Murphy A Z, Behbehani M M
Department of Physiology and Cell Biophysics, University of Cincinnati, College of Medicine, OH 45267-0576.
Brain Res. 1993 Mar 19;606(1):68-78. doi: 10.1016/0006-8993(93)91571-9.
Numerous studies have shown that the lateral reticular nucleus (LRN), located in the caudal ventrolateral medulla, is an important nuclear region in the descending analgesia system. Activation of this brainstem region, either electrically or chemically, results in a reduction in nociceptive threshold. In addition, destruction of LRN abolishes the tonic descending inhibition present on dorsal horn neurons. Recent neuroanatomical tracing studies have shown that the nucleus raphe magnus (NRM), long implicated in nociception, sends direct projections to LRN; however, no information exists regarding the physiological characteristics of this pathway, nor its role in the endogenous descending analgesia system. The purpose of this study was to physiologically characterize the synaptic influence(s) of projections from the NRM to the LRN using electrophysiological recording, electrical and chemical stimulation, and iontophoretic techniques. Sixty-one percent of LRN neurons responded to single pulse stimulation of NRM; 52% of the responsive cells were excited and 48% were inhibited. The mean latency to onset of excitation was 4.9 +/- 1.2 ms. High frequency (100 Hz) electrical stimulation of NRM influenced 69/102 neurons; 52% (36/69) were excited, while 48% (33/69) were inhibited. Microinjection of glutamate into NRM significantly modified the discharge of 83% (93/112) of LRN cells tested; of these, 71% were inhibited, while 29% were excited. In 35 cells the effects of the excitatory amino acid antagonist kynurenic acid (KYN) were studied. In 75% of the cells excited by glutamate administration into the NRM (18/24), KYN partially antagonized this response. In 11 LRN cells inhibited by NRM chemical stimulation, KYN had no effect on this inhibition. Overall, 95% of the LRN cells responsive to NRM stimulation were also responsive to noxious peripheral stimulation, indicating that these cells are receiving ascending information from the spinal cord regarding somatosensory stimulation as well as receiving descending input from the NRM. It is concluded that LRN neurons are highly responsive to both noxious peripheral stimulation and NRM efferent activation, and that this region plays a significant role as an integrator for both ascending and descending information.
大量研究表明，位于延髓尾端腹外侧的外侧网状核（LRN）是下行镇痛系统中的一个重要核团区域。对这个脑干区域进行电刺激或化学刺激，会导致痛觉阈值降低。此外，破坏LRN会消除存在于背角神经元上的紧张性下行抑制。最近的神经解剖追踪研究表明，长期以来被认为与痛觉有关的中缝大核（NRM）直接投射到LRN；然而，关于这条通路的生理特征及其在内源性下行镇痛系统中的作用尚无相关信息。本研究的目的是利用电生理记录、电刺激和化学刺激以及离子电泳技术，从生理学角度描述NRM向LRN投射的突触影响。61%的LRN神经元对NRM单次脉冲刺激有反应；52%的反应性细胞被兴奋，48%被抑制。兴奋开始的平均潜伏期为4.9±1.2毫秒。对NRM进行高频（100赫兹）电刺激影响了102个神经元中的69个；52%（36/69）被兴奋，而48%（33/69）被抑制。向NRM微量注射谷氨酸显著改变了所测试的112个LRN细胞中83%（93/112）的放电；其中，71%被抑制，29%被兴奋。在35个细胞中研究了兴奋性氨基酸拮抗剂犬尿氨酸（KYN）的作用。在通过向NRM注射谷氨酸而兴奋的细胞中，75%（18/24）的细胞中KYN部分拮抗了这种反应。在11个被NRM化学刺激抑制的LRN细胞中，KYN对这种抑制没有影响。总体而言，95%对NRM刺激有反应的LRN细胞也对有害的外周刺激有反应，这表明这些细胞既接收来自脊髓的关于躯体感觉刺激的上行信息，也接收来自NRM的下行输入。得出的结论是，LRN神经元对有害的外周刺激和NRM传出激活都高度敏感，并且该区域作为上行和下行信息的整合器发挥着重要作用。
