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.

Effects of the combination of chronic unpredictable stress and environmental enrichment on anxiety-like behavior assessed using the elevated plus maze in Swiss male mice: Hypothalamus-Pituitary-Adrenal Axis-mediated mechanisms.

Environmental enrichment (EE) is a paradigm that offers the animal a plethora of stimuli, including physical, cognitive, sensory, and social enrichment. Exposure to EE can modulate both anxiety responses and plasma corticosterone. In this study, our objective was to explore how chronic unpredictable stress (CUS) impacts anxiety-related behaviors in male Swiss mice raised in EE conditions. Additionally, we investigated corticosterone and adrenocorticotropic hormone (ACTH) levels to assess the involvement of the hypothalamic-pituitary-adrenal (HPA) axis in mediating these responses. Mice were housed under either EE or standard housing conditions for 21 days. Afterward, they were exposed to 11 days of CUS while still reared in their distinct housing conditions, with half of the mice receiving daily pretreatment with the vehicle and the other half receiving daily metyrapone (MET) injections, an inhibitor of steroid synthesis, 30 mins before CUS exposure. Blood samples were obtained to assess plasma corticosterone and ACTH levels. The 11-day CUS protocol induced anxiety-like phenotype and elevated ACTH levels in EE mice. Chronic MET pretreatment prevented anxiety-like behavior in the EE-CUS groups, by mechanisms involving increased plasma corticosterone levels and decreased ACTH. These results suggest a role of the HPA axis in the mechanism underlying the anxiogenic phenotype induced by CUS in EE mice and shed light on the complex interplay between environmental factors, stress, and the HPA axis in anxiety regulation.

Carbetocin Inhibits Behavioral Sensitization to Ethanol in Male and Female Mice, Independent of Corticosterone Levels.

Oxytocin (OXT), a pro-social peptide, is increasingly recognized as a potential protective substance against drug addiction. In the context of ethanol, previous research has shown OXT's properties in reducing self-administration, alleviating motor impairment in rodents, and reducing craving in humans. However, its role in behavioral sensitization, a neuroadaptive response resulting from repeated drug exposure linked to an increased drug incentive, remains unexplored. OXT is recognized for its role in regulating the hypothalamic-pituitary-adrenal (HPA) axis, in which corticosterone is acknowledged as a significant factor in the development of behavioral sensitization. This study aimed to investigate the effects of carbetocin (CBT), an analogue of OXT, on the expression of behavioral sensitization to ethanol and the concurrent alterations in plasma corticosterone levels in male and female Swiss mice. We also aimed to confirm previous studies on OXT's impact on ethanol consumption in male mice, but with a focus on CBT, using the two-bottle choice model and the drinking in the dark (DID) methodology. For the sensitization study, the mice received either ethanol (1.8 g/kg, i.p.) or saline treatments daily for 15 consecutive days, followed by treatment with carbetocin (0.64 mg/kg, i.p.) or a vehicle for 6 days. Subsequently, on day 22, all the animals underwent an ethanol challenge to assess the expression of behavioral sensitization. The plasma corticosterone levels were measured on days 21 and 22. The CBT effectively prevented the expression of ethanol-induced behavioral sensitization in both male and female subjects, with no alterations having been detected in their corticosterone levels. In the ethanol consumption study, following an initial phase of ethanol acquisition, the male mice underwent a 6-day treatment with CBT i.p. or saline before being re-exposed to ethanol. We also found a reduction in their ethanol consumption due to the CBT treatment. In conclusion, carbetocin emerges as a promising and effective intervention for mitigating ethanol-induced behavioral sensitization and reducing ethanol intake, highlighting its potential significance in alcohol addiction treatment.

Juvenile variable stress modulates, in female but not in male Wistar rats, ethanol intake in adulthood.

