Effects of environmental enrichment upon ethanol-induced conditioned place preference and pre-frontal BDNF levels in adolescent and adult mice

Environmental enrichment enhances ethanol preference over social reward in male swiss mice: Involvement of oxytocin-dopamine interactions

The impact of environmental enrichment (EE) on natural rewards, including social and appetitive rewards, was investigated in male Swiss mice. EE, known for providing animals with various stimuli, was assessed for its effects on conditioned place preference (CPP) associated with ethanol and social stimuli. We previously demonstrated that EE increased the levels of the prosocial neuropeptide oxytocin (OT) in the hypothalamus and enhanced ethanol rewarding effects via an oxytocinergic mechanism. This study also investigated the impact of EE on social dominance and motivation for rewards, measured OT-mediated phospholipase C (PLC) activity in striatal membranes, and assessed OT expression in the hypothalamus. The role of dopamine in motivating rewards was considered, along with the interaction between OT and D1 receptors (DR) in the nucleus accumbens (NAc). Results showed that EE mice exhibited a preference for ethanol reward over social reward, a pattern replicated by the OT analogue Carbetocin. EE mice demonstrated increased social dominance and reduced motivation for appetitive taste stimuli. Higher OT mRNA levels in the hypothalamus were followed by diminished OT receptor (OTR) signaling activity in the striatum of EE mice. Additionally, EE mice displayed elevated D1R expression, which was attenuated by the OTR antagonist (L-368-889). The findings underscore the reinforcing effect of EE on ethanol and social rewards through an oxytocinergic mechanism. Nonetheless, they suggest that mechanisms other than the prosocial effect of EE may contribute to the ethanol pro-rewarding effect of EE and Carbetocin. They also point towards an OT-dopamine interaction potentially underlying some of these effects.

One day away from mum has lifelong consequences on brain and behaviour

This chapter presents a brief overview of attachment theory and discusses the importance of the neonatal period in shaping an individual's physiological and behavioural responses to stress later in life, with a focus on the role of the parent-infant relationship, particularly in rodents. In rodents, the role of maternal behaviours goes far beyond nutrition, thermoregulation and excretion, acting as hidden regulators of the pup's physiology and development. In this review, we will discuss the inhibitory role of specific maternal behaviours on the ACTH and corticosterone (CORT) stress response. The interest of our group to explore the long-term consequences of maternal deprivation for 24 h (DEP) at different ages (3 days and 11 days) in rats was sparked by its opposite effects on ACTH and CORT levels. In early adulthood, DEP3 animals (males and females alike) show greater negative impact on affective behaviours and stress related parameters than DEP11, indicating that the latter is more resilient in tests of anxiety-like behaviour. These findings create an opportunity to explore the neurobiological underpinnings of vulnerability and resilience to stress-related disorders. The chapter also provides a brief historical overview and highlights the relevance of attachment theory, and how DEP helps to understand the effects of childhood parental loss as a risk factor for depression, schizophrenia, and PTSD in both childhood and adulthood. Furthermore, we present the concept of environmental enrichment (EE), its effects on stress responses and related behavioural changes and its benefits for rats previously subjected to DEP, along with the clinical implications of DEP and EE.

A potential role of hippocampus on impulsivity and alcohol consumption through CB1R

There are a few studies suggesting that the hippocampus is involved in the regulation of impulsivity, and which attempt to explain drug seeking behavior in addiction. In addition, cannabinoid receptor 1 (CB1R) is highly expressed in the hippocampus (HPP). To further understand the potential role of the hippocampal CB1R in impulsive and drug seeking behaviors, we characterized impulsivity in adolescent and adult male rats, by means of a delay discounting task (DDT) by evaluating preference and seeking motivation for alcohol (10 % v/v) consumption, and analyzing CB1R expression in CA1, CA3 and the dentate gyrus (DG) of the HPP as well as in the medial prefrontal cortex (mPFC). Our results show that adolescent rats display more impulsive choices than adult rats in the DDT. The k value is statistically higher in adolescents, further supporting that they are more impulsive. Besides, adolescent rats have higher forced and voluntary alcohol consumption and display a higher alcohol conditioned place preference (CPP) vs. adult rats. In addition, CB1R expression in CA3 and the DG is higher in adolescent vs. adult rats. Our data further support the role of the hippocampus in impulsivity with the potential involvement of the endocannabinoid system, considering that CB1R in CA3 and DG is higher in adolescents, who display impulsivity and alcohol seeking and consumption.

