Effects of stress, corticosterone, and epinephrine administration on learning in place and response tasks

Abstract

These experiments examined the effects of prior stress, corticosterone, or epinephrine on learning in mazes that can be solved efficiently using either place or response strategies. In a repeated stress condition, rats received restraint stress for 6 h/day for 21 days, ending 24 h before food-motivated maze training. In two single-stress conditions, rats received a 1-h episode of restraint stress ending 30 min or 24 h prior to training. Single stress ending 30 min prior to training resulted in a significant interaction of stress and learning on the two tasks, with significant enhancement of learning in the response task and non-significant impairment in the place task. Neither acute nor chronic stress significantly altered learning in either task when the stress ended 24 h before training. Thus, the anterograde effects of stress on maze learning ended within a single day. Two stress-related hormones, corticosterone and epinephrine, were tested for effects on learning parallel to those of acute stress. When administered 30 min prior to training, a corticosterone dose (40 mg/kg) that enhanced memory on a spontaneous alternation task did not significantly enhance or impair learning in either task. Two doses of epinephrine that modulate memory in other settings were used to test the effects of epinephrine on learning. Pretraining injections of 0.03 mg/kg epinephrine impaired place learning, while 0.1 mg/kg epinephrine impaired response learning. The epinephrine results mimicked those seen with acute stress on the place task, but were opposite those seen after acute stress on the response task. Thus, corticosterone does not appear to be a major factor mediating the effects of acute stress on place and response learning and epinephrine is, at most, a partial contributor to these effects.

Chronic stress may facilitate the recruitment of habit- and addiction-related neurocircuitries through neuronal restructuring of the striatum

“…The present study identified a pattern suggesting that a larger proportion of rats exposed to CVS used habitual (i.e., stimulus-response) strategies, whereas a larger proportion of non-stressed rats used spatial strategies. These findings, while not statistically significant, demonstrate a similar pattern as those found by others (Sadowski et al, 2009). Sadowski and colleagues (2009) tested rats on a modified version of the Dual Solution T-maze, wherein the number of trials to learn either the spatial (place) version or the habitual (response) version of the task were measured.…”

“…These findings, while not statistically significant, demonstrate a similar pattern as those found by others (Sadowski et al, 2009). Sadowski and colleagues (2009) tested rats on a modified version of the Dual Solution T-maze, wherein the number of trials to learn either the spatial (place) version or the habitual (response) version of the task were measured. These authors found a less robust but similar pattern, in that rats exposed to chronic restraint stress (6h/d/21d) required a greater number of trials to learn the spatial task as compared to non-stressed control rats (Sadowski et al, 2009).…”

“…Sadowski and colleagues (2009) tested rats on a modified version of the Dual Solution T-maze, wherein the number of trials to learn either the spatial (place) version or the habitual (response) version of the task were measured. These authors found a less robust but similar pattern, in that rats exposed to chronic restraint stress (6h/d/21d) required a greater number of trials to learn the spatial task as compared to non-stressed control rats (Sadowski et al, 2009). Furthermore, other studies, utilizing more complex or operant tasks, have identified that chronic stress exposure results in increased use of habitual systems (i.e., striatal), while decreasing the use of spatial systems (Schwabe et al, 2008, Dias-Ferreira et al, 2009).…”

“…Rats were then given 1 h food access for a maximum of six additional days to reduce body weight. The target weight was 85% of ad libitum weight (Korol et al, 2004, Sadowski et al, 2009) with a minimum of 75% ad libitum weight. Rats that weighed less than 85% of their ad libitum weight for five consecutive days were given an additional 1 h of feeding until weight increased to above 85%.…”

“…A hypothesis that encompasses many of these maladaptive behaviors is that the development of drug addiction involves a transition from initial, voluntary and goal-directed drug use to habitual and compulsive drug use (Everitt et al, 2008, Everitt and Robbins, 2013). Interestingly, both chronic and acute stress facilitate habitual learning and behaviors (i.e., behaviors that are inflexible or insensitive to a reduction in reward value), at the expense of goal-directed or spatial learning and memory (Schwabe et al, 2008, Dias-Ferreira et al, 2009, Sadowski et al, 2009). Thus, the ability of chronic stress to facilitate both the recruitment of habitual processes and the transition to addiction may be mediated by increased engagement of the neurocircuitries underlying habitual behavior and addiction (Everitt et al, 2008, Packard, 2009, Schwabe et al, 2011).…”