Localized calcium signalling and neuronal integration in cerebellar Purkinje neurones.

The use of high resolution imaging techniques has revealed new forms of dendritic signal integration in neurones. In contrast to electrical signals that have a more widespread influence on the cell, brief Ca2+ transients resulting from synaptic activation are often restricted to a small part of the dendritic tree. In cerebellar Purkinje neurones, different levels of Ca2+ signalling have been observed that may involve the entire neurone or be spatially limited to fine dendritic structures. The Ca2+ signals accompanying subthreshold excitatory postsynaptic potentials resulting from stimulation of the excitatory parallel fibre input can be restricted to regions as small as a spiny dendrite or a single dendritic spine. With the recruitment of increasing numbers of inputs there is a summation of Ca2+ signals in highly restricted regions of the spiny dendrites that is independent of electrical summation at the soma. Of a number of potential sources that could provide the Ca2+ responsible for the postsynaptic changes, Ca2+ entry through voltage-gated Ca2+ channels has received the most support, although other sources like Ca2+ entry through ligand-gated channels and especially Ca2+ release from intracellular stores need to be considered.