Distribution of LHRH-like Substance in the Vertebrate Brain as Revealed by Immunohistochemistry

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Abstract
Distribution of immunoreactive LHRH[luteinizing hormone releasing hormone]-like substance was studied by PAP [peroxidase-rabbit-anti-peroxidase complex] method using 2 different anti-LHRH sera (AsI: anti-Tyr5-BSA[bovine serum albumin]-LHRH serum; AsII: anti-Gly10-BSA-LHRH serum) in the brain of several species selected from each class of vertebrates. Although LHRH-immunoreactivity was slightly stronger in AsI than AsII, LHRH-like substance was found in the median eminence of all tetrapods tested. LHRH-positive perikarya were detected by AsI and AsII primarily in the septo-preoptic region of the cat, Elaphe climacophora, Rana catesbeiana, Xenopus laevis and Cynopus pyrrhogaster ensicauda. However, in the guinea pig, those perikarya were detected only by AsI in the medial basal hypothalamic region in addition to the septo-preoptic region. In most of those animals, LHRH-positive fiber pathways to the median eminence were also demonstrated. Among the teleosts examined, immunoreactive products were detectable in the fiber terminals of the neurohypophysis of Anguilla japonica and Fugu niphobles, but not in the 3 other species. In the former 2 species, however, LHRH-immunoreactivity was slightly stronger in AsI than AsII. When AsI was applied to the hypothalamic sections of the lamprey Entospenus japonica, a dense immunoreactive product was found in the nerve perikarya of the preoptic nucleus and in the fiber terminals of the neurohypophysis. However, when AsII was applied to the lamprey, only a little immunoreactive product was detectable in the same regions. No immunoreactive product was detected in the brain of the dogfish (Triakis scyllia) and the hagfish (Eptatretus burgeri) in either case of AsI or AsII.