The relationship between hindlimb disturbances, forelimb disturbances and catalepsy after increasing doses of muscimol injected into the striatal-pallidal complex

Abstract

To establish the role of the GABA-ergic mechanism within the striatal-pallidal complex in hindlimb disturbances, forelimb disturbances and catalepsy and the relationship between these phenomena, the effects of the locally injected GABA agonist muscimol (0.5 microliter per side) were investigated in rats using several specific tests of catalepsy. The time required for retracting free-hanging hindlimbs was dose-dependently prolonged by 2-10 ng muscimol. The time required for releasing a rod that was clasped between the forelegs of otherwise free-hanging rats was dose-dependently prolonged by 5-10 ng muscimol. Likewise, the time required for retracting the free-hanging forelimbs was dose-dependently prolonged over the same dose range. Finally, the time during which standing rats kept their forelimbs on a block of 9 cm height (the dependent variable used in "classic" tests of catalepsy) was only prolonged at the highest dose (10 ng) of muscimol. The effects of the latter dose, which lasted at least 30 min, were inhibited by the GABA antagonist bicuculline (50 ng) for a minimum period of 5 min. The present data show that the GABA-ergic mechanisms within the striatal-pallidal complex are involved in hindlimb disturbances, forelimb disturbances and catalepsy, and that catalepsy requires a stronger dysfunctioning of these GABA-ergic mechanisms than do disturbances in hindlimbs and forelimbs.