Involvement of rat dopaminergic system of nucleus accumbens in nicotine-induced anxiogenic-like behaviors

Dopamine D2-like receptors on conditioned and unconditioned fear: A systematic review of rodent pharmacological studies

Growing evidence supports dopamine's role in aversive states, yet systematic reviews focusing on dopamine receptors in defensive behaviors are lacking. This study presents a systematic review of the literature examining the influence of drugs acting on dopamine D2-like receptors on unconditioned and conditioned fear in rodents. The review reveals a predominant use of adult male rats in the studies, with limited inclusion of female rodents. Commonly employed tests include the elevated plus maze and auditory-cued fear conditioning. The findings indicate that systemic administration of D2-like drugs has a notable impact on both innate and learned aversive states. Generally, antagonists tend to increase unconditioned fear, while agonists decrease it. Moreover, both agonists and antagonists typically reduce conditioned fear. These effects are attributed to the involvement of distinct neural circuits in these states. The observed increase in unconditioned fear induced by D2-like antagonists aligns with dopamine's role in suppressing midbrain-mediated responses. Conversely, the reduction in conditioned fear is likely a result of blocking dopamine activity in the mesolimbic pathway. The study highlights the need for future research to delve into sex differences, explore alternative testing paradigms, and identify specific neural substrates. Such investigations have the potential to advance our understanding of the neurobiology of aversive states and enhance the therapeutic application of dopaminergic agents.

Role of brain monoamines in acetamiprid-induced anxiety-like behavior

Neonicotinoid (NN) pesticides have been linked to increased brain dysfunction in mammals, such as anxiety-like behavior; this is thought to involve monoamines (MA), neurotransmitters that control behavior, memory, and learning. However, the mechanism by which NNs affect the central nervous system is not fully understood. In this study, we aimed to investigate whether MAs affect NNs-induced anxiety-like behavior. Mice were orally administered acetamiprid (ACE), an NN, at the no observed adverse effect level (NOAEL) of mouse (20 mg/kg body mass) set by the Food Safety Commission of Japan, and the elevated zero-maze (EZM) test was performed 30 min after administration. After behavioral analysis, levels of four MA (dopamine, 3-MT, serotonin, and histamine) in selected brain regions were determined by liquid chromatography mass spectrometry (LC/MS/MS). In the exposed group, a trend toward increased anxiety-like behavior was observed, and at least one MA concentration was significantly increased in each region. Further, significant correlations were found between behavioral test results and hippocampal serotonin and striatal dopamine concentrations, as well as between dopamine and serotonin concentrations, in the exposed group. As anxiety can influence activity in the behavioral tests, the activity of neurons in the raphe nuclei (RN), a brain region greatly involved in anxiety via the serotonergic system, was examined by staining with anti-serotonin antibodies, and increased serotonergic activity was observed. Taken together, these results suggest that ACE regulates MA levels, notably serotonin levels in the hippocampus and that RN plays an important role in ACE-induced anxiety-like behavior.

Social environment enrichment alleviates anxiety-like behavior in mice: Involvement of the dopamine system

Rearing environment plays a vital role in maintaining physical and mental health of both animals and humans. Plenty of studies have proved that physical environment enrichment in adolescence has protective effects on emotion, social behavior, learning and memory deficits. However, the following effects of social environment enrichment in adolescence remain largely elusive. Using the paradigm of companion rotation (CR), the present study found that social environment enrichment reduced anxiety-like behaviors of early adult male C57BL/6J mice. CR group also showed significantly higher expression of tyrosine hydroxylase in the ventral tegmental area and dopamine 1 receptor mRNA in the nucleus accumbens shell than control group. Taken together, these findings demonstrate that CR from adolescence to early adulthood can suppress the level of anxiety and upregulate dopaminergic neuron activity in early adult male C57BL/6J mice.

