Extracellular single-unit recordings have been carried out in the caudal part of the nucleus tractus solitarius of male rats anesthetized by i.v. infusion with Ketamine. The sensitivity of 38 cells to 0.2 ml of 0.55 M glucose i.v. administration has been studied. The spike frequency of 75% of these cells was affected by the induced moderate hyperglycemia and a majority of them was activated. Immunohistochemical data on 9 glycemia-sensitive neurons showed that all recording sites were within TH-immunoreactive regions of the caudal part of the nucleus (either in the A2 noradrenergic group, or the C2 adrenergic group). These results confirm the existence of glycemia-sensitive neurons in the nucleus tractus solitarius, and suggest that these cells might mediate the effects of physiological fluctuations in blood glucose level on the control of food intake and metabolic regulations. The localization of these cells in catecholaminergic regions suggests that adrenaline and/or noradrenaline efferents might convey feeding relevant information concerning glycemic level or satiety signal from the nucleus tractus solitarius to forebrain structures involved in food intake, such as the perifornical lateral hypothalamic area and the paraventricular nucleus.