TAURINE INDUCES A LONG-LASTING INCREASE OF SYNAPTIC EFFICACY AND AXONEXCITABILITY IN THE HIPPOCAMPUS

The physiological role of taurine, one of the most abundant free amino acids in the mammalian brain, is still poorly understood. We have fou nd that bath application of the amino acid taurine induces two opposit e actions on field excitatory synaptic potentials (fEPSP) recorded in the CA1 area of hippocampal slices: a decrease in fEPSP slope prevente d by GABA(A) antagonists, and a long-lasting potentiation of fEPSP ind ependent of GABA(A) or NMDA receptor activation. Two long-lasting proc esses account for this taurine-induced potentiation: (1) an increase i n synaptic efficacy that is accompanied neither by modifications in th e basic postsynaptic membrane electrical properties nor by those presy naptic changes involved in fEPSP paired-pulse facilitation; and (2) an increase in the axon excitability revealed by a reduction in the thre shold for antidromic action potential activation. In addition, taurine perfusion also induces a long-lasting increase in intracellularly rec orded EPSPs and monosynaptically activated IPSPs. A number of experime ntal observations such as temperature dependence, extracellular Na+ co ncentration dependence, and saturation studies, although they are not unequivocally conclusive, suggest that the taurine uptake system is re quired for the taurine-induced fEPSP potentiation. Our data describe a new taurine action defined as a potentiation of synaptic transmission due in part to an increment in presynaptic axon excitability and in s ynaptic efficacy.