Department of Pharmacological and Physiological Science, St. Louis University Medical School , St. Louis, MO, USA.
Front Neurosci. 2014 Jun 5;8:136. doi: 10.3389/fnins.2014.00136. eCollection 2014.
Few trigeminal sensory fibers project centrally beyond the trigeminal sensory complex, with only projections of fibers carried in its sensory anterior ethmoidal (AEN) and intraoral nerves described. Fibers of the AEN project into the brainstem reticular formation where immunoreactivity against substance P and CGRP are found. We investigated whether the source of these peptides could be from trigeminal ganglion neurons by performing unilateral rhizotomies of the trigeminal root and looking for absence of label. After an 8-14 days survival, substance P immunoreactivity in the trigeminal sensory complex was diminished, but we could not conclude that the sole source of this peptide in the lateral parabrachial area and lateral reticular formation arises from primary afferent fibers. Immunoreactivity to CGRP after rhizotomy however was greatly diminished in the trigeminal sensory complex, confirming the observations of others. Moreover, CGRP immunoreactivity was nearly eliminated in fibers in the lateral parabrachial area, the caudal ventrolateral medulla, both the peri-ambiguus and ventral parts of the rostral ventrolateral medulla, in the external formation of the nucleus ambiguus, and diminished in the caudal pressor area. The nearly complete elimination of CGRP in the lateral reticular formation after rhizotomy suggests this peptide is carried in primary afferent fibers. Moreover, the arborization of CGRP immunoreactive fibers in these areas mimics that of direct projections from the AEN. Since electrical stimulation of the AEN induces cardiorespiratory adjustments including an apnea, peripheral vasoconstriction, and bradycardia similar to those seen in the mammalian diving response, we suggest these perturbations of autonomic behavior are enhanced by direct somatic primary afferent projections to these reticular neurons. We believe this to be first description of potential direct somatoautonomic projections to brainstem neurons regulating autonomic activity.
仅有穿过三叉神经感觉复合体的三叉神经感觉前筛（AEN）和口腔内神经纤维的投射被描述为纤维的投射。AEN 纤维投射到脑干网状结构，其中发现对 P 物质和 CGRP 的免疫反应性。我们通过进行三叉神经根的单侧切断术并寻找标记缺失，来研究这些肽的来源是否可能来自三叉神经节神经元。在 8-14 天的存活后，三叉神经感觉复合体中的 P 物质免疫反应性减弱，但我们不能得出结论，认为外侧臂旁区和外侧网状结构中这种肽的唯一来源来自初级传入纤维。然而，在切断术后 CGRP 的免疫反应性在三叉神经感觉复合体中大大减弱，证实了其他人的观察结果。此外，CGRP 免疫反应性在外侧臂旁区、尾侧腹外侧髓质、疑核的近-模糊部和腹侧部、疑核的外部形成以及加压区的纤维中几乎被消除。切断术后外侧网状结构中 CGRP 的几乎完全消除表明该肽由初级传入纤维携带。此外，CGRP 免疫反应性纤维在这些区域中的分支类似于来自 AEN 的直接投射。由于 AEN 的电刺激引起类似于哺乳动物潜水反应中所见的心血管呼吸调整，包括呼吸暂停、外周血管收缩和心动过缓，我们认为这些自主行为的干扰通过直接躯体初级传入投射到这些网状神经元而增强。我们认为这是首次描述潜在的直接躯体自主投射到调节自主活动的脑干神经元。
