Supplier-dependent differences in intermittent voluntary alcohol intake and response to naltrexone in Wistar rats

Vitamin D attenuates monosodium glutamate-induced behavioural anomalies, metabolic dysregulation, cholinergic impairment, oxidative stress, and astrogliosis in rats

BACKGROUND

Monosodium glutamate (MSG) is a commonly used flavor enhancer that has raised concerns due to its potential adverse effects on various organs. This study explored the neuroprotective potential of Vitamin D, a beneficial micronutrient, in mitigating MSG-induced neurotoxicity.

MATERIALS AND METHODS

Adult male Wistar rats were categorized into five groups: control (2 ml/kg PBS orally for 30 days), MSG (40 mg/kg orally for 30 days), VIT-D (oral cholecalciferol; 500 IU/kg for 30 days), MSG+VIT-D (MSG for 30 days followed by VIT-D for another 30 days), and VIT-D/MSG (concurrent VIT-D and MSG for 30 days). The rats underwent neurobehavioral, histochemical, and biochemical analyses following the treatments.

RESULTS

MSG treatment caused a decline in both long and short-term memory, along with reduced exploratory and anxiogenic behavior, mitigated by vitamin D treatment. MSG exposure also induced impaired behavior, dyslipidemia, oxidative stress, lipid peroxidation, altered cholinergic transmission, and increased chromatolysis and neuroinflammation in the frontal cortex, hippocampus, and cerebellum.

CONCLUSIONS

VIT-D demonstrated a mitigating effect on MSG-induced adverse outcomes, highlighting its potential to attenuate neurodegenerative cascades. This investigation contributes to understanding MSG-associated neurotoxicity and suggests vitamin D as a valuable and potential intervention for neuroprotection.

Protein restriction during pregnancy alters Cdkn1c silencing, dopamine circuitry and offspring behaviour without changing expression of key neuronal marker genes

We tracked the consequences of in utero protein restriction in mice throughout their development and life course using a luciferase-based allelic reporter of imprinted Cdkn1c. Exposure to gestational low-protein diet (LPD) results in the inappropriate expression of paternally inherited Cdkn1c in the brains of embryonic and juvenile mice. These animals were characterised by a developmental delay in motor skills, and by behavioural alterations indicative of reduced anxiety. Exposure to LPD in utero resulted in significantly more tyrosine hydroxylase positive (dopaminergic) neurons in the midbrain of adult offspring as compared to age-matched, control-diet equivalents. Positron emission tomography (PET) imaging revealed an increase in striatal dopamine synthesis capacity in LPD-exposed offspring, where elevated levels of dopamine correlated with an enhanced sensitivity to cocaine. These data highlight a profound sensitivity of the developing epigenome to gestational protein restriction. Our data also suggest that loss of Cdkn1c imprinting and p57KIP2 upregulation alters the cellular composition of the developing midbrain, compromises dopamine circuitry, and thereby provokes behavioural abnormalities in early postnatal life. Molecular analyses showed that despite this phenotype, exposure to LPD solely during pregnancy did not significantly change the expression of key neuronal- or dopamine-associated marker genes in adult offspring.

Neuroprotective effect of chitosan oligosaccharide on alcohol-induced hippocampal injury using proteomic analysis

Alcoholism is a serious public health problem, and the abuse of drinking seriously damages the health of people. Chitosan oligosaccharides (COSs) are small-molecule oligosaccharides with amino groups that have many unique properties. The neuroprotective effect of COS on alcohol-induced hippocampal injury in Sprague-Dawley (SD) rats was investigated. The discrimination ratio of the COS group in the Y-maze experiment was 59.3% higher than that of the ETOH group. Meanwhile, the discrimination index was less than 0 in the ETOH group but greater than 0 in the COS group during the object recognition test. The cells in the COS group were more tightly arranged than those in the ETOH group. Proteomics was used to identify differentially expressed proteins in the hippocampus. There were 27 differentially expressed proteins in the COS and ETOH group for further bioinformatic analysis. There are three enriched pathway categories, namely, primary immunodeficiency, hedgehog signaling, and sulfur relay system. Next, sonic hedgehog signaling pathway-related proteins were verified through western blotting. The protein expression level of β-arrestin-2 in the COS group was 2.85 times higher than that in the ETOH group. This work may contribute to understanding the underlying mechanism of the neuroprotective effect of COS against alcohol-induced hippocampal injury in SD rats.

Umbelliferone Ameliorates Memory Impairment and Enhances Hippocampal Synaptic Plasticity in Scopolamine-Induced Rat Model

Alzheimer's disease (AD) is a neurodegenerative disorder, characterized by memory loss and cognitive decline. Among the suggested pathogenic mechanisms of AD, the cholinergic hypothesis proposes that AD symptoms are a result of reduced synthesis of acetylcholine (ACh). A non-selective antagonist of the muscarinic ACh receptor, scopolamine (SCOP) induced cognitive impairment in rodents. Umbelliferone (UMB) is a Apiaceae-family-derived 7-hydeoxycoumarin known for its antioxidant, anti-tumor, anticancer, anti-inflammatory, antibacterial, antimicrobial, and antidiabetic properties. However, the effects of UMB on the electrophysiological and ultrastructure morphological aspects of learning and memory are still not well-established. Thus, we investigated the effect of UMB treatment on cognitive behaviors and used organotypic hippocampal slice cultures for long-term potentiation (LTP) and the hippocampal synaptic ultrastructure. A hippocampal tissue analysis revealed that UMB attenuated a SCOP-induced blockade of field excitatory post-synaptic potential (fEPSP) activity and ameliorated the impairment of LTP by the NMDA and AMPA receptor antagonists. UMB also enhanced the hippocampal synaptic vesicle density on the synaptic ultrastructure. Furthermore, behavioral tests on male SD rats (7-8 weeks old) using the Y-maze test, passive avoidance test (PA), and Morris water maze test (MWM) showed that UMB recovered learning and memory deficits by SCOP. These cognitive improvements were in association with the enhanced expression of BDNF, TrkB, and the pCREB/CREB ratio and the suppression of acetylcholinesterase activity. The current findings indicate that UMB may be an effective neuroprotective reagent applicable for improving learning and memory against AD.

