PROJECT SUMMARY. Despite the prevalence of combination antiretroviral therapy (cART) many HIV-infected individuals experience neurocognitive deficits, including decreased emotional processing, impulse control, and memory that interfere with daily living. Opiates can further exacerbate HIV-1 associated neurocognitive deficits by altering neuronal structure and function. However, HIV does not uniformly target the brain and certain regions are differentially affected. The striatum exhibits increased dendritic pathology (varicosity formation, beading, fragmentation, and pruning) and dendritic spine losses; whereas the anterior cingulate cortex (ACC) within the prefrontal cortex exhibits alterations in inhibitory, but not excitatory, synaptic connections. These interneuronal deficits are accompanied by increased depressive-like behavior. Opiates impact HIV-induced behavioral dysfunction and we hypothesize that this is caused by disruptions to inhibitory synaptic function within the ACC resulting in a net disruption in the excitatory/inhibitory balance of ACC pyramidal cells and overexcitation. Aim 1 will characterize the impact of opiates on HIV-Tat-induced GABAergic neurophysiological dysfunction in ACC pyramidal neurons using whole-cell, patch-clamp recordings and associated depressive-like behavior. Neurons will be biocytin-filled and subsequently analyzed via 3D-reconstruction for dendritic pathology, spine density, and inhibitory puncta. The effects of morphine and HIV-Tat on interneuronal subpopulations within the ACC will also be assessed. Aim 2 will determine how GABA signaling impacts HIV/HIV-proteins and morphine changes in ACC neuron ion homeostasis (Ca2+ and Cl−), structure, and survival using Cre/TdTomatoflox/flox pyramidal neuron and Gad1-eGFP interneuron reporter mice, and human induced pluripotent stem cell (iPSC)-derived cortical neurons. The proposed studies will further our understanding of the mechanisms by which opiates exacerbate HIV-induced neurocognitive deficits and pathology within the ACC, and identify possible targets for therapeutic interventions.