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Updated: Jul 16, 2026
Morris Water Maze Test: Optimization for Mouse Strain and Testing Environment
Published on: June 22, 2015
Mu opioid receptor knockout mice in the Morris Water Maze: a learning or motivation deficit?
Marianne E Lubbers1, Ruud van den Bos, Berry M Spruijt
1Ethology & Welfare, Department of Animals, Science and Society, Faculty of Veterinary Medicine, Utrecht University and Rudolf Magnus Institute of Neuroscience, University Medical Centre, Utrecht, The Netherlands. M.Lubbers@vet.uu.nl
Abstract:
An earlier study done by Kas et al. [Kas MJ, van den Bos R, Baars AM, Lubbers M, Lesscher HM, Hillebrand JJ, et al. Mu-opioid receptor knockout mice show diminished food-anticipatory activity. Eur J Neurosci 2004;20(6):1624-32] suggested that mu opioid receptor (MOR) knockout mice have deficits in the motivational component rather than in the information processing component of learning. To substantiate this difference further, MOR knockout mice and wildtype littermates were tested in the Morris Water Maze (MWM), which allows for testing both components of learning. On traditional parameters for performance, no significant differences between genotypes were found. However, swimming velocity, indicative of motivation, decreased for MOR knockout mice during the course of training but not for wildtype mice. In contrast, probe trial performance was comparable between genotypes. Again, these results suggest normal information processing abilities but a decreased motivation in this MOR knockout mouse. Our conclusion is discussed in the light of other studies using MOR knockout mice that do find differences on information processing between genotypes in MWM performance.
Insights
Mu-opioid receptor (MOR) knockout mice show normal learning but decreased motivation. These findings in the Morris Water Maze suggest MORs are crucial for motivation in learning tasks.
Area of Science:
- Neuroscience
- Behavioral Neuroscience
- Pharmacology
Background:
- Previous research suggested mu-opioid receptor (MOR) knockout mice exhibit deficits in learning motivation, not information processing.
- The mu-opioid receptor system plays a role in reward and motivation, influencing behavior.
Purpose of the Study:
- To further investigate the role of mu-opioid receptors in the motivational and information processing components of learning.
- To differentiate between deficits in learning strategy and motivation in MOR knockout mice.
Main Methods:
- Utilized the Morris Water Maze (MWM) to assess spatial learning and memory in MOR knockout mice and wildtype littermates.
- Monitored traditional performance parameters and swimming velocity as an indicator of motivation.
Main Results:
- No significant differences in traditional MWM performance parameters were observed between MOR knockout mice and wildtype littermates.
- MOR knockout mice exhibited decreased swimming velocity during training, suggesting reduced motivation.
- Probe trial performance, assessing memory retention, was comparable between both groups.
Conclusions:
- The results indicate that MOR knockout mice possess intact information processing abilities for spatial learning.
- A deficit in motivation, rather than cognitive processing, is implicated in the behavioral changes observed in MOR knockout mice.
- These findings support a specific role for mu-opioid receptors in regulating the motivational drive for learning.
