Anxiolytic Response Research Articles

Rapid Amygdala Kindling Causes Motor Seizure and Comorbidity of Anxiety- and Depression-Like Behaviors in Rats.

Amygdala kindling is a model of temporal lobe epilepsy (TLE) with convulsion. The rapid amygdala kindling has an advantage on quick development of motor seizures and for antiepileptic drugs screening. The rapid amygdala kindling causes epileptogenesis accompanied by an anxiolytic response in early isolation of rat pups or depressive behavior in immature rats. However, the effect of rapid amygdala kindling on comorbidity of anxiety- and depression-like behaviors is unexplored in adult rats with normal breeding. In the present study, 40 amygdala stimulations given within 2 days were applied in adult Wistar rats. Afterdischarge (AD) and seizure stage were recorded throughout the amygdala kindling. Anxiety-like behaviors were evaluated by the elevated plus maze (EPM) test and open field (OF) test, whereas depression-like behaviors were assessed by the forced swim (FS) and sucrose consumption (SC) tests. A tonic-clonic convulsion was provoked in the kindle group. Rapid amygdala kindling resulted in a significantly lower frequency entering an open area of either open arms of the EPM or the central zone of an OF, lower sucrose intake, and longer immobility of the FS test in the kindle group. Our results suggest that rapid amygdala kindling elicited severe motor seizures comorbid with anxiety- and depression-like behaviors.

Low-dose L-methionine-associated Changes in Behavioural Indices in Young Rats

Objective: The study objectives were to investigate the effects of L-methionine (at low doses) on open-field novelty-induced behaviours, anxiety-related behaviours, working-memory and brain S-adenosyl-methionine (SAMe) levels in young rats. This was with a view to determine whether administration of low doses of L-methionine can significantly alter behavioural parameters, working-memory and brain SAMe levels, or not. Methodology: Wistar rats (40-45 g each) were given distilled water or L-methionine (5 and 10 mg/kg body weight) orally for 21 days. Behaviours were assessed after the first and last dose of L-methionine. Results: In the open field, significant increases in horizontal locomotion and rearing were seen after the first dose, while repeated administration led to their suppression. Suppression of grooming behaviour was observed at both times of assessment. Working-memory in the radial-arm maze was significantly reduced following repeated administration; while the elevated plus-maze test revealed anxiolytic responses following both acute and repeated administration. Patterns of changes in horizontal locomotion in the y-maze and radial-arm maze were similar to that of the open-field. There was no significant difference in brain levels of SAMe at end of study. Conclusion: The study demonstrated an association between low dose L-methionine administration and behavioural changes in young rats. It therefore brings to light, the behavioural changes that may occur due to addition of low doses of L-methionine to the diet.

Chronic fluoxetine treatment induces anxiolytic responses and altered social behaviors in medaka, Oryzias latipes

Medaka (Oryzias latipes) is a small freshwater teleost that is an emerging model system for neurobehavioral research and toxicological testing. The selective serotonin reuptake inhibitor class of antidepressants such as fluoxetine is one of the widely prescribed drugs, but little is known about the effects of these drugs on medaka behaviors. To assess the behavioral effects of fluoxetine, we chronically administrated fluoxetine to medaka adult fish and analyzed the anxiety-related and social behaviors using five behavioral paradigms (diving, open-field, light–dark transition, mirror-biting, and social interaction) with an automated behavioral testing system. Fish chronically treated with fluoxetine exhibited anxiolytic responses such as an overall increased time spent in the top area in the diving test and an increased time spent in center area in the open-field test. Analysis of socially evoked behavior showed that chronic fluoxetine administration decreased the number of mirror biting times in the mirror-biting test and increased latency to first contact in the social interaction test. Additionally, chronic fluoxetine administration reduced the horizontal locomotor activity in the open-field test but not the vertical activity in the diving test. These investigations are mostly consistent with previous reports in the other teleost species and rodent models. These results indicate that behavioral assessment in medaka adult fish will become useful for screening of effects of pharmaceutical and toxicological compounds in animal behaviors.

