Effects of a tachykinin NK3 receptor antagonist, SR 142801, studied in isolated neonatal rat spinal cord

Effects of a nonpeptide tachykinin NK3 receptor antagonist, SR 142801,were studied in the isolated spinal cord preparation of the neonatal rat. Potent ial changes were recorded extracellularly from a lumbar ventral root. Bath- application of neurokinin B induced a dose-dependent depolarization of the ventral root. SR 142801 caused rightward shifts of the concentration-respon se curve for neurokinin B with pA(2) of 6.57, but did not affect the depola rizing responses to other agonists. Stimulation of a dorsal root evoked in the ipsilateral ventral root of the same segment monosynaptic and polysynap tic reflexes of fast time course which were followed by a slow depolarizati on (ipsilateral slow ventral root potential). SR 142801 depressed the ipsil ateral slow ventral root potential. The present results indicate that SR 14 2801 is a specific antagonist for tachykinin NK, receptors in the spinal co rd and suggest that NK, receptors are involved in primary afferent-evoked n ociceptive responses of spinal neurones.