Sade M. Spencer - US grants

DESCRIPTION (provided by applicant): There is a growing body of evidence to suggest that mood disorders, such as bipolar disorder, may be associated with disruptions in circadian rhythms. Previous work in our lab has shown that mice with a mutation in their Clock gene, a critical component of the core circadian machinery, display a behavioral phenotype similar to human patients in the manic phase of bipolar disorder. Importantly, when a functional Clock is introduced into the Ventral Tegmental Area (VTA), this regional rescue is sufficient to restore some of the behaviors back to wild type levels offering an important clue as to where Clock function may be important for modulating mood-related behaviors. The VTA is an important brain region of the limbic dopaminergic circuit providing projections to brain regions such as the Nucleus Accumbens (NAc). Understanding how circadian genes may interact with the dopamine system to regulate mood and reward related behaviors is critical in designing new treatments for affective disorders. This proposal seeks to characterize this interaction using the Clock mutant mice as a model of mania. In specific aim 1, we plan to determine the effects of disruption of Clock gene function on the rhythmic expression patterns of TH in the VTA and the NAc. We have preliminary evidence suggesting the dopaminergic system may be dysregulated in the Clock mutant mice. We will examine both the diurnal and circadian rhythms by assaying gene expression over six time points under both 12 hour light-dark (LD) and constant darkness (DD) conditions. Gene expression changes may or may not be mirrored by changes at the protein level, therefore we will assay for these alterations in the protein expression of Tyrosine Hydroxylase (TH) and p-TH (ser 31) by western blot. We will also examine the total levels of striatal dopamine by high performance liquid chromatography. We will repeat these experiments in the presence of lithium to determine whether molecular alterations are rescued by the treatment as we have observed with the behavioral changes in the Clock mutants. In specific aim 2, we will try to determine if the Clock mutation alters the regulation of the TH gene and whether the TH promoter is a target of lithium's action. First, we will assay for changes in rhythmic gene expression of transcription factors Clock, Bmal1, and Creb which are implicated in regulation of TH transcription. Additionally, we will investigate changes in the protein levels of CLOCK, BMAL1, CREB, and p-CREB (ser 133) over six time points. We will also directly examine binding at the TH promoter by performing Chromatin Immunoprecipitation assays using antibodies specific for CLOCK, BMAL1, and CREB. These experiments will be performed both with and without lithium treatment to determine if the drug alters activity at the TH promoter in the Clock mutant mice. In specific aim 3, we plan to establish a role for dopamine in the development of the manic-like behaviors of the Clock mutant mice. We will employ two different methods to manipulate the dopamine system in an effort to modulate the behavior of the Clock mutants. First, we will systemically administer Alpha-methyl-p-tyrosine to inhibit TH activity and decrease dopamine levels followed by a battery of behavioral experiments including locomotor activity, anxiety, and depression-related behaviors. We will also manipulate the firing rate of VTA neurons by delivering a K+ channel virus, HSV Kir2.1, directly into the VTA. This construct has been previously published and verified. These animals will similarly be tested for their mood-related behaviors. PUBLIC HEALTH RELEVANCE: The circadian clock is increasingly being implicated in the etiology of psychiatric diseases including bipolar mania. The goal of this proposal is to improve our understanding of the role of the circadian clock in the brain's mesolimbic dopaminergic circuit and the role that disruption of circadian genes plays in dysregulation of dopaminergic neurotransmission.

DESCRIPTION (provided by applicant): Drug addiction is a chronic disease characterized by high relapse rates, even following extended abstinence from drug use. Altered glutamatergic plasticity at nucleus accumbens (NAc) synapses after chronic cocaine is identified as a key feature underlying relapse vulnerability. Among the important neuroadaptations that have been identified in NAc are enhancement of prefrontal cortex (PFC) release probability, changes in glutamate receptor composition, expression and currents, and alterations in dendritic spine morphology. However, the underlying mechanisms of drug-induced changes in NAc synaptic plasticity are not fully known. The voltage gated Ca2+ channel (VGCC) auxiliary subunit ¿2¿-1 is upregulated by non-contingent administration of multiple drugs of abuse. The ¿2¿-1 subunit couples to various subtypes of VGCCs which control neurotransmitter release, influence neuronal excitability, and modify gene transcription. In addition, astrocyte-derived thrombospondin (TSP) proteins bind to ¿2¿-1 facilitating the formation of excitatory synapses through a Ca2+ channel-independent mechanism. Gabapentin (GBP), an ¿2¿-1 ligand, disrupts the interaction between TSP and ¿2¿-1 and inhibits synapse formation. My preliminary data show that ¿2¿-1 and TSP-1 are increased after extinction from cocaine self-administration. Moreover, I find that intra-NAc delivery of GBP decreases cocaine-induced reinstatement of drug-seeking. The current proposal is aimed at further clarifying GBP's actions at the ¿2¿-1 subunit and determining the mechanism of action of GBP on cocaine-induced drug- seeking. I hypothesize that upregulated ¿2¿-1 promotes relapse to cocaine-seeking after self-administration, and conversely, inhibiting ¿2¿-1 reduces cocaine-induced reinstatement. I further hypothesize that GBP's effects are due to its actions at presynaptic ¿2¿-1 subunits to inhibit neurotransmitter release induced by VGCC activation OR disrupting the scaffolding of TSP proteins thereby interfering with synaptic remodeling. Specific Aim 1: I will knockdown ¿2¿-1 with anti-sense vivo-morpholino to validate the role of ¿2¿-1 in cocaine reinstatement. Specific Aim 2: Using in vivo microdialysis, I will evaluate my hypothesis that GBP's actions involve inhibition of neurotransmitter release by measuring levels of glutamate and dopamine during cocaine- induced reinstatement with reverse-dialysis of GBP. Specific Aim 3: I will determine the effects of recombinant TSP on cocaine reinstatement and identify whether drug-induced dendritic spine changes are modified by GBP or recombinant TSP treatment using quantitative dendritic spine morphology measurements. Results from these behavioral and biochemical studies will shed light on a shared neurobiological mechanism contributing to drug relapse and clarify the mechanism of action of GBP as an anti-addiction agent.

? DESCRIPTION (provided by applicant): Cocaine produces enduring alterations in nucleus accumbens core (NAcore) synaptic plasticity associated with relapse vulnerability. Specifically, cocaine self-administration causes enduring increases in dendritic spine head diameter, AMPA/NMDA ratios, and matrix metalloproteinase (MMP) activity. Re-exposure to cocaine- conditioned cues after extinction produces further rapid, transient synaptic potentiation (t-SP) within 15 min that is quantified with any of these measurements. However, when inducing reinstatement with a noncontingent cocaine injection the time course of t-SP differs in that the maximal response is not observed until 45 min. This discrepancy led to the hypothesis that while cues immediately drive forward drug seeking and t-SP, when reinstatement is initiated by noncontingent cocaine, the drug initially suppresses drug seeking and t-SP until pharmacological effects diminish below a threshold. A reinstatement model to evaluate this interaction between cue-induced cocaine seeking leading to cocaine use modeling many important features of human relapse was developed. Preliminary data show that contingent cocaine reverses cue-induced t-SP and discontinuation of this access rapidly restores t-SP. Cocaine increases synaptic dopamine (DA) as a competitive inhibitor of the dopamine transporter, thus dopaminergic mechanisms were hypothesized to contribute to cocaine's effects on cue-induced t-SP. Here, the role of cocaine-induced ventral tegmental area (VTA) DA transmission in t-SP reversal is examined using viral-based designer receptors exclusively activated by designer drugs (DREADD) and tyrosine hydroxylase-Cre (TH-Cre) transgenic rats to introduce anatomical and cell-type specificity. To accomplish this, the candidate will learn in vivo zymography to analyze MMP activity and patch clamp electrophysiology (Aim 1), as well as employ dendritic spine analysis and intracranial microinjection skills acquired during F32 NRSA training. In the K99 aims, the contribution of VTA DA in cocaine-induced reversal of NAcore t-SP will be characterized. Preliminary data show that cocaine-trained rats with Gq-DREADD in VTA TH+ cells will reinstate to a CNO priming injection and it will be further assessed whether this activation likewise blunts cue-induced t-SP. The impact of selective activation (Aim 2B) or inactivation of VTA DA cell bodies (Aim 2A) or terminal field regions (Aim 2C) on cue-induced t-SP and cocaine-induced suppression of t- SP will be examined. During the R00 period, chronic Gq-DREADD activation with CNO self-administration will be used to test the sufficiency for VTA DA activity to reproduce potentiated neuroplasticity produced by chronic cocaine (Aim 3). Furthermore, the dynamic regulation of glutamate and DA release in the reinstatement model will be assessed with microdialysis (Aim 4). These experiments have the potential to contribute to the development of novel therapeutic options aimed at reversing cocaine-induced neurobiological alterations.