Anxiolytic potential of astaxanthin on experimental animal model

Background: Astaxanthin is a naturally occurring carotenoid found in nature primarily in marine organisms. Carotenoids are well known for their therapeutic benefits in the aging process and various diseases, because of their antioxidant properties. Additionally, astaxanthin has well-documented anti-inflammatory and immune-stimulating effects. It is a known fact that oxidative stress is associated with depression, anxiety, and related psychiatric disorders. Astaxanthin may also reduce oxidative stress in the nervous system, reducing the risk of neurodegenerative diseases. Although astaxanthin has the ability to cross the blood–brain barrier and has a beneficial effect on the CNS, the effects of astaxanthin on anxiety and depression have not been reported. Methods: In this study, to investigate the effects of astaxanthin on anxiety, we performed some behavioural tests including elevated plus maze test, hole-board test, light/dark exploration test. Results: In elevated plus maze test the time spent in the closed arm by astaxanthin treated rats was significantly (P <0.05) decreased as compared to control. The number of readings in both the arms was significantly (P <0.05) increased in astaxanthin treated rats as compared to control. In hole board apparatus, it showed anxiolytic response by significantly reduced the number of head poking. Increased number of entries in the bright side and decrease of time spent by the animal in dark side were observed in the light/dark exploration test. Conclusions: The present study indicates that Astaxanthin produces anxiolytic response at the dose of 3 mg/kg on experimental animal model.

Anti-Obesity Effect of the CB2 Receptor Agonist JWH-015 in Diet-Induced Obese Mice.

The cannabinoid receptor 2 (CB2) is well known for its immune modulatory role. However, recent localisation of CB2 receptors in metabolically active tissue suggests that the CB2 receptor plays a significant role in energy homeostasis. This study was designed to investigate the impact of chronic CB2 receptor stimulation on food intake, body weight and mood. Lean male C57BL/6 mice were injected i.p. with the selective CB2 receptor agonist, JWH-015 (0.0, 1.0, 5.0 and 10.0 mg kg-1) to establish dose response parameters. Mice made obese following exposure to a diet consisting of 19.4 MJ/kg (4641 Kcal/kg) of energy (19.0% protein, 21.0% total fat, 4.7% crude fiber, and 4.7% AD fiber were given either vehicle or 10 mg/kg JWH-015. Impact on mood, food intake, body weight, plasma metabolites, expression of key metabolic proteins in the brown adipose tissue (BAT) and white adipose tissue (WAT), and markers of inflammation were measured. High dose (10 mg/kg) JWH-015 reduced food intake after 1, 2, 4, and 24 h in lean mice. When given to diet induced obese (DIO) mice, a 10 mg/kg dose of JWH-015 significantly reduced body weight compared to vehicle. This dose led to a shift in markers of lipid metabolism and inflammation in WAT consistent with lipolysis and improved immune response. Furthermore, JWH-015 (10 mg/kg) produced a transient reduction in food intake and significant reduction in fat mass and adipocyte cell size. Importantly, JWH-015 produced an anxiolytic response in the elevated plus maze while having no effect on immobility time in the forced swim test. It should be noted that though the 10 mg/kg dose produced positive effects on the obese state, the possibility that these effects are mediated via non-CB2 receptor mechanisms cannot be ruled out. These results demonstrate a role for CB2 receptors in modulating energy homeostasis and obesity associated metabolic pathologies in the absence of any adverse impact on mood.

Effect of non-alcohol beer on anxiety: Relationship of 5-HIAA

Beer contains hop (Humulus lupulus L.) as flavoring and preservative. This cannabaceae plant, which possesses sedative and hypnotic properties, is present in non-alcoholic beer as well. Likewise regular beer, non-alcoholic beer includes the essential amino acid lysine with relaxing effects, which are related to the inhibition of serotonin receptors. It is known that the main neuroendocrine signal from stress is the release of the hormone cortisol, alongside with the altered levels of the hormone melatonin and the neurotransmitter serotonin. In this study we aimed to analyze the possible anxiolytic effect of non-alcoholic beer on neuroendocrine levels of cortisol, melatonin and serotonin, in a population under stress. To achieve this goal, a healthy student population was enrolled under the stressful conditions evoked by official academic exams. They consumed 1 non-alcoholic beer (330 mL) at dinner time for 14 nights. Melatonin, serotonin and cortisol levels were measured by quantifying their early morning urinary metabolites collected weekly. The consumption of non-acoholic beer reduced significantly the nocturnal serotonin levels whereas there were no substantial changes on melatonin and cortisol levels. However and in line with this, Anxiety/State parameters underwent a significant decreased after consumption of non-alcoholic beer at dinner time regarding to control values. These results point to the anxiolytic response of non-alcoholic beer is performed through the serotoninergic pathway. All in all, consumption of non-alcoholic beer might be an additional tool to deal with serotonin-related stress profile.

