The origin of the spinomesencephalic tract in the rat: An anatomical study using the retrograde transport of horseradish peroxidase

Abstract

An anatomical technique based on the retrograde transport of horseradish peroxidase (HRP) was used to investigate the projections of spinal cord neurons to the mesencephalic tegmentum in the rat. Restricted unilateral injections were confined to central grey, cuneiformis areas, and superior colliculus. Injections into all these loci produced labeling in similar spinal areas. Only quantitative differences were noted. In the spinal grey matter, numerous labeled cells were regularly encountered in the marginal zone, the lateral part of the neck of the dorsal horn, and the dorsal grey commissure. Projections from the marginal zone and neck of the dorsal horn were predominantly contralateral. In the white matter, a pronounced bilateral labeling was observed in the nucleus of the dorsolateral funiculus, thus confirming our previous electrophysiological findings (Menétrey et al., '80). This distribution of labeled cells was commonly observed throughout the whole length of the cord. Additional sites of projecting cells have also been identified at the most rostral levels (obex, C1, C2). They mostly derived from spinal extensions of the dorsal column nuclei and lateral cervical nucleus contralaterally; from the lateral ventral horns bilaterally and from the nucleus commissuralis ipsilaterally. This study is thus a clear confirmation that the mesencephalic tegmentum constitutes a target for various somatosensory inputs originating from spinal cord, dorsal column nuclei, and lateral cervical nucleus. Moreover, from these results together with those obtained for the spinothalamic tract in the rat, it appears that marginal and dorsolateral funiculus neurons preferentially project to the mesencephalic tegmentum. The importance of marginal zone projections underlines the involvement of the spinomesencephalic tract in pain mechanisms.

Multisegmental Aδ- and C-Fiber Input to Neurons in Lamina I and the Lateral Spinal Nucleus

“…They can integrate multisegmental root inputs for projection to supraspinal centers (Menétrey et al, 1982;Pechura and Liu, 1986;Menétrey and Basbaum, 1987;Leah et al, 1988;Burstein et al, 1990a,b) and via axon collaterals to the spinal gray matter (Olave and Maxwell, 2004). Our data support the idea of involvement of LSN neurons in nociceptive processing (Olave and Maxwell, 2004).…”

“…The LSN differs from the superficial dorsal horn in the nature of its neuropil, where the cell bodies are found surrounded by the rostrocaudally oriented myelinated axons. LSN neurons project through ascending tracts to the brainstem, hypothalamus, and thalamus (Menétrey et al, 1982;Pechura and Liu, 1986;Menétrey and Basbaum, 1987;Leah et al, 1988;Burstein et al, 1990a,b) and can be activated by noxious stimulation (Olave and Maxwell, 2004). However, little is known about the afferent inputs to the LSN.…”

Neurons in the lateral part of the lumbar spinal cord show distinct novel axon trajectories and are excited by short propriospinal ascending inputs

“…6a). Earlier morphological studies in the LSN described neurons with dendrite oriented either laterally (Bresnahan et al, 1984;Rethelyi, 2003), medially (Menetrey et al, 1982;Rethelyi, 2003) or rostrocaudally (Rethelyi, 2003). LSN neurons in our sample showed a combination of these features and were either spherical (e.g.…”

“…LSN neurons can be activated by noxious stimulation (Olave and Maxwell, 2004), receiving afferent input from C-fibers innervating muscles (Olave and Maxwell, 2004) and viscera (Sugiura et al, 1989) and project through ascending tracts to the brainstem, hypothalamus, and thalamus (Menetrey et al, 1982;Pechura and Liu, 1986;Menetrey and Basbaum, 1987;Leah et al, 1988;Burstein et al,1990). At the same time little is known about the input to LSN cells from neighboring neurons and almost nothing about the course and local branching of their axon.…”

Fos expression in the midbrain periaqueductal grey after trigeminovascular stimulation

“…In the rat retro and anterograde tracing studies show that the upper cervical spinal cord cells project to the lateral and ventrolateral regions of the PAG (Menetrey et al 1982 ;Yezierski, 1991). Neurons in lamina I of the dorsal horn of the cervical spinal cord relay nociceptive, thermoreceptive and visceroreceptive information to the PAG via a contralateral projection travelling in the spinomesencephalic tract (Blomqvist & Craig, 1991).…”