Rapid plasticity at inhibitory and excitatory synapses in the hippocampus induced by ictal epileptiform discharges.

Epileptic seizures can induce pathological processes of plasticity in the brain that tend to promote the generation of further seizures. However, the immediate impact of epileptic seizures on cellular excitability remains poorly understood. In order to unravel such early mechanisms of epilepsy-induced plasticity, we studied synaptic transmission before and shortly after three ictal discharges induced by transient elevation of extracellular K(+) in mouse hippocampal slices.

Hyperexcitability of CA3 pyramidal cells in mice lacking the potassium channel subunit Kv1.1.

Purpose: To investigate further the membrane properties and postsynaptic potentials of the CA3 pyramidal cells in mice that display spontaneous seizures because of a targeted deletion of the Kcna1 potassium channel gene (encoding the Kv1.1 protein subunit).

Methods: Intracellular recordings were obtained from CA3 pyramidal cells in hippocampal slices prepared from Kcna1-null and control littermates.

Lack of vesicular zinc in mossy fibers does not affect synaptic excitability of CA3 pyramidal cells in zinc transporter 3 knockout mice.

Zinc is found throughout the CNS in synaptic vesicles of glutamatergic neurons and has been suggested to have a modulatory role in the brain because of its interaction with voltage- and ligand-gated ion channels. We took advantage of zinc transporter 3 knockout mice, which lack vesicular zinc, to study the possible physiological role of this heavy metal in hippocampal mossy fiber neurotransmission. We examined postsynaptic responses evoked by mossy fiber activation, recorded in CA3 pyramidal cells in hippocampal slices prepared from zinc transporter 3 knockout and wild-type mice.

GABA(A)-dependent chloride influx modulates reversal potential of GABA(B)-mediated IPSPs in hippocampal pyramidal cells.

Changes in intracellular chloride concentration, mediated by chloride influx through GABA(A) receptor-gated channels, may modulate GABA(B) receptor-mediated inhibitory postsynaptic potentials (GABA(B) IPSPs) via unknown mechanisms. Recording from CA3 pyramidal cells in hippocampal slices, we investigated the impact of chloride influx during GABA(A) receptor-mediated IPSPs (GABA(A) IPSPs) on the properties of GABA(B) IPSPs. At relatively positive membrane potentials (near -55 mV), mossy fiber--evoked GABA(B) IPSPs were reduced (compared with their magnitude at -60 mV) when preceded by GABA(A) receptor--mediated chloride influx.

GABAA-Dependent chloride influx modulates GABAB-mediated IPSPs in hippocampal pyramidal cells.

The relationship between postsynaptic inhibitory responses [the fast GABA(A)-mediated inhibitory postsynaptic potential (IPSP) and the slow GABA(B)-mediated IPSP] were investigated in hippocampal CA3 pyramidal cells. Mossy fiber-evoked GABA(B)-mediated IPSPs were, paradoxically, of greater amplitude in cells with resting membrane potential of -62 mV (13.6 +/- 0.