Hallucinogenic activity, neurotransmitters release, anxiolytic and neurotoxic effects in Rat's brain following repeated administration of novel psychoactive compound 25B-NBOMe

2-(4-Bromo-2,5-dimethoxyphenyl)-N-(2-methoxybenzyl)etanoamine (25B-NBOMe) is a highly selective 5-HT2A receptor agonist, exhibiting a potent hallucinogenic activity. In the present study, we investigated the effect of a 7-day treatment with 25B-NBOMe in a dose of 0.3 mg/kg on the following: the neurotransmitter release in vivo using microdialysis in freely moving animals, hallucinogenic activity measured in the Wet Dog Shake (WDS) test, anxiety level as measured in the light/dark box (LDB) and locomotor activity in the open field (OF) test, DNA damage with the comet assay, and on a number of neuronal and glial cells with immunohistochemistry. Repeated administration of 25B-NBOMe decreased the response to a challenge dose (0.3 mg/kg) on DA, 5-HT and glutamatergic neurons in the rats' frontal cortex, striatum, and nucleus accumbens. The WDS response dropped drastically after the second day of treatment, suggesting a rapid development of tolerance. LDB and OF tests showed that the effect of 25B-NBOMe on anxiety depends on the treatment and environmental settings. Results obtained with the comet assay indicate a genotoxic properties in the frontal cortex and hippocampus. An increase in immunopositive glial but not neuronal cells was observed in the cortical regions but not in the hippocampus. In conclusion, our study showed that a chronic administration of 25B-NBOMe produces the development of tolerance observed in the neurotransmitters release and hallucinogenic activity. The oxidative damage of cortical and hippocampal DNA implies the generation of free radicals by the drug, resulting in genotoxicity but rather not in neurotoxic tissue damage. Behavioral tests show that 25B-NBOMe exerts anxiogenic effect after single and repeated treatment.

Recent advances in dopamine D2 receptor ligands in the treatment of neuropsychiatric disorders

Dopamine is a biologically active amine synthesized in the central and peripheral nervous system. This biogenic monoamine acts by activating five types of dopamine receptors (D_1-5 Rs), which belong to the G protein-coupled receptor family. Antagonists and partial agonists of D₂ Rs are used to treat schizophrenia, Parkinson's disease, depression, and anxiety. The typical pharmacophore with high D₂ R affinity comprises four main areas, namely aromatic moiety, cyclic amine, central linker and aromatic/heteroaromatic lipophilic fragment. From the literature reviewed herein, we can conclude that 4-(2,3-dichlorophenyl), 4-(2-methoxyphenyl)-, 4-(benzo[b]thiophen-4-yl)-1-substituted piperazine, and 4-(6-fluorobenzo[d]isoxazol-3-yl)piperidine moieties are critical for high D₂ R affinity. Four to six atoms chains are optimal for D₂ R affinity with 4-butoxyl as the most pronounced one. The bicyclic aromatic/heteroaromatic systems are most frequently occurring as lipophilic appendages to retain high D₂ R affinity. In this review, we provide a thorough overview of the therapeutic potential of D₂ R modulators in the treatment of the aforementioned disorders. In addition, this review summarizes current knowledge about these diseases, with a focus on the dopaminergic pathway underlying these pathologies. Major attention is paid to the structure, function, and pharmacology of novel D₂ R ligands, which have been developed in the last decade (2010-2021), and belong to the 1,4-disubstituted aromatic cyclic amine group. Due to the abundance of data, allosteric D₂ R ligands and D₂ R modulators from patents are not discussed in this review.

Adolescent nicotine administration impacts working memory and reversal learning but not cognitive flexibility

There has been increased interest in early exposure to nicotine through tobacco products and vaping specifically as it relates to addiction, yet fewer studies have focused on whether behavioral effects resulting from early nicotine exposure may persist into adulthood. Our experiments tested the hypothesis that exposure to nicotine during adolescence would impair selective aspects of behavioral cognition in rodents in adulthood. Male and female adolescent rats received either nicotine (0.4 mg/kg) or vehicle injections (intraperitoneal) once daily for 10 days (PND 29-38) followed by a washout period before behavioral testing. Animals were followed in a longitudinal design and evaluated on a battery of both behavioral and cognitive tasks during adulthood (PND 90+) that included locomotor activity, working memory (novel object recognition), cognitive flexibility (attentional set-shifting task, ASST), and anxiety-like behaviors. Data suggested that subchronic exposure to nicotine during adolescence produced significant changes in working memory, in two reversal problems in the ASST, and in anxiety-related behaviors. Taken together these data may suggest that limited early exposure to nicotine may produce selective longer term impairments in cognitive and behavioral processes related to working memory and reversal learning.

