Do Developing Merkel Cells in Vibrissal Tactile Receptors Provide a Template for Pattern Formation in the Trigeminal System?

The trigeminal pathway in rodents has served as an important model for studying pattern formation in the central nervous system. In this pathway there is a topographic point-to-point relation between the array of mystacial vibrissae on the whisker pad and their central projections in the barrel-field of the somatosensory cortex (Woolsey and Van der Loos, 1970; Welker, 1976; Belford and Killackey, 1980). Among the peripheral receptor sites the aggregates of Merkel cells, which are involved in tactile sensation in the vibrissal follicles, have been proposed as candidates for the master pattern or template for the central maps (Killackey, 1980). Support for this idea would be strengthened if the development of Merkel cells in the vibrissae should occur independently of retrograde influences within the whisker-to-barrel pathway. To test this we have investigated in the rat the effects of neonatal deafferentation of the whisker pad on Merkel cell development in the vibrissae using the quinacrine fluorescence technique (Nurse et al., 1983). Merkel cells are also present in the overlying whisker pad epidermis and these provided an additional population for comparing the effects of denervation. Since the method permits rigorous quantification of Merkel cell populations, this study was expected to address further the controversial issue of the role of sensory nerves on the development and maintenance of Merkel cells in different epithelial locations (Nurse et al., 1984).