Influence of inflammatory nociception on the anxiolytic-like effect of diazepam and buspirone in rats

Chronic knockdown of the tetraspanin gene CD81 in the mouse nucleus accumbens modulates anxiety and ethanol-related behaviors

CD81, a member of the tetraspanin family, plays important roles in many physiological processes, such as cell motility, attachment, and entry. Yet, CD81 functions in the brain remain unclear. In this study, we investigated the effects of CD81 knockdown, using lentiviral vectors (LV), on anxiety- and ethanol-related behaviors. For this purpose, mice were stereotaxically injected with CD81 shRNA-expressing LV into the nucleus accumbens (Nacc) and were assessed for anxiety-like behavior using the elevated plus maze (EPM) and open field (OF) tests. Alcohol's sedative effects were studied using loss-of-righting-reflex (LORR) and voluntary ethanol intake was assessed using a two-bottle choice (TBC) procedure. Results showed that mice depleted of CD81 exhibited an anxiolytic-like response in the EPM and OF tests with no effect on locomotor activity. In addition, genetic reduction of CD81 in the Nacc increased mice' sensitivity to alcohol's sedative effects in the LORR test, although plasma alcohol concentrations were unaffected. Interestingly, CD81 loss-of-function-induced anxiolysis was accompanied by a significant decrease in ethanol, but not saccharin nor quinine, intake in the TBC procedure. Finally, and following CD81 mRNA quantification, Pearson's correlations showed a significant positive relationship between accumbal CD81 mRNA with anxiety and ethanol-related behaviors. Our data indicate that CD81 is implicated in the pathogenesis of anxiety and alcoholism. Indeed the targeted disruption of CD81, with the resultant decrease in CD81 mRNA in the Nacc, converted ethanol-"preferring" mice into ethanol "non-preferring" mice. Collectively, these findings demonstrate that future CD81-targeted pharmacotherapies may be beneficial for the treatment of anxiety and alcoholism.

Diazepam and SL-327 synergistically attenuate anxiety-like behaviours in mice - Possible hippocampal MAPKs specificity

Intracellular signalling pathways have been extensively studied as therapeutic targets for the treatment of mental diseases. Our attention has been caught by two kinases potentially involved in anxiety, ERK1/2 and CaMKII. The study aimed to examine changes in the activation of ERK1/2 and CaMKII concerning anxiolytic-like behaviours in mice. To evaluate anxiety-related response in mice, we used the open field test and the elevated plus maze test. Behavioural studies were complemented with the immunoblotting analysis to identify proteins of interest in the cortex, hippocampus, and striatum. We analysed the phosphorylation status of ERK1/2 and CaMKII in mice treated with a well-known anxiolytic drug - diazepam. Next, the blockade of ERK1/2 pathway by SL-327, a selective MEK1/2 inhibitor, was checked for anxiolytic action. Finally, the co-administration of subeffective doses of diazepam and SL-327 was investigated for a potential synergistic anxiolytic effect. Anxiolytic effects of acute diazepam are accompanied by decreased p-ERK1/2 and upregulation of p-CaMKII. Subchronic treatment with SL-327 leads to the manifestation of anxiolytic-like behaviours and changes in the phosphorylation status of both kinases in a diazepam-like manner. Co-administration of subeffective doses of SL-327 and diazepam induces anxiolysis, which is CaMKII-independent and correlates to selectively decreased phosphoactive ERK1/2 in the hippocampus. The MEK-ERK pathway is significantly involved in anxiolytic action of diazepam and its prolonged inhibition produces anxiolytic-like phenotype in mice. ERK inhibition could be used to manage anxiety symptoms in a benzodiazepine-sparing regimen for treatment of anxiety.

Evaluation of different intraarticular injection volumes to assess optimum efficient amount; an experimental study in rat knee joints

INTRODUCTION

The injection amount of solutions differs in wide ranges, from 20 to 200 μL in intraarticular injections experiments that was carried out with rats. The 10-fold difference between applied volumes is not acceptable since injection errors might affect the outcomes of the studies significantly. The excessive amount of solution that was injected into the knee joint of rats might end up with leakage of the solution from injection aperture, and damage the articular structures etc. In our preliminary experiments, we mentioned problems during the injection of excessive amount of solution into the rat knee joint. The main purpose of the present study, which was performed with rat knee joints, was to evaluate the applicability of different amounts of solutions used in experiments and to determine the optimal volume for intraarticular injection in rats.