Almond intake during pregnancy in rats improved the cognitive performance of adult male offspring

Background: Based on evidence there are accepted links among early nutrition, epigenetic processes, and cognitive performance. Almond as a nutritious food could exert neuroprotective effects and improve anxiety, learning, and memory.Methods: In the current study, female rats were fed with a diet containing 5% (w/w) almonds during the mating period (two days) and gestation period (21 consecutive days). Then, the effect of the almond diet on short-term memory (Y maze), anxiety (elevated plus maze), and stress adaptation (forced swimming test) were investigated in the adult male offspring. The hippocampus (HIP), prefrontal cortex (PFC), and amygdala (AMY) of offspring were collected, and the level of cyclic AMP response element-binding proteins (CREB), brain-derived neurotrophic factor (BDNF) was assessed by western blotting. Also, Monoamine oxidases (MAO)-A and B activity were evaluated via enzymatic assays.Results: Our results indicated that prenatal almond consumption improved memory, made a modest reduction in anxiety-like behavior, and increased stress adaptation in adult male offspring. Also, molecular assessments showed an increased level of CREB phosphorylation and BDNF in the HIP and PFC of the almond group, while the activity of MAO-A and MAO-B was inhibited by almond consumption in mentioned areas.Discussion: These findings introduce almonds as a beneficial diet during pregnancy, for improving short-term memory, stress adaptation, and cognitive performance in adult offspring.

Dopaminergic neurons project to the nucleus accumbens regulates anxiety-like behaviors through dopamine D1 signaling

Dopamine (DA) transmission is important in the regulation of mood and anxiety behaviors. However, how specific dopaminergic signaling pathways respond to anxiogenic stimuli as well as regulate behaviors remains unknown. To understand how DA regulates the animal behaviors under anxiety we performed retrograde labeling and c-Fos staining of midbrain DA neurons. Our c-Fos labeling results showed that DA neurons projected to nucleus accumbens (NAc) are activated in animals treated with the elevated plus-maze (EPM). Real-time measurement of DA release using fast scanning cyclic voltammetry (FSCV) in NAc of freely behaving mice showed that increased DA release and more DA transients in the close arms than the open arms in the EPM. Meanwhile, we also observed a reduction of DA level from the close arms to the open arms. Local infusion of DA D₁ receptor antagonist, SCH23390 in the core of NAc, leads to an anxiolytic-like effect in the open-field and EPM. These anxiolytic effects were not observed in animals received D₂ receptor antagonist sulpiride infusion in the core of NAc. Taken together, our results reveal a novel function of the mesolimbic DA pathway through the D₁ receptor in the regulation of anxiety-like behaviors.

Nicotine inhibits the VTA-to-amygdala dopamine pathway to promote anxiety

Nicotine stimulates dopamine (DA) neurons of the ventral tegmental area (VTA) to establish and maintain reinforcement. Nicotine also induces anxiety through an as yet unknown circuitry. We found that nicotine injection drives opposite functional responses of two distinct populations of VTA DA neurons with anatomically segregated projections: it activates neurons that project to the nucleus accumbens (NAc), whereas it inhibits neurons that project to the amygdala nuclei (Amg). We further show that nicotine mediates anxiety-like behavior by acting on β2-subunit-containing nicotinic acetylcholine receptors of the VTA. Finally, using optogenetics, we bidirectionally manipulate the VTA-NAc and VTA-Amg pathways to dissociate their contributions to anxiety-like behavior. We show that inhibition of VTA-Amg DA neurons mediates anxiety-like behavior, while their activation prevents the anxiogenic effects of nicotine. These distinct subpopulations of VTA DA neurons with opposite responses to nicotine may differentially drive the anxiogenic and the reinforcing effects of nicotine.

Neuropeptide Y neurons in the nucleus accumbens modulate anxiety-like behavior

Neuropeptide Y (NPY) is a 36-amino acid neuropeptide that is widely expressed in the central nervous system, including the cerebral cortex, nucleus accumbens (NAc) and hypothalamus. We previously analyzed the behavior of transgenic mice exclusively expressing an unedited RNA isoform of the 5-HT_2C receptor. These mice showed decreased NPY gene expression in the NAc and exhibited behavioral despair, suggesting that NAc NPY neurons may be involved in mood disorder; however, their role in this behavior remained unknown. Therefore, in the present study, we investigated the functional role of NAc NPY neurons in anxiety-like behavior by examining the impact of specific ablation or activation of NAc NPY neurons using NPY-Cre mice and Cre-dependent adeno-associated virus. Diphtheria toxin-mediated ablation of NAc NPY neurons significantly increased anxiety-like behavior in the open field and elevated plus maze tests, compared with before toxin treatment. Moreover, chemogenetic activation of NAc NPY neurons reduced anxiety-like behavior in both behavioral tests compared with control mice. These results suggest that NPY neurons in the NAc are involved in the modulation of anxiety in mice.

