Gender-specific alteration of energy balance and circadian locomotor activity in the Crtc1 knockout mouse model of depression.

Obesity and depression are major public health concerns, and there is increasing evidence that they share etiological mechanisms. CREB-regulated transcription coactivator 1 (CRTC1) participates in neurobiological pathways involved in both mood and energy balance regulation. Crtc1 -/- mice rapidly develop a depressive-like and obese phenotype in early adulthood, and are therefore a relevant animal model to explore possible common mechanisms underlying mood disorders and obesity. Here, the obese phenotype of male and female Crtc1 -/- mice was further characterized by investigating CRTC1's role in the homeostatic and hedonic regulation of food intake, as well as its influence on daily locomotor activity. Crtc1 -/- mice showed a strong gender difference in the homeostatic regulation of energy balance. Mutant males were hyperphagic and rapidly developed obesity on normal chow diet, whereas Crtc1 -/- females exhibited mild late-onset obesity without hyperphagia. Overeating of mutant males was accompanied by alterations in the expression of several orexigenic and anorexigenic hypothalamic genes, thus confirming a key role of CRTC1 in the central regulation of food intake. No alteration in preference and conditioned response for saccharine was observed in Crtc1 -/- mice, suggesting that mutant males' hyperphagia was not due to an altered hedonic regulation of food intake. Intriguingly, mutant males exhibited a hyperphagic behavior only during the resting (diurnal) phase of the light cycle. This abnormal feeding behavior was associated with a higher diurnal locomotor activity indicating that the lack of CRTC1 may affect circadian rhythmicity. Collectively, these findings highlight the male-specific involvement of CRTC1 in the central control of energy balance and circadian locomotor activity.

Smoking, Alcohol, Drug Use, Abuse and Dependence in Narcolepsy and Idiopathic Hypersomnia: A Case-Control Study.

STUDY OBJECTIVES: Basic experiments support the impact of hypocretin on hyperarousal and motivated state required for increasing drug craving. Our aim was to assess the frequencies of smoking, alcohol and drug use, abuse and dependence in narcolepsy type 1 (NT1, hypocretin-deficient), narcolepsy type 2 (NT2), idiopathic hypersomnia (IH) (non-hypocretin-deficient conditions), in comparison to controls. We hypothesized that NT1 patients would be less vulnerable to drug abuse and addiction compared to other hypersomniac patients and controls from general population. METHODS: We performed a cross-sectional study in French reference centres for rare hypersomnia diseases and included 450 adult patients (median age 35 years; 41.3% men) with NT1 (n = 243), NT2 (n = 116), IH (n = 91), and 710 adult controls. All participants were evaluated for alcohol consumption, smoking habits, and substance (alcohol and illicit drug) abuse and dependence diagnosis during the past year using the Mini International Neuropsychiatric Interview. RESULTS: An increased proportion of both tobacco and heavy tobacco smokers was found in NT1 compared to controls and other hypersomniacs, despite adjustments for potential confounders. We reported an increased regular and frequent alcohol drinking habit in NT1 versus controls but not compared to other hypersomniacs in adjusted models. In contrast, heavy drinkers were significantly reduced in NT1 versus controls but not compared to other hypersomniacs. The proportion of patients with excessive drug use (codeine, cocaine, and cannabis), substance dependence, or abuse was low in all subgroups, without significant differences between either hypersomnia disorder categories or compared with controls. CONCLUSIONS: We first described a low frequency of illicit drug use, dependence, or abuse in patients with central hypersomnia, whether Hcrt-deficient or not, and whether drug-free or medicated, in the same range as in controls. Conversely, heavy drinkers were rare in NT1 compared to controls but not to other hypersomniacs, without any change in alcohol dependence or abuse frequency. Although disruption of hypocretin signaling in rodents reduces drug-seeking behaviors, our results do not support that hypocretin deficiency constitutes a protective factor against the development of drug addiction in humans.

The hypocretins and the reward function: what have we learned so far?

A general consensus acknowledges that drug consumption (including alcohol, tobacco, and illicit drugs) constitutes the leading cause of preventable death worldwide. But the global burden of drug abuse extends the mortality statistics. Indeed, the comorbid long-term debilitating effects of the disease also significantly deteriorate the quality of life of individuals suffering from addiction disorders. Despite the large body of evidence delineating the cellular and molecular adaptations induced by chronic drug consumption, the brain mechanisms responsible for drug craving and relapse remain insufficiently understood, and even the most recent developments in the field have not brought significant improvement in the management of drug dependence. Though, recent preclinical evidence suggests that disrupting the hypocretin (orexin) system may serve as an anticraving medication therapy. Here, we discuss how the hypocretins, which orchestrate normal wakefulness, metabolic health and the execution of goal-oriented behaviors, may be compromised and contribute to elicit compulsive drug seeking. We propose an overview on the most recent studies demonstrating an important role for the hypocretin neuropeptide system in the regulation of drug reward and the prevention of drug relapse, and we question the relevance of disrupting the hypocretin system to alleviate symptoms of drug addiction.

Insulin induces long-term depression of ventral tegmental area dopamine neurons via endocannabinoids.

The prevalence of obesity has markedly increased over the past few decades. Exploration of how hunger and satiety signals influence the reward system can help us understand non-homeostatic feeding. Insulin may act in the ventral tegmental area (VTA), a critical site for reward-seeking behavior, to suppress feeding. However, the neural mechanisms underlying insulin effects in the VTA remain unknown. We demonstrate that insulin, a circulating catabolic peptide that inhibits feeding, can induce long-term depression (LTD) of mouse excitatory synapses onto VTA dopamine neurons. This effect requires endocannabinoid-mediated presynaptic inhibition of glutamate release. Furthermore, after a sweetened high-fat meal, which elevates endogenous insulin, insulin-induced LTD is occluded. Finally, insulin in the VTA reduces food anticipatory behavior in mice and conditioned place preference for food in rats. Taken together, these results suggest that insulin in the VTA suppresses excitatory synaptic transmission and reduces anticipatory activity and preference for food-related cues.

What keeps us awake: the neuropharmacology of stimulants and wakefulness-promoting medications.

Numerous studies dissecting the basic mechanisms that control sleep regulation have led to considerable improvement in our knowledge of sleep disorders. It is now well accepted that transitions between sleep and wakefulness are regulated by complex neurobiologic mechanisms, which, ultimately, can be delineated as oscillations between two opponent processes, one promoting sleep and the other promoting wakefulness. The role of several neurotransmitter or neuromodulator systems, including noradrenergic, serotonergic, cholinergic, adenosinergic, and histaminergic systems and, more recently, the hypocretin/orexin and dopamine systems, has been clearly established. Amphetamine-like stimulants are known to increase wakefulness by blocking dopamine reuptake, by stimulating dopamine release, or by both mechanisms. Modafinil may increase wakefulness through activation of noradrenergic and dopaminergic systems, possibly through interaction with the hypocretin/orexin system. Caffeine inhibits adenosinergic receptors, which in turn can produce activation via interaction with GABAergic and dopaminergic neurotransmission. Nicotine enhances acetylcholine neurotransmission in the basal forebrain and dopamine release. Understanding the exact role of the hypocretin/orexin and dopamine systems in the physiology and pharmacology of sleep-wake regulation may reveal new insights into current and future wakefulness-promoting drugs.