Somatic pain sensitivity under the injury of gastric mucosa and small intestine induced by cold-restraint stress in rats

Visceral pain is one of the symptoms of gastrointestinal diseases, including peptic ulcer. Unlike somatic pain, which has a precise localization, visceral pain is diffuse and can radiate to somatic areas. Understanding the general patterns of interaction between visceral and somatic pain sensitivity is important for developing methods for early diagnosis of gastrointestinal diseases. The aim of the study was to investigate somatic pain sensitivity under a pathological condition in the stomach and small intestine induced by an ulcerogenic stressor (cold restraint, 3 h, 10 °C). Somatic pain sensitivity was evaluated by paw licking latency in the hot plate test (PLL). In rats starved for 24 h, cold-restraint stress caused the formation of gastric erosions and small intestine injury. Stress-induced injury of the stomach and small intestine in starved rats was accompanied by an increase in PLL 4 and 24 hours after completion of the action of the ulcerogenic stressor suggesting a decrease of somatic pain sensitivity (somatic hypoalgesia). In non-starved rats, the ulcerogenic stressor did not lead to the formation of pronounced hemorrhagic erosions in the stomach or injury of the small intestine, while no change in somatic pain sensitivity was observed. Thus, somatic hypoalgesia induced by cold restraint may be an indicator of a pathological process in the gastrointestinal tract.