Cognitive mechanisms underlying decision making involving risk of explicit punishment in male and female rats

Individuals engage in the process of risk-based decision making on a daily basis to navigate various aspects of life. There are, however, individual differences in this form of decision making, with some individuals exhibiting preference for riskier choices (risk taking) and others exhibiting preference for safer choices (risk aversion). Recent work has shown that extremes in risk taking (e.g., excessive risk taking or risk aversion) are not only cognitive features of neuropsychiatric diseases, but may in fact predispose individuals to the development of such diseases. To better understand individual differences in risk taking, and thus the mechanisms by which they confer disease vulnerability, the current study investigated the cognitive contributions to risk taking in both males and females. Rats were first behaviorally characterized in a decision-making task involving risk of footshock punishment and then tested on a battery of cognitive behavioral assays. Individual variability in risk taking was compared with performance on these tasks. Consistent with prior work, females were more risk averse than males. With the exception of the Set-shifting Task, there were no sex differences in performance on other cognitive assays. There were, however, sex-dependent associations between risk taking and specific cognitive measures. Greater risk taking was associated with better cognitive flexibility in males whereas greater risk aversion was associated with better working memory in females. Collectively, these findings reveal that distinct cognitive mechanisms are associated with risk taking in males and females, which may account for sex differences in this form of decision making.

Decreased sensitivity to antidepressant drugs in Wistar Hannover rats submitted to two animal models of depression

The Wistar Hannover rat (WHR) is a strain commonly used for toxicity studies but rarely used in studies investigating depression neurobiology. In this study, we aimed to characterise the behavioural responses of WHR to acute and repeated antidepressant treatments upon exposure to the forced swim test (FST) or learned helplessness (LH) test. WHR were subjected to forced swimming pre-test and test with antidepressant administration (imipramine, fluoxetine, or escitalopram) at 0, 5 h and 23 h after pre-test. WHR displayed high immobility in the test compared to unstressed controls (no pre-swim) and failed to respond to the antidepressants tested. The effect of acute and repeated treatment (imipramine, fluoxetine, escitalopram or s-ketamine) was then tested in animals not previously exposed to pre-test. Only imipramine (20 mg/kg, 7 days) and s-ketamine (acute) reduced the immobility time in the test. To further investigate the possibility that the WHR were less responsive to selective serotonin reuptake inhibitors, the effect of repeated treatment with fluoxetine (20 mg/kg, 7 days) was investigated in the LH model. The results demonstrated that fluoxetine failed to reduce the number of escape failures in two different protocols. These data suggest that the WHR do not respond to the conventional antidepressant treatment in the FST or the LH. Only s-ketamine and repeated imipramine were effective in WHR in a modified FST protocol. Altogether, these results indicate that WHR may be an interesting tool to investigate the mechanisms associated with the resistance to antidepressant drugs and identify more effective treatments.

The Effect of Thymoquinone on Oxidative Stress Parameters and Apolipoprotein E in Alzheimer Model in Rats

INTRODUCTION

In this study, it was aimed to investigate the effect of thymoquinone (TQ) on oxidative stress and apolipoprotein E (ApoE) in an experimental Alzheimer's model created with AlCl3 and D-galactose in rats.

METHODS

Thirty-six Wistar Albino male rats saline group (Group 1), aluminum chloride (AlCl3) + D-galactose (D-Gal) group (Group 2), AlCl3 + D-Gal + TQ group (Group 3) were divided into 3 groups. The study was completed with 33 rats. Group 1 was given saline intraperitoneally (i.p) for 28 days. 2nd group; D-Gal at a dose of 60 mg/kg/day and AlCl3 at a dose of 40 mg/kg/day were given i.p. daily for 28 days. 3rd group; D-Gal at a dose of 60 mg/kg/day and AlCl3 at a dose of 40 mg/kg/day were given i.p. daily for 28 days. Group 3 rats were given 20 mg/kg/day TQ in corn oil by gavage for 14 days. Malonyl dialdehyde (MDA), superoxide dismutase (SOD), total antioxidant capacity (TAS), total oxidant capacity (TOS), glutathione peroxidase (GsH-Px), and ApoE levels were determined in the blood and brain tissues of rats in all three groups. One-way ANOVA test was used in the statistical analysis of the data.

RESULTS

Means of TAS, TOS, GSH-Px, SOD, MDA, and ApoE in blood and brain tissue of all three groups (excluding ApoE in brain tissue) were different from each other and this difference was statistically significant (p < 0.05).

CONCLUSION

In this study, TQ, it was determined that all oxidative stress parameters examined had positively affected and decreased blood tissue ApoE levels. TQ can be used as an antioxidant and curative in Alzheimer's disease.

