Taurine in hippocampus: localization and postsynaptic action.

Both immunocytochemical and electrophysiological methods have been employed to determine whether the localization of the taurine synthetic enzyme, cysteine sulfinic acid decarboxylase, (CSAD) and the postsynaptic action of taurine in the CA1 region of rat hippocampus are consistent with the hypothesis that taurine may be used as a neurotransmitter by some hippocampal neurons. At the light microscopic level, CSAD-immunoreactivity (CSAD-IR) was found in the pyramidal basket cells, and around pyramidal cells in stratum pyramidale and stratum radiatum. At the electron microscopic level, CSAD-IR was seen most often in the soma and the dendrites and was rather infrequent in the axon or the nerve terminals. Electrophysiological observations on the in vitro hippocampal slice demonstrated that pyramidal neurons respond to artificially applied taurine with inhibition that depended in large part upon an increased chloride conductance. Although electrophysiological observations are consistent with a neurotransmitter role for taurine, results from immunocytochemical studies suggest a minor role for taurine as a neurotransmitter. In fact, immunocytochemical observations suggested that taurine may be used as a neurotransmitter only by a small number of pyramidal basket interneurons, the vast majority of CSAD-positive neurons may use taurine for other functions.