Electrophysiological properties of in vitro Purkinje cell dendrites in mammalian cerebellar slices.

Abstract

Intradendritic recordings from guinea pig Purkinje cells in vitro indicated that white matter stimulation produced large synaptic responses by the activation of the climbing afferent, but antidromic potentials did not actively invade the dendritic tree. Climbing fiber responses may be reversed in a manner similar to that at the somatic level. The reversal showed no biphasicity often seen at somatic level. Input resistance of these dendrites ranged from 15-30 M.OMEGA.. Non-linear properties seen at the somatic level for depolarizing currents were encountered. Less anomalous rectification was apparent. Repetitive firing of Purkinje cells elicited by outward DC current was analyzed. In antidromic invasion, the fast somatic potentials (s.s.) did not invade the dendrite actively. The dendritic spike bursts (d.s.b.s) interposed between the s.s. potentials were most prominent at dendritic level. Two types of voltage-dependent Ca responses were observed. At low stimulus level a plateau-like depolarization was accompanied by a prominent conductance change; further depolarization produced large dendritic action potentials. These 2 classes of response were TTX[tetrodo toxin]-resistant but were blocked by Cd, Co, Mn or D600 [methoxy verapamil] or the removal of extracellular Ca. Following blockage of the Ca conductance, plateau potentials produced by a non-inactivating Na conductance were observed mainly near the soma. This voltage-dependent conductance was probably associated with the somatic membrane. Spontaneous fiing in Purkinje cell dendrites was very similar to that observed at the soma. The amplitude of these bursts was larger at the dendritic level. These TTTX-insensitive spikes apparently were generated at multiple sites along the dendritic tree. Six ionic conductances seem involved in Purkinje cell electroresponsiveness: an inactivating and a non-inactivating Na conductance at or near the soma, a spike- and a plateau-generating Ca conductance, and voltage-dependent and Ca-dependent K currents. The possible role of these conductances in Purkinje cell integration is discussed.