DENDRITIC SPINE ANALYSIS IN TOXOPLASMA GONDII INFECTED MICE

Abstract

Toxoplasma gondii (T. gondii) is a ubiquitous intracellular parasite that establishes a life-long infection in the central nervous system (CNS) of many warm-blooded mammals, including humans and rodents. As chronic infection of the CNS is unusual, a number of studies have sought to determine if T. gondii might affect human and rodent behavior. While the human data remain contradictory, multiple labs have shown that T. gondii infected rats and mice lose their innate aversion of feline odors. Although the mechanisms by which T. gondii infection changes rodent behavior remain unclear, dendritic spine loss, the typical pathology observed in neurodegenerative diseases associated with behavioral and cognitive changes, has been reported in T. gondii-infected mice. However, these studies lacked the ability to determine if this dendritic spine decrease occurred globally or only in neurons that have directly interacted with parasites. To address this gap, my thesis project was to take advantage of the T. gondii-Cre system, a method which identifies neurons that have directly interacted with the parasite in vivo, to quantify dendritic spine densities in neurons that interacted with parasites and neurons that did not. As the T. gondii-Cre system only labels neurons that interacted with the parasite, our first goal was to label dendritic spines of neurons that have not interacted with the parasite. To label these ‘bystander’ neurons, we experimented with lipophilic dye DiI, Golgi-Cox staining, and endogenous YFP expression. Unfortunately, despite significant effort to make these techniques viable, we were unable to effectively label the bystander neurons in a way that made dendritic spine analysis feasible. Given this technical difficulty, we altered our goal to instead evaluate the direct effects of T. gondii by comparing spine densities among dendrites harboring parasites vs dendrites not harboring parasites (i.e. in the same neuron). Results of this analysis are pending.