INTRATHECAL GALANIN BLOCKS THE PROLONGED INCREASE IN SPINAL-CORD FLEXOR REFLEX EXCITABILITY INDUCED BY CONDITIONING STIMULATION OF UNMYELINATED MUSCLE AFFERENTS IN THE RAT

The effect of intrathecal (i.t.) galanin (GAL) on the prolonged increase of spinal reflex excitability produced by conditioning stimulation (CS) of unmyelinated muscle afferents was studied in decerebrate, spinalized, unanesthetized rats. A CS train (1 Hz, 20 s) applied to the unmyelinated fibers in the gastrocnemius muscle nerve facilitated the ipsilateral flexor reflex for about 1 h. Pretreatment with GAL (0.1-10-mu-g) decreased reflex facilitation induced by the gastrocnemius nerve CS. The present results indicate that GAL is capable of blocking the prolonged increase in spinal cord excitability after stimulation of unmyelinated muscle afferents, possibly by antagonizing the facilitatory effect of tachykinins and calcitonin gene-related peptide released at the intraspinal terminals of these fibers.