title: Analysis of GABA-induced inhibition of spontaneous firing in chick accessory lobe neurons.
abstract: It has been hypothesized that chick accessory lobes (ALs) contain functional neurons and act as a sensory organ of equilibrium. It was reported that neurons located in an outer layer of ALs showed γ-aminobutyric acid (GABA)- and glutamic acid decarboxylase (GAD)-like immunoreactivity more strongly than centrally located neurons, which were surrounded by the GAD-immunoreactive terminals. We investigated effects of GABA on the electrical activity of AL neurons. About 50% of embryonic AL neurons exhibited spontaneous firing. In the on-cell recording, GABA, muscimol, and GABA in combination with CGP35348 inhibited this firing. In whole-cell voltage clamp recordings, GABA and muscimol evoked a transient current. The mean reversal potential of GABA-evoked currents was close to the theoretical reversal potential of Cl⁻. These results indicate that GABA exerts the inhibitory effect on the firing through the activation of GABA(A) receptors. In addition, the intracellular concentration of Cl⁻ was estimated to be about 16 mM in measurements with the gramicidin-perforated configuration, indicating the physiological reversal potential of the GABA current was about -60 mV. In conclusion, AL neurons have an intrinsic mechanism to evoke the spontaneous firing, which can be arrested by the inhibitory mechanism through the activation of the GABA(A) receptors.
authors.affiliation: The United Graduate School of Veterinary Science, Yamaguchi University, 1677-1 Yoshida, Yamaguchi 753-8515, Japan.
authors.forename: Yuko
authors.initials: Y
authors.lastname: Yamanaka
authors.forename: Naoki
authors.initials: N
authors.lastname: Kitamura
authors.forename: Hikaru
authors.initials: H
authors.lastname: Shinohara
authors.forename: Keita
authors.initials: K
authors.lastname: Takahashi
authors.forename: Izumi
authors.initials: I
authors.lastname: Shibuya
mesh_terms: D000818:Animals; D001640:Bicuculline / Q000494:pharmacology; D002642:Chick Embryo; D058785:GABA-A Receptor Agonists / Q000494:pharmacology; D058787:GABA-A Receptor Antagonists / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects* / Q000502:physiology; D009118:Muscimol / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects* / Q000502:physiology; D013116:Spinal Cord / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology*
chemical_list: D058785:GABA-A Receptor Agonists; D058787:GABA-A Receptor Antagonists; D009118:Muscimol; D005680:gamma-Aminobutyric Acid; D001640:Bicuculline