This is a revised application for Project by Masliah that has been extensively modified to address the reviewers' concerns by: 1) expanding our analysis to include stereology and quantitative real time PCR (qRT-PCR), 2) broadening our neuropathological and in vitro studies of astroglial cells, and 3) incorporating new preliminary data in support of the more innovative concept that interferons (IFNs) produced by HIV and HCV-infected cells might, in conjunction with METH, enhance astroglial responses that might promote neurodegeneration and block the effects of neurotrophic factors such as fibroblast growth factors (FGFs) on calbindin (CB) and dopaminergic neurons. Specifically, we hypothesize that loss of CB-IR in the neocortex and hippocampus will be associated with cognitive deficits, while loss of markers in the nigrostiatal system will correlate with motor and cognitive deficits. For the renewal and in collaboration with other components of the PPG our aims are: 1) To elucidate patterns of regional neuronal damage and astrogliosis in the brains of METH+, HIV+ cases and their relationship with neuropathological markers of HIVE and levels of IFN expression and trophic factors selective for cortical interneurons and NS cells. 2} To determine the relationship between regional patterns of neuronal injury and astrogliosis in the brains of METH-using HIV infected cases who vary in HCV status, specific cerebrospinal fluid (CSF) biomarkers and behavioral alterations. 3) To investigate the synergistic neurotoxic effects of METH and HIV in vitro via alterations in astroglial IFN-alpha and IFI gene expression and neuronal FGF/SHH signaling. Dissection of the molecular mechanisms will be performed in neuronal cell lines, primary neuronal cultures, and human fetal brain aggregates exposed to HIV proteins in the presence or absence of METH and FGF2, or FGFS and SHH. These studies will help advance understanding of the cellular and molecular mechanisms of cognitive and motor alterations in HIV infected METH users and in developing novel treatment strategies for these complex disorders.