Aging and the regulation of striatal dopaminergic mechanisms in mice.

Compensatory responses of striatal dopaminergic mechanisms to chronic drug treatment were tested in C57BL/6J and C57BL/6NNia male mice during the adult lifespan (5, 12, and 24 to 26 months). Chronic treatment with haloperidol (dopamine antagonist) (1.2 or 2 mg/kg/day for 21 days) induced supersensitivity in younger mice (5 and 12 months) as monitored by increased striatal spiroperidol binding sites and increased intensity of apomorphine-induced stereotyped behavior; in contrast, old mice were unaffected. However, chronic treatment with bromocriptine (dopamine agonist) (15 mg/kg/day for 7 days) induced desensitization at all ages, as monitored by reduced spiroperidol binding sites and reduced intensity of stereotyped behavior.