Central administration of GPR55 receptor agonist and antagonist modulates anxiety‐related behaviors in rats

G-protein-coupled receptor 55 (GPR55) has been proposed as an atypical cannabinoid receptor, which is activated by lysophosphatidylinositols and some synthetic or endogenous cannabinoid molecules. The exact role of GPR55 receptors in the central nervous system especially in anxiety needs to be evaluated. In this study, the effects of intracerebroventricular (i.c.v.) administration of agonist and antagonist of GPR55 receptor on anxiety-related behaviors in rats were investigated. Here, O-1602 (GPR55 agonist) at the doses of 0.2, 1, and 5μg/rat increased %OAT and %OAE but not the locomotor activity, showing an anxiolytic response, whereas i.c.v. injection of ML193 (GPR55 antagonist) at the doses of 0.1 and 1μg/rat increased anxiety-like behaviors while causing locomotor impairment. The antagonistic effect of ML193 on the anxiolytic-like effect of O-1602 was also evaluated. The results showed that ML193 decreased the anxiolytic-like effect of O-1602. Based on these results, it may be concluded that central GPR55 may have a role in modulation of anxiety-like behaviors in rats. Further experiments are needed to elucidate the exact role of these receptors in anxiety.

Paradoxical widespread c-Fos expression induced by a GABA agonist in the forebrain of transgenic mice with ectopic expression of the GABAA α6 subunit

A GABA-site agonist gaboxadol (4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol) at 3mg/kg induces strong anxiolytic response in a transgenic Thy1α6 mouse line ectopically expressing the GABAA receptor α6 subunit gene under the Thy-1.2 promoter. Now, we compared brain activation patterns between Thy1α6 and wild-type mice to identify brain structures potentially mediating this anxiolytic response. Acutely efficient anxiolytics such as benzodiazepines typically depress most brain regions while activating specifically neurons within the central extended amygdala. Gaboxadol treatment (3mg/kg, i.p., 2h) induced a significant increase in c-Fos expression selectively in many Thy1α6 brain regions including the limbic cortex, anterior olfactory nucleus, septal area and central and basolateral nuclei of amygdala. It failed to activate the lateral part of mediodorsal thalamic nucleus (MDL) in the Thy1α6 mice that was activated in the wild-type mice. Detailed mapping of the α6 subunit mRNA by in situ hybridization revealed expression in the middle layers of the isocortex, olfactory areas, hippocampal formation and basolateral nucleus of amygdala (BLA) in the Thy1α6 forebrain. The ligand autoradiographies (t-butylbicyclophosphoro[35S]thionate ([35S]TBPS) and [3H]Ro 15-4513) revealed high levels of pharmacologically active extrasynaptic α6β and α6βγ2 GABAA receptors in these same areas. However, c-Fos induction by gaboxadol treatment in Thy1α6 brain was not restricted to areas highly expressing the α6-containing GABAA receptors suggesting that indirect pathways lead to the paradoxically widespread activation. Interestingly, the activation pattern by gaboxadol at the dose that is anxiolytic in Thy1α6 mice resembled closely that observed after various fear- and stress-provoking challenges. However, our results are consistent with a recent observation that optogenetic activation of specific neuronal pathways in the extended amygdala mediates anxiolytic responses. Our results suggest that the widespread neuronal inhibition as typically associated with benzodiazepines is not the exclusive mechanism of anxiolysis.

