Preparing Aquatic Research for an Extreme Future: Call for Improved Definitions and Responsive, Multidisciplinary Approaches.

Extreme events have increased in frequency globally, with a simultaneous surge in scientific interest about their ecological responses, particularly in sensitive freshwater, coastal, and marine ecosystems. We synthesized observational studies of extreme events in these aquatic ecosystems, finding that many studies do not use consistent definitions of extreme events. Furthermore, many studies do not capture ecological responses across the full spatial scale of the events. In contrast, sampling often extends across longer temporal scales than the event itself, highlighting the usefulness of long-term monitoring. Many ecological studies of extreme events measure biological responses but exclude chemical and physical responses, underscoring the need for integrative and multidisciplinary approaches. To advance extreme event research, we suggest prioritizing pre- and postevent data collection, including leveraging long-term monitoring; making intersite and cross-scale comparisons; adopting novel empirical and statistical approaches; and developing funding streams to support flexible and responsive data collection.

Reducing adverse impacts of Amazon hydropower expansion.

Proposed hydropower dams at more than 350 sites throughout the Amazon require strategic evaluation of trade-offs between the numerous ecosystem services provided by Earth's largest and most biodiverse river basin. These services are spatially variable, hence collective impacts of newly built dams depend strongly on their configuration. We use multiobjective optimization to identify portfolios of sites that simultaneously minimize impacts on river flow, river connectivity, sediment transport, fish diversity, and greenhouse gas emissions while achieving energy production goals. We find that uncoordinated, dam-by-dam hydropower expansion has resulted in forgone ecosystem service benefits. Minimizing further damage from hydropower development requires considering diverse environmental impacts across the entire basin, as well as cooperation among Amazonian nations. Our findings offer a transferable model for the evaluation of hydropower expansion in transboundary basins.

A unifying framework for analyzing temporal changes in functional and taxonomic diversity along disturbance gradients.

Frameworks exclusively considering functional diversity are gaining popularity, as they complement and extend the information provided by taxonomic diversity metrics, particularly in response to disturbance. Taxonomic diversity should be included in functional diversity frameworks to uncover the functional mechanisms causing species loss following disturbance events. We present and test a predictive framework that considers temporal functional and taxonomic diversity responses along disturbance gradients. Our proposed framework allows us to test different multidimensional metrics of taxonomic diversity that can be directly compared to calculated multidimensional functional diversity metrics. It builds on existing functional diversity-disturbance frameworks both by using a gradient approach and by jointly considering taxonomic and functional diversity. We used previously unpublished stream insect community data collected prior to, and for the two years following, an extreme flood event that occurred in 2013. Using 14 northern Colorado mountain streams, we tested our framework and determined that taxonomic diversity metrics calculated using multidimensional methods resulted in concordance between taxonomic and functional diversity responses. By considering functional and taxonomic diversity together and using a gradient approach, we were able to identify some of the mechanisms driving species losses following this extreme disturbance event.

Caring for Children With Autism in an Emergency Department Setting.

OBJECTIVE: Patients with autism spectrum disorder (ASD) and other developmental delays represent a unique patient population. We described a cohort of children with ASD cared for in an emergency department (ED) setting and the specific health care resources used for their care. METHODS: This is an observational study of consecutive children (<18 years) with ASD presenting for ED care. Comparisons of interest were evaluated using Wilcoxon rank sum and χ2 tests. Odds ratios (ORs) are reported with 95% confidence intervals (CIs). RESULTS: There were 238 ED visits over a 9-month period among 175 children. Median age was 9 years, and 62% were male. Reasons for ED visit were medical (51%), psychiatric (18%), injury/assault/trauma (16%), neurological (11%), and procedure related (4%.)Children with psychiatric complaints had longer lengths of stay than those with other chief complaints (P < 0.0001; OR, 5.8; CI, 2.8-11.9) and were more likely to have urine (OR, 8.5; CI, 3.9-18.3) and blood work ordered (OR, 2.5; CI, 1.2-4.9) and less likely to have x-rays ordered (OR, 0.10; CI, 0.02-0.44).Eighteen (8%) children received sedation. None required physical restraint. A total of 30% were admitted to the hospital. Those with psychiatric complaints were more likely to be admitted (54.8% vs 24.5%; OR, 3.7; CI, 1.9-7.4) than those with other chief complaints. CONCLUSIONS: The care for children with ASD varied with age and health care issues. There was a high prevalence of psychiatric complaints, and many of these children were boarded in the ED waiting for an inpatient psychiatric bed. Those with psychiatric complaints were more likely to have multiple tests ordered and were more likely to be admitted.

