Cognitive impairment is a debilitating outcome of Alzheimer's Disease and Minor Cognitive Impairment. Cognitive impairment reduces quality of life and increases treatment costs. Relatively modest increases in cognitive function produce relatively large increases in quality of life and large decreases in cost of care. Palliative treatments enhancing cognitive function would benefit many patients until treatments for their underlying disorders are developed. One promising pharmacological target for such cognitive enhancers is the benzodiazepine (BZ) binding site on the gamma-aminobutyric acid (GABA) type A (GABAA) receptor- complex. Subtype-selective ligands have been developed for the GABAA-a5 BZ receptor (GABAAa5- BZr), which is predominately expressed in the hippocampus, a site important for memory function. Studies in rodent and nonhuman primate memory assays indicate that GABAAa5-BZr inverse agonists improve cognition with few adverse effects. In the proposed studies, 8 rhesus monkeys will be trained to perform tests from the CANTAB nonhuman primate neuropsychological testing battery. 4 monkeys will be also be trained on the delayed-match-to- sample test and implanted with radio-telemetry devices to measure cardiovascular and respiratory responses for dose-ranging studies. The dose-ranging cohort will determine active doses of the compounds in primates and also screen for compounds producing adverse effects prior to full cognitive testing in the CANTAB-trained monkeys. Novel compounds will be tested for toxicity in mice prior to testing in the dose- ranging or CANTAB-trained monkeys. The effects of GABAAa5-BZr ligands on cognitive function in macaques will be determined by pretreatments of GABAAa5-BZr agonists, antagonists and inverse agonists. These studies will test the hypothesis that activity at the GABAAa5-BZr can bi-directionally modulate cognition with agonists impairing cognitive performance and inverse agonists enhancing performance. The regional specificity of the CANTAB neuropsychological test battery will also allow for testing of the hypothesis that GABAAa5-BZr cognitive modulation will occur in tests mediated by temporal brain structures (i.e. the hippocampus) as opposed to tests mediated by frontal cortical structures. In addition, the ability of GABAAa5-BZr inverse agonists to reverse scopolamine-induced cognitive impairment will determine the potential effectiveness of these compounds as treatments for the cognitive impairment produced by Alzheimer's disease. Understanding the effects of GABAAa5-BZr ligands has important implications to the neuro- pharmacology, neuropsychology and neuroanatomy of cognition and will further development of a novel class of therapeutics for cognitive dysfunction in Alzheimer's disease and Minor Cognitive Impairment.
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