Galanin Receptor Binding Sites in Adult Rat Spinal Cord Respond Differentially to Neonatal Capsaicin, Dorsal Rhizotomy and Peripheral Axotomy

The discrete distribution and possible changes in specific [¹²⁵I]galanin binding sites were evaluated in the rat spinal cord following neonatal capsaicin treatment, dorsal rhizotomy and sciatic nerve section. The highest density of [¹²⁵I]galanin binding sites in the normal rat spinal cord was particularly evident in the superficial layers of the dorsal horn whereas moderate to low amounts of labelling were associated with the deeper dorsal horn, areas around the central canal and the ventral horn. Capsaicin-treated rats, compared to littermate controls, showed a significant bilateral increase in [¹²⁵I]galanin binding in the superficial laminae of the dorsal horn. Similarly, unilateral dorsal rhizotomy evoked a significant increase in the density of [¹²⁵I]galanin binding sites in the superficial dorsal horn ipsilateral to surgery. Section of the sciatic nerve, on the other hand, induced a significant depletion in [¹²⁵I]galanin binding in laminae I and II of the ipsilateral dorsal horn. These results, in parallel to those reported for galanin immunoreactivity under similar conditions, suggest that [¹²⁵I]galanin binding sites are preferentially located postsynaptically to the primary afferent fibre terminals in the dorsal horn of the spinal cord. Thus it seems that galanin, at the level of the dorsal spinal cord, regulates the processing of nociceptive information by acting on its own class of specific receptors located postsynaptically to primary sensory terminals.