One major topic in epilepsy is factors contributing to neuronal excitability. This chapter considers depolarizing sources from cationic currents. These ion channels of the TRP-type are permeable to Na, K and sometimes Ca, and show a slow time dynamics. They can therefore provide the dendrites with integrative properties over seconds and perhaps even minutes. This makes them powerful as integrators of synaptic input. Further, their activation depends to a large degree on intracellular calcium. They may therefore during seizures become strongly activated and thereby further contribute to epileptogenic activity directly by depolarization and indirectly by their calcium permeability. Cationic currents are widely distributed throughout the nervous system, including cortical, cerebellar and subcortical neurons. This chapter describes the work in entorhinal cortex and, specifically, the plateau firing characteristics found in pyramidal cells of layer V. These cells show persistent action potential firing at plateaus, which may last over ten minutes. Intriguingly, these plateaus are graded in that input, synaptic or by current injection, can shift them up and down in frequency. After the original finding, graded plateaus have been found also in perirhinal cortex and amygdala. Functionally, cationic neuronal integrator capacity has been shown to be involved in sensory-motor integration. Finally, anticonvulsants like lamotrigine and phenytoin have been found to reduce depolarizations involving cationic currents. Cation currents may therefore be targets in treatments of epilepsy.
Elsevier, 2008. 215-231 p.