Effects of Corticosteroids on Behavior in DMD Mouse Models

Duchenne muscular dystrophy (DMD) is a serious genetic disorder that mainly affects boys. It happens in about 1 in every 5,000 males. This condition leads to severe muscle weakness and wasting. Over time, the condition worsens, and many patients lose the ability to walk. DMD can also harm the heart and lungs, which may lead to early death, often around ages 30 to 40.

Besides muscle problems, many DMD patients experience cognitive and behavioral issues. Up to 30% of them may have conditions like autism, obsessive-compulsive disorder, attention deficit hyperactivity disorder (ADHD), depression, Anxiety, and problems with attention and Memory. Families often report that these challenges affect their overall quality of life.

#What Causes DMD?

DMD is caused by changes or mutations in the DMD gene. This gene is crucial because it produces a protein called dystrophin, which helps keep muscles healthy. The DMD gene has seven areas that control its activity, leading to different forms of dystrophin found in various body parts. One of these forms, called Dp427m, is mostly found in muscle. Other forms are present in the brain, mainly in areas responsible for emotions and memory.

Depending on where the mutation is in the DMD gene, patients may miss some or all of these dystrophin forms. About 45% of patients only miss Dp427, while another 45% miss both Dp427 and a form called Dp140. A small group of around 3-10% does not have any dystrophin forms at all. Studies suggest that the number of missing dystrophin forms may relate to the severity of cognitive and behavioral issues.

#Treatment and Its Challenges

Many DMD patients take Corticosteroids, such as prednisolone or deflazacort. These medicines help slow muscle damage. While they can positively affect muscle health, they can also lead to weight gain, bone problems, short stature, changes in behavior, cataracts, and other serious side effects. Families often cite these behavior changes as a common reason to stop corticosteroid treatment.

In healthy individuals, using corticosteroids can lead to negative emotions, trouble focusing, and memory issues. Unfortunately, research on how these treatments affect behavior and thinking in DMD patients is limited. The few studies available show mixed results. Some suggest an increase in irritability, while others do not find clear links between corticosteroids and behavioral changes in DMD patients. It's also known that different types of corticosteroids may lead to different effects. For example, prednisolone is linked to more behavioral changes compared to deflazacort.

Research about how these treatments influence the brain in models of DMD, like mice, is still not well understood. The most used mouse model for DMD, called mdx, lacks the full-length Dp427 dystrophin form. These mice show signs of increased anxiety, fear, and memory issues. Some other mouse models lacking additional forms of dystrophin show even more challenges.

#Behavioral Tests in Mouse Models

Using mouse models can help researchers learn more about how corticosteroids affect behavior and thinking. In healthy mice, corticosteroid treatment is connected with increased anxiety, avoidance, and learning problems. However, the specific effects in DMD mouse models remain unclear, especially in those lacking multiple dystrophin forms.

This study aimed to examine how corticosteroid treatment affects behavior in different DMD mouse models. Mice without one dystrophin form (mdx) and those missing more than one form (mdx4cv) were analyzed to see if they responded differently to corticosteroid treatment.

Corticosteroid treatment was given through a slow-release pellet. After the pellets were placed, mice underwent various behavioral tests to assess anxiety, social behavior, and memory.

#Unexpected Challenges with the Study

Due to technical issues, the pellets released their medicine for a shorter time than expected. Tests assessing memory and other Behaviors had to be left out because they occurred when the pellets were no longer working effectively. Some early findings showed that, compared to placebo-treated mice, those treated with prednisolone showed slightly less anxious behavior, but this was not consistent across all tests.

No significant changes were observed in social behavior or memory. Overall, the presence of prednisolone did not lead to notable behavioral changes in the mice.

#Details of the Study Setup

Male mouse models of DMD and healthy control mice were bred and housed in a controlled environment. Mice were treated with either prednisolone or a placebo from 7 weeks of age. Their body weights were monitored, and after a week of recovery, behavioral tests were conducted.

Performance in the tests was impacted by the reduced effectiveness of the pellets over time. Researchers analyzed behavioral outcomes, focusing primarily on anxiety levels, social preferences, and memory.

#Behavioral Tests Conducted

#Dark Light Box

In this test, mice were placed in a box with a bright side and a dark side. They were monitored to see how much time they spent exploring the bright area. Less time in the light area suggests higher anxiety. Results showed that DMD mouse models spent significantly less time in the light than healthy mice, indicating they were more anxious. Corticosteroid treatment seemed to lead to slightly more exploration of the light area during specific visits.

#Open Field Test

Mice were placed in a large open space and their activities were tracked. The main focus was to see how much they moved and how close they stayed to the walls of the field. Results indicated that treated mice moved less and stayed close to the walls, which is common for anxious behavior. However, this lower activity could also stem from weight loss experienced by treated animals.

#Social Interaction Test

Mice were given the choice to interact with either an object or another mouse. The focus was on whether the mice preferred social interaction. Results showed that DMD mice preferred to interact with the other mouse, but corticosteroid treatment did not change this behavior.

#Barnes Maze

The Barnes maze tested spatial learning and memory. Mice were placed in a maze with a hidden escape box. They had to learn where to find the exit. Results indicated that there were no differences in how well the various groups of mice learned or remembered the maze layout, regardless of treatment.

#Conclusion

In summary, the study found minimal or no effects of corticosteroid treatment on behavior in DMD mouse models. A slight decrease in anxiety was observed in one test, but this was not consistent across all measures. Additionally, the treatment did not seem to affect social interactions or memory performance.

These findings are surprising since corticosteroids have been shown to influence behavior in other models. Potential explanations for these discrepancies include the specific doses used, the timing of behavioral tests, and the long-term effects of chronic corticosteroid use.

Future research is essential to explore how different treatment strategies can minimize negative impacts while maximizing the benefits of corticosteroid use in managing DMD. Understanding the long-term effects and refining treatment methods could lead to better care for DMD patients.