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.