Contribution of locus coeruleus-derived galanin to opioid reward and reinforcement

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Project Summary The opioid epidemic has been declared a national public health emergency. Current treatments have abuse liability, target acute overdose only, and/or are ineffective for many people suffering from opioid addiction, and new therapies are desperately needed. One promising target is the brain galanin system; reducing galanin levels exacerbates morphine reward and withdrawal, while increasing galanin opposes opioid addiction-like behaviors. However, the neuroanatomical source and target of this protective galanin have not been identified, and the effects of galanin on voluntary opioid intake have not been investigated. The locus coeruleus (LC) modulates the activity of the mesolimbic reward pathway and has been implicated in opioid addiction, and 80% of noradrenergic neurons in this nucleus co-express galanin. We have assembled a set of genetically altered mice that either lack or overexpress galanin specifically in noradrenergic neurons to test the hypothesis that LC-derived galanin suppresses the ability of opioids to disinhibit dopamine (DA) neurons in the ventral tegmental area (VTA) and attenuates opioid reward/reinforcement, as well as acts in an autocrine manner to prevent LC hyperactivity and reduces withdrawal symptoms. In Aim 1, we will use in situ hybridization to determine the neurochemical identity of galanin receptor-expressing cells in the VTA, and slice and in vivo electrophysiology to investigate the circuitry and cellular mechanisms underlying the ability of galanin to oppose opioid-induced VTA DA neuron activity. In Aim 2, we will use the transgenic mice described above to test the hypothesis that LC-derived galanin inhibits opioid reinforcement using an operant i.v. opioid self- administration paradigm. In Aim 3, we will assess the ability of galanin to suppress LC hyperactivity, cellular plasticity, and aversive symptoms during opioid withdrawal. Completion of these aims will lay the groundwork for LC/galanin-based therapies for opioid addiction.