Morphological and physiological studies on cultured nerve cells from guinea pigs infected with herpes simplex virus in vivo.

Adult guinea pigs were inoculated with type 2 herpes simplex virus (HSV) on the whole back skin, and nerve cells from the dorsal root ganglia (DRG) 6 days after infection were grown in tissue culture. Morphological and physiological properties of the cultured nerve cells from HSV-infected animals (HSV-NC) were compared to those of nerve cells of DRG from the control, non-virus infected animals (CON-NC). During the early period of the culture (0-4 days) growth of nerve cells and non-neuronal cells from the HSV infected animals was essentially the same as that from the control animals. HSV-antigen was present in only a small percentage of the HSV-NC by immunofluorescence (IF). Electrophysiological examination revealed that most of the HSV-NC exhibited a reduced capability of generating spikes, which was quantitatively described as a reduction in the Vmax of the Na spikes. This was interpreted as a reduction in the number of Na channel molecules in the plasma membrane of the HSV-NC, while the resting membrane properties of the same cells, such as the resting membrane potential, input resistance and capacitance, were essentially the same as those of the CON-NC. On 4-5 days in culture, some HSV-NC regained a full capability to generate Na spikes. We considered these nerve cells to have overcome the HSV infection and were now entering a latent period of HSV infection. About 1/3 of the HSV-NC still remained incapable of generating Na spikes. Viral antigen was detected in only 10% of the nerve cells. In the late stage of the culture, HSV infection in vitro was first observed as lysis of non-neuronal cells growing close to some HSV-NC. Nerve cells then started to lose their neurites and became spherical. Finally on 8-9 days most of the cells, including the nerve cells, were lost from the dishes as a result of a generalized infection of supporting cells, i.e. fibroblasts and Schwann cells. This study confirms our previous finding that the electrophysiological technique is much more sensitive than the IF method for the detection of HSV-infection in nerve cells. The results indicate that some nerve cells infected with HSV overcome the infection in vitro. This is interpreted as the entering of these nerve cells into a latent period of HSV infection in vitro.