Early stress can increase vulnerability to psychopathological disorders, including substance use disorders. The effects of stress in the juvenile period of the rat, that extends between weaning and the onset of adolescence (equivalent to late human childhood), have received little attention. This study assessed short and long-term behavioral effects of juvenile stress, with a focus on effects on ethanol intake. Male and female Wistar rats were exposed to variable stress (restraint, elevated platform, forced swimming, and social instability) or to restraint stress only, between postnatal days 26 to 29 (PDs 26-29). During adolescence, patterns of anxiety (PD 31) and depression (PD 33), ethanol intake (PDs 36-45) and behavioral sensitivity to the effects of acute stress (PD 47) were evaluated. In adulthood, alcohol ingestion was assessed through two-bottle ethanol intake tests (PDs 75-85). An additional experiment measured blood ethanol levels after a limited access intake session in adolescence. Exposure to juvenile variable stress exerted very mild effects in adolescence, but reduced ethanol ingestion in adulthood, in females only. Ethanol intake during the limited access session was significantly correlated to blood alcohol levels. The results indicate that a schedule of juvenile variable stress that did not significantly alter anxiety-related behaviors induced, nonetheless, sexually dimorphic effects on ethanol intake in adulthood. Early stress exposure that reduced alcohol intake in Wistar rats has been associated with changes on brain opioid and dopamine receptors. These results highlight the impact of early stress exposure on adult female ethanol consumption and its possible underlying neurobiological changes, involving opioid and dopamine receptors.

The effect of MK-801 on stress-ethanol cross-sensitization is dissociable from its effects on nNOS activity.

Locomotor behavioral sensitization represents an animal model for understanding neuroadaptive processes related to repeated drug exposure. Repeated stress can elicit a cross-sensitization to the stimulant response of ethanol, which involves neuronal nitric oxide synthase (nNOS). Activation of N-methyl d-aspartate (NMDA) glutamate receptors triggers nNOS and the synthesis of nitric oxide (NO). In this study, we investigated the effects of blocking NMDA receptors using the NMDA receptor antagonist MK-801 on the cross-sensitization between restraint stress and ethanol. We also evaluated the nNOS activity in the prefrontal cortex (PFC) and hippocampus. Mice were pretreated with saline or MK-801 30 min before an injection of saline or stress exposure for 14 days. On the following day, they were challenged with either saline or 1.8 g/kg ethanol. Swiss male mice pretreated with 0.25 mg/kg MK-801 exhibited a sensitized response to ethanol. Moreover, MK-801 potentiated the cross-sensitization between stress and ethanol. However, MK-801 prevented the enhanced nNOS activity in stress-exposed groups (challenged with saline or ethanol) in the PFC; the antagonist also prevented the ethanol-induced increase in nNOS activity and reduced this enzyme activity in mice exposed to stress in the hippocampus. These data indicate that systemic treatment with the NMDA antagonist potentiated, rather than blocked, ethanol-induced behavioral sensitization and that this effect is dissociable from the capacity of NMDA antagonists to reduce ethanol/stress-induced NOS stimulation in the PFC and hippocampus.

Environmental Enrichment Increased Bdnf Transcripts in the Prefrontal Cortex: Implications for an Epigenetically Controlled Mechanism.

Environmental enrichment (EE) is a condition characterized by its complexity regarding social contact, exposure to novelty, tactile stimuli and voluntary exercise, also is considered as a eustress model. The impact of EE on brain physiology and behavioral outcomes may be at least partly underpinned by mechanisms involving the modulation of the brain-derived neurotrophic factor (BDNF), but the connection between specific Bdnf exon expression and their epigenetic regulation remain poorly understood. This study aimed to dissect the transcriptional and epigenetic regulatory effect of 54-day exposure to EE on BDNF by analysing individual BDNF exons mRNA expression and the DNA methylation profile of a key transcriptional regulator of the Bdnf gene, exon IV, in the prefrontal cortex (PFC) of C57BL/6 male mice (sample size = 33). Bdnf exons II, IV, VI and IX mRNA expression were upregulated and methylation levels at two CpG sites of exon IV were reduced in the PFC of EE mice. As deficit in exon IV expression has also been causally implicated in stress-related psychopathologies, we also assessed anxiety-like behavior and plasma corticosterone levels in these mice to determine any potential correlation. However, no changes were observed in EE mice. The findings may suggest an EE-induced epigenetic control of BDNF exon expression via a mechanism involving exon IV methylation. The findings of this study contribute to the current literature by dissecting the Bdnf gene topology in the PFC where transcriptional and epigenetic regulatory effect of EE takes place.

