Time course effect and sequential morphological changes of subepidermal nerve fibers in guinea pig skin after application of histamine ointment: a laser scanning confocal fluorescence microscopic and electron microscopic study.

Abstract

This study was undertaken to elucidate the morphological effects of histamine on subepidermal nerve fibers. A 10% histamine ointment was topically applied to the back skin of 17 adult male Hartley guinea pigs. Biopsy specimens were obtained at times from 5 min to 24 h, and were examined by conventional immunofluorescence (IF), laser scanning confocal fluorescence microscopy (LSCM) and transmission electron microscopy. On IF and LSCM, marked diminutions in the immunoreactivity of protein gene product 9.5-immunoreactive (PGP 9.5-IR) fibers as well as of substance P-immunoreactive (SP-IR) and calcitonin gene-related peptide-immunoreactive (CGRP-IR) substances were observed 5 min after histamine application. By 30 min, immunoreactivity of PGP 9.5, SP and CGRP was completely lost. By 2 h, however, immunoreactivity of PGP 9.5-IR fibers and CGRP-IR substances started to show recovery. By 4 h, immunoreactivity of PGP 9.5, SP and CGRP had almost recovered, but the recovery time for each substance was slightly different (PGP 9.5 first, CGRP next, and SP last). By 6 h after histamine application, immunoreactivity of all these substances had fully recovered. Ultrastructurally, 5 min after histamine application, axonal and mitochondrial swelling and glycogen deposition were seen in the axons of subepidermal nerve fibers. By 30 min, severe axonal degeneration had occurred in some of the axons. It was only by 4 to 6 h that almost normal ultrastructural features were observed. Schwann cells and perineurial cells did not show any pathological changes. These findings demonstrate that 10% histamine ointment produced organic changes in the axons in the subepidermal nerve fibers of guinea pig skin, but these morphological changes were short-lived, reversible and transitory.