Peter R. Patrylo - US grants

DESCRIPTION: (Adapted from the application) Although epidemiological studies have demonstrated an increased incidence and prevalence of seizure disorders in the elderly, the underlying mechanisms are not known. The goal of this project is to investigate physiological mechanisms that could contribute to this epileptogenicity. Aged rodents will be used as the model system since several studies suggest a similar increase in seizure susceptibility during aging. The applicant s preliminary studies corroborate these findings and demonstrate that an increased propensity to generate epileptiform activity can also be seen in neuronal tissue in isolation following exposure to a GABA-A receptor antagonist. This suggests that alterations may occur in the CNS during aging that could underlie an increased seizure susceptibility. The dentate gyrus will be examined since it is believed to play a critical role in some forms of epilepsy and anatomical changes have been described in the aged dentate gyrus that could be epileptogenic in nature. Their primary hypothesis is that changes in recurrent excitation and/or inhibition underlie the increased seizure susceptibility in the aged CNS. They will also examine whether alterations in nonsynaptic mechanisms may be involved. Several electrophysiological techniques will be used to test these two hypotheses in aged rats. Intra- and extracellular recordings will be made from granule cells to test for the presence of new recurrent excitatory circuits and to examine the strength of synaptic inhibition. Extracellular recordings will be made in low [Ca2+]o and elevated [K+]o media containing amino acid receptor antagonists to determine if there is an increased susceptibility to generate nonsynaptic seizures in the dentate of aged rats. Anatomical studies will be performed to evaluate changes in axonal elaboration. These experiments should begin to address whether synaptic reorganization and/or altered nonsynaptic interactions underlie the increased seizure susceptibility in the elderly. One of the long-term objectives is to understand the mechanisms of epileptogenesis in the elderly so that patients can be diagnosed and treated more effectively. Additionally, synaptic reorganization may also affect other hippocampal processes such as learning and memory. Thus, by examining synaptic reorganization within the aged CNS they may also provide insight into the basic mechanisms of epilepsy and learning and memory within the overall population.

This proposal focuses on two research objectives: animal models of aging and functional senescence. The long term goal of this research project is to understand the neurological properties of a novel animal model of extended life span that contribute to its capacity to retain learned memories during aging. In general, studies indicate that the ability to learn and remember declines, on average, in the latter part of the life span (e.g., decreased retention of spatial memory). Recently, an animal model of extended life span has been described by investigators in our research group, the growth hormone receptor knockout (GH-R-KO) mouse, that shows enhanced retention of memories during aging (28 days post training) relative to controls. Furthermore, these mice do not show any deficit in memory retention when compared with young control animals. The acquisition and storage of memory is believed to be associated with an underlying modification of synapses. Two forms of synaptic modification that have been proposed to be putative biological substrates for cognitive function (learning and memory) are long term potentiation (LTP) and long term depression (LTD). While only limited evidence directly links LTP or LTD with the mechanisms used by the brain in vivo, several studies have noted a correlation between the inability of aged animals to retain spatial memory and a quicker decay of LTP. Furthermore, recent data suggest that the ability to elicit LTD, and reverse LTP may also be enhanced during aging. In this study, behaviorally haracterized (Le., inhibitory ,avoidance task, water maze) adult and aged GH-R-KO mice and controls will be used to test two hypotheses concerning mechanisms that may contribute to a preservation of memory retention during aging. Hippocampal region CA1 will be examined. Hypothesis 1: Aged GH-R-KO mice showing retention of learned memory do not display an accelerated decay of LTP. If LTP is indeed a cellular correlate for learning and memory, then one would predict that its accelerate decay could account for an impairment in memory retention during aging. Adult and aged GH-R-KO mice and controls will be behaviorally characterized. Subsequently, hippocampal slices will be prepared from these animals and extracellular recordings will be made in CA1 (stratum radiatum) to characterize the time course of LTP decay. LTP will be induced using 4 trains of 100 Hz stimulation (1s duration) every 5 min. Hypothesis 2: Aged GH-R-KO mice showing little or no impairment in memory retention do not show an enhanced capacity to evoke LTD or reverse LTP in vitro. Since altering these properties could also contribute to a decrease in retention performance during aging (Le., increase in forgetting) extracellular recordings will be made in hippocampal region CA1 of brain slices prepared from behaviorally characterized animals to assess: 1) the capacity to evoke LTD using prolonged low frequency stimulation (LFS; 900 lpulses/l Hz) and 2) the capacity to reverse LTP using multiple short-duration LFS bursts (30pulses/lHz; 10 min between bursts).

[unreadable] DESCRIPTION (provided by applicant): Epilepsy is a widespread neurological disorder that affects 1-4% of the world's population. While many anti-epileptic drugs (AEDs) are available, approximately 25% of cases are non-responsive including cases associated with temporal lobe sclerosis and cortical malformations (CM). Thus, there is a tremendous need for additional research that focuses on the cause of seizure generation in these forms of epilepsy and potential therapeutic strategies. In both temporal lobe sclerosis and CM-related epilepsy, abnormal pro-convulsive circuits have been reported to occur in the dentate gyrus of the hippocampal formation and have been suggested to contribute to the generation of seizures. What we do not understand however, is why seizures occur only sporadically in these types of epilepsy, yet the aberrant pro-convulsive circuits are a permanent feature. This research project will focus on determining whether the presence of aberrant kainate receptors in these abnormal pro-convulsive circuits underlie their capacity to generate seizures sporadically. In this study, a combination of biochemical, anatomical and electrophysiological techniques and two models of epilepsy will be used to characterize the kainate receptors found in pro-convulsive circuits and to determine whether blocking or desensitizing them suppresses seizure generation during repetitive stimulation. If seizure generation can be suppressed, and the characteristics of these kainate receptors identified, new AEDs can be designed that specifically target kainate receptors in aberrant pro-convulsive circuits and thereby suppress seizure generation in patients afflicted with these types of epilepsy. PUBLIC HEALTH RELEVANCE: Epilepsy affects approximately 1-4% of the world's population with up to 25% of cases being unresponsive to currently available anti-epileptic drugs. Based on preliminary data this research project proposes to investigate whether aberrant kainate receptors contribute to the generation of seizures in epileptic tissue from models of temporal lobe sclerosis and cortical malformation-related epilepsy. This is a novel hypothesis regarding ictogenesis that should provide insight into a new therapeutic strategy for treating medically-intractable epilepsy. [unreadable] [unreadable] [unreadable] [unreadable]