Knockdown of the histone di-methyltransferase G9a in nucleus accumbens shell decreases cocaine self-administration, stress-induced reinstatement, and anxiety

Comorbid neuropsychiatric disorders such as addiction and anxiety could involve common underlying mechanisms. One potential mechanism involves epigenetic regulation of histone 3 dimethylation at lysine 9 residues (H3K9me2) by the histone dimethyltransferase G9a. Here we provide evidence that local AAV-RNAi-mediated knockdown of G9a expression in nucleus accumbens shell (NAcSh) of male rats reduces both addictive-related and anxiety-related behaviors. Specifically, G9a knockdown reduces sensitivity to low dose cocaine reinforcement when cocaine is freely available (fixed ratio schedule). Similarly, G9a knockdown reduces motivation for cocaine under higher effort demands (progressive ratio schedule). Following several weeks of forced abstinence, G9a knockdown attenuates extinction responding and reinstatement triggered by either cocaine-priming injections or footshock stress. This decrease in addictive behavior is associated with a long-term reduction in anxiety-like behavior as measured by the elevated plus maze (EPM). G9a knockdown also reduces basal anxiety-like behavior in EPM and marble burying tests in drug-naïve rats. These results complement our previous work showing that increased G9a expression in NAcSh enhances addictive-related and anxiety-related behaviors, indicating that G9a bi-directionally controls these responses. These results also suggest that regulation of G9a-influenced gene expression could be a common epigenetic mechanism for co-morbid anxiety and psychostimulant addiction.

Effects of Maternal Deprivation on Anxiety, Depression, and Empathy in Male and Female Offspring of Wistar Rats in the Face of Novel Objects

Background:

Early life stress (ELS) models such as maternal deprivation (MD) are used to investigate behavioral changes in rodents under stressful situations. MD is a situation in which rat pups are separated from the dam; MD has different paradigms. The purpose of this research is to evaluate the effects of maternal deprivation on anxiety, depression, and empathy in adult Wistar rats.

Materials and Methods:

MD was applied to pups as per specifically designed protocol to compare rats of the control group with maternal deprivation rats and also the group, which faced novel objects. Each group consisted of eight rats. In this study, separation started from postnatal day (PND) 14 for various periods up to PND 60. EPM test was undertaken to measure anxiety; moreover, FST was used to indicate levels of depression. Also, changes in the empathy ratio were also demonstrated. One-way analysis of variance (ANOVA), Tukey’s post hoc analysis, and t-test were applied to analyze the results.

Results:

MD-treated rats showed a significant decrease in anxiety and empathy indexes compared with those in the control group (P<0.05). However, MD significantly increased depression in both male and female rats (P<0.05). Finally, exposure to novel objects decreased depression but did not have any effect on anxiety and empathy levels in MD rats (P<0.05).

Conclusion:

ELS may lead to various states of mood and behavior in adulthood. According to the findings of this study, depression increases due to MD, though both anxiety and empathy decrease in both male and female Wistar rats. Moreover, exposure to novel objects decreases depression, while anxiety and empathy do not change significantly with exposure to novel objects.

Progressive modulation of accumbal neurotransmission and anxiety-like behavior following protracted nicotine withdrawal

Due to the highly addictive properties of nicotine, a low percentage of users successfully maintain cessation for longer periods of time. This might be linked to neuroadaptations elicited by the drug, and understanding progressive changes in neuronal function might provide critical insight into nicotine addiction. We have previously shown that neurotransmission in the nucleus accumbens (nAc), a key brain region with respect to drug reinforcement and relapse, is suppressed for as long as seven months after a brief period of nicotine treatment. Studies were therefore performed to define the temporal properties of these effects, and to assess behavioral correlates to altered neurotransmission. Ex vivo electrophysiology revealed progressive depression of synaptic efficacy in the nAc of rats previously receiving nicotine. In addition, following three months of nicotine withdrawal, the responses to GABA_A receptor modulating drugs were blunted together with downregulation of several GABA_A receptor subunits. In correlation to reduced accumbal neurotransmission, a reduced anxiety-like behavior; assessed in the elevated plus-maze and marble burying tests, were identified in animals pre-treated with nicotine. Lastly, to test the causal relationship between suppressed excitability in the nAc and reduced anxiety-like behavior, rats received local administration of diazepam in the nAc while monitoring behavioral effects on the elevated plus-maze. These results show that nicotine produces long-lasting changes in the GABAergic system, which are observed first after extended withdrawal. Our data also suggest that nicotine produces a progressive suppression of accumbal excitability, which could result in behavioral alterations that may have implications for further drug intake.

