Bilateral asymmetrical changes in the nigral release of [3H]GABA induced by unilateral application of acetylcholine in the cat caudate nucleus.

In halothane anaesthetized cats, a push-pull cannula was implanted into the right caudate nucleus (CN) and in each substantia nigra (SN). The release of [3H]GABA continuously formed from [3H]glutamine was estimated in each structure. Acetylcholine (ACh, 5 x 10(-5) M) added in presence of eserine (5 x 10(-5) M) for 50 min in the right caudate nucleus 2 h after the onset of superfusion with [3H]glutamine, stimulated the [3H]GABA release locally. The effect was biphasic when ACh application was made in the median two-thirds of the structure and it was monophasic and transient when the ACh application was restricted to the lateral part. ACh application in the right caudate nucleus also induced changes in [3H]GABA released in the anterior (pars reticulata) and posterior (pars compacta) parts of both SN. While [3H]GABA release was enhanced in the ipsilateral anterior SN, it was reduced in the contralateral anterior SN. Respective opposite effects were observed in the posterior parts of the ipsi- and contralateral SN. These bilateral asymmetrical changes in [3H]GABA release were not dependent on the site of ACh application in the right caudate nucleus. These results indicate that the facilitation of cholinergic transmission in one caudate nucleus influences in an opposite way the striato-nigral GABA neurones on both sides of the brain.