Environmental enrichment augments binge-like alcohol drinking in Sardinian alcohol-preferring rats

Exposure of Sardinian alcohol-preferring (sP) rats to an enriched environment (EE) reduced different aspects of operant alcohol self-administration. The present study was aimed at expanding investigation of the effect of EE exposure upon a model of binge drinking composed of daily 1-h drinking sessions with unpredictable access to multiple alcohol concentrations; binge-like alcohol intakes were observed when the drinking session occurred at the last hours of the dark phase of the light/dark cycle. Starting from postnatal day (PND) 21, male sP rats were kept under three different housing conditions: impoverished environment (IE; single housing with no environmental enrichment); standard environment (SE; 3 rats/cage and no environmental enrichment); EE (6 rats/cage and multiple elements of environmental enrichment). From PND 69, rats were exposed daily to a 1-hour drinking session under the 4-bottle "alcohol (10%, 20%, and 30%, v/v) vs. water" choice regimen, during the dark phase, and with timing of alcohol exposure changed each day. In all three rat groups (IE, SE, and EE), alcohol intake increased progressively as the drinking session moved from the first to last hours of the dark phase. The slope of the regression line was steeper in EE than IE and SE rats, suggestive of higher intakes of alcohol in EE than IE and SE rats when the drinking session occurred over the last hours of the dark phase. These results are discussed hypothesizing that the stressful attributes of alcohol expectation were potentiated by the increased "emotionality" that rats living in a comfortable environment (i.e., EE) may experience when facing new, challenging events or environments. Blood alcohol levels, assessed at the end of a final drinking session occurring at the 12th hour of the dark phase, did not differ among the three rat groups and averaged approximately 150 mg%, confirming that this experimental procedure may generate intoxicating levels of alcohol drinking in sP rats.

Neurobehavioral effects of environmental enrichment and drug abuse vulnerability: An updated review

Environmental enrichment consisting of social peers and novel objects is known to alter neurobiological functioning and have an influence on the behavioral effects of drugs of abuse in preclinical rodent models. An earlier review from our laboratory (Stairs and Bardo, 2009) provided an overview of enrichment-specific changes in addiction-like behaviors and neurobiology. The current review updates the literature in this extensive field. Key findings from this updated review indicate that enrichment produces positive outcomes in drug abuse vulnerability beyond just psychostimulants. Additionally, recent studies indicate that enrichment activates key genes involved in cell proliferation and protein synthesis in nucleus accumbens and enhances growth factors in hippocampus and neurotransmitter signaling pathways in prefrontal cortex, amygdala, and hypothalamus. Remaining gaps in the literature and future directions for environmental enrichment and drug abuse research are identified.

BDNF and its Role in the Alcohol Abuse Initiated During Early Adolescence: Evidence from Preclinical and Clinical Studies

Brain-derived neurotrophic factor (BDNF) is a crucial brain signaling protein that is integral to many signaling pathways. This neurotrophin has shown to be highly involved in brain plastic processes such as neurogenesis, synaptic plasticity, axonal growth, and neurotransmission, among others. In the first part of this review, we revise the role of BDNF in different neuroplastic processes within the central nervous system. On the other hand, its deficiency in key neural circuits is associated with the development of psychiatric disorders, including alcohol abuse disorder. Many people begin to drink alcohol during adolescence, and it seems that changes in BDNF are evident after the adolescent regularly consumes alcohol. Therefore, the second part of this manuscript addresses the involvement of BDNF during adolescent brain maturation and how this process can be negatively affected by alcohol abuse. Finally, we propose different BNDF enhancers, both behavioral and pharmacological, which should be considered in the treatment of problematic alcohol consumption initiated during the adolescence.

