The neural network that regulates energy balance is responsive to glucocorticoids and insulin and also regulates HPA axis responsivity at a site proximal to CRF neurons

For a variety of reasons, some serendipitous and not related to the topic of this paper, we have had cause to examine the tight association between feeding, metabolism, and activity in the hypothalamo-pituitary-adrenal (HPA) axis in recent years, although our interest in this association is long-standing.(1) What follows is a review first of our more recent studies that suggest strongly that the HPA axis serves as one arm of a two-hormone system (corticosteroids and insulin) that regulates energy balance over the long term. Next, we will describe our results on the effect of the diurnal rhythm and of caloric intake on the magnitude of ACTH responses to stress, corticosteroid feedback, and prior stress-induced facilitation in acutely restrained rats. We will also describe the profound effects on HPA axis activity during an overnight fast in young rats. Finally, we will discuss briefly the relationship between neuropeptide Y (NPY) and the HPA axis. Throughout the paper, we observe that NPY may be the major integrator of activities in the feeding and adrenocortical system.