Tian G F, Duffin J
Department of Physiology, University of Toronto, Ontario, Canada.
Exp Brain Res. 1996 Sep;111(2):178-86. doi: 10.1007/BF00227296.
We examined the synaptic connections from ventral-group bulbospinal inspiratory neurons to upper-cervical inspiratory neurons and phrenic and intercostal motoneurons in decerebrate rats using cross-correlation. Inspiratory neurons were recorded in the medulla (n = 28) at the level of the obex and from the upper-cervical segments (C1 and C2) of the spinal cord (n = 29) in 18 vagotomized, paralyzed, ventilated, and decerebrated rats. The neurons were identified by their inspiratory firing pattern and antidromic activation from the spinal cord at C7. Whole-nerve recordings were made using bipolar electrodes from the central cut ends of the C5 phrenic nerve and the external and internal intercostal nerves at various thoracic levels. Cross-correlation histograms were computed between these recordings to detect short time scale synchronizations indicative of synaptic connections. Cross-correlation histograms (n = 20), computed between the activities of ventral-group bulbospinal inspiratory neurons and the phrenic nerve, all showed peaks (mean half-amplitude width +/- SD, 1.1 +/- 0.3 ms) at short latencies (mean latency +/- SD, 2.0 +/- 0.6 ms) suggestive of monosynaptic excitation. Cross-correlation histograms (n = 33), computed between the activities of ventral-group bulbospinal inspiratory neurons and upper-cervical inspiratory neurons, displayed four (12%) peaks (mean half-amplitude width +/- SD, 0.9 +/- 0.1 ms) at short latencies (mean latency +/- SD, 1.8 +/- 0.6 ms) suggestive of monosynaptic excitation, and six (18%) peaks (mean half-amplitude width +/- SD, 1.4 +/- 0.4 ms) at latencies near zero suggestive of excitation from a common source. Cross-correlation histograms (n = 34), computed between the activities of ventral-group bulbospinal inspiratory neurons and the internal and external intercostal nerves at various thoracic levels (T2-8), showed six (18%) peaks (mean half-amplitude width +/- SD, 2.5 +/- 0.5 ms) at short latency (mean latency +/- SD, 4.5 +/- 1.1 ms) suggestive of oligosynaptic connections. Cross-correlation histograms (n = 42) computed between activities of intercostal nerves at various levels of the thoracic spinal cord showed central peaks suggestive of excitation from a common source. Although the size of the peaks decreased with segmental separation, the displacement of the peaks from time zero did not increase with segmental separation (mean displacement +/- SD, 0.6 +/- 0.6 ms) as would be expected if the common excitation resulted from a descending monosynaptic excitation by a source such as the ventral-group bulbospinal inspiratory neurons. We conclude that all ventral-group bulbospinal inspiratory neurons make monosynaptic connections to phrenic motoneurons, a few make monosynaptic connections to upper-cervical, inspiratory neurons, but connections to intercostal motoneurons are made via interneurons.
我们采用互相关分析方法，研究了去大脑大鼠中腹侧组延髓脊髓吸气神经元与颈上段吸气神经元以及膈神经和肋间运动神经元之间的突触连接。在18只经迷走神经切断、麻痹、通气和去大脑处理的大鼠中，在闩平面的延髓（n = 28）以及脊髓颈上段（C1和C2）（n = 29）记录吸气神经元。通过吸气放电模式和来自C7脊髓的逆向激活来识别神经元。使用双极电极在C5膈神经以及不同胸段水平的肋间内、外神经的中枢切断端进行全神经记录。计算这些记录之间的互相关直方图，以检测表明突触连接的短时间尺度同步性。腹侧组延髓脊髓吸气神经元活动与膈神经之间计算得到的互相关直方图（n = 20），均在短潜伏期（平均潜伏期±标准差，2.0±0.6毫秒）出现峰值（平均半峰宽±标准差，1.1±0.3毫秒），提示单突触兴奋。腹侧组延髓脊髓吸气神经元活动与颈上段吸气神经元之间计算得到的互相关直方图（n = 33），在短潜伏期（平均潜伏期±标准差，1.8±0.6毫秒）出现四个（12%）峰值（平均半峰宽±标准差，0.9±0.1毫秒），提示单突触兴奋，在潜伏期接近零时出现六个（18%）峰值（平均半峰宽±标准差，1.4±0.4毫秒），提示来自共同源的兴奋。腹侧组延髓脊髓吸气神经元活动与不同胸段水平（T2 - 8）的肋间内、外神经之间计算得到的互相关直方图（n = 34），在短潜伏期（平均潜伏期±标准差，4.5±1.1毫秒）出现六个（18%）峰值（平均半峰宽±标准差，2.5±0.5毫秒），提示多突触连接。不同胸段脊髓水平肋间神经活动之间计算得到的互相关直方图（n = 42）显示中央峰值，提示来自共同源的兴奋。尽管峰值大小随节段距离增加而减小，但峰值相对于时间零点的位移并未随节段距离增加（平均位移±标准差，0.6±0.6毫秒），而如果共同兴奋是由腹侧组延髓脊髓吸气神经元等来源的下行单突触兴奋引起的话，预期会增加。我们得出结论，所有腹侧组延髓脊髓吸气神经元均与膈运动神经元形成单突触连接，少数与颈上段吸气神经元形成单突触连接，但与肋间运动神经元的连接是通过中间神经元实现的。