Modulatory effects of the basolateral amygdala α2-adrenoceptors on nicotine-induced anxiogenic-like behaviours of rats in the elevated plus maze

The present study was designed to clarify whether α2-adrenoceptors of the basolateral amygdala (BLA) are involved in nicotine-induced anxiogenic-like behaviours. Adult male Wistar rats were bilaterally cannulated in the BLA and anxiety-like behaviours were assessed in an elevated plus maze (EPM) task. Systemic intraperitoneal (i.p.) administration of nicotine (0.3, 0.5 and 0.7 mg/kg) dose-dependently decreased open arm time (%OAT) and open arm entry (%OAE), indicating the anxiogenic-like effect of nicotine. The activation of the BLA α2-adrenoceptors by the injection of α2-receptor agonist, clonidine (0.1, 0.3 and 0.5 μg/rat) into the BLA (intra-BLA) reversed nicotine-induced anxiogenic-like behaviours. It is important to note that intra-BLA injection of a higher dose of clonidine (0.5 μg/rat) by itself increased %OAT, but not %OAE which showed an anxiolytic effect of the agonist. On the other hand, intra-BLA injection of different doses of α2-adrenoceptor antagonist, yohimbine (1, 3 and 5 μg/rat) in combination with an ineffective dose of nicotine (0.3 mg/kg) decreased %OAT and %OAE, suggesting a potentiative effect of the antagonist on nicotine response. In addition, intra-BLA injection of the same doses of yohimbine did not alter %OAT and %OAE. Interestingly, intra-BLA injection of yohimbine (0.5 and 1 μg/rat) significantly reversed the inhibitory effect of clonidine on nicotine-induced anxiogenic-like behaviours. It should be considered that the drug treatments had no effect on locomotor activity in all experiments. Taken together, it can be concluded that nicotine produces anxiogenic-like behaviours which may be mediated through the BLA α2-adrenoceptor mechanism.

Hazelnut and neuroprotection: Improved memory and hindered anxiety in response to intra-hippocampal Aβ injection

OBJECTIVES

Corylus avellana L. (hazelnut) is known to be a delicious and nutritious food. This study was carried out to evaluate the use of hazelnut as a therapy for memory impairment because in Iranian traditional medicine, it is recommended for those suffering from a particular type of dementia, with symptoms of Alzheimer's disease.

METHODS

In this study, rats were fed with hazelnut kernel [(without skin) 800 mg/kg/day] during 1 week before stereotaxic surgery to 24 hours before behavioral testing (in general, for 16 consecutive days) and the effect of hazelnut eating on memory, anxiety, neuroinflammation and apoptosis was assessed in the amyloid beta-injected rat.

RESULTS

The results of this study showed that feeding with hazelnut improved memory, (which was examined by using Y-maze test and shuttle box apparatus), and reduced anxiety-related behavior, that was evaluated using elevated plus maze. Also, western blotting analysis of cyclooxygenase-2, interleukin-1β, tumor necrosis factor-α, B-cell lymphoma 2 (Bcl-2), Bcl-2-associated X protein, and caspase-3 showed that hazelnut has an ameliorating effect on the neuroinflammation and apoptosis caused by Aβ.

DISCUSSION

These findings suggest that hazelnut, as a dietary supplement, improves healthy aging and could be a beneficial diet for the treatment of AD.

Complexity of Compensatory Effects in Nrf1 Knockdown: Linking Undeveloped Anxiety-Like Behavior to Prevented Mitochondrial Dysfunction and Oxidative Stress

Anxiety-related disorders are complex illnesses that underlying molecular mechanisms need to be understood. Mitochondria stand as an important link between energy metabolism, oxidative stress, and anxiety. The nuclear factor, erythroid-derived 2,-like 1(Nrf1) is a member of the cap "n" collar subfamily of basic region leucine zipper transcription factors and plays the major role in regulating the adaptive response to oxidants and electrophiles within the cell. Here, we injected small interfering RNA (siRNA) targeting Nrf1 in dorsal third ventricle of adult male albino Wistar rats and subsequently examined the effect of this silencing on anxiety-related behavior. We also evaluated apoptotic markers and mitochondrial biogenesis factors, along with electron transport chain activity in three brain regions: hippocampus, amygdala, and prefrontal cortex. Our data revealed that in the group that received Nrf1-siRNA, anxiety-related behavior did not show any significant changes compared to the control group. Caspase-3 did not increase in Nrf1-siRNA-injected rats even though Bax/Bcl2 ratio markedly elevated in Nrf1-knockdown rats in all three mentioned regions compared to control rats. Also, Nrf1 silencing of complex I and II-III did not alter, generally. In addition, Nrf1-knockdown affected mitochondrial biogenesis markers. The level of peroxisome proliferator-activated receptor gamma coactivator-1α and cytochrome-c increased, which indicates a possible role for mitochondrial biogenesis in anxiety.

