Following acute infection of cattle with bovine herpesvirus-1 (BHV-1), cyclin expression was examined in trigeminal ganglia (TG). Cyclin A was primarily detected in the nucleus of TG neurons. In contrast, cyclin D1 and cyclin E were detected in the nucleus and cytoplasm of TG neurons. Uninfected or latently infected calves did not express detectable levels of these cyclins in TG neurons. Following dexamethasone-induced reactivation, cyclins D1, E and A were also detected in TG neurons. In situ hybridization of consecutive sections demonstrated that many neurons expressing cyclins contained viral nucleic acid, demonstrating that they were infected. Based on these observations, we hypothesize that BHV-1 infection activates neuronal cyclin expression to enhance productive infection. It is also possible that the stress of neuronal infection or reactivation leads to cyclin expression.
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