Firing frequency and entrainment maintained in primary auditory neurons in the presence of combined BDNF and NT3

Primary auditory neurons rely on neurotrophic factors for development and survival. We previously determined that exposure to brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT3) alters the activity of hyperpolarization-activated currents (I(h)) in this neuronal population. Since potassium channels are sensitive to neurotrophins, and changes in I(h) are often accompanied by a shift in voltage-gated potassium currents (I(K)), this study examined I(K) with exposure to both BDNF and NT3 and the impact on firing entrainment during high frequency pulse trains. Whole-cell patch-clamp recordings revealed significant changes in action potential latency and duration, but no change in firing adaptation or total outward I(K). Dendrotoxin-I (DTX-I), targeting voltage-gated potassium channel subunits K(V)1.1 and K(V)1.2, uncovered an increase in the contribution of DTX-I sensitive currents with exposure to neurotrophins. No difference in Phrixotoxin-1 (PaTX-1) sensitive currents, mediated by K(V)4.2 and K(V)4.3 subunits, was observed. Further, no difference was seen in firing entrainment. These results show that combined BDNF and NT3 exposure influences the contribution of K(V)1.1 and K(V)1.2 to the low voltage-activated potassium current (I(KL)). Whilst this is accompanied by a shift in spike latency and duration, both firing frequency and entrainment to high frequency pulse trains are preserved.