Abstract
The localization of immunoreactive neuropeptides such as arginin vasopressin (AVP), oxytocin (OT), luteinizing hormone-releasing hormone (LHRH), somatostatin (SOM), corticotropin-releasing factor (CRF), thyrotropin-releasing hormone (TRH), met-enkephalin (ENK) and substance P (SP) was studied immunocytochemically in the ventral hypothalamus of the cat. Each peptidergic neuron system represents its own peculiar distributional pattern in the hypothalamus, while some nuclei in the ventral hypothalamus contain many kinds of neuropeptide-producing neurons, which show an overlapped or mosaic-like distribution. The overlapped distribution of different peptidergic systems suggests their functional correlations through the information exchange within the central nervous system. In the median eminence, many kinds of peptide-containing fibers show a mosaic-like distribution. In the internal zone, AVP- and OT-fibers pass to the neural lobe via supraoptico-hypophysial tract. AVP-, CRF-, TRH-, and ENK- immunoreactive fibers are distributed exclusively in the external layer of the anterior part of the median eminence and terminate on the basement membrane of the external surface of the median eminence in intimate contact with the anterior primary capillary plexus of the portal vessels. LHRH- and SOM-immunoreactive fibers are more numerous in the external layer of the posterior part of the median eminence. The intrinsic distribution of each peptide-containing fiber in the median eminence suggests the regional control mechanisms of the pars distalis by the discharge of each peptide into the respective portal vessels.
