Control by GABA and tachykinins of the evoked release of acetylcholine in striatal compartments under different modalities of NMDA receptor stimulation

Abstract

The contribution of endogenously released dopamine, GABA and its co-transmitters, substance P (SP) and neurokinin A (NKA), to the control of the evoked release of acetylcholine was investigated in vitro in the striosomes and the matrix of the rat striatum under various modalities of NMDA receptor stimulation (NMDA 50 μM or 1 mM without or with 10 μM d-serine). Sulpiride, bicuculline, SR140333 and SR48968, the antagonists of D 2, GABA A, NK 1 and NK 2 tachykinin receptors, respectively, were used for this purpose. (1) In both striatal compartments, the dopamine-mediated inhibitory regulation of the evoked release of acetylcholine only occurred when d-serine was co-applied with 50 μM or 1 mM NMDA. (2) In striosomes, the dopamine-dependent inhibitory effects of SP and NKA on the evoked release of acetylcholine only occurred when d-serine was co-applied with 50 μM or 1 mM NMDA. (3) A similar inhibitory regulation by NKA, but not SP, was found in the matrix when 1 mM NMDA was co-applied with d-serine. (4) In contrast, the dopamine-dependent facilitatory effect of GABA on the evoked release of acetylcholine did not require added d-serine and was more important with 1 mM than 50 μM NMDA. In the presence of d-serine, and depending on the NMDA concentration, the facilitatory regulation of GABA was reduced (matrix) or suppressed (striosomes). This latter effect was partially restored in the presence of SR48968. Therefore, the dopamine-dependent inhibitory effects of tachykinins on the evoked release of acetylcholine only occurred when NMDA receptors were stimulated in the presence of saturating concentrations of d-serine.