The anticonvulsant lamotrigine enhances Ih in layer 2/3 neocortical pyramidal neurons of patients with pharmacoresistant epilepsy

Alterations of the hyperpolarization activated nonselective cation current (I-h) are associated with epileptogenesis. Accordingly, the second-generation antiepileptic drug lamotrigine (LTG) enhances I-h in rodent hippo campus. We directly evaluated here whether LTG fails to enhance I-h in neocortical slices from patients with pharmacoresistant epilepsy. With somatic current clamp recordings we observed that LTG depolarized the membrane potential, decreased the input resistance and increased the sag in human layer 2/3 neocortical pyramidal neurons when confounding I-Kir was blocked. In subsequent voltage clamp recordings we confirmed a LTG induced increase of I-h that was qualitatively similar to the one we found in rat neocortical and hippocampal pyramidal neurons. This increase is sufficient to curtail single excitatory postsynaptic potentials (EPSPs) and reduces their temporal summation in human neocortical pyramidal neurons under physiological conditions, i.e. without blocking any other currents, as estimated by sharp microelectrode recordings. Taken together LTG increases I-h and thereby alters neuronal excitability, even in neurons of pharmacoresistant patients. However, whether this increase fully countervails the deficits of I-h, in epileptic patients, remains elusive.