In vivo release of [3H]GABA in cat caudate nucleus and substantia nigra. I. Bilateral changes induced by a unilateral nigral application of muscimol.

Push-pull cannulae were implanted in both caudate nuclei and both substantiae nigrae (SN) of halothane-anesthetized cats and the release of [3H]GABA, continuously synthesized from [3H]glutamine, was measured in these structures during 4 h of superfusion. In some experiments, multi-unit neuronal activity was recorded at the tip of the nigral push-pull cannulae, using a bipolar electrode. Two hours after the onset of superfusion with [3H]glutamine, 10(-6)M of muscimol was added (for 1 h) in the superfusion medium delivered to one SN. This treatment increased locally the release of [3H]GABA and enhanced the neuronal activity of the nigral cells in the zona reticulata. An increased release of [3H]GABA was also observed in the contralateral SN, in association with an inhibition of the activity of the zona reticulata cells. The unilateral nigral application of muscimol also induced asymmetric changes in the release of [3H]GABA in both caudate nuclei, since [3H]GABA release was increased ipsilaterally and reduced on the contralateral side. The present findings are considered in relation to possible GABAergic neuronal populations affected by this local pharmacological treatment.