5–HT1A and 5–HT1B Agonists Produce Opposite Effects on the Ejaculatory Response Induced by Amphetamine in Rats

d–Amphetamine, when given in large dosages, releases not only the catecholamines, noradrenaline (NA), and dopamine (DA) but also 5–hydroxytryptamine (5–HT) (Sloviter et al., 1978). Consequently, it produces a behavioural syndrome which includes e.g. hindlimb abduction, forepaw treading, the wet dog shake response (WDSR) (Bedard & Pycock, 1983), and the ejaculatory response (ER). The ER induced by the nonselective endogenous neurotransmitter, 5–HT, and by the nonselective postsynaptic 5–HT agonist, 5–methoxy–N,N–dimethyltryptamine (5–MeODMT) was recently introduced as a model for detecting changes in functions mediated by central 5–HT receptors (Rényi, 1985). The ER like the WDSR is a multitransmitter response. Only a nonselective agonism of the 5–HT receptors results in the ER and WDSR since they require both 5–HT₁ and 5–HT₂ receptors (Green et al., 1981; Yap & Taylor, 1983; Rényi, 1987). Indeed, none of these behaviours could be induced by the 5–HT_1A agonist, 8–hydroxy–2–(di–n–propylamino)–tetralin (8–OH–DPAT) (Middlemiss & Fozard, 1983), or by the 5–HT_1B agonist, 5–methoxy–3(l,2,3,6–tetrahydro– pyridin–4–yl)lH indole (RU 24969) (Hunt & Oberlander. 1983), even at large doses (Rényi, 1985; Tricklebank et al., 1985, 1986). Furthermore, both the ER and the WDSR is facilitated by NA and inhibited by DA (Bedard & Pycock, 1977; Handley & Brown, 1982; Dickinson & Curzon, 1983; Rényi, 1985). Thus, these behaviours can be influenced in many ways. The aim of the present study was to separate the 5–HT₁ receptors functionally and to investigate some connections between the 5–HT and the catecholamine systems.