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Substance use disorder (SUD) is associated with disruptions in circadian rhythms. The circadian transcription factor neuronal PAS domain protein 2 (NPAS2) is enriched in reward-related brain regions and regulates reward, but its role in SU is unclear. To examine the role of NPAS2 in drug taking, we measured intravenous cocaine self-administration (acquisition, dose-response, progressive ratio, extinction, cue-induced reinstatement) in wild-type (WT) and Npas2 mutant mice at different times of day. In the light (inactive) phase, cocaine self-administration, reinforcement, motivation and extinction responding were increased in all Npas2 mutants. Sex differences emerged during the dark (active) phase with Npas2 mutation increasing self-administration, extinction responding, and reinstatement only in females as well as reinforcement and motivation in males and females. To determine whether circulating hormones are driving these sex differences, we ovariectomized WT and Npas2 mutant females and confirmed that unlike sham controls, ovariectomized mutant mice showed no increase in self-administration. To identify whether striatal brain regions are activated in Npas2 mutant females, we measured cocaine-induced ΔFosB expression. Relative to WT, ΔFosB expression was increased in D11 neurons in the nucleus accumbens (NAc) core and dorsolateral (DLS) striatum in Npas2 mutant females after dark phase self-administration. We also identified potential target genes that may underlie the behavioral responses to cocaine in Npas2 mutant females. These results suggest NPAS2 regulates reward and activity in specific striatal regions in a sex and time of day (TOD)-specific manner. Striatal activation could be augmented by circulating sex hormones, leading to an increased effect of Npas2 mutation in females. [ABSTRACT FROM AUTHOR]

The GABAA receptor mediates fast, inhibitory signaling, and cortical expression of the α1 subunit increases during postnatal development. Certain pathological stimuli such as stressors or prenatal cocaine exposure can interfere with this process, but causal relationships between GABAAα1 deficiency and complex behavioral outcomes remain unconfirmed. We chronically reduced GABAAα1 expression selectively in the medial prefrontal cortex (prelimbic subregion) of mice using viral-mediated gene silencing of Gabra1. Adolescent-onset Gabra1 knockdown delayed the acquisition of a cocaine-reinforced instrumental response but spared cocaine seeking in extinction and in a cue-induced reinstatement procedure. To determine whether response acquisition deficits could be associated with impairments in action-outcome associative learning and memory, we next assessed behavioral sensitivity to instrumental contingency degradation. In this case, the predictive relationship between familiar actions and their outcomes is violated. Adolescent-onset knockdown, although not adult-onset knockdown, delayed the expression of goal-directed response strategies in this task, resulting instead in inflexible habit-like modes of response. Thus, the maturation of medial prefrontal cortex GABAAα1 systems during adolescence appears necessary for goal-directed reward-related decision making in adulthood. These findings are discussed in the light of evidence that prolonged Gabra1 deficiency may impair synaptic plasticity. [ABSTRACT FROM AUTHOR]

Synthetic opioids like fentanyl are highly potent and prevalent in the illicit drug market, leading to tolerance, dependence, and opioid use disorder (OUD). Chronic opioid use disrupts sleep and circadian rhythms, which persist even during treatment and abstinence, increasing the risk of relapse. The body's molecular clock, regulated by transcriptional and translational feedback loops, controls various physiological processes, including the expression of endogenous opioids and their receptors. The circadian transcription factor NPAS2, highly expressed in the nucleus accumbens, may have a crucial function in opioid-related behaviors. Our study found sex-specific roles for NPAS2-mediated reward behaviors in male and female mice, including in fentanyl seeking and craving. We also identified specific cell types and transcriptional targets in the nucleus accumbens of both mice and humans by which NPAS2 may mediate the impact of fentanyl on brain physiology and in opioid reward-related behaviors. Ultimately, our findings begin to uncover the mechanisms underlying circadian rhythm dysfunction and opioid addiction.

Previous studies have shown that there are rhythms in gene expression in the mouse prefrontal cortex (PFC); however, the contribution of different cell types and potential variation by sex has not yet been determined. Of particular interest are excitatory pyramidal cells and inhibitory parvalbumin (PV) interneurons, as interactions between these cell types are essential for regulating the excitation/inhibition balance and controlling many of the cognitive functions regulated by the PFC. In this study, we identify cell-type specific rhythms in the translatome of PV and pyramidal cells in the mouse PFC and assess diurnal rhythms in PV cell electrophysiological properties. We find that while core molecular clock genes are conserved and synchronized between cell types, pyramidal cells have nearly twice as many rhythmic transcripts as PV cells (35% vs. 18%). Rhythmic transcripts in pyramidal cells also show a high degree of overlap between sexes, both in terms of which transcripts are rhythmic and in the biological processes associated with them. Conversely, in PV cells, rhythmic transcripts from males and females are largely distinct. Moreover, we find sex-specific effects of phase on action potential properties in PV cells that are eliminated by environmental circadian disruption. Together, this study demonstrates that rhythms in gene expression and electrophysiological properties in the mouse PFC vary by both cell type and sex. Moreover, the biological processes associated with these rhythmic transcripts may provide insight into the unique functions of rhythms in these cells, as well as their selective vulnerabilities to circadian disruption., Competing Interests: The authors declare no competing financial interests.

The forced swim and tail suspension tests are commonly used to determine the effects of circadian-related pharmacological, genetic, and environmental manipulations on depression-like behavior in rodents. Both tests involve scoring immobility of rodents in an inescapable condition. Here we describe how to set up and carry out these tests.

The GABAA receptor mediates fast, inhibitory signaling, and cortical expression of the α1 subunit increases during postnatal development. Certain pathological stimuli such as stressors or prenatal cocaine exposure can interfere with this process, but causal relationships between GABAA α1 deficiency and complex behavioral outcomes remain unconfirmed. We chronically reduced GABAA α1 expression selectively in the medial prefrontal cortex (prelimbic subregion) of mice using viral-mediated gene silencing of Gabra1. Adolescent-onset Gabra1 knockdown delayed the acquisition of a cocaine-reinforced instrumental response but spared cocaine seeking in extinction and in a cue-induced reinstatement procedure. To determine whether response acquisition deficits could be associated with impairments in action-outcome associative learning and memory, we next assessed behavioral sensitivity to instrumental contingency degradation. In this case, the predictive relationship between familiar actions and their outcomes is violated. Adolescent-onset knockdown, although not adult-onset knockdown, delayed the expression of goal-directed response strategies in this task, resulting instead in inflexible habit-like modes of response. Thus, the maturation of medial prefrontal cortex GABAA α1 systems during adolescence appears necessary for goal-directed reward-related decision making in adulthood. These findings are discussed in the light of evidence that prolonged Gabra1 deficiency may impair synaptic plasticity., (© 2015 Federation of European Neuroscience Societies and John Wiley & Sons Ltd.)