An electrophysiological analysis of deep cerebellar nuclei, with particular focus on Kv3 channels

Abstract

Deep cerebellar nuclei (DCN) form three symmetrical, bilateral nuclei, deep within the white matter of the cerebellum and represent the sole output of the cerebellum to the central nervous system. Although innervated by spontaneously active inhibitory Purkinje cells, DCN neurons also fire action potentials spontaneously at a relatively high frequency, a property attributed to Kv3 channels. In the present study, an electrophysiological approach was carried out on DCN neurons, the purpose of which was to investigate the properties and elucidate the involvement of Kv3 channels. Using whole-cell patch clamp techniques, electrophysiological recordings from the dentate nucleus were obtained from coronal cerebellar slices of Wistar rats (P 12) in both current and voltage clamp modes. Kv3-mediated currents were investigated in the presence of tetrodotoxin (1 mM), by applying low concentration tetraethyl ammonium (TEA) (100 mM). Current-clamp recordings revealed a population of tonically firing neurons, exhibiting a maximum action potential firing frequency of 18.1+ 6.9 Hz and a steady firing frequency of 14.2+4.8 Hz (n 1⁄4 6). These neurons were also shown to exhibit a mean action potential amplitude of 48.7+ 9.5 mV, mean half-width of 2.9+ 1 ms and mean afterhyperpolarization amplitude of 19.6+ 7.5 mV. Depolarizing sag (indicative of the Ih current), followed by rebound depolarization, was observed in all neurons. Voltageclamped neurons revealed a voltage-dependent slowly inactivating outward current with a peak amplitude of 1538.5+1096.6 pA (n 1⁄4 10). Application of low concentration TEA (100 mM) reduced the current by a statistically significant 19.4+13.4% (P, 0.05; paired t-test) and this effect was reversible. Application of a Boltzmann function yielded a V1/2 value of 9.9 mV for the TEA-sensitive current. As Kv3 channels have been previously localized in DCN, the results suggest that the TEA-sensitive current ( 20% of the total outward current exhibited) is mediated by Kv3 channels.