Simulated responses of cerebellar Purkinje cells are independent of the dendritic location of granule cell synaptic inputs

Cerebellar Purkinje cell responses to granule cell synaptic inputs were examined with a computer model including active dendritic conductances. Dendritic P-type Ca²⁺ channels amplified postsynaptic responses when the model was firing at a physiological rate. Small synchronous excitatory inputs applied distally on the large dendritic tree resulted in somatic responses of similar size to those generated by more proximal inputs. In contrast, in a passive model the somatic postsynaptic potentials to distal inputs were 76% smaller. The model predicts that the somatic firing response of Purkinje cells is relatively insensitive to the exact dendritic location of synaptic inputs. We describe a mechanism of Ca²⁺-mediated synaptic amplification, based on the subspiking threshold recruitment of P-type Ca²⁺ channels in the dendritic branches surrounding the input site.