Lipski J, Zhang X, Kruszewska B, Kanjhan R
Department of Physiology, School of Medicine, University of Auckland, New Zealand.
Brain Res. 1994 Mar 21;640(1-2):171-84. doi: 10.1016/0006-8993(94)91871-6.
The aim of this study was to examine medullary and spinal axonal projections of inspiratory bulbospinal neurons of the rostral ventral respiratory group (VRG) in the rat. A direct visualization of long (9.8-33 mm) axonal branches, including those projecting to the contralateral side of the medulla oblongata and the spinal cord, was possible due to intracellular labeling with neurobiotin and long survival times (up to 22 h) after injections. Seven of the nine labeled neurons had bilateral descending axons, which were located in discrete regions of the spinal white matter; ipsilateral axons in the lateral and dorsolateral funiculus, contralateral in the ventral and ventromedial funiculus. The collaterals issued by these axons at the mid-cervical level formed close appositions with dendrites of phrenic motoneurons, which had also been labeled with neurobiotin. None of these collaterals crossed the midline. The significance of this finding is discussed in relation to the crossed-phrenic phenomenon. Additional spinal collaterals were identified in the C1 and T1 segments. Within the medulla, collaterals with multiple varicosities were identified in the lateral tegmental field and in the dorsomedial medulla (in the hypoglossal nucleus and in the nucleus of the solitary tract). These results demonstrate that inspiratory VRG neurons in the rat have some features which have not been previously described in the cat, including frequent bilateral spinal projection and projection to the nucleus of the solitary tract. In addition, this study shows that intracellular labeling with neurobiotin offers an effective way of tracing long axonal projections, supplementing results previously obtainable only with antidromic mapping, and providing morphological details which could not be observed in previous studies using labeling with horseradish peroxidase.
本研究的目的是检测大鼠延髓头端腹侧呼吸组（VRG）吸气性延髓脊髓轴突投射。由于使用神经生物素进行细胞内标记以及注射后较长的存活时间（长达22小时），得以直接观察到长（9.8 - 33毫米）轴突分支，包括那些投射到延髓和脊髓对侧的分支。9个标记神经元中有7个具有双侧下行轴突，它们位于脊髓白质的离散区域；同侧轴突位于外侧和背外侧索，对侧轴突位于腹侧和腹内侧索。这些轴突在颈中部水平发出的侧支与膈运动神经元的树突形成紧密接触，膈运动神经元也用神经生物素进行了标记。这些侧支均未越过中线。结合膈神经交叉现象讨论了这一发现的意义。在C1和T1节段还发现了额外的脊髓侧支。在延髓内，在外侧被盖区和延髓背内侧（舌下神经核和孤束核）发现了具有多个曲张体的侧支。这些结果表明，大鼠吸气性VRG神经元具有一些猫中未曾描述过的特征，包括频繁的双侧脊髓投射和向孤束核的投射。此外，本研究表明，用神经生物素进行细胞内标记提供了一种追踪长轴突投射的有效方法，补充了以前仅通过逆向映射获得的结果，并提供了以前使用辣根过氧化物酶标记的研究中无法观察到的形态学细节。