Age-related differences in the effect of chronic alcohol on cognition and the brain: a systematic review

Adolescence is an important developmental period associated with increased risk for excessive alcohol use, but also high rates of recovery from alcohol use-related problems, suggesting potential resilience to long-term effects compared to adults. The aim of this systematic review is to evaluate the current evidence for a moderating role of age on the impact of chronic alcohol exposure on the brain and cognition. We searched Medline, PsycInfo, and Cochrane Library databases up to February 3, 2021. All human and animal studies that directly tested whether the relationship between chronic alcohol exposure and neurocognitive outcomes differs between adolescents and adults were included. Study characteristics and results of age-related analyses were extracted into reference tables and results were separately narratively synthesized for each cognitive and brain-related outcome. The evidence strength for age-related differences varies across outcomes. Human evidence is largely missing, but animal research provides limited but consistent evidence of heightened adolescent sensitivity to chronic alcohol's effects on several outcomes, including conditioned aversion, dopaminergic transmission in reward-related regions, neurodegeneration, and neurogenesis. At the same time, there is limited evidence for adolescent resilience to chronic alcohol-induced impairments in the domain of cognitive flexibility, warranting future studies investigating the potential mechanisms underlying adolescent risk and resilience to the effects of alcohol. The available evidence from mostly animal studies indicates adolescents are both more vulnerable and potentially more resilient to chronic alcohol effects on specific brain and cognitive outcomes. More human research directly comparing adolescents and adults is needed despite the methodological constraints. Parallel translational animal models can aid in the causal interpretation of observed effects. To improve their translational value, future animal studies should aim to use voluntary self-administration paradigms and incorporate individual differences and environmental context to better model human drinking behavior.

Inbred mouse strain differences in alcohol and nicotine addiction-related phenotypes from adolescence to adulthood

Understanding the genetic basis of a predisposition for nicotine and alcohol use across the lifespan is important for public health efforts because genetic contributions may change with age. However, parsing apart subtle genetic contributions to complex human behaviors is a challenge. Animal models provide the opportunity to study the effects of genetic background and age on drug-related phenotypes, while controlling important experimental variables such as amount and timing of drug exposure. Addiction research in inbred, or isogenic, mouse lines has demonstrated genetic contributions to nicotine and alcohol abuse- and addiction-related behaviors. This review summarizes inbred mouse strain differences in alcohol and nicotine addiction-related phenotypes including voluntary consumption/self-administration, initial sensitivity to the drug as measured by sedative, hypothermic, and ataxic effects, locomotor effects, conditioned place preference or place aversion, drug metabolism, and severity of withdrawal symptoms. This review also discusses how these alcohol and nicotine addiction-related phenotypes change from adolescence to adulthood.

Exposure to an enriched environment reduces alcohol self-administration in Sardinian alcohol-preferring rats

Living in an enriched environment (EE) produces a notable impact on several rodent behaviors, including those motivated by drugs of abuse. This picture is somewhat less clear when referring to alcohol-motivated behaviors. With the intent of contributing to this research field with data from one of the few rat lines selectively bred for excessive alcohol consumption, the present study investigated the effect of EE on operant oral alcohol self-administration in Sardinian alcohol-preferring (sP) rats. Starting from Postnatal Day (PND) 21, male sP rats were kept under 3 different housing conditions: impoverished environment (IE; single housing in shoebox-like cages with no environmental enrichment); standard environment (SE; small colony cages with 3 rats and no environmental enrichment); EE (large colony cages with 6 rats and multiple elements of environmental enrichment, including 2 floors, ladders, maze, running wheels, and shelter). From PND 60, rats were exposed to different phases of shaping and training of alcohol self-administration. IE, SE, and EE rats were then compared under (i) fixed ratio (FR) 4 (FR4) schedule of alcohol reinforcement for 20 daily sessions and (ii) progressive ratio (PR) schedule of alcohol reinforcement in a final single session. Acquisition of the lever-responding task (shaping) was slower in EE than IE and SE rats, as the likely consequence of a "devaluation" of the novel stimuli provided by the operant chamber in comparison to those to which EE rats were continuously exposed in their homecage or an alteration, induced by EE, of the rat "emotionality" state when facing the novel environment represented by the operant chamber. Training of alcohol self-administration was slower in EE than IE rats, with SE rats displaying intermediate values. A similar ranking order (IE>SE>EE) was also observed in number of lever-responses for alcohol, amount of self-administered alcohol, and breakpoint for alcohol under FR4 and PR schedules of reinforcement. These data suggest that living in a complex environment reduced the reinforcing and motivational properties of alcohol in sP rats. These results are interpreted in terms of the reinforcing and motivational properties of the main components of EE (i.e., social interactions, physical activities, exploration, novelty) substituting, at least partially, for those of alcohol.