METHODS

The volume of 100 μL water-based stain was administered into knee joints of non-living rats. The legs were dissected to evaluate the possible presence of injected solution outside the knee joint. Then, the decreasing volumes (100 μL, 50 μL, 40 μL and 30 μL) of X-ray contrast solution (lobitridol) were applied into the knees of living rats to investigate whether systemic circulation acts on the leakage outside the joint. The X-ray images of all these joints were also taken to confirm the results.

RESULTS

In nonliving rats, the place where water-based strain overflow from the knee joint was pointed out. The place of leakage is where the tendo musculi extensor digitorum longus leaves outside the joint. In living rats, by using contrast solution, an overflow was noticed in the subdermal place with the intraarticular injection volumes of 100 μL, 50 μL, and 40 μL. No overflow was observed with the intraarticular injection volumes of 30 μL X-ray contrast solution.

DISCUSSION

In conclusion, the injection volume for the knee joints of rats should not exceed the 30 μL for optimum efficiency.

Hippocampus-specific deletion of tissue plasminogen activator "tPA" in adult mice impairs depression- and anxiety-like behaviors

Anxiety and depression are multifactorial disorders that have become prominent health problems all over the world. Neurotrophic factors have emerged underlying pathogenesis of these diseases. Although a number of studies indicate that the hippocampus-brain-derived neurotrophic factor (BDNF) may be involved in these psychiatric illnesses, little is known about the molecular mediators of these disorders. In this study we further investigate the role of tissue plasminogen activator (tPA), a serine protease involved in pro-BDNF cleavage to BDNF, in depression and anxiety-like behaviors in adult mice. To address this issue, we investigated the effect of hippocampus tPA manipulation, using viral vectors, on anxiety- and depression-like behaviors, including the marble burying test (MBT), elevated plus maze (EPM), tail suspension test (TST), novelty suppressed feeding (NSF) and forced swim test (FST). Our results showed that tPA knock-down - using lentiviral vectors expressing specific short hairpin RNAs (LV-shRNA) - increased the number of buried marbles together with the digging time in the MBT and decreased the time spent in open the arms of an EPM. In addition, tPA-knock down in the hippocampus increased immobility in the FST and TST, and increased time to feed in the NSF test. These effects were reversed when tPA-over-expressing vectors (LV-tPA) were injected in the hippocampus. We also found that BDNF protein levels were elevated in the hippocampus of mice receiving tPA-expressing vectors. Together, our results imply that tPA manipulation may provide an effective therapeutic intervention for depression and anxiety disorders.

Buspirone blocks the enhancing effect of the anxiogenic drug RS 79948-197 on consolidation of habit memory

Previous findings indicate that post-training administration of the anxiogenic α(2)-adrenoceptor antagonist RS 79948-197 facilitates the consolidation of dorsal striatal-dependent habit memory. The present study examined the effect of concurrent administration of the anxiolytic serotonin 5-HT(1A) receptor partial agonist buspirone on anxiety-induced facilitation of habit memory. Male Long-Evans rats were trained in a response learning version of a water plus-maze task that requires animals to learn to make the same body turn response on each trial in order to reach a hidden escape platform. Immediately following training on days 1-3, rats received peripheral injections of either saline, buspirone (1.5 mg/kg, 2.0 mg/kg, or 5.0 mg/kg), RS 79948-197 (0.1 mg/kg), or RS 79948-197 and buspirone together. Post-training injections of RS 79948-197 alone significantly enhanced memory consolidation. The highest dose of buspirone (5.0 mg/kg) also enhanced response learning. However, concurrent administration of a dose of buspirone (1.5 mg/kg) that itself had no effect on acquisition blocked the memory enhancing effects of RS 79948-197. These findings suggest that the facilitation of habit memory observed following drug-induced anxiety can be prevented by co-administration of an anxiolytic agent.

