Involvement of the dopamine D(1) and D(2) receptors in the ventral tegmental area (VTA) in the micturition reflex was investigated using female Sprague Dawley rats under urethane anesthesia. Cystometrograms during continuous infusion of warmed saline into the bladder were recorded. When intervals of bladder contraction became constant, the excitatory amino acid DL-homocysteic acid (DLH) was microinjected into the VTA and changes in the cystometric parameters were observed. The selective D(1) antagonist SCH23390 (0.3 mg/kg) or D(2) antagonist eticlopride (0.1 mg/kg) was subcutaneously injected (s.c.) 15 min prior to the DLH treatment. A low dose of DLH (3 microg) facilitated the micturition reflex, whereas a high dose of DLH (30 microg) inhibited the micturition reflex. However, a middle dose of DLH (10 microg) did not show any effect. The facilitated micturition reflex induced by a low dose of DLH was inhibited by the selective dopamine D(2) antagonist eticlopride, but unaltered by SCH23390, a selective dopamine D(1) antagonist. In contrast, the inhibitory effect induced by a high dose of DLH on the micturition reflex was suppressed by SCH23390 but not eticlopride. These results suggested that the facilitated micturition reflex might be mediated via the dopamine D(2) receptors, while the inhibitory effects on the micturition reflex was mediated via the dopamine D(1) receptors.