SeriesVisceral pain
Section snippets
Transmission of visceral pain
In the past few years there have been new insights into the neural mechanisms of the clinical features of visceral pain that have challenged the established paradigm. Traditionally, the two schools of thought among pain researchers were: that the viscera are innervated by separate classes of sensory receptors, some concerned with autonomic regulation and some concerned with sensation, including pain; or that internal organs are innervated by a single and homogeneous class of sensory receptors
Biochemistry of visceral pain
There are two distinct biochemical classes of fine calibre unmyelinated primary afferents that innervate somatic and visceral tissues: the first class contain neurones that express peptide neurotransmitters, such as substance P and calcitonin-gene-related peptide (CGRP); and the other class does not express these substances.11 These two classes can also be distinguished by various enzymes, such as fluoride-resistant acid phosphatase found in the nonpeptide group, and receptors, such as the
Wind up: central-nervous-system changes due to visceral afferent signals
Nociceptive afferent discharges in visceral afferents can evoke profound changes in the central nervous system; for example, repetitive noxious stimulation of the viscera evokes increases in the excitability of viscerosomatic neurons in the spinal cord.14 Such changes are highly selective and organised such that they occur on only those viscerosomatic cells that are driven by the conditioning visceral stimulus. In somatic nociceptive systems, a common correlate of the increased excitability is
Central pathways that transmit visceral pain
The traditional view of the transmission of visceral and other types of pain is that signals are carried by crossed anterolateral pathways, mainly the spinothalamic and spinoreticular tracts. This theory, however, has been challenged by the discovery of three previously undescribed pathways that carry visceral nociceptive information: the dorsal column pathway, the spino(trigemino)-parabrachioamygdaloid pathway, and the spinohypothalamic pathway.
The experimental evidence for the importance of
New techniques for study of visceral pain
New electrophysiological and imaging techniques have advanced our understanding of visceral pain perception. Microstimulation of the thalamus, for example, can evoke visceral pain experiences, such as angina or labour pain, sometimes years after the original episode.25, 26 These observations highlight the integrative role of the thalamus in processing memories of pain and the existence of longlived neural mechanisms that are capable of storing the results of a previous painful experience for
Putting research into clinical practice
Most clinical specialists continue to treat visceral pain as just a symptom and not as a distinct neurological entity. Whether or not their patients will obtain effective pain relief will depend on the views of each specialist towards the management of pain. However, it is likely that the findings of basic research into visceral pain will soon start to have an effect on clinical thought and practice. This process is already happening in the management of socalled functional abdominal pain
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