Maternal deprivation effect on morphine-induced CPP is related to changes in Opioid receptors in selected rat brain regions (hippocampus, prefrontal cortex, and nucleus accumbens)

Early-life environmental conditions affect offspring's development. Maternal deprivation (MD) can induce persistent changes that give rise to neuropsychiatric diseases including substance abuse disorders. However, long-lasting mechanisms that determine vulnerability to drug addiction remain unknown. We hypothesized that MD could induce changes in Opioid system, HPA (hypothalamic-pituitary-adrenal) axis, and BDNF (brain-derived neurotrophic factor), so may be involved in the drug abuse in later life. Male offspring of Wistar rats (n=8 per group) were subjected to 3h of daily MD during postnatal days 1-14. In adulthood, morphine-induced CPP (conditioned place preference) was investigated using two doses of morphine (3 and 5mg/kg). Serum corticosterone level was measured by ELISA method. The expression level of genes in selected brain regions (hippocampus, prefrontal cortex, and nucleus accumbens) was determined by qPCR (quantitative PCR). A greater morphine-induced CPP was observed in MD rats with 3 and 5mg/kg morphine compared to controls. MD group had a higher corticosterone level. A significant decrease was observed in the expression of BDNF gene (in all of the selected brain regions) and GR (glucocorticoid receptor) gene (in the hippocampus and nucleus accumbens) in MD rats. Also, a significant increase in the expression of μ Opioid receptor (in all of the selected brain regions) and κ Opioid receptor (in the prefrontal cortex and nucleus accumbens) was observed in MD rats. Our results suggest that MD induces alterations in the HPA axis function, BDNF level, and Opioid receptors system that enhance vulnerability to morphine at adulthood.

Rrn3 gene knockout affects ethanol-induced locomotion in adult heterozygous zebrafish

Genome-wide analysis has identified the transcription factor, RRN3 (or TIF-1A), on human chromosome 16p13.11 as a candidate gene associated with mental disorders. Both genetic and biochemical experiments have demonstrated that RRN3 plays a major role in the transcriptional regulation of ribosomal DNA and cell growth. Previous research has suggested that loss of RRN3 from mature neurons reproduces the chronic nature of neurodegenerative processes. Here, we report the first generation and characterization of rrn3 mutant zebrafish in larval and adult stages using the CRISPR/Cas9 genome editing technique. Homozygous knockout zebrafish exhibited morphological changes, such as pericardial oedema and deformed heads, and died at the larval stage of embryonic development. Behaviourally, the locomotion and shoaling behaviour of adult rrn3^+/- zebrafish was not significantly different compared with rrn3^+/+ zebrafish. Notably, rrn3^+/- zebrafish demonstrated abnormal locomotor activity in response to ethanol. We found decreased norepinephrine expression in the brains of rrn3^+/- zebrafish when treated with ethanol. In summary, our results indicated that rrn3 was closely associated with early embryonic development in zebrafish. Furthermore, behavioural and neurochemical research revealed the importance of genetic differences in drug sensitivity. The results suggest that caution should be taken when treating RRN3 heterozygous patients.

