Extracellular calcium and action potentials of soma and dendrites of hippocampal pyramidal cells.

Calcium activity ([Ca2+]0) and focal potentials were recorded from dendritic and cell body layers of CA1 and CA3 regions of slices of hippocampal tissue. Responses were evoked by focal stimulation of afferent fiber bundles. In order to evoke a detectable decrease of [Ca2+]0, stimulation had to be intense enough to cause postsynaptic discharge of action potentials; evoking EPSPs alone was insufficient. Responses of [Ca2+] were consistently greater in stratum pyramidale than in stratum radiatum. It is concluded that in hippocampal tissue activation of soma and proximal dendritic membranes is the most important contribution to the decrease of [Ca2+]0 in response to afferent stimulation.