THE EFFECTS OF GLOBUS-PALLIDUS LESIONS ON DOPAMINE-DEPENDENT MOTOR BEHAVIOR IN RATS

Motor effects of bilateral lesions of the globus pallidus induced by q uinolinic acid (30 and 60 nmol in 0.5 mu l) were investigated in rats. Globus pallidus lesions with 60 nmol quinolinic acid produced a signi ficant reduction of spontaneous motor activity measured by a reduced l ocomotor activity in an open field and by a reduced sniffing activity in an experimental chamber. In addition, D-amphetamine (1 mg/kg, i.p.) -induced hyperlocomotion and D-amphetamine (3 mg/kg, i.p.)-induced ste reotyped sniffing were significantly reduced in animals with quinolini c acid lesions (60 nmol). Globus pallidus lesions with 60 nmol quinoli nic acid potently reversed catalepsy induced by systemic administratio n of the dopamine D-1 receptor antagonist SCH23390 (0.75 and 1 mg/kg, i.p.) or the dopamine D-2 receptor antagonist raclopride (1.25 and 5 m g/kg, i.p.), while lesions with 30 nmol quinolinic acid exerted anti-c ataleptic effects which were only partly significant. In line with cur rent models of basal ganglia functions, these findings indicate that i nactivation of the globus pallidus reduced spontaneous motor activity and motor hyperactivity after dopamine receptor stimulation. However, the present data also demonstrate that inactivation of the globus pall idus reversed motor hypoactivity induced by a blockade of dopamine D-1 and D-2 receptors. Therefore, a more complex functional model of the globus pallidus is required to account for the opposite effects on mot or behaviour observed after lesions of this basal ganglia nucleus. (C) 1998 IBRO. Published by Elsevier Science Ltd.