Electronic Thesis and Dissertation Repository

Degree

Master of Science

Program

Neuroscience

Supervisor

Inoue, Wataru

2nd Supervisor

Prado, Marco A.M.

Co-Supervisor

3rd Supervisor

Prado, Vania F.

Co-Supervisor

Abstract

Peripheral inflammation can profoundly alter motivational processes and generate behavioral symptoms of sickness. Microglia, the innate immune cells of the brain, orchestrate neuroinflammation and have long been thought to be important for sickness behavior. However, their precise roles remain obscure due to their complex bidirectional interactions with neurons in vivo, which regulate how microglia respond to inflammatory signals and interact with neurons. Neuron-microglia interactions can be at least partially mediated by various types of G-protein coupled receptors (GPCRs) expressed by microglia. Here, we generated a microglia specific hM3Gq-DREADD (designer receptors exclusively activated by designer drugs) mouse line in which hM3Gq is selectively expressed in microglia, allowing for selective stimulation of calcium signalling in vivo. In primary cultures, clozapine-N-oxide (CNO) application induced the predicted rise in intracellular Ca2+ concentration only in hM3Gq-expressing microglia. In vivo, we validated that tamoxifen-induced hM3Gq expression was highly efficient and specific to microglia. Systemic administration of CNO (1 mg/kg, i.p.) for 3 consecutive days did not cause any changes in behavior indicative of sickness behavior, demonstrating that microglial hM3Gq signaling alone did not cause overt inflammatory response in vivo. We then challenged these mice with a low-dose lipopolysaccharide (LPS) injection (0.1 mg/kg i.p.) to trigger bona fide sickness behavior. We found that pre-treatment with CNO for 3 days alleviated classic LPS-induced sickness behavior including, depression of social interaction and locomotor activity. This treatment also suppressed LPS-induced upregulation of mRNA of proinflammatory cytokines in the hippocampus. Our work demonstrates that manipulation of GPCR signalling using this new ‘microglia-DREADD’ mouse line can help to reveal how microglia modulates inflammatory responses and abnormal behavior in vivo.

Available for download on Sunday, August 30, 2020

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