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.

The Matricellular Protein Hevin Is Involved in Alcohol Use Disorder.

Astrocytic-secreted matricellular proteins have been shown to influence various aspects of synaptic function. More recently, they have been found altered in animal models of psychiatric disorders such as drug addiction. Hevin (also known as Sparc-like 1) is a matricellular protein highly expressed in the adult brain that has been implicated in resilience to stress, suggesting a role in motivated behaviors. To address the possible role of hevin in drug addiction, we quantified its expression in human postmortem brains and in animal models of alcohol abuse. Hevin mRNA and protein expression were analyzed in the postmortem human brain of subjects with an antemortem diagnosis of alcohol use disorder (AUD, n = 25) and controls (n = 25). All the studied brain regions (prefrontal cortex, hippocampus, caudate nucleus and cerebellum) in AUD subjects showed an increase in hevin levels either at mRNA or/and protein levels. To test if this alteration was the result of alcohol exposure or indicative of a susceptibility factor to alcohol consumption, mice were exposed to different regimens of intraperitoneal alcohol administration. Hevin protein expression was increased in the nucleus accumbens after withdrawal followed by a ethanol challenge. The role of hevin in AUD was determined using an RNA interference strategy to downregulate hevin expression in nucleus accumbens astrocytes, which led to increased ethanol consumption. Additionally, ethanol challenge after withdrawal increased hevin levels in blood plasma. Altogether, these results support a novel role for hevin in the neurobiology of AUD.

Aerobic Training and Circulating Neurotrophins in Alzheimer's Disease Patients: A Controlled Trial.

OBJECTIVE: to verify the effects of aerobic exercise training in circulating BDNF, VEGF165 and IGF-1 plasma levels and cognitive function in Alzheimer's Disease (AD) patients. METHODS: 34 AD patients participated in the study, divided in two groups: Control Group (CG; n = 16) and Training Group (TG; n = 18 - Moderate aerobic training on the treadmill, three times a week, for 12 weeks). BDNF, VEGF165, and IGF-1 plasma levels were considered as a primary outcome. Secondary outcomes included cognitive functions and aerobic fitness. RESULTS: After 12 weeks, maintenance of executive functioning in the TG was found, yet no significant changes on circulating neurotrophins levels were identified. For aerobic fitness, there was an increment in TG group. CONCLUSION: Twelve weeks of aerobic training were neither effective in improving cognitive functioning significantly, nor influential on circulating neurotrophins levels in AD patients.

Circulating levels of vascular endothelial growth factor in patients with Alzheimer's disease: A case-control study.

BACKGROUND: Vascular endothelial growth factor (VEGF) and platelets seem to reflect the Alzheimer's disease (AD) associated either with vascular impairment or disease. This study aimed to compare the circulating levels of VEGF and platelets between AD patients and healthy older adults. METHODS: Seventy-two older adults, divided in 40 older adults (Clinical Dementia Rating Scale - CDR = 0); and 32 Alzheimer's disease patients (clinically diagnosed - CRD = 1) participated in the present study. The groups were paired by sex, age, comorbidities and educational level. The primary outcomes included circulating plasma VEGF and platelet levels obtained by blood collection. RESULTS: The VEGF levels were significantly different between the groups (p = 0.03), with having a large effect size ( η2 =18.15), in which the AD patients presented lower levels compared to healthy older adults. For platelets, the comparison showed a tendency to difference (p = 0.06), with a large effect size (η2 =12.95) between the groups. CONCLUSION: The VEGF levels and the platelet numbers were reduced in AD patients, suggesting that angiogenic factors could be modified due to AD.

Chronic escalating-dose and acute binge cocaine treatments change the hippocampal cholinergic muscarinic system on drug presence and after withdrawal.

