As a step to clarify the profiles of tachykinin receptors in the mammalian central nervous system, we examined the effects of various tachykinin receptor agonists and antagonists on motoneurons in isolated spinal cord preparations from rats, gerbils and hamsters. After treatment with tetrodotoxin, potential changes were recorded extracellularly from lumbar ventral roots at 27 o C. Bath-application of tachykinin NK 1 , NK 3 receptor agonists produced depolarizing responses of ventral roots. In contrast, selective NK 2 agonists exerted no or only marginal depolarizing action. Neurokinin A (NKA), however, exerted a distinct depolarizing action on motoneurons. Tachykinin NK 1 receptor antagonists antagonized the actions of SPOMe and NKA in a competitive manner. The present results suggest that tachykinin NK 1 and NK 3 receptors are present on spinal motoneurons of newborn rats, gerbils and hamsters, and that NKA acts on the NK 1 receptors.