Assessment of Stress Effects on Cognitive Flexibility using an Operant Strategy Shifting Paradigm

Summary

Stressful life events impair cognitive function, increasing the risk of psychiatric disorders. This protocol illustrates how stress affects cognitive flexibility using an automated operant strategy shifting paradigm in male and female Sprague Dawley rats. Specific brain areas underlying particular behaviors are discussed, and translational relevance of results are explored.

Abstract

Stress affects cognitive function. Whether stress enhances or impairs cognitive function depends on several factors, including the 1) type, intensity, and duration of the stressor; 2) type of cognitive function under study; and 3) timing of the stressor in relation to learning or executing the cognitive task. Furthermore, sex differences among the effects of stress on cognitive function have been widely documented. Described here is an adaptation of an automated operant strategy shifting paradigm to assess how variations in stress affect cognitive flexibility in male and female Sprague Dawley rats. Specifically, restraint stress is used before or after training in this operant-based task to examine how stress affects cognitive performance in both sexes. Particular brain areas associated with each task in this automated paradigm have been well-established (i.e., the medial prefrontal cortex and orbitofrontal cortex). This allows for targeted manipulations during the experiment or the assessment of particular genes and proteins in these regions upon completion of the paradigm. This paradigm also allows for the detection of different types of performance errors that occur after stress, each of which has defined neural substrates. Also identified are distinct sex differences in perseverative errors after a repeated restraint stress paradigm. The use of these techniques in a preclinical model may reveal how stress affects the brain and impairs cognition in psychiatric disorders, such as post-traumatic stress disorder (PTSD) and major depressive disorder (MDD), which display marked sex differences in prevalence.

Introduction

In humans, stressful life events can impair cognitive function (i.e, cognitive flexibility¹), which denotes the ability to adapt cognitive processing strategies to face new conditions in the environment². Impairment in cognition precipitates and exacerbates many psychiatric disorders, such as Post Traumatic Stress Disorder (PTSD) and Major Depressive Disorder (MDD)^3,4. These disorders are twice as prevalent in females^5,6,7,8, yet the bi....

Protocol

All procedures in this study were approved by the Institutional Animal Care and Use Committee (IACUC) at Bryn Mawr College. Obtain IACUC or otherwise applicable regulatory approval before ordering laboratory animals and beginning experimentation.

1. Animal preparation

1. Acquire male and female adult Sprague Dawley rats.
   NOTE: The rats can be delivered before 65 days of age, but do not begin procedures until after this point to ensure that both males and females are fully mature.
2. Pair-house same-sex rats for as long as possible, as long-term isolation is a stressor²⁴. For food restricti....

Results

The adapted automated operant strategy shifting paradigm outlined above was used to determine if repeated restraint stress affects cognition in male and female Sprague Dawley rats. Representative behavioral data are described in Figure 2 below. In short, control and repeatedly restrained rats performed this operant strategy shifting test, which consisted of a series of tasks: side discrimination, side reversal, and light discrimination.

Trials to criterion for eac.......

Discussion

The protocol demonstrates how to measure the effects of stress on cognitive function. Specifically, a modified operant strategy shifting paradigm is used in rodents, which measures cognitive flexibility (analogous to the Wisconsin Card Sorting Task in humans)¹. Cognitive flexibility denotes the ability to adapt cognitive processing strategies to face new conditions in the environment, and it is crucial for normal daily functioning². As human studies on cognitive flexibility.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
3 inch glass pipette eye droppers	Amazon	4306-30-012LC	For vaginal lavage
Alcohol Wipes	VWR	15648-990	To clean trays in set shifting boxes between rats
Biotin-SP-conjugated AffiniPure Donkey Anti-Mouse lgG (H+L), minimal cross reaction to bovine, chicken, goat, guinea pig, hamster, horse, human, rabbit, sheep serum proteins	Jackson ImmunoResearch	715-065-150	All other DAB protocol staining materials are standard buffers/DAB and are not specified here, as this is not the main focus of the methods paper
C-fos mouse monoclonal primary antibody	AbCam	ab208942	To stain neural activation in brain areas after set shifting
Dustless Food Pellets	Bio Serv	F0021	For set shifting boxes (dispenser for reward)
GraphPad Prism			Used for data analysis
Leica DM4 B Microscope and associated imaging software	Leica		Lots of different parts for the microscope and work station, for imaging lavage and/or cfos
MatLab			Software; code to help analyze set shifting data, available upon request.
Med-PC Software Suite	Med Associates	SOF-736	Software; uses codes to operate operant chambers
Operant Chambers	Med PC	MED-008-B2	Many different parts for the chamber set up and software to work with it; we also wrote a separate code for set shifting, available upon request.
Rat Bedding	Envigo	T.7097
Rat Chow	Envigo	T.2014.15
Restraint Devices	Bryn Mawr College	Made by our shop	For stress exposure; specifications available upon request.
Scribbles 3d fabric paint	Amazon	54139	For vaginal lavage
Sprague Dawley Rats	Envigo		At least D65 Males and Females
VWR Superfrost Plus Micro Slide	VWR	48311-703	For vaginal lavage and/or brain slices/staining for c-fos