The sensory innervation of the nasal glabrous skin in the short-nosed bandicoot (Isoodon macrourus) and the opossum (Didelphis virginiana).

Abstract

The glabrous skin at the anterior end of the snout of the short-nosed bandicoot and the American opossum was investigated by electron microscopy. In both species of animals, this region was lined by skin with broad epidermal pegs, innervated by three types of intraepidermal nerves. These were intraepidermal nerves which penetrated the epidermis up to the level of the stratum spinosum or the stratum granulosum, intraepidermal nerves in the basal layer of the epidermis partially surrounded by Schwann cell lamellae and intraepidermal nerves associated with Merkel cells. There were two types of free nerve endings in the dermis. The first type was derived from the deep dermal nerve plexus and had the typical characteristics of nerve terminals such as mitochondria, vesicles, irregularly arranged neurotubules and neurofilaments, and glycogen granules. There was a one-to-one relationship between Schwann cell lamellae and these nerve terminals. The second type of nerve ending was brush-like and the ends of the 'brushes' were enclosed in groups by a single Schwann cell lamella. Encapsulated nerve endings in the two types of animals differed in their structure. In the bandicoot, they consisted of a nerve terminal which had one to three branches. These terminals were rounded in profile and were surrounded by Schwann cell lamellae in a stack-like arrangement. An unusual finding was that the terminal sometimes left the corpuscle and made contact with the basal lamina of the epidermis before passing into its basal layer. These corpuscles did not have a perineural capsule. In the opossum, however, simple corpuscles with inner cores completely surrounded by a perineural capsule were seen. The glabrous skin of both types of animals was innervated with Eimer's organs consisting of intraepidermal nerves, Merkel cell nerve endings and encapsulated end-organs, as well as two types of dermal nerve endings.