Caveolin-1 regulates medium spiny neuron structural and functional plasticity.

RATIONALE: Caveolin-1 (CAV1) is a structural protein critical for spatial organization of neuronal signaling molecules. Whether CAV1 is required for long-lasting neuronal plasticity remains unknown. OBJECTIVE AND METHODS: We sought to examine the effects of CAV1 knockout (KO) on functional plasticity and hypothesized that CAV1 deficiency would impact drug-induced long-term plasticity in the nucleus accumbens (NAc). We first examined cell morphology of NAc medium spiny neurons in a striatal/cortical co-culture system before moving in vivo to study effects of CAV1 KO on cocaine-induced plasticity. Whole-cell patch-clamp recordings were performed to determine effects of chronic cocaine (15 mg/kg) on medium spiny neuron excitability. To test for deficits in behavioral plasticity, we examined the effect of CAV1 KO on locomotor sensitization. RESULTS: Disruption of CAV1 expression leads to baseline differences in medium spiny neuron (MSN) structural morphology, such that MSNs derived from CAV1 KO animals have increased dendritic arborization when cultured with cortical neurons. The effect was dependent on phospholipase C and cell-type intrinsic loss of CAV1. Slice recordings of nucleus accumbens shell MSNs revealed that CAV1 deficiency produces a loss of neuronal plasticity. Specifically, cocaine-induced firing rate depression was absent in CAV1 KO animals, whereas baseline electrophysiological properties were similar. This was reflected by a loss of cocaine-mediated behavioral sensitization in CAV1 KO animals, with unaffected baseline locomotor responsiveness. CONCLUSIONS: This study highlights a critical role for nucleus accumbens CAV1 in plasticity related to the administration of drugs of abuse.

Optogenetic-induced sympathetic neuromodulation of brown adipose tissue thermogenesis.

The brown adipose tissue (BAT) is a thermogenic organ that plays a major role in energy balance, obesity, and diabetes due to the potent glucose and lipid clearance that fuels its thermogenesis, which is largely mediated via sympathetic nervous system activation. However, thus far there has been little experimental validation of the hypothesis that selective neuromodulation of the sympathetic nerves innervating the BAT is sufficient to elicit thermogenesis in mice. We generated mice expressing blue light-activated channelrhodopsin-2 (ChR2) in the sympathetic nerves innervating the BAT using two different strategies: injecting the BAT of C57Bl/6J mice with AAV6-hSyn-ChR2 (H134R)-EYFP; crossbreeding tyrosine hydroxylase-Cre mice with floxed-stop ChR2-EYFP mice. The nerves in the BAT expressing ChR2 were selectively stimulated with a blue LED light positioned underneath the fat pad of anesthetized mice, while the BAT and core temperatures were simultaneously recorded. Using immunohistochemistry we confirmed the selective expression of EYFP in TH positive nerves fibers. In addition, local optogenetic stimulation of the sympathetic nerves induced significant increase in the BAT temperature followed by an increase in core temperature in mice expressing ChR2, but not in the respective controls. The BAT activation was also paralleled by increased levels of pre-UCP1 transcript. Our results demonstrate that local optogenetic stimulation of the sympathetic nerves is sufficient to elicit BAT and core thermogenesis, thus suggesting that peripheral neuromodulation has the potential to be exploited as an alternative to pharmacotherapies to elicit organ activation and thus ameliorate type 2 diabetes and/or obesity.

