Weinberg R J, Rustioni A
Department of Cell Biology and Anatomy, University of North Carolina, Chapel Hill 27599.
J Comp Neurol. 1989 Apr 1;282(1):142-56. doi: 10.1002/cne.902820111.
Neurons in the pontomedullary tegmentum have been proposed as a final common pathway subserving descending inhibition in the dorsal column nuclei. To investigate the anatomical substrate for these descending effects, brainstem projections to the cuneate nucleus of rats were studied with injections of lectin-conjugated horseradish peroxidase. In rats with iontophoretic tracer injections in this nucleus, many labeled neurons were detected near the injection site, especially ventral and caudal to it. Intrinsic reciprocal projections were observed after injections in caudal, middle, or rostral levels of the cuneate nucleus. Neurons were labeled in the red nucleus, in agreement with previous anatomical studies, and also in the trigeminal, vestibular, and cochlear nuclei. An ipsilateral dorsomedial group of neurons was labeled in the upper cervical segments and scattered neurons were also labeled bilaterally near the central canal. Sparse retrograde labeling in the tegmentum was focused in the lateral paragigantocellular nucleus and caudal raphe. Consistent with the retrograde experiments, anterograde labeling after pressure injections of lectin-conjugated horseradish peroxidase in the pontomedullary tegmentum was very sparse within the dorsal column nuclei; labeling was dense, however, in the region immediately ventral to these nuclei. These results confirm previous work indicating that the activity of cuneate neurons is modulated by brainstem sensory nuclei. However, it appears that direct projections to the cuneate nucleus from pontine and rostral medullary regions are sparser than previously suggested. The last link of a polysynaptic descending inhibitory pathway may include GABAergic neurons immediately adjacent to the dorsal column nuclei and/or intrinsic to these nuclei.
脑桥延髓被盖区的神经元被认为是背柱核中下行抑制的最终共同通路。为了研究这些下行效应的解剖学基础，通过注射凝集素结合辣根过氧化物酶对大鼠楔束核的脑干投射进行了研究。在对该核进行离子电渗示踪剂注射的大鼠中，在注射部位附近检测到许多标记神经元，尤其是在其腹侧和尾侧。在楔束核的尾侧、中间或头侧水平注射后观察到了内在的相互投射。与先前的解剖学研究一致，在红核中发现了标记神经元，在三叉神经核、前庭核和蜗神经核中也发现了标记神经元。在上颈段标记了同侧背内侧神经元群，在中央管附近也双侧标记了散在的神经元。被盖区的稀疏逆行标记集中在外侧巨细胞旁核和尾侧中缝核。与逆行实验一致，在脑桥延髓被盖区压力注射凝集素结合辣根过氧化物酶后的顺行标记在背柱核内非常稀疏；然而，在这些核紧腹侧的区域标记密集。这些结果证实了先前的研究工作，即楔束神经元的活动受脑干感觉核的调节。然而，似乎从脑桥和延髓头侧区域到楔束核的直接投射比先前认为的要稀疏。多突触下行抑制通路的最后一环可能包括紧邻背柱核的GABA能神经元和/或这些核内的固有神经元。
