Effect of isopregnanolone on rapid tolerance to the anxiolytic effect of ethanol

Neuronal nicotinic acetylcholine receptor of the central amygdala modulates the ethanol-induced tolerance to anxiolysis and withdrawal-induced anxiety in male rats

The nicotine acetylcholinergic receptor (nAchR) in the central nucleus of the amygdala (CeA) is known to modulate anxiety traits as well as ethanol-induced behavioral effects. Therefore, the present study investigated the role of CeA nAChR in the tolerance to ethanol anxiolysis and withdrawal-induced anxiety-related effects in rats on elevated plus maze (EPM). To develop ethanol dependence, rats were given free access to an ethanol-containing liquid diet for 10 days. To assess the development of tolerance, separate groups of rats were challenged with ethanol (2 g/kg, i.p.) on days 1, 3, 5, 7 and 10 during the period of ethanol exposure, followed by an EPM assessment. Moreover, expression of ethanol withdrawal was induced after switching ethanol-dependent rats to a liquid diet on day 11, and withdrawal-induced anxiety-like behavior was noted at different post-withdrawal time points using the EPM test. The ethanol-dependent rats were pretreated with intra-CeA (i.CeA) (bilateral) injections of nicotine (0.25 µg/rat) or mecamylamine (MEC) (5 ng/rat) before the challenge dose of ethanol on subthreshold tolerance on the 5th day or on peak tolerance day, that is, 7th or 10th, and before assessment of postwithdrawal anxiety on the 11th day on EPM. Bilateral i.CeA preadministration of nicotine before the challenge dose of ethanol on days 5, 7 and 10 exhibited enhanced tolerance, while injection of MEC, completely mitigated the tolerance to the ethanol-induced antianxiety effect. On the other hand, ethanol-withdrawn rats pretreated i.CeA with nicotine exacerbated while pretreatment with MEC, alleviated the ethanol withdrawal-induced anxiety on all time points. Thus, the present investigation indicates that stimulation of nAChR in CeA negatively modulates the ethanol-induced chronic behavioral effects on anxiety in rats. It is proposed that nAChR antagonists might be useful in the treatment of alcohol use disorder and ethanol withdrawal-related anxiety-like behavior.

Sex Differences in the Alcohol-Mediated Modulation of BLA Network States

Alcohol use, reported by 85% of adults in the United States, is highly comorbid with mood disorders, like generalized anxiety disorder and major depression. The basolateral amygdala (BLA) is an area of the brain that is heavily implicated in both mood disorders and alcohol use disorder. Importantly, the modulation of BLA network/oscillatory states via parvalbumin (PV)-positive GABAergic interneurons has been shown to control the behavioral expression of fear and anxiety. Further, PV interneurons express a high density of δ subunit-containing GABAA receptors (GABAARs), which are sensitive to low concentrations of alcohol. Therefore, we hypothesized that the effects of alcohol may modulate BLA network states that have been associated with fear and anxiety behaviors via δ-GABAARs on PV interneurons in the BLA. Given the impact of ovarian hormones on the expression of δ-GABAARs, we also examined the ability of alcohol to modulate local field potentials in the BLA from male and female C57BL/6J and Gabrd-/- mice after acute and repeated exposure to alcohol. Here, we demonstrate that acute and repeated alcohol can differentially modulate oscillatory states in male and female C57BL/6J mice, a process that involves δ-GABAARs. This is the first study to demonstrate that alcohol is capable of altering network states implicated in both anxiety and alcohol use disorders.

