Modulatory Action of Taurine on the Release of GABA in Cerebellar Slices of the Guinea Pig

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Abstract
For the purpose of demonstrating the action of taurine as a neuromodulator in addition to its suggested neurotransmitter function, the effects of taurine and muscimol on the depolarization‐induced Ca‐dependent release of [3H]γ‐aminobutyric acid (pH]GABA) and l‐[3H]glutamate in cerebellar slices from guinea pigs were investigated. The release of [3H]GABA was found to be greatly decreased by a GABA agonist, muscimol, and by taurine, but not by glycine. The release of l‐[3H]glutamate was little affected by taurine. The release of [3H]GABA was enhanced by bicuculline and strychnine, but not by picrotoxin, and the suppressive action of muscimol on the GABA release was antagonized by bicuculline, picrotoxin, and strychnine, suggesting the possible existence of presynaptic autoreceptors for GABA in the cerebellum. The suppressive action of taurine on the release of [3H]GABA, on the other hand, was blocked only by bicuculline. These results suggest that taurine reduced the release of [3H]GABA from cerebellar slices by acting on the GABA autoreceptors or, more likely, on other types of receptors that are sensitive to bicuculline. As a possible mechanism for this modulatory action of taurine, the blockade by this amino acid of the influx of Ca2+ into cerebellar tissues was tentatively suggested.