The development of receptors in the glabrous forepaw skin of pouch young opossums

Abstract

To determine the state of development of mechanoreceptors during the period in which central neurol regions can be altered by peripheral lesions, the distribution of terminal neurites and specialized receptors was examined in the glabrous forepaw skin of a developmental series of pouch young opossums, using the silver stain of Sevier & Munger (1965) and electron microscopic observations. At 10 days after birth bundles of neurites approach the dermal-epidermal junction, but neither neurites nor receptors are seen in the epidermis. Some neuntes enter the epidermis by 20 days; by 25 days developing Merkel cells are seen in the epidermis; at 30 days mature Merkel cells and primordial Pacinian corpuscles are present, respectively, in the epidermis and deep dermis; at 42 postnatal days dermal papillae containing neurites were observed at the dermal-epidermal junction, which may be developing Meissner corpuscles. Numbers of neurites, and of their branchings, increase up to 60 days; as do the size, number and degree of differentiation of the Pacinian corpuscles. The critical period for the effects of peripheral lesions upon the morphology of the cuneate-gracile nuclear complex, as well as the times of initial massive synaptogenesis, cell migration and differentiation in this first and second order mechanosensory synaptic region, are completed prior to the innervation of the epidermis and the appearance of specialized mechanoreceptors. Thus input from epidermal and specialized receptors cannot be responsible for guidance of these developmental processes.