Study of innervation, sensory neuropeptides, and serotonin in murine contact allergic skin

Density of nerve fibers, axonal growth, calcitonin gene-related peptide (CGRP), and substance P, and serotonin immunoreactivity as well as concentration were all determined in a murine model of contact allergy. Female Balb/c mice were sensitized on the back with oxazolone and 6 days later challenged with the same antigen on the dorsal surface of the ears, while control mice received the vehicle only. Then, 24 hr postchallenge, one ear was processed for immunohistochemical staining, while the other was frozen and processed for gas chromatography-mass spectrometry or radioimmunoassay (RIA). Protein gene product 9.5 (PGP 9.5) positive nerve fibers showed a tendency to increase in inflamed ears versus control ears in epidermis as well as the dermis. Growth-associated protein-43 (GAP-43) positive fibers in the epidermis were increased (p < .01) in inflamed ears, compared with control ears, as was the case for the dermal fibers, indicating increased axonal growth. Total (epidermis and dermis) numbers of CGRP and substance P positive nerve fibers tended to increase in the inflamed skin in contrast to control skin. In contrast, RIA demonstrated a lower (p < .05) concentration of CGRP in the inflamed ears compared with controls and a tendency for substance P to decrease in concentration in eczematous ears versus controls. There was no difference in serotonin concentration, or in the number of serotonin positive mast cells, between the inflamed and control skin, whereas semiquantification of serotonin positive platelets showed an increase in the inflamed (++) compared with control ears (+). Our results indicate that 24 hr after being challenged with the antigen, at the peak of murine skin inflammation, axonal growth, sensory neuropeptides, as well as serotonin may be involved.