The present study examined monoaminergic activity at the level of the lateral hypothalamus (LH), ventromedial hypothalamus (VMH) and ventral striatum associated with the conditioned cephalic phase insulin release. Partially food-deprived male Wistar rats were divided into 3 groups. Two of the groups were conditioned to drink a 50% glucose solution each morning for 3 weeks; the control group received an amount of glucose equal to the amount drunk by the experimental animals with their afternoon meal. On test day, conditioned animals were sacrificed either just prior to glucose presentation or 2 min following consumption of the solution; control animals were sacrificed at the same time. Gas chromatography/mass spectrometry was used to determine the levels of the monoamines noradrenaline (NA), dopamine (DA) and serotonin (5-HT), as well as their principal metabolites dihydroxyphenylethyleneglycol, 3,4-dihydroxyphenylacetic acid (DOPAC) and 5-hydroxyindoleacetic acid (5-HIAA) in the LH and VMH. DA and DOPAC levels were assayed in the striatum. Although serum glucose levels were unchanged, animals conditioned to drink glucose had significantly higher serum insulin levels. This increased insulin was associated with increased content of 5-HT and 5-HIAA at the level of the LH and VMH, increased NA content in the LH, increased DOPAC levels in the VMH as well as increases in the ratio of DOPAC to DA in the striatum. A regression analysis showed that 5-HIAA at the level of the LH related closely to serum insulin levels.(ABSTRACT TRUNCATED AT 250 WORDS)
