Intra-accumbal orexin-1 receptor inhibition prevents the anxiolytic-like effect of ethanol and leads to increases in orexin-A content and receptor expression

Blockade of orexin receptor 1 attenuates morphine protracted abstinence-induced anxiety-like behaviors in male mice

One negative emotional state from morphine protracted abstinence is anxiety which can drive craving and relapse risk in opioid addicts. Although the orexinergic system has been reported to be important in mediating emotion processing and addiction, the role of orexinergic system in anxiety from drug protracted abstinence remains elusive. In this study, by using behavioral test, western blot, electrophysiology and virus-mediated regulation of orexin receptor 1 (OX1R), we found that: (1) Intraperitoneal and intra-VTA administration of a selective OX1R antagonist SB334867 alleviated anxiety-like behaviors in open field test (OFT) but not in elevated plus maze test (EPM) in morphine protracted abstinent male mice. (2) OX1R expression in the VTA was upregulated by morphine withdrawal. (3) Virus-mediated knockdown of OX1R in the VTA prevented morphine abstinence-induced anxiety-like behaviors and virus-mediated overexpression of OX1R in the VTA was sufficient to produce anxiety-like behaviors in male mice. (4) The VTA neuronal activity was increased significantly induced by morphine protracted abstinence, which was mediated by OX1R. (5) OX1R was widely distributed in the neuronal soma and processes of dopaminergic and non-dopaminergic neurons in the VTA. The findings revealed that the OX1R mediates morphine abstinence-induced anxiety-like behaviors and the VTA plays a critical role in this effect.

Regulation of the central amygdala on intestinal motility and behavior via the lateral hypothalamus in irritable bowel syndrome model mice

BACKGROUND

Impaired bidirectional communication between the gastrointestinal tract and the central nervous system (CNS) is closely related to the development of irritable bowel syndrome (IBS). Studies in patients with IBS have also shown significant activation of the hypothalamus and amygdala. However, how neural circuits of the CNS participate in and process the emotional and intestinal disorders of IBS remains unclear.

METHODS

The GABAergic neural pathway projecting from the central amygdala (CeA) to the lateral hypothalamus (LHA) in mice was investigated by retrograde tracking combined with fluorescence immunohistochemistry. Anxiety, depression-like behavior, and intestinal motility were observed in the water-immersion restraint stress group and the control group. Furthermore, the effects of the chemogenetic activation of the GABAergic neural pathway of CeA-LHA on behavior and intestinal motility, as well as the co-expression of orexin-A and c-Fos in the LHA, were explored.

KEY RESULTS

In our study, Fluoro-Gold retrograde tracking combined with fluorescence immunohistochemistry showed that GABAergic neurons in the CeA were projected to the LHA. The microinjection of the gamma-aminobutyric acid (GABA) receptor antagonist into the LHA relieved anxiety, depression-like behavior, and intestinal motility disorder in the IBS mice. The chemogenetic activation of GABAergic neurons in the CeA-LHA pathway led to anxiety, depression-like behavior, and intestinal motility disorder. In addition, GABAergic neurons in the CeA-LHA pathway inhibited the expression of orexin-A in the LHA, and orexin-A was co-expressed with GABAA receptors.

CONCLUSIONS & INFERENCES

The CeA-LHA GABAergic pathway might participate in the occurrence and development of IBS by regulating orexin-A neurons.

Acute orexin antagonism selectively modulates anticipatory anxiety in humans: implications for addiction and anxiety

Research indicates that heightened anticipatory anxiety underlies several forms of psychopathology. Anticipatory anxiety can be reliably and objectively measured in the laboratory using the No-Predictable-Unpredictable (NPU) threat paradigm. The NPU paradigm is an ideal research tool for the NIH 'Fast-Fail' approach of screening promising compounds and testing human target engagement. Evidence from preclinical studies suggests that the hypocretin/orexin (ORX) hypothalamic neuropeptide system is a potential means for modulating anticipatory anxiety and disrupting stress-related alcohol use. The current study tested this question using a psychophysiological probe of the ORX system in humans. We examined whether a single dose of suvorexant (SUV; 10 mg; dual ORX receptor antagonist) can effectively and selectively target a well-validated human laboratory index of exaggerated anticipatory anxiety using a within-subjects placebo-controlled design. A total of twenty-one volunteers completed two laboratory sessions during acute administration of 10 mg SUV or placebo. Across sessions, we administered the NPU paradigm probing sustained anticipatory anxiety and fear while startle eyeblink was recorded as an index of aversive reactivity. Questionnaires assessing mood states and subjective drug effects were also collected. Results indicated SUV was well-tolerated. Compared with placebo, SUV was associated with decreased startle reactivity during anticipatory anxiety but not fear or no-threat conditions. Therefore, SUV selectively and effectively reduced objective indicators of anticipatory anxiety in humans and engaged our laboratory target of psychopathology. ORX antagonism may be a promising strategy for modulating human anxiety and potentially, stress-related alcohol use.

