How Do Different Types of Repetitive Behaviors Manifest in a Mouse Model of OCD?

What you need to know

• Mice lacking the Sapap3 gene show multiple types of repetitive behaviors beyond just excessive grooming
• The mice display sudden twitching movements similar to tics seen in Tourette syndrome
• Excessive scratching behavior may be responsible for skin lesions previously attributed to grooming
• Treatment with aripiprazole, a medication used for tics, reduces most repetitive behaviors except complex grooming sequences

A Closer Look at Different Repetitive Behaviors

The study examined mice lacking the Sapap3 gene, which have traditionally been used to study obsessive-compulsive disorder (OCD). While these mice were known to show excessive grooming behavior, researchers discovered they actually display several distinct types of repetitive movements:

Sudden Twitching Movements

The researchers observed rapid, sudden head and body twitches in the mice that were similar to tics seen in people with Tourette syndrome. These movements:

• Occurred much more frequently in mice lacking Sapap3 compared to normal mice
• Were quick, isolated movements rather than complex behavioral sequences
• Responded well to treatment with aripiprazole, a medication commonly used to treat tics in humans

Excessive Scratching

The study found that the mice engaged in frequent scratching with their hind paws that:

• Was significantly more common than in normal mice
• Often targeted areas like the neck and back
• Appeared to cause many of the skin lesions previously attributed to excessive grooming
• Also improved with aripiprazole treatment

Two Types of Grooming

The researchers distinguished between two different kinds of grooming behavior:

1. Short, simple grooming movements lasting less than 3 seconds
2. Longer, complex grooming sequences involving multiple coordinated movements

Only the short, simple grooming movements were reduced by aripiprazole treatment. The longer grooming sequences, while still excessive compared to normal mice, did not respond significantly to the medication.

Why This Matters for Understanding Human Conditions

These findings are important because:

1. They show that these mice display behaviors similar to multiple conditions that often occur together in humans - particularly OCD and Tourette syndrome

2. The different types of repetitive behaviors responded differently to medication, suggesting they may involve different brain circuits

3. This helps explain why many people with OCD also experience tics or other repetitive behaviors, and why some symptoms may respond better to certain treatments than others

Brain Circuits Involved

The study suggests these behaviors involve two main circuits in the brain:

1. The “associative” circuit - connects areas involved in planning and decision-making to the striatum (a region that helps control movement)

2. The “sensorimotor” circuit - connects movement-related brain areas to the striatum

Previous research focused mainly on the associative circuit in OCD, but this study suggests both circuits may be important in conditions involving repetitive behaviors.

Practical Implications for Treatment

The findings have several important implications for treatment:

1. Different types of repetitive behaviors may need different treatment approaches

2. Medications that work for tics (like aripiprazole) might help with certain repetitive behaviors but not others

3. Looking at the specific types of repetitive behaviors a person shows might help predict which treatments will work best

Conclusions

• Repetitive behaviors in neuropsychiatric conditions may be more complex than previously thought, with distinct types that respond differently to treatment

• The overlap between different types of repetitive behaviors helps explain why conditions like OCD and Tourette syndrome often occur together

• Understanding the different types of repetitive behaviors and their underlying brain circuits could lead to more targeted and effective treatments