Neuropeptide Y (NPY) neurons in the arcuate nucleus (ARH) and dorsomedial nucleus (DMH), areas activated during lactation, project to the paraventricular nucleus of the hypothalamus (PVH)

Lactation induces an increase in NPY activity in two neuronal populations in the hypothalamus: the arcuate nucleus (ARH) and the dorsomedial nucleus (DMH) area. To determine if NPY neurons from these areas project to the paraventricular nucleus of the hypothalamus (PVH), the retrograde tracer, fluorogold (FG), was injected into the PVH of lactating females. FG-labeled NPY cells (identified by in situ hybridization for NPY mRNA) were observed throughout the ARH; however, a greater number of double-labeled cells were found in the caudal portion than the rostral portion of the ARH. Thus, NPY neurons in the caudal portion of the ARH provide the major ARH NPY input into the PVH area. If these results are combined with our previous data showing that activation of NPY neurons in the ARH during lactation is confined to the caudal portion, it is very likely that the lactation-activated NPY neurons project to the PVH. FG-labeled NPY cells were also identified in the DMH area, providing the first evidence that the NPY neurons in the DMH area activated during lactation also project to the PVH. Taken together, the increase in NPY activity may be important in modulating some of the physiological alterations occurring during lactation, such as the increase in food intake, in part through modulating PVH neuronal activity. Copyright (C) 1998 Elsevier Science B.V.