Chronic NGF treatment induces somatic hyperexcitability in cultured dorsal root ganglion neurons of the rat

Abstract

Adult rat dorsal root ganglion (DRG) neurons cultured in the presence of 100-ng/mL NGF were reported to show spontaneous action potentials in the cell-attached recording. In this study, underlying mechanisms were examined in the whole-cell and outside-out voltage clamp recording. In 75% neurons with on-cell firing, transient inward current spikes were repetitively recorded in the voltage clamp mode at -50 mV in the whole-cell configuration (named "Isp"). Isp with stable amplitudes occurred in an all-or-none fashion, and was abolished by TTX (< 100 nM), lidocaine (< 1 mM) and a reduction of extracellular Na+ (154 to 100 mM) in an all-or-none fashion, suggesting that Isp reflects spontaneous dicharges occurring at the loosely voltage-clamped regions. Isp was also observed in the excised outside-out patches and the kinetics and the sensitivity to TTX and lidocaine resembled those in the whole-cell. Spontaneous action potentials were also recorded in the current clamp mode. Small subthreshold spikes often preceded the action potentials. When the localized discharge affected a whole-somatic membrane potential to overcome a threshold, the action potential generated. These results indicate that the triggering sources of the action potential exist in the somatic membrane itself in NGF-treated DRG neurons.