Circadian rhythms and the genes that make up the molecular clock have long been implicated in bipolar disorder. Genetic evidence in bipolar patients suggests that the central transcriptional activator of molecular rhythms, CLOCK, may be particularly important. However, the exact role of this gene in the development of this disorder remains unclear. Here we show that mice carrying a mutation in the Clock gene display an overall behavioral profile that is strikingly similar to human mania, including hyperactivity, decreased sleep, lowered depression-like behavior, lower anxiety, and an increase in the reward value for cocaine, sucrose, and medial forebrain bundle stimulation. Chronic administration of the mood stabilizer lithium returns many of these behavioral responses to wild-type levels. In addition, the Clock mutant mice have an increase in dopaminergic activity in the ventral tegmental area, and their behavioral abnormalities are rescued by expressing a functional CLOCK protein via viral-mediated gene transfer specifically in the ventral tegmental area. These findings establish the Clock mutant mice as a previously unrecognized model of human mania and reveal an important role for CLOCK in the dopaminergic system in regulating behavior and mood. bipolar disorder ͉ circadian rhythms ͉ dopamine

Endogenous opioids seem to play a critical role in the regulation of mood states. For example, there is accumulating evidence that stimulation of -opioid receptors, upon which the endogenous opioid dynorphin acts, can produce depressivelike behaviors in laboratory animals. Here we examined whether systemic administration of salvinorin A (SalvA), a potent and highly selective -opioid agonist, would produce depressivelike effects in the forced swim test (FST) and intracranial selfstimulation (ICSS) test, which are behavioral models often used to study depression in rats. We extracted, isolated, and purified SalvA from Salvia divinorum plant leaves and examined its effects on behavior in the FST and ICSS test across a range of doses (0.125-2.0 mg/kg) after systemic (intraperitoneal) administration. SalvA dose dependently increased immobility in the FST, an effect opposite to that of standard antidepressant drugs. Doses of SalvA that produced these effects in the FST did not affect locomotor activity in an open field. Furthermore, SalvA dose dependently elevated ICSS thresholds, an effect similar to that produced by treatments that cause depressive symptoms in humans. At a dose that caused the depressivelike effects in both the FST and ICSS assays, SalvA decreased extracellular concentrations of dopamine (DA) within the nucleus accumbens (NAc), a critical component of brain reward circuitry, without affecting extracellular concentrations of serotonin (5-HT). These data provide additional support for the hypothesis that stimulation of brain -opioid receptors triggers depressive-like signs in rats and raise the possibility that decreases in extracellular concentrations of DA within the NAc contribute to these effects.Although much research on depression has focused on brain norepinephrine and serotonin (5-HT) systems, there is substantial evidence that other systems have important roles in the neurobiology of mood and affective disorders. For example, the mesolimbic dopamine (DA) systemwhich projects from the ventral tegmental area to the nucleus accumbens (NAc)-contributes importantly to the hedonic (rewarding) effects of food, sexual behavior, and addictive drugs (see Wise, 1998;Nestler and Carlezon, 2005). It has been proposed that disruption of DA function within the NAc causes anhedonia (reduced ability to experience reward) (Wise, 1982), a hallmark sign of clinical depression. The mesolimbic DA system is modulated by noradrenergic and serotonergic inputs (Pasquier et al., 1977), as well as endogenous opioid peptides (Devine et al., 1993;Shippenberg and Rea, 1997;Svingos et al., 1999). Agents that selectively affect the function of -opioid receptors cause profound alterations in mood in humans (Pfeiffer et al., 1986;Roth et al., 2002) and motivated behaviors in laboratory animals (Shippenberg and Herz, 1987;Todtenkopf et al., 2004), suggesting that manipulations targeting brain -opioid systems might be useful in the study and treatment of depressive disorders.

