Journal of Neuroscience, Vol 16, 92-102, Copyright © 1996 by Society for Neuroscience
Taurine induces a long-lasting increase of synaptic efficacy and axon excitability in the hippocampus
M Galarreta, J Bustamante, R Martin del Rio and JM Solis
Departamento de Investigacion, Hospital Ramon y Cajal, Madrid, Spain.
The physiological role of taurine, one of the most abundant free amino
acids in the mammalian brain, is still poorly understood. We have found
that bath application of the amino acid taurine induces two opposite
actions on field excitatory synaptic potentials (fEPSP) recorded in the CA1
area of hippocampal slices: a decrease in fEPSP slope prevented by GABAA
antagonists, and a long-lasting potentiation of fEPSP independent of GABAA
or NMDA receptor activation. Two long-lasting processes account for this
taurine-induced potentiation: (1) an increase in synaptic efficacy that is
accompanied neither by modifications in the basic postsynaptic membrane
electrical properties nor by those presynaptic changes involved in fEPSP
paired-pulse facilitation; and (2) an increase in the axon excitability
revealed by a reduction on the threshold for antidromic action potential
activation. In addition, taurine perfusion also induces a long-lasting
increase in intracellularly recorded EPSPs and monosynaptically activated
IPSPs. A number of experimental observations such as temperature
dependence, extracellular Na+ concentration dependence, and saturation
studies, although they are not unequivocally conclusive, suggest that the
taurine uptake system is required 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 synaptic efficacy.