Differential role of AMPA receptors in mouse tests of antidepressant and anxiolytic action

Depression and anxiety often co-occur, and conventional monoamine-facilitating antidepressants show efficacy against symptoms in both disorders. Rodent studies indicate that antidepressant effects of monoamine-based antidepressants involve increased α-amino-3-hydroxy-5- methyl-4-isoxazolepropionic acid glutamate receptor (AMPAR) neurotransmission, and positive allosteric modulators (PAMs) at AMPARs produced antidepressant-like effects in rodents. While this suggests that increased AMPAR-mediated neurotransmission is beneficial in depression management, preclinical studies addressing AMPARs in relation to anxiety have given ambiguous results with both anxiolytic-like and anxiogenic-like effects observed after AMPAR blockade. This study systematically compared the effects of the AMPAR potentiator LY451646 and the AMPAR antagonist GYKI-53655 on depression-related behaviour using the mouse forced swim (FST) and tail suspension tests (TST), and anxiety-related behaviour using the elevated zero maze (EZM), marble burying (MB) and novelty-induced hypophagia (NIH) tests. The serotonin-selective antidepressant citalopram was included for comparison. Due to the importance of AMPARs in learning and memory we also tested if GYKI-53655 disrupted performance in the V-maze test for attention-dependent behaviour, and the social transmission of food preference (STFP) test of long-term memory. LY451646 (3 mg/kg) showed an antidepressant-like profile in the FST and TST, and GYKI-53655 (≥5 mg/kg) had a depressogenic-like effect in the TST but no effect in the FST. Conversely, GYKI-53655 produced marked anxiolytic-like effects in the EZM (≥2.5 mg/kg), MBT (≥2.5 mg/kg), and NIH tests (≥5 mg/kg), while LY451646 (≥3 mg/kg) increased anxiety-like behaviour in the EZM. Citalopram showed an antidepressant-like effect in the FST (≥10 mg/kg), but not TST, an anxiolytic-like effect in the EZM (≥3 mg/kg) and MB test (≥2.5 mg/kg), and an anxiogenic-like effect in the NIH test (≥30 mg/kg). GYKI-53655 did not affect cognitive performance in the V-maze or STFP tests. Collectively, these findings suggest a differential role of AMPARs in depression and anxiety, with AMPAR activation promoting antidepressant responses and AMPAR inhibition promoting anxiolytic responses. The potential of AMPARs as a novel target in depression and anxiety pharmacotherapy is discussed.

Evaluation of anxiolytic potency of essential oil and S-(+)-linalool from Cinnamomum osmophloeum ct. linalool leaves in mice

Cinnamomum osmophloeum ct. linalool (土肉桂 tǔ ròu guì) is one chemotype of the indigenous cinnamons in Taiwan. This study examined the anxiolytic potency of leaf essential oil (LEO) from C. osmophloeum ct. linalool and its main constituent on 4-week ICR mice using an open field test (OFT), a light–dark test (LDT) and an elevated plus maze test (EPT). After oral administration of corn oil, LEO (250 mg/kg and 500 mg/kg), S-(+)-linalool (500 mg/kg), R-(−)-linalool (500 mg/kg), and trazodone hydrochloride (75 mg/kg) for 14 days, the anxiolytic effects on mice behavior were evaluated. The results showed that LEO from C. osmophloeum ct. linalool leaves and S-(+)-linalool can significantly increase the time mice remained in the center area of the OFT, the illuminated area of the LDT and the open arms of the EPT without any side effects affecting motor activity, indicating excellent anxiolytic responses. Furthermore, results from the measurements of monoamines in mice brain revealed decreases in serotonin, dopamine, and norepinephrine, which are consistent with their anxiolytic effects in animal models. The findings obtained suggest that LEO from C. osmophloeum ct. linalool and its major compound, S-(+)-linalool, possess anxiolytic properties without any side effects and thus support their potential use in treatment of anxiety disorders.