Sex differences in baseline and drug-induced behavioural responses in classical behavioural tests

Behavioural pharmacology relies on animal models which are primarily validated using the male laboratory rat. Many researchers solely employ male animals in studies; this is primarily due to concerns about the impact of variations in the female estrous cycle on behavioural responses. The objective of the present study therefore was to examine whether sex has any effect in some commonly employed behavioural pharmacology tests. Male and female Sprague Dawley rats were examined in the following behavioural pharmacology tests: diazepam (DZP) effects on anxiolytic behaviour in the elevated plus maze (EPM); desipramine (DMI) effects on immobility time in the forced swim test (FST); amphetamine (AMP) and apomorphine (APO) effects on locomotor activity in the homecage monitoring apparatus (HCMA). Baseline investigations revealed that females were more active than males in all three tests. DZP increased open arm time and entries for males but not for females. Similarly, significant reduction in immobility time with DMI was found for males in the FST, with no effect observed in females. There was a significant effect of AMP dose on distance moved for both sexes; the peak locomotor stimulating effects were seen following 1-2 mg kg⁻¹ AMP doses for males, while 0.5 mg kg⁻¹ produced the greatest effect in females. APO impaired locomotor activity in both sexes. These results demonstrate that male and female rats respond differently to psychotropic drugs. The absence of female responses to the effects of DZP and DMI in the EPM and FST respectively was due to the high baseline activity levels seen with females; thus behavioural tests must be designed to account for sex differences in baseline behaviours to allow for unambiguous extrapolation of the results.

Increased anxiety-like behaviors in rats experiencing chronic inflammatory pain

For many patients, chronic pain is often accompanied, and sometimes amplified, by co-morbidities such as anxiety and depression. Although it represents important challenges, the establishment of appropriate preclinical behavioral models contributes to drug development for treating chronic inflammatory pain and associated psychopathologies. In this study, we investigated whether rats experiencing persistent inflammatory pain induced by intraplantar injection of complete Freund's adjuvant (CFA) developed anxiety-like behaviors, and whether clinically used analgesic and anxiolytic drugs were able to reverse CFA-induced anxiety-related phenotypes. These behaviors were evaluated over 28 days in both CFA- and saline-treated groups with a variety of behavioral tests. CFA-induced mechanical allodynia resulted in increased anxiety-like behaviors as evidenced by: (1) a significant decrease in percentage of time spent and number of entries in open arms of the elevated-plus maze (EPM), (2) a decrease in number of central squares visited in the open field (OF), and (3) a reduction in active social interactions in the social interaction test (SI). The number of entries in closed arms in the EPM and the distance traveled in the OF used as indicators of locomotor performance did not differ between treatments. Our results also reveal that in CFA-treated rats, acute administration of morphine (3mg/kg, s.c.) abolished tactile allodynia and anxiety-like behaviors, whereas acute administration of diazepam (1mg/kg, s.c) solely reversed anxiety-like behaviors. Therefore, pharmacological treatment of anxiety-like behaviors induced by chronic inflammatory pain can be objectively evaluated using multiple behavioral tests. Such a model could help identify/validate alternative potential targets that influence pain and cognitive dimensions of anxiety.

Evaluation of the Analgesic Effect of Aqueous Extract of Brugmansia suaveolens Flower in Mice: Possible Mechanism Involved

The study was conducted to test the aqueous extract of Brugmansia suaveolens (AEBs) flowers for their antinociceptive effects in mice. In the hot plate test, a significant increase in reaction time for two doses of AEBs at 60, 90, 120, and 150 min after treatment was noted. Pretreatment of animals with naloxone (5 mg/kg, intraperitoneally [IP]) left the antinociceptive effect of AEBs at a dose of 100 mg/kg unaffected at 60, 90, 120, and 150 min after treatment and at a dose of 300 mg/kg at 30 min but not at 90, 120, and 150 min. In the writhing test, the AEBs significantly inhibited acetic acid—induced abdominal constriction and was equally potent at both doses. Pretreatment with naloxone (5 mg/kg, IP) left the antinociceptive effect of both doses of AEBs unaffected. Pretreatment with NG-nitro-L-arginine methyl ester (L-NAME; 20 mg/kg, IP) caused a significant change in the number of abdominal constrictions but did not change the antinociceptive effect of AEBs. Pretreatment of animals with methylene blue also did not change the effect of AEBs on the number of writhing movements in mice. Flumazenil (5 mg/kg, IP) antagonized the antinociceptive effects of diazepam and also reversed the antinociceptive effect of AEBs. AEBs showed a depressant effect on the central nervous system, and the treatment of mice with pentobarbital combined with AEBs increased the animals’ sleeping time in a dose-dependent manner. These results suggest that the antinociceptive activity of AEBs may be related in part to benzodiazepine receptors, although peripheral mechanisms cannot be excluded.