A global perspective on tropical montane rivers.

Tropical montane rivers (TMR) are born in tropical mountains, descend through montane forests, and feed major rivers, floodplains, and oceans. They are characterized by rapid temperature clines and varied flow disturbance regimes, both of which promote habitat heterogeneity, high biological diversity and endemism, and distinct organisms' life-history adaptations. Production, transport, and processing of sediments, nutrients, and carbon are key ecosystem processes connecting high-elevation streams with lowland floodplains, in turn influencing soil fertility and biotic productivity downstream. TMR provide key ecosystem services to hundreds of millions of people in tropical nations. In light of existing human-induced disturbances, including climate change, TMR can be used as natural model systems to examine the effects of rapid changes in abiotic drivers and their influence on biodiversity and ecosystem function.

Synaptic Depotentiation and mGluR5 Activity in the Nucleus Accumbens Drive Cocaine-Primed Reinstatement of Place Preference.

Understanding the neurobiological processes that incite drug craving and drive relapse has the potential to help target efforts to treat addiction. The NAc serves as a critical substrate for reward and motivated behavior, in part due to alterations in excitatory synaptic strength within cortical-accumbens pathways. The present studies investigated a causal link between cocaine-induced reinstatement of conditioned place preference and rapid reductions of cocaine-dependent increases in NAc shell synaptic strength in male mice. Cocaine-conditioned place preference behavior and ex vivo whole-cell electrophysiology showed that cocaine-primed reinstatement and synaptic depotentiation were disrupted by inhibiting AMPAR internalization via intra-NAc shell infusion of a Tat-GluA23Y peptide. Furthermore, reinstatement was driven by an mGluR5-dependent reduction in AMPAR signaling. Intra-NAc shell infusion of the mGluR5 antagonist MTEP blocked cocaine-primed reinstatement and corresponding depotentiation, whereas infusion of the mGluR5 agonist CHPG itself promoted reinstatement and depotentiated synaptic strength in the NAc shell. Optogenetic examination of circuit-specific plasticity showed that inhibition of infralimbic cortical input to the NAc shell blocked cocaine-primed reinstatement, whereas low-frequency stimulation (10 Hz) of this pathway in the absence of cocaine triggered a reduction in synaptic strength akin to that observed with cocaine, and was sufficient to promote reinstatement in the absence of a cocaine challenge. These data support a model in which mGluR5-mediated reduction in GluA2-containing AMPARs at NAc shell synapses receiving input from the infralimbic cortex is a critical factor in triggering reinstatement of cocaine-primed conditioned approach behavior.SIGNIFICANCE STATEMENT These studies identified a sequence of neural events whereby reexposure to cocaine activates a signaling cascade that alters synaptic strength in the NAc shell and triggers a behavioral response driven by a drug-associated memory.

Extinction and Reinstatement of Cocaine-seeking in Self-administering Mice is Associated with Bidirectional AMPAR-mediated Plasticity in the Nucleus Accumbens Shell.

Experience-dependent synaptic plasticity is an important component of both learning and motivational disturbances found in addicted individuals. Here, we investigated the role of cocaine experience-dependent plasticity at excitatory synapses in the nucleus accumbens shell (NAcSh) in relapse-related behavior in mice with a history of volitional cocaine self-administration. Using an extinction/reinstatement paradigm of cocaine-seeking behavior, we demonstrate that cocaine-experienced mice with extinguished cocaine-seeking behavior show potentiation of synaptic strength at excitatory inputs onto NAcSh medium spiny neurons (MSNs). Conversely, we found that exposure to various distinct types of reinstating stimuli (cocaine, cocaine-associated cues, yohimbine "stress") after extinction can produce a relative depotentiation of NAcSh synapses that is strongly associated with the magnitude of cocaine-seeking behavior exhibited in response to these challenges. Furthermore, we show that these effects are due to α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR)-specific mechanisms that differ depending on the nature and context of the reinstatement-inducing stimuli. Together, our findings identify common themes as well as differential mechanisms that are likely important for the ability of diverse environmental stimuli to drive relapse to addictive-like cocaine-seeking behavior.

