Abstract

The effects of intrathecally (i.t.) injected selective tachykinin NK 2 receptor antagonists, MEN 10,207, MEN 10,376 and R396, on the spinal effect of neurokinin A were studied in decerebrate, spinalized, unanesthetized rats. I.t neurokinin A (7 pmol) briefly facilitated the flexor reflex, an effect that was dose dependently inhibited by pretreatment with MEN 10,207 and MEN 10,376 with similar and high potency. I.t. R396 itself caused strong facilitation of the flexor reflex. At lower doses, the effect of i.t. neurokinin A was potentiated by R396. R396 only exhibited moderate antagonism of neurokinin A-induced reflex facilitation even at very high doses. It has been proposed that the tachykinin NK 2 receptor may be further classified into two subtypes, NK 2A and NK 2B, with MEN 10,207 and MEN 10,376 having high affinity for the former and R396 for the latter. Our results suggested that the tachykinin NK 2 receptor in rat spinal cord which mediates the excitatory effect of neurokinin A may belong to the NK 2A subpopulation of receptors.

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