Behavioral evidence for supersensitivity after chronic bromocriptine administration.

Behavioral evidence for tolerance and supersensitivity during and after chronic (30 day) administration of bromocriptine (BRC) or bromocriptine + L-dopa in mice was assessed by measuring wheel running (WR) behavior during and after chronic drug administration, and apomorphine- and methylphenidate-(MP-)induced stereotyped gnawing after termination of chronic injections. In both BRC and BRC + L-dopa groups, tolerance developed fairly quickly to the depressing effect of BRC on WR seen on day 1 of drug administration. Mice receiving BRC showed significant increases in WR by week 2 of chronic drug administration, which persisted for at least two days after the termination of chronic injections. During the first week after termination of chronic injections, low doses of both apomorphine and MP induced significantly more stereotyped gnawing in BRC and BRC + L-dopa mice than in the control mice or the mice treated with L-dopa alone. This behavioral evidence for dopaminergic supersensitivity after chronic BRC administration may have relevance for the clinical use of BRC in combination with L-dopa or other dopamine agonists.