Behavioral analogues of anxiety. Animal models

Anxiolytic-like effects of YL-IPA08, a potent ligand for the translocator protein (18 kDa) via regulating the synaptic plasticity in hippocampus

TSPO, translocator protein (18 kDa) ligands have demonstrated consistent antidepression and anxiolytic effects in several preclinical studies. This study aimed to examine whether YL-IPA08[N-ethyl-N-(2-pyridinylmethyl)-2-(3,4-ichlorophenyl) -7-methylimidazo [1,2-a] pyridine-3-acetamide hydrochloride], a potent and selective TSPO ligand synthesized by our institute, could alleviate anxiety-related behaviors induced by electric shock (ES) and investigate its underlying mechanism. As expected, we showed that chronic treatment with YL-IPA08 significantly reversed anxiety-related behaviors induced by electrical stimulation (0.5 mA, 12 times, duration 1s, interval 10s) exposure. Using the analysis of RNA-sequencing (RNA-seq) technology, it was found that the differential genes associated with the anxiolytic effect of YL-IPA08 were mainly related to synaptic plasticity. Furthermore, YL-IPA08 restored the decreased levels of brain-derived neurotrophic factor (BDNF), synapse-related protein (e.g. synapsin-1 and post-synaptic density95, PSD95), and the number of doublecortin (DCX) + neurons in the hippocampus of post-ES mice. In addition, YL-IPA08 also enhanced the dendritic complexity and dendritic spine density of hippocampal dentate gyrus (DG) granule neurons. Meanwhile, the induction of long-term potentiation (LTP) was significantly enhanced by YL-IPA08. In summary, the findings from the current study showed that YL-IPA08 exerted a clear anxiolytic effect, which might be partially mediated by promoting hippocampal neuroplasticity.

Pentylenetetrazol-like stimulus is not produced following naloxone-precipitated mitragynine withdrawal in rats

RATIONALE

Kratom (Mitragyna speciosa Korth), a native medicinal plant of Southeast Asia, is proposed to exhibit potential therapeutic value as an opioid substitute. However, studies of its negative emotional states resulting from withdrawal particularly of its main psychoactive compound, mitragynine (MG), are limited.

OBJECTIVES

Using the pentylenetetrazol (PTZ) discrimination assay, this study aims to investigate the effects of MG in responding to the PTZ stimulus and to assess the generalisation effects of withdrawal from MG to the PTZ stimulus.

METHODS

Rats (n = 20) were trained on a tandem (FR-10, VI-15) schedule of food reinforcement to press one lever after administration of the anxiogenic compound PTZ (16 mg/kg, i.p.) and an alternate lever after vehicle. Following acute tests, training was suspended, and rats were chronically treated with MG or morphine at 8-h intervals for 9 days and withdrawal was precipitated on the tenth day using naloxone (1 mg/kg, i.p.). The rats were tested for generalisation to PTZ at 2, 8 and 24 h after the last dose of MG or morphine administration.

RESULTS

Unlike morphine that produced dose-related PTZ-like stimulus, MG at 3, 10, 30 and 45 mg/kg doses showed no substitution to the PTZ discriminative stimulus. In contrast to morphine which produced a time-dependent generalisation to the PTZ stimulus, naloxone did not precipitate withdrawal effects in MG-treated rats as they selected the vehicle lever at three withdrawal time points.

CONCLUSION

These results demonstrate that MG produces a very different response to morphine withdrawal that is not associated with anxiogenic-like subjective symptoms. These characteristics of MG may provide further support for use as a novel pharmacotherapeutic intervention for managing opioid use disorder.

Recent advances with 5-HT3 modulators for neuropsychiatric and gastrointestinal disorders

Serotonin (5-hydroxytryptophan [5-HT]) is a biologically active amine expressed in platelets, in gastrointestinal (GI) cells and, to a lesser extent, in the central nervous system (CNS). This biogenic compound acts through the activation of seven 5-HT receptors (5-HT_1-7 Rs). The 5-HT₃ R is a ligand-gated ion channel belonging to the Cys-loop receptor family. There is a wide variety of 5-HT₃ R modulators, but only receptor antagonists (known as setrons) have been used clinically for chemotherapy-induced nausea and vomiting and irritable bowel syndrome treatment. However, since the discovery of the setrons in the mid-1980s, a large number of studies have been published exploring new potential applications due their potency in the CNS and mild side effects. The results of these studies have revealed new potential applications, including the treatment of neuropsychiatric disorders such as schizophrenia, depression, anxiety, and drug abuse. In this review, we provide information related to therapeutic potential of 5-HT₃ R antagonists on GI and neuropsychiatric disorders. The major attention is paid to the structure, function, and pharmacology of novel 5-HT₃ R modulators developed over the past 10 years.

