We ( 11) previously reported that neonatal rats subjected to MS had impaired epithelial barrier function even at the time of separation. Adult rats that are not genetically susceptible to stress can also develop similar abnormalities following exposure to a mild acute stressor if they have been subjected to neonatal MS ( 7, 37). Exposure to stress during this time results in the formation of a dysregulated axis with a compromised ability to downregulate the synthesis of corticotrophin-releasing factor (CRF), a key stress hormone ( 26).Īdult rats of a stress susceptible strain that are subjected to daily separation from the dam during the neonatal period demonstrate increased colonic permeability ( 2) and visceral hyperalgesia ( 28).
The physiological response to stress is controlled by the hypothalamic-pituitary adrenal (HPA) axis, which develops during the neonatal period. Maternal separation (MS) is a well-characterized model of early life stress used in the study of anxiety and depression ( 17, 31) as well as intestinal dysfunction ( 1, 2, 7, 28, 37). The neonatal period is an important developmental period in humans and rodents, and stress during this time can have long-lasting effects on behavior and physiology. Our study provides evidence that MS stimulates synthesis of acetylcholine, which, together with released CRF, creates a condition conducive to the development of epithelial barrier defects. These findings suggest that CRF, via CRF receptor 2, acts on cholinergic nerves to induce epithelial barrier dysfunction. Using selective receptor antagonists, we identified that CRF receptor 2 was involved in mediating this effect. In MS tissues, nonselective CRF receptor antagonism inhibited the enhanced flux, and the addition of atropine did not produce further inhibition. Since a previous study indicated that corticotrophin-releasing factor (CRF) mediates barrier dysfunction in MS pups, we examined if the two pathways were linked. Western blots and immunohistochemistry of colonic tissues demonstrated increased expression of choline acetyltransferase (ChAT) in MS pups, indicating greater synthesis of acetylcholine. The cholinergic component was greater in tissues from MS versus NS pups, suggesting that increased cholinergic activity was responsible for the MS elevated permeability. The enhanced flux was inhibited by the cholinergic muscarinic antagonist atropine and the nicotinic antagonist hexamethonium.
HRP flux was increased in MS versus NS pups. Horseradish peroxidase (HRP) flux was used to measure macromolecular permeability. On day 20, colonic tissues were removed and mounted in Ussing chambers. Pups were separated from the dam for 3 h/day ( days 4– 20) nonseparated (NS) pups served as controls. Our aim was to examine if enhanced epithelial permeability in such pups resulted from abnormal regulation by enteric nerves. Neonatal maternal separation (MS) predisposes adult rats to develop stress-induced mucosal barrier dysfunction/visceral hypersensitivity and rat pups to develop colonic epithelial dysfunction.
0 kommentar(er)
