Developmental shift in bidirectional functions of taurine-sensitive chloride channels during cortical circuit...

Taurine (2-aminoethanesulfonic acid) is the most abundant free amino acid in the developing mammalian cerebral cortex, however, few studies have reported its neurobiological functions during development. In this study, by means of whole-cell patch-clamp recordings, we examined the effects of taurine on chloride channel receptors in neocortical neurons from early to late postnatal stages, which cover a critical period in cortical circuit formation. We show here that taurine activates chloride channels in cortical neurons throughout the postnatal stages examined (from postnatal day 2 to day 36). The physiological effects of taurine changed from excitatory to inhibitory due to variations in the intracellular Cl- concentration during development. An antagonist blocking analysis also demonstrated a developmental shift in the receptor target of taurine, from glycine receptors to GABAA receptors. Taken together, these results may reflect genetically programmed, bidirectional functions of taurine. At the early developmental stage, taurine acting on glycine receptors would serve to promote cortical circuit formation. As cortical circuit has to be regulated in the later stages, taurine would serve as a safeguard against hyperexcitable circuit.