Pain mechanisms: A commentary on concepts and issues

Abstract

This commentary on ideas about neural mechanisms underlying pain is aimed at providing perspective for a reader who does not work in the field of mammalian somatic sensation. It is not a comprehensive review of the literature. The organization is historical to chronicle the evolution of ideas. The aim is to call attention to source of concepts and how various ideas have fared over time. One difficulty in relating concepts about pain is that the term is used to refer to human and animal reactions ranging from protective spinal reflexes to complex affective behaviors. As a result, the spectrum of “pain”-related neural organization extends to operation of multiple neuronal arrangements. Thinking about pain has shadowed progress in understanding biological mechanisms, in particular the manner of function of nervous systems. This essay concentrates on the evolution of information and concepts from the early 19th century to the present. Topics include the assumptions underlying currently active theories about pain mechanisms. At the end, brief consideration is given to present-day issues, e.g., chronic pain, central pain, and the view of pain as an emotion rather than a sensation. The conceptual progression shows that current controversies have old roots and that failed percepts often resurface after seemingly having been put to rest by argument and evidence.

Estrogenic influences in pain processing

“…Traditionally, two major views on pain processing exist in the scientific community. One states that pain is processed by specific pathways ("labeled lines") made up of distinct sets of neurons peripherally as well as centrally, whereas the other claims that pain is not signaled by a specific system of neurons as such but instead by activation in multimodal neurons that also react to other sensory stimuli (for reviews, see Craig, 2003a;Perl, 2011).…”

Efeitos da amitriptilina sobre a modulação da dor aguda, em ratos submetidos à ligadura do nervo ciático

“…O aumento da inervação simpática poderia explicar porque o tratamento com amitriptilina restaurou a resposta à formalina, aumentando-a, na presença ou ausência de reserpina, nos animais submetidos à ligadura do ciático. A sensibilização dos nociceptores depende do tipo da fibra, da intensidade do estímulo e dos mediadores envolvidos 10 . A ligadura do ciático poderia ter causado aumento da inervação simpática, que poderia ser detectada com o aumento na concentração de noradrenalina, pelo tratamento com amitriptilina.…”

“…O estímulo lesivo é conduzido da periferia para o sistema nervoso central por meio de fibras mielinizadas e amielínicas de diferentes espessuras. Cada tipo de fibra está relacionada a condução de sensações específicas, localizadas ou difusas 10 . A avaliação da hiperalgesia ou alodínia mecânica, no presente estudo, foi testada com os filamentos de Von Frey.…”

TRPs and Pain

“…The architecture of the central pain-processing pathway is generally agreed (Ossipov et al 2010;Perl 2011), although refinements of the wiring have been proposed to account for the range of pain sensations evoked by different stimuli (Craig 2003). The primary afferent nociceptor terminates centrally on relay neurons and interneurons of the dorsal horn in the spinal cord, mostly in laminae I and II.…”