Galanin-like peptide is target for regulation by orexin in the rat hypothalamus

Galanin-like peptide (GALP) is a newly discovered 60 amino acid peptide from the porcine hypothalamus. GALP has been shown to be expressed predominantly in the arcuate nucleus (ARC) of the rat hypothalamus, a region considered to be one of the most important feeding-regulating centers in the brain. GALP-containing neurons in the ARC express leptin receptors, but relationships between GALP and other feeding-regulating neurons have not yet been fully elucidated. Given that Orexin (OX)-containing neurons make synaptic inputs to the ARC, we thus examined the relationship between GALP and OX in the ARC by use of a dual immunostaining technique. OX-immunoreactive fibers appeared to be closely apposed to GALP-immunoreactive cell bodies and their processes. We also examined whether the OX receptor, OX(1)-R was expressed in the GALP-containing neurons. Immunoreactivity for both OX(1)-R and GALP was detectable in 9.6 % neurons (range 4.2-14.6%) in the ARC. These findings strongly suggest that GALP may participate in the regulation of feeding behavior under the influence of leptin and OX.