Ethanol's disruptive effects upon early breathing plasticity and blood parameters associated with hypoxia and hypercapnia

Early ethanol exposure affects respiratory neuroplasticity; a risk factor associated with the Sudden Infant Death Syndrome. High and chronic ethanol doses exert long-lasting effects upon respiratory rates, apneic episodes and ventilatory processes triggered by hypoxia. The present study was performed in 3-9-day-old rat pups. Respiratory processes under normoxic and hypoxic conditions were analyzed in pups intoxicated with different ethanol doses which were pre-exposed or not to the drug. A second major goal was to examine if acute and/or chronic early ethanol exposure affects blood parameters related with hypercapnic or hypoxic states. In Experiment 1, at postnatal day 9, animals previously treated with ethanol (2.0 g/kg) or vehicle (0.0 g/kg) were tested sober or intoxicated with 0.75, 1.37 or 2.00 g/kg ethanol. The test involved sequential air conditions defined as initial normoxia, hypoxia and recovery normoxia. Motor activity was also evaluated. In Experiment 2, blood parameters indicative of possible hypoxic and hypercapnic states were assessed as a function of early chronic or acute experiences with the drug. The main results of Experiment 1 were as follows: i) ethanol's depressant effects upon respiratory rates increased as a function of sequential treatment with the drug (sensitization); ii) ethanol inhibited apneic episodes even when employing the lowest dose at test (0.75 g/kg); iii) the hyperventilatory response caused by hypoxia negatively correlated with the ethanol dose administered at test; iv) ventilatory long-term facilitation (LTF) during recovery normoxia was observed in pups pre-exposed to the drug and in pups that received the different ethanol doses at test; v) self-grooming increased in pups treated with either 1.37 or 2.00 g/kg ethanol. The main result of Experiment 2 indicated that acute as well as chronic ethanol exposure results in acidosis-hypercapnia. The results indicate that early and brief experiences with ethanol are sufficient to affect different respiratory plasticity processes as well as blood biomarkers indicative of acidosis-hypercapnia. An association between the LTF process and the acidosis-hypercapnic state caused by ethanol seems to exist. The mentioned experiences with the drug are sufficient to result in an anomalous programming of respiratory patterns and metabolic conditions.

Chronic nicotine increases alcohol self-administration in adult male Wistar rats

RATIONALE

Alcohol and nicotine co-dependence is common in humans, and nicotine increases alcohol drinking in humans without alcohol use disorder (AUD). Nevertheless, there is little basic research on the interactions between the reinforcing effects of these two drugs.

OBJECTIVES

The aim of this study was to investigate the effects of chronic nicotine injections on oral alcohol self-administration in alcohol non-dependent rats.

METHODS

After stable alcohol self-administration was reached (baseline) and a period without alcohol access, adult male rats were treated with chronic nicotine or saline injections for 105 days during which time they were tested intermittently for alcohol self-administration. There were 3 experimental groups: (1) saline, rats treated with saline for 105 days; (2) early nicotine, rats treated with nicotine for 70 days, and then with saline for 35 days; and (3) late nicotine: rats treated with saline for 35 days, and then with nicotine for 70 days.

RESULTS

Our results indicate that (1) chronic nicotine increases alcohol consumption regardless of whether exposure to alcohol was interrupted (early nicotine) or not (late nicotine) before the start of nicotine treatment, (2) the number of alcohol reinforcements correlates to blood-alcohol levels, and (3) alcohol self-administration rapidly decreases when nicotine is no longer available (early nicotine).

CONCLUSIONS

These discoveries may have clinical implications in social drinkers that use nicotine products, in that chronic nicotine can escalate alcohol drinking and cessation of nicotine exposure may decrease alcohol use.

