Although a few reports describe application of stereological methods to quantify neuropathological features in correlation with behavioral changes to study encephalitis, none have investigated the effect of an EE on viral encephalitis. Indeed, only two studies have investigated the effect of an EE on brain infections using experimental models, but their approach to quantifying neuropathological changes was not based on unbiased stereological estimations. As a result, quantitative associations between neuropathological features and behavioral changes in murine models of encephalitis and the effect of EE have previously not been firmly established. To quantify neuropathological changes, we applied the optical fractionator, an accurate method of quantification combining properties of an optical dissector and the fractionator that has been used in a variety of studies to determine cell numbers in multiple brain regions. The optical fractionator is Selumetinib MEK inhibitor unaffected by histological changes, shrinkage, or damage-induced expansion by injury, an issue of particular importance when studying brain diseases. With these tools, we have shown here that the behavioral and neuropathological consequences of Piry virus encephalitis are more severe in animals living under IE conditions in comparison with encephalitis outcomes in mice housed under EE conditions. The occurrence of neuronal death after encephalitis induced by rhabdoviruses remains controversial, but in general, when it is unequivocally AB1010 detected, it seems to be a microglialmediated event. To investigate possible losses of neuronal numbers in correlation with microglial activation after Piry virus encephalitis, we used NeuN as a selective immunohistochemical marker. The microglial host response was more intense and generalized in the brain parenchyma at 8 dpi compared to 20 or 40 dpi. Viral neuroinvasion mainly included the olfactory pathways, septum, amygdala, and ventral CA3 and polymorphic layer of the ventral dentate gyrus. There was an association between the intensity of viral antigen labeling in the parenchyma, a higher number of microglias, and a greater reduction of PNs, especially type I, without significant neuronal death. In addition, the intense immunolabeling of T lymphocytes in the brain was associated with environmental enrichment suggesting a higher mobilization of these cells to the brain parenchyma during Piry viral encephalitis.