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Cannabinoid dependence induces sustained changes in GABA release in the globus pallidus without affecting dopamine release in the dorsal striatum: A dual microdialysis probe study

Disruption of motor behavior is a common symptom found in cannabinoid‐dependent animals. It is probably derived from dysregulation of basal ganglia circuits, especially the strio‐pallidal efferent pathway as suggested by previous reports. In the present study, we analyzed the functional consequences of the chronic administration of the synthetic cannabinoid WIN 55 212 (2 mg/kg, twice a day for 14 days) on GABA and dopamine release in the basal ganglia of dependent animals by means of dual microdialysis monitoring. GABA release was measured in the globus pallidus externus, whereas dopamine release was monitored in the dorsal striatum. Chronic administration of WIN 55 212‐2 resulted in almost a twofold tonic increase in GABA release in the globus pallidus, whereas it did not affect dopamine release. The systemic administration of the dopamine D2 receptor agonist quinpirole (0.5 mg/kg) resulted in a decrease of both, dopamine release in the striatum and GABA release in the globus pallidus that was equal in magnitude in both control and cannabinoid‐dependent animals. However, the biphasic behavioral responses to quinpirole of cannabinoid‐dependent animals were clearly more intense than those observed in control animals. Cannabinoid‐dependent animals exhibited greater immobility in the first phase and more stereotypies in the second phase, indicating the presence of a dysregulated behavioral response. This enhanced sensitivity to dopamine D2 agonists is probably associated to the altered GABA transmission in the efferent pathway of the basal ganglia, reflected in the tonic enhanced release of this inhibitory transmitter in the globus pallidus.