Distribution of beacon immunoreactivity in the rat brain.

Beacon is a novel peptide isolated from the hypothalamus of Israeli sand rat. In the present study, we determined the distribution of beacon in the rat brain using immunohistochemical approach with a polyclonal antiserum directed against the synthetic C-terminal peptide fragment (47-73). The hypothalamus represented the major site of beacon-immunoreactive (IR) cell bodies that were concentrated in the paraventricular nucleus (PVN) and the supraoptic nucleus (SON). Additional immunostained cells were found in the septum, bed nucleus of the stria terminalis, subfornical organ and subcommissural organ. Beacon-IR fibers were seen with high density in the internal layer of the median eminence and low to moderate density in the external layer. Significant beacon-IR fibers were also seen in the nucleus of the solitary tract and lateral reticular formation. The beacon neurons found in the PVN were further characterized by double label immunohistochemistry. Several beacon-IR neurons that resided in the medial PVN were shown to coexpress corticotrophin-releasing hormone (CRH) and most labeled beacon fibers in the external layer of median eminence coexist with CRH. The topographical distribution of beacon-IR in the brain suggests multiple biological activities for beacon in addition to its proposed roles in modulating feeding behaviors and pituitary hormone release.