ABSTRACT
The synthesis of serotonin (5–HT) receptor subtype selective agonists and/or antagonists has given the behavioural pharmacologist the opportunity to discover the functions for these receptors. A great variety of changes in rodent behaviour by drugs has been related to serotonin receptor activation. At present there is sufficient information to suggest that drug–induced penile erection is due to activation of the 5–HT1B receptor (Berendsen and Broekkamp 1987) and that drug induced head shakes are mediated by the 5–HT2 receptor (Yap and Taylor, 1983). Goodwin et al. (1987) suggested that activation of the presynaptic 5–HT1A receptor mediates hypothermia in mice and rats whereas Tricklebank et al. (1985) found that activation of the postsynaptic 5–HT1A receptor mediates forepaw treading. The 5–HT1A agonist 8–OH–N,N–dipropyl–2 aminotetralin (8–OH–DPAT) also induces hyperactivity in rats (Dourish et al., 1985), hypoactivity in mice and a recently discovered symptom which we described as lower lip retraction (Berendsen et al., 1988). Compounds with activity on more than one subtype of 5–HT receptor do not always induce the above mentioned behaviour. For example the compound RU 24969, (5 methoxy–3(l,2,3,6–tetra–hydropiridin–4–yl) 1H indole) which has both 5–HT1B and 5–HT1A activity in vitro (Doods et al., 1985), does not induce the 5–HT1B related penile erections (Berendsen and Broekkamp, 1987) or the 5–HT1A related forepaw treading, but we do observe 5–HT1A related lower lip retraction. On the other hand 5–methoxy–N,N–dimethyltryptamine (5–MeODMT), a compound with 5–HT1A activity and some 5–HT2 and 5–HT1B activity (Engel et al., 1986), does not induce lower lip retraction but does induce forepaw treading (Berendsen et al., unpublished).