Effect of rutin on anxiety-like behavior and activity of acetylcholinesterase isoforms in specific brain regions of pentylenetetrazol-treated mice

The aim of the present study was to investigate the effect of rutin administration (100 mg/kg/day) to pentylenetetrazol (PTZ)-treated Balb-c mice (60 mg/kg/day), with respect to anxiety-like behavior using both open-field and elevated plus-maze (EPM) tests, and acetylcholinesterase (AChE) activity in salt-soluble (SS) fraction and detergent-soluble (DS) fraction of the cerebral cortex, hippocampus, striatum, midbrain, and diencephalon. Our results demonstrated that the administration of PTZ in 3 doses and the induction of seizures increased significantly anxiety behavior of mice and reduced significantly DS-AChE activity in all brain regions examined, while the reduction in the SS fraction was brain region-specific. Rutin administration to normal mice did not affect their behavior, while it induced a brain region-specific reduction in SS-AChE and a significant decrease in DS-AChE in all brain regions. We demonstrated for the first time that pretreatment of PTZ-mice with rutin (PTZ + Rutin group) prevented the manifestation of anxiety and induced interestingly a further significant reduction on the SS- and DS-AChE activities only in the cerebral cortex and striatum, in comparison with PTZ group. Our results show that rutin exhibits an important anxiolytic effect and an anticholinesterase activity in specific brain areas in the seizure model of PTZ.

Dexamethasone impairs encoding and expression of aversive conditioning promoted by pentylenetetrazole

Behavioral and neuroendocrine responses following threatening situations promote the release of corticosterone, which is known to modulate trauma-related learning and memory process. However, it remains unknown whether the aversive learning generated by interoceptive fear conditioning is affected by glucocorticoid modulation. Therefore, the present study aimed to investigate the role of dexamethasone suppression in encoding and expression of pentylenetetrazole-induced olfactory fear conditioning (OFC) and in contextual second-order conditioning promoted by the conditioned odor. Adult male Long-Evans rats were treated with dexamethasone 60 min before the encoding or the expression in both OFC and contextual second-order conditioning. Dexamethasone treatment impaired encoding and expression of the OFC, but failed to impair encoding and expression of the contextual second-order conditioning. Altogether, our results show that although OFC and thereafter contextual second-order conditioning may allow the study of traumatic memories, each order of conditioning seems to present specific features related to their pharmacological modulation. These findings highlight the importance of addressing the role of neuromodulatory systems in first-order and second-order conditioning to gain a better understanding of these phenomena and support future therapies related to traumatic memories.

Myogenic differentiation of VCP disease-induced pluripotent stem cells: A novel platform for drug discovery

Valosin Containing Protein (VCP) disease is an autosomal dominant multisystem proteinopathy caused by mutations in the VCP gene, and is primarily associated with progressive muscle weakness, including atrophy of the pelvic and shoulder girdle muscles. Currently, no treatments are available and cardiac and respiratory failures can lead to mortality at an early age. VCP is an AAA ATPase multifunction complex protein and mutations in the VCP gene resulting in disrupted autophagic clearance. Due to the rarity of the disease, the myopathic nature of the disorder, ethical and practical considerations, VCP disease muscle biopsies are difficult to obtain. Thus, disease-specific human induced pluripotent stem cells (hiPSCs) now provide a valuable resource for the research owing to their renewable and pluripotent nature. In the present study, we report the differentiation and characterization of a VCP disease-specific hiPSCs into precursors expressing myogenic markers including desmin, myogenic factor 5 (MYF5), myosin and heavy chain 2 (MYH2). VCP disease phenotype is characterized by high expression of TAR DNA Binding Protein-43 (TDP-43), ubiquitin (Ub), Light Chain 3-I/II protein (LC3-I/II), and p62/SQSTM1 (p62) protein indicating disruption of the autophagy cascade. Treatment of hiPSC precursors with autophagy stimulators Rapamycin, Perifosine, or AT101 showed reduction in VCP pathology markers TDP-43, LC3-I/II and p62/SQSTM1. Conversely, autophagy inhibitors chloroquine had no beneficial effect, and Spautin-1 or MHY1485 had modest effects. Our results illustrate that hiPSC technology provide a useful platform for a rapid drug discovery and hence constitutes a bridge between clinical and bench research in VCP and related diseases.