Altering gain of the infralimbic-to-accumbens shell circuit alters economically dissociable decision-making algorithms.

The nucleus accumbens shell (NAcSh) is involved in reward valuation. Excitatory projections from infralimbic cortex (IL) to NAcSh undergo synaptic remodeling in rodent models of addiction and enable the extinction of disadvantageous behaviors. However, how the strength of synaptic transmission of the IL-NAcSh circuit affects decision-making information processing and reward valuation remains unknown, particularly because these processes can conflict within a given trial and particularly given recent data suggesting that decisions arise from separable information-processing algorithms. The approach of many neuromodulation studies is to disrupt information flow during on-going behaviors; however, this limits the interpretation of endogenous encoding of computational processes. Furthermore, many studies are limited by the use of simple behavioral tests of value which are unable to dissociate neurally distinct decision-making algorithms. We optogenetically altered the strength of synaptic transmission between glutamatergic IL-NAcSh projections in mice trained on a neuroeconomic task capable of separating multiple valuation processes. We found that induction of long-term depression in these synapses produced lasting changes in foraging processes without disrupting deliberative processes. Mice displayed inflated reevaluations to stay when deciding whether to abandon continued reward-seeking investments but displayed no changes during initial commitment decisions. We also developed an ensemble-level measure of circuit-specific plasticity that revealed individual differences in foraging valuation tendencies. Our results demonstrate that alterations in projection-specific synaptic strength between the IL and the NAcSh are capable of augmenting self-control economic valuations within a particular decision-making modality and suggest that the valuation mechanisms for these multiple decision-making modalities arise from different circuits.

Extreme streams: species persistence and genomic change in montane insect populations across a flooding gradient.

The ecological and evolutionary consequences of extreme events are poorly understood. Here, we tested predictions about species persistence and population genomic change in aquatic insects in 14 Colorado mountain streams across a hydrological disturbance gradient caused by a one in 500-year rainfall event. Taxa persistence ranged from 39 to 77% across sites and declined with increasing disturbance in relation to species' resistance and resilience traits. For taxa with mobile larvae and terrestrial adult stages present at the time of the flood, average persistence was 84% compared to 25% for immobile taxa that lacked terrestrial adults. For two of six species analysed, genomic diversity (allelic richness) declined after the event. For one species it greatly expanded, suggesting resilience via re-colonisation from upstream populations. Thus, while resistance and resilience traits can explain species persistence to extreme disturbance, population genomic change varies among species, challenging generalisations about evolutionary responses to extreme events at landscape scales.

Membrane estrogen receptor signaling impacts the reward circuitry of the female brain to influence motivated behaviors.

Within the adult female, estrogen signaling is well-described as an integral component of the physiologically significant hypothalamic-pituitary-gonadal axis. In rodents, the timing of ovulation is intrinsically entwined with the display of sexual receptivity. For decades, the importance of estradiol activating intracellular estrogen receptors within the hypothalamus and midbrain/spinal cord lordosis circuits has been appreciated. These signaling pathways primarily account for the ability of the female to reproduce. Yet, often overlooked is that the desire to reproduce is also tightly regulated by estrogen receptor signaling. This lack of emphasis can be attributed to an absence of nuclear estrogen receptors in brain regions associated with reward, such as the nucleus accumbens, which are associated with motivated behaviors. This review outlines how membrane-localized estrogen receptors affect metabotropic glutamate receptor signaling within the rodent nucleus accumbens. In addition, we discuss how, as estrogens drive increased motivation for reproduction, they also produce the untoward side effect of heightening female vulnerability to drug addiction.

