NON-5-HT1A/5-HT1C [H-3] 5-HT BINDING-SITES IN THE HAMSTER, OPOSSUM, AND RABBIT BRAIN SHOW SIMILAR REGIONAL DISTRIBUTION BUT DIFFERENT SENSITIVITY TO BETA-ADRENOCEPTOR ANTAGONISTS

We have used receptor autoradiography to investigate the distribution and pharmacological profile of non 5-HT1A/5-HT1C[H-3]5-hydroxytryptamine binding sites in the brain of rabbits, hamsters and opossums. These data were compared to those found under similar conditions in the brain of rats and guinea pigs, species which are known to possess 5-HT1B and 5-HT1D receptors, respectively. In the presence of 100 nM 8-OH-DPAT and mesulergine, the regional distribution of [H-3]5-hydroxytryptamine binding sites was very similar in the brain of all species investigated; densest labelling was observed in the globus pallidus, substantia nigra and superior colliculus. In all species, 5-carboxamidotryptamine competed for the labelled sites in a biphasic manner and metergoline displayed a subnanomolar affinity. In contrast, the beta-adrenoceptor blocking agents (-)propranolol, (-)pindolol, and (+/-)SDZ 21009 were potent displacers only in the rat, hamster and opossum brains. These data indicate that non 5-HT1A/5-HT1C[H-3]5-HT binding sites display a high affinity for these agents in a particular rodent suborder as well as in opossum, a phylogenetically unrelated species.