Perinatal exposure to insecticide fipronil: effects on the reproductive system in male rats

Fipronil is an insecticide widely used in agriculture, veterinary medicine and public health that has recently been listed as a potential endocrine disrupter. In the present study we evaluated the effects of perinatal exposure to fipronil during the period of sexual brain differentiation and its later repercussions on reproductive parameters in male rats. Pregnant rats were exposed (via gavage) to fipronil (0.03, 0.3 or 3 mg kg–1) from Gestational Day 15 until Postnatal Day 7. Fipronil exposure did not compromise the onset of puberty. In adulthood, there was no effect on organ weight or sperm production. Furthermore, there were no adverse effects on the number of Sertoli cells per seminiferous tubule, testicular and epididymal histomorphometry or histopathology or expression patterns of androgen receptor in the testis. Similarly, no changes were observed in the sexual behaviour or hormone levels. However, in rats exposed to fipronil, changes in sperm motility were observed, with a decrease in motile spermatozoa and an increase in non-mobile spermatozoa, which can compromise sperm quality in these rats. Perinatal exposure to fipronil has long-term effects on sperm parameters, and the epididymis can be a target organ. Additional studies should be undertaken to identify the mechanisms by which fipronil affects sperm motility.

Potential role of organochlorine pesticides in the pathogenesis of neurodevelopmental, neurodegenerative, and neurobehavioral disorders: A review

Organochlorine pesticides (OCPs) are persistent and bioaccumulative environmental contaminants with potential neurotoxic effects. The growing body of evidence has demonstrated that prenatal exposure to organochlorines (OCs) is associated with impairment of neuropsychological development. The hypothesis is consistent with recent studies emphasizing the correlation of environmental as well as genetic factors to the pathophysiology of neurodevelopmental and neurobehavioral defects. It has been suggested that maternal exposure to OCPs results in impaired motor and cognitive development in newborns and infants. Moreover, in utero exposure to these compounds contributes to the etiology of autism. Although impaired neurodevelopment occurs through prenatal exposure to OCs, breastfeeding causes postnatal toxicity in the infants. Parkinson's disease (PD) is another neurological disorder, which has been associated with exposure to OCs, leading to α-synuclein accumulation and depletion of dopaminergic neurons. The study aimed to review the potential association between pre- and post-natal exposure to OCs and impaired neurodevelopmental processes during pregnancy and neuropsychological diseases such as PD, behavioral alterations, seizures and autism.

2-(4-substituted piperazin-1-yl)-1,8-naphthyridine-3-carboxylic acids: Novel 5-HT3 receptor antagonists with anxiolytic-like activity in rodent behavioral models

The aim of this study was to investigate the anxiolytic potential of a series of novel carboxylic acid based 1,8 naphthyridines as 5-HT3 receptor antagonists. The pA2 values of all the compounds were determined against agonist 2-methyl-5-hydroxytryptamine in longitudinal muscle myenteric plexus preparations from guinea pig ileum. Compounds with higher pA2 values, particularly those greater than ondansetron, a standard 5-HT3 receptor antagonist, and optimal log P values were screened in mice by using behavioral tests such as a light–dark (L/D) aversion test, elevated plus maze (EPM) test, and an open field test (OFT). In the L/D test, compounds 7a, 7b, 7d, 7e, and 7i (2 mg/kg body mass, intraperitoneal) significantly (P < 0.05) increased the latency time to leave the light compartment, total time spent in the light compartment, and the number of transitions between the light and dark compartments. Compounds 7a, 7d, 7f, 7h, and 7i (2 mg/kg, i.p.) significantly (P < 0.05) increased the time spent in the open arms and the number of entries into the open arms in the EPM test. In addition, compounds 7a, 7d, 7e, 7f, and 7h (2 mg/kg, i.p.) significantly (P < 0.05) increased the ambulation scores and the frequency of rearing in the OFT.

