Figure 1.

Experimental (a) and model (b) DAPs and their associated calcium transients. Data taken from a whole-cell recording from the SON of a hypothalamic slice; spikes were evoked with a 5 msec depolarizing pulse and have been truncated for clarity. Left panels, Single spike followed by a DAP that is subthreshold for firing. The decay of the DAP tracks that of intracellular calcium, returning to rest with a time constant of τ = ∼1.85 sec (Roper et al., 2003). Right panels, DAP summation and the initiation of phasic activity: the stimulation protocol elicits two spikes, and the resulting summed DAP crosses spike threshold. The consequent action potentials further raise intracellular calcium, which in turn maintains the suppression of I_K,leak and so supports a regenerative plateau potential.