Responses to drugs affecting
5-hydroxytryptamine (5-HT) and dopaminergic (DA) system have been examined in rats after repeated immobilization. Groups of rats were immobilized for 2 h per day for up to 7 days. Twenty-four hours later their behavioural responses to various drugs were tested. Rats immobilized for 7 days showed decreased sniffing and increased grooming and body shakes. When given
amphetamine (3 mg/kg, i.p.) the intensity of classical
dopamine-dependent behaviours was similar to that of non-immobilized controls. Some responses to the
5-HT releaser
p-chloroamphetamine (PCA) (4 and 10 mg/kg, i.p.) and the
5-HT agonist 5-methoxy-N,N-dimethyltryptamine (5-MEODMT) (5 mg/kg, i.p.) (forepaw treading and
tremor) were enhanced after 7 days immobilization but others (limb abduction and headweaving) were not. These responses were not enhanced after 1 or 3 days immobilization. Backward walking and body shakes induced by PCA were also enhanced after 7 days immobilization. Concentrations of
5-HT, DA and their metabolites in striatum, cortex, hippocampus, hypothalamus and midbrain of non-
drug-treated control and immobilized groups were comparable. Brain PCA concentrations 30 min after injection were also comparable. The above biochemical and behavioural data suggest that repeated immobilization increases some
5-HT postsynaptic functions. These results are discussed in relation to non-
drug-provoked behavioural abnormalities occurring 24 h after the first immobilization but no longer evident after 7 periods of immobilization.