Potentiation of frequency by ATP is dose dependent. A, ∫XII nerve recordings from a medullary slice preparation illustrating the response to local application of 0.01 and 0.1 mm ATP to site of maximum ATP sensitivity in the VLM. B, Group data showing the dose-dependent effects of ATP (0.01, 0.1, and 1 mm; n = 5, 6, and 4, respectively) on frequency. Rel. Freq., Relative frequency. *Significantly different from control; #significantly different from 0.01 mm ATP response. Error bars indicate SEM.