title: Activity-dependent endogenous taurine release facilitates excitatory neurotransmission in the neocortical marginal zone of neonatal rats.
abstract: In the developing cerebral cortex, the marginal zone (MZ), consisting of early-generated neurons such as Cajal-Retzius cells, plays an important role in cell migration and lamination. There is accumulating evidence of widespread excitatory neurotransmission mediated by γ-aminobutyric acid (GABA) in the MZ. Cajal-Retzius cells express not only GABAA receptors but also α2/β subunits of glycine receptors, and exhibit glycine receptor-mediated depolarization due to high [Cl(-)]i. However, the physiological roles of glycine receptors and their endogenous agonists during neurotransmission in the MZ are yet to be elucidated. To address this question, we performed optical imaging from the MZ using the voltage-sensitive dye JPW1114 on tangential neocortical slices of neonatal rats. A single electrical stimulus evoked an action-potential-dependent optical signal that spread radially over the MZ. The amplitude of the signal was not affected by glutamate receptor blockers, but was suppressed by either GABAA or glycine receptor antagonists. Combined application of both antagonists nearly abolished the signal. Inhibition of Na(+), K(+)-2Cl(-) cotransporter by 20 µM bumetanide reduced the signal, indicating that this transporter contributes to excitation. Analysis of the interstitial fluid obtained by microdialysis from tangential neocortical slices with high-performance liquid chromatography revealed that GABA and taurine, but not glycine or glutamate, were released in the MZ in response to the electrical stimulation. The ambient release of taurine was reduced by the addition of a voltage-sensitive Na(+) channel blocker. Immunohistochemistry and immunoelectron microscopy indicated that taurine was stored both in Cajal-Retzius and non-Cajal-Retzius cells in the MZ, but was not localized in presynaptic structures. Our results suggest that activity-dependent non-synaptic release of endogenous taurine facilitates excitatory neurotransmission through activation of glycine receptors in the MZ.
authors.affiliation: Department of Neurophysiology, Hamamatsu University School of Medicine Hamamatsu, Japan.
authors.forename: Taizhe
authors.initials: T
authors.lastname: Qian
authors.affiliation: Institute of Physiology, University Medical Center of the Johannes Gutenberg-University Mainz, Germany.
authors.forename: Rongqing
authors.initials: R
authors.lastname: Chen
authors.affiliation: Department of Psychology and Behavioral Neuroscience, Hamamatsu University School of Medicine Hamamatsu, Japan.
authors.forename: Masato
authors.initials: M
authors.lastname: Nakamura
authors.affiliation: Department of Neurophysiology, Hamamatsu University School of Medicine Hamamatsu, Japan.
authors.forename: Tomonori
authors.initials: T
authors.lastname: Furukawa
authors.affiliation: Department of Neurophysiology, Hamamatsu University School of Medicine Hamamatsu, Japan ; Department of Occupational Therapy, Tokoha University Hamamatsu, Japan.
authors.forename: Tatsuro
authors.initials: T
authors.lastname: Kumada
authors.affiliation: Department of Neurophysiology, Hamamatsu University School of Medicine Hamamatsu, Japan.
authors.forename: Tenpei
authors.initials: T
authors.lastname: Akita
authors.affiliation: Institute of Physiology, University Medical Center of the Johannes Gutenberg-University Mainz, Germany.
authors.forename: Werner
authors.initials: W
authors.lastname: Kilb
authors.affiliation: Institute of Physiology, University Medical Center of the Johannes Gutenberg-University Mainz, Germany.
authors.forename: Heiko J
authors.initials: HJ
authors.lastname: Luhmann
authors.affiliation: Department of Psychology and Behavioral Neuroscience, Hamamatsu University School of Medicine Hamamatsu, Japan.
authors.forename: Daiichiro
authors.initials: D
authors.lastname: Nakahara
authors.affiliation: Department of Neurophysiology, Hamamatsu University School of Medicine Hamamatsu, Japan.
authors.forename: Atsuo
authors.initials: A
authors.lastname: Fukuda
keywords: GABA; GABAA receptor; NKCC1; glycine receptor; marginal zone; microdialysis; taurine