The Role of Midbrain to Prelimbic Cortex Glutamatergic projections in Stress-induced Drug Seeking

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SUMMARY Despite the recognized correlation between post-traumatic stress disorder (PTSD) and substance use disorder (SUD), it is unknown how trauma exposure and substance use may interact to alter the probability of an individual to develop either of these two disorders. Although some studies have revealed participation of the ventral tegmental area (VTA) and the medial prefrontal cortex (mPFC) in both PTSD and SUD, it is not yet known if the experience of a traumatic event alters the communication between these two structures in a way that may increase the risk of acquiring SUD. VTA projections to the mPFC are known to play an important role in the development of cocaine addiction; and other studies have shown that PTSD pathogenesis induces neurophysiological changes in the interaction between the amygdala, (VTA), mPFC, and hippocampus. Recently, studies showed that VTA glutamatergic neurons that co-release dopamine project towards the nucleus accumbens (NAc) and the prelimbic cortex (PL). Interestingly, VTA-NAc glutamatergic projections are involved in reward-seeking behavior; but the role of the VTA-PL glutamatergic projections in reward-seeking is still unknown. The overall goal of this investigation is to understand the mechanisms and adaptations of the brain when exposed to a traumatic event that leads to increased susceptibility of SUD acquisition. More specifically, the objective is to elucidate how the VTA glutamatergic projections into the PL are affected by stress and how this influences cocaine-seeking behavior in male and female rats. Our preliminary behavioral data show that stress prior to cocaine self-administration increases cocaine acquisition and cocaine-induced reinstatement, compared with the no-stress group in male rats. Our central hypothesis is that stress will strengthen synaptic transmission in the VTA-PL glutamatergic synapses, thus enhancing sensitivity to the reinforcing effects of cocaine and leading to increased cocaine-seeking behavior. To test this hypothesis, we will first evaluate the behavioral effects of fear conditioning prior to cocaine exposure on acquisition and reinstatement of cocaine- seeking (Aim 1a). Secondly, we will assess the neurophysiological changes of glutamatergic projections from the VTA to the PL using optical stimulation with whole cell patch-clamp recordings (ex-vivo) to measure synaptic changes (AMPA to NMDA ratio) in the VTA-PL glutamatergic synapses from cocaine-exposed rats with or without prior stress (Aim 1b). These experiments shall reveal how VTA modulates the PL neurons in the presence of stress and how this in turn, influences the drug seeking behavior.