Expression of the novel galanin receptor subtype GALR2 in the adult rat CNS: distinct distribution from GALR1.

Recent molecular cloning studies by our laboratory and others have identified the existence of a novel rat galanin receptor subtype, GALR2. In the present study, we examined the regional and cellular distribution of GALR2 mRNA in the rat central nervous system (CNS) by in situ hybridization. For comparative purposes, adjacent sections were probed for GALR1 mRNA expression. Our findings indicate that dorsal root ganglia express by far the highest levels of GALR2 mRNA in the rat CNS. Hybridization signal is mainly concentrated over small and intermediate primary sensory neurons. In spinal cord, the large alpha motoneurons of the ventral horn are moderately labeled and several small, but less intensely labeled, cells are scattered throughout the gray matter. In brain sections, the highest levels of GALR2 mRNA are detected in granule cells of the dentate gyrus, in the mammillary nuclei, and in the cerebellar cortex. Moderate levels of GALR2 mRNA are observed in the olfactory bulb, olfactory tubercle, piriform and retrospinal cortices, hypothalamus (namely the preoptic area, arcuate nucleus, and dorsal hypothalamic area), substantia nigra pars compacta, and sensory trigeminal nucleus. Moderate to weak hybridization signal is also present in several other hypothalamic nuclei, specific layers of the neocortex, periaqueductal gray, and several nuclei within the pons and medulla, including locus coeruleus, lateral parabrachial, motor trigeminal, pontine reticular, hypoglossal, vestibular complex, ambiguus, and facial and lateral reticular nuclei. This novel pattern of GALR2 distribution within the rat CNS differs considerably from that of GALR1, suggesting that specific physiologic effects of galanin may be ascribed to the GALR2 galanin receptor subtype.