Local versus indirect action of glucose on the lateral hypothalamic neurons sensitive to glycemic level

The neuronal activity in the lateral hypothalamus may be affected by moderate changes in blood glucose. The present study aimed to specify the direct or indirect origin of this sensitivity to glycemia, by recording the unit responses in this area to both local glucose application (by means of microelectrophoresis) and hyperglycemia (induced by an IV glucose injection). The activity of approximately 25% of the recorded LHA neurons was modified by topically ejected glucose. However, a large majority of these neurons sensitive to local glucose failed to respond to hyperglycemia. Conversely, only 1/3 of the glycemia-sensitive cells responded in the same direction to systemic and local glucose administration. Therefore, the response to IV glucose of the other 2/3 glycemia-sensitive cells could not result from the direct action of glucose molecules on these neurons, but probably involved an indirect afferent pathway conveying the glycemic cues from some central or peripheral glucose sensors to the cell under investigation.