GABAergic control of neostriatal dopamine D receptor binding and behaviors in the rat.

PURPOSE

The present study assessed the influence of the GABA receptor agonist muscimol and the GABA receptor antagonist bicuculline on neostriatal dopamine D receptor binding in relation to motor and exploratory behaviors in the rat.

METHODS

D receptor binding was measured in baseline and after challenge with either 1mg/kg muscimol or 1mg/kg bicuculline. In additional rats, D receptor binding was measured after injection of saline. After treatment with muscimol, bicuculline and saline, motor and exploratory behaviors were assessed for 30min in an open field prior to administration of [I]S-3-iodo-N-(1-ethyl-2-pyrrolidinyl)methyl-2-hydroxy-6-methoxybenzamide ([I]IBZM). For baseline and challenges, striatal equilibrium ratios (V″) were computed as estimation of the binding potential.

RESULTS

Muscimol but not bicuculline reduced D receptor binding relative to baseline and to saline. Travelled distance, duration of rearing and frequency of rearing and of head-shoulder motility were lower after muscimol compared to saline. In contrast, duration of rearing and grooming and frequency of rearing, head-shoulder motility and grooming were elevated after bicuculline relative to saline. Moreover, bicuculline decreased duration of sitting and head-shoulder motility.

CONCLUSIONS

The muscimol-induced decrease of motor/exploratory behaviors can be related to an elevation of striatal dopamine levels. In contrast, bicuculline is likely to elicit a decline of synaptic dopamine, which, however, is compensated by the time of D receptor imaging studies. The results indicate direct GABAergic control over D receptor binding in the neostriatum in relation to behavioral action, and, thus, complement earlier pharmacological studies.