Normal and Pathological Function of the Dentate Gyrus

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The neuronal circuitry within the dentate gyrus is massively disrupted in temporal lobe epilepsy patients and in experimental models of this disorder. This proposal builds upon our laboratory’s previous findings, which demonstrate that the dentate gyrus circuitry within the epileptic hippocampus retains an embedded coding network of dentate granule cells which can reemerge and restore appropriate cognitive function following treatments to suppress degraded pathologic activity. The maintained competence of this embedded dentate granule cell network occurs despite the significant structural pathology which is unaffected by therapeutic interventions. In this proposal, we will build upon this foundation, and examine and manipulate dentate granule cells in both epileptic and control animals to generate a mechanistic understanding of how these epilepsy- associated disruptions to normal circuit functioning can be targeted to restore downstream, emergent properties of the hippocampus, such as learning and memory and emotional behaviors. The CENTRAL HYPOTHESIS of the present proposal is that the epilepsy-associated degradation in coding properties of dentate granule cells contributes significantly to both the cognitive and behavioral comorbidities that constitute key components of the core phenotypes of temporal lobe epilepsy. To test this Central Hypothesis, we propose to conduct a series of experiments centered on 3 SPECIFIC AIMS: Aim 1. Characterize the local circuit properties defining the active dentate granule cell network in epileptic and control mice. Aim 2. Determine the capacity, time course, and extent of long-term dentate gyrus circuit specific intervention strategies to rescue cognitive and behavioral function in epileptic mice. Aim 3. Assess the contribution of dentate granule cell hyperexcitability in epileptic mice to disrupted hippocampal spatial coding. We know little about the mechanisms that mediate the sparse yet deterministic firing properties of neuronal populations in the hippocampal dentate gyrus that are responsible for their role in information coding and plasticity. We know even less about how disease-associated degradation in these critical dentate granule cell properties develop, and in turn how this excitability disruption may erode cognitive and affective functions that the hippocampus normally supports. In addition to the enhanced excitability responsible for seizure generation, patients with epilepsy exhibit severe cognitive comorbidities, including deficits in emotion, mood, and learning and memory, processes typically thought of as limbic system functions. Understanding how epilepsy development alters the basic circuit properties within the limbic system may be important not only in targeting new therapies for seizure amelioration, but also in developing new treatments to reduce comorbid conditions accompanying epilepsy development, a largely unexplored area of therapy development.