Cognitive effects of acute restraint stress in male albino rats and the impact of pretreatment with quetiapine versus ghrelin

Stress is any condition that seriously affects the balance of the organism physiologically and psychologically. Stress activates the hypothalamic-pituitary-adrenal (HPA) releasing glucocorticoid hormones that produce generalized effects on different body systems including the nervous system. This study aimed to investigate the effect of acute restraint stress (ARS) on cognitive performance by measuring spatial working memory in Y-maze, behavior (anxiety and exploratory behavior) in open field test, expression of synaptophysin and glial fibrillary acidic protein (GFAP) in the hippocampus by immunohistochemistry, dopaminergic receptors (D2) in the basal ganglia by gene expression and comparing the effect of ghrelin and quetiapine on the previous parameters. 36 adult male albino rats constituted the animal model of this work and have been divided into six groups: control group, control group exposed to ARS, quetiapine group, quetiapine group exposed to ARS, ghrelin group and ghrelin group exposed to ARS. We demonstrated more neuroprotective effect for quetiapine compared to ghrelin on stress response, anxiety behavior and working spatial memory impairment due to ARS.

Lipoic acid and pentoxifylline mitigate nandrolone decanoate-induced neurobehavioral perturbations in rats via re-balance of brain neurotransmitters, up-regulation of Nrf2/HO-1 pathway, and down-regulation of TNFR1 expression

Behavioral perturbations associated with nandrolone decanoate abuse by athletes and adolescents may be attributed to oxidative stress and inflammation. However, the underlying mechanisms are not yet fully explored. On the other hand, the natural antioxidant lipoic acid can pass the blood brain barrier and enhance Nrf2/HO-1 (nuclear factor erythroid-2 related factor 2/heme oxygenase-1) pathway. In addition, the phosphodiesterase-IV inhibitor xanthine derivative pentoxifylline has a remarkable inhibitory effect on tumor necrosis factor-alpha (TNF-α). Therefore, this study aimed at investigation of the possible protective effects of lipoic acid and/or pentoxifylline against nandrolone-induced neurobehavioral alterations in rats. Accordingly, male albino rats were randomly distributed into seven groups and treated with either vehicle, nandrolone (15mg/kg, every third day, s.c.), lipoic acid (100mg/kg/day, p.o.), pentoxifylline (200mg/kg/day, i.p.), or nandrolone with lipoic acid and/or pentoxifylline. Rats were challenged in the open field, rewarded T-maze, Morris water maze, and resident-intruder aggression behavioral tests. The present findings showed that nandrolone induced hyperlocomotion, anxiety, memory impairment, and aggression in rats. These behavioral abnormalities were accompanied by several biochemical changes, including altered levels of brain monoamines, GABA, and acetylcholine, enhanced levels of malondialdehyde and TNF-α, elevated activity of acetylcholinesterase, and up-regulated expression of TNF-α receptor-1 (TNFR1). In addition, inhibited catalase activity, down-regulated Nrf2/HO-1 pathway, and suppressed acetylcholine receptor expression were observed. Lipoic acid and pentoxifylline combination significantly mitigated all the previously mentioned deleterious effects mainly via up-regulation of Nrf2/HO-1 pathway, inhibition of TNF-α and down-regulation of TNFR1 expression. In conclusion, the biochemical and histopathological findings of this study revealed the protective mechanisms of lipoic acid and pentoxifylline against nandrolone-induced behavioral changes and neurotoxicity in rats.

