THE DISTRIBUTION OF MONO-SYNAPTIC CONNECTIONS FROM INSPIRATORY BULBOSPINAL NEURONS TO INSPIRATORY MOTONEURONES IN THE CAT
THE DISTRIBUTION OF MONO-SYNAPTIC CONNECTIONS FROM INSPIRATORY BULBOSPINAL NEURONS TO INSPIRATORY MOTONEURONES IN THE CAT
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DOI：
10.1113/jphysiol.1985.sp015846
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发表时间：
1985-01-01
影响因子：
5.5
通讯作者：
SEARS, TA
中科院分区：
文献类型：
--
作者：
DAVIES, JGM;KIRKWOOD, PA;SEARS, TA
麻醉猫的球脊髓吸气神经元与C5膈神经或肋间神经的吸气运动神经元之间存在单突触连接；通过这些神经元自发放电的相互关联直方图中存在窄峰来识别它们。与膈神经一起接受测试的球脊髓神经元中，大约有一半出现了单突触连接，而与肋间神经一起接受测试的神经元中，只有不到一半出现了单突触连接。一些神经元将两者连接起来。对于球脊髓神经元对和肋间神经，295例中有50例（17%）出现连接。没有证据表明不同节段有系统的连接模式。一些神经元将连接连接到相邻的部分，另一些神经元将连接连接到相隔5个部分。球脊髓神经元与肋间运动神经元的连接不具有同等的能力。如果一个神经元连接到一个部分，那么它更有可能连接到另一个部分，而不是随机预测。腹呼吸组连接较强的神经元集中于吻侧至腹侧；腹侧组和背侧组的尾侧神经元连接较弱。髓质内连接膈运动神经元的神经元比例的区域差异未见，特别是背侧组（16个中的8个）和腹侧组（11个中的5个）的神经元是相等的。当用k（交叉相关直方图中峰值计数与基线计数的比值）来评估连接强度时，膈神经（k = 1.113）和肋间运动神经元（k = 1.114）的平均强度相似。然而，由于肋间的连接较少，因此膈肌（k = 1.055）的总体平均值（没有窄峰，取k = 1.0）要强于肋间肌（k = 1.019）。对于膈肌，运动神经元的明显连接强度（用k来评估）对于产生大尖峰的运动神经元要比产生小尖峰的运动神经元强得多。同样的结果可能也适用于肋间肌。通过几个假设，计算了膈肌或肋间运动神经元在单突触激励时的总去极化，发现肋间约为1 mV，膈肌约为3-4 mV。讨论了这一点的功能含义，即大多数运动神经元的突触去极化可能来自中间神经元。
Monosynaptic connexions were sought between bulbospinal inspiratory neurones and inspiratory motoneurones of the C5 phrenic nerve or the intercostal nerves of up to six segments in the anesthetized cat; they were identified by the presence of narrow peaks in cross-correlation histograms constructed from the spontaneous discharges of these neurons. About half of the bulbospinal neurons tested with the phrenic gave a monosynaptic connexion, as did just under half of those tested with the intercostal nerves. Some neurons gave connexions to both. For pairs of bulbospinal neurons and intercostal nerves, connexions were seen in 50 out of 295 instances (17%). No evidence was found of systematic patterns of connexions to different segments. Some neurons gave connexions to adjacent segments, others up to five segments apart. Bulbospinal neurons were not equipotent at giving connexions to the intercostal motoneurons. If a neuron gave a connexion to one segment, it was more likely to give connexion to another segment than chance would predict. The neurons with strong connexions were concentrated rostral to obex in the ventral respiratory group; neurons in both the caudal part of the ventral group and in the dorsal group gave weaker connexions. Regional variation within the medulla in the proportions of neurons giving connexions to the phrenic motoneurons was not seen, in particular neurons of the dorsal group (eight out of sixteen) and the ventral group (five out of eleven) were equipotent. When the strength of the connexions was assessed by k, the ratio of the peak count in the cross-correlation histogram to the base-line count, the mean strength was similar for the peaks seen for the phrenic (k = 1.113) and the intercostal (k = 1.114) motoneurons. However, because, on a segment-by-segment basis, fewer connexions were seen for the intercostals, the over-all mean value of k (absence of a narrow peak taken as k = 1.0) was stronger for the phrenic (k = 1.055) than for the intercostals (k = 1.019). For the phrenic, the apparent strength of connexion (assessed by k) was considerably stronger for the motoneurons giving large spikes than for those giving small ones. The same result was probably also true for the intercostals. With several assumptions, the total depolarization during inspiration derived monosynaptically in phrenic or intercostal motoneurones was calculated and found to be low, about 1 mV for the intercostals and 3-4 mV for the phrenic. The functional implications of this, i.e., that most of the synaptic depolarization of the motoneurons is likely to be derived from interneurons, is discussed.