Neuroscience and Actometry: an example of the benefits of the precise measurement of behavior

Viral vector-mediated SLC9A6 gene replacement reduces cerebellar dysfunction in the shaker rat model of Christianson syndrome

Background

Christianson syndrome (CS) is an x-linked recessive neurodevelopmental and neurodegenerative condition characterized by severe intellectual disability, cerebellar degeneration, ataxia, and epilepsy. Mutations to the SLC9A6 gene encoding NHE6 are responsible for CS, and we recently demonstrated that a mutation to the rat Slc9a6 gene causes a similar phenotype in the spontaneous shaker rat model, which exhibits cerebellar degeneration with motor dysfunction. In previous work, we used the PhP.eB-L7-Slc9a6-GFP adeno-associated viral (AAV) vector to demonstrate that gene replacement in Purkinje cells reduced the shaker motor and molecular phenotype.

Methods

We carried out a 20-week longitudinal study evaluating the impact of Purkinje cell-specific gene replacement on ataxia and tremor. Taking advantage of the high homology between human SLC9A6 and rat Slc9a6, we tested a more clinically relevant construct, AAV9-CAG-hSLC9A6 AAV vector in the shaker rat. In both experimental cohorts, we performed molecular studies to evaluate expression of NHE6 and key cerebellar markers. We then characterized the relationship between molecular markers and motor function, as well between tremor and ataxia.

Results

Administration of either of PhP.eB-L7-Slc9a6-GFP or AAV9-CAG-hSLC9A6 AAV vectors led to significant improvement in the molecular and motor phenotypes. The abundance of each disease-relevant cerebellar proteins was significantly correlated to motor ataxia. Further, we found that the relationship between cerebellar ataxia and tremor devolved over time, with disease modifying therapy disrupting their temporal relationship.

Conclusions

These findings impact future SLC9A6-targeted gene therapy efforts for CS and strongly support gene replacement as a viable therapeutic strategy. Furthermore, tremor and ataxia phenotypes may arise from dissociable cerebellar mechanisms.

A novel naïve Bayes approach to identifying grooming behaviors in the force-plate actometric platform

BACKGROUND

Self-grooming behavior in rodents serves as a valuable behavioral index for investigating stereotyped and perseverative responses. Most current grooming analyses rely on video observation, which lacks standardization, efficiency, and quantitative information about force. To address these limitations, we developed an automated paradigm to analyze grooming using a force-plate actometer.

NEW METHOD

Grooming behavior is quantified by calculating ratios of relevant movement power spectral bands. These ratios are input into a naïve Bayes classifier, trained with manual video observations. The effectiveness of this method was tested using CIN-d mice, an animal model developed through early-life depletion of striatal cholinergic interneurons (CIN-d) and featuring prolonged grooming responses to acute stressors. Behavioral monitoring was simultaneously conducted on the force-place actometer and by video recording.

RESULTS

The naïve Bayes approach achieved 93.7% accurate classification and an area under the receiver operating characteristic curve of 0.894. We confirmed that male CIN-d mice displayed significantly longer grooming durations than controls. However, this elevation was not correlated with increases in grooming force. Notably, the dopaminergic antagonist haloperidol reduced grooming force and duration.

COMPARISON WITH EXISTING METHODS

In contrast to observation-based approaches, our method affords rapid, unbiased, and automated assessment of grooming duration, frequency, and force.

CONCLUSIONS

Our novel approach enables fast and accurate automated detection of grooming behaviors. This method holds promise for high-throughput assessments of grooming stereotypies in animal models of neuropsychiatric disorders.

A novel naïve Bayes approach to identifying grooming behaviors in the force-plate actometric platform

Background

Self-grooming behavior in rodents serves as a valuable model for investigating stereotyped and perseverative responses. Most current grooming analyses primarily rely on video observation, which lacks standardization, efficiency, and quantitative information about force. To address these limitations, we developed an automated paradigm to analyze grooming using a force-plate actometer.

New Method

Grooming behavior is quantified by calculating ratios of relevant movement power spectral bands. These ratios are then input into a naïve Bayes classifier, trained with manual video observations. To validate the effectiveness of this method, we applied it to the behavioral analysis of the early-life striatal cholinergic interneuron depletion (CIN-d) mouse, a model of tic pathophysiology recently developed in our laboratory, which exhibits prolonged grooming responses to acute stressors. Behavioral monitoring was simultaneously conducted on the force-place actometer and by video recording.

Results

The naïve Bayes approach achieved 93.7% accurate classification and an area under the receiver operating characteristic curve of 0.894. We confirmed that male CIN-d mice displayed significantly longer grooming durations compared to controls. However, this elevation was not correlated with increases in grooming force. Notably, haloperidol, a benchmark therapy for tic disorders, reduced both grooming force and duration.

Comparison with Existing Methods

In contrast to observation-based approaches, our method affords rapid, unbiased, and automated assessment of grooming duration, frequency, and force.

Conclusions

Our novel approach enables fast and accurate automated detection of grooming behaviors. This method holds promise for high-throughput assessments of grooming stereotypies in animal models of tic disorders and other psychiatric conditions.

Slc9a6 mutation causes Purkinje cell loss and ataxia in the shaker rat

The shaker rat carries a naturally occurring mutation leading to progressive ataxia characterized by Purkinje cell (PC) loss. We previously reported on fine-mapping the shaker locus to the long arm of the rat X chromosome. In this work, we sought to identify the mutated gene underlying the shaker phenotype and confirm its identity by functional complementation. We fine-mapped the candidate region and analyzed cerebellar transcriptomes, identifying a XM_217630.9 (Slc9a6):c.[191_195delinsA] variant in the Slc9a6 gene that segregated with disease. We generated an adeno-associated virus (AAV) targeting Slc9a6 expression to PCs using the mouse L7-6 (L7) promoter. We administered the AAV prior to the onset of PC degeneration through intracerebroventricular injection and found that it reduced the shaker motor, molecular and cellular phenotypes. Therefore, Slc9a6 is mutated in shaker and AAV-based gene therapy may be a viable therapeutic strategy for Christianson syndrome, also caused by Slc9a6 mutation.