N stained with Ponceau S. Once rinsed, membranes were blocked for an hour at room temperature with continual mixing using 5 skim milk in TBS with 0.05 Tween-20 (BDNF, PSD-95) and 5 skim milk in PBS with 0.05 Tween-20 (?actin). Membranes were then washed 3 times for 5 minutes in 
wash buffer (TBS with 0.05 Tween for pro and mature BDNF and PSD-95; PBS with 0.05 Tween for ?actin). Samples were incubated in primary antibody (polyclonal rabbit anti-BDNF, 1:1000; mouse anti-PSD-95, 1:500, both Chemicon, CA, USA; polyclonal mouse anti-?actin, 1:20,000, Millipore, MA, USA) overnight at 25033180 4uC. After being washed in the appropriate buffer, membranes were incubated with secondary antibody (goat antirabbit 1:15,000 or goat anti-mouse, 1:5000, both KPL, Maryland, USA). Blots were developed using an enhanced chemiluminescence detection method (ECL Plus, Buckinghamshire, UK). Band intensity was assessed using a BioRad Gel Doc Imaging System with Quantity One software (BioRad, CA, USA). Protein quantity 
was assessed from the adjusted band intensity using the volume rectangle analysis tools and linear regression methods. Each sample value was divided by the total protein loading value (the intensity of ?actin) and localFigure 1. CUS and learning were both stressful. Animals that underwent CUS did not gain weight over the 2-week period of stressor exposure, whereas control animals did (A). Exposure to the CUS paradigm raised corticosterone levels, as did learning in the RAWM (B). Note, however, that learning did not further elevate corticosterone in stressed animals. *significantly different from baseline, { significantly different from Post CUS control. doi:10.1371/journal.pone.0053126.gHippocampal Subregions, Stress and Learningend of CUS, however, control animals had gained significantly more weight than stressed animals (see Figure 1A). To determine whether CUS and learning experience were stressful to the animals, we assessed corticosterone levels. Fecal samples were collected from 12 randomly selected control and stressed rats that underwent the RAWM task. Control and stressed animals did not differ in corticosterone levels before onset of CUS (baseline). However, at the end of CUS, stressed animals had significantly higher corticosterone levels compared to controls, and had more than Sermorelin doubled their baseline levels. Corticosterone levels were significantly elevated in the controls by exposure to the RAWM to the point that they were no longer significantly different from CUS animals (see Figure 1B). CUS animals, however, did not show further elevation of corticosterone due to RAWM exposure.Chronic Unpredictable Stress Enhanced Long-term Spatial MemoryFollowing CUS, control and stressed animals were exposed to the RAWM to evaluate spatial learning and memory. There was no difference between groups in latency to find the hidden platform or number of errors made during the acquisition (trials 1?12) of the RAWM learning task (see Figure 2A ). Furthermore, there was no order Pentagastrin significant difference between groups for latency or errors for the short-term memory trial. However, stressed animals found the platform significantly faster and made fewer errors in the long-term memory trial.Chronic Unpredictable Stress most Severely Affected Neurogenesis in the Ventral Dentate GyrusTo determine the effects of CUS on hippocampal neurogenesis, we stereologically quantified cell proliferation (CldU+ cells), survival (IdU+ cells) and neuronal differentiation (DCX+ cells.N stained with Ponceau S. Once rinsed, membranes were blocked for an hour at room temperature with continual mixing using 5 skim milk in TBS with 0.05 Tween-20 (BDNF, PSD-95) and 5 skim milk in PBS with 0.05 Tween-20 (?actin). Membranes were then washed 3 times for 5 minutes in wash buffer (TBS with 0.05 Tween for pro and mature BDNF and PSD-95; PBS with 0.05 Tween for ?actin). Samples were incubated in primary antibody (polyclonal rabbit anti-BDNF, 1:1000; mouse anti-PSD-95, 1:500, both Chemicon, CA, USA; polyclonal mouse anti-?actin, 1:20,000, Millipore, MA, USA) overnight at 25033180 4uC. After being washed in the appropriate buffer, membranes were incubated with secondary antibody (goat antirabbit 1:15,000 or goat anti-mouse, 1:5000, both KPL, Maryland, USA). Blots were developed using an enhanced chemiluminescence detection method (ECL Plus, Buckinghamshire, UK). Band intensity was assessed using a BioRad Gel Doc Imaging System with Quantity One software (BioRad, CA, USA). Protein quantity was assessed from the adjusted band intensity using the volume rectangle analysis tools and linear regression methods. Each sample value was divided by the total protein loading value (the intensity of ?actin) and localFigure 1. CUS and learning were both stressful. Animals that underwent CUS did not gain weight over the 2-week period of stressor exposure, whereas control animals did (A). Exposure to the CUS paradigm raised corticosterone levels, as did learning in the RAWM (B). Note, however, that learning did not further elevate corticosterone in stressed animals. *significantly different from baseline, { significantly different from Post CUS control. doi:10.1371/journal.pone.0053126.gHippocampal Subregions, Stress and Learningend of CUS, however, control animals had gained significantly more weight than stressed animals (see Figure 1A). To determine whether CUS and learning experience were stressful to the animals, we assessed corticosterone levels. Fecal samples were collected from 12 randomly selected control and stressed rats that underwent the RAWM task. Control and stressed animals did not differ in corticosterone levels before onset of CUS (baseline). However, at the end of CUS, stressed animals had significantly higher corticosterone levels compared to controls, and had more than doubled their baseline levels. Corticosterone levels were significantly elevated in the controls by exposure to the RAWM to the point that they were no longer significantly different from CUS animals (see Figure 1B). CUS animals, however, did not show further elevation of corticosterone due to RAWM exposure.Chronic Unpredictable Stress Enhanced Long-term Spatial MemoryFollowing CUS, control and stressed animals were exposed to the RAWM to evaluate spatial learning and memory. There was no difference between groups in latency to find the hidden platform or number of errors made during the acquisition (trials 1?12) of the RAWM learning task (see Figure 2A ). Furthermore, there was no significant difference between groups for latency or errors for the short-term memory trial. However, stressed animals found the platform significantly faster and made fewer errors in the long-term memory trial.Chronic Unpredictable Stress most Severely Affected Neurogenesis in the Ventral Dentate GyrusTo determine the effects of CUS on hippocampal neurogenesis, we stereologically quantified cell proliferation (CldU+ cells), survival (IdU+ cells) and neuronal differentiation (DCX+ cells.