The transcription factor, ⌬FosB, is robustly and persistently induced in striatum by several chronic stimuli, such as drugs of abuse, antipsychotic drugs, natural rewards, and stress. However, very few studies have examined the degree of ⌬FosB induction in the two striatal medium spiny neuron (MSN) subtypes. We make use of fluorescent reporter BAC transgenic mice to evaluate induction of ⌬FosB in dopamine receptor 1 (D1) enriched and dopamine receptor 2 (D2) enriched MSNs in ventral striatum, nucleus accumbens (NAc) shell and core, and in dorsal striatum (dStr) after chronic exposure to several drugs of abuse including cocaine, ethanol, ⌬(9)-tetrahydrocannabinol, and opiates; the antipsychotic drug, haloperidol; juvenile enrichment; sucrose drinking; calorie restriction; the serotonin selective reuptake inhibitor antidepressant, fluoxetine; and social defeat stress. Our findings demonstrate that chronic exposure to many stimuli induces ⌬FosB in an MSN-subtype selective pattern across all three striatal regions. To explore the circuit-mediated induction of ⌬FosB in striatum, we use optogenetics to enhance activity in limbic brain regions that send synaptic inputs to NAc; these regions include the ventral tegmental area and several glutamatergic afferent regions: medial prefrontal cortex, amygdala, and ventral hippocampus. These optogenetic conditions lead to highly distinct patterns of ⌬FosB induction in MSN subtypes in NAc core and shell. Together, these findings establish selective patterns of ⌬FosB induction in striatal MSN subtypes in response to chronic stimuli and provide novel insight into the circuit-level mechanisms of ⌬FosB induction in striatum.

Background Prenatal cannabis exposure has been linked to addiction vulnerability, but the neurobiology underlying this risk is unknown. Methods Striatal dopamine and opioid-related genes were studied in human fetal subjects exposed to cannabis (as well as cigarettes and alcohol). Cannabis-related gene disturbances observed in the human fetus were subsequently characterized using an animal model of prenatal delta-9-tetrahydrocannabinol (THC; 0.15 mg/kg) exposure. Results Prenatal cannabis exposure decreased dopamine receptor D2 (DRD2) mRNA expression in the human ventral striatum (nucleus accumbens; NAc), a key brain reward region. No significant alterations were observed for the other genes in cannabis-exposed subjects. Maternal cigarette use was associated with reduced NAc prodynorphin mRNA expression and alcohol exposure induced broad alterations primarily in the dorsal striatum of most genes. To explore the mechanisms underlying the cannabis-associated disturbances, we exposed pregnant rats to THC and examined the epigenetic regulation of the NAc Drd2 gene in their offspring at postnatal day 2, comparable to the human fetal period studied, and in adulthood. Chromatin immunoprecipitation of the adult NAc revealed increased 2meH3K9 repressive mark and decreased 3meH3K4 and RNA polymerase II at the Drd2 gene locus in the THC-exposed offspring. Decreased Drd2 expression was accompanied by reduced D2R binding sites and increased sensitivity to opiate reward in adulthood. Conclusions These data suggest that maternal cannabis use alters developmental regulation of mesolimbic D2R in offspring through epigenetic mechanisms that regulate histone lysine methylation, and the ensuing reduction of D2R may contribute to addiction vulnerability later in life.

Recent attention has been focused on the long-term impact of cannabis exposure, for which experimental animal studies have validated causal relationships between neurobiological and behavioral alterations during the individual's lifetime. Here, we show that adolescent exposure to Δ(9)-tetrahydrocannabinol (THC), the main psychoactive component of cannabis, results in behavioral and neurobiological abnormalities in the subsequent generation of rats as a consequence of parental germline exposure to the drug. Adult F1 offspring that were themselves unexposed to THC displayed increased work effort to self-administer heroin, with enhanced stereotyped behaviors during the period of acute heroin withdrawal. On the molecular level, parental THC exposure was associated with changes in the mRNA expression of cannabinoid, dopamine, and glutamatergic receptor genes in the striatum, a key component of the neuronal circuitry mediating compulsive behaviors and reward sensitivity. Specifically, decreased mRNA and protein levels, as well as NMDA receptor binding were observed in the dorsal striatum of adult offspring as a consequence of germline THC exposure. Electrophysiologically, plasticity was altered at excitatory synapses of the striatal circuitry that is known to mediate compulsive and goal-directed behaviors. These findings demonstrate that parental history of germline THC exposure affects the molecular characteristics of the striatum, can impact offspring phenotype, and could possibly confer enhanced risk for psychiatric disorders in the subsequent generation.

