Immunohistochemical study to Localize the distribution of glucocorticoid receptors in the brain of frog Rana Ridibunda. (a)

Glucocorticoids play essential role in, development, growth, behavior, neuroendocrine regulation and metabolic processes that are mediated by the glucocorticoid receptor (GR). During stress, activation of the hypothalamic- pituitary-adrenal (HPA) axis induces the release of high concentration of glucocorticoids which bind to GR through the central nervous system to maintain homeostasis. Although, the GR has been considerably studied in mammals, little is known about the distribution of GR in amphibians. Thus, the aim of the present study was to localize the GR-expressing cells in the diencephalon and telencephalon within the brain of frog Rana ridibunda. We demonstrate by Immunohistochemical process that GR-immunoreactive cells are widely distributed in the anterior preoptic area (Poa) of hypothalamus, a homolog of the mammalian supraoptic and paraventricular nucleus (PVN) and known to contain corticotrophin-releasing factor (CRF), and in the organum vasculosum known as the supraoptic crest. Also, in the telencephalon, several limbic system regions contain GR-immunoreactive neurons distributed notably in the medial pallium (mp, homolog of the mammalian hippocampus), lateral pallium, medial amygdala, lateral amygdala, and ventral amygdale, and Bed nucleus of the pallial commissure. Moreover, we observed GR- immunoreactivity in thalamic structures such as dorsal habenular nucleus, ventral habenular nucleus, thalamic eminence, and the ventromedial thalamic nucleus. In most GR-immunoreactive cells, the immunostaining was observed in both the cytoplasm and the nucleus. These results support the idea that the general patterns of glucocorticoid receptor distribution in the neuroendocrine nuclei and limbic system of the central nervous system are highly conserved among vertebrates. Thus GR is likely to play roles in mediating the effects of corticosteroids on frog brain similar to those in mammals, suggesting that the basic regulatory pathways for modulating the responsiveness of the stress axis may be an evolutionary conserved mechanism in vertebrates. Our data represent the first step to map the distribution of GR in the brain of the frog Rana ridibunda.