Environmental- and Ethanol-Induced Effects on Reference and Short-Term Memory in the Rat
Environmental enrichment (EE) is a combination of complex physical and social stimulation beyond that which would be received in standard or isolated laboratory housing. Continuous enrichment paradigms have been shown, among other influences, to increase neurogenesis and dendritic branching, and enhance learning and memory. Recently, the preventative effects of enrichment have been considered, specifically relating to drugs of abuse (Solinas, Thiret, Chauvet, & Jaber 2010; Stairs & Bardo 2009). This series of studies examined the effects of daily EE on reference memory and short-term memory, as assessed in the radial arm water maze (RAWM) and Morris water maze (MWM). Sprague-Dawley rats (N=18) were exposed to either EE or isolation for 4 hours/day for 4 weeks prior to and during the experiments. Animals were first trained and tested with non-spatial cues located at the entrance of the maze alleys in the RAWM (Experiment 1); but, they were unable to successfully learn the task. In Experiment 2, distal spatial cues were added to the maze. The rats learned the task, as evident in their reduced rates of errors. They were then trained to consume a 10% ethanol-Polycose gel (Rowland, Nasrallah, Robertson, 2005) and subsequently tested in the RAWM. Ethanol negatively affected reference memory in both treatment groups, but only disrupted short-term memory in isolated rats. EE may have protected against harmful ethanol effects on memory. In Experiment 3, reference and short-term memory were evaluated in a hidden platform and a moving platform paradigm, respectively, of the MWM. Enrichment significantly enhanced learning in the hidden platform paradigm. The short-term memory paradigm failed as a measure of short-term memory; however, due to the enriched rats’ unexpected development of a search strategy that did not depend on short-term memory. Ethanol consumption adversely affected enriched rats’ performance. This may be because ethanol can disrupt strategy use, affecting enriched rats. Isolated rats did not appear to use an alternate strategy regardless of ethanol consumption. Overall, a small enrichment effect on learning and memory was observed, which may be task dependent. Whereas ethanol negatively affected memory, EE appears to have protected against some detrimental ethanol effects on short-term memory.
environmental enrichment, reference memory, short-term memory, radial arm water maze, Morris water maze, Experimental Analysis of Behavior
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