Reinnervation of the rat touch dome restores the Merkel cell population reduced after denervation

By using the fluorescent dye quinacrine as a marker for the Merkel cells in the rat touch dome, we previously showed that a sustained denervation of the dome causes a rapid and persistent loss of about 60% of its Merkel cells [Nurse, Macintyre and Diamond (1984) Neuroscience 11, 521-533]. We now show that if the sensory nerves to the skin are crushed (or cut) in 2-week old pups and allowed to regenerate, the Merkel cell population within touch domes shows a biphasic response; there is an initial loss of Merkel cells associated with the early phase of denervation, followed by an increase, associated with the phase of reinnervation. Physiological tests revealed that many (though not all) domes within initially deafferented skin had become functionally reinnervated and had their Merkel cell numbers either wholly or partially restored some 40-100 days post operatively. In one case an adult reinnervated dome, that appeared normal physiologically and by its complement of quinacrine fluorescent (Merkel) cells, also had normal histological features in toluidine blue sections and normally innervated Merkel cells in the electron microscope. These results, based on the use of quinacrine to visualize the Merkel cell population in the touch dome, suggest that sensory nerves may induce the differentiation of new Merkel cells in domes where these cells have become reduced after denervation.