Abstract
Seizures are characterized by sudden bursts of electrical activity caused by abnormal
neuronal hypersynchrony. Epilepsy is a chronic neurological disorder marked by
recurrent seizures. Despite antiseizure medications being the first line of management,
almost one-third of individuals who experience recurring seizures remain seizure-prone.
Therefore, it is important to explore new cellular mechanisms beyond traditional neuron-
to-neuron interactions. Neuroinflammation caused by microglia, the resident immune
cells within the brain, has been identified to have an influence on seizure generation
and recovery. Nevertheless, the accurate involvement of microglia and the various
molecular mediators that may influence their regulation of seizures remains unclear.
To begin to elucidate microglial contributions to seizures in this dissertation, I first used
pharmacological depletion with PLX3397 to selectively remove microglia and determine
their contribution to seizures within multiple experimental models, namely
chemoconvulsive, electrical, and hyperthermic (febrile) seizures. These experiments
showed that microglial depletion reproducibly aggravated seizure severity to
demonstrate that microglia play a widely protective seizure-limiting role within different
seizure models.
To overcome the limitations of pharmacological depletion strategies which often affect
peripheral macrophages and other immune cells, I subsequently employed
Csf1rΔFIRE/ΔFIRE (FIRE) mice, which lack microglia but possess other CNS macrophage
populations. By combining FIRE mice within models of chemoconvulsive and electrical
seizure, I observed that a microglial-selective depletion increased seizure severity and
facilitated the emergence of spontaneous recurrent seizures, further validating the
finding that microglia serve to constrain network hyperexcitability.
To clarify the molecular mechanisms of this protective role, I examined P2RY12, a
microglia-specific purinergic receptor responsible for chemotaxis. With global and
constitutive knockout mice, I identified that a lack of P2RY12 led to exacerbated seizure
severity and mortality, with reduced microglial process ramification during seizures.
Immunohistochemical examination showed increased neuronal activation (c-Fos
expression) and a reduction of inhibitory VGAT coverage.
Altogether, these results confirm microglia to be protective regulators of seizure severity
in multiple seizure paradigms and establish P2RY12 signaling to be an integral
mechanism by which microglia maintain homeostasis and constrain pathological
hyperexcitability.
