The hyperpolarization-activated cation current IH regulates the electrical activity of many excitable cells, but its precise function varies across cell types. The antiepileptic drug lamotrigine (LTG) recently was shown to enhance IH in hippocampal CA1 pyramidal neurons, revealing a potential anticonvulsant mechanism, as IH can dampen dendrito-somatic propagation of excitatory postsynaptic potentials in these cells. However, IH also is expressed in many hippocampal interneurons that provide synaptic inhibition to CA1 pyramidal neurons, and thus, IH modulation may indirectly regulate inhibitory control of principal cells via direct modulation of interneuron activity. Whether IH in hippocampal interneurons is sensitive to modulation by LTG, and how this may affect synaptic inhibition of pyramidal cells has not been investigated. In this study, we examined the effects of LTG on IH and spontaneous firing of area CA1 s.o. interneurons, and on spontaneous inhibitory postsynaptic currents (sIPSCs) in CA1 pyramidal neurons in immature rat brain slices. LTG (100 µM) significantly increased IH in the majority of interneurons, and depolarized interneurons from rest, promoting spontaneous firing. LTG also caused an increase in the frequency of spontaneous (but not miniature) IPSCs in pyramidal neurons without significantly altering amplitudes or rise and decay times. These data indicate that IH in CA1 interneurons can be increased by LTG, similarly to IH in pyramidal neurons, that IH enhancement increases interneuron excitability, and that these effects are associated with increased basal synaptic inhibition of CA1 pyramidal neurons.

Kv2.1 channels mediate cell death–enabling loss of cytosolic potassium in neurons following plasma membrane insertion at somatodendritic clusters. Overexpression of the carboxyl terminus (CT) of the cognate channel Kv2.2 is neuroprotective by disrupting Kv2.1 surface clusters. Here, we define a seven–amino acid declustering domain within Kv2.2 CT (DP-2) and demonstrate its neuroprotective efficacy in a murine ischemia-reperfusion model. TAT-DP-2, a membrane-permeable derivative, induces Kv2.1 surface cluster dispersal, prevents post-injurious pro-apoptotic potassium current enhancement, and is neuroprotective in vitro by disrupting the association of Kv2.1 with VAPA. TAT-DP-2 also induces Kv2.1 cluster dispersal in vivo in mice, reducing infarct size and improving long-term neurological function following stroke. We suggest that TAT-DP-2 induces Kv2.1 declustering by disrupting Kv2.1-VAPA association and scaffolding sites required for the membrane insertion of Kv2.1 channels following injury. We present the first evidence of targeted disruption of Kv2.1-VAPA association as a neuroprotective strategy following brain ischemia.

Purpose Cerebral hypoxia is a major cause of neonatal seizures, and can lead to epilepsy. Pathological anatomical and physiological changes in the dentate gyrus have been associated with epileptogenesis in many experimental models, as this region is widely believed to gate the propagation of limbic seizures. However, the consequences of hypoxia-induced seizures for the immature dentate gyrus have not been extensively examined. Methods Seizures were induced by global hypoxia (5–7% O2 for 15 minutes) in rat pups on postnatal day 10. Whole-cell voltage-clamp recordings were used to examine A-type potassium currents (IA) in dentate granule cells in hippocampal slices obtained 1–17 days after hypoxia treatment. Key Findings Seizure-inducing hypoxia resulted in decreased maximum IA amplitude in dentate granule cells recorded within the first week but not at later times after hypoxia treatment. The decreased IA amplitude was not associated with changes in the voltage-dependence of activation or inactivation removal, or in sensitivity to inhibition by 4-aminopyridine (4-AP). However, consistent with the role of IA in shaping firing patterns, we observed in the hypoxia group a significantly decreased latency to first spike with depolarizing current injection from hyperpolarized potentials. These differences were not associated with changes in resting membrane potential or input resistance, and were eliminated by application of 10 mM 4-AP. Significance Given the role of IA to slow action potential firing, decreased IA could contribute to long-term hippocampal pathology after neonatal seizure-inducing hypoxia by increasing DG cell excitability during a critical window of activity-dependent hippocampal maturation.