Effect on Emotional Behavior and Stress by Inhalation of the Essential oil from Chamaecyparis obtusa

Various effects have been reported in the literature for the essential oil from Chamaecyparis obtusa (EOCO), such as antibacterial and antifungal activity. In this study, we examined the effect of EOCO on emotional behavior and stress-induced biomarkers. Male ICR mice, aged 5 weeks at the start of each experiment, were individually housed in cages for 1 week. After placing each mouse in a glass container and exposing it to EOCO for 90 min, we then investigated the influence on emotional behavior using the elevated-plus maze (EPM) test, which is one of the evaluation methods for anxiolytic-like behavior. Significant anxiolytic-like effects were observed for the 7.0 mg/L air EOCO ( P<0.05). After the EPM test, mice were dissected and changes in the stress-induced biomarkers within the brain were investigated by examining the amounts of fast nerve growth factor receptor (NGFR) and activity regulated cytoskeletal-associated protein (Arc) gene expression, and brain-derived neurotrophic factor (BDNF) and galactokinase 1 (GLK1) protein expression. Significant increases were observed in the amount of NGFR after inhalation of 7.0 mg/L air EOCO ( P<0.05). These results indicate that EOCO has both anxiolytic-like and stress mitigation effects.

Acquisition of Pavlovian fear conditioning using β-adrenoceptor activation of the dorsal premammillary nucleus as an unconditioned stimulus to mimic live predator-threat exposure

In the present work, we sought to mimic the internal state changes in response to a predator threat by pharmacologically stimulating the brain circuit involved in mediating predator fear responses, and explored whether this stimulation would be a valuable unconditioned stimulus (US) in an olfactory fear conditioning paradigm (OFC). The dorsal premammillary nucleus (PMd) is a key brain structure in the neural processing of anti-predatory defensive behavior and has also been shown to mediate the acquisition and expression of anti-predatory contextual conditioning fear responses. Rats were conditioned by pairing the US, which was an intra-PMd microinjection of isoproterenol (ISO; β-adrenoceptor agonist), with amyl acetate odor-the conditioned stimulus (CS). ISO (10 and 40 nmol) induced the acquisition of the OFC and the second-order association by activation of β-1 receptors in the PMd. Furthermore, similar to what had been found for contextual conditioning to a predator threat, atenolol (β-1 receptor antagonist) in the PMd also impaired the acquisition and expression of OFC promoted by ISO. Considering the strong glutamatergic projections from the PMd to the dorsal periaqueductal gray (dPAG), we tested how the glutamatergic blockade of the dPAG would interfere with the OFC induced by ISO. Accordingly, microinjections of NMDA receptor antagonist (AP5, 6 nmol) into the dPAG were able to block both the acquisition, and partially, the expression of the OFC. In conclusion, we have found that PMd β-1 adrenergic stimulation is a good model to mimic predatory threat-induced internal state changes, and works as a US able to mobilize the same systems involved in the acquisition and expression of predator-related contextual conditioning.

Diphenyl diselenide exerts anxiolytic-like effect in Wistar rats: putative roles of GABAA and 5HT receptors

Diphenyl diselenide [(PhSe)2] is an organoselenium compound which presents pharmacological antioxidant, anti-inflammatory, antinociceptive and antidepressant properties. The present study was designed to investigate the anxiolytic effect of (PhSe)2 in rats, employing the elevated plus maze task. The involvement of 5HT and GABA receptors in the anxiolytic-like effect was also evaluated. (PhSe)2 (5, 25 and 50 micromol/kg, i.p.) did not affect locomotor activity as evaluated in the open open-field test, and learning and memory when assessed in the inhibitory foot-shock avoidance task. However, (PhSe)2 at the 50 micromol/kg dose produced signs of an anxiolytic action, namely a decreased number of fecal boli in the open-field arena and an increased time spent in as well as an increased number of entries to the open arms of the elevated plus maze test. To evaluate the role of GABA and 5HT receptors in the anxiolytic-like effect of (PhSe)2, a selective GABAA receptor antagonist bicuculline, (0.75 mg/kg, i.p.), a non-selective 5HT2A/2C receptor antagonist, ritanserin (2 mg/kg, i.p.), a selective 5HT2A receptor antagonist, ketanserin (1 mg/kg, i.p.), and a selective 5HT1A receptor antagonist, WAY100635 (0.1 mg/kg, i.p.) were used. All the antagonists used were able to abolish the anxiolytic effect of (PhSe)2 suggesting that GABAA and 5HT receptors may play a role in the pharmacological property of this selenocompound in the central nervous system.