Genotypic and sex differences in anxiety-like behavior and alcohol-induced anxiolysis in High Drinking in the Dark selected mice

Alcohol use disorders and anxiety disorders are highly comorbid in humans. In rodent lines selected for alcohol drinking, differences in anxiety-like behavior are also seen. The High Drinking in the Dark (HDID) lines of mice are selectively bred for drinking to intoxication during limited access to alcohol, and these mice represent a genetic model of risk for binge-like drinking. The present studies investigated whether these selected lines differ from control (HS) mice in basal anxiety behavior or in anxiolytic response to alcohol. We also assessed the genetic correlation between alcohol drinking in the dark (DID) and basal anxiety-like behavior using existing inbred strain data. Mice of both sexes and HDID replicates (HDID-1 and HDID-2) were tested on an elevated zero maze immediately following a DID test. In general, HDID mice showed more time spent in the open arms after drinking alcohol than HS mice, and open-arm time was significantly correlated with blood alcohol concentration. HDID-1 male mice also showed less anxiety-like behavior at baseline (water-drinking controls). In a separate experiment, HDID-1 and HS mice were tested for anxiolytic dose-response to acute alcohol injections. Both genotypes showed increasing time spent in the open arms with increasing alcohol doses, and HDID-1 and female mice had greater open-arm time across all doses. HDID-1 control males showed lower anxiety-like behavior than the HS control males. Inbred strain data analysis also showed no significant genetic relationship between alcohol DID and anxiety. These findings suggest that HDID selection has not produced systematic changes in anxiety-like behavior or sensitivity to alcohol-induced anxiolysis, though there is a tendency in the male mice of the first replicate toward reduced basal anxiety-like behavior. Therefore, anxiety state and sensitivity to alcohol's anxiolytic effects do not appear to contribute significantly to the high drinking behavior of the HDID mice.

Quantitative cross-species extrapolation between humans and fish: the case of the anti-depressant fluoxetine.

Fish are an important model for the pharmacological and toxicological characterization of human pharmaceuticals in drug discovery, drug safety assessment and environmental toxicology. However, do fish respond to pharmaceuticals as humans do? To address this question, we provide a novel quantitative cross-species extrapolation approach (qCSE) based on the hypothesis that similar plasma concentrations of pharmaceuticals cause comparable target-mediated effects in both humans and fish at similar level of biological organization (Read-Across Hypothesis). To validate this hypothesis, the behavioural effects of the anti-depressant drug fluoxetine on the fish model fathead minnow (Pimephales promelas) were used as test case. Fish were exposed for 28 days to a range of measured water concentrations of fluoxetine (0.1, 1.0, 8.0, 16, 32, 64 µg/L) to produce plasma concentrations below, equal and above the range of Human Therapeutic Plasma Concentrations (HTPCs). Fluoxetine and its metabolite, norfluoxetine, were quantified in the plasma of individual fish and linked to behavioural anxiety-related endpoints. The minimum drug plasma concentrations that elicited anxiolytic responses in fish were above the upper value of the HTPC range, whereas no effects were observed at plasma concentrations below the HTPCs. In vivo metabolism of fluoxetine in humans and fish was similar, and displayed bi-phasic concentration-dependent kinetics driven by the auto-inhibitory dynamics and saturation of the enzymes that convert fluoxetine into norfluoxetine. The sensitivity of fish to fluoxetine was not so dissimilar from that of patients affected by general anxiety disorders. These results represent the first direct evidence of measured internal dose response effect of a pharmaceutical in fish, hence validating the Read-Across hypothesis applied to fluoxetine. Overall, this study demonstrates that the qCSE approach, anchored to internal drug concentrations, is a powerful tool to guide the assessment of the sensitivity of fish to pharmaceuticals, and strengthens the translational power of the cross-species extrapolation.

Single trial nicotine conditioned place preference in pre-adolescent male and female rats

