Duman C H, Bodznick D
Department of Biology, Shanklin Laboratory, Wesleyan University, Middletown, CT 06459-0170, USA.
J Comp Physiol A. 1996 Dec;179(6):797-807. doi: 10.1007/BF00207358.
The electrosensory primary afferents in elasmobranchs are responsive to electric potentials created by the animal's own ventilation, while the second-order neurons (AENs) which receive this afferent input in the medulla suppress responses to ventilatory potentials but retain their extreme sensitivity to electric signals in the environment. Ventilatory potentials are common mode signals in elasmobranchs and a common mode rejection mechanism is one way the AENs suppress ventilatory noise. By pressure injecting the GABA-A receptor antagonist SR95531 while extracellularly recording from AENs, we tested the hypothesis that the subtractive circuitry that selectively reduces common mode signals in AENs utilizes GABA, and that a GABAergic component of the dorsal nucleus commissural pathway mediates crossed inhibition of AENs. Local application of SR95531 increased the spontaneous activity and the responsiveness of AENs to electrosensory stimuli. AEN responses to a common mode stimulus were selectively increased compared to responses to a localized stimulus due to SR95531 application. Contralateral inhibition of AENs was blocked by SR95531, indicating that GABAergic commissural cells may inhibit AENs when the contralateral side of the body is stimulated, as with common mode stimulation. We conclude that GABAergic inhibition contributes significantly to the shaping of AEN responses including common mode rejection.
软骨鱼类的电感觉初级传入神经对动物自身呼吸产生的电势有反应，而在延髓中接收这种传入输入的二级神经元（AENs）会抑制对呼吸电势的反应，但对环境中的电信号仍保持极高的敏感性。呼吸电势是软骨鱼类中的共模信号，共模抑制机制是AENs抑制呼吸噪声的一种方式。通过在从AENs进行细胞外记录时压力注射GABA - A受体拮抗剂SR95531，我们测试了以下假设：在AENs中选择性减少共模信号的减法电路利用GABA，并且背核连合通路的GABA能成分介导AENs的交叉抑制。局部应用SR95531增加了AENs的自发活动以及对电感觉刺激的反应性。与对局部刺激的反应相比，由于应用SR95531，AENs对共模刺激的反应选择性增加。SR95531阻断了AENs的对侧抑制，表明当身体的对侧受到刺激时，如共模刺激，GABA能连合细胞可能会抑制AENs。我们得出结论，GABA能抑制对AENs反应的形成有显著贡献，包括共模抑制。
