Tetrodotoxin-resistant dendritic spikes in avian Purkinje cells

Electrophysiological evidence for the existence of dendritic spikes in the Purkinje cells of pigeon cerebellar cortex is presented. Intradendritic records indicate that the electroresponsive properties of the dendrites linger after voltage-dependent sodium and potassium conductances are reduced by superfusion of the cortex with Ringer's solution containing 20 mug/ml tetrodotoxin and 5 mM 3-aminopyridine. Dendritic spikes could be evoked, in the complete absence of activity from all cerebellar afferents and from the soma and axon of the Purkinje cells, by direct electrical activation of the surface of the cerebellar cortex or by intracellular injection of current via the recording electrode. The denritic electroresponsiveness was blocked by superfusion with 20 mM Mn2+ or Co2+. It is thus concluded that dendrites of Purkinje cells in birds are capable of generating calcium-dependent spikes. The possible role of such a calcium current in neuronal function is discussed.