The mean age of first voluntary tobacco inhalation is 12.3years (DiFranza et al., 2004). 60% of smokers start smoking before the age of 14 and 90% are dependent before reaching the age of 19. Females are typically more sensitive to nicotine than males yet few studies examine the effects of nicotine on the reward systems in pre-adolescent female subjects. This study utilized the single trial conditioned place preference (CPP) test in very young (postnatal day 25–27) rats of both sexes. Latent effects on anxiety and amphetamine response were determined 5 and 7days following a second nicotine exposure. Results show that 0.05mg/kg nicotine induced CPP in females following a single trial while both sexes showed CPP following the 0.5mg/kg dose. Five days later, rats dosed with 0.05mg/kg show increased time on the open arm of the elevated plus maze, an anxiolytic response. While baseline activity was increased in nicotine-exposed males 7days following dosing, amphetamine response was not affected by the treatments in either sex. Therefore, our data suggest that young females are more sensitive to nicotine reward than males supporting a heightened sensitivity of the mesolimbic dopamine system in very young females. However, alterations in baseline activity were only seen in males suggesting that different components of the system are affected by nicotine in each sex. An anxiolytic response to nicotine 5days after dosing may suggest that this very young age group is uniquely affected by this very low nicotine dose. Clearly, nicotine has substantial acute and lasting effects during pre-adolescence at doses substantially lower than seen at older ages as reported by others. These effects, which could potentially result from cigarette or e-cigarette smoking by 11–12year old children , focus attention on the vulnerability of this age group to nicotine.

Hippocampal HDAC4 Contributes to Postnatal Fluoxetine-Evoked Depression-Like Behavior

Fluoxetine treatment in adulthood evokes antidepressant and anxiolytic responses. Paradoxically, postnatal fluoxetine (PNFlx) induces persistent depression- and anxiety-like behaviors. The mechanistic underpinnings of this paradox remain poorly understood. Here, we examined specific molecular changes in the rat hippocampus that accompany perturbed emotionality observed across life following PNFlx. PNFlx-induced hippocampal gene regulation observed in microarray and quantitative PCR studies indicate functional enrichment of genes involved in response to organic substances, protein kinase pathways, DNA binding, and transcriptional repression. We noted specific transcripts (Hdac4, mammalian target of rapamycin (mTOR), Gnai1, protein kinase C gamma (Prkcc), and hyperpolarization-activated cyclic nucleotide-gated channel 1 (Hcn1)) that were consistently dysregulated across life, and selectively influenced by postnatal, but not adult, fluoxetine. Increased histone deacetylase-4 (HDAC4) recruitment, accompanied by decreased activating histone acetylation marks at the mTOR and Gnai1 promoters, indicate a role for HDAC4 in PNFlx-mediated gene dysregulation. Strikingly, coadministration of the HDAC inhibitor sodium butyrate with PNFlx prevented the dysregulation of Hdac4 and mTOR, and the emergence of depression- and anxiety-like behavior. Importantly, we also find that retreatment of PNFlx animals with fluoxetine in adulthood reversed the increased Hdac4 expression, prevented HDAC4 recruitment to the mTOR and Gnai1 promoters, and attenuated the decline in mTOR and Gnai1 expression, coincident with normalization of PNFlx-evoked depression- and anxiety-like behavior. Further, we show that viral-mediated hippocampal overexpression of Hdac4 was sufficient to induce depression-, but not anxiety-, like behavior in adulthood. Our results highlight the unique nature of molecular signatures evoked by PNFlx, and implicate HDAC4 in the dysregulated gene expression and emergence of perturbed emotionality following fluoxetine exposure in early life.

Central Effects of Lipoic Acid Associated With Paroxetine in Mice

Antidepressants, including selective serotonin reuptake inhibitors, are commonly prescribed for the treatment of affective disorders such as anxiety and depression. The purpose of this study was to investigate the central effects of acute administration of paroxetine (PXT) combined with lipoic acid (LA) on various behavioral models in mice. Paroxetine (10 and 20 mg/kg), LA (100 mg/kg), or vehicle was administered, intraperitoneally, 30 minutes before the tests. The results showed that PXT (10 mg/kg) alone and in combination with LA increased locomotor activity. In the anxiety models studied, an anxiolytic effect was observed after the administration of LA and PXT. In the tail suspension test, PXT at both doses and in combination with LA caused a significant decrease in immobility time. These results indicate possible anxiolytic and antidepressant effects of LA associated with PXT. These data suggest that coadministration of LA and PXT may improve anxiolytic and antidepressant responses, and being more effective than each drug alone. However, further studies are necessary to investigate the mechanism by which antioxidants exert antidepressant or anxiolytic action.

