Pain without nociception?

Abstract

We describe a young woman with complete cervical spinal cord transsection, who developed significant abdominal pain, triggered by gastric distension and deep abdominal palpation. On the basis of the nature of her spinal cord injury, her brain-gut axis was limited to vagal pathways. Studies in mammalian models of human visceral sensation consistently showed that the subdiaphragmatic vagus contains a homogeneous population of afferents that are activated by low-intensity stimuli, which are generally believed to be important in regulating autonomic function and perhaps contributing to visceral sensory experiences triggered by such low-intensity stimuli (e.g. fullness, nausea), but not pain, although many fibers encode stimuli well into the noxious range. In contrast, spinal afferent pathways include fibers with high-activation thresholds that are thought to represent specialized nociceptors. This illustrative case argues against an exclusive role of specialized nociceptive pathways in visceral pain, but supports a concept of intensity coding with the composite of vagal and spinal input contributing to conscious perception and pain.

Unique Molecular Characteristics of Visceral Afferents Arising from Different Levels of the Neuraxis: Location of Afferent Somata Predicts Function and Stimulus Detection Modalities

“…For example, in the case of pain arising from abdominal organs (including the colon), spinal afferents have been proposed as the transducer of noxious pain (e.g., sharp, burning) whereas nodose afferents transmit affective aspects of visceral pain (e.g., fear, anxiety, nausea) (Berthoud and Neuhuber, 2000;Grundy, 2002;Sengupta, 2009). These distinctions are supported by patient reports of sensations produced by whole vagal nerve stimulation (Sackeim et al, 2001;Ben-Menachem, 2002), but contradicted by the similarities in firing properties of nodose and spinal afferents innervating the gut (Sengupta et al, 1990;Ozaki and Gebhart, 2001;Yu et al, 2005;Bielefeldt et al, 2006) and the anecdotal reports of noxious gut pain in patients with spinal transections, i.e., patients that lack ascending input from spinal afferents (Charney et al, 1975;Yung and Groah, 2001;Finnerup et al, 2008;Levinthal and Bielefeldt, 2012)).…”

Anatomic connections of the diaphragm influence of respiration on the body system

“…If these do not work properly, they may produce a nonphysiologic afferent environment, both for the diaphragm and for the structures connected to it 100. It is important to emphasize that when an organ such as the liver or the gallbladder does not function properly, the phrenic nerve will be affected 101,102.…”

Transcutaneous auricular VNS applied to experimental pain: A paired behavioral and EEG study using thermonociceptive CO2 laser

“…The pain-related effects of taVNS appear predominantly on tonic stimuli, which are known to produce a temporal increase of pain perception mostly by alterations in the affective components of the pain experience, rather than that of sensory-processing [ 113 ]. Traditionally, the vagus nerve is also highly investigated for its therapeutical effect on mood regulation [ 29 ] and was suggested to relay the emotional aspect of pain perception [ 84 , 114 ]. Hence, while acute taVNS can be useful to primarily explore the sensory modulation related to pain perception, the chronic use of taVNS might offer complementary insight into the changes induced on the subjective component of the pain experience [ 115 ].…”