Morphological description of a possible nerve-eosinophilic granule cell relationship in the rainbow trout small intestine

This investigation examined a morphological relationship between the eosinophilic granule cells (EGC) of the rainbow trout intestine and intrinsic non-myelinated nerves of the intestinal mucosa. Adult fish were injected intraperitoneally with capsaicin, substance P, serotonin, bovine serum albumin or saline vehicle alone. A significant proportion of the EGCs were found to be in close association with non-myelinated enteric nerves in both control and experimental tissues. Both capsaicin and substance P induced ultrastructural changes in FCCs of both the stratum compactum and the lamina propria. Serotonin, bovine serum albumin and saline had no effect on EGC morphology. Upon stimulation with capsaicin or substance P morphological and distributional changes to the EGC population take place. There were no significant changes in the number of granule cells with serotonin or the controls. EGCs appear to be closely associated with the intrinsic non-myelinated nerves of the trout intestine being in both close apposition and possibly stimulated by capsaicin. The degranulatory actions of capsaicin and substance P suggest that an endogenous substance P-like compound is the likely mediator. (Abstract shortened by UMI.).