Expiratory neurons in the caudal ventral respiratory group extend descending axons to the lumbar and sacral spinal cord, and they possess axon collaterals, the distribution of which has been well-documented. Likewise, these expiratory neurons extend axons to the thoracic spinal cord and innervate thoracic expiratory motoneurons. These axons also give rise to collaterals, and their distribution may influence the strength of synaptic connectivity between the axons and the thoracic expiratory motoneurons. We investigated the distribution of axon collaterals in the thoracic spinal cord using a microstimulation technique. This study was performed on cats; one cat was used to make an anatomical atlas and six were used in the experiment. Extracellular spikes of expiratory neurons were recorded in artificially ventilated cats. The thoracic spinal gray matter was microstimulated from dorsal to ventral sites at 100-μm intervals using a glass-insulated tungsten microelectrode with a current of 150–250 μA. The stimulation tracks were made at 1 mm intervals along the spinal cord in segments Th9 to Th13, and the effective stimulating sites of antidromic activation in axon collaterals were systematically mapped. The effective stimulating sites in the contralateral thoracic spinal cord with expiratory neurons in the caudal ventral respiratory group (cVRG) occupied 14.4% of the total length of the thoracic spinal cord examined. The mean percentage of effective stimulating tracks per unit was 18.6 ± 4.4%. The distribution of axon collaterals of expiratory neurons in the feline thoracic spinal cord indeed resembled that reported in the upper lumbar spinal cord. We propose that a single medullary expiratory neuron exerts excitatory effects across multiple segments of the thoracic spinal cord via its collaterals.

尾侧腹侧呼吸群中的呼气神经元将下降轴突延伸至腰椎和骶脊髓，并且它们具有轴突侧支，其分布已被充分记录。同样，这些呼气神经元将轴突延伸至胸脊髓并支配胸部呼气运动神经元。这些轴突还产生侧支循环，它们的分布可能会影响轴突和胸廓呼气运动神经元之间突触连接的强度。我们使用微刺激技术研究了胸脊髓中轴突侧支的分布。这项研究是在猫身上进行的；一只猫被用来制作解剖图谱，六只猫被用于实验。在人工通气的猫中记录了呼气神经元的细胞外尖峰。使用电流为 150-250 μA 的玻璃绝缘钨微电极，以 100 μm 的间隔从背侧到腹侧对胸椎灰质进行微刺激。沿脊髓 Th9 至 Th13 节段以 1 mm 间隔进行刺激轨迹，并系统地绘制轴突侧支中逆行激活的有效刺激位点。尾腹呼吸组（cVRG）呼气神经元对侧胸脊髓的有效刺激位点占受检胸脊髓总长度的14.4%。每单位有效刺激轨迹的平均百分比为 18.6 ± 4.4%。猫胸脊髓中呼气神经元轴突侧支的分布确实与上腰脊髓中报道的相似。我们提出，单个髓质呼气神经元通过其侧枝对胸脊髓的多个节段产生兴奋作用。