Modulation of taurine release by metabotropic receptors in the developing hippocampus.

Abstract

Taurine abounds in the hippocampus14, particularly in the immature hippocampus26, and taurine-like immunoreactivity has been located in hippocampal interneurons, pyramidal neurons and dentate granule cells15. Taurine inhibits the firing of hippocampal pyramidal neurons, increases membrane chloride conductance and causes hyperpolarization20. In the hippocampus, the taurine-synthesizing enzyme cysteine sulphinate decarboxylase has also been identified in pyramidal basket interneurons20. Taurine has been held to have a special role in immature brain tissue12,21. Besides being an osmoregulator and neuromodulator it seems to be essential for the development and survival of neural cells29. The excitatory glutamatergic innervation in the hippocampus is modulated by inhibitory GABA-releasing interneurons8. These mechanisms could also regulate taurine release. Ionotropic glutamate receptors modify taurine release in the hippocampus16,25, as do GABAA receptors in the cerebral cortex and cerebellum24. The hippocampal innervation also includes a large family of metabotropic glutamate receptors (mGluRs) coupled to second messenger systems via GTP-binding proteins. At least eight subtypes of them have been cloned, divided into three major groups based on pharmacology, second-messenger coupling and sequence homology6,22. Metabotropic GABAB receptors, which initiate slow inhibition via Gprotein-coupled action on Ca2+ and K+ channels18, also exist in the hippocampus7. We have now characterized the regulation of taurine release