Visualization of PGP 9.5 immunoreactive nerve terminals in the mouse snout epidermis

Intraepidermal free nerve endings were investigated in the mouse snout skin by means of an immunohistochemical procedure using a rabbit antiserum against protein gene product 9.5 (PGP 9.5). Immunoperoxidase reactivity was detected in different subtypes of intraepidermal nerves and cells. The great majority of axons observed in the stratified epithelium were varicose; a small percentage was either smooth (non-varicose) or irregularly shaped. Intraepidermal nerves ended at different levels within the epidermis, often with a terminal knob-like swelling. Various patterns of intraepidermal innervation could be distinguished. Most fibres entering the epidermis originated from large bundles running a horizontal course below the dermo-epidermal junction. Such fibres ascended vertically through the stratified epithelium in a "candelabrum-like" fashion, without emitting collaterals. Other fibres branched profusely and ended in complex intraepidermal neural networks. Less frequently, intraepidermal fibres terminated with large irregularly shaped expansions of different morphologies. Some of these were the intraepidermal continuations of axons within Meissner's corpuscles. Some fibres appeared to come into contact with PGP 9.5-immunoreactive cells (which closely resembled Merkel cells) located in the stratum basale. Rare suprabasal dendritic cells (Langerhans cells?) also became visible.