NK-1 tachykinin receptor in rat and guinea pig brains: pharmacological and autoradiographical evidence for a species difference.

The affinities of a large variety of peptide or nonpeptide tachykinin analogues were determined on membranes from rat and guinea pig brains using the selective NK-1 radioligand 3H-[Pro9]SP. Nonpeptide antagonists clearly revealed a species difference; (+/-)CP-96,345 was more potent in the guinea pig, while RP 67580 was found to be a better competitor of 3H-[Pro9]SP binding to rat brain membranes. This was confirmed on brain slices by autoradiography. Numerous brain structures were analyzed by optical densitometry. From these data, a heterogeneity of NK-1 binding sites among different structures can be excluded in both rat and guinea pig brains.