Overexpression of the Histone Dimethyltransferase G9a in Nucleus Accumbens Shell Increases Cocaine Self-Administration, Stress-Induced Reinstatement, and Anxiety.

Repeated exposure to cocaine induces lasting epigenetic changes in neurons that promote the development and persistence of addiction. One epigenetic alteration involves reductions in levels of the histone dimethyltransferase G9a in nucleus accumbens (NAc) after chronic cocaine administration. This reduction in G9a may enhance cocaine reward because overexpressing G9a in the NAc decreases cocaine-conditioned place preference. Therefore, we hypothesized that HSV-mediated G9a overexpression in the NAc shell (NAcSh) would attenuate cocaine self-administration (SA) and cocaine-seeking behavior. Instead, we found that G9a overexpression, and the resulting increase in histone 3 lysine 9 dimethylation (H3K9me2), increases sensitivity to cocaine reinforcement and enhances motivation for cocaine in self-administering male rats. Moreover, when G9a overexpression is limited to the initial 15 d of cocaine SA training, it produces an enduring postexpression enhancement in cocaine SA and prolonged (over 5 weeks) increases in reinstatement of cocaine seeking induced by foot-shock stress, but in the absence of continued global elevations in H3K9me2. The increase in stress-induced reinstatement is paralleled by heightened anxiety measures, suggesting that countering the cocaine-induced decreases in endogenous G9a with ectopic G9a overexpression leads to lasting anxiogenic effects. Finally, we found an enduring reduction in phosphorylated cAMP-response element binding protein levels in the NAcSh that could account for the increased anxiety. These data demonstrate a novel role for G9a in promoting comorbid cocaine addiction and anxiety and suggest that increased epigenetic repression of transcription through H3K9 during cocaine use can have long-lasting and unexpected negative consequences on behavior.SIGNIFICANCE STATEMENT Cocaine addiction is a neuropsychiatric disorder that is detrimental to society and currently has no effective treatments. The difficulty in treating drug addiction is compounded by the high comorbidity with other psychiatric illnesses, including anxiety disorders. Here, we demonstrate that G9a, an epigenetic repressor of gene expression, acting in the nucleus accumbens, a brain reward region, is capable of increasing both addiction- and anxiety-like behaviors in rats. These findings are intriguing because repeated cocaine exposure decreases G9a in this region and thereby enhances expression of certain addiction-promoting genes. However, our results suggest that countering this cocaine-induced decrease in G9a activity actually exacerbates addiction and sensitivity to relapse under stressful situations.

HDAC5 and Its Target Gene, Npas4, Function in the Nucleus Accumbens to Regulate Cocaine-Conditioned Behaviors.

Individuals suffering from substance-use disorders develop strong associations between the drug's rewarding effects and environmental cues, creating powerful, enduring triggers for relapse. We found that dephosphorylated, nuclear histone deacetylase 5 (HDAC5) in the nucleus accumbens (NAc) reduced cocaine reward-context associations and relapse-like behaviors in a cocaine self-administration model. We also discovered that HDAC5 associates with an activity-sensitive enhancer of the Npas4 gene and negatively regulates NPAS4 expression. Exposure to cocaine and the test chamber induced rapid and transient NPAS4 expression in a small subpopulation of FOS-positive neurons in the NAc. Conditional deletion of Npas4 in the NAc significantly reduced cocaine conditioned place preference and delayed learning of the drug-reinforced action during cocaine self-administration, without affecting cue-induced reinstatement of drug seeking. These data suggest that HDAC5 and NPAS4 in the NAc are critically involved in reward-relevant learning and memory processes and that nuclear HDAC5 limits reinstatement of drug seeking independent of NPAS4.

BDNF-TrkB controls cocaine-induced dendritic spines in rodent nucleus accumbens dissociated from increases in addictive behaviors.

