Mason P, Fields H L
Department of Neurology, University of California, San Francisco 94143-0114.
J Comp Neurol. 1989 Oct 8;288(2):185-207. doi: 10.1002/cne.902880202.
Two physiologically defined classes of pontomedullary raphe neurons were intracellularly labeled in order to determine the target nuclei of their axonal projections. In the lightly anesthetized cat, cells either increased (on-cells) or decreased (off-cells) their discharge rate during the paw withdrawal reflex evoked by noxious pinch or heat. On- and off-cells were injected with horseradish peroxidase and the initial course of labeled axons through the lower brainstem was reconstructed. On-cell projections to the pontomedullary raphe and medial reticular nuclei were sparse. On-cells projected densely to regions of the lateral reticular formation and the ventrolateral medulla at both rostral and caudal medullary levels. In general, on-cells had few collaterals and spare axonal swellings. In contrast to on-cells, most off-cells had axons that collateralized densely within the brainstem raphe and adjacent reticular formation. Such collaterals were either local, within the neuron's dendritic field, or distant, involving a projection of 1-8 mm. One off-cell had a dense terminal field within the sensory trigeminal complex, a projection that may subserve the inhibition of trigeminal sensory neurons produced by raphe magnus stimulation. Well-labeled off-cells had numerous collaterals and dense regions of axonal swellings. In summary, off-cells terminated densely in the raphe magnus and adjacent reticular formation whereas on-cells projected predominantly to the ventrolateral medulla, a region implicated in autonomic control. Local off-cell collaterals provide an anatomical substrate that would enable off-cells to coordinate the activity of on- and off-cells through synaptic contacts.
为了确定脑桥延髓缝际神经元轴突投射的靶核，对两类生理学定义的脑桥延髓缝际神经元进行了细胞内标记。在轻度麻醉的猫中，在由有害夹捏或热刺激诱发的爪退缩反射期间，细胞放电率要么增加（开细胞）要么降低（关细胞）。对开细胞和关细胞注射辣根过氧化物酶，并重建标记轴突通过低位脑干的起始行程。开细胞向脑桥延髓缝际核和内侧网状核的投射稀疏。开细胞密集地投射到延髓头端和尾端水平的外侧网状结构区域和延髓腹外侧。一般来说，开细胞几乎没有侧支和多余的轴突膨体。与开细胞不同，大多数关细胞的轴突在脑干缝际和相邻网状结构内密集发出侧支。这些侧支要么是局部的，在神经元的树突野内，要么是远距离的，涉及1 - 8毫米的投射。一个关细胞在感觉三叉神经复合体中有密集的终末野，这种投射可能有助于中缝大核刺激对三叉神经感觉神经元的抑制。标记良好的关细胞有许多侧支和密集的轴突膨体区域。总之，关细胞在中缝大核和相邻网状结构中密集终末，而开细胞主要投射到与自主控制有关的延髓腹外侧。局部关细胞侧支提供了一个解剖学基础，使关细胞能够通过突触联系协调开细胞和关细胞的活动。