Rivastigmine Reverses the Decrease in Synapsin and Memory Caused by Homocysteine: Is There Relation to Inflammation?

Elevated levels of homocysteine (Hcy) in the blood, called hyperhomocysteinemia (HHcy), is a prevalent risk factor for it has been shown that Hcy induces oxidative stress and increases microglial activation and neuroinflammation, as well as causes cognitive impairment, which have been linked to the neurodegenerative process. This study aimed to evaluate the effect of mild hyperhomocysteinemia with or without ibuprofen and rivastigmine treatments on the behavior and neurochemical parameters in male rats. The chronic mild HHcy model was chemically induced in Wistar rats by subcutaneous administration of Hcy (4055 mg/kg body weight) twice daily for 30 days. Ibuprofen (40 mg/kg) and rivastigmine (0.5 mg/kg) were administered intraperitoneally once daily. Motor damage (open field, balance beam, rotarod, and vertical pole test), cognitive deficits (Y-maze), neurochemical parameters (oxidative status/antioxidant enzymatic defenses, presynaptic protein synapsin 1, inflammatory profile parameters, calcium binding adapter molecule 1 (Iba1), iNOS gene expression), and cholinergic anti-inflammatory pathway were investigated. Results showed that mild HHcy caused cognitive deficits in working memory, and impaired motor coordination reduced the amount of synapsin 1 protein, altered the neuroinflammatory picture, and caused changes in the activity of catalase and acetylcholinesterase enzymes. Both rivastigmine and ibuprofen treatments were able to mitigate this damage caused by mild HHcy. Together, these neurochemical changes may be associated with the mechanisms by which Hcy has been linked to a risk factor for AD. Treatments with rivastigmine and ibuprofen can effectively reduce the damage caused by increased Hcy levels.

Behavioral Profiles of Adolescent Alcohol-Preferring/Non-preferring (P/NP) and High/Low Alcohol-Drinking (HAD/LAD) Rats Are Dependent on Line but Not Sex

Initial contact with alcohol generally occurs during adolescence, and high consumption during this period is associated with increased risk for later alcohol (AUDs) and/or substance use disorders (SUDs). Rodents selectively bred for high or low alcohol consumption are used to identify behavioral characteristics associated with a propensity for high or low voluntary alcohol intake. The multivariate concentric square field™ (MCSF) is a behavioral test developed to study rodents in a semi-naturalistic setting. Testing in the MCSF creates a comprehensive behavioral profile in a single trial. The current aim was to examine the behavioral profiles of adolescent, bidirectionally selectively bred male and female high alcohol-consuming (P and HAD1/2) and low alcohol-consuming (NP and LAD1/2) rat lines, and outbred Wistar rats. Alcohol-naïve rats were tested once in the MCSF at an age between postnatal days 30 and 35. No common behavioral profile was found for either high or low alcohol-consuming rat lines, and the effect of sex was small. The P/NP and HAD2/LAD2 lines showed within pair-dependent differences, while the HAD1/LAD1 lines were highly similar. The P rats displayed high activity and risk-associated behaviors, whereas HAD2 rats displayed low activity, high shelter-seeking behavior, and open area avoidance. The results from P rats parallel clinical findings that denser family history and risk-taking behavior are strong predictors of future AUDs, often with early onset. Contrarily, the HAD2 behavioral profile was similar to individuals experiencing negative emotionality, which also is associated with a vulnerability to develop, often with a later onset, AUDs and/or SUDs.

Individual strategies in the rat gambling task are related to voluntary alcohol intake, but not sexual behavior, and can be modulated by naltrexone

INTRODUCTION

Gambling disorder (GD) is the first non-substance or behavioral addiction to be included in substance-related and addictive disorders in DSM-5. Since GD is a younger phenomenon relative to alcohol and substance use disorders, little is known about potential unique features in GD and to what extent characteristics are shared with alcohol and substance use disorders. The rat gambling task (rGT) is used to study decision-making in rats. This study aimed to identify individual differences in rGT strategies and explore the stability of these strategies over time. Moreover, motor impulsivity, sexual behavior, and voluntary alcohol intake were examined in rats with different rGT strategies. Finally, the response to naltrexone on performance in rats with different rGT strategies was investigated.

METHODS

Male Lister hooded rats (n = 40) underwent repeated testing in the rGT, repeated copulatory behavioral tests, and 7 weeks of voluntary alcohol intake through a modified intermittent two-bottle free-choice paradigm. Finally, rats were treated with naltrexone prior to testing in the rGT.

RESULTS

The results revealed individual choice strategies in the rGT that were stable over time, even after multiple interruptions and other behavioral testing. The rats with a risky choice strategy displayed higher motor impulsivity and voluntary alcohol intake than the other groups. No difference in sexual behavior was found between the different rGT groups. Finally, in all rats irrespectively of rGT strategy, treatment with naltrexone decreased the number of completed trials and premature responses, and increased omissions, which indicates an overall lowered motivation.

DISCUSSION

In conclusion, rats with risky rGT strategies had higher voluntary alcohol intake but not elevated sexual behavior, indicating shared underlying mechanisms between rGT strategies and alcohol intake but not natural rewards in terms of sexual behavior. Finally, naltrexone treatment resulted in an overall lowered motivation in the rGT.

