Method Article

The Use of the Puzzle Box as a Means of Assessing the Efficacy of Environmental Enrichment

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DOI:

10.3791/52225

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December 29th, 2014

 ,  ,  , 
1Discipline of Physiology, University of Sydney, 2Bosch Animal Behavioural Facility, University of Sydney

In This Article

Summary

Environmental enrichment provides a potential protective effect against neurodegenerative disorders. Currently, however, there is no easy way of determining the efficacy of enrichment procedures. This protocol describes a simple “Puzzle Box” method for assessing an animal’s cognitive function, in order to reveal the effectiveness of environmental enrichment.

Abstract

Environmental enrichment can dramatically influence the development and function of neural circuits. Further, enrichment has been shown to successfully delay the onset of symptoms in models of Huntington’s disease 1-4, suggesting environmental factors can evoke a neuroprotective effect against the progressive, cellular level damage observed in neurodegenerative disorders. The ways in which an animal can be environmentally enriched, however, can vary considerably. Further, there is no straightforward manner in which the effects of environmental enrichment can be assessed: most methods require either fairly complicated behavioral paradigms and/or postmortem anatomical/physiological analyses. This protocol describes the use of a simple and inexpensive behavioral assay, the Puzzle Box 5-7 as a robust means of determining the efficacy of increased social, sensory and motor stimulation on mice compared to cohorts raised in standard laboratory conditions. This simple problem solving task takes advantage of a rodent’s innate desire to avoid open enclosures by seeking shelter. Cognitive ability is assessed by adding increasingly complex impediments to the shelter’s entrance. The time a given subject takes to successfully remove the obstructions and enter the shelter serves as the primary metric for task performance. This method could provide a reliable means of rapidly assessing the efficacy of different enrichment protocols on cognitive function, thus paving the way for systematically determining the role specific environmental factors play in delaying the onset of neurodevelopmental and neurodegenerative disease.

Introduction

Environmental enrichment (EE) may be defined as surroundings that provide animals with increased opportunity for social interaction, motor activity, and greater sensory stimulation than usually experienced in a standard laboratory environment.EE has been shown to consistently affect the behavior of animals, bringing about changes such as reduction of stress and anxiety-related activity 8-10, improved performance in learning and memory tasks 8,11, early onset of motor coordination and exploratory activity 11, changes in maternal care 8 as well as resistance to addictive substances 12-15. Further, EE has been revealed to ameliorate the effects of neurodegenerative disorders, delaying the onset and decreasing the severity of symptoms in animal models of Huntington’s 1-4,16, Parkinson’s 17 and Alzheimer’s disease 18.

These changes correlate with the anatomical and molecular alterations EE is known to induce throughout the brain. Animals raised in enriched environments from early stages of development show a myriad of neural changes, including increased brain weight and cortical thickness, dendritic branching 9,2-22 and synaptic density 23. EE can alter both the level and timing of growth factor expression 9,24-30, which has been shown to contribute to accelerated development of sensory 25,26,28,29, mnemonic 30, as well as motor circuits 31,32.

Previous work has revealed at times contradictory findings when investigating the impact of EE, without taking into account the different types of animals and environments used within individual studies 9,24,27,30. Currently, there is no consistent and simple behavioral task that can be used to measure the effectiveness of various EE paradigms in different strains and species of animals.

The Puzzle Box task was designed as a simple test to determine an animal’s native problem solving ability 7. Animals placed in the open area are required to remove obstructing materials situated within a small opening in order to access a covered region/shelter. Each subject is given three trials with the same obstruction in order to assess three different cognitive attributes. The first trial yields a baseline indication of inherent or native problem solving ability. The second trial, run on the same day, gives some indication of the animal’s ability to improve upon and thus reinforce strategies for removing the specific obstruction. The third trial, conducted on the following day, provides insight into the ability of the subject to retain and recall the learned solution to the task.

The motivation for solving these “obstruction puzzles” by the animals can be varied, potentially evoking an innate desire to avoid open fields and seek shelter, as well as an inherent drive to explore their surroundings 6,7. The multitude of potential behavioral drivers underlying the desire to solve the Puzzle Box suggests that various areas of the brain are involved in mediating task performance. Previous work has shown that in murine models of schizophrenia, the prefrontal cortex as well as the hippocampus are involved in the acquisition of this task 5. A lesion study in rats has also revealed a large number of brain regions involved in Puzzle Box performance, including various thalamic nuclei, the hypothalamus, the cerebellum, and limbic structures. Together, these findings indicate that engaging in this problem solving task involves a host of neural structures associated with cognitive function.

