Early Sociability and Social Memory Impairment in the A53T Mouse Model of Parkinson's Disease Are Ameliorated by Chemogenetic Modulation of Orexin Neuron Activity.

Parkinson's disease (PD) is a multi-layered progressive neurodegenerative disease. Signature motor system impairments are accompanied by a variety of other symptoms such as mood, sleep, metabolic, and cognitive disorders. Interestingly, social cognition impairments can be observed from the earliest stages of the disease, prior to the onset of the motor symptoms. In this study, we investigated age-related reductions in sociability and social memory in the A53T mouse model of PD. Since inflammation and astrogliosis are an integral part of PD pathology and impair proper neuronal function, we examined astrogliosis and inflammation markers and parvalbumin expression in medial pre-frontal cortex (mPFC), part of the brain responsible for social cognition regulation. Finally, we used DREADDs (Designer Receptors Exclusively Activated by Designer Drugs) for the stimulation and inhibition of orexin neuronal activity to modulate sociability and social memory in A53T mice. We observed that social cognition impairment in A53T mice is accompanied by an increase in astrogliosis and inflammation markers, in addition to loss of parvalbumin neurons and inhibitory pre-synaptic terminals in the mPFC. Moreover, DREADD-induced activation of orexin neurons restores social cognition in the A53T mouse model of PD. SIGNIFICANCE STATEMENT: Social cognition is severely affected in the early stages of Parkinson's disease. In this study, we identified the A53T mouse as a model of social cognitive impairment in PD. Observed alterations in sociability and social memory are accompanied by loss of parvalbumin positive neurons and loss of inhibitory input to mPFC. Stimulating orexin neurons using a chemogenetic approach (DREADDs) ameliorated social cognitive impairment. This study identifies a role for orexin neurons in social cognition in PD and suggests potential therapeutic targets for PD-related social cognition impairments.