Abstract
The deleterious effects of prolonged sleep deprivation on behavior and cognition are a concern in modern society. Persons at risk for impaired performance and health-related issues resulting from prolonged sleep loss would benefit from agents capable of reducing these detrimental effects at the time they are sleep deprived. Agents capable of improving cognition by enhancing brain activity under normal circumstances may also have the potential to reduce the harmful or unwanted effects of sleep deprivation. The significant prevalence of excitatory α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) glutamatergic receptors in the brain provides a basis for implementing a class of drugs that could act to alter or remove the effects of sleep deprivation. The ampakine CX717 (Cortex Pharmaceuticals), a positive allosteric modulator of AMPA receptors, was tested for its ability to enhance performance of a cognitive, delayed match-to-sample task under normal circumstances in well-trained monkeys, as well as alleviate the detrimental effects of 30–36 h of sleep deprivation. CX717 produced a dose-dependent enhancement of task performance under normal alert testing conditions. Concomitant measures of regional cerebral metabolic rates for glucose (CMRglc) during the task, utilizing positron emission tomography, revealed increased activity in prefrontal cortex, dorsal striatum, and medial temporal lobe (including hippocampus) that was significantly enhanced over normal alert conditions following administration of CX717. A single night of sleep deprivation produced severe impairments in performance in the same monkeys, accompanied by significant alterations in task-related CMRglc in these same brain regions. However, CX717 administered to sleep-deprived monkeys produced a striking removal of the behavioral impairment and returned performance to above-normal levels even though animals were sleep deprived. Consistent with this recovery, CMRglc in all but one brain region affected by sleep deprivation was also returned to the normal alert pattern by the drug. The ampakine CX717, in addition to enhancing cognitive performance under normal alert conditions, also proved effective in alleviating impairment of performance due to sleep deprivation. Therefore, the ability to activate specific brain regions under normal alert conditions and alter the deleterious effects of sleep deprivation on activity in those same regions indicate a potential role for ampakines in sustaining performance under these types of adverse conditions.
Highlights
The importance of a-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors in learning and memory is becoming increasingly more apparent [1]
The AMPA receptor modulator CX717, given to monkeys engaged in cognitive processing and short-term memory, improved performance in all aspects of the DMS task
In addition to the effects on normal alert performance, the present findings demonstrated that CX717 removed severe performance deficits produced by subjecting the animals to prolonged periods of sleep deprivation
Summary
The importance of a-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors in learning and memory is becoming increasingly more apparent [1]. Ampakines have been shown to facilitate performance in several behavioral paradigms in rodents and primates [6,7,8,9] and to enhance cognition in humans [10,11,12]. The ubiquitous distribution of AMPA receptor subtypes on various types of neurons in nearly every brain region [13,14] provides a feasible substrate for ampakines to enhance brain function under normal conditions as well as in more difficult or disruptive circumstances where performance may be compromised. One circumstance that has been consistently shown to interfere with the performance of complex behavioral tasks and cognition in both humans and animal models is prolonged sleep deprivation [15,16,17,18,19].
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