Introduction

The Environmental Enrichment Housing Cage is a large, multilevel housing cage used to provide rodents with environmental enrichment. It contains ladders, tunnels, and cross ropes that allow rodents to traverse from one level to another. The Environmental Enrichment Housing Cage can be used as part of various experimental protocols that test the effect of environmental enrichment on rodent behavior. It can particularly be useful for experimental protocols involving motor training after injury since the multilevel design of the cage challenges motor performances in rodents. 

Environmental enrichment housing conditions help provide rodents with stimulus-enriched environments that have long-lasting behavioral and neurobiological effects. Moreover, enriched housing conditions also help provide motor stimulation and promote the physical well-being of rodents (Hakon et al., 2017).  The Environmental Enrichment Housing Cage helps provide rodents with cognitive and motor stimulation. Apart from the ladders and the tunnels, it contains a running wheel to promote physical exercise. In addition, toys, woodblocks, and other environmental enrichment objects can also be placed. The Environmental Enrichment Housing Cage can also provide social stimulation by housing the subjects in groups. Furthermore, the cage is large enough to place apparatuses for behavioral testing, such as a trough training device used to evaluate forelimb motor performance. 

Other environmental enrichment cages used for housing rodents include the Environmental Enrichment (EE) Cage and the Environmental Enrichment (EE) Room. 

Apparatus and Equipment

The Environmental Enrichment Housing Cage is a multilevel cage that measures 93.9 cm in length, 61.60 cm in width, and 142.24 cm in height. The cage contains ladders, tunnels, and cross ropes placed in different parts of the cage that allow rodents to traverse from one level to another. In addition, a running wheel is also present.  

Training Protocol

Clean the apparatus regularly. Appropriately light the apparatus. A tracking and recording system such as the Noldus Ethovision XT can be used to assist with observations.

The following is a sample protocol used to measure the effects of forelimb function improvement following spinal cord injury using the Environmental Enrichment Housing Cage:

Pre-training 

Single Pellet Test Training 

Train the subjects in an acrylic glass reaching chamber (45 cm deep; 40 cm tall; 12.5 cm wide) containing a 1 cm wide slot in the front wall. Place a chocolate food pellet in the food well 1.5 cm away from the chamber. Allow the subject to reach the food pellet with its right forelimb through the wide slit of the chamber. Allow the subject to shuttle back and forth in the chamber between reaches. Conduct training until the subject consistently reaches the pellet using its right forelimb in at least 8 out of 20 trials. Conduct 5 training sessions per day for six weeks.

Staircase Test Training

Train the subjects in a small chamber that has an opening on end, which leads to a plinth on top of a platform with a staircase on each side with seven wells equally placed along the side of the platform. Bait each well with three 45-mg food pellets. Allow the subject to retrieve the pellets from each well by reaching its forelimb out. Conduct two 15 minute sessions a day for two weeks. 

Environmental Enrichment Housing Cage Task

Perform C3-C4 right side contusions to all the subjects. Five days following surgery, divide the subjects into control and experimental groups. In the control group, house two subjects per cage in standard cages with no enrichment. House the experimental groups 5 per cage in the Environmental Enrichment Housing Cage. Provide the subjects with a food-restricted diet. Allow the subjects to remain in their respective housing conditions throughout the study. 

Post-operative Skilled Motor Training (Forelimb Motor Training Trough Task) 

Conduct motor training trials, 13 days following spinal cord injury. Place the trough task apparatus, which is a small chamber (35 x 6 cm) with an opening on one end and a platform on the other end, in the Environmental Enrichment Housing Cage. Fill the trough on the ride side of the platform with flavored food pellets. Allow the subject to obtain the food pellets to observe their grasping abilities. Conduct training seven days a week for 12 weeks. 

Post-operative Behavioral Testing

Single Pellet Reaching Test

Conduct trials similar to single pellet test training to assess forelimb-reaching performance.

Spontaneous (untrained) Locomotor Test

Allow the subject to walk on an elevated grid (36 cm length; 38 cm width; 30 cm height, with 3 cm length and 2 cm width openings) for 2 minutes to assess sensorimotor integration. 

