Differential biochemical and behavioral effects of single and chronic administration of amphetamine and apomorphine.

The single and repeated effects of apomorphine (AP) and amphetamine (AM) administrations were compared on rearing behaviour in an open field (RF) and on rearing stereotyped behaviour (RSB). Single AP treatment did not modify RSB while decreased the ability of low doses of AP to inhibit RF. Opposite data were observed after AM single administration. Repeated treatment with both drugs reduced the inhibitory effects of AP low doses on open field behaviour. The AP repeated administration enhanced the dihydroxyphenilacetic (DOPAC) and homovanilic acid (HVA) striatal levels while the same AM treatment was unable to affect the dopamine (DA) metabolites levels. Taken together, our results support the view that behavioural changes observed after AP single and repeated treatment are a result of DA autoreceptors subsensitivity. Nevertheless, the behavioural changes detected after AM treatments are probably related to mechanisms other than the development of DA autoreceptors subsensitivity.