Exposure to Running Wheels Prevents Ethanol Rewarding Effects: The Role of CREB and Deacetylases SIRT-1 and SIRT-2 in the Nucleus Accumbens and Prefrontal Cortex

Alcohol use disorder is one of the most prevalent addictions, strongly influenced by environmental factors. Voluntary physical activity (VPA) has proven to be intrinsically reinforcing and we hypothesized that, as a non-drug reinforcer, VPA could mitigate ethanol-induced rewarding effects. The transcriptional factor cAMP response element binding protein (CREB), and deacetylases isozymes sirtuins 1 and 2 (SIRT-1 and SIRT-2) have a complex interplay and both play a role in the rewarding effects of ethanol. To test whether the exposure of mice to running wheels inhibits the development of ethanol-induced conditioned place preference (CPP), mice were assigned into four groups: housed in home cages with locked ("Sedentary") or unlocked running wheels (VPA), and treated with saline or 1.8 g/kg ethanol during the conditioning phase. The groups were referred as Saline-Sedentary, Saline-VPA, Ethanol-Sedentary and Ethanol-VPA. The expression of CREB, SIRT-1 and SIRT-2 were evaluated in the prefrontal cortex (PFC) and nucleus accumbens (NAc). VPA prevented the development of ethanol-induced CPP. VPA, ethanol and the combination of both inhibited pCREB and pCREB/CREB ratio in the NAc, suggesting that both reward stimuli can share similar patterns of CREB activation. However, we have found that ethanol-induced increased CREB levels were prevented by VPA. Both VPA groups presented lower SIRT-1 levels in the NAc compared to the Sedentary groups. Thus, exposure to running wheels prevented ethanol-rewarding effects and ethanol-induced increases in CREB in the NAc. The molecular alterations underlying CPP prevention may be related to a lower expression of CREB in the NAc of Ethanol-VPA compared to the respective Sedentary group, given the positive correlation between CPP and CREB levels in the Ethanol-Sedentary group.

Environmental Enrichment During Adolescence Mitigates Cognitive Deficits and Alcohol Vulnerability due to Continuous and Intermittent Perinatal Alcohol Exposure in Adult Rats

Perinatal alcohol exposure affects ontogenic neurodevelopment, causing physical and functional long-term abnormalities with limited treatment options. This study investigated long-term consequences of continuous and intermittent maternal alcohol drinking on behavioral readouts of cognitive function and alcohol vulnerability in the offspring. The effects of environmental enrichment (EE) during adolescence were also evaluated. Female rats underwent continuous alcohol drinking (CAD)—or intermittent alcohol drinking paradigm (IAD), along pregestation, gestation, and lactation periods—equivalent to the whole gestational period in humans. Male offspring were reared in standard conditions or EE until adulthood and were then assessed for declarative memory in the novel object recognition test; spatial learning, cognitive flexibility, and reference memory in the Morris water maze (MWM); alcohol consumption and relapse by a two-bottle choice paradigm. Our data show that perinatal CAD decreased locomotor activity, exploratory behavior, and declarative memory with respect to controls, whereas perinatal IAD displayed impaired declarative memory and spatial learning and memory. Moreover, both perinatal alcohol-exposed offspring showed higher vulnerability to alcohol consummatory behavior than controls, albeit perinatal IAD rats showed a greater alcohol consumption and relapse behavior with respect to perinatal-CAD progeny. EE ameliorated declarative memory in perinatal CAD, while it mitigated spatial learning and reference memory impairment in perinatal-IAD progeny. In addition, EE decreased vulnerability to alcohol in both control and perinatal alcohol-exposed rats. Maternal alcohol consumption produces drinking pattern-related long-term consequences on cognition and vulnerability to alcohol in the offspring. However, increased positive environmental stimuli during adolescence may curtail the detrimental effects of developmental alcohol exposure.