Forelimb Locomotor Score (FLS).

Place the subject in the Open Field Apparatus and observe its behavior for 4 minutes. 

Literature Review

Investigation of forelimb motor performance after spinal cord injury in rats

Krisa et al. (2012) investigated the effect of amphetamine (AMPH) enhanced training, skilled forelimb training, and environmental enrichment housing on forelimb motor performance after spinal cord injury in rats. One hundred and one adult male Sprague Dawley rats received C3–C4 right side contusions since spinal cord injury to these segments affects the muscles used to perform skilled reaching and grasping. Twenty-five of the subjects were used in a dose-response study to determine the optimal dose of AMPH, of which nine received 0.5, seven received 0.7, and nine received 2.0 mg/kg amphetamine. The remaining subjects were divided into five experimental groups: injured controls (n = 13); training only (n = 12); drug only (n = 10); AMPH and training (n = 14); and AMPH and training and EE housing (n = 10). The control subjects were housed in standard housing conditions with no enrichment, while the EE housing groups were housed in the Environmental Enrichment Housing Cage. Pre-operative training was performed, which consisted of single-pellet test training and staircase test training. In the single pellet training test, the subjects were trained using a chamber that contained a slit. The subjects were trained to reach a food pellet placed 1.5 cm away from the slit using their right forelimb. In the staircase test training, the subjects were trained in a chamber with an opening at one end that leads to a platform with a staircase on each side. The staircase contained seven wells, and each well contained three food pellets. The subjects were trained to reach the food pellets from each well. Thirteen days following surgery, post-operative training began that included training on a trough reaching task and a tray reaching task. In addition, during the first week of training, the subjects were trained to climb an inclined grid surface to reach cereal rewards to encourage them to use their injured forepaw. In the trough reaching task, a trough task apparatus was placed in the Environmental Enrichment Housing Cage. The trough on the right side of the platform contained pellets, and the subjects were trained to reach the pellets to observe their grasping ability. In the tray reaching task, the subjects were trained to reach food pellets placed on a tray. Post-operative behavioral testing was then performed. The subjects were required to perform skilled tests that included the single pellet test, staircase-reaching test, spontaneous (untrained) locomotor test, and forelimb locomotor score test. The single pellet test and staircase reaching test were performed in the same manner as training. In the spontaneous locomotor test, the subjects were required to walk on an elevated grid to test their sensorimotor integration. In the forelimb locomotor test, the subject’s movements were observed in an open field. Results indicated that the spinal cord injury initially produced a moderate deficit in forelimb function. The administration of AMPH caused significantly more locomotor movements than saline alone throughout the experiment. Among the doses tested, the 2.0 mg/kg AMPH dose produced the most locomotor activity and greater activity in training. However, 1.0 mg/kg was chosen as the optimal dose for subsequent experiments. Qualitative results from the skilled forelimb reaching tests indicated that the AMPH and training group performed significantly better than control or drug only groups. In contrast, quantitative results showed deficits in task performance, with no differences seen among all groups. Results from the grid walking test indicated deficits in the right forelimb, with no significant differences among groups. In the forelimb locomotor test performed during the final testing week, few locomotor deficits were observed with no significant difference among groups. In the subjects that were housed in the enriched cage and received drug and training, skilled motor performance was significantly worse as compared to other groups. Therefore, results indicated no benefit of AMPH enhanced training on forelimb recovery.

