Neuroanatomy of the Pain System and of the Pathways That Modulate Pain

Abstract

We review many of the recent findings concerning mechanisms and pathways for pain and its modulation, emphasizing sensitization and the modulation of nociceptors and of dorsal horn nociceptive neurons. We describe the organization of several ascending nociceptive pathways, including the spinothalamic, spinomesencephalic, spinoreticular, spinolimbic, spinocervical, and postsynaptic dorsal column pathways in some detail and discuss nociceptive processing in the thalamus and cerebral cortex. Structures involved in the descending analgesia systems, including the periaqueductal gray, locus ceruleus, and parabrachial area, nucleus raphe magnus, reticular formation, anterior pretectal nucleus, thalamus and cerebral cortex, and several components of the limbic system are described and the pathways and neurotransmitters utilized are mentioned. Finally, we speculate on possible fruitful lines of research that might lead to improvements in therapy for pain.

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“…20,21 These neurotransmitters are well known to be the main components of the inhibitory pain pathway. 22 In our study, the absorption of vitamin C was evidenced by the higher plasma level in the vitamin C group compared with the placebo group. The pharmacokinetics of vitamin C are well described in the literature.…”

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“…In the present study, noxious stimuli of different stimulus intensities were used to modulate the impact of the US. When using different stimulus intensities, the unpleasantness and the sensory discriminative aspects of the noxious stimuli are modulated in parallel [32,34,44]. This explains the absence of dissociation between the Vx-SEP and the SI-SEP with respect to their correlation with the unpleasantness of the noxious stimuli.…”

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“…Such pathways may be direct, such as the spino-thalamic cortical pathway (Dong et al 1978;Burstein et al 1996;Willis and Westlund 1997) and others may be indirect, such as cortico-cortical pathways or cortical-subcortical pathways. 'Bilateral' representation at the level of the cortex may also be due to bilateral receptive fields terminating in the spinal cord or brainstem.…”