Functional Consequences Following Infection of the Olfactory System by Intranasal Infusion of the Olfactory Bulb Line Varient (OBLV) of Mouse Hepatitis Strain JHM

Abstract

The present study assessed the functional consequences of viral infection with a neurotropic coronavirus, designated MHV OBLV, that specifically targets central olfactory structures. Using standard operant techniques and a `go, no-go' successive discrimination paradigm, six BALB/c mice were trained to discriminate between the presentation of an air or odor stimulus (three mice for each of the odorants propanol and propyl acetate). Two additional BALB/c mice were trained to discriminate between the presentation of air and the presentation of either vanillin or propionic acid. Following criterion performance, each mouse received an additional 2000 trials of overtraining. At completion of overtraining one mouse from the propanol and propyl acetate groups were allocated as untreated. The remaining six mice were inoculated with 300 μl of the OBLV stock per nostril for a total of 1.5 × 10⁶ p.f.u. in 600 μl. Following a 1 month rest, untreated and inoculated animals were again tested on their respective air versus odor discrimination task. Untreated animals immediately performed at criterion levels. In contrast, inoculated animals varied in their capacity to discriminate between air and odorant. Five of the six inoculated mice showed massive disruption of the olfactory bulb, including death of mitral cells; the other was more modestly affected. In addition, the density of innervation of the olfactory mucosa by substance P-containing trigeminal fibers is also affected by inoculation. Those mice that remained anosmic to the training odorants had the most severe reduction in mitral cell number and substance P fiber density among the inoculated animals.