A total of 17 young adult (four months old) and 20 aged (22–28 months old) male Fischer 344 × Brown Norway F1 hybrid rats (NIA colony) were used for this study. Twelve young and 12 aged rats underwent cognitive training. An additional five young and eight aged rats were trained to traverse a track for a food reward but did not undergo cognitive training. This group was also scanned longitudinally at a similar interval as the cognitively trained animals, was similarly food restricted, received palatable food rewards for traversing a track, and was considered the activity-matched control group. Because of the lack of availability of female rats of this strain at the time of these experiments, sex as a biological variable could not be considered.
Rats were single-housed in standard Plexiglas cages and maintained on a 12-h reverse light/dark cycle (lights off at 8 A.M.). All rodent handling, feeding, and behavior was conducted during the dark phase, 5–7 d per week at approximately the same time each day. Upon arrival, rats were given one week of acclimatization to the facility. They were then placed on food restriction to induce appetitive motivation before behavioral testing. The diet consisted of moist chow (standard rat maintenance diet, Purina, and water 1:1 ratio). Throughout training and testing, rats were weighed daily to ensure they maintained a target weight between 80–85% of their normal baseline weight (i.e., the weight at which they have a body condition score, or BCS, of 3). Rats also underwent weekly health screens to ensure their BCS did not drop below 2.5 and that they did not acquire tumors or other physical impairments. BCS for each rat were assigned by assessing palpable fat deposits over the lumbar vertebrae and pelvic bones (Ullman-Culleré and Foltz, 1999 (link); Hickman and Swan, 2010 (link)). Water was provided ad libitum. All experimental procedures were performed in accordance with National Institutes of Health guidelines and were approved by Institutional Animal Care and Use Committees at the University of Florida.
Rats were single-housed in standard Plexiglas cages and maintained on a 12-h reverse light/dark cycle (lights off at 8 A.M.). All rodent handling, feeding, and behavior was conducted during the dark phase, 5–7 d per week at approximately the same time each day. Upon arrival, rats were given one week of acclimatization to the facility. They were then placed on food restriction to induce appetitive motivation before behavioral testing. The diet consisted of moist chow (standard rat maintenance diet, Purina, and water 1:1 ratio). Throughout training and testing, rats were weighed daily to ensure they maintained a target weight between 80–85% of their normal baseline weight (i.e., the weight at which they have a body condition score, or BCS, of 3). Rats also underwent weekly health screens to ensure their BCS did not drop below 2.5 and that they did not acquire tumors or other physical impairments. BCS for each rat were assigned by assessing palpable fat deposits over the lumbar vertebrae and pelvic bones (Ullman-Culleré and Foltz, 1999 (link); Hickman and Swan, 2010 (link)). Water was provided ad libitum. All experimental procedures were performed in accordance with National Institutes of Health guidelines and were approved by Institutional Animal Care and Use Committees at the University of Florida.
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