During withdrawal from extended-access cocaine self-administration, rats exhibit a progressive intensification (incubation) of cue-induced cocaine craving that is associated with synaptic adaptations in the nucleus accumbens (NAc) including alterations in in AMPA receptor subunit composition and group I metabotropic glutamate receptor (mGluR) plasticity. Recent work from our lab suggests these adaptations are maintained by dysregulated local protein translation. Aberrant translation has a profound impact on cellular function and is a key feature in Fragile X syndrome and some other disorders of the nervous system. Treatments to normalize protein synthesis have proven successful in reversing certain behavioral and cellular abnormalities in a mouse model of Fragile X. Currently, little is known about mechanisms regulating translation in the NAc. Furthermore, the possibility of long-term alterations in translation following cocaine exposure has been largely uninvestigated and provides an intriguing novel target for therapeutic intervention. The objective of this proposal is to identify mechanisms through which excitatory synaptic transmission regulates translation under control conditions and after incubation of cocaine craving, focusing on two receptors implicated in regulation of translation in other brain regions: NMDA receptors (NMDARs) and group I mGluRs. The central hypothesis is that incubation of cocaine craving is associated with dysregulation of protein translation in NAc dendrites.
Aim 1 will characterize protein translation in the NAc during the incubation of cocaine craving. 35S-Met/Cys incorporation will be used to measure protein translation in NAc tissue at two different time-points after discontinuing cocaine self-administration: withdrawal day 1 (WD1), before synaptic adaptations have occurred, and WD40, when craving has incubated and NAc synaptic transmission is altered. Basal translation, as well as regulation of translation by NMDARs and group I mGluRs will be compared between cocaine rats and saline controls. Then, translation of GluA1 and GluA2 will be specifically assessed after immunoprecipitation.
Aim 2 will determine if NMDARs and group I mGluRs regulate translation in NAc dendrites. Experiments in Aim 1 are not able to distinguish between translation occurring in the soma versus the dendrites, which also contain the machinery for protein translation. To isolate dendritic translation, neurons from postnatal rat NAc (co- cultured with cortical neurons to restore glutamate synapses) will be grown in microfluidic chambers that isolate soma from dendrites, allowing media in each compartment to be selectively manipulated. Drugs affecting NMDARs and group I mGluRs will be added to the dendritic chamber to determine if they specifically regulate dendritic translation. These studies are the first to characterize how excitatory transmission regulates protein translation in the NAc under basal conditions and whether drugs of abuse cause persistent alterations in the regulation of translation. While this work is underway, I will participate in a multi-faceted Training Plan designed to develop the non-bench skills needed to reach my goal of becoming a PI in an academic setting.
This proposal utilizes a rat model to study the long-lasting changes in the brain that underlie intensification (incubation) of cocaine craving, changes thought to contribute to heightened relapse vulnerability, and a topic highly relevant to public health. It examines the impact of enhanced cocaine craving following withdrawal on protein translation in the nucleus accumbens, a brain structure critically involved in reward learning and addiction. Determining how the regulation of protein translation is altered by and ultimately influences the development of an addiction will help identify new targets and novel therapeutic interventions aimed at normalizing or reversing these drug-induced alterations.
|Stefanik, Michael T; Milovanovic, Mike; Werner, Craig T et al. (2018) Withdrawal From Cocaine Self-administration Alters the Regulation of Protein Translation in the Nucleus Accumbens. Biol Psychiatry 84:223-232|
|Werner, Craig T; Stefanik, Michael T; Milovanovic, Mike et al. (2018) Protein Translation in the Nucleus Accumbens Is Dysregulated during Cocaine Withdrawal and Required for Expression of Incubation of Cocaine Craving. J Neurosci 38:2683-2697|
|Scheyer, Andrew F; Loweth, Jessica A; Christian, Daniel T et al. (2016) AMPA Receptor Plasticity in Accumbens Core Contributes to Incubation of Methamphetamine Craving. Biol Psychiatry 80:661-670|