Approximately 1% of the population suffers from a chronic seizure disorder, and of these temporal lobe epilepsy is the most common epileptic syndrome. one of the most widely accepted animal models of human temporal lobe epilepsy is referred to as kindling, a process in which daily low-intensity stimulation of limbic or forebrain structures gradually leads to development of limbic convulsions. Evidence suggests that the mechanisms underlying kindling involve changes in transmission at excitatory glutamatergic synapses. However, the precise mechanisms involved in kindling-induced epileptogenesis are unknown. Fast excitatory synaptic transmission at glutamatergic synapses is mediated by activation of heteromeric glutamate receptor cation channels. Preliminary studies indicate that kindling results in a selective reduction in one of four known subunits of the AMPA subtype of glutamate receptor, termed GluR2. This effect occurs only in piriform cortex, a brain region that has been implicated as playing a major role in kindling. Interestingly, the GluR2 AMPA receptor subunit plays a unique role in reducing the calcium permeability of AMPA receptors. AMPA receptors that contain GluR2 are calcium impermeable whereas AMPA receptors that lack GluR2 are highly permeable to calcium. If the kindling-induced reduction in GluR2 leads to an increase in calcium permeability of AMPA receptors, this could play an important role in induction of calcium-dependent forms of synaptic plasticity that eventually lead to epileptogenesis. However, it is not known whether the kindling-induced change in GluR2 leads to a physiologically relevant change in AMPA receptor function. A series of experiments is proposed in which electrophysiological techniques will be used to test the hypothesis that the kindling-induced reduction in GluR2 leads to a functionally relevant change in AMPA receptor subunit composition and an increase in AMPA receptor calcium permeability. Another change that occurs in glutamatergic systems with kindling is a long lasting increase in extracellular glutamate concentrations. This may be mediated by a kindling-induced reduction in levels of glutamate transport proteins. However, this hypothesis has not been tested directly. Three glutamate transport proteins have now been cloned. Antibodies that specifically react with each of the cloned glutamate transporters will be used with quantitative western blotting to test the hypothesis that kindling reduces levels of glutamate transport proteins. A series of experiments will then be performed to test the hypothesis that this leads to a functionally relevant reduction in glutamate uptake. If we find that kindling induces physiologically relevant changes in levels of GluR2 and transport proteins, we ultimately hope to determine the overall impact of these changes on transmission through specific neuronal circuits that are known to play an important role in temporal lobe epilepsy.
