Documentation

Introduction

The Environmental Enrichment (EE) room is a large cage that contains enrichment objects and is used to house subjects. It can be used as part of different experimental protocols that test the effect of environmental enrichment on rodent behaviors.

Environmental enrichment helps provide rodents with sensory and motor stimulation by placing inanimate objects in their environment, such as toys, swings, running wheels, and ladders, as well as through the introduction of structural modifications such as increased floor space. It helps promote the physical and psychological well-being of rodents through exercise and cognitive challenges.  Moreover, environmental enrichment can also provide social stimulation by housing the animals in groups in a spacious cage (Bayne, 2018). The EE room provides sufficient environmental enrichment. It is a large cage that contains three floors and can easily house up to 13 animals. It contains enrichment objects of different shapes and textures to provide different forms of stimulation. The stairs and running wheels help provide exercise, the see-saw helps provide somatosensory stimulation, and the toys, large tubes, tunnels, wood pieces, and hanging items help provide cognitive stimulation. Training usually involves housing the subjects in either standard housing or environmental enrichment groups to observe their behavioral differences. 

Rodents housed in enriched environments perform better in learning and memory tasks as compared to standard housing with little to no enrichment (Harati et al., 2011). In addition, environmental enrichment also helps reduce stress and anxiety in rodents (Bahi, 2017). Therefore, the EE Room can also be used to improve animal welfare for subjects that are housed in standard cages. 

Other apparatuses used to study rodent behaviors include the Y-Maze, the Social Reward Chamber, and the Passive Avoidance Test Apparatus.

Apparatus and Equipment

The EE room consists of a large cage that measures 40 x 60 x 90 cm. It has three floors that are connected by ramps. Running wheels, toys, plastic tunnels, see-saw, wood pieces, Lego blocks, large tubes, and hanging items are present throughout the cage. 

Training Protocol

Clean the apparatus regularly. Add new objects or remove old objects from the apparatus once a week. Clean the apparatuses used for behavioral tests after every trial to avoid the influence of olfactory cues from previous trials. A tracking and recording system such as the Noldus Ethovision XT can be used to assist with observations.

The following is a sample protocol for the assessment of cognitive performances in adult rats placed in standard housing versus an enriched environment using the EE Room:

EE Room Task

Divide the subjects into control and environmental enrichment (EE) groups. Place the EE groups (10 to 13 animals per group) into the EE Room when they are 21 days old until they reach 60 days of age. Place the control group (6 animals per group) in standard housing that contains no enrichment. Perform behavioral tasks when the subjects are 60 days old. 

Open Field Task 

Divide the floor of the Open Field arena into nine rectangles by marking it with black lines. Place the subjects into the center of the arena and allow it to explore the arena for 5 minutes. Remove the subject from the arena and place it back into its home cage. After 24 hours, perform another trial. 

Step-down Inhibitory Avoidance Task

Place the subject on the platform of the Step-down Avoidance apparatus. Administer a 0.4-mA foot shock for 2 seconds when the subject steps down on the grid. Return the subject to its home cage. After 24 hours, perform another trial without administering the foot shock.

Data Analysis

The following can be observed using the EE Room:

• Exploratory and locomotor activity differences between subjects living in standard housing vs. the EE Room.
• Memory retention abilities of the subjects after living in standard housing vs. the EE Room.

Literature Review

Investigation of the effect of environmental enrichment on the cognitive behaviors of adult rats that survived childhood pneumococcal meningitis

Barichello et al. (2014) investigated whether environmental enrichment (EE) could reverse cognitive impairment in adult Wistar rats that survived childhood pneumococcal meningitis. The EE room was used as environmental enrichment in the experiment. The subjects were divided into the following groups: control, control + EE, meningitis, and meningitis + EE. The meningitis group was induced with pneumococcal meningitis, and the control group was administered with artificial cerebrospinal fluid (CSF) on postnatal day 11. The subjects remained with their mothers until they were 21 days old and then shifted to either standard housing or the EE room where they remained until they were 60 days of age. Behavioral tasks included the open field test and the step-down passive avoidance test and were performed when the subjects were 60 days old. The tasks were divided into training trials and testing trials that were performed after 24 hours. The open-field test was used to observe the subjects’ locomotor activity and exploratory behavior. The floor of the open field was divided into nine squares by black lines to observe the number of times the subjects crossed the lines and also to observe their rearing movements. A reduction in the number of crossings and rearing movements between the two sessions was used as a measure of retention memory. Results indicated that no differences in the number of crossings and rearing movements were observed between all the groups in the training trials. However, the meningitis groups displayed similar performances in training and test sessions, which indicated a memory impairment. In contrast, all the other groups displayed significantly different performances in the training and test sessions, which indicated memory retention of the previous experience. The step-down inhibitory avoidance task measured the latency of the subjects to step down on the grid. Results indicated no significant difference in latency to step down on the grid between any of the groups in training sessions. The meningitis groups displayed no differences in latency between training and test sessions, which indicated a memory impairment. In contrast, all the other groups displayed significantly different latencies between the training and test sessions, which indicated a demonstration of aversive memory. After the behavioral tests, the subjects were decapitated, and their hippocampus and CSF were isolated to analyze their cytokine and brain-derived neurotrophic factor (BDNF) levels. In the hippocampus, it was observed that interleukin (IL)-10, IL-4, and BDNF levels increased in meningitis and meningitis + EE groups as compared to the other groups. However, the TNF-a, IL-6, and CINC-1 levels did not change. In the CSF, BDNF levels increased in meningitis and meningitis + EE groups as compared to the other groups, and TNF-a levels did not change. 

