ABSTRACT
Although an anatomical relationship between substance P (SP) and serotonin (5–HT) has been recognized for almost a decade (Chan-Palay et al., 1978; Hokfelt et al., 1978; Neekers et al., 1979; Johansson et al., 1981; Magoul et al., 1986; Pretel & Ruda, 1986), its functional significance is less clearly defined. SP is known to release 5–HT both in vivo and in vitro (Reubi et al., 1978; Forchetti et al., 1982; Reisine et al., 1982) and it has been suggested that this is mediated via an inhibitory action on 5–HT terminal autoreceptors (Mitchell & Fleetwood-Walker, 1981). Previous studies examining the interactions of these two transmitters on unconditioned behaviour have pointed to a modulatory effect of each on behaviours induced by the other (Hylden & Wilcox, 1983; Ogren et al., 1985; Fasmeret al., 1987).
