Roles of Cl- transporter and neurotransmitter amino acids of synaptic transmission in neonatal rat marginal zone

Abstract

Cajal-Retzius cells in marginal zone (MZ) play important roles in the construction of the cerebral cortex. Details of synaptic transmission in MZ are yet to be elucidated. Several reports have proved excitatory GABAergic neurotransmission in the MZ. Tangential slices were made from MZ of postnatal 0-3 rats and optical imaging using voltage-sensitive dye (JPW1114) was performed. Action potentials evoked by single electrical stimulations spread out radially over MZ. The spread of excitation were completely blocked by TTX and Ca²⁺-free. They were not affected by glutamate receptor blockers (AP5, CNQX). On the other hand, they were inhibited by either GABA_A receptor antagonists (bicuculline, picrotoxin) or glycine receptor antagonist (strychnine). Co-application of GABA_A and glycine receptor blockers completely abolished evoked EPSPs and spread of excitation. A Na⁺, K⁺-2Cl⁻ cotransporter inhibitor (bumetanide) also reduced the spread of excitation. By using the microdialysis with HPLC analysis, we have proved that taurine, a glycine receptor agonist, but not glycine was released by stimulation and that TTX reduced the basal level of taurine. The results indicate that the excitatory action of taurine based on high [Cl⁻]_i plays an important role in neurotransmission in the MZ. [Jpn J Physiol 55 Suppl:S150 (2005)]