Novel expression of neuropeptide Y (NPY) mRNA in hypothalamic regions during development: Region-specific effects of maternal deprivation on NPY and agouti-related protein mRNA

During development there is novel expression of NPY mRNA in the dorsomedial hypothalamic nucleus (DMH) and perifornical region (PFR), in addition to t he arcuate nucleus (ARH). Furthermore, NPY mRNA levels peak in all regions on postnatal d 16 (P16) and decrease to adult levels by P30. The purpose of the present study was to determine whether NPY and agouti-related protein (AGRP) mRNA expression in the different hypothalamic regions on P11 and P16 are similarly affected by fasting. An examination of the full rostral to c audal extent of the hypothalamus revealed two additional regions displaying novel NPY mRNA expression, the parvocellular division of the paraventricul ar nucleus (PVH) and lateral hypothalamus (LH). Maternal deprivation for 36 h, used to bring about a fast, similarly increased (23-29%) NPY and AGRP m RNA expression in the ARH on P11 and P16. In contrast, NPY expression in th e DMH and PFR were significantly decreased (19-30% and 48-53%, respectively ), whereas NPY mRNA levels in the PVH and LH were not altered by this treat ment. The increase in NPY and AGRP mRNA expression in the ARH in response t o maternal deprivation suggests that these neuronal populations respond to signals of energy balance. In contrast, NPY expression in the DMH, PFR, PVH , and LH is differentially regulated by maternal deprivation or other facto rs associated with maternal separation.