Repeated administration of methamphetamine (mAMPH) to rodents in a single-day "binge" regimen damages forebrain monoaminergic nerve terminals and produces subsequent cognitive deficits. Here we investigate performance on a social odor-based task, demonstrating enduring mAMPH-induced deficits in recognition memory. Three weeks after a neurotoxic mAMPH regimen, singly-housed male Long-Evans rats had four wooden beads placed in their home cage: three beads containing odors from their home cage (HC beads) and one bead from a cage of a rat not present in the colony room (N1 bead). Exploration times for each bead were recorded during three 1-min habituation trials separated by 1-min intertrial intervals. Twenty-four hours later, a 1-min memory test was conducted, in which animals were presented with two HC beads, one N1 bead, and one bead from another novel animal (N2). Saline- and mAMPH-treated rats showed similar, progressive decreases in exploration time for the N1 bead during the habituation trials, indicating equivalent short-term olfactory habituation to the novel odor. By contrast, during the subsequent memory test, saline-treated rats showed a strong preference for the N2 bead over the N1 bead while mAMPH-treated rats showed no preference. The use of the rats' primary sensory modality (olfaction) coupled with the social significance (from conspecifics) of the odors produces strong, long-lasting memories. Our results show that prior treatment with a neurotoxic regimen of mAMPH impairs long-term memory for the previously experienced odors. As compared with previously employed object recognition tasks, this test may be advantageous for investigating mAMPH-induced memory impairments in rodents.
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