Interactions of Glucocorticoids, NPY and Hypothalamic Serotonin

Neuropeptide Y (NPY), insulin, corticosterone (CORT) and 5-hydroxytryptamine (5-HT), or serotonin, are all involved in energy homeostasis. To show how they might interact, the effects of NPY on plasma insulin and on 5-HT metabolism in the paraventricular hypothalamic nucleus (PVN), the ventromedial hypothalamic nucleus (VMN), the arcuate nucleus (ARC), and the locus coeruleus (LC) were measured in separate groups of intact, adrenalectomized (ADX), or ADX and CORT replaced Sprague-Dawley rats. Fifteen minutes after ICV injection of NPY, no effect on 5-HT metabolism in the intact animal was observed. 5-HT and its metabolite, 5-HIAA, increased in the PVN as a result of ADX, an effect that was reversed with CORT replacement. NPY also reversed these effects. Similar effects of ADX, CORT replacement and NPY were noted with 5-HIAA in the ARC. This suggests a role for 5-HT in the attenuation of weight gain in ADX animals. NPY also caused an increase in plasma insulin in the CORT replaced animal, but not the intact animal. This was most likely due to an inability of CORT replaced animals to adjust their CORT levels in response to NPY.