Tyrosine hydroxylase activity in the superior cervical ganglion during herpes simplex virus infection: correlation with viral titers and viral antigen.

The activity of tyrosine hydroxylase (TH) was measured in the superior cervical ganglion (SCG) of the mouse during herpes simplex virus (HSV) infection. TH activity remained at control levels or actually increased during acute infection at a time when viral titers of SCG homogenates were at their peak and viral antigen was detected in from one-third to one-half of ganglionic neurons. A rapid decline in TH activity followed and coincided with falling viral titers, disappearance of viral antigen and replacement of neurons by inflammatory cells. Immunization partially prevented this reduction of TH activity. In addition, when mice were immunosuppressed by cyclophosphamide, TH activity was relatively preserved early in the course of infection despite high viral titers in the ganglion and the presence of viral antigen and histopathological alterations in nearly 100% of neurons. These results suggest that a cellular 'luxury function', in this case TH activity, can be preserved and perhaps even augmented during neuronal HSV infection. Indeed, activity of this enzyme may persist until late into the acute phase of infection, perhaps up to the point of cell death induced either by immune-mediated or direct virus-induced cell lysis.