Tolerance to alcohol: A critical yet understudied factor in alcohol addiction

Alcohol tolerance refers to a lower effect of alcohol with repeated exposure. Although alcohol tolerance has been historically included in diagnostic manuals as one of the key criteria for a diagnosis of alcohol use disorder (AUD), understanding its neurobiological mechanisms has been neglected in preclinical studies. In this mini-review, we provide a theoretical framework for alcohol tolerance. We then briefly describe chronic tolerance, followed by a longer discussion of behavioral and neurobiological aspects that underlie rapid tolerance in rodent models. Glutamate/nitric oxide, γ-aminobutyric acid, opioids, serotonin, dopamine, adenosine, cannabinoids, norepinephrine, vasopressin, neuropeptide Y, neurosteroids, and protein kinase C all modulate rapid tolerance. Most studies have evaluated the ability of pharmacological manipulations to block the development of rapid tolerance, but only a few studies have assessed their ability to reverse already established tolerance. Notably, only a few studies analyzed sex differences. Neglected areas of study include the incorporation of a key element of tolerance that involves opponent process-like neuroadaptations. Compared with alcohol drinking models, models of rapid tolerance are relatively shorter in duration and are temporally defined, which make them suitable for combining with a wide range of classic and modern research tools, such as pharmacology, optogenetics, calcium imaging, in vivo electrophysiology, and DREADDs, for in-depth studies of tolerance. We conclude that studies of the neurobiology of alcohol tolerance should be revisited with modern conceptualizations of addiction and modern neurobiological tools. This may contribute to our understanding of AUD and uncover potential targets that can attenuate hazardous alcohol drinking.

Essential Role of Histone Methyltransferase G9a in Rapid Tolerance to the Anxiolytic Effects of Ethanol

BACKGROUND

Tolerance to ethanol-induced anxiolysis promotes alcohol intake, thus contributing to alcohol use disorder development. Recent studies implicate histone deacetylase-mediated histone H3K9 deacetylation in regulating neuropeptide Y expression during rapid ethanol tolerance to the anxiolytic effects of ethanol. Furthermore, the histone methyltransferase, G9a, and G9a-mediated H3K9 dimethylation (H3K9me2) have recently emerged as regulators of addiction and anxiety; however, their role in rapid ethanol tolerance is unknown. Therefore, we investigated the role of G9a-mediated H3K9me2 in neuropeptide Y expression during rapid ethanol tolerance.

METHODS

Adult male rats were administered one injection of n-saline followed by single acute ethanol injection (1 g/kg) 24 hours later (ethanol group) or 2 injections (24 hours apart) of either n-saline (saline group) or ethanol (tolerance group). Anxiety-like behaviors and global and Npy-specific G9a and H3K9me2 levels in the amygdala were measured. Effects of G9a inhibitor (UNC0642) treatment on behavioral and epigenetic measures were also examined.

RESULTS

Acute ethanol produced anxiolysis and decreased global H3K9me2 and G9a protein levels in the central and medial nucleus of the amygdala as well as decreased occupancy levels of H3K9me2 and G9a near a putative binding site for cAMP-response element binding protein on the Npy gene. Two identical doses of ethanol produced no behavioral or epigenetic changes relative to controls, indicating development of rapid ethanol tolerance. Interestingly, treatment with UNC0642, before the second ethanol dose reversed rapid ethanol tolerance, decreased global H3K9me2 and increased neuropeptide Y levels in the central and medial nucleus of the amygdala.

CONCLUSIONS

These results implicate amygdaloid G9a-mediated H3K9me2 mechanisms in regulating rapid tolerance to the anxiolytic effects of ethanol via neuropeptide Y expression regulation.

Emerging Role of Epigenetic Mechanisms in Alcohol Addiction

Alcohol use disorder (AUD) is a complex brain disorder with an array of persistent behavioral and neurochemical manifestations. Both genetic and environmental factors are known to contribute to the development of AUD, and recent studies on alcohol exposure and subsequent changes in gene expression suggest the importance of epigenetic mechanisms. In particular, histone modifications and DNA methylation have emerged as important regulators of gene expression and associated phenotypes of AUD. Given the therapeutic potential of epigenetic targets, this review aims to summarize the role of epigenetic regulation in our current understanding of AUD by evaluating known epigenetic signatures of brain regions critical to addictive behaviors in both animal and human studies throughout various stages of AUD. More specifically, the effects of acute and chronic alcohol exposure, tolerance, and postexposure withdrawal on epigenetically induced changes to gene expression and synaptic plasticity within key brain regions and the associated behavioral phenotypes have been discussed. Understanding the contribution of epigenetic regulation to crucial signaling pathways may prove vital for future development of novel biomarkers and treatment agents in ameliorating or preventing AUD.