Despite the high prevalence of marijuana use among pregnant women and adolescents, the impact of cannabis on the developing brain is still not well understood. However, growing evidence supports that the endocannabinoid system plays a major role in CNS patterning in structures relevant for mood, cognition, and reward, such as the mesocorticolimbic system. It is thus clear that exposure to cannabis during early ontogeny is not benign and potential compensatory mechanisms that might be expected to occur during neurodevelopment appear insufficient to eliminate vulnerability to neuropsychiatric disorders in certain individuals. Both human longitudinal cohort studies and animal models strongly emphasize the long-term influence of prenatal cannabinoid exposure on behavior and mental health. This review provides an overview of the endocannabinoid system and examines the neurobiological consequences of cannabis exposure in pregnancy and early life by addressing its impact on the development of neurotransmitters systems relevant to neuropsychiatric disorders and its association with these disorders later in life. It posits that studying in utero cannabis exposure in association with genetic mutations of neural systems that have strong relationships to endocannabinoid function, such as the dopamine, opioid, glutamate, and GABA, might help to identify individuals at risk. Such data could add to existing knowledge to guide public health platform in regard to the use of cannabis and its derivatives during pregnancy.

Prenatal development is highly sensitive to maternal drug use due to the vulnerability for disruption of the fetal brain where the ongoing neurodevelopmental, resulting in lifelong consequences that can enhance risk for psychiatric disorders. Cannabis and cigarettes are the most commonly used illicit and licit substances, respectively, among pregnant women. While the behavioral consequences of prenatal cannabis and cigarette exposure have been well-documented in epidemiological and clinical studies, only recently have investigations into the molecular mechanisms associated with the developmental impact of early drug exposure been addressed. This article reviews the literature relevant to long-term gene expression disturbances in the human fetal brain in relation to maternal cannabis and cigarette use. To provide translational insights, we discuss animal models in which protracted molecular consequences of prenatal cannabis and cigarette exposure can be better explored and enable future evaluation of epigenetic pathways such as DNA methylation and histone modification that could potentially maintain abnormal gene regulation and related behavioral disturbances. Altogether, this information may help to address the current gaps of knowledge regarding the impact of early drug exposure that set in motion lifelong molecular disturbances that underlie vulnerability to psychiatric disorders.

The transcription factor cAMP response element-binding protein (CREB) within the nucleus accumbens (NAc) plays an important role in regulating mood. In rodents, increased CREB activity within the NAc produces depression-like signs including anhedonia, whereas disruption of CREB activity by expression of a dominant-negative CREB (mCREB, which acts as a CREB antagonist) has antidepressantlike effects. We examined how disruption of CREB activity affects brain reward processes using intracranial self-stimulation (ICSS) and inducible bitransgenic mice with enriched expression of mCREB in forebrain regions including the NAc. Mutant mice or littermate controls were prepared with lateral hypothalamic stimulating electrodes, and trained in the ICSS procedure to determine the frequency at which the stimulation becomes rewarding (threshold). Inducible expression of mCREB did not affect baseline sensitivity to brain stimulation itself. However, mCREB-expressing mice were more sensitive to the rewarding (threshold-lowering) effects of cocaine. Interestingly, mCREB mice were insensitive to the depressive-like (threshold-elevating) effects of the -opioid receptor agonist U50,488. These behavioral differences were accompanied by decreased mRNA expression of G-protein receptor kinase-3 (GRK3), a protein involved in opioid receptor desensitization, within the NAc of mCREB mice. Disruption of CREB or GRK3 activity within the NAc specifically by viral-mediated gene transfer enhanced the rewarding impact of brain stimulation in rats, establishing the contribution of functional changes within this region. Together with previous findings, these studies raise the possibility that disruption of CREB in the NAc influences motivation by simultaneously facilitating reward and reducing depressive-like states such as anhedonia and dysphoria.