ANATOMICAL INTERACTIONS OF PROOPIOMELANOCORTIN (POMC)-RELATED PEPTIDES, NEUROPEPTIDE-Y (NPY) AND DOPAMINE BETA-HYDROXYLASE (D-BETA-H) FIBERS AND THYROTROPIN-RELEASING-HORMONE (TRH) NEURONS IN THE PARAVENTRICULAR NUCLEUS OF RAT HYPOTHALAMUS

In order to determine the nature of afferent fibres contacting thyrotropin-releasing hormone (TRH)-synthesizing neuronal cell bodies in the rat hypothalamic paraventricular nucleus, we used dual immunostaining procedures which employed antibodies to ACTH (to label proopiomelanocortin (POMC) neurons), neuropeptide Y (NPY) and dopamine-beta-hydroxylase (D-beta-H) and peroxidase-labeled goat anti-rabbit IgG as a first sequence and antibodies to a cryptic fragment (Phe 178-Glu 199) of pro-TRH (to label TRH neurons) and alkaline phosphatase-labeled goat anti-rabbit IgG as the second sequence. A rich innervation of the paraventricular nucleus by immunoreactive POMC, NPY and D-beta-H fibres was observed. Numerous NPY and POMC fibres were in intimate anatomic proximity and often appeared to surround in remarkable density TRH-containing cell bodies. Less frequent appositions between D-beta-H fibres and TRH cell bodies were detected. These results strongly suggest that TRH neurons might be regulated by POMC, NPY as well as adrenergic and/or noradrenergic systems. These interactions might be the neuroanatomical basis for the already observed effects of opiate peptides, NPY and catecholamines on TSH secretion.