Cocaine addiction is a relapsing disorder with loss of control in limiting drug intake. Considering the involvement of acetylcholine in the neurobiology of the disease, our aim was to evaluate whether cocaine induces plastic changes in the hippocampal cholinergic muscarinic system. Male Swiss-Webster mice received saline or cocaine (ip) three times daily (60-min intervals) either acutely or in an escalating-dose binge paradigm for 14 days. Locomotor activity was measured in all treatment days. Dopaminergic and cholinergic muscarinic receptors (D1R, D2R, M1-M5, mAChRs), choline acetyltransferase (ChAT), vesicular acetylcholine transporter (VAChT) and acetylcholinesterase (AChE) were quantified in the hippocampus by immunoblotting one hour after the last injection (on drug) or after 14 days of abstinence (withdrawal). Escalating-dose group showed cocaine-induced locomotor sensitization from day 2. M3 mAChR and ChAT significantly increased after the on-drug acute binge treatment. Escalating-dose on-drug group showed increased ChAT, M1, M5 mAChR and D2R; and decreased D1R. Acute-binge withdrawal group showed increased VAChT, M2 mAChR, D1R, and D2R; and decreased M1 mAChR. Escalating-dose withdrawal group presented increased D1R and VAChT and decreased M1 mAChR and D2R. Locomotor activity was negatively correlated with M1 mAChR and AChE in on-drug group and positively correlated with VAChT in withdrawal group. M1 mAChR was positively correlated with M2 mAChR and ChAT in on-drug group, whereas ChAT was positively correlated with M5 mAChR in withdrawal group. The results indicate that cocaine induced an increase in the hippocampal cholinergic tone in the presence of the drug, whereas withdrawal causes a resetting in the system.

Rewarding and Antidepressant Properties of Ketamine and Ethanol: Effects on the Brain-Derived Neurotrophic Factor and TrkB and p75NTR Receptors.

There is a high level of comorbidity between depression and alcohol use disorder. Subanesthetic doses of ketamine induce short-acting and enduring antidepressant effects after a single or a few administrations. Considering such comorbidity, we assessed, in Swiss male mice, if ketamine-induced antidepressant-like effects would alter ethanol's rewarding effects; and, if ethanol pretreatment would alter the rewarding and antidepressant effects of ketamine. The role of the brain-derived neurotrophic factor (BDNF) and its high and low affinity receptors TrkB and p75NTR, respectively, in both reward and depression-related behaviors is well established. The present study assessed, in outbred Swiss male mice, the expression of these proteins in the prefrontal cortex and hippocampus. Ketamine did not alter the development of ethanol-induced conditioned place preference (CPP), yet ethanol inhibited the expression of CPP induced by 50 mg/kg ketamine. The antidepressant action of 50 mg/kg ketamine was attenuated after repeated treatment (i.e., developed tolerance), an effect blocked by ethanol preexposure; ethanol also inhibited the antidepressant effect of 30 mg/kg ketamine. Ketamine (50 mg/kg) and Ethanol-Ketamine (50 mg/kg) groups showed lower levels of 145 kDa TrkB in the hippocampus than Saline-treated group. Ethanol-Ketamine (50 mg/kg) decreased the hippocampal expression of p75NTR compared to Saline-Saline and Saline-Ethanol groups. Ketamine (50 mg/kg) induced hippocampal downregulation of 145 kDa TrkB may contribute to ketamine-induced antidepressant tolerance. Likewise, a relationship between low hippocampal levels of p75NTR in the Ethanol-Ketamine (50 mg/kg) and ketamine-induced CPP blockade may be considered. The findings underscore potential ethanol-ketamine interactions likely to undermine ketamine putative antidepressant effects.

Sex-dependent impact of microbiota status on cerebral µ-opioid receptor density in fischer rats.

