ABSTRACT
Title
Role of NOP receptors in the decrease of mucosal mast cells caused by acute stress in the rat colon
Authors
G. Morini1, M. Massi2, D. Grandi1, R. Guerrini3
1Dept. of Human Anatomy, Pharmacology and Forensic Medicine, University of Parma, Parma, Italy; 2 Dept. of Experimental Medicine and Public Health, University of Camerino, Camerino, Italy; 3 Dept. of Pharmaceutical Sciences and Biotechnology Center, University of Ferrara, Ferrara, Italy.
1Dept. of Human Anatomy, Pharmacology and Forensic Medicine, University of Parma, Parma, Italy; 2 Dept. of Experimental Medicine and Public Health, University of Camerino, Camerino, Italy; 3 Dept. of Pharmaceutical Sciences and Biotechnology Center, University of Ferrara, Ferrara, Italy.
Abstract
A great deal of evidence supports a key role of mucosal mast cells (MMC) in the development of stress-related gastrointestinal disturbances. The neuropeptide nociceptin/orphanin FQ (N/OFQ), acting on the N/OFQ peptide (NOP) receptor, both widely distributed in the central and the peripheral nervous system, is involved in the modulation of stress-related behaviour. Evidence is provided that N/OFQ exerts anti-stress and anxiolytic-like actions.
The present study is aimed to evaluate the effect of acute exposure to cold restraint stress and peripheral infusion of N/OFQ on the density of mucosal mast cells in the distal colon of adult male Wistar rats. N/OFQ was continuously administered subcutaneously via Alzet mini-osmotic pumps at the doses of 0.1, 1 and 10 µg/kg/h, 0.93 µl/h for 4 hours and at the dose of 1 µg/kg/h for 4 hours, 52 hours, 7 days and 14 days. Control rats received saline. Stress was induced by restraining the rats into individual wire-mesh restraint cages in a cold room at 3 °C for 3 h. Mucosal mast cells (MMC) were identified immunohistochemically with a monoclonal antibody to rat mast cell protease (RMCP) II. In saline-infused non-stressed rats, MMCs were distributed in the lamina propria throughout the entire thickness of the colonic mucosa, their number being 63.3 ± 3.9/mm2. Exposure to acute cold-restraint stress caused a decrease in their number by 54% (n=5, P<0.01). The effect of continuous infusion of N/OFQ was dose- and time-dependent. Infusion of N/OFQ, 0.1-10 µg/kg/h for 4 hours, resulted in a dose-dependent decrease in MMC number. The maximal decrease (69% , n=5, P<0.01) was obtained with N/OFQ at 1 µg/kg/h and it was slightly higher than that observed in saline-infused stressed rats. There was no further significant decrease in MMC number with the higher dose (10 µg/kg/h) while at the lower dose (0.1 µg/kg/h), the peptide infusion did not result in significant changes in MMC number. Following the infusion of N/OFQ at 1 µg/kg/h for 4 h and 52 h, MMC density was decreased to comparable extent, while after 7 and 14 day continuous infusion, MMC density returned to values observed in saline-infused non-stressed rats.
Present results provide evidence that acute stress causes a decrease in the density of MMCs in the rat colonic mucosa and that the effect of acute stress was mimicked by short-term peripheral infusion of N/OFQ. In contrast to the inhibitory effect presently observed in the colon, both acute stress and peripherally infused N/OFQ promoted an intense increase in MMC density in the rat gastric fundus. It is noteworthy that both in the distal colon and in the gastric fundus, N/OFQ mimicked the effect of stress, suggesting that the endogenous N/OFQ/NOP receptor system contribute to the influence of stress on MMC recruitment.
The present study is aimed to evaluate the effect of acute exposure to cold restraint stress and peripheral infusion of N/OFQ on the density of mucosal mast cells in the distal colon of adult male Wistar rats. N/OFQ was continuously administered subcutaneously via Alzet mini-osmotic pumps at the doses of 0.1, 1 and 10 µg/kg/h, 0.93 µl/h for 4 hours and at the dose of 1 µg/kg/h for 4 hours, 52 hours, 7 days and 14 days. Control rats received saline. Stress was induced by restraining the rats into individual wire-mesh restraint cages in a cold room at 3 °C for 3 h. Mucosal mast cells (MMC) were identified immunohistochemically with a monoclonal antibody to rat mast cell protease (RMCP) II. In saline-infused non-stressed rats, MMCs were distributed in the lamina propria throughout the entire thickness of the colonic mucosa, their number being 63.3 ± 3.9/mm2. Exposure to acute cold-restraint stress caused a decrease in their number by 54% (n=5, P<0.01). The effect of continuous infusion of N/OFQ was dose- and time-dependent. Infusion of N/OFQ, 0.1-10 µg/kg/h for 4 hours, resulted in a dose-dependent decrease in MMC number. The maximal decrease (69% , n=5, P<0.01) was obtained with N/OFQ at 1 µg/kg/h and it was slightly higher than that observed in saline-infused stressed rats. There was no further significant decrease in MMC number with the higher dose (10 µg/kg/h) while at the lower dose (0.1 µg/kg/h), the peptide infusion did not result in significant changes in MMC number. Following the infusion of N/OFQ at 1 µg/kg/h for 4 h and 52 h, MMC density was decreased to comparable extent, while after 7 and 14 day continuous infusion, MMC density returned to values observed in saline-infused non-stressed rats.
Present results provide evidence that acute stress causes a decrease in the density of MMCs in the rat colonic mucosa and that the effect of acute stress was mimicked by short-term peripheral infusion of N/OFQ. In contrast to the inhibitory effect presently observed in the colon, both acute stress and peripherally infused N/OFQ promoted an intense increase in MMC density in the rat gastric fundus. It is noteworthy that both in the distal colon and in the gastric fundus, N/OFQ mimicked the effect of stress, suggesting that the endogenous N/OFQ/NOP receptor system contribute to the influence of stress on MMC recruitment.