Investigation of the effect of amphetamine and physical activity on motor recovery in rats

Auriat and Colbourne (2008) investigated the effect of amphetamine (AMP) and environmental enrichment housing on motor recovery after intracerebral hemorrhage in rats. Sixty, seven-week-old rats were used in the study and housed in standard cages. The subjects were then required to undergo behavioral training that included the staircase test, tray test, horizontal ladder walking test, and beam walking test. In the staircase test, the subjects were trained to reach for three food pellets per stair for a total of 21 pellets per limb to assess their forelimb reaching ability. In the tray test, the subjects were trained to reach for food pellets placed on a tray through vertical bars of the cage. In the horizontal ladder walking test, the subjects were trained to cross a horizontal ladder. Similar to the horizontal ladder walking test, in the beam walking test, the subjects were trained to cross an elevated beam. After behavioral training, surgery was performed, producing a moderate-sized intracerebral hemorrhage (ICH) in the subjects. Five days following surgery, the subjects were assigned to environmental enrichment (EE) housing conditions or group housing (GH), where they remained in their standard cages. The rats were then injected with either AMPH (2 mg/kg) or sterile saline (SAL). Therefore, four treatment groups were studied:   GH+ SAL, GH+AMP, EE + SAL, and EE +AMP.  The AMP injections or saline were given on days 7, 9, and 11 days following ICH surgery. The subjects from the EE conditions were given rehabilitation training 30 minutes after injections, which consisted of elevated beam training and the tray task training. Behavioral testing was also performed on the elevated beam, tray task, horizontal ladder, and staircase test. Results from the beam walking tests indicated EE treatment improved beam walking, but AMP did not. It was observed that the EE + SAL group performed significantly better than the GH + SAL and GH + AMP groups. However, no significant differences were observed between the GH + SAL and GH + AMP groups and between EE + AMP and EE + SAL groups, which indicated no significant effect of AMP. Similar results were observed on the ladder test in which EE improved ladder test performance, but AMP did not. In the staircase reaching test, performance improved across testing in all groups, and no significant differences in performance were observed between all groups. In the tray task, large differences in dropout rates were observed across testing, so tray data were not analyzed. 

Data Analysis

Behavioral differences after living in the Environmental Enrichment Housing Cage vs. standard housing.

Strengths and Limitations

Strengths 

The Environmental Enrichment Housing Cage is used to provide rodents with environmental enrichment. The multilevel design of the cage challenges the motor performances of rodents, which can be used as rehabilitation following motor injury. Ladder, tunnels, and cross ropes are present throughout the cage. The cage also includes a running wheel. Moreover, other environmental enrichment objects such as toys and wood blocks can also be placed. The Environmental Enrichment Housing Cage can be used as part of various experimental protocols that test the effect of environmental enrichment on rodent behavior or physical performance. In addition, it can also be used to house rodents to improve their welfare. 

Limitations 

Environmental enrichment objects inside the cage may have to be replaced with new objects weekly so that the rodents do not lose interest in them. Factors such as age, gender, and strain of rodents may affect the level of cognitive and motor stimulation received through the cage. 

Summary

• The Environmental Enrichment Housing Cage is a multilevel housing cage used to provide rodents with environmental enrichment.
• The Environmental Enrichment Housing Cage includes ladders, cross ropes, and tunnels that help rodents to traverse from one level to the other and helps provide rodents with motor stimulation. 
• The Environmental Enrichment Housing Cage can be used as rehabilitation after motor injury. It can also be used as part of various experimental protocols that test the effect of environmental enrichment on rodent behavior. 
• The Environmental Enrichment Housing Cage can also be used to house subjects to improve their welfare. 

References

1. Auriat, A. M., & Colbourne, F. (2008). Influence of amphetamine on recovery after intracerebral hemorrhage in rats. Behavioral brain research, 186(2), 222–229. https://doi.org/10.1016/j.bbr.2007.08.010
2. Hakon, J., Quattromani, M. J., Sjölund, C., Tomasevic, G., Carey, L., Lee, J. M., Ruscher, K., Wieloch, T., & Bauer, A. Q. (2017). Multisensory stimulation improves functional recovery and resting-state functional connectivity in the mouse brain after stroke. NeuroImage. Clinical, 17, 717–730. https://doi.org/10.1016/j.nicl.2017.11.022
3. Krisa, L., Frederick, K. L., Canver, J. C., Stackhouse, S. K., Shumsky, J. S., & Murray, M. (2012). Amphetamine-enhanced motor training after cervical contusion injury. Journal of neurotrauma, 29(5), 971–989. https://doi.org/10.1089/neu.2011.1767