Gautier A, Geny D, Bourgoin S, Bernard J F, Hamon M
INSERM UMR 894 - Centre de Psychiatrie et Neurosciences, Université Paris Descartes, 75014, Paris, France.
IBRO Rep. 2017 Apr 9;2:72-80. doi: 10.1016/j.ibror.2017.04.001. eCollection 2017 Jun.
Convergent data showed that bulbo-spinal serotonergic projections exert complex modulatory influences on nociceptive signaling within the dorsal horn. These neurons are located in the B3 area which comprises the median raphe magnus (RMg) and the lateral paragigantocellular reticular (LPGi) nuclei. Because LPGi 5-HT neurons differ from RMg 5-HT neurons regarding both their respective electrophysiological properties and responses to noxious stimuli, we used anatomical approaches for further characterization of the respective spinal projections of LPGi RMg 5-HT neuron subgroups. Adult Sprague-Dawley rats were stereotaxically injected into the RMg or the LPGi with the anterograde tracer Phaseolus vulgaris leucoagglutinin (PHA-L). The precise location of injection sites and RMg vs LPGi spinal projections into the different dorsal horn laminae were visualized by PHA-L immunolabeling. Double immunofluorescent labeling of PHA-L and the serotonin transporter (5-HTT) allowed detection of serotonergic fibers among bulbo-spinal projections. Anterograde tracing showed that RMg neurons project preferentially into the deep laminae V-VI whereas LPGi neuron projections are confined to the superficial laminae I-II of the ipsilateral dorsal horn. All along the spinal cord, double-labeled PHA-L/5-HTT immunoreactive fibers, which represent only 5-15% of all PHA-L-immunoreactive projections, exhibit the same differential locations depending on their origin in the RMg the LPGi. The clear-cut distinction between dorsal horn laminae receiving bulbo-spinal serotonergic projections from the RMg the LPGi provides further anatomical support to the idea that the descending serotonergic pathways issued from these two bulbar nuclei might exert different modulatory influences on the spinal relay of pain signaling neuronal pathways.
趋同数据表明，延髓-脊髓5-羟色胺能投射对背角内的伤害性信号传导施加复杂的调节影响。这些神经元位于B3区，该区包括中缝大核（RMg）和外侧旁巨细胞网状核（LPGi）。由于LPGi 5-羟色胺能神经元与RMg 5-羟色胺能神经元在各自的电生理特性和对有害刺激的反应方面均有所不同，我们采用解剖学方法进一步表征LPGi和RMg 5-羟色胺能神经元亚群各自的脊髓投射。将成年Sprague-Dawley大鼠立体定位注射逆行示踪剂菜豆凝集素（PHA-L）到RMg或LPGi。通过PHA-L免疫标记观察注射部位的精确位置以及RMg和LPGi向不同背角层的脊髓投射。对PHA-L和5-羟色胺转运体（5-HTT）进行双重免疫荧光标记可检测延髓-脊髓投射中的5-羟色胺能纤维。逆行示踪显示，RMg神经元优先投射到深层V-VI层，而LPGi神经元投射局限于同侧背角的浅层I-II层。在整个脊髓中，双重标记的PHA-L/5-HTT免疫反应性纤维（仅占所有PHA-L免疫反应性投射的5%-15%）根据其起源于RMg还是LPGi呈现相同的不同定位。接受来自RMg和LPGi的延髓-脊髓5-羟色胺能投射的背角层之间的明确区分，为来自这两个延髓核的下行5-羟色胺能通路可能对疼痛信号神经元通路的脊髓中继施加不同调节影响这一观点提供了进一步的解剖学支持。
