Nakayama K, Niwa M, Sasaki S I, Ichikawa T, Hirai N
Center for Medical Sciences, Ibaraki Prefectural University of Health Sciences, Japan.
J Comp Neurol. 1998 Sep 7;398(4):459-72.
A reconstruction was made of the trajectory of primary spindle afferents from the intercostal muscles in the spinal cord of the cat. Intraaxonal recordings were performed from the primary spindle afferents that were identified by their response to lung inflation and stimulus threshold to activate the action potentials. The afferents were stained by using intraaxonal injection of horseradish peroxidase (HRP). Results were obtained mainly from internal intercostal Ia fibers, which entered the spinal cord and bifurcated into ascending and descending branches. The ascending branches could be traced up to 10.7 mm, and the descending branches could be traced up to 7.3 mm. The ascending branches extended to the next segment. Collaterals ranging from one to six were given off from these branches. The distances between adjacent collaterals ranged from 0.9 mm to 4.7 mm. Each collateral had similar morphological characteristics. The collaterals entered the dorsal horn and ran toward lamina IX through the medial half of the gray matter. Fine branches and boutons were given off in laminae V, VII, VIII, and IX. The aggregations of these branches were found in lamina VII, mainly in the region of Clarke's column and in the ventral and ventrolateral regions thereof and in lamina IX, mainly in the nucleus lateromedialis. Most terminals did not contact the somata of target neurons in all laminae in which terminals were found. However, a few terminals were found to contact large neurons in lamina IX. In addition to these aggregates, there were some terminals scattered throughout the ventral horn. Thus, it was concluded that single intercostal Ia afferents project to the region of Clarke's column, to the intercostal motor nucleus, and to the intermediate regions.
对猫脊髓中来自肋间肌的初级肌梭传入纤维的轨迹进行了重建。通过对初级肌梭传入纤维对肺扩张的反应和激活动作电位的刺激阈值来识别这些纤维，并进行轴突内记录。通过轴突内注射辣根过氧化物酶（HRP）对传入纤维进行染色。结果主要来自肋间内肌Ia纤维，这些纤维进入脊髓并分为升支和降支。升支可追踪至10.7毫米，降支可追踪至7.3毫米。升支延伸至下一节段。这些分支发出1至6条侧支。相邻侧支之间的距离在0.9毫米至4.7毫米之间。每个侧支具有相似的形态特征。侧支进入背角，穿过灰质内侧半部向IX层延伸。在V、VII、VIII和IX层发出细支和终扣。这些分支的聚集主要见于VII层，主要在克拉克柱区域及其腹侧和腹外侧区域，以及IX层，主要在外侧内侧核。在发现终末的所有层中，大多数终末不与靶神经元的胞体接触。然而，发现少数终末与IX层的大神经元接触。除了这些聚集外，还有一些终末散在于整个腹角。因此，得出结论：单个肋间肌Ia传入纤维投射到克拉克柱区域、肋间运动核和中间区域。
