The phorbol ester PDBu reduces firing in tonic neurons. A, Direct activation of PKC with phorbol 12,13-dibutyrate (PDBu, 0.5 μM, bottom trace) prolonged the APs and reduced firing (top trace, control) in tonic firing neurons. Firing in response to a current injection 600 ms long and 250 pA in intensity. B, Average firing before and after PDBu in 4 neurons. C, Dependence of firing on stimulus intensity for experiment in B, before (Control, empty circles) and after PDBu (0.5 μM, filled circles).