Role of toll-like receptor 4 and sex in 6-hydroxydopamine-induced behavioral impairments and neurodegeneration in mice

Parkinson's disease (PD) is a neurodegenerative disease characterized by progressive loss of the nigrostriatal dopaminergic neurons that are associated with motor alterations and non-motor manifestations (such as depression). Neuroinflammation is a process with a critical role in the pathogenesis of PD. In this regard, toll-like receptor 4 (TLR4) is a central mediator of immune response in PD. Moreover, there are gender-related differences in the incidence, prevalence, and clinical features of PD. Therefore, we aimed to elucidate the role of TLR4 in the sex-dependent response to dopaminergic denervation induced by 6-hydroxydopamine (6-OHDA) in mice. Female and male adult wildtype (WT) and TLR4 knockout (TLR4-/-) mice were administered with unilateral injection of 6-OHDA in the dorsal striatum, and non-motor and motor impairments were evaluated for 30 days, followed by biochemistry analysis in the substantia nigra pars compacta (SNc), dorsal striatum, and dorsoventral cortex. Early non-motor impairments (i.e., depressive-like behavior and spatial learning deficits) induced by 6-OHDA were observed in the male WT mice but not in male TLR4-/- or female mice. Motor alterations were observed after administration of 6-OHDA in both strains, and the lack of TLR4 was also related to motor commitment. Moreover, ablation of TLR4 prevented 6-OHDA-induced dopaminergic denervation and microgliosis in the SNc, selectively in female mice. These results reinforced the existence of sex-biased alterations in PD and indicated TLR4 as a promising therapeutic target for the motor and non-motor symptoms of PD, which will help counteract the neuroinflammatory and neurodegenerative processes.

Unconventional anxiety pharmacology in zebrafish: Drugs beyond traditional anxiogenic and anxiolytic spectra

Anxiety is the most prevalent brain disorder and a common cause of human disability. Animal models are critical for understanding anxiety pathogenesis and its pharmacotherapy. The zebrafish (Danio rerio) is increasingly utilized as a powerful model organism in anxiety research and anxiolytic drug screening. High similarity between human, rodent and zebrafish molecular targets implies shared signaling pathways involved in anxiety pathogenesis. However, mounting evidence shows that zebrafish behavior can be modulated by drugs beyond conventional anxiolytics or anxiogenics. Furthermore, these effects may differ from human and/or rodent responses, as such 'unconventional' drugs may affect zebrafish behavior despite having no such profiles (or exerting opposite effects) in humans or rodents. Here, we discuss the effects of several putative unconventional anxiotropic drugs (aspirin, lysergic acid diethylamide (LSD), nicotine, naloxone and naltrexone) and their potential mechanisms of action in zebrafish. Emphasizing the growing utility of zebrafish models in CNS drug discovery, such unconventional anxiety pharmacology may provide important, evolutionarily relevant insights into complex regulation of anxiety in biological systems. Albeit seemingly complicating direct translation from zebrafish into clinical phenotypes, this knowledge may instead foster the development of novel CNS drugs, eventually facilitating innovative treatment of patients based on novel 'unconventional' targets identified in fish models.

Intensive longitudinal characterization of multidimensional biobehavioral dynamics in laboratory rats

Rats have been used as animal models for human diseases for more than a century, yet a systematic understanding of basal biobehavioral phenotypes of laboratory rats is still missing. In this study, we utilize wireless tracking technology and videography, collect and analyze more than 130 billion data points to fill this gap, and characterize the evolution of behavior and physiology of group-housed male and female rats (n = 114) of the most commonly used strains (Lister Hooded, Long-Evans, Sprague-Dawley, and Wistar) throughout their development. The resulting intensive longitudinal data suggest the existence of strain and sex differences and bi-stable developmental states. Under standard laboratory 12-h light/12-h dark conditions, our study found the presence of multiple oscillations such as circatidal-like rhythms in locomotor activity. The overall findings further suggest that frequent movement along cage walls or thigmotaxic activity may be a physical feature of motion in constrained spaces, critically affecting the interpretation of basal behavior of rats in cages.

Baclofen and naltrexone, but not N-acetylcysteine, affect voluntary alcohol drinking in rats regardless of individual levels of alcohol intake

In humans, there is profound individual variation in the risk of alcohol use disorder (AUD). Because GABA, opioid and glutamate neurotransmission have been implicated in AUD, functional differences in these neural systems may underlie the individual vulnerability to AUD. We therefore determined the effects of drugs affecting GABA, opioid and glutamatergic neurotransmission on alcohol consumption in rats that differed in baseline alcohol intake. Subgroups of low-, medium- and high-alcohol-drinking rats were selected on the basis of alcohol consumption using an intermittent alcohol access procedure. The subgroups were treated with the GABAB receptor agonist baclofen, the opioid receptor antagonist naltrexone and the cysteine precursor N-acetylcysteine, and the effects on alcohol intake and preference were determined. Both baclofen and naltrexone reduced alcohol consumption, but N-acetylcysteine did not. These effects were comparable for low-, medium- and high-alcohol-drinking rats. However, there was a substantial degree of individual variation in the responsivity to baclofen and naltrexone, across the subgroups. Taken together, these results suggest that variation in alcohol consumption does not predict the responsivity to baclofen and naltrexone. This implies that individual variability in alcohol consumption on the one hand and sensitivity to treatment with these drugs on the other hand represent separate processes that likely involve distinct biological mechanisms.

