Brockhaus J, Ballanyi K
II. Physiologisches Institut, Universität Göttingen, Germany.
Eur J Neurosci. 1998 Dec;10(12):3823-39. doi: 10.1046/j.1460-9568.1998.00396.x.
Gramicidin-perforated patch-clamp recording revealed phasic Cl(-)-mediated hyperpolarizations in respiratory neurons of the brainstem-spinal cord preparation from newborn rats. The in vitro respiratory rhythm persisted after block of gamma-aminobutyric acid (GABA), i.e. GABAA, receptor-mediated inhibitory postsynaptic potentials (IPSPs) with bicuculline and/or glycinergic IPSPs with strychnine. In one class of expiratory neurons, bicuculline unmasked inspiration-related excitatory postsynaptic potentials (EPSPs), leading to spike discharge. Bicuculline also blocked hyperpolarizations and respiratory arrest due to bath-applied muscimol, whereas strychnine antagonized similar responses to glycine. The reversal potential of respiration-related IPSPs and responses to GABA, muscimol or glycine was not affected by CO2/HCO3(-)-free solutions, but shifted from about -65 mV to values more positive than -20 mV upon dialysis of the cells with 144 instead of 4 mM Cl-. Impairment of GABA uptake with nipecotic acid or glycine uptake with sarcosine evoked a bicuculline- or strychnine-sensitive decrease of respiratory frequency which could lead to respiratory arrest. Also, the GABAB receptor agonist baclofen led to reversible suppression of respiratory rhythm. This in vitro apnoea was accompanied by a K+ channel-mediated hyperpolarization (reversal potential -88 mV) of tonic cells, whereas membrane potential of neighbouring respiratory neurons remained almost unaffected. Both baclofen-induced hyperpolarization and respiratory depression were antagonised by 2-OH-saclofen, which did not affect respiration-related IPSPs per se. The results show that synaptic inhibition is not essential for rhythmogenesis in the isolated neonatal respiratory network, although (endogenous) GABA and glycine have a strong modulatory action. Hyperpolarizing IPSPs mediated by GABAA and glycine receptors provide a characteristic pattern of membrane potential oscillations in respiratory neurons, whereas GABAB receptors rather appear to be a feature of non-respiratory neurons, possibly providing excitatory drive to the network.
短杆菌肽穿孔膜片钳记录显示，新生大鼠脑干 - 脊髓标本的呼吸神经元中存在阶段性氯离子介导的超极化。在用荷包牡丹碱阻断γ-氨基丁酸（GABA），即GABAA受体介导的抑制性突触后电位（IPSPs）和/或用士的宁阻断甘氨酸能IPSPs后，体外呼吸节律仍持续存在。在一类呼气神经元中，荷包牡丹碱揭示了与吸气相关的兴奋性突触后电位（EPSPs），导致动作电位发放。荷包牡丹碱还阻断了由于浴加蝇蕈醇引起的超极化和呼吸停止，而士的宁拮抗了对甘氨酸的类似反应。与呼吸相关的IPSPs以及对GABA、蝇蕈醇或甘氨酸反应的反转电位不受无CO2/HCO3(-)溶液的影响，但在用144 mM而非4 mM氯离子透析细胞后，从约 -65 mV 移至比 -20 mV更正的值。用尼克酸损害GABA摄取或用肌氨酸损害甘氨酸摄取会引起荷包牡丹碱或士的宁敏感的呼吸频率降低，这可能导致呼吸停止。此外，GABAB受体激动剂巴氯芬导致呼吸节律的可逆性抑制。这种体外呼吸暂停伴随着紧张性细胞的钾离子通道介导的超极化（反转电位 -88 mV），而相邻呼吸神经元的膜电位几乎不受影响。巴氯芬诱导的超极化和呼吸抑制均被2-羟基巴氯芬拮抗，2-羟基巴氯芬本身不影响与呼吸相关的IPSPs。结果表明，虽然（内源性）GABA和甘氨酸具有强大的调节作用，但突触抑制对于孤立的新生呼吸网络中的节律发生并非必不可少。由GABAA和甘氨酸受体介导的超极化IPSPs在呼吸神经元中提供了膜电位振荡的特征模式，而GABAB受体似乎更是非呼吸神经元的特征，可能为该网络提供兴奋性驱动。
