The Melikian Lab seeks a creative and motivated PhD neurobiologist to join our investigative team to study the mechanisms that govern addictive and motivated behaviors, with a focus on circuits that converge on and modulate dopaminergic terminals. We leverage intersectional approaches spanning from molecules to behavior, and utilize mouse genetic, viral, optogenetic and photometric methods. We are seeking postdoctoral applicants with a strong track record of productivity, who will take the lead on a novel project. Applicants will optimally have experience in mouse handling and modern neurobiology approaches (e.g. optogenetics, photometry), but other strong candidates will also be considered. The Neurobiology Department at UMASS Chan Medical School is the hub of a vibrant multidisciplinary neuroscience community, with research strengths in neuropsychiatric disorders, neurodegeneration, neuroinflammation, neuroplasticity, and neurodevelopment. Under the leadership of our recently appointed Chair, Dr. Danny Winder, the department provides an exceptional and interactive training environment that emphasizes team science in a diverse and inclusive space. Interested applicants should submit a CV and names of three references to Dr. Melikian: haley(dot)melikian(at)umassmed(dot)edu.
Potential Rotation Projects 1. Dopamine Transporter (DAT) Trafficking in Cocaine Addiction DAT is a membrane protein in dopamine (DA) axon teminals whose primary function is to remove released dopamine and thereby terminate synpatic transmission. Addictive psychostimulants, such as cocaine, block DAT function, which increases extracellular DA and is responsible for cocaine's addictive properties. DAT is not static at the plasma membrane, but is dynamically regulated by membrane traffficking. This project is to determine whether DAT membrane trafficking is required for cocaine addiction. Our lab has developed a novel, AAV-mediated, in vivo molecular replacement strategy, that replaces wildytpe DAT with DAT trafficking dysregulated mutants in adult mice. There are 2 possible rotation projects: Project 1a: Rotation students will assist in behaviorally assessing replacement mice as compared to controls, and will additionally use immumohistochemical approaches to validate mutant protein expression in dopamine neurons in situ. Students will gain experience in mouse behavior, brain dissection, preparation of brain slices, and immunhistochemical techniques in mouse brain. Project 1b: Rotation students will develop a CRISPR/Cas9 guide RNA in order to perform gene editing and mutate DAT in vivo, and will test its efficacy in vitro. Students will learn guide RNA design, and mammalian tissue culture, and genomic sequencing. Cocaine's Synaptic Actions at the Dopamine Transporter. Synaptic models. (A) Dopamine released into the extracellular space is rapidly cleared by the dopamine transporter (purple), thereby limiting the postsynaptic dopamine signal. (B) Cocaine binds to and blocks the dopamine transporter, allowing dopamine to accumulate extracellularly and enhancing the postsynaptic signal.
2. Modulatory glutamate signaling: impact on motor function, novelty, and cocaine addiction Glutamate is the major excitatory neurotransmitter in the brain, but also has a modulatory role by signaling through metabotropic glutamate receptors (mGluRs). Recent work from our laboratory revealed that mGluR5 expression in DA neurons is required for DA signaling and several DA-dependent behaviors including motor learning and cocaine reward. However, the circuit- and mechanistic-specific underpinnings of these processes are unkonwn. Using a novel conditional knockout model, we are leveraging genetically encoded DA sensors to determine how DAergic mGluR5 impacts DA neuron function and DA-dependent behaviors in mice. Rotation students will learn to behaviorally assess cocaine addiction in this mouse model, and will learn immunohistochemical approaches to validate viral expression Cocaine Fails to increase DA in mGluR5-DA-silenced mice. Fiber photometry using genetically-encoded DA sensors during cocaine response. Control or mGluR5-DA-silenced mice were injected with 7.5 mg/kg cocaine and DA signals were recorded in the nucleus accumbens using dLight 1.2 sensor. Control mice: Cocaine caused a significant increase in the total DA signal from 3-5 min post-injection as compared to saline-injections. mGluR5-DA-silenced mice: Cocaine failed to significantly increase DA signals. *p<0.05, paired Student's t test, n=4-5.
3. Nociceptin: A neuropeptide that impacts cocaine sensitivity Nociceptin is an endogenous opiate-like neuropeptide that is implicated in pain and reward motivation. Recent studies suggest that nociceptin has the capacity to block cocaine's initial addictive properties, but the mechanisms underlying nociceptin's actions are largely unknown. Work in our lab has discovered that nociceptin blocks cocaine reward, and does so by acting directly on DA axon terminals in the nucleus accumbens, the brain's "reward center". In addition, our results suggest that nociceptin likely shifts cocaine sensitivity, and does so by controlling reward tone differentially in males vs. females. These exciting results may pave the way towards harnesing nociceptin signaling as a potential addiction therapeutic. However, the mechanisms underlying nociceptin's actions are unknown, nor is it known whether nociceptin specificallly impacts cocaine reward, or other drugs of abuse. There are two possible rotation projects: Project 3a: Impact of nociceptin signaling on other drugs of abuse. Students will conduct addiction behavioral assays while infusing nociceptin directly into the nucleus accumbens in mice. Students will learn mouse handling and stereotaxic surgery, and mouse behavioral assays. Project 3b: Sex-specific differences in nociceptin signalig. Students will use RT-qPCR to test whether males and female mouse midbrain neurons express differing amounts of the nociceptin receptor, NOPR. Students will learn mouse handling skills, brain harvesting, and RT-qPCR. Nociceptin infusion into the nucleus accumbens blocks cocaine preference in females. Conditioned Place Preference Assay (CPP). Wildtype female mice received either saline or 10mg/kg cocaine (I.P.) and were trained for 3 days in a 3-chambered CPP aparatus, while being infused with either vehicle or 500nM nociceptin. Preference scores were determined on test days. Control-infused mice exhibited signifiant preference to the cocaine-paired chamber as compared to the saline-paired chamber (****p<0.001), whereas mice infused with nociceptin failed to establish cocaine preference (p=0.74). Two-way ANOVA with Tukey's multiple comparison test, n=4-10.