Chronic cocaine use is associated with prominent morphological changes in nucleus accumbens shell (NACsh) neurons, including increases in dendritic spine density along with enhanced motivation for cocaine, but a functional relationship between these morphological and behavioral phenomena has not been shown. Here we show that brain-derived neurotrophic factor (BDNF) signaling through tyrosine kinase B (TrkB) receptors in NACsh neurons is necessary for cocaine-induced dendritic spine formation by using either localized TrkB knockout or viral-mediated expression of a dominant negative, kinase-dead TrkB mutant. Interestingly, augmenting wild-type TrkB expression after chronic cocaine self-administration reverses the sustained increase in dendritic spine density, an effect mediated by TrkB signaling pathways that converge on extracellular regulated kinase. Loss of TrkB function after cocaine self-administration, however, leaves spine density intact but markedly enhances the motivation for cocaine, an effect mediated by specific loss of TrkB signaling through phospholipase Cgamma1 (PLCγ1). Conversely, overexpression of PLCγ1 both reduces the motivation for cocaine and reverses dendritic spine density, suggesting a potential target for the treatment of addiction in chronic users. Together, these findings indicate that BDNF-TrkB signaling both mediates and reverses cocaine-induced increases in dendritic spine density in NACsh neurons, and these morphological changes are entirely dissociable from changes in addictive behavior.

Incubation of cue-induced reinstatement of cocaine, but not sucrose, seeking in C57BL/6J mice.

Prior studies have shown that drug-seeking behaviors increase, rather than dissipate, over weeks to months after withdrawal from drug self-administration. This phenomenon - termed incubation - suggests that drug-craving responses elicited by conditioned environmental or discrete cues may intensify over pronged abstinence. While most of this work is conducted in rats with intravenous drug self-administration models, there is less evidence for incubation in mice that have greater utility for molecular genetic analysis and perturbation. We tested whether incubation of cocaine-seeking behavior is evident in C57BL/6J mice following 3weeks (5days/week) of cocaine self-administration in 2h self-administration sessions. We compared cocaine-seeking (drug-paired lever) responses 1, 7, or 28days after withdrawal from cocaine self-administration, and over similar times following sucrose pellet self-administration. We found that the initial re-exposure to the self-administration test chambers elicited increased reward-seeking behavior in both sucrose and cocaine self-administering mice, with maximal responses found at 7days compared to 1 or 28days after self-administration with either reinforcer. However, following extinction training, reinstatement of cocaine seeking reinforced by response-contingent presentation of reward-associated cues (tone/light) was significantly higher after 28days compared to 1 or 7days following cocaine self-administration. In contrast, cue-induced reinstatement of sucrose-paired lever pressing did not increase over this time frame, demonstrating a drug-specific incubation effect not seen with a natural reward. Thus, C57BL/6J mice display incubation of cue-induced reinstatement of cocaine seeking similar to findings with rats, but only show a transient incubation of context-induced cocaine seeking.

Reversal of morphine-induced cell-type-specific synaptic plasticity in the nucleus accumbens shell blocks reinstatement.

Drug-evoked plasticity at excitatory synapses on medium spiny neurons (MSNs) of the nucleus accumbens (NAc) drives behavioral adaptations in addiction. MSNs expressing dopamine D1 (D1R-MSN) vs. D2 receptors (D2R-MSN) can exert antagonistic effects in drug-related behaviors, and display distinct alterations in glutamate signaling following repeated exposure to psychostimulants; however, little is known of cell-type-specific plasticity induced by opiates. Here, we find that repeated morphine potentiates excitatory transmission and increases GluA2-lacking AMPA receptor expression in D1R-MSNs, while reducing signaling in D2-MSNs following 10-14 d of forced abstinence. In vivo reversal of this pathophysiology with optogenetic stimulation of infralimbic cortex-accumbens shell (ILC-NAc shell) inputs or treatment with the antibiotic, ceftriaxone, blocked reinstatement of morphine-evoked conditioned place preference. These findings confirm the presence of overlapping and distinct plasticity produced by classes of abused drugs within subpopulations of MSNs that may provide targetable molecular mechanisms for future pharmacotherapies.

