Related Experiment Videos
Suppression of apomorphine-induced oral stereotypy in rats by microinjection of muscimol into midbrain
Abstract:
Rats with large lesions of the superior colliculus do not display the oral stereotypy normally induced by high systemic doses of dopamine-agonists. It has been suggested that collicular lesions have such an effect because they destroy the GABAergic nigrotectal pathway. This suggestion was investigated by observing the effects of bilateral microinjections of the GABA-agonist muscimol into midbrain sites in rats given 8 mg/kg subcutaneous apomorphine. A low dose of muscimol (25 ng in 0.5 ul saline/side) injected into regions of the superior colliculus with nigrotectal innervation almost abolished apomorphine-induced licking and gnawing. Control microinjections of saline into the superior colliculus, or of muscimol into overlying cerebral cortex, were ineffective. This result is consistent with the GABAergic nigrotectal projection being important for the expression of dopamine-related oral stereotypy. It was also found, however, that 25 ng of muscimol suppressed oral stereotypy when microinjected into the mesencephalic reticular formation underlying the superior colliculus. The anatomical basis of this latter effect is uncertain.
Insights
The GABAergic nigrotectal pathway in rats is crucial for dopamine-agonist-induced oral stereotypy. Inhibiting this pathway with muscimol abolished apomorphine-induced behaviors, suggesting its importance in dopamine signaling.
Area of Science:
- Neuroscience
- Pharmacology
- Behavioral Science
Background:
- Superior colliculus lesions abolish dopamine-agonist-induced oral stereotypy in rats.
- This effect is hypothesized to result from disruption of the GABAergic nigrotectal pathway.
Purpose of the Study:
- To investigate the role of the GABAergic nigrotectal pathway in mediating dopamine-related oral stereotypy.
- To determine if inhibiting this pathway affects apomorphine-induced behaviors.
Main Methods:
- Bilateral microinjections of muscimol (GABA-agonist) into rat midbrain sites.
- Administration of subcutaneous apomorphine (dopamine-agonist) at 8 mg/kg.
- Observation of oral stereotypy (licking and gnawing) following treatments.
Main Results:
- Low-dose muscimol (25 ng) in the superior colliculus significantly reduced apomorphine-induced licking and gnawing.
- Control injections of saline or muscimol in the cerebral cortex were ineffective.
- Muscimol in the mesencephalic reticular formation also suppressed oral stereotypy, though its anatomical basis is unclear.
Conclusions:
- The GABAergic nigrotectal projection plays a significant role in the expression of dopamine-related oral stereotypy.
- Further research is needed to elucidate the anatomical basis of muscimol's effect in the mesencephalic reticular formation.