Age-contingent influence over accumbal neurotransmission and the locomotor stimulatory response to acute and repeated administration of nicotine in Wistar rats

Nicotine addiction is one of the leading contributors to the global burden of disease, and early onset smokers report a more severe addiction with lower chance of cessation than those with a late onset. Preclinical research supports an age-dependent component to the rewarding and reinforcing properties of nicotine, and the aim of this study was to define behavioral adaptations and changes in accumbal neurotransmission that arise over 15 days of intermittent nicotine treatment (0.36 mg/kg/day) in rats of three different ages (5 weeks, 10 weeks, 36 weeks old). Repeated treatment increased the locomotor stimulatory response to nicotine in all age groups, but significantly faster in the two younger groups. In addition, nicotine decreased rearing activity in a way that sustained even after repeated administration in aged rats but not in the younger age groups. Electrophysiological field potential recordings revealed a decline in input/output function in the nucleus accumbens (NAc) of animals intermittently treated with nicotine starting at 5 weeks of age, but not in older animals. In drug naïve rats, acute administration of nicotine modulated both accumbal dopamine output and excitatory transmission in a partially age-dependent manner. Fifteen days of intermittent nicotine treatment did not alter the acute effect displayed by nicotine on dopamine levels or evoked field potentials. The data presented here show that both acute and repeated nicotine administration modulates accumbal neurotransmission and behavior in an age-contingent manner and that these age-dependent differences could reflect important neurobiological underpinnings associated with the increased vulnerability for nicotine-addiction in adolescents.

The reinforcing effects of ethanol within the posterior ventral tegmental area depend on dopamine neurotransmission to forebrain cortico-limbic systems

Ethanol can be self-infused directly into the posterior ventral tegmental area (pVTA) and these effects involve activation of local dopamine neurons. However, the neuro-circuitry beyond the pVTA involved in these reinforcing effects has not been explored. Intra-pVTA microinjection of ethanol increases dopamine release in the nucleus accumbens (NAC), medial prefrontal cortex (mPFC) and ventral pallidum (VP). The present study tested the hypothesis that the reinforcing effects of ethanol within the pVTA involve the activation of dopamine projections from the pVTA to the NAC, VP and mPFC. Following the acquisition of self-infusions of 200 mg% ethanol into the pVTA, either the dopamine D2 receptor antagonist sulpiride (0, 10 or 100 μM) or the D1 receptor antagonist SCH-23390 (0, 10 or 100 μM) was microinjected into the ipsilateral NAC shell (NACsh), NAC core (NACcr), VP or mPFC immediately prior to the self-infusion sessions to assess the involvement of the different dopamine projections in the reinforcing effects of ethanol. Microinjection of each compound at higher concentration into the NACsh, VP or mPFC, but not the NACcr, significantly reduced the responses on the active lever (from 40-50 to approximately 20 responses). These results indicate that activation of dopamine receptors in the NACsh, VP or mPFC, but not the NACcr, is involved in mediating the reinforcing effects of ethanol in the pVTA, suggesting that the 'alcohol reward' neuro-circuitry consist of, at least in part, activation of the dopamine projections from the pVTA to the NACsh, VP and mPFC.

Evaluation of sub-chronic toxic effects of petroleum ether, a laboratory solvent in Sprague-Dawley rats

BACKGROUND

In general, organic solvents are inhibiting many physiological enzymes and alter the behavioural functions, but the available scientific knowledge on laboratory solvent induced organ specific toxins are very limited. Hence, the present study was planned to determine the sub-chronic toxic effects of petroleum ether (boiling point 40-60°C), a laboratory solvent in Sprague-Dawley (SD) rats.

MATERIALS AND METHODS

The SD rats were divided into three different groups viz., control, low exposure petroleum ether (250 mg/kg; i.p.) and high exposure petroleum ether (500 mg/kg; i.p.) administered group. The animals were exposed with petroleum ether once daily for 2 weeks. Prior to the experiment and end of the experiment animals behaviour, locomotor and memory levels were monitored. Before initiating the study animals were trained for 2 weeks for its learning process and its memory levels were evaluated. Body weight (BW) analysis, locomotor activity, anxiogenic effect (elevated plus maze) and learning and memory (Morris water navigation task) were monitored at regular intervals. On 14(th) day of the experiment, few ml of blood sample was collected from all the experimental animals for estimation of biochemical parameters. At the end of the experiment, all the animals were sacrificed, and brain, liver, heart, and kidney were collected for biochemical and histopathological analysis.

RESULTS

In rats, petroleum ether significantly altered the behavioural functions; reduced the locomotor activity, grip strength, learning and memory process; inhibited the regular body weight growth and caused anxiogenic effects. Dose-dependent organ specific toxicity with petroleum ether treated group was observed in brain, heart, lung, liver, and kidney. Extrapyramidal effects that include piloerection and cannibalism were also observed with petroleum ether administered group. These results suggested that the petroleum ether showed a significant decrease in central nervous system (CNS) activity, and it has dose-dependent toxicity on all vital organs.