The Puzzle Box has been used successfully to assess the problem solving ability of mice, as well as cognitive deficits exhibited by murine models of schizophrenia 5-7. Performance on the task has been shown to be highly consistent, and correlate well with outcomes of other cognitive behavioral tests 6. The goal of this work was thus to adapt the Puzzle Box task to become a simple and reliable means of determining the effectiveness of EE.

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Protocol

Ethics statement: All procedures were approved by the Animal Ethics Committee of the University of Sydney and conformed to National Health and Medical Research Council of Australia guidelines. Procedures were performed on C57/BL6J mice which were reared at the University of Sydney Bosch Rodent Facility. All mice were housed in a single adequately-ventilated room in 21 °C ambient temperature on a 12 hr light-dark cycle with lights on at 0600 hr in individually ventilated cages with ad libitum access to dry food and water. Late-pregnancy females were randomly assigned to standard or environmentally enriched housing conditions.

1. Housing (Enrichment Levels):

  1. Obtain 4 late-pregnancy adult female mice. Randomly assign 2 to the standard condition and place each of them into a clean standard mouse cage (overall dimensions 391 x 199 x 160 mm) containing one red mouse igloo. For the enriched condition, place the remaining 2 mice into a single clean rat-sized cage (overall dimensions 462 x 403 x 404 mm).
  2. Into the enrichment cage, place a variety of objects designed to increase sensory and motor stimulation (e.g. running wheels, visual stimuli, scented cotton balls, Velcro strips).
  3. Every 2 to 3 days move these objects about within the cage; refresh any that have been destroyed.
  4. Upon weaning at 21 days postnatal, sex animals and place into male-female segregated housing consistent with the environmental condition they were raised. For the enriched condition ensure that there are between 3 and 10 mice per cage with 2 and 5 mice for standard. Commence behavioral testing once animals reach adulthood (12–14 weeks of age).

2. Construction of the Puzzle Box

  1. Obtain 6 pieces of white acrylic (or other non-porous material): one 750 x 280 mm, two 280 x 250 mm, two 750 x 250 mm, and one 150 x 280 mm (see Figure 1).
  2. Obtain one piece of black acrylic 280 x 250 mm, with a 40 x 40 mm square opening cut into one side of this piece (see Figure 1).
  3. Assemble the Puzzle Box as follows: use the 750 x 280 mm piece as the bottom of the box, use 280 x 250 mm pieces as the ends of the box, and the 750 x 250 mm pieces as the sides of the box.
  4. Measure 150 mm into the box from one end, and place the black piece of acrylic across the box so that it splits it into two compartments (one large, one small) with the opening flush with the bottom of the box.
  5. Take the 150 x 280 mm piece of white acrylic and place it atop the smaller compartment of the box making sure it covers this area completely, providing a dark “goal-box” chamber. Affix this piece of acrylic to the body of the main box by hinges, or leave free to be completely removed during behavioral testing.
  6. Take 3 pieces of acrylic (three 4 x 120 mm) and join to make a “u-shaped” channel.

Box diagram with labeled dimensions: 750x280x250 mm, 40 mm cutout, structural design.
Figure 1: Schematic diagram of the Puzzle Box task. The Puzzle Box is an acrylic box consisting of an open-field area (600 x 280 mm) and a sheltered goal-box area (150 x 280 mm), measuring 750 x 280 mm in all. A 40 x 40 mm opening within the partition (grey) separating the two areas allows animals to access to the covered goal-box area from the open field. This opening is blocked with obstructions that are increasingly difficult to remove as testing progresses. Animals undergo a five-day protocol, consisting of four obstruction conditions with three trials for each condition.