Linking peripheral IL-6, IL-1β and hypocretin-1 with cognitive impairment from major depression

BACKGROUND

Cognitive impairment has long challenged the patients with major depressive disorder (MDD), hypocretins and inflammation have recently been implicated in cognitive function. However, limited studies have compressively assessed their associations with cognitive impairment in MDD.

METHODS

A total of 100 MDD patients and 100 healthy controls (HC) were recruited for this study. They were tested with HAMD, HAMA, and MCCB scales. The plasma level of selected inflammatory factors (IL-1β, IL-6, and TNF-α) and hypocretin-1 were determined using enzyme-linked immunosorbent assay (ELISA). Correlation analysis was performed to explore the relationship between the plasma level of the factors and clinical performances.

RESULTS

Patients with MDD showed cognitive impairment in each MCCB subdomain except working memory compared with HC. The levels of IL-6, IL-1β and hypocretin-1 in MDD patients were higher than HC. Besides, IL-1β levels was negatively correlated with overall cognitive function in the combined group. Hypocretin-1 was positively correlated with socially cognitive impairment in MDD patients. A negative correlation between plasma hypocretin-1 levels and HAMA scales was also observed in MDD patients.

LIMITATION

The study was cross-sectional, thereby limiting causal inference, and had a relatively small sample size. There are no subcategories for MDD based on characteristics.

CONCLUSION

IL-1β, IL-6 and Hypocretin-1 were reported as potential factors involved in MDD pathology. Hypocretin-1 could contribute to the biological mechanisms of anxiety relief. Hypocretin-1, therefore, may be important in exploring the pathological mechanisms of social cognitive impairment in MDD patients. Conclusively, this study provides new insights for exploring cognitive impairment in depression.

Sex Differences in the Neurobiology of Alcohol Use Disorder

Sex differences may play a critical role in modulating how chronic or heavy alcohol use impacts the brain to cause the development of alcohol use disorder (AUD). AUD is a multifaceted and complex disorder driven by changes in key neurobiological structures that regulate executive function, memory, and stress. A three-stage framework of addiction (binge/intoxication; withdrawal/negative affect; preoccupation/anticipation) has been useful for conceptualizing the complexities of AUD and other addictions. Initially, alcohol drinking causes short-term effects that involve signaling mediated by several neurotransmitter systems such as dopamine, corticotropin releasing factor, and glutamate. With continued intoxication, alcohol leads to dysfunctional behaviors that are thought to be due in part to alterations of these and other neurotransmitter systems, along with alterations in neural pathways connecting prefrontal and limbic structures. Using the three-stage framework, this review highlights examples of research examining sex differences in drinking and differential modulation of neural systems contributing to the development of AUD. New insights addressing the role of sex differences in AUD are advancing the field forward by uncovering the complex interactions that mediate vulnerability.

Early ethanol pre-exposure alters breathing patterns by disruptions in the central respiratory network and serotonergic balance in neonate rats

Early ethanol exposure alters neonatal breathing plasticity. Respiratory EtOH's effects are attributed to central respiratory network disruptions, particularly in the medullary serotonin (5HT) system. In this study we evaluated the effects of neonatal pre-exposure to low/moderate doses upon breathing rates, activation patterns of brainstem's nuclei and expression of 5HT 2A and 2C receptors. At PD9, breathing frequencies, tidal volumes and apneas were examined in pups pre-exposed to vehicle or ethanol (2.0 g/kg) at PDs 3, 5 and 7. This developmental stage is equivalent to the 3^rd human gestational trimester, characterized by increased levels of synaptogenesis. Pups were tested under sobriety or under the state of ethanol intoxication and when subjected to normoxia or hypoxia. Number of c-Fos and 5HT immunolabelled cells and relative mRNA expression of 5HT 2A and 2C receptors were quantified in the brainstem. Under normoxia, ethanol pre-exposed pups exhibited breathing depressions and a high number of apneas. An opposite phenomenon was found in ethanol pre-treated pups tested under hypoxia where an exacerbated hypoxic ventilatory response (HVR) was observed. The breathing depression was associated with an increase in the neural activation levels of the raphe obscurus (ROb) and a high mRNA expression of the 5HT 2A receptor in the brainstem while desactivation of the ROb and high activation levels in the solitary tract nucleus and area postrema were associated to the exacerbated HVR. In summary, early ethanol experience induces respiratory disruptions indicative of sensitization processes. Neuroadaptive changes in central respiratory areas under consideration appear to be strongly associated with changes in their respiratory plasticity.