Environmental enrichment during adolescence heightens ethanol intake in female, but not male, adolescent rats that are selectively bred for high and low ethanol intake during adolescence

Background: Discriminating between adolescents who will eventually have ethanol use problems from those who do not is important. Environmental enrichment is a promising approach to reduce drug-related problems, but its impact on ethanol's effects and intake is being scrutinized. Objective: We tested the effects of environmental enrichment on ethanol intake, preference, and anxiety-like response as well as shelter seeking and risk-taking behaviors. Methods: Experiment 1 examined ethanol intake, preference, and anxiety-like responses in 46 male and 54 female Wistar rats that were derived from a short-term breeding program that selected for high and low ethanol drinking during adolescence (ADHI₂ and ADLO₂ lines, respectively). Shelter-seeking and risk-taking behaviors were assessed (Experiment 2) in ADHI₂ and ADLO₂ rats (73 males, 76 females) reared under environmental enrichment or standard housing conditions and given doses of ethanol (2.5 g/kg, intraperitoneal) for 3 weeks. Environmental enrichment was applied on postnatal days 21-42. Ethanol intake was measured on postnatal days 42-68. Anxiety-like behavior and exploratory responses were assessed using the light-dark box and multivariate concentric square field test. Results: In Experiment 1, environmental enrichment increased ethanol intake in female, but not male, ADHI₂ and ADLO₂ rats (p < 0.05). In the baseline measurement of Experiment 2, ADHI₂ rats exhibited reduced risk-taking and increased anxiety-like behavior (p < .05). After exposure to environmental enrichment the ADHI and ADLO rats, both males and females, exhibited increased risk-taking and exploratory behavior (p < 0.05). Conclusions: Environmental enrichment appears to increase ethanol intake in female rats by promoting the exploration of new environments or stimuli. The findings indicate that environmental enrichment increased ethanol intake in female, but not male, rats. Clinical programs that treat alcohol use disorder by emphasizing environmental stimulation should be designed with caution.

Murine Models for the Study of Fetal Alcohol Spectrum Disorders: An Overview

Prenatal alcohol exposure is associated to different physical, behavioral, cognitive, and neurological impairments collectively known as fetal alcohol spectrum disorder. The underlying mechanisms of ethanol toxicity are not completely understood. Experimental studies during human pregnancy to identify new diagnostic biomarkers are difficult to carry out beyond genetic or epigenetic analyses in biological matrices. Therefore, animal models are a useful tool to study the teratogenic effects of alcohol on the central nervous system and analyze the benefits of promising therapies. Animal models of alcohol spectrum disorder allow the analysis of key variables such as amount, timing and frequency of ethanol consumption to describe the harmful effects of prenatal alcohol exposure. In this review, we aim to synthetize neurodevelopmental disabilities in rodent fetal alcohol spectrum disorder phenotypes, considering facial dysmorphology and fetal growth restriction. We examine the different neurodevelopmental stages based on the most consistently implicated epigenetic mechanisms, cell types and molecular pathways, and assess the advantages and disadvantages of murine models in the study of fetal alcohol spectrum disorder, the different routes of alcohol administration, and alcohol consumption patterns applied to rodents. Finally, we analyze a wide range of phenotypic features to identify fetal alcohol spectrum disorder phenotypes in murine models, exploring facial dysmorphology, neurodevelopmental deficits, and growth restriction, as well as the methodologies used to evaluate behavioral and anatomical alterations produced by prenatal alcohol exposure in rodents.

Potentiation of morphine-induced antinociception by harmaline: involvement of μ-opioid and ventral tegmental area NMDA receptors

RATIONAL

Morphine is one of the most well-known and potent analgesic agents; however, it can also induce various side effects. Thus, finding drugs and mechanisms which can potentiate the analgesic effects of low doses of morphine will be a good strategy for pain management.

OBJECTIVE

The involvement of μ-opioid receptors and ventral tegmental area (VTA) glutamatergic system in harmaline and morphine combination on the nociceptive response were investigated. Also, we examined reward efficacy and tolerance expression following the drugs.

METHODS

Animals were bilaterally cannulated in the VTA by stereotaxic instrument. A tail-flick (TF) apparatus and conditioned place preference (CPP) paradigm were used to measure nociceptive response and rewarding effects in male NMRI mice respectively.