3. Running of the Puzzle Box Task

  1. Thoroughly clean the Puzzle Box with 70% alcohol. Repeat this step between each animal tested.
  2. Place a clean red mouse igloo within the goal-box area of the Puzzle Box, and replace the lid on the goal-box.
  3. If there is an obstruction condition being tested, place the obstruction within the doorway of the goal-box (see Figure 2).
  4. Place the mouse being tested into the open-field section of the Puzzle Box, oriented towards the goal-box, and at the end furthest from the goal-box.
  5. Record the time taken for all four paws of the animal to enter the goal-box section of the Puzzle Box.
  6. If an animal does not enter the goal-box, terminate the trial once the set time limit is reached (see Table 1).
  7. Once a trial is finished, remove the animal from the Puzzle Box and place it into a separate holding cage until the next trial begins. Keep a 60 to 180 sec gap between trials for each animal.
  8. For each animal, perform three trials per day for five consecutive days of testing, with four obstruction conditions and three trials of each condition. The third trial of a given obstruction condition should always administered on a subsequent day (see Table 1).

Trial conditions table detailing obstruction and time limits per day.
Table 1: Scheme of the Puzzle Box task. The Puzzle Box task is run for five days, and consists of four obstruction conditions. There are three trials on each of the first four days, and one on the fifth day. Each obstruction condition has three trials; the first two on one day, and the third the day immediately following. The first trial of an obstruction condition aims to test native problem-solving ability, the second trial examines task acquisition and reinforcement, and the third trial is used as an assay for solution retention and recall.

Maze experiment diagram with rat exploring obstacles to demonstrate spatial learning and memory.
Figure 2: Obstruction conditions within the Puzzle Box task. Schematic diagrams of the Puzzle Box arena and the obstruction conditions used within this study. (A) Condition 0 (C0), with no obstruction present within the doorway between the open-field and goal-box areas. (B) Condition 1 (C1), with a “u shaped” channel present within the doorway between the open-field and goal-box areas. (C) Condition 2 (C2), where the channel is filled with clean bedding material. (D) Condition 3 (C3), with a “tissue plug” present within the doorway between the open-field and goal-box areas. (E) Condition 4 (C4) with a “foam plug” present within the doorway between the open-field and goal-box areas. Dimensions of the arena are as per listed in Methods and Figure 1.

4. Interpretation of Data

  1. Represent data as either time taken to complete the trial (including null trials where animals did not complete the task within the specified time limit) or as the number of null trials.
  2. Use a repeated measures ANOVA to assess the effect of housing condition upon performance within the Puzzle Box, with obstruction type/condition (C) and task number (T) within-subjects factors and enrichment level (standard versus enriched) as between-subjects factor.

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Results

The results described here are a representative sample, with data taken from several cohorts consisting of different litters. All behavioral testing was conducted between 0700 and 1100 hr, with randomized testing order of animals within a cohort. Animals raised in an enriched environment (n = 14, 7 female and 7 male) took significantly less time to solve the obstruction tasks within the Puzzle Box than those raised within a standard environment (n = 15, 7 female and 8 male) (see Figure 3) (Repeated measu...

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Discussion

The data presented demonstrate that the Puzzle Box can be used effectively to assess the impact of EE. Mice raised in enriched environments consistently took significantly less time to solve obstruction puzzles within this behavioral assay than did animals raised within standard laboratory conditions. Moreover, this difference was most prominent in the first trial for three of the four conditions tested, suggesting EE has a greater influence on an animal’s native problem-solving ability, relative to their capacity ...

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Disclosures

The authors declare they have no competing financial interests.

Acknowledgements

The authors have no acknowledgements.

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Materials

List of materials used in this article
NameCompanyCatalog NumberComments
Black Acrylic Board280 x 250 mm with a 40 x 40 mm "door" cut into one side
White Acrylic Board280 x 250 mm
White Acrylic Board280 x 250 mm
White Acrylic Board750 x 250 mm
White Acrylic Board750 x 250 mm
White Acrylic Board150 x 280 mm
White Acrylic Board
Underpass3 pieces of 40 x 120 mm plexiglass or acrylic
Note: If unable to access acrylic board, plexiglass or similar non-porous material will suffice.
WebcamLogitechC210Fix to roof with electrical tape. Alternatively, use a tripod.
VirtualDub v1.10.4VirtualDubN/A Software for recording behaviour videos. Input from webcam.
TopScan v 3.0CleverSys Inc.N/A Software for automated top-view tracking and analysis of mouse behaviour. Captured videos are analysed post-hoc.

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Cognitive FunctionBehavioral AssayMouse ModelShelter SeekingObstruction TaskHousing ConditionsRepeated Measures ANOVACognitive Load

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