Characterization of acute pain-induced behavioral passivity in mice: Insights from statistical modeling

Affective-motivational disturbances are highly inconsistent in animal pain models. The reproducibility of the open-field test in assessing anxiety, malaise or disability remains controversial despite its popularity. While traumatic, persistent or multiregional pain models are commonly considered more effective in inducing negative affect or functional impairment, the early psychobehavioral changes before pain chronification are often underexplored. Here, we aimed to clarify the fundamental relationship between hypernociception and passive distress-like behavior using a model of transient inflammatory pain. To minimize latent confounders and increase data consistency, male C57BL/6N mice were habituated to the open-field arena 6 times before receiving the unilateral intraplantar injection of prostaglandin E2 (PGE2) or vehicle. Open-field (40-min exploration) and nociceptive behavior were evaluated repeatedly along the course of hypernociception in both wild-type and transgenic mice with a known pronociceptive phenotype. To reduce subjectivity, multivariate open-field behavioral outcomes were analyzed by statistical modeling based on exploratory factor analyses, which yielded a 2-factor solution. Within 3 hr after PGE2 injection, mice developed significantly reduced center exploration (factor 1) and a marginally significant increase in their habituation tendency (factor 2), which were not apparent in vehicle-injected mice. The behavioral passivity generally improved as hypernociception subsided. Therefore, transient inflammatory irritation is sufficient to suppress mouse open-field exploratory activity. The apparent absence of late affective-motivational changes in some rodents with prolonged hypernociception may not imply a lack of preceding or underlying neuropsychological alterations. Procedural pain after invasive animal experiments, however small, should be assessed and adequately controlled as a potential research confounder.

Recovery profiles from reward downshift are correlated with operant licking maintained by alcohol, but not with genetic variation in the mu opioid receptor

After ten 5-min sessions of access to 32% sucrose, a reward downshift (RD) to 2% sucrose induces a transient rejection of the reward. Animals were segregated according to the speed of recovery from RD into Fast-recovery and Slow-recovery subgroups. Animals were subsequently trained in an operant licking (OL) task in which licking at an empty tube provided 10 s of access to a second tube containing 66% alcohol. Licking on the first tube was subjected to a progressive ratio (PR) schedule with a step of 4 licks. Fast-recovery animals (both males and females) licked to a higher ratio than Slow-recovery animals. Animals were also exposed to a well-lit open field (OF) for 20 min. Fast- and Slow-recovery males and females exhibited equal levels of activity in the OF. Tissue samples from tails were assessed for two well-known allelic variations of the human opioid receptor gene, OPRM1, known to affect mu opioid sensitivity: The C17T and A118G single nucleotide polymorphisms. There was no evidence of a relationship between genotype and behavior, suggesting that these genetic mechanisms in humans do not account for the individual differences in recovery from RD and OL for alcohol in rats.

Gene Therapy Vector Encoding Neuropeptide Y and Its Receptor Y2 for Future Treatment of Epilepsy: Preclinical Data in Rats

Gene therapy to treat pharmacoresistant temporal lobe epilepsy in humans is now being developed using an AAV vector (CG01) that encodes the combination of neuropeptide Y and its antiepileptic receptor Y2. With this in mind, the present study aimed to provide important preclinical data on the effects of CG01 on the duration of transgene expression, cellular tropism, and potential side effects on body weight and cognitive function. The CG01 vector was administered unilaterally into the dorsal and ventral hippocampus of adult male rats and expression of both transgenes was found to remain elevated without a sign of decline at 6 months post-injection. CG01 appeared to mediate expression selectively in hippocampal neurons, without expression in astrocytes or oligodendrocytes. No effects were seen on body weight as well as on short- or long-term memory as revealed by testing in the Y-maze or Morris water maze tests. Thus these data show that unilateral CG01 vector treatment as future gene therapy in pharmacoresistant temporal lobe epilepsy patients should result in stable and long-term expression predominantly in neurons and be well tolerated without side effects on body weight and cognitive function.

An amylin and calcitonin receptor agonist modulates alcohol behaviors by acting on reward-related areas in the brain

Alcohol causes stimulatory behavioral responses by activating reward-processing brain areas including the laterodorsal (LDTg) and ventral tegmental areas (VTA) and the nucleus accumbens (NAc). Systemic administration of the amylin and calcitonin receptor agonist salmon calcitonin (sCT) attenuates alcohol-mediated behaviors, but the brain sites involved in this process remain unknown. Firstly, to identify potential sCT sites of action in the brain, we used immunohistochemistry after systemic administration of fluorescent-labeled sCT. We then performed behavioral experiments to explore how infused sCT into the aforementioned reward-processing brain areas affects acute alcohol-induced behaviors in mice and chronic alcohol consumption in rats. We show that peripheral sCT crosses the blood brain barrier and is detected in all the brain areas studied herein. sCT infused into the LDTg attenuates alcohol-evoked dopamine release in the NAc shell in mice and reduces alcohol intake in rats. sCT into the VTA blocks alcohol-induced locomotor stimulation and dopamine release in the NAc shell in mice and decreases alcohol intake in rats. Lastly, sCT into the NAc shell prevents alcohol-induced locomotor activity in mice. Our data suggest that central sCT modulates the ability of alcohol to activate reward-processing brain regions.

