Immunocytochemical localization of growth hormone and growth hormone‐releasing hormone immunoreactivity in the brain and pituitary of the little brown bat

Abstract

Anterior pituitary cells exhibiting growth hormone (GH) immunoreactivity and forebrain neurons containing growth hormone-releasing hormone (GHRH) immunoreactivity were identified in little brown bats (Myotis lucifugus) using light microscopic immunocytochemistry. Pituitary somatotropes appeared as ovoid or polyhedral cells that were distributed throughout most of the pars distalis, with the exception of its most rostral region where this cell type was scarce. GH-immunoreactive cells occupied approximately one-third of the total volume of the pars distalis; this proportion did not differ significantly between males and females or in bats collected at different times of year. Neuronal perikarya containing immunoreactive GHRH were observed in the hypothalamic arcuate and suprachiasmatic nuclei, as well as in the cortical and subcortical telencephalon. Fibers were most evident in the median eminence, paraventricular and periventricular nuclei, and molecular layer of the cerebral cortex. Fine fibers were also accumulated in the bed nucleus of the stria terminalis and in the amygdala.

Endocrine Control of the Reproductive Activity in Hibernating Bats

“…Seasonal changes of the hypothalamic neuropeptides in mammalian hibernators, especially the changes of neuropeptide-producing cells associated with hibernation, have been reported in hedgehogs, hamsters, dormice and ground squirrels (Nürnberger, 1995). Though there are several reports on the hypothalamic neuropeptides in bats (Mikami et al ., 1988b;Anthony et al ., 1991), detailed analyses have only been performed on gonadotropin-releasing hormone (GnRH). GnRH is the key hypothalamic hormone responsible for the regulation of reproductive function.…”

“…Annual changes in corticotrophs are related to the so-called fat cycle in tropical vespertilionid bats (Singh and Krishna, 1996b). In vespertilionid bats inhabiting the temperate zone, there were no seasonal variations in somatotrophs (Anthony et al ., 1991). In several species of bats inhabiting the temperate zone or tropical zone, immunohistochemical studies have also verified changes in mammotrophs (lactotrophs) relating to reproductive cycle and seasonality (Richardson, 1981b;Jemenez et al ., 1987;Mikami et al ., 1988a;Ishibashi and Shiino, 1989;Muñiz et al ., 1991;Singh and Krishna, 1996a).…”