Characterization of the distribution and ontogeny of galanin containing systems during the development of the brain
The distribution of galanin (GAL) containing systems was characterized in the brain of the adult and developing Brazilian opossum (Monodelphis domestica). Nuclear groups containing GAL-like immunoreactivity (GAL-IR) in cell bodies and fibers were seen throughout the adult and developing opossum brain. In the developing brain, GAL-IR was seen as early as 1 day postnatal (PN) in the developing hypothalamus and brainstem. Since neurogenesis and brain morphogenesis are actively occurring postnatally in the opossum, galanin (GAL) may be playing a role in the differentiation of specific regions of the brain;In the second study we used autoradiography to investigate the distribution of GAL receptors in the forming Brazilian opossum brain. [superscript]125I-GAL binding was detected as early as 1 PN in regions of the brain which were still undergoing neurogenesis. High levels of GAL binding correlated with our previous results on GAL-IR during development. In addition, a transient binding pattern was seen in the anterior pituitary;In the third study, we utilized immunohistochemistry to characterize the developmental profiles of glial fibrillary acidic protein (GFAP) and vimentin (VIM) and their possible relationship to GAL in the brain of the Brazilian opossum. At 1 PN VIM-like immunoreactivity was present throughout the brain. The density of VIM-IR was maximal at 10 PN and decreased with age. In contrast, GFAP-like immunoreactivity increased dramatically with age. These results indicate that GFAP and VIM are reciprocally related during periods of morphogenesis and differentiation of the opossum brain;In the fourth and final study, the distribution of GAL-IR in the developing hypothalamus was compared to several substances involved in controlling the hypothalamic-pituitary axis. All of these substances were detected with immunohistochemistry in the developing opossum brain, but only arginine vasopressin (AVP) was comparable in distribution to GAL-IR in the hypothalamus. Immunoreactive AVP and GAL cells and fibers were found to be located in close association but double labelled cells were not visualized. In contrast, GAL and AVP were colocalized in the adult opossum hypothalamus. The results from these studies indicate that GAL may be involved in early hypothalamic development and regulation.