RESULTS

Morphine (2 mg/kg, i.p.) had no effect in TF test. Also, harmaline (1.25 and 5 mg/kg, i.p.) could not change pain threshold. Combination of a non-effective dose of harmaline (5 mg/kg) and morphine (2 mg/kg) produced antinociception and also prevented morphine tolerance but had no effect on the acquisition of CPP. Systemic administration of naloxone (0.5 and 1 mg/kg) and intra-VTA microinjection of NMDA (0.06 and 0.1 μg/mouse) before harmaline (5 mg/kg) plus morphine (2 mg/kg) prevented antinociception induced by the drugs. D-AP5 (0.5 and 1 μg/mouse, intra-VTA) potentiated the effect of low-dose harmaline (1.25 mg/kg) and morphine (2 mg/kg) and induced antinociception. Microinjection of the same doses of NMDA or D-AP5 into the VTA alone had no effect on pain threshold.

CONCLUSION

The findings showed that harmaline potentiated the analgesic effect of morphine and reduced morphine tolerance. Glutamatergic and μ-opioidergic system interactions in the VTA seem to have a modulatory role in harmaline plus morphine-induced analgesia.

Early exposure to environmental enrichment modulates the effects of prenatal ethanol exposure upon opioid gene expression and adolescent ethanol intake

Prenatal ethanol exposure (PEE) promotes ethanol consumption in the adolescent offspring accompanied by the transcriptional regulation of kappa opioid receptor (KOR) system genes. This study analysed if environmental enrichment (EE, from gestational day 20 to postnatal day 26) exerts protective effects upon PEE-modulation of gene expression, ethanol intake and anxiety responses. Pregnant rats were exposed to PEE (0.0 or 2.0 g/kg ethanol, gestational days 17-20) and subsequently the dam and offspring were reared under EE or standard conditions. PEE upregulated KOR mRNA levels in amygdala (AMY) and prodynorphin (PDYN) mRNA levels in ventral tegmental area (VTA) with the latter effect associated with lower DNA methylation at the gene promoter. These effects were normalized by exposure to EE. PEE modulated BDNF mRNA levels in VTA and Nucleus accumbens (AcbN), and EE mitigated the changes in AcbN. EE induced a protective effect on ethanol intake and preference, an effect more noticeable in males than in females, and in prenatal vehicle-treated (PV) than in PEE rats. The male offspring drank significantly less ethanol than the female offspring. The latter result suggests that the protective effect of EE on ethanol drinking may only emerge at lower levels of drinking. In the dams, PEE induced an upregulation of PDYN and KOR in AcbN. PDYN gene expression was normalized by exposure to EE. These results suggest that EE is a promising treatment to inhibit the effects of PEE. The results confirm that PEE effects are mediated by alterations in the transcriptional regulation of KOR system genes.

Cocaine-induced behavioral sensitization is greater in adolescent than in adult mice and heightens cocaine-induced conditioned place preference in adolescents

Adolescents are more sensitive than adults to the neural and behavioral effects of psychostimulants, and exhibit greater vulnerability to drug abuse, dependence or relapse into these conditions. We have reported that cocaine pretreatment during adolescence promotes the expression of behavioral sensitization to a greater extent than when the pretreatment occurs at adulthood. Behavioral sensitization has been associated to the transition from drug use to addiction and is postulated to indicate heightened sensitivity to the appetitive motivational effects of drugs. The relationship between behavioral sensitization and conventional measures of drug reward, such as conditioned place preference (CPP), has yet to be thoroughly investigated, and little is known about age-related differences in this phenomenon. The present study tested cocaine-induced CPP in adolescent and adult mice exposed to cocaine (or vehicle) pretreatment, either in an intermittent or "binge" (i.e., heavy cocaine use on a single occasion, which increases the likelihood of experiencing cocaine-related problems) fashion. Cocaine administration induced behavioral sensitization to a greater extent in adolescent than in adult mice. Cocaine-induced CPP was fairly similar in vehicle pretreated adolescent and adult mice, yet greater in adolescent vs. adults after cocaine-induced sensitization. The results confirmed the higher sensitivity of adolescent mice to cocaine-induced behavioral sensitization and suggest its association with greater sensitivity to cocaine's rewarding effects.