Asparagus racemosus attenuates anxiety-like behavior in experimental animal models.

Asparagus racemosus Linn. (AR) is used worldwide as a medicinal plant. In the present study, the anxiolytic activity of standardized methanolic extract of root of AR (MAR) was evaluated in open-field test (OFT), hole-board, and elevated plus maze (EPM) tests. Rats received oral pretreatment of MAR in the doses of 50, 100, and 200 mg/kg daily for 7 days and then were evaluated for the anxiolytic activity in different animal models. Both MAR (100 and 200 mg/kg) and diazepam (1 mg/kg, p.o.) increased the grooming behavior, number of central squares crossed, and time spent in the central area during OFT. Further, MAR (100 and 200 mg/kg) increased the head-dip and head-dip/sniffing behavior, and decreased sniffing activity in hole-board test. Furthermore, MAR (100 and 200 mg/kg) increased the percentage entries and time spent to open arm in EPM test paradigm. The anxiolytic activity in the experimental models was similar to that of diazepam. MAR (100 and 200 mg/kg) enhanced the level of amygdalar serotonin and norepinephrine. It also increased the expression of 5-HT2A receptors in the amygdala. In another set of experiment, flumazenil attenuated the anxiolytic effect of minimum effective dose of MAR (100 mg/kg) in OFT, hole-board, and EPM tests, indicating GABAA-mediated mechanism. Moreover, the anxiolytic dose of MAR did not show sedative-like effect in OFT and EPM tests compared to diazepam (6 mg/kg, p.o.). Thus, the anxiolytic response of MAR may involve GABA and serotonergic mechanisms. These preclinical data show that AR can be a potential agent for treatment of anxiety disorders.

Chronic Paroxetine Treatment: Effects on Other Non-Serotonergic Neurotransmitter Systems

Due to its efficacy and acceptability, paroxetine is situated in the top ten of drugs prescribed for the treatment of major depression and essentially all anxiety disorders. Adults under paroxetine treatment report relief after 4-6 weeks of administration; furthermore, this drug can be prescribed for periods lasting longer than one year. Therefore, paroxetine treatment has a pattern of ingestion that is mainly chronic rather than acute. There is a considerable number of reviews in the literature concerning the effects of paroxetine on the serotonergic system; however, the alterations caused by chronic ingestion of this drug in other neurotransmitter systems have received little attention. For this reason, we consider very important to review the experimental studies concerning the effects of chronic paroxetine intake on neurotransmitter levels, neuronal firing rate and the expression of receptors and transporters in different neurotransmitter systems in the brain. According to the experimental data analyzed in this work, we can establish that long-term paroxetine intake has the ability to increase GABA, glutamate, dopamine and noradrenaline levels in the brain. Furthermore, high levels of AMPA, orexine-1,2 and histamine-1 receptors have been reported in different brain regions after treatment with paroxetine over several weeks. In addition, paroxetine has differential effects on neuropeptide systems, such as galanine, opioid receptors and substance P. Available data lead us to establish that chronic ingestion of paroxetine induces changes in several neurotransmitters and neuropeptides, thus illuminating how each one may contribute to the antidepressant and anxiolytic response elicited by this drug. We consider that all reported changes in the neurotransmitter systems should be further considered to individualize clinical treatment and, in the case of patients taking a drug "cocktail", to gain better control over drug interactions and adverse effects.

Paracetamol (Acetaminophen) Administration During Neonatal Brain Development Affects Cognitive Function and Alters Its Analgesic and Anxiolytic Response in Adult Male Mice

