We describe a novel preclinical model of stress-induced relapse to cocaine use in rats using social defeat stress, an ethologically-valid psychosocial stressor in rodents that closely resembles stressors that promote craving and relapse in humans. Rats self-administered cocaine for 20 days. On days 11, 14, 17, and 20, animals were subjected to social defeat stress or a non-stressful control condition following the session, with discrete environmental stimuli signaling the impending event. After extinction training, reinstatement was assessed following reexposure to these discrete cues. Animals reexposed to psychosocial stress-predictive cues exhibited increased serum corticosterone and significantly greater reinstatement of cocaine seeking than the control group, and “active” coping behaviors during social defeat episodes were associated with subsequent reinstatement magnitude. These studies are the first to describe an operant model of psychosocial stress-induced relapse in rodents and lay the foundation for future work investigating its neurobiological underpinnings.

Adolescents have increased vulnerability for the development of a range of psychiatric disorders, including substance abuse disorders (SUD) and mood disorders. Adolescents also have increased rates of sensation seeking and risk taking. The mesolimbic dopamine system plays a role in all these behaviors and disorders and reorganization of the dopamine system during adolescence may be important in mediating these developmental changes in behavior and vulnerability. Here, we used ex vivo fast scan cyclic voltammetry to examine developmental differences in dopamine release and its local circuitry regulation across the striatum. We found that adolescents have significantly decreased dopamine release in the nucleus accumbens core across a range of stimulation frequencies that model tonic and phasic firing of mesolimbic dopamine neurons. We show this is not mediated by differences in rate of dopamine uptake, but may be driven by hypersensitive dopamine autoreceptors, indicated by increased inhibition in dopamine release following agonism of D2/D3 receptors, in the adolescent nucleus accumbens core. Additionally, we observed increases in dopamine uptake in the dorsomedial striatum. No other significant differences between release, uptake, or D2 autoreceptor function was observed between adolescent and adult rats in all brain areas tested (nucleus accumbens shell, nucleus accumbens core, dorsomedial striatum, and dorsolateral striatum). These developmental differences in dopamine release may be important in mediating some of the unique behavioral repertoire seen in adolescents, such as increases in sensation seeking, and its associated vulnerabilities..

An increasingly older population is one of the major social and medical challenges we currently face. Between 2010 and 2050, it is estimated that the proportion of adults over 65 years of age will double from 8% to 16% of the global population. A major concern associated with aging is the changes in health that can lead to various diseases such as cancer and neurogenerative diseases, which are major burdens on individuals and societies. Thus, it is imperative to better understand changes in sleep and circadian rhythms that accompany aging to improve the health of an older population and target diseases associated with aging. Circadian rhythms play a role in most physiological processes and can contribute to age-related diseases. Interestingly, there is a relationship between circadian rhythms and aging. For example, many older adults have a shift in chronotype, which is an individual’s natural inclination to sleep certain times of the day. As adults age, most people tend to go to sleep earlier while also waking up earlier. Numerous studies also suggest that disrupted circadian rhythms may be indicative of developing age-related diseases, like neurodegenerative disorders and cancer. Better understanding the relationship between circadian rhythms and aging may allow us to improve current treatments or develop novel ones that target diseases commonly associated with aging.

Dopamine β-hydroxylase (DBH) converts dopamine (DA) to norepinephrine (NE) in noradrenergic/adrenergic cells. DBH deficiency prevents NE production and causes sympathetic failure, hypotension and ptosis in humans and mice; DBH knockout (Dbh -/-) mice reveal other NE deficiency phenotypes including embryonic lethality, delayed growth, and behavioral defects. Furthermore, a single nucleotide polymorphism (SNP) in the human DBH gene promoter (-970C>T; rs1611115) is associated with variation in serum DBH activity and with several neurological- and neuropsychiatric-related disorders, although its impact on DBH expression is controversial. Phenotypes associated with DBH deficiency are typically treated with L-3,4-dihydroxyphenylserine (DOPS), which can be converted to NE by aromatic acid decarboxylase (AADC) in the absence of DBH. In this study, we generated transgenic mice carrying a human bacterial artificial chromosome (BAC) encompassing the DBH coding locus as well as ~45 kb of upstream and ~107 kb of downstream sequence to address two issues. First, we characterized the neuroanatomical, neurochemical, physiological, and behavioral transgenic rescue of DBH deficiency by crossing the BAC onto a Dbh -/- background. Second, we compared human DBH mRNA abundance between transgenic lines carrying either a “C” or a “T” at position -970. The BAC transgene drove human DBH mRNA expression in a pattern indistinguishable from the endogenous gene, restored normal catecholamine levels to the peripheral organs and brain of Dbh -/- mice, and fully rescued embryonic lethality, delayed growth, ptosis, reduced exploratory activity, and seizure susceptibility. In some cases, transgenic rescue was superior to DOPS. However, allelic variation at the rs1611115 SNP had no impact on mRNA levels in any tissue. These results indicate that the human BAC contains all of the genetic information required for tissue-specific, functional expression of DBH and can rescue all measured Dbh deficiency phenotypes, but did not reveal an impact of the rs11115 variant on DBH expression in mice.

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