Differential effects of single and long-term amphetamine and apomorphine administrations on locomotor activity of rats.

The effects of single and long-term administration of apomorphine (AP) and amphetamine (AM) on the locomotor behaviour of rats observed in an open-field (LF), and on the locomotion stereotyped behaviour (LSB) of rats were compared in the present study. Single AP treatment did not modify LF and LSB. Single AM treatment reduced the duration of LSB 2 and 3 days after drug administration, but did not alter the LF. Long-term treatment with both drugs reduced the inhibitory effects of low AP doses on open-field behaviour. Subsensitivity of dopaminergic autoreceptors induced by the long-term dopaminergic agonist administration was considered to be involved in the differences observed.