Permethrin exposure affects neurobehavior and cellular characterization in rats' brain

This study investigated the neurotoxic effects of permethrin on the cerebellum, hippocampus and prefrontal cortex of Wistar rats and its effects on some behavioral patterns. Fifteen adult male Wistar rats were grouped into three categories: Group A received 0.1 mL normal saline (control), and Groups B and C received mixed feed with 500 mg/kg and 1,000 mg/kg of 0.6% permethrin, respectively, for 14 days. The animals were assessed for memory, anxiety and exploratory locomotion and thereafter anesthetized and transcardially perfused with normal saline and 4% paraformaldehyde (PFA). Cerebellum, hippocampus and prefrontal cortex were excised from the whole brain and processed for tissue histology, histochemistry and immunohistochemistry. Oxidative status and lipid peroxidation were also assessed using catalase, glutathione peroxidase, superoxide dismutase and malondialdehyde as biomarkers. Results revealed dosedependent decrease in body weights but increase in cerebellar and prefrontal weights, depletion of endogenous antioxidant markers, cognitive deficits, reduced locomotor activities, degenerative changes in the microarchitecture at high doses and presence of chromatolytic cells at both low and high doses of permethrin. Astrocytes were activated while synaptophysin expression was downregulated. Permethrin causes dose-dependent neurotoxicity on the morphology, neurochemistry and oxidative status of different brain regions, and these could affect behavioral performance and other neurologic functions.

Exposure to pyrethroids induces behavioral impairments, neurofibrillary tangles and tau pathology in Alzheimer's type neurodegeneration in adult Wistar rats

This study investigated the exposure of pyrethroids in the development of Alzheimer's type neurodegeneration by analyzing β- amyloid, tau and Glial Fibrillary Acidic Protein (GFAP) in adult Wistar rats. Forty adult Wistar rats (130-150 g) of both sexes were assigned into five groups (n = 8). Groups A-C were treated with three different sub-lethal doses (75, 50 and 25%)of the pyrethroids formulation diluted with olive oil once/daily for 45 days, while groups D&E received olive oil and distilled water respectively (as control groups). During the treatments, physical clinical signs were monitored for cognitive behavioral studies involving object recognition tasks and novel object identification test. At the end of treatment, the rats were sacrificed by cervical dislocation, the brains were harvested and the hippocampus located and dissected out for immunohistochemical studies. Standard histochemical techniques were employed. The results showed a significant decrease (p ≤ 0.05) in the spontaneous alternation and discrimination index in the treatment groups when compared to the control groups. Histological observation showed nuclear fragmentation in treated rats in a dose dependent manner when compared to the controls. Amyloid plaques were further observed and markedly stained with Congo-red in the treated rats compared to the control groups. Immunohistochemical observation revealed that exposure to pyrethroids increased immunoreactivity of GFAP and tau protein in both CA3 and Dentate gyrus (DG) regions in the treated rats indicative of Alzheimer's type degenerative diseases.

Effects of pair housing on voluntary alcohol intake in male and female Wistar rats

A number of different voluntary alcohol intake paradigms are available for home cage drinking studies. Traditionally, these paradigms involve single housing in order for individual intake to be measured. This study aimed at investigating the effects of pair housing on voluntary alcohol intake. Male and female Wistar rats were housed in pairs or individually for studies of voluntary alcohol intake using the modified intermittent access paradigm with alcohol access during three consecutive days per week followed by four days of water only. Individual intake of 20% alcohol solution and water was measured during 12 sessions, i.e., 4 weeks. Pair-housed animals could interact freely with their cage mate for four consecutive days each week and were then separated by an inserted mesh divider for three consecutive days each week during alcohol intake sessions. Alcohol intake and preference were compared between pair-housed and individually housed rats. The results revealed higher alcohol intake in females than in males. Pair-housed males had a higher alcohol intake and preference during the first 3 weeks, but not during the fourth week, compared to individually housed males No effect of housing condition was observed in female rats. The alcohol intake was higher on the first day of access relative to the two consecutive days in pair-housed males and higher on the first two days relative to the third day in female rats. Social rank or female estrus cycle had no effect on alcohol intake or preference. Taken together, the use of a divider during alcohol intake sessions had no impact on alcohol intake in female rats and may not exert long-term influences in male rats. Future studies are needed in order to elucidate whether the use of a divider can constitute an experimental refinement as an alternative to individual housing in studies of voluntary alcohol intake using the limited access and/or intermittent access paradigms.

Effects of ethanol, naltrexone, nicotine and varenicline in an ethanol and nicotine co-use model in Sprague-Dawley rats

BACKGROUND

As alcohol and nicotine use disorders are entwined, it may be possible to develop a single medication to treat both. We previously developed a model for ethanol (EtOH) and nicotine co-use in female selectively bred alcohol-preferring (P) rats. To model co-use in a genetically diverse population, we adapted the model to outbred Sprague-Dawley rats of both sexes and assessed the effect of drug pretreatments.

METHODS

In phase 1, rats were trained in a 2-bottle choice between water and a sweetened or unsweetened EtOH solution in operant chambers. In phase 2, rats were trained in nicotine self-administration under an increasing fixed ratio (FR) schedule with 2 bottles containing water or saccharin-sweetened EtOH also available. In phase 3, rats were pretreated with EtOH (0.5, 1.5 g/kg), naltrexone (0.3 mg/kg), nicotine (0.2, 0.6 mg/kg), varenicline (3.0 mg/kg) or vehicle before the session.

