Brain Stem Terminations of the Trigeminal and Upper Spinal Ganglia Innervation of the Cerebrovascular System: WGA-HRP Transganglionic Study

Abstract

The central projections of the nerve fibers innervating the middle cerebral and basilar arteries were investigated by transganglionic tracing of wheat germ agglutinin conjugated with horseradish peroxidase (WGA-HRP) in the rat. WGA-HRP was applied to the exposed basilar and/or middle cerebral arteries. Sections of the brain, trigeminal and upper spinal ganglia were reacted with tetramethylbenzidine for detection of the tracer. The results demonstrate that trigeminal neurons that innervate the middle cerebral artery project to the trigeminal main sensory nucleus, pars oralis, and the dorsocaudal two-fifths of pars interpolaris of the trigeminal brain stem nuclear complex. Terminals were also visible in the ipsilateral nucleus motorius dorsalis nervi vagi (dmnX) and in the lateral nucleus tractus solitarius (nTs) bilaterally at the level of the obex. The ventral periaqueductal gray, including the dorsal raphe and C₂ dorsal horn, were also innervated by nerve fibers from the middle cerebral artery. Ipsilateral trigeminal rhizotomy prior to WGA-HRP application over the middle cerebral artery impeded the visualization of nerve terminations throughout the brain stem. Pretreatment with capsaicin reduced the density of labeled neurons and terminals within the trigeminal ganglion and the brain stem, respectively, following WGA-HRP application over the middle cerebral artery. Basilar artery fibers terminate in the C₂ dorsal horn, the cuneate nuclei, dmnX, and nTs bilaterally. A few projections were also labeled in the ventral periaqueductal gray. Unilateral upper two spinal dorsal rhizotomy prior to WGA-HRP application over the exposed basilar artery resulted in terminal labeling within the C₂ dorsal horn, the cuneate nucleus, dmnX, and nTs contralateral to the rhizotomy, whereas the ipsilateral side was devoid of any labeling. Bilateral superior cervical ganglionectomy prior to WGA-HRP administration to the middle cerebral and basilar arteries did not alter the visualization of nerve terminations throughout the brain stem.