- By using the fluorescent dye quinacrine as a marker for the Merkel cells in rat touch domes we have shown that denervation results in a progressive reduction in the number of these cells to a level that remains relatively constant at about 40% of that present at the time of denervation. The time-course of quinacrine fluorescent cell changes after denervation could be described by assuming that (i) there are two populations of quinacrine fluorescent cells, one labile and the other stable, and (ii) the labile population is the one most sensitive to denervation and disappears exponentially with a half-time of ca 10 days. It appeared that this time-course of decay of the labile quinacrine fluorescent cells was the same whether the denervation was performed during the period of postnatal development studied (at 7 and 14 days), when normally Merkel cells are rapidly added to the dome, or later (at 35 and 60 days) when the adult population is virtually established. Correlative electron microscopic studies confirmed that quinacrine fluorescent cell counts reflect fairly accurately the Merkel cell population in denervated domes. These quantitative findings based on the use of quinacrine to visualize the entire Merkel cell population of touch domes show that the normal development and maintenance of these cells are trophically dependent on sensory nerves, although a subpopulation may persist even in long-term denervated domes. In addition, the similarity of the first order rate constant for the decay of quinacrine fluorescent cells after denervation and for the normal generation of quinacrine fluorescent cells suggests that the labile Merkel cell population is one that turns over continuously in the normally innervated touch dome.