Antiandrogenic effect of perinatal exposure to the endocrine disruptor di-(2-ethylhexyl) phthalate increases anxiety-like behavior in male rats during sexual maturation

Di-2-ethylhexyl phthalate (DEHP) is the most widely used phthalate to convey flexibility and transparency to plastic products made of polyvinyl chloride. It has been recognized as endocrine disruptor and associated with reproductive toxic effects. We examined the effects of perinatal exposure to DEHP on anxiety-like behavior, using the Elevated Plus Maze (EPM) test, in male and female rats at different stages of sexual development. Anxiety-like behavior was expressed as a) frequency of open arm entries over the total arm entries (% FEO); b) time spent in them compared with total time the animal stayed in the EPM (% TSO) and c) time spent in closed arms (TSC). Because DEHP has anti-androgenic action we also tested control and exposed immature male rats pretreated with testosterone. We found sex differences in behavior induced by DEHP; while male rats of 45 and 60 days of age showed a significant decrease in FEO and TSO percentages, as well as an increase in TSC, no changes were observed in anxiety-like behavior in perinatal DEHP exposed females at these ages of sexual maturation. In 60-day-old male rats, DEHP exposure produced a significant decrease in serum testosterone levels. Testosterone replacement was able to antagonize the adverse effects of DEHP exposure on LH, activating the negative feed-back mechanism of this steroid on reproductive axis, as well as increasing FEO and TSO percentages to similar values observed in the control group. These findings suggest that the anti-androgenic action of this chemical could be one possible mechanism underlie anxiogenic-like behavior produced by perinatal DEHP exposure in 60-day-old male rats.

Psychological stress on female mice diminishes the developmental potential of oocytes: a study using the predatory stress model

Although the predatory stress experimental protocol is considered more psychological than the restraint protocol, it has rarely been used to study the effect of psychological stress on reproduction. Few studies exist on the direct effect of psychological stress to a female on developmental competence of her oocytes, and the direct effect of predatory maternal stress on oocytes has not been reported. In this study, a predatory stress system was first established for mice with cats as predators. Beginning 24 h after injection of equine chorionic gonadotropin, female mice were subjected to predatory stress for 24 h. Evaluation of mouse responses showed that the predatory stress system that we established increased anxiety-like behaviors and plasma cortisol concentrations significantly and continuously while not affecting food and water intake of the mice. In vitro experiments showed that whereas oocyte maturation and Sr(2+) activation or fertilization were unaffected by maternal predatory stress, rate of blastocyst formation and number of cells per blastocyst decreased significantly in stressed mice compared to non-stressed controls. In vivo embryo development indicated that both the number of blastocysts recovered per donor mouse and the average number of young per recipient after embryo transfer of blastocysts with similar cell counts were significantly lower in stressed than in unstressed donor mice. It is concluded that the predatory stress system we established was both effective and durative to induce mouse stress responses. Furthermore, predatory stress applied during the oocyte pre-maturation stage significantly impaired oocyte developmental potential while exerting no measurable impact on nuclear maturation, suggesting that cytoplasmic maturation of mouse oocytes was more vulnerable to maternal stress than nuclear maturation.