CONCLUSION

The dose-dependent CNS and organ specific toxicity was observed with sub-chronic administration of petroleum ether in SD rats.

Involvement of Nrf2 in development of anxiety-like behavior by linking Bcl2 to oxidative phosphorylation: estimation in rat hippocampus, amygdala, and prefrontal cortex

Anxiety-related disorders are complex illnesses that underlying molecular mechanisms of these complicated emotional disorders are poorly understood. Nuclear factor erythroid 2-related factor 2 (Nrf2) is the most important regulator of the antioxidant defense system. Its protective actions are not only limited to antioxidative transactivation, but also plays important roles in encountering various physiological and pathological stresses. In this study, we evaluated whether silencing of Nrf2 plays a role in development of anxiety-related behavior. In this regard, we exerted small interfering RNA (siRNA) targeting Nrf2 in dorsal third ventricle and subsequently examined the effect of this silencing on anxiety-related behavior along with supposed molecular mechanisms. Therefore, we evaluated apoptotic markers and mitochondrial electron transport chain (ETC) activity in three brain regions: hippocampus, amygdala, and prefrontal cortex. Based on our result, Nrf2-silenced rats exhibited greater anxiety-like behavior compared to control group. Furthermore, Nrf2 silencing increased activity of ETC complexes. Also, Bax/Bcl2 ratio of all mentioned areas of the brain and cleavage of caspase-3 in hippocampus increased in Nrf2 silenced group, however, with a distinct pattern.

Erythrina mulungu alkaloids are potent inhibitors of neuronal nicotinic receptor currents in mammalian cells

Crude extracts and three isolated alkaloids from Erythrina mulungu plants have shown anxiolytic effects in different animal models. We investigated whether these alkaloids could affect nicotinic acetylcholine receptors and if they are selective for different central nervous system (CNS) subtypes. Screening experiments were performed using a single concentration of the alkaloid co-applied with acetylcholine in whole cell patch-clamp recordings in three different cell models: (i) PC12 cells natively expressing α3* nicotinic acetylcholine receptors; (ii) cultured hippocampal neurons natively expressing α7* nicotinic acetylcholine receptors; and (iii) HEK 293 cells heterologoulsy expressing α4β2 nicotinic acetylcholine receptors. For all three receptors, the percent inhibition of acetylcholine-activated currents by (+)-11á-hydroxyerysotrine was the lowest, whereas (+)-erythravine and (+)-11á-hydroxyerythravine inhibited the currents to a greater extent. For the latter two substances, we obtained concentration-response curves with a pre-application protocol for the α7* and α4β2 nicotinic acetylcholine receptors. The IC₅₀ obtained with (+)-erythravine and (+)-11á-hydroxyerythravine were 6 µM and 5 µM for the α7* receptors, and 13 nM and 4 nM for the α4β2 receptors, respectively. Our data suggest that these Erythrina alkaloids may exert their behavioral effects through inhibition of CNS nicotinic acetylcholine receptors, particularly the α4β2 subtype.

Developmental alterations in locomotor and anxiety-like behavior as a function of D1 and D2 mRNA expression

The majority of smokers start smoking in adolescence, beginning a potentially lifelong struggle with nicotine use and abuse. In rodent models of the effects of nicotine, the drug has been shown to elicit both locomotor and anxiety-like behavioral effects. Research suggests that these behavioral effects may be due in part to dopamine (DA) receptors D1 and D2 in the mesolimbic system, specifically the nucleus accumbens (NAc). We examined early adolescent (P28), late adolescent (P45), and adult (P80) male Long-Evans rats in the elevated plus maze (EPM) under normal conditions and the open field (OF) post-nicotine in order to test locomotor and anxiety-like behavior. These behavioral findings were then correlated with expression of DA D1 and D2 mRNA levels as determined via in situ hybridization. Nicotine-induced locomotor behavior was found to be significantly different between age groups. After a single injection of nicotine, early adolescents exhibited increases in locomotor behavior, whereas both late adolescents and adults responded with decreases in locomotor behavior. In addition, it was found that among, early adolescents, open arm and center time in the EPM were negatively correlated with D2 mRNA expression. In contrast, among adults, distance traveled in the center and center time in the OF were negatively correlated with D2 mRNA expression. This study suggests that DA D2 receptors play a role in anxiety-like behavior and that the relationship between observed anxiety-like behaviors and D2 receptor expression changes through the lifespan.