Rovainen C M
Neuroscience. 1983 Nov;10(3):875-82. doi: 10.1016/0306-4522(83)90225-7.
The roles of Cl-dependent synaptic inhibition in the generation of fictive breathing were tested in isolated brains of adult lampreys, Ichthyomyzon unicuspis. Only a few inhibitory synaptic potentials were recorded in respiratory motoneurons between excitatory bursts. This was also true after Cl- injections inverted them to depolarizing potentials. A weak and variable phase of Cl-sensitive synaptic inhibition occurred at the ends of excitatory bursts. Respiratory motoneurons had a pronounced post-spike hyperpolarization, which was distinct from synaptic inhibition and appeared to be a more important mechanism for termination of firing. The production of the basic rhythm for respiration was tested in strychnine, picrotoxin, bicuculline and Cl-free fluid. Low concentrations of the blocking drugs prevented the inhibitory effects of bath-applied glycine and gamma-aminobutyric acid, but essentially normal respiratory bursts still occurred. Equilibration of isolated brains in high concentrations of strychnine and picrotoxin did not prevent periodic activities, but burst durations were increased and inter-burst intervals were longer and less regular than normal. Similar bursts could also occur transiently in Cl-free fluid. Recordings from the IX and X motor nuclei indicated that respiratory neurons produced the periodic bursts in the presence of strychnine and picrotoxin. Hemisections of the brain behind the V motor nuclei eliminated the bursts ipsilaterally. This indicated that descending excitation was necessary during pattern generation both in normal fluid and in the presence of antagonists of synaptic inhibition. Conventional synaptic inhibition does not appear to be essential for respiratory pattern generation in the adult lamprey but may contribute to its modulation. The hypothetical neural oscillator may consist of excitatory bursting interneurons.
在成年单角七鳃鳗（Ichthyomyzon unicuspis）的离体脑内，对氯离子依赖性突触抑制在虚构呼吸产生过程中的作用进行了测试。在兴奋性爆发之间，呼吸运动神经元中仅记录到少数抑制性突触电位。在注射氯离子使其反转成去极化电位后，情况也是如此。在兴奋性爆发结束时，出现了一个微弱且多变的氯离子敏感性突触抑制阶段。呼吸运动神经元具有明显的锋后超极化，这与突触抑制不同，似乎是终止放电的更重要机制。在士的宁、印防己毒素、荷包牡丹碱和无氯离子溶液中，对呼吸基本节律的产生进行了测试。低浓度的阻断药物可阻止浴加甘氨酸和γ-氨基丁酸的抑制作用，但仍会出现基本正常的呼吸爆发。将离体脑置于高浓度的士的宁和印防己毒素中平衡后，并未阻止周期性活动，但爆发持续时间增加，爆发间期延长且比正常情况更不规则。在无氯离子溶液中也可短暂出现类似的爆发。对第九和第十运动核的记录表明，在存在士的宁和印防己毒素的情况下，呼吸神经元产生了周期性爆发。在第五运动核后方对脑进行半切，消除了同侧的爆发。这表明在正常溶液以及存在突触抑制拮抗剂的情况下，模式产生过程中下行兴奋是必需的。传统的突触抑制对于成年七鳃鳗的呼吸模式产生似乎并非必不可少，但可能有助于其调节。假设的神经振荡器可能由兴奋性爆发中间神经元组成。