Animal models of anxiety and anxiolytic drug action

Animal models of anxiety attempt to represent some aspect of the etiology, symptomatology, or treatment of human anxiety disorders, in order to facilitate their scientific study. Within this context, animal models of anxiolytic drug action can be viewed as treatment models relevant to the pharmacological control of human anxiety. A major purpose of these models is to identify novel anxiolytic compounds and to study the mechanisms whereby these compounds produce their anxiolytic effects. After a critical analysis of "face," "construct," and "predictive" validity, the biological context in which animal models of anxiety are to be evaluated is specified. We then review the models in terms of their general pharmacological profiles, with particular attention to their sensitivity to 5-HTIA agonists and antidepressant compounds. Although there are important exceptions, most of these models are sensitive to one or perhaps two classes of anxiolytic compounds, limiting their pharmacological generality somewhat, but allowing in depth analysis of individual mechanisms of anxiolytic drug action (e.g., GABAA agonism). We end with a discussion of possible sources of variability between models in response to 5-HTIA agonists and antidepressant drugs.

The relationship between basal level of anxiety and the affective response to inflammation

Pain is a multidimensional experience and is modulated by a number of factors. One such factor that plays a critical role in pain modulation is anxiety. However, the influence of individual differences in anxiety on higher order pain processing in rodents remains unclear. Therefore, the purpose of this study was to identify animals that have baseline levels of high and low anxiety using the elevated plus maze and then measure pain threshold and place escape/avoidance responding (a measure of pain affect) in the animals. As expected, there was a range of baseline behavior in the elevated plus maze that was used to separate animals into high and low anxiety groups. Following carrageenan injection, both groups of animals developed a similar degree of mechanical hypersensitivity and both groups showed similar place escape/avoidance behavior. These findings suggest that individual differences in baseline anxiety levels do not significantly contribute to the development of mechanical sensitivity and do not modulate higher order pain processing related to pain affect and motivation.

Influence of pharmacologically-induced experimental anxiety on nociception and antinociception in rats

Animal studies reveal that diverse environmental stimuli that generate anxiety-like behaviors also induce antinociception; conversely, clinical data show that pain perception is reduced under anxiolysis. This study was conducted to investigate the influence of pharmacologically induced-anxiety on nociception and antinociception. Experimental anxiety levels were measured using the rat burying behavior test. Diazepam (0, 0.5, 1.0 and 2.0 mg/kg, i.p.) or yohimbine (0, 0.5 and 1.0 mg/kg, i.p.) were used as anxiolytic or anxiogenic drugs, respectively. To evaluate the influence of different experimental anxiety levels on nociception, the pain-induced functional impairment in the rat (PIFIR model) was used. Nociception was induced by an intra-articular injection of 15% uric acid into the knee joint of the right hind limb. Diazepam or yohimbine were administered 15 min before uric acid and the ability of the rat to use the injured hind limb was recorded. To analyze the influence of different levels of anxiety on the antinociceptive effects produced by acetylsalicylic acid (0, 31, 100 and 310 mg/kg, p.o.); this analgesic was administered 3.5 h after uric acid. Fifteen min before diazepam (2.0 mg/kg) or yohimbine (1.0 mg/kg) were administered. We found that, in the burying behavior test, diazepam and yohimbine produced a dose-dependent decrease or augment in the cumulative time of burying, effects denoting reduced or increased experimental anxiety, respectively. Diazepam or yohimbine, administered alone, was unable to produce nociception. The results showed an influence of anxiety on nociception since a decreased (by diazepam) or increased (by yohimbine) experimental anxiety prevented nociception. Control experiments showed that acetylsalicylic acid did not modify experimental anxiety in the burying behavior test, but effectively reversed the nociception induced by uric acid (15%) in the PIFIR model. Such antinociceptive effect was unmodified by the anxiolytic or anxiogenic actions of diazepam or yohimbine. Data are discussed on the bases of clinical- and animal-studies revealing interactions between anxiety and nociception.