Taurine activates GABA(A) but not GABA(B) receptors in rat hippocampal CA1area

We investigated if taurine, an endogenous GABA analog, could mimic both hyp erpolarizing and depolarizing GABA(A)-mediated responses as well as pre- an d postsynaptic GABA(B)-mediated actions in the CAI region of rat hippocampa l slices. Taurine (10 mM) perfusion induced changes in membrane potential a nd input resistance that are compatible with GABA(A) receptor activation. L ocal pressure application of taurine and GABA from a double barrel pipette positioned along the dendritic shaft of pyramidal cells revealed that rauri ne evoked a very small change of membrane potential and resistance compared with the large changes induced by GABA in these parameters. Moreover, in t he presence of GABA(A) antagonists, local application of GABA on the dendri tes evoked a GABA(B)-mediated hyperpolarization while taurine did not induc e any change. Taurine neither mimicked baclofen inhibitory actions on presy naptic release of glutamate and GABA as judging by the lack of taurine effe ct on paired-pulse facilitation ratio and slow inhibitory postsynaptic pote ntials, respectively. These results show that taurine mainly activates GABA (A) receptors located on the cell body, indicating therefore that if taurin e has any action on the dendrites it will not be mediated by either GABA(A) or GABA(B) receptors activation. (C) 2000 Elsevier Science B.V. All rights reserved.