TACHYKININ RECEPTORS ON MOTONEURONS IN THE SPINAL-CORDS OF NEONATAL RATS, GERBILS AND HAMSTERS

As a step to clarify the profiles of tachykinin receptors in the mamma lian central nervous system, we examined the effects of various tachyk inin receptor agonists and antagonists on motoneurons in isolated spin al cord preparations from rats, gerbils and hamsters. After treatment with tetrodotoxin, potential changes were recorded extracellularly fro m lumbar ventral roots at 27 degrees C. Bath-application of tachykinin NK1, NK3 receptor agonists produced depolarizing responses of ventral roots, In contrast, selective NK2 agonists exerted no or only margina l depolarizing action. Neurokinin A (NKA), however, exerted a distinct depolarizing action on motoneurons. Tachykinin NK1 receptor antagonis ts antagonized the actions of SPOMe and NKA in a competitive manner. T he present results suggest that tachykinin NK1 and NK3 receptors are p resent on spinal motoneurons of newborn rats, gerbils and hamsters, an d that NKA acts on the NK1 receptors.