RESULTS

Sweetening the EtOH solution was required to obtain pharmacologically relevant levels of consumption in Phase 1, with males showing increased sweetened EtOH preference compared to females. In Phase 2, increasing the FR requirement for nicotine decreased nicotine infusions, but increased EtOH consumption. In Phase 3, EtOH, naltrexone, and nicotine failed to alter EtOH consumption; however, varenicline decreased both EtOH and nicotine intake.

CONCLUSIONS

The co-use model was successfully adapted to Sprague-Dawley rats by adding saccharin to the EtOH solution. In contrast to previous results in P rats, varenicline reduced both EtOH and nicotine intake, indicating it may be a useful monotherapy for co-use in a genetically diverse population.

Boldness in Male and Female Zebrafish (Danio rerio) Is Dependent on Strain and Test

Differences in selection pressure in nature and labs have profound effects on zebrafish strains. The widely used AB strain of zebrafish has been domesticated over several decades. Recently, there has been an upsurge in the availability of genetically modified lines, e.g., the spiegeldanio (spd), which has a mutation in the fibroblast growth factor receptor 1a (fgfr1a) gene. This mutant strain (fgfr1a) has previously been reported to be bolder than fish of the Tübingen strain, from which it was generated. Our knowledge on behavioral differences between different zebrafish strains, relative to wild-caught zebrafish, is limited. In the present study we compare behaviors related to interpretation of boldness in male and female offspring (F1) of wild-caught fish, AB and fgfr1a ^-/- zebrafish. A second aim of the study was to compare the behavior of fish from these strains when tested in different behavioral assays, i.e., shelter seeking, novel tank diving and scototaxis tests. The results demonstrate that behavioral variation exists both within and between the strains, but interpretation of boldness reveals a complex pattern in which behavior differs between strains but is also related to sex and test. Therefore, a careful assessment of various strains of fish using both males and females is warranted in order to strengthen interpretation of results. This is especially important in studies where zebrafish are used as model organisms for human conditions as well as studies evaluating the effects of pharmacological or toxicological substances on behavior.

An amylin analogue attenuates alcohol-related behaviours in various animal models of alcohol use disorder

Recent findings have identified salmon calcitonin (sCT), an amylin receptor agonist and analogue of endogenous amylin, as a potential regulator of alcohol-induced activation of the mesolimbic dopamine system and alcohol consumption. Providing that the role of amylin signalling in alcohol-related behaviours remains unknown, the present experiments investigate the effect of sCT on these behaviours and the mechanisms involved. We showed that repeated sCT administration decreased alcohol and food intake in outbred rats. Moreover, single administration of the potent amylin receptor antagonist, AC187, increased short-term alcohol intake in outbred alcohol-consuming rats, but did not affect food intake. Acute administration of sCT prevented relapse-like drinking in the "alcohol deprivation effect" model in outbred alcohol-experienced rats. Additionally, acute sCT administration reduced operant oral alcohol self-administration (under the fixed ratio 4 schedule of reinforcement) in selectively bred Sardinian alcohol-preferring rats, while it did not alter operant self-administration (under the progressive ratio schedule of reinforcement) of a highly palatable chocolate-flavoured beverage in outbred rats. Lastly, we identified differential amylin receptor expression in high compared to low alcohol-consuming rats, as reflected by decreased calcitonin receptor and increased receptor activity modifying protein 1 expression in the nucleus accumbens (NAc) of high consumers. Collectively, our data suggest that amylin signalling, especially in the NAc, may contribute to reduction of various alcohol-related behaviours.

Alcohol, psychomotor-stimulants and behaviour: methodological considerations in preclinical models of early-life stress

BACKGROUND

In order to assess the risk associated with early-life stress, there has been an increase in the amount of preclinical studies investigating early-life stress. There are many challenges associated with investigating early-life stress in animal models and ensuring that such models are appropriate and clinically relevant.

OBJECTIVES

The purpose of this review is to highlight the methodological considerations in the design of preclinical studies investigating the effects of early-life stress on alcohol and psychomotor-stimulant intake and behaviour.

METHODS

The protocols employed for exploring early-life stress were investigated and summarised. Experimental variables include animals, stress models, and endpoints employed.

RESULTS

The findings in this paper suggest that there is little consistency among these studies and so the interpretation of these results may not be as clinically relevant as previously thought.

CONCLUSION

The standardisation of these simple stress procedures means that results will be more comparable between studies and that results generated will give us a more robust understanding of what can and may be happening in the human and veterinary clinic.

Episodic Ethanol Exposure in Adolescent Rats Causes Residual Alterations in Endogenous Opioid Peptides

Adolescent binge drinking is associated with an increased risk of substance use disorder, but how ethanol affects the central levels of endogenous opioid peptides is still not thoroughly investigated. The aim of this study was to examine the effect of repeated episodic ethanol exposure during adolescence on the tissue levels of three different endogenous opioid peptides in rats. Outbred Wistar rats received orogastric (i.e., gavage) ethanol for three consecutive days per week between 4 and 9 weeks of age. At 2 h and 3 weeks, respectively, after the last exposure, beta-endorphin, dynorphin B and Met-enkephalin-Arg⁶Phe⁷ (MEAP) were analyzed with radioimmunoassay. Beta-endorphin levels were low in the nucleus accumbens during ethanol intoxication. Remaining effects of adolescent ethanol exposure were found especially for MEAP, with low levels in the amygdala, and high in the substantia nigra and ventral tegmental area three weeks after the last exposure. In the hypothalamus and pituitary, the effects of ethanol on beta-endorphin were dependent on time from the last exposure. An interaction effect was also found in the accumbal levels of MEAP and nigral dynorphin B. These results demonstrate that repeated episodic exposure to ethanol during adolescence affected opioid peptide levels in regions involved in reward and reinforcement as well as stress response. These alterations in opioid networks after adolescent ethanol exposure could explain, in part, the increased risk for high ethanol consumption later in life.

