Figure 4. Urothelial and non-urothelial neurons exhibit different intrinsic electrophysiological properties.

Differential interference contrast (DIC) and epifluorescence were used to identify DiI-positive PN bladder neurons that were retrogradely labeled by the IPar (A) or IVes (B) method. Passive and active characteristics were determined, and a comparison between neuron types revealed several differences, as shown by representative traces in (C). Both non-urothelial (IPar-labeled) and urothelial (IVes-labeled) neurons exhibited an inflected somal spike pattern in the repolarization phase (D). Resting membrane potential was similar between groups (E), but rheobase was significantly lower in urothelial than in non-urothelial neurons (F). AP threshold (G) and AP width (H) did not differ and 90% (9/10) of the neurons in each grouped fired single APs (I), as shown by the red traces in (C). Urothelial neurons, however, were more likely to fire rebound APs than non-urothelial neurons (J), as indicated by the arrow in the lower panel of (C). Rebound APs may be a result of significantly higher hyperpolarization-activated “sag” potential in urothelial versus non-urothelial neurons (K), as shown by the blue traces in (C). Sag potential was measured as the difference in potentials between the black and white triangles (C). Finally, input resistance was lower (L) and cell capacitance higher (M) in non-urothelial neurons. N=10 neurons obtained from 3 animals/group. * indicates P<0.05; ** indicates P<0.01; *** indicates P<0.001.