Investigation of the effect of environmental enrichment on the behavioral, biochemical, and physiologic responses of rats

Konkle, Kentner, Baker, Stewart, and Bielajew (2010) investigated the behavioral, biochemical, and physiologic consequences of environmental enrichment (EE) in rats. Fifty-eight male rats: 30 Sprague-Dawley, and 28 Long Evans were used in the experiment. The experiment was divided into two studies. In the first study, 16 subjects from each stock (8 per group) first received sucrose training and stabilization. The subjects were then housed in the EE room for six weeks and were required to perform weekly tests of sucrose intake and preference. The subjects’ trunk blood and adrenal glands were collected after the treatment phase to measure their weight to calculate their stress response. Results indicated an 18% increase in body weight in the Long Evans rats and a 12% increase in body weight in Sprague–Dawley rats. The enriched group had a 15% increase in body weight, and the control group had a 10% increase. In the second study, 12 Long Evans (6 per group) and 14 Sprague–Dawley (7 per group) rats received a stimulating electrode implant in the ventral tegmental area. The subjects were then trained to press a lever to self-administer brain stimulation reward on a continuous reinforcement schedule. The subjects were then divided and housed in either control or EE housing conditions for six weeks. After the six weeks, the subjects were required to perform two trials on the Forced Swim Test (FST) apparatus, and their active, passive, or other swimming behaviors were observed. Results indicated that the Sprague–Dawley rats were more active than Long Evans rats in the FST. The subjects from the enriched group displayed a decrease in the overall duration of active behaviors and a greater increase in other swimming behaviors such as swimming without struggling and grooming from the first to the second test day as compared to the control group. The Long Evans rats showed a higher grooming frequency on the second day versus the first day than the Sprague-Dawley rats. 

Strengths and Limitations

Strengths 

The EE Room is a large cage that can easily house around 13 subjects or more. It has three floors and contains sufficient environmental enrichment of different shapes and textures such as running wheels, toys, stairs, wooden blocks, hanging items, a see-saw, plastic tunnels, and tubes. The enrichment objects can easily be replaced and moved around the cage. It can be used as part of experimental protocols that test the effect of environmental enrichment on learning and memory behaviors, stress, anxiety, age-related cognition, as well as operant conditioning. It can also be used to house subjects instead of standard cages to improve their welfare. 

Limitations 

The enrichment objects have to be routinely changed or moved around so that the subjects do not lose interest in them. The EE Room may provide different levels of stimulation depending on factors such as age, gender, and strain of the subjects.

Summary

• The EE Room is a large cage that is used to house subjects and contains abundant enrichment objects such as running wheels, toys, hanging items, and plastic tunnels. It also contains three floors and has adequate room for the subjects to move around.

• It can be used as part of different experimental protocols that test the effect of environmental enrichment on learning and memory behaviors, stress and anxiety behaviors, and age-related cognition.

• It can also be used to house subjects instead of placing them in standard cages that lack enrichment to improve their welfare.

References

1. Bahi A. (2017). Environmental enrichment reduces chronic psychosocial stress-induced anxiety and ethanol-related behaviors in mice. Progress in neuro-psychopharmacology & biological psychiatry, 77, 65–74. https://doi.org/10.1016/j.pnpbp.2017.04.001
2. Barichello, T., Fagundes, G. D., Generoso, J. S., Dagostin, C. S., Simões, L. R., Vilela, M. C., Comim, C. M., Petronilho, F., Quevedo, J., & Teixeira, A. L. (2014). Environmental enrichment restores cognitive deficits induced by experimental childhood meningitis. Revista brasileira de psiquiatria (Sao Paulo, Brazil : 1999), 36(4), 322–329. https://doi.org/10.1590/1516-4446-2014-1443
3. Bayne K. (2018). Environmental enrichment and mouse models: Current perspectives. Animal models and experimental medicine, 1(2), 82–90. https://doi.org/10.1002/ame2.12015
4. Harati, H., Majchrzak, M., Cosquer, B., Galani, R., Kelche, C., Cassel, J. C., & Barbelivien, A. (2011). Attention and memory in aged rats: Impact of lifelong environmental enrichment. Neurobiology of aging, 32(4), 718–736. https://doi.org/10.1016/j.neurobiolaging.2009.03.012
5. Konkle, A. T., Kentner, A. C., Baker, S. L., Stewart, A., & Bielajew, C. (2010). Environmental-enrichment-related variations in behavioral, biochemical, and physiologic responses of Sprague-Dawley and Long Evans rats. Journal of the American Association for Laboratory Animal Science: JAALAS, 49(4), 427–436.