µ-opioid receptors (MOPr) play a critical role in social play, reward and pain, in a sex- and age-dependent manner. There is evidence to suggest that sex and age differences in brain MOPr density may be responsible for this variability; however, little is known about the factors driving these differences in cerebral MOPr density. Emerging evidence highlights gut microbiota's critical influence and its bidirectional interaction with the brain on neurodevelopment. Therefore, we aimed to determine the impact of gut microbiota on MOPr density in male and female brains at different developmental stages. Quantitative [3 H]DAMGO autoradiographic binding was carried out in the forebrain of male and female conventional (CON) and germ-free (GF) rats at postnatal days (PND) 8, 22 and 116-150. Significant 'microbiota status X sex', 'age X brain region' interactions and microbiota status- and age-dependent effects on MOPr binding were uncovered. Microbiota status influenced MOPr levels in males but not females, with higher MOPr levels observed in GF versus CON rats overall regions and age groups. In contrast, no overall sex differences were observed in GF or CON rats. Interestingly, within-age planned comparison analysis conducted in frontal cortical and brain regions associated with reward revealed that this microbiota effect was restricted only to PND22 rats. Thus, this pilot study uncovers the critical sex-dependent role of gut microbiota in regulating cerebral MOPr density, which is restricted to the sensitive developmental period of weaning. This may have implications in understanding the importance of microbiota during early development on opioid signalling and associated behaviours.

Psychedelics and Mental Health: An Alternative Strategy to Treat Mental Impairments Triggered or Aggravated by COVID-19.

Despite the discovery of vaccines for COVID-19, one of the best security measures to contain the spread of the virus is social distancing and isolation. However, isolation might trigger negative mental outcomes, such as onset of a depressive and anxious condition, increased consumption of alcohol and drugs, relapse to substances of abuse, and even induce post-traumatic stress disorder. Interestingly, recent research with psychedelics suggests that when these substances are used in combination with psychotherapy, they may reduce these mental impairments. Nevertheless, scientists are still working to elucidate the possible mechanisms behind these phenomena.

Sex differences in GABAA receptor subunit transcript expression are mediated by genotype in subjects with alcohol-related cirrhosis of the liver.

Male and female human subjects show contrasting propensities to misuse drugs of addiction, including alcohol. These differences lead to different psychological and neurological consequences, such as the likelihood of developing dependence. The pattern and extent of brain damage in alcohol-use disorder cases also varies with comorbid disease. To explore mechanisms that might underlie these outcomes, we used autopsy tissue to determine mRNA transcript expression in relation to genotype for two GABAA receptor subunit genes. We used quantitative Real-Time PCR to measure GABRA6 and GABRA2 mRNA concentrations in dorsolateral prefrontal and primary motor cortices of alcohol-use disorder subjects and controls of both sexes with and without liver disease who had been genotyped for these GABAA receptor subunit genes. Cirrhotic alcohol-use disorder cases had significantly higher expression of GABRA6 and GABRA2 transcripts than either controls or non-cirrhotic alcohol-use disorder cases. Differences were observed between sexes, genotypes and brain regions. We show that sex differences in subjects with GABRA6 and GABRA2 variants may contribute to differences in susceptibility to alcohol-use disorder and alcohol-induced cirrhosis.

Oxytocin and vasopressin: Signalling, behavioural modulation and potential therapeutic effects.

Oxytocin (OT) and vasopressin (AVP) are endogenous ligands for OT and AVP receptors in the brain and in the peripheral system. Several studies demonstrate that OT and AVP have opposite roles in modulating stress, anxiety and social behaviours. Interestingly, both peptides and their receptors exhibit high sequence homology which could account for the biased signalling interaction of the peptides with OT and AVP receptors. However, how and under which conditions this crosstalk occurs in vivo remains unclear. In this review we shed light on the complexity of the roles of OT and AVP, by focusing on their signalling and behavioural differences and exploring the crosstalk between the receptor systems. Moreover, we discuss the potential of OT and AVP receptors as therapeutic targets to treat human disorders, such as autism, schizophrenia and drug abuse. LINKED ARTICLES: This article is part of a themed issue on Building Bridges in Neuropharmacology. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v179.8/issuetoc.