Expression of galanin receptor-1 (GALR1) in the rat trigeminal ganglia and molar teeth.

The expression of galanin receptor-1 (GALR1) was investigated in the rat trigeminal ganglion by using immunocytochemistry and in situ hybridization. In addition, the regional distribution of GALR1-immunoreactive pulpal nerves and their ultrastructure were examined in the molar teeth. In the trigeminal ganglion, the immunoreactivity for GALR1 was recognizable in about 30% of the total number of neurons. Most of the cell bodies were small to medium in size. Analysis of serially cut sections alternately stained with GALR1 and galanin antisera demonstrated that some GALR1-positive cells displayed immunoreactivity for galanin. In situ hybridization analysis, expression of GALR1 mRNA was detected in trigeminal ganglion cells. The cell size distribution was similar to that of GALR1-immunoreactive cells. In the dental pulp, a small number of nerve fibers displayed immunoreactivity for GALR1. The labeled fibers formed terminal arbors in the coronal pulp around and within the odontoblast cell layer, but never penetrated into the predentin and dentin. Ultrastructurally, GALR1 immunoreactivity in the dental pulp was confined to the axoplasm of unmyelinated nerve fibers. The present study provided new evidence that unmyelinated primary afferents innervating dental pulp possessed galanin receptor, and suggests the existence of nociceptive primary afferents functioning as autocrine cells.