GLUTAMATE PATHWAYS MEDIATE SOMATOSTATIN RESPONSES TO GLUCOSE IN NORMAL AND DIABETIC RAT HYPOTHALAMUS

We investigated the role of hypothalamic glutamate receptors in mediat ing the stimulatory effect of low glucose (< 5 mM) on somatostatin rel ease. We also studied whether alteration in glutamate release might co ntribute to the reduced hypothalamic somatostatin response to low gluc ose observed in diabetic (Goto-Kakizaki) rat hypothalami. Hypothalamic somatostatin release in response to incubation with 1 mM D-glucose wa s inhibited by the ionotropic glutamate receptor antagonists MK801, D- AP5 and DNQX but not by the metabotropic antagonists L-AP3 or MCPG., T he release of somatostatin was increased by the ionotropic agonists NM DA, AMPA and kainate but not by metabotropic agonists t-ACPD or L-AP4. Basal and peak glutamate release in response to incubation with 1 mM glucose, were significantly lower from GK hypothalami There were no si gnificant differences in the basal or stimulated release of serine and GABA. These data indicate that ionotropic NMDA/AMPA/kainate receptors and not metabotropic receptors mediate the effects of glucose on rat hypothalamic somatostatin release. Reduced hypothalamic somatostatin r elease in response to low glucose in diabetic (Goto-Kakizaki) rats may well be secondary, at least in part, to reduced glutamate release.