Immunohistochemical identification of galanin and growth hormone-releasing factor-containing neurons projecting to the median eminence of the rat.

Through the combined demonstration of the retrograde transport of True blue and the immunohistochemical staining of galanin (GAL), the GAL neurons that project to the median eminence were identified. Moreover, the distribution of GAL and growth hormone-releasing factor (GRF) was analyzed in the arcuate nucleus (ARC) with an elution-restaining procedure. Following the injection of True blue into the median eminence, GAL-positive cells labeled with True blue were found mainly in the ARC. In addition, a few GAL neurons in the periventricular, the paraventricular and the supraoptic nuclei were labeled with True blue. The elution-restaining results revealed that many retrogradely labeled GAL neurons in the ARC contained GRF. These findings suggest that a subpopulation of GAL neurons in the ARC sending axons to the median eminence produces, stores and releases a GRF-like peptide.