Few long-term consequences after prolonged maternal separation in female Wistar rats

Environmental factors during the early-life period are known to have long-term consequences for the adult phenotype. An intimate interplay between genes and environment shape the individual and may affect vulnerability for psychopathology in a sex-dependent manner. A rodent maternal separation model was here used to study the long-term effects of different early-life rearing conditions on adult behavior, HPA axis activity and long-term voluntary alcohol intake in female rats. Litters were subjected to 15 min (MS15) or 360 min (MS360) of daily maternal separation during postnatal day 1–21. In adulthood, the behavioral profiles were investigated using the multivariate concentric square field™ (MCSF) test or examined for HPA axis reactivity by cat-odor exposure with subsequent characterization of voluntary alcohol intake and associated changes in HPA axis activity. Adult female MS360 offspring showed mostly no, or only minor, effects on behavior, HPA axis reactivity and long-term alcohol intake relative to MS15. Instead, more pronounced effects were found dependent on changes in the natural hormonal cycle or by the choice of animal supplier. However, changes were revealed in corticosterone load after long-term alcohol access, as females subjected to MS360 had higher concentrations of fecal corticosterone. The present findings are in line with and expand on previous studies on the long-term effects of maternal separation in female rats with regard to behavior, HPA axis activity and voluntary alcohol intake. It can also be a window into further studies detailing how early-life experiences interact with other risk and protective factors to impact the adult phenotype and how possible sex differences play a role.

Transcriptional profiling of the rat nucleus accumbens after modest or high alcohol exposure

Alcohol use disorder is a chronic relapsing brain disorder and a global health issue. Prolonged high alcohol consumption increases the risk for dependence development, a complex state that includes progressive alterations in brain function. The molecular mechanisms behind these changes remain to be fully disclosed, but several genes show altered expression in various regions of the rat brain even after modest alcohol exposure. The present study utilizes whole-transcriptome sequencing (RNA-seq) to investigate expression changes in the brain nucleus accumbens (NAc), an area of particular interest in addictive disorders, of alcohol consuming rats. The impact on gene expression after eight weeks of moderate voluntary alcohol consumption or voluntary consumption combined with forced excessive exposure was explored in two separate experiments. The results point to a lack of strong and consistent expression alterations in the NAc after alcohol exposure, suggesting that transcriptional effects of alcohol are weak or transient, or occur primarily in brain regions other than NAc.

Altered corticosterone levels and social play behavior after prolonged maternal separation in adolescent male but not female Wistar rats

Early-life socio-environmental factors are crucial for normal developmental processes; adverse experiences early in life can therefore lead to detrimental effects in several physiological systems. The aim of this study was to examine short-term effects of early adverse experiences in a maternal separation (MS) rodent model. In this study two separation conditions were used: daily 15- (MS15) or 360-min (MS360) separation of the litter from the dam during postnatal day 1-21. In early adolescence, male and female offspring were subjected to a single-isolation procedure with analysis of corticosterone levels prior to and after isolation. In addition, social play behavior was assessed during mid-adolescence. There was a clear difference between male and female offspring in both tests performed. There was no difference in corticosterone levels between the female MS groups, whereas MS360 males showed higher baseline and recovery corticosterone levels than MS15 males. The amount of pinning, a specific social play behavior, was affected by rearing with MS360 males having a higher frequency than MS15 males, while there was no difference between the female MS groups. The observation that males but not females are affected by MS360 has previously been reported for adult animals, and herein we show that this difference is present already in adolescence. Changes in corticosterone levels and social behavior following early-life adversity have been associated with adult behavioral alterations, and our results confirm that these changes emerge already within adolescence.

Prevalence and influence of cys407* Grm2 mutation in Hannover-derived Wistar rats: mGlu2 receptor loss links to alcohol intake, risk taking and emotional behaviour

Modulation of metabotropic glutamate 2 (mGlu2) receptor function has huge potential for treating psychiatric and neurological diseases. Development of drugs acting on mGlu2 receptors depends on the development and use of translatable animal models of disease. We report here a stop codon mutation at cysteine 407 in Grm2 (cys407*) that is common in some Wistar rats. Therefore, researchers in this field need to be aware of strains with this mutation. Our genotypic survey found widespread prevalence of the mutation in commercial Wistar strains, particularly those known as Han Wistar. Such Han Wistar rats are ideal for research into the separate roles of mGlu2 and mGlu3 receptors in CNS function. Previous investigations, unknowingly using such mGlu2 receptor-lacking rats, provide insights into the role of mGlu2 receptors in behaviour. The Grm2 mutant rats, which dominate some selectively bred lines, display characteristics of altered emotionality, impulsivity and risk-related behaviours and increased voluntary alcohol intake compared with their mGlu2 receptor-competent counterparts. In addition, the data further emphasize the potential therapeutic role of mGlu2 receptors in psychiatric and neurological disease, and indicate novel methods of studying the role of mGlu2 and mGlu3 receptors. This article is part of the Special Issue entitled 'Metabotropic Glutamate Receptors, 5 years on'.