We consider here a single-compartment model of these neurons which is capable
of describing many of the known features of spike generation, particularly the
slow rhythmic pacemaking activity often observed in these cells in a variety of
species. Included in the model are ten kinds of voltage dependent ion channels
as well as calcium-dependent potassium current. Calcium dynamics includes
buffering and pumping. In sections 3-9, each component is considered in detail
and parameters estimated from voltage clamp data where possible. In the next
two sections simplified versions of some components are employed to explore the
effects of various parameters on spiking, using a systematic approach, ending
up with the following eleven components: a fast sodium current INaβ, a
delayed rectifier potassium current IKDRβ, a transient potassium current
IAβ, a low-threshold calcium current ITβ, two high threshold calcium
currents ILβ and INβ, small and large conductance potassium currents
ISKβ and IBKβ, a hyperpolarization-activated cation current IHβ, a
leak current ILeakβ and intracellular calcium ion concentration Caiβ.
Attention is focused on the properties usually associated with these neurons,
particularly long duration of action potential, pacemaker-like spiking and the
ramp-like return to threshold after a spike. In some cases the membrane
potential trajectories display doublets or have kinks or notches as have been
reported in some experimental studies. The computed time courses of IAβ and
ITβ during the interspike interval support the generally held view of a
competition between them in influencing the frequency of spiking. Spontaneous
spiking could be obtained with small changes in a few parameters from their
values with driven spiking.Comment: The abstract has been truncate