Hypothalamic monoamines associated with the cephalic phase insulin response

This study elucidated the hypothalamic monoamine systems associated with the cephalic phase insulin release. Male Wistar rats conditioned to drink a glucose solution were killed 2 min after the onset of their scheduled feeding; control rats were killed at the same time. The ventromedial (VMH) and lateral (LH) portions of the hypothalamus were analyzed for the monoamines and their principal metabolites. Serum was assayed for insulin and glucose. The results showed that the experimental animals had significantly higher serum insulin levels than did the control animals, although glucose levels were unchanged. In the LH, there were increased levels of norepinephrine, its metabolite dihydroxyphenylethylene glycol (DHPG), and serotonin [(5-hydroxytryptamine (5-HT)]. In the VMH, 5-HT, its metabolite 5-hydroxyindoleacetic acid, and the dopamine metabolite 3,4-dihydroxyphenylacetic acid (DOPAC) were all higher in the conditioned animals. 5-HT levels in the LH and DOPAC levels in the VMH were closely associated with serum insulin (r = 0.80 and 0.71, respectively). This study has defined, in the normal animal, changes in monoamines in specific areas of the hypothalamus associated with the cephalic phase insulin release.