Onimaru H, Arata A, Homma I
Department of Physiology, Showa University School of Medicine, Tokyo, Japan.
Exp Brain Res. 1995;106(1):57-68. doi: 10.1007/BF00241356.
In brainstem-spinal cord preparations isolated from newborn rats, intrinsic burst-generating properties of preinspiratory (Pre-I) neurons in the rostral ventrolateral medulla, which have been suggested to be primary respiratory rhythm-generating neurons, were studied by "perforated" whole-cell recordings using the antibiotic nystatin. Nystatin causes small pores to be formed in the cells, through which pass small monovalent ions. For blockade of chemical synaptic transmission, perfusate Ca2+ concentration was lowered to 0.2 mM and the Mg2+ concentration was increased to 5 mM. In low-Ca2+, high-Mg2+ solution (referred to here as "low Ca"), 10 of 55 Pre-I neurons generated rhythmic bursts (burst type), 14 fired tonically (tonic type), and 31 were silent (silent type). Burst-type neurons showed periodic depolarization of 5-12 mV in low Ca, at a rate of 12 +/- 6.5/min. Hyperpolarization of the membrane caused decrease in or disappearance of the periodic depolarization and prolongation of the cycle period. Thus, the burst generations were voltage dependent. The firing frequency of tonic-type neurons was 2.3 +/- 1.6 Hz and was decreased by hyperpolarization. In 6 of these neurons, the firing patterns changed to burst patterns during continuous hyperpolarization. Membrane depolarization by continuous outward current injection into some silent-type neurons (3 of 11 tested) induced bursting activity. Activity of C4 and Pre-I neurons was completely silent with 0.1-1 microM tetrodotoxin (TTX) added to the standard perfusate. In low Ca, burst-type neurons (n = 3) were also silent with 1 microM TTX perfusion. Inspiratory neurons either became silent (n = 4) or fired tonically (n = 1) in low Ca. The present study by "perforated" whole-cell recordings confirmed that some Pre-I neurons possess intrinsic burst-generating properties, which were not attributable to phasic synaptic inputs.
在从新生大鼠分离的脑干-脊髓标本中，使用抗生素制霉菌素通过“穿孔”全细胞记录法研究了延髓头端腹外侧前吸气（Pre-I）神经元的内在爆发产生特性，这些神经元被认为是主要的呼吸节律产生神经元。制霉菌素使细胞形成小孔，小的单价离子可通过这些小孔。为了阻断化学突触传递，将灌流液中Ca2+浓度降至0.2 mM，并将Mg2+浓度增至5 mM。在低Ca2+、高Mg2+溶液（此处称为“低钙”溶液）中，55个Pre-I神经元中有10个产生节律性爆发（爆发型），14个持续放电（紧张型），31个无活动（沉默型）。爆发型神经元在低钙溶液中表现出5-12 mV的周期性去极化，频率为12±6.5次/分钟。膜超极化导致周期性去极化减少或消失，以及周期延长。因此，爆发的产生是电压依赖性的。紧张型神经元的放电频率为2.3±1.6 Hz，超极化使其降低。在这些神经元中有6个，在持续超极化期间放电模式转变为爆发模式。通过向一些沉默型神经元（11个测试中有3个）持续注入外向电流使膜去极化可诱导爆发活动。向标准灌流液中添加0.1-1 μM河豚毒素（TTX）时，C4和Pre-I神经元的活动完全消失。在低钙溶液中，用1 μM TTX灌流时，爆发型神经元（n = 3）也无活动。吸气神经元在低钙溶液中要么无活动（n = 4），要么持续放电（n = 1）。本研究通过“穿孔”全细胞记录法证实，一些Pre-I神经元具有内在的爆发产生特性，这并非由阶段性突触输入所致。