Paracetamol (acetaminophen) is one of the most commonly used drugs for the treatment of pain and fever in children, both at home and in the clinic, and is now also found in the environment. Paracetamol is known to act on the endocannabinoid system, involved in normal development of the brain. We examined if neonatal paracetamol exposure could affect the development of the brain, manifested as adult behavior and cognitive deficits, as well as changes in the response to paracetamol. Ten-day-old mice were administered a single dose of paracetamol (30 mg/kg body weight) or repeated doses of paracetamol (30 + 30 mg/kg body weight, 4h apart). Concentrations of paracetamol and brain-derived neurotrophic factor (BDNF) were measured in the neonatal brain, and behavioral testing was done when animals reached adulthood. This study shows that acute neonatal exposure to paracetamol (2 × 30 mg) results in altered locomotor activity on exposure to a novel home cage arena and a failure to acquire spatial learning in adulthood, without affecting thermal nociceptive responding or anxiety-related behavior. However, mice neonatally exposed to paracetamol (2 × 30 mg) fail to exhibit paracetamol-induced antinociceptive and anxiogenic-like behavior in adulthood. Behavioral alterations in adulthood may, in part, be due to paracetamol-induced changes in BDNF levels in key brain regions at a critical time during development. This indicates that exposure to and presence of paracetamol during a critical period of brain development can induce long-lasting effects on cognitive function and alter the adult response to paracetamol in mice.

Alterations in Ethanol-Induced Behaviors and Consumption in Knock-In Mice Expressing Ethanol-Resistant NMDA Receptors

Ethanol's action on the brain likely reflects altered function of key ion channels such as glutamatergic N-methyl-D-aspartate receptors (NMDARs). In this study, we determined how expression of a mutant GluN1 subunit (F639A) that reduces ethanol inhibition of NMDARs affects ethanol-induced behaviors in mice. Mice homozygous for the F639A allele died prematurely while heterozygous knock-in mice grew and bred normally. Ethanol (44 mM; ∼0.2 g/dl) significantly inhibited NMDA-mediated EPSCs in wild-type mice but had little effect on responses in knock-in mice. Knock-in mice had normal expression of GluN1 and GluN2B protein across different brain regions and a small reduction in levels of GluN2A in medial prefrontal cortex. Ethanol (0.75–2.0 g/kg; IP) increased locomotor activity in wild-type mice but had no effect on knock-in mice while MK-801 enhanced activity to the same extent in both groups. Ethanol (2.0 g/kg) reduced rotarod performance equally in both groups but knock-in mice recovered faster following a higher dose (2.5 g/kg). In the elevated zero maze, knock-in mice had a blunted anxiolytic response to ethanol (1.25 g/kg) as compared to wild-type animals. No differences were noted between wild-type and knock-in mice for ethanol-induced loss of righting reflex, sleep time, hypothermia or ethanol metabolism. Knock-in mice consumed less ethanol than wild-type mice during daily limited-access sessions but drank more in an intermittent 24 h access paradigm with no change in taste reactivity or conditioned taste aversion. Overall, these data support the hypothesis that NMDA receptors are important in regulating a specific constellation of effects following exposure to ethanol.

Effects of intra-prelimbic prefrontal cortex injection of cannabidiol on anxiety-like behavior: Involvement of 5HT1A receptors and previous stressful experience

The prelimbic medial prefrontal cortex (PL) is an important encephalic structure involved in the expression of emotional states. In a previous study, intra-PL injection of cannabidiol (CBD), a major non-psychotomimetic cannabinoid present in the Cannabis sativa plant, reduced the expression of fear conditioning response. Although its mechanism remains unclear, CBD can facilitate 5HT1A receptor-mediated neurotransmission when injected into several brain structures. This study was aimed at verifying if intra-PL CBD could also induce anxiolytic-like effect in a conceptually distinct animal model, the elevated plus maze (EPM). We also verified if CBD effects in the EPM and contextual fear conditioning test (CFC) depend on 5HT1A receptors and previous stressful experience. CBD induced opposite effects in the CFC and EPM, being anxiolytic and anxiogenic, respectively. Both responses were prevented by WAY100,635, a 5HT1A receptor antagonist. In animals that had been previously (24h) submitted to a stressful event (2h-restraint) CBD caused an anxiolytic, rather than anxiogenic, effect in the EPM. This anxiolytic response was abolished by previous injection of metyrapone, a glucocorticoid synthesis blocker. Moreover, restraint stress increased 5HT1A receptors expression in the dorsal raphe nucleus, an effect that was attenuated by injection of metyrapone before the restraint procedure. Taken together, these results suggest that CBD modulation of anxiety in the PL depend on 5HT1A-mediated neurotransmission and previous stressful experience.