The role of the GABA mechanisms of the globus pallidus in mediating catalepsy, stereotypy and locomotor activity.

Muscimol, picrotoxin and bicuculline were injected bilaterally through permanently implanted cannulae into either anterior (GPa) or posterior parts of the globus pallidus (GPp) of rats. Both the muscimol injected into the GPa and the picrotoxin injected into the GPp abolished or strongly inhibited spiperone (0.2 mg/kg, IP)-induced catalepsy. Muscimol alone (25-200 ng/0.2 microliter/GP) injected into the GPa evoked a dose-dependent biphasic effect: at first catalepsy (throughout 7.3 min), and then a long-lasting (more than 2 hr) locomotor stimulation and stereotyped sniffing. Muscimol (200 ng/GP) injected into GPp inhibited both the spontaneous motility and amphetamine-induced hyperactivity. Picrotoxin (200 and 400 ng/GP) injections into GPa and GPp produced an increase of the locomotor activity as well as stereotyped sniffing. Picrotoxin started to block muscimol hyperactivity when its own stimulatory action disappeared, thus also for picrotoxin the second phase of action could be detected. The globus pallidus is shown to be a relay station of impulses mediating neuroleptic catalepsy. Furthermore, it is suggested that behavioural changes induced by muscimol resulted from the action of the drug on at least 2 different neuronal systems, both being controlled by GABA receptors. One of them seems to be responsible for inducing neuroleptic-like catalepsy, and the other one for the hyperactivity and blockade of spiperone-catalepsy.