71 Investigating the Role of Microglia Function in the Brain

Faculty Mentor; Naveen Nagarajan (Human Genetics, University of Utah)

 Background

The purpose of this study is to investigate the physiological function in the microglia in response to behavior induction in mice. Grooming is a normal behavior among most animal species. The gene Hoxb8 is required for normal grooming behavior in mice. A mutation in this gene results in pathological over-grooming behaviors in mice that can be related to OCD behaviors in humans. Hox genes are primarily involved in body patterning. Microglia functions as the brain’s monitor and responder of immune activity. It was then discovered in 2010 by Capecchi and Chen that the cell in the brain that implements grooming behavior are microglia cells derived from Hoxb8. The findings of this research shed light on how the brain generates complex behaviors such as OCD. Such mechanistic insight is necessary to understand other neuropsychiatric and neurodegenerative diseases such as Autism, Dementia, and Alzheimer’s disease.

Methods

The mice in this study are composed of a specific genetic cross between Hoxb8-IRESCre (male) and GCaMP5 (female). The results of this cross will produce a new generation of offspring that will exhibit GCaMP5 expressed in Hoxb8-positive cells. There are two methods being used to induce specific behaviors in the mice: the first method is a micro water sprinkle assay to induce grooming behaviors and the second method is a visual looming assay to induce anxiety behaviors. Microglia uses calcium to communicate with neurons to drive behaviors. To measure the fluctuations in calcium levels during the behavioral shifts, a calcium sensor called GCaMP will be used. A miniature lens will be inserted into the brain and attached to a miniaturized integrated microscope that will be used to inspect the calcium fluctuation changes mediated by the GCAMP sensor. Using this procedure, there will be 5 minutes of prestimulation, 10 minutes of during behavioral stimulation, and 10 minutes of post-stimulation recording.

Results

This is an ongoing study, however, it is expected that microglia will produce calcium transients in response to the behavioral shifts in the mice. The nature of calcium transients is dependent on the intensity of the behavior; if there is more grooming happening, there is an expectation of having more calcium transients.

Conclusions

Genetic lineage tracing identified that the Hoxb8 gene is turned on only in microglia (approximately 30%) in the brain. In conducting the proposed study, we anticipate measuring calcium transients in microglia during behavioral shifts. However, hypothetically, there can be an unexpected limitation to this experiment in that anxiety behavior can shut the calcium transients down.