Neuronal Excitation in the Ventral Tegmental Area Modulates the Micturition Reflex Mediated Via the Dopamine D_1 and D_2 Receptors inRats

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Involvement of the dopamine D1 and D2 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 <sc>DL</sc>-homocysteic acid (DLH) was microinjected into the VTA and changes in the cystometric parameters were observed. The selective D1 antagonist SCH23390 (0.3 mg/kg) or D2 antagonist eticlopride (0.1 mg/kg) was subcutaneously injected (s.c.) 15 min prior to the DLH treatment. A low dose of DLH (3 μg) facilitated the micturition reflex, whereas a high dose of DLH (30 μg) inhibited the micturition reflex. However, a middle dose of DLH (10 μg) did not show any effect. The facilitated micturition reflex induced by a low dose of DLH was inhibited by the selective dopamine D2 antagonist eticlopride, but unaltered by SCH23390, a selective dopamine D1 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 D2 receptors, while the inhibitory effects on the micturition reflex was mediated via the dopamine D1 receptors.
社団法人日本薬理学会の論文
2003-06-01