Acute and chronic ethanol differentially modify the emotional significance of a novel environment: implications for addiction

Using open-field behaviour as an experimental paradigm, we demonstrated a complex interaction between the rewarding/stimulating effects and the anxiogenic/stressful effects of both novelty and acute or chronic amphetamine in mice. As a consequence of this interaction, acute amphetamine-induced hyperlocomotion was inhibited, whereas the expression of its sensitization was facilitated in a novel environment. In the present study, we aimed to investigate the interactions between exposure to a novel environment and the acute and chronic effects of ethanol (Eth), a drug of abuse known to produce anxiolytic-like behaviour in mice. Previously habituated and non-habituated male Swiss mice (3 months old) were tested in an open field after receiving an acute injection of Eth or following repeated treatment with Eth. Acute Eth administration increased locomotion with a greater magnitude in mice exposed to the apparatus for the first time, and this was thought to be related to the attenuation of the stressful effects of novelty produced by the anxiolytic-like effect of acute Eth, leading to a subsequent prevalence of its stimulant effects. However, locomotor sensitization produced by repeated Eth administration was expressed only in the previously explored environment. This result might be related to the well-known tolerance of Eth-induced anxiolytic-like behaviour following repeated treatment, which would restore the anxiogenic effect of novelty. Our data suggest that a complex and plastic interaction between the emotional and motivational properties of novelty and drugs of abuse can critically modify the behavioural expression of addiction-related mechanisms.

Histone deacetylases (HDAC)-induced histone modifications in the amygdala: a role in rapid tolerance to the anxiolytic effects of ethanol

BACKGROUND

Rapid tolerance to the anxiolytic effects of ethanol appears to be an important factor in the development of alcoholism. Here, we investigated the involvement of amygdaloid histone deacetylases (HDAC)-induced epigenetic changes in rapid ethanol tolerance (RET).

METHODS

RET in rats was induced by 2 ethanol injections administered 24 hours apart. Both ethanol-tolerant and control rats were treated with the HDAC inhibitor, trichostatin A (TSA), and anxiety-like behaviors were measured. HDAC activity, histone (H3 and H4) acetylation, and neuropeptide Y (NPY) expression in the amygdala of these rats were also measured.

RESULTS

A single ethanol exposure was able to produce an anxiolytic response, inhibit amygdaloid HDAC activity, and increase both histone acetylation and NPY expression (mRNA and protein levels) in the central nucleus of amygdala (CeA) and medial nucleus of amygdala (MeA) of rats. In contrast, 2 exposures of the same dose of ethanol (24 hours apart) neither elicited a similar anxiolytic response nor modulated HDAC activity, histone acetylation, or NPY expression in the amygdala. However, exposure to a higher dose of ethanol on the second day was able to produce an anxiolytic response and also inhibit amygdaloid HDAC activity. TSA treatment caused the reversal of RET by inhibiting HDAC activity, thereby increasing histone acetylation and NPY expression in the CeA and MeA.

CONCLUSIONS

Cellular tolerance to the initial acute ethanol-induced inhibition of HDAC activity and the subsequent upregulation of histone acetylation and NPY expression in the amygdala may be involved in the mechanisms underlying rapid tolerance to the anxiolytic effects of ethanol.

Effects of prenatal stress on motor performance and anxiety behavior in Swiss mice

Stressor presence during the last weeks of gestation has been associated with behavioral disorders in later life. In this study we support further research on the long term effects of prenatal stress on Swiss mice descendant's behavior. Prenatal stress procedure consisted on restraining the dams under bright light for 45 min, three times per day from the 15th day of pregnancy, until birth. After weaning, offspring's motor performance and spontaneous exploratory behavior were measured by the tight-rope and T-maze tests, respectively. We also evaluated anxiety behavior using elevated plus maze test. We found that maternal stress improves the performance of the animals in the tight rope test and that this effect was sex and age dependent: prenatal stressed males obtained the best scores during the first month of life, while in females the same was achieved at the second month. Spontaneous exploratory behavior analysis revealed that it was elevated in prenatal stressed males and that this effect persisted on time. However, we did not find significant differences on this behavioral response among both females groups. Finally, differences on anxiety behavior were found only in females: prenatally stressed animals showed a higher proportion of entries into the open arms of a plus maze (reduced anxiety) compared to the control group. Our results show that prenatal stress modifies the normal behavior of the progeny: prenatal stressed animals have a better performance in the carried out test. These notably results suggest the existence of an adaptive response to prenatal stress.