SENSITIVITY OF LATERAL HYPOTHALAMIC NEURONS TO GLYCEMIC LEVEL - POSSIBLE INVOLVEMENT OF AN INDIRECT ADRENERGIC MECHANISM

Most of the lateral hypothalamic neurons responding to moderate changes in blood glucose fail to be affected by direct glucose applications. Therefore their sensitivity to glycemic level must be mediated by an indirect mechanism. In order to test whether adrenergic afferents might be involved, the activity of lateral hypothalamic neurons was recorded during hyperglycemia and local glucose and epinephrine microiontophoresis. A majority of the recorded cells sensitive to local epinephrine responded to this substance with a decrease in activity. While no consistent correspondence was found between the responses of the same cells to local glucose and epinephrine ejections, almost all the neurons sensitive to glycemic alterations responded in the same direction to hyperglycemia and iontophorised epinephrine. These results support the view that the activity of lateral hypothalamic cells can be modulated in relation to changes in glycemic level through adrenergic signals released by some neurons which are sensitive to the blood glucose. The possible localization in the solitary tract area of such neurons projecting to the lateral hypothalamus is discussed.