GnRH localization in the equine brain and infundibulum: an immunohistochemical study

Immunohistochemical localization of the decapeptide gonadotropin releasing hormone (GnRH) in neural structures in the pony brain and infundibulum (INF) was conducted at the light-microscopic level. This procedure utilized an antiserum generated against GnRH conjugated to bovine serum albumin. In the rostral INF, GnRH was distributed mainly in the external layer, with greatest concentrations adjacent to the long capillary loops of the hypophyseal portal system. The intermediate portion of the INF contained the hormone throughout the external layer, especially in the dorsolateral regions just ventral and medial to the tuberoinfundibular sulcus (TIS) with lesser amounts dorsal to the TIS. Caudally, GnRH was very concentrated along the medial border of the Tis, and in small amounts within the medial portion of the INF just rostral to the mammillary bodies. Throughout the INF, reaction product was noted in the internal layer, although the concentration was less than that observed in the external layer. The hormone was localized in axons of the brain from the medial and lateral septal nuclei through the mammillary region. GnRH positive perikarya were localized in the lamina terminalis, infundibular nucleus and the caudal periventricular nucleus. Preabsorption of the specific antiserum with synthetic GnRH abolished staining in both axons and perikarya, whereas preabsorption with other hypothalamic peptides did not affect staining intensity.