Recommended housing densities for research mice: filling the gap in data-driven alternatives

Space recommendations for mice made in the Guide for Care and Use of Laboratory Animals have not changed since 1972, despite important improvements in husbandry and caging practices. The 1996 version of the Guide put forth a challenge to investigators to produce new data evaluating the effects of space allocation on the well-being of mice. In this review, we summarize many studies published in response to this challenge. We distinguish between studies using ventilated or nonventilated caging systems and those evaluating reproductive performance or general well-being of adult mice. We discuss how these studies might affect current housing density considerations in both production and research settings and consider gaps in mouse housing density research. Additionally, we discuss reliable methods used to monitor and quantify general well-being of research mice. Collectively, this large body of new data suggests that husbandry practices dictating optimal breeding schemes and space allocation per mouse can be reconsidered. Specifically, these data demonstrate that prewean culling of litters has no benefit, trio breeding is an effective production strategy without adversely affecting pup survival and well-being, and housing of adult mice at densities of up to twice current Guide recommendations does not compromise well-being for most strains.-Svenson, K. L., Paigen, B. Recommended housing densities for research mice: filling the gap in data-driven alternatives.

Interaction Between Stress and Addiction: Contributions From Latin-American Neuroscience

Drug addiction is a chronic neuropsychiatric disorder that escalates from an initial exposure to drugs of abuse, such as cocaine, cannabis, or heroin, to compulsive drug-seeking and intake, reduced ability to inhibit craving-induced behaviors, and repeated cycles of abstinence and relapse. It is well-known that chronic changes in the brain’s reward system play an important role in the neurobiology of addiction. Notably, environmental factors such as acute or chronic stress affect this system, and increase the risk for drug consumption and relapse. Indeed, the HPA axis, the autonomic nervous system, and the extended amygdala, among other brain stress systems, interact with the brain’s reward circuit involved in addictive behaviors. There has been a growing interest in studying the molecular, cellular, and behavioral mechanisms of stress and addiction in Latin-America over the last decade. Nonetheless, these contributions may not be as strongly acknowledged by the broad scientific audience as studies coming from developed countries. In this review, we compile for the first time a series of studies conducted by Latin American-based neuroscientists, who have devoted their careers to studying the interaction between stress and addiction, from a neurobiological and clinical perspective. Specific contributions about this interaction include the study of CRF receptors in the lateral septum, investigations on the neural mechanisms of cross-sensitization for psychostimulants and ethanol, the identification of the Wnt/β-catenin pathway as a critical neural substrate for stress and addiction, and the emergence of the cannabinoid system as a promising therapeutic target. We highlight animal and human studies, including for instance, reports coming from Latin American laboratories on single nucleotide polymorphisms in stress-related genes and potential biomarkers of vulnerability to addiction, that aim to bridge the knowledge from basic science to clinical research.

Social Factors in Ethanol Sensitization

Behavioral sensitization is a neuroadaptive process characterized by an increase in a particular behavior after repeated exposure to drugs or other stimuli, such as stress. Sensitization can also be extended to neurochemical and neuroendocrine sensitization. Several factors can influence sensitization to the effects of ethanol. For instance, stress is an important component in addiction that can strengthen ethanol-induced behaviors. In animal models, stressful situations can be induced by alterations in social aspects of the animal's environment, such as maternal separation, social conflicts, and housing conditions. Social conflict models involve acute, chronic or intermittent interaction of an animal to a conspecific and can occur at any stage of life, including preweaning, adolescence or adulthood. These events can influence ethanol-induced behavioral sensitization in different ways, such as increases in locomotion, drug reward, and drug-taking behaviors. On the other hand, environmental enrichment can produce a protective phenotype against drug-related behaviors. In this chapter, we discuss findings regarding consequences of social stress and environmental enrichment on sensitization to ethanol.