Corticostriatal circuit defects in Hoxb8 mutant mice

Hoxb8 mutant mice exhibit compulsive grooming and hair removal dysfunction similar to humans with the OCD-spectrum disorder, trichotillomania. Since, in the mouse brain, the only detectable cells that label with Hoxb8 cell lineage appear to be microglia, we suggested that defective microglia cause the neuropsychiatric disorder. Does the Hoxb8 mutation in microglia lead to neural circuit dysfunctions? We demonstrate that Hoxb8 mutants contain corticostriatal circuit defects. Golgi staining, ultra-structural, and electrophysiological studies of mutants reveal excess dendritic spines, pre- and post-synaptic structural defects, long-term potentiation and miniature postsynaptic current defects. Hoxb8 mutants also exhibit hyperanxiety and social behavioral deficits similar to mice with neuronal mutations in Sapap3, Slitrk5 and Shank3, reported models of OCD and autism spectrum disorders (ASD’s). Long-term treatment of Hoxb8 mutants with fluoxetine, a serotonin reuptake inhibitor (SSRI), reduces excessive grooming, hyperanxiety and social behavioral impairments. These studies provide linkage between the neuronal defects induced by defective Hoxb8-microglia, and neuronal dysfunctions directly generated by mutations in synaptic components that result in mice that display similar pathological grooming, hyperanxiety and social impairment deficits. Our results shed light on Hoxb8 microglia driven circuit-specific defects and therapeutic approaches that will become essential to developing novel therapies for neuropsychiatric diseases such as OCD and ASD’s with Hoxb8-microglia being the central target.