In vivo calcium imaging during appetitive learning in HIV Tat transgenic mice exposed to cannabis

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Project Summary In the context of human immunodeficiency virus (HIV) infection, cannabis use is an important topic and is the most commonly used drug among people living with HIV (PWH), despite the success of combined antiretroviral therapy (cART). Cannabis use is known to alleviate common symptoms and complications in PWH on cART, including chronic pain, nausea, and anxiety/depression, but contradicting results have been reported for cannabis use on cognitive performance. As cART does not cross the blood brain barrier the prevalence of mild to moderate forms of cognitive impairments, known as HIV-1-associated neurocognitive disorders (HAND), remain high (50%). Brain regions that are specifically vulnerable to HIV include the frontostriatal system, involving deficits in learning, memory and reward-related behaviors. HIV-1 proteins released by HIV-1 infected cells, including the transactivator of transcription (Tat) protein, are known to play a major role in the underlying HAND neuropathology, including lasting changes in neuronal excitability, inflammatory processes, and synaptic communication. Nevertheless, it is not clear how neuronal activity is altered by HIV Tat during learning while an animal is performing a behavioral task, i.e in the context of reward. With the establishment of in vivo calcium imaging, it has been shown that dorsomedial prefrontal cortex neurons that project to the nucleus accumbens (PFC-NAc) increase their neuronal activity after successful appetitive discrimination learning. The goal of the proposed study is to determine cannabis-induced changes on neuronal activity in a neuroHIV mouse model during performance of a behavioral reward-related learning task and its relation to the endocannabinoid (eCB) system. To achieve this goal, we will make use of a well-established mouse model of neuroHIV and propose two aims. Aim 1 will determine how CBD:THC ratios alter prefrontal neuronal activity in HIV Tat transgenic male and female mice performing a reward-related learning task. Animals will undergo viral injections to visualize in vivo calcium activity in PFC-NAc neurons and drug administration starts with behavioral assessment. Head-fixed mice will be trained to perform a Pavlovian conditioning task, that presents reward-predictive cues, and tests animal’s ability to learn to discriminate between a conditioned stimulus that predicts sucrose reward (CS+) but not the other (CS-). Neuronal activity will be recorded throughout training and compared before and after learning. Aim 2 will determine the effect of different CBD:THC ratios (1:15, 1:1, 15:1) on the eCB system and pathology in relation to appetitive discrimination learning in HIV Tat transgenic mice. Immunohistochemistry will be used to assess cell-specific localization of cannabinoid-like receptors (CB1R, CB2R, GPR55) and catabolic enzymes (FAAH, MAGL) on neurons, astrocytes, and microglia in the dorsomedial PFC and NAc; (non-)eCB ligands (e.g. AEA, 2-AG, AA, OEA, PEA) will be quantified using ultraperformance liquid chromatography- tandem mass spectrometry. This work will advance the understanding about how alterations in neuronal activity, inflammation, and cannabis-induced changes in the eCB system contribute to HIV-related symptoms.