Brain reward deficits accompany withdrawal (hangover) from acute ethanol in rats

Withdrawal from an acute bolus injection of ethanol produces affective or emotional signs that include anxiogenic-like behavior and conditioned place aversion. This study assessed whether brain reward deficits that accompany withdrawal from chronic ethanol dependence are also observed upon withdrawal from acute intoxication. Rats were implanted with stimulating electrodes aimed at the medial forebrain bundle in the lateral hypothalamus and trained on a discrete-trial current-intensity brain stimulation reward threshold paradigm. Ethanol intoxication was produced by bolus intraperitoneal injections of ethanol (1.0, 1.5, or 2.0 g/kg). Brain reward thresholds were monitored periodically following the bolus injection (3, 6, 9, 12, 24, 48, 72, 96 h postethanol). Blood samples taken at various intervals postethanol revealed that peak blood alcohol levels (BAL) at all doses tested were reached within 10 min of injection. Following doses of 1.0, 1.5, and 2.0 g/kg ethanol, BAL had declined to undetectable levels within 3-6h postinjection. Withdrawal from a single injection of ethanol resulted in a significant but transient increase in brain reward thresholds only with the highest ethanol dose tested (2.0 g/kg). When acute intoxication and withdrawal episodes were repeated two additional times at weekly intervals, the peak magnitude and duration of threshold elevation increased significantly at the 2.0 g/kg dose of ethanol. A significant but transient increase in thresholds was also seen in the group treated with 1.5 g/kg ethanol during the third and final week of testing. Results indicate that withdrawal from a single exposure to an intoxicating dose of ethanol produces significant brain reward deficits in addition to other affective disturbances previously reported, and that repeated weekly intoxication and withdrawal results in a progressive increase in magnitude and duration of the reward deficit.

Nicotine antagonizes caffeine- but not pentylenetetrazole-induced anxiogenic effect in mice

RATIONALE

Nicotine and caffeine are widely consumed licit psychoactive drugs worldwide. Epidemiological studies showed that they were generally used concurrently. Although some studies in experimental animals indicate clear pharmacological interactions between them, no studies have shown a specific interaction on anxiety responses.

OBJECTIVES

The present study investigates the effects of nicotine on anxiety induced by caffeine and another anxiogenic drug, pentylenetetrazole, in mice. The elevated plus-maze (EPM) test was used to evaluate the effects of drugs on anxiety.

METHODS

Adult male Swiss Webster mice (25-32 g) were given nicotine (0.05-0.25 mg/kg s.c.) or saline 10 min before caffeine (70 mg/kg i.p.) or pentylenetetrazole (15 and 30 mg/kg i.p.) injections. After 15 min, mice were evaluated for their open- and closed-arm time and entries on the EPM for a 10-min session. Locomotor activity was recorded for individual groups by using the same treatment protocol with the EPM test.

RESULTS

Nicotine (0.05-0.25 mg/kg) itself did not produce any significant effect in the EPM test, whereas caffeine (70 mg/kg) and pentylenetetrazole (30 mg/kg) produced an anxiogenic effect, apparent with decreases in open-arm time and entry. Nicotine (0.25 mg/kg) pretreatment blocked the caffeine- but not pentylenetetrazole-induced anxiety. Administration of each drug and their combinations did not produce any effect on locomotor activity.

CONCLUSIONS

Our results suggest that the antagonistic effect of nicotine on caffeine-induced anxiety is specific to caffeine, instead of a non-specific anxiolytic effect. Thus, it may extend the current findings on the interaction between nicotine and caffeine.

Exposure to Common Anesthetic Agents Alters Pup-retrieval Response in Lactating Rtas

This study investigated the lactating stage of rats to determine the effect on maternal behavior of a single exposure to general anesthetic. Lactating Wistar rats were treated with anesthetic doses of pentobarbital (PENT) or ketamine (KET) on day 3 or 9 of lactation, and their behavioral responses were evaluated during a 50-min nursing period, after a 4-h mother-pup separation, on day 12. Exposure to KET on day 9 led to a significantly longer latency to pup-retrieval than that of the control. Duration of pup-retrieval in mothers treated with KET on day 3 and 9 was significantly longer than in the control. Other components of maternal behavior did not differ between the groups. The present findings suggested that general anesthetics have an impact upon pup-retrieval activities, which indirectly represent maternal motivation.

Chlorpyrifos shares stimulus properties with pentylenetetrazol as evaluated by an operant drug discrimination task

Based on previous data from elevated plus-maze tests suggesting a possible anxiogenic effect of the insecticide chlorpyrifos (CPF), the experiment reported here was designed to determine whether this organophosphate (