Electrical activity and neuronal cell fusion in pseudorabies virus infection

Abstract

The pathologies of alphaherpesvirus infections tend to manifest as neuropathies of the peripheral nervous system: the tingle of an imminent cold sore, the neuralgia of shingles, or the "mad itch" of pseudorabies virus infection. In this thesis I report on studies concerning two phenomena related to these dysfunctions: cell fusion and electrical activity induced by pseudorabies virus (PRV) infection.

Investigation of cell fusion is motivated by seeking both a more thorough understanding of viral pathogenesis, and the capability of generating neuronal tracing viruses that do not so thoroughly disrupt the physiology of the cells they are used to study. I describe the current understanding of cell fusion induced by herpesviruses, and several approaches attempting to separate the propensity of PRV to induce cell fusion from its capacity to spread infection among neurons. All of the strains tested which were capable of spread also induced fusion. Notably, the cleavage of a particular protein (glycoprotein B) is ruled out as being required for induction of cell fusion.

The increased electrical activity in peripheral neurons infected by alphaherpesviruses is generally understood to be the proximate cause of peripheral neuropathies. I test the hypothesis that spread of infection is dependent upon this electrical activity, by testing the capacity of PRV to spread from neurons under different electrophysiological perturbations. Infected neurons are prevented from firing with a chemical neurotoxin, and induced to fire by both chemical methods and a novel application of optogenetics, which involves the use of light-gated ion channels to give precise control of excitation in neurons. These experiments reveal that electrical activity is not required for spread of infection, and further that increased activity can reduce the efficiency of spread. The results suggest that the electrical activity induced by PRV infection confers no benefits to viral survival or spread of infection at the cellular level.