H trial were randomized, but never included the goal arm, which remained the same throughout all trials. If the rat could not find the platform within 1 minute, it was guided to and allowed to sit on the platform during the intertrial interval. During the 1-minute intertrial interval, animals remained on the platform. The 12 acquisition Title Loaded From File trials were divided into two blocks of six consecutive trials, interspersed with a 5-minute break. Following the acquisition trials, the animals underwent a Title Loaded From File short-term memory trial (30 minutes later) and a long-term memory trial (24 hours later). For each trial, latency to locate the platform and number of errors were recorded. Errors were operationally defined as anytime the animal’s entire body entered an arm that was not the goal arm, as well as anytime an animal entered the goal arm but did not find the hidden platform.Corticosterone AssessmentTo verify that CUS and learning experience were stressful, we assessed corticosterone levels, using fecal boli, since they can be obtained without stress to the animal and fecal corticosterone is highly correlated with serum corticosterone [22,23]. Fecal boli were collected from 12 randomly selected animals that experienced learning in the RAWM (control, n = 6; stress, n = 6). Baseline levels of corticosterone were determined from samples collected after animals had acclimated to their environment for a week but before CUS commenced. In order to see what impact CUS and the RAWM had on corticosterone, fecal samples were collected 24 hours after the last stressor and again following the long-term memory trial for the RAWM. Corticosterone levels were quantified using a commercially available Enzyme Immunoassay Kit (Assay Designs, Michigan, USA), according to the manufacturer’s instructions.Materials and Methods Ethics StatementAll experimental procedures were conducted in accordance with the Guide for the Care and Use of Laboratory Animals of the National Institutes of Health. The relevant animal protocol was approved by the University of Houston Institutional Animal Care and Use Committee (protocol number 10?39).Animals and CUS ParadigmAdult male Long Evans rats (3 months old at the start of experiments) were individually housed in clear plastic cages with ad libitum food and water. Upon arrival, animals habituated for one week to the vivarium environment. CUS was administered as previously described [9,16] for 14 days. Briefly, two different daily stressors (e.g., tilted cages, vinegar-laced water, exposure to strobe light, predator odor and predator calls) as well as the timing of the stressors, were determined by a random number generator. All stressors were conducted in a room separate from where control animals were housed.HistologyOne day after the end of CUS, control (n = 9) and stress (n 1527786 = 9) animals were overdosed with anesthetic and intracardially perfused with 4 paraformaldehyde. Brains were removed and post-fixed overnight, then stored in 30 sucrose. Brains were cut into 50 mm sections on a freezing microtome and stored in cryoprotectant in 96-well microtiter plates at 220uC. To label doublecortin-positive (DCX+) cells, standard immunohistochemical procedures were used to process every sixth section throughout the rostrocaudal extent of the hippocampus. Following treatment in 0.6 hydrogen peroxide and blocking in 3 donkey serum, sections were incubated for 72 hours at 4uC in primary antibody (goat anti-DCX, Santa Cruz Biotechnology, Inc., CA, USA,.H trial were randomized, but never included the goal arm, which remained the same throughout all trials. If the rat could not find the platform within 1 minute, it was guided to and allowed to sit on the platform during the intertrial interval. During the 1-minute intertrial interval, animals remained on the platform. The 12 acquisition trials were divided into two blocks of six consecutive trials, interspersed with a 5-minute break. Following the acquisition trials, the animals underwent a short-term memory trial (30 minutes later) and a long-term memory trial (24 hours later). For each trial, latency to locate the platform and number of errors were recorded. Errors were operationally defined as anytime the animal’s entire body entered an arm that was not the goal arm, as well as anytime an animal entered the goal arm but did not find the hidden platform.Corticosterone AssessmentTo verify that CUS and learning experience were stressful, we assessed corticosterone levels, using fecal boli, since they can be obtained without stress to the animal and fecal corticosterone is highly correlated with serum corticosterone [22,23]. Fecal boli were collected from 12 randomly selected animals that experienced learning in the RAWM (control, n = 6; stress, n = 6). Baseline levels of corticosterone were determined from samples collected after animals had acclimated to their environment for a week but before CUS commenced. In order to see what impact CUS and the RAWM had on corticosterone, fecal samples were collected 24 hours after the last stressor and again following the long-term memory trial for the RAWM. Corticosterone levels were quantified using a commercially available Enzyme Immunoassay Kit (Assay Designs, Michigan, USA), according to the manufacturer’s instructions.Materials and Methods Ethics StatementAll experimental procedures were conducted in accordance with the Guide for the Care and Use of Laboratory Animals of the National Institutes of Health. The relevant animal protocol was approved by the University of Houston Institutional Animal Care and Use Committee (protocol number 10?39).Animals and CUS ParadigmAdult male Long Evans rats (3 months old at the start of experiments) were individually housed in clear plastic cages with ad libitum food and water. Upon arrival, animals habituated for one week to the vivarium environment. CUS was administered as previously described [9,16] for 14 days. Briefly, two different daily stressors (e.g., tilted cages, vinegar-laced water, exposure to strobe light, predator odor and predator calls) as well as the timing of the stressors, were determined by a random number generator. All stressors were conducted in a room separate from where control animals were housed.HistologyOne day after the end of CUS, control (n = 9) and stress (n 1527786 = 9) animals were overdosed with anesthetic and intracardially perfused with 4 paraformaldehyde. Brains were removed and post-fixed overnight, then stored in 30 sucrose. Brains were cut into 50 mm sections on a freezing microtome and stored in cryoprotectant in 96-well microtiter plates at 220uC. To label doublecortin-positive (DCX+) cells, standard immunohistochemical procedures were used to process every sixth section throughout the rostrocaudal extent of the hippocampus. Following treatment in 0.6 hydrogen peroxide and blocking in 3 donkey serum, sections were incubated for 72 hours at 4uC in primary antibody (goat anti-DCX, Santa Cruz Biotechnology, Inc., CA, USA,.