Workplace violence in the emergency department: giving staff the tools and support to report.

Workplace violence is increasing across the nation's Emergency Departments, and nurses often perceive it as part of their job. Reporting processes were inconsistent, and nurses often did not know what acts constitute violence and underreported it. A staff nurse-led workgroup developed an initial survey and a reporting tool, and education was provided. A posteducation survey documented the reporting of violent acts has increased, and staff perceived the Emergency Department to be a safer environment.

Optogenetic stimulation of accumbens shell or shell projections to lateral hypothalamus produce differential effects on the motivation for cocaine.

Previous studies suggest that pharmacological or molecular activation of the nucleus accumbens shell (AcbSh) facilitates extinction of cocaine-seeking behavior. However, overexpression of CREB, which increases excitability of AcbSh neurons, enhances cocaine-seeking behavior while producing depression-like behavior in tests of mood. These discrepancies may reflect activity in differential AcbSh outputs, including those to the lateral hypothalamus (LH), a target region known to influence addictive behavior and mood. Presently, it is unknown whether there is a causal link between altered activity in the AcbSh-LH pathway and changes in the motivation for cocaine. In this study, we used an optogenetics approach to either globally stimulate AcbSh neurons or to selectively stimulate AcbSh terminal projections in the LH, in rats self-administering cocaine. We found that stimulation of the AcbSh-LH pathway enhanced the motivation to self-administer cocaine in progressive ratio testing, and led to long-lasting facilitation of cocaine-seeking behavior during extinction tests conducted after withdrawal from cocaine self-administration. In contrast, global AcbSh stimulation reduced extinction responding. We compared these opposing motivational effects with effects on mood using the forced swim test, where both global AcbSh neuron and selective AcbSh-LH terminal stimulation facilitated depression-like behavioral despair. Together, these findings suggest that the AcbSh neurons convey complex, pathway-specific modulation of addiction and depression-like behavior, and that these motivation and mood phenomenon are dissociable.

Cocaine self-administration behaviors in ClockΔ19 mice.

RATIONALE: A key role has been identified for the circadian locomotor output cycles kaput (Clock) gene in the regulation of drug reward. Mice bearing a dominant negative mutation in the Clock gene (ClockΔ19 mice) exhibit increased cocaine-induced conditioned place preference, reduced anxiety- and depression-like behavior, increased sensitivity to intracranial self-stimulation, and increased dopaminergic cell activity in the ventral tegmental area. OBJECTIVES: We sought to determine if this hyperhedonic phenotype extends to cocaine self-administration and measures of motivation. METHODS: Two separate serial testing procedures were carried out (n = 7-10/genotype/schedule). Testing began with acquisition of sucrose pellet self-administration, implantation of intravenous catheter, acquisition of cocaine self-administration, and dose-response testing (fixed ratio or progressive ratio). To evaluate diurnal variations in acquisition behavior, these sessions occurred at Zeitgeber 2 (ZT2) or ZT14. RESULTS: WT and ClockΔ19 mice exhibited similar learning and readily acquired food self-administration at both ZT2 and ZT14. However, only ClockΔ19 mice acquired cocaine self-administration at ZT2. A greater percentage of ClockΔ19 mice reached acquisition criteria at ZT2 and ZT14. ClockΔ19 mice self-administered more cocaine than WT mice. Using fixed ratio and progressive ratio schedules of reinforcement dose-response paradigms, we found that cocaine is a more efficacious reinforcer in ClockΔ19 mice than in WT mice. CONCLUSION: Our results demonstrate that the Clock gene plays an important role in cocaine reinforcement and that decreased CLOCK function increases vulnerability for cocaine use.