Characteristics of glycemia-sensitive neurons in the nucleus tractus solitarii: possible involvement in nutritional regulation.

Single unit responses to moderate glycemic variations were extracellularly recorded in the caudal division of the nucleus tractus solitarii of rats anesthetized by i.v. infusion of ketamine. As previously observed, a majority of recorded neurons (70%) were either activated or depressed by moderate hyperglycemia. Responses were consistently reproducible and amplitude was dependent on the maximum level of hyperglycemia. All glycemia-sensitive neurons responded in opposite directions to induced hyperglycemia and hypoglycemia, and almost all displayed the same type of response to local and i.v. glucose administration. Most glycemia-sensitive neurons were depressed by iontophoresis of clonidine, suggesting that they were adrenergic or noradrenergic. Based on these findings, we speculate that glycemia-sensitive neurons in the caudal nucleus tractus solitarii may act as glucose sensors that transmit glycemic information corresponding to different nutritional states, as well as other relevant signals toward hypothalamic structures involved in feeding and metabolic regulation via ascending adrenergic and noradrenergic pathways.