Evidence that 5-HT agonist-induced rotational behaviour in the rat is mediated via 5-HT1 receptors

The rotational behaviour induced by 5-HT agonists has been investigated in rats with lesions of the dorsal raphe' nucleus (DRN). We have previously reported that 5-methyoxy-N,N-dimethyl-tryptamine (5-MeODMT) caused dose-related contralateral rotation in rats with 5,7-dihydroxytryptamine (5,7-DHT) lesions of the DRN. Similar findings are now presented for the 5-HT1 agonists 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) and 5-methoxy-3 (1,2,3,6-tetrahydropyridin-4-yl) (1H indole) (RU24969). In this model, in agreement with the behavioural studies, both agonists were shown to have a greater affinity for the 5-HT1 binding site when compared with the 5-HT2 binding site. Antagonist studies using selective 5-HT2 antagonists (ketanserin and pirenperone) at non-sedative doses failed to inhibit this behaviour. In contrast, the classical 5-HT antagonist methysergide caused significant inhibition of the rotational behaviour. These results suggest that 5-HT agonist-induced rotation in the rat is mediated via 5-HT1 receptors, probably located in the substantia nigra.