Glycine-induced changes in acetylcholine release from guinea-pig brain slices

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Abstract
1 The effect of glycine (Gly) on acetylcholine (ACh) release from superfused, resting or electrically-stimulated slices of guinea-pig caudate nucleus (CN), brain stem (BS) and cerebral cortex (CC) was studied. 2 The amino acid 1 × 10−4-6 × 10−3mol l−1 reduced the electrically-induced release and increased the spontaneous and KCl-evoked transmitter outflow, mostly in CN but also in BS, whereas it was ineffective in CC. Taurine, chosen as a structurally related compound, moderately affected only the spontaneous release in CN. 3 Strychnine 2 × 10−7 mol l−1 was per se ineffective, but prevented most Gly effects. The Gly-induced increase of ACh outflow in resting CN slices, however, could be completely antagonized only by administering strychnine and picrotoxin together. 4 These findings suggest that: (i) the overall pattern of Gly influence on cholinergic function is similar to that previously described for γ-aminobutyric acid (GAB A); (ii) specific receptors seem to be present in BS and, above all, in CN; (iii) a positive cooperation between endogenous GAB A and Gly is evident in resting CN slices; (iv) the absence of any apparent endogenous glycinergic control on the cholinergic neurones casts doubt on but does not exclude the existence of glycinergic neurones in CN.