http://yael-nissan.weebly.com/uploads/5/2/9/2/5292348/the_introduction_to_pain_an_integrative_review_-_millan.pdf

The induction of pain: an integrative review

https://www.gastrojournal.org/article/S0016-5085(16)00184-0/pdf

Fundamentals of neurogastroenterology: Basic science

Current concepts and basic principles of neurogastroenterology in relation to functional gastrointestinal disorders are reviewed. Neurogastroenterology is emphasized as a new and advancing subspecialty of clinical gastroenterology and digestive science. As such, it embraces the investigative sciences dealing with functions, malfunctions, and malformations in the brain and spinal cord, and the sympathetic, parasympathetic and enteric divisions of the autonomic innervation of the digestive tract. Somatomotor systems are included insofar as pharyngeal phases of swallowing and pelvic floor involvement in defecation, continence, and pelvic pain are concerned. Inclusion of basic physiology of smooth muscle, mucosal epithelium, and the enteric immune system in the neurogastroenterologic domain relates to requirements for compatibility with neural control mechanisms. Psychologic and psychiatric relations to functional gastrointestinal disorders are included because they are significant components of neurogastroenterology, especially in relation to projections of discomfort and pain to the digestive tract.

https://gut.bmj.com/content/gutjnl/45/suppl_2/II6.full.pdf

Fundamentals of neurogastroenterology

Neural mechanisms of pelvic organ cross-sensitization.

The widespread convergence of information from visceral, cutaneous, and muscle tissues onto CNS neurons invites the question of how to identify pain as being from the viscera. Despite referral of visceral pain to cutaneous areas, individuals regularly distinguish cutaneous and visceral pain and commonly have contrasting behavioral reactions to each. Our study addresses this dilemma by directly comparing human neural processing of intensity-equated visceral and cutaneous pain. Seven subjects underwent fMRI scanning during visceral and cutaneous pain produced by balloon distention of the distal esophagus and contact heat on the midline chest. Stimulus intensities producing nonpainful and painful sensations, interleaved with rest periods, were presented in each functional run. Analyses compared painful to nonpainful conditions. A similar neural network, including secondary somatosensory and parietal cortices, thalamus, basal ganglia, and cerebellum, was activated by visceral and cutaneous painful stimuli. However, cutaneous pain evoked higher activation bilaterally in the anterior insular cortex. Further, cutaneous but not esophageal pain activated ventrolateral prefrontal cortex, despite higher affective scores for visceral pain. Visceral but not cutaneous pain activated bilateral inferior primary somatosensory cortex, bilateral primary motor cortex, and a more anterior locus within anterior cingulate cortex. Our results reveal a common cortical network subserving cutaneous and visceral pain that could underlie similarities in the pain experience. However, we also observed differential activation patterns within insular, primary somatosensory, motor, and prefrontal cortices that may account for the ability to distinguish visceral and cutaneous pain as well as the differential emotional, autonomic and motor responses associated with these different sensations.

https://www.physiology.org/doi/pdf/10.1152/jn.01048.2002

Differentiation of visceral and cutaneous pain in the human brain.

1 Previous studies in the rat have shown that the hypogastric nerve conveys input from the cervix and uterus mainly to the T13-L3 segments of the spinal cord, whereas the pelvic nerve conveys input from the cervix and vaginal canal mainly to the L6-S2 segments 2 To study the effects of this input, the dorsal horns of the T13-L1, L6-S2, and L4-L5 segments in 13 decerebrate, T10-spinalized, unanesthetized, and paralyzed adult female rats in estrus were searched for neurons responsive to gentle mechanical stimulation of the cervix The 87 neurons found were then further tested for their responses to gentle mechanical stimulation of the skin and to distension of both uterine horns, distension of the colon, and shearing stimulation of the colon and vaginal canal 3 Neurons responsive to cervix stimulation, primarily by excitation, were readily found in the ventral part of the dorsal horn in T13-L1 and throughout the dorsal horn in L6-S2 Cervix-responsive neurons were less readily found throughout the dorsal horn in L4-L5, where 25% were inhibited by the stimulation All but one neuron had cutaneous receptive fields 4 The 30 cervix-responsive neurons in T13-L1 had large bilateral cutaneous receptive fields covering the perineum and hind-limbs Most (76%) also responded, primarily by excitation, to uterine distension, as well as to colonic stimulation (59%) More than half were activated by both types of stimulation 5 The 33 cervix-responsive neurons in L6-S2 had cutaneous receptive fields in the same regions as those in T13-L1, but generally smaller, particularly for neurons in the dorsal part of the dorsal horn, many of whose receptive fields were confined to the perineum The L6-S2 neurons also exhibited less convergent input from other visceral structures, particularly the uterus Fewer neurons (42%) responded to uterine distension, mostly by being inhibited, whereas about the same proportion (51%) responded with excitation to colonic stimulation Only 24% responded to both uterus and colon 6 All 24 cervix-responsive neurons in medial L4-L5 had small cutaneous receptive fields on the toes, and the neurons received less convergent input from other visceral structures (25% from the uterus, 33% from the colon, 13% from both) 7 These results indicate the presence of an extensive system of neurons throughout the caudal spinal cord of the rat, concentrated in separated thoracolumbar and lumbosacral segments, that is concerned with input from the reproductive tract(ABSTRACT TRUNCATED AT 400 WORDS)

P. D. Wall

Papers

Neuronal responses to stimulation of the cervix, uterus, colon, and skin in the rat spinal cord.