Jacquin M F, Chiaia N L, Rhoades R W
Department of Anatomy and Neurobiology, St. Louis University School of Medicine, Missouri 63104.
Somatosens Mot Res. 1990;7(2):153-83. doi: 10.3109/08990229009144705.
Prior studies have documented a trigeminal (V) mandibular primary afferent projection to the dorsomedial portion of the contralateral medullary and cervical dorsal horns in cat, hamster, and rat. We now report the existence of a much more substantial V ophthalmic primary afferent projection to the ventrolateral portion of contralateral medullary and cervical dorsal horns in rat. Horseradish peroxidase (HRP) injections into the V ganglion or V brainstem complex anterogradely labeled a fascicle of primary afferent axons that exited the caudal ventrolateral V spinal tract to form a rostrocaudally continuous, transversely oriented, V primary afferent decussation. These fibers terminated most heavily in laminae III-V of the ventrolateral dorsal horn in contralateral caudal medulla and the first and second cervical segments. Retrograde tracing with diamidino yellow (DY) or fluorogold and anterograde tracing with Phaseolus vulgaris leucoagglutinin also demonstrated a substantial commissural projection of central origin in medullary dorsal horn laminae I-VII. The latter projection had a more diffuse trajectory and termination pattern than that of the V primary afferent decussation. Unilateral HRP injections into medullary and cervical dorsal horns also retrogradely labeled V primary afferent collaterals contralateral to the injection site in corresponding regions of dorsal horn, and also in ventromedial interpolaris, oralis, and principalis, rostral to their decussation. Axons (1.5 +/- 0.8 microns mean diameter; 0.4-3.9 microns range) therefore terminated both ipsi- and contralateral to their cells of origin. These HRP injections also labeled an average of 40.4 +/- 13.0 V ganglion cells (mean +/- SD, corrected for split somata) in dorsomedial, ophthalmic regions of the contralateral ganglion. Their mean diameter was slightly larger than that of cells labeled ipsilaterally (29.9 vs. 26.3 microns). Double-labeling studies assessed possible ophthalmic receptor surfaces innervated by centrally crossing primary afferents. DY was injected into right medullary and cervical dorsal horns, and HRP was applied to either the left cornea, the ethmoid nerve, or the dura overlying cerebral cortex. Though DY labeled from 75 to 125 left ganglion cells per animal, no cells were double-labeled. All of these findings suggest that nociceptive-specific ganglion cells are not a source of the crossed ophthalmic primary afferent projection. Unilateral transection of the infraorbital nerve on the day of birth did not alter the crossed primary afferent projection to the partially deafferented side of the brainstem. This is further evidence of an absence of central sprouting in spared V primary afferents following neonatal V deafferentation.
先前的研究已证明，在猫、仓鼠和大鼠中，三叉神经（V）下颌初级传入纤维投射至对侧延髓和颈髓背角的背内侧部分。我们现在报告，在大鼠中存在一条更为显著的V眼神经初级传入纤维投射，至对侧延髓和颈髓背角的腹外侧部分。将辣根过氧化物酶（HRP）注射到V神经节或V脑干复合体中，顺行标记了一束初级传入轴突，这些轴突从尾侧腹外侧V脊髓束穿出，形成一条头尾连续、横向排列的V初级传入纤维交叉。这些纤维主要终止于对侧尾侧延髓腹外侧背角的III - V层以及颈髓第一和第二节段。用双脒基黄（DY）或荧光金进行逆行追踪，以及用菜豆凝集素进行顺行追踪，也证实了延髓背角I - VII层中存在大量起源于中枢的连合投射。后者的投射轨迹和终止模式比V初级传入纤维交叉更为弥散。将HRP单侧注射到延髓和颈髓背角，也逆行标记了注射部位对侧背角相应区域以及交叉上方的腹内侧极间核、口核和主核中的V初级传入侧支。轴突（平均直径1.5±0.8微米；范围0.4 - 3.9微米）因此在其起源细胞的同侧和对侧均有终止。这些HRP注射还标记了对侧神经节背内侧眼神经区域平均40.4±13.0个V神经节细胞（平均±标准差，校正了分裂的胞体）。它们的平均直径略大于同侧标记细胞的平均直径（29.9对26.3微米）。双重标记研究评估了由中枢交叉初级传入纤维支配的可能的眼神经受体表面。将DY注射到右侧延髓和颈髓背角，并将HRP应用于左侧角膜、筛神经或覆盖大脑皮质的硬脑膜。尽管每只动物的DY标记了75至125个左侧神经节细胞，但没有细胞被双重标记。所有这些发现表明，伤害性特异性神经节细胞不是交叉的眼神经初级传入纤维投射的来源。出生当天单侧切断眶下神经，并未改变至脑干部分去传入侧的交叉初级传入纤维投射。这进一步证明了新生期V去传入后，保留的V初级传入纤维中不存在中枢侧支发芽。
