Stress impairs decision-making in rats

Stress influences various types of memory, but its effects on other cognitive functions are relatively unknown. We investigated the effects of uncontrollable stress on subsequent decision-making in rats, using a computer vision-based water foraging choice task. Stress impaired the animals' ability to bias their responses toward the larger reward when transitioning from equal to unequal quantities, and this stress effect was dependent on the amygdala

Strain and sex differences in fear conditioning: 22 kHz ultrasonic vocalizations and freezing in rats

Abstract Strain and sex differences in fear conditioning were investigated in two commonly used laboratory rats: Sprague Dawleys and Long-Evans. Twenty-two kHz ultrasonic vocalization (USV) distress calls and freezing behavior were used to measure fear responses to contextual and auditory conditioned stimuli (CSs), which were previously paired with a footshock unconditioned stimulus (US). Both strain and sex had significant effects on USVs and freezing during training and subsequent context and tone tests. Overall, the male Sprague Dawley rats froze and emitted USVs more than the other groups. Additionally, levels of freezing and USVs were differentially influenced by the type of CS (context or tone). These results suggest that species-specific defense responses in laboratory rats are highly influenced by the strain and sex of the subject, and that these factors should be considered in future fear conditioning studies

Stress impairs optimal behavior in a water foraging choice task in rats

Stress is a biologically significant social–environmental factor that plays a pervasive role in influencing human and animal behaviors. While stress effects on various types of memory are well characterized, its effects on other cognitive functions are relatively unknown. Here, we investigated the effects of acute, uncontrollable stress on subsequent decision-making performance in rats, using a computer vision-based water foraging choice task. Experiencing stress significantly impaired the animals' ability to progressively bias (but not maintain) their responses toward the larger reward when transitioning from equal to unequal reward quantities. Temporary inactivation of the amygdala during stress, however, blocked impairing effects on decision making

Prefrontal cortex and hippocampus subserve different components of working memory in rats

Both the medial prefrontal cortex (mPFC) and hippocampus are implicated in working memory tasks in rodents. Specifically, it has been hypothesized that the mPFC is primarily engaged in the temporary storage and processing of information lasting from a subsecond to several seconds, while the hippocampal function becomes more critical as the working memory demand extends into longer temporal scales. Although these structures may be engaged in a temporally separable manner, the extent of their contributions in the “informational content” of working memory remains unclear. To investigate this issue, the mPFC and dorsal hippocampus (dHPC) were temporarily inactivated via targeted infusions of the GABAA receptor agonist muscimol in rats prior to their performance on a delayed alternation task (DAT), employing an automated figure-eight maze that required the animals to make alternating arm choice responses after 3-, 30-, and 60-sec delays for water reward. We report that inactivation of either the mPFC or dHPC significantly reduced DAT at all delay intervals tested. However, there were key qualitative differences in the behavioral effects. Specifically, mPFC inactivation selectively impaired working memory (i.e., arm choice accuracy) without altering reference memory (i.e., the maze task rule) and arm choice response latencies. In contrast, dHPC inactivation increased both reference memory errors and arm choice response latencies. Moreover, dHPC, but not mPFC, inactivation increased the incidence of successive working memory errors. These results suggest that while both the mPFC and hippocampus are necessarily involved in DAT, they seem to process different informational components associated with the memory task