Differential distribution and regulation of galanin receptors- 1 and -2 in the rat lumbar spinal cord

The expression of the galanin receptor-1 and -2 (Gal1 and Gal2) messenger ribonucleic acids (mRNAs) was studied in the lower spinal cord of rat by means of in situ hybridization, using ribonucleic acid probes (riboprobes). Naïve rats as well as rats with unilateral axotomy of the sciatic nerve or unilateral inflammation of the hindpaw were analyzed. In naïve rats, numerous Gal1 mRNA-positive (+) neurons were detected in lamina (L) I–III. In addition, several Gal1 mRNA+ neurons were seen in deeper layers, including the ventral horns, area X, and the lateral spinal nucleus. In contrast, few and comparatively weakly labeled Gal2 mRNA+ neurons were observed, mostly in the ventral horns and in area X, with fewer in the dorsal horn and in the sympathetic and parasympathetic intermediate lateral cell columns. Axotomy induced a strong increase in intensity and number of Gal2 mRNA+ motoneurons ipsilateral to the lesion. In contrast, nerve cut or hindpaw inflammation did not alter the expression of Gal1 or Gal2 in the dorsal horn. The present (and previous) results suggest that galanin, acting through Gal1 and Gal2 receptors, has a modulatory role on spinal excitability, not only via interneurons in superficial dorsal horn, but also on neurons in deep layers and area X, as well as on the sympathetic and parasympathetic outflow. Furthermore, the nerve injury-induced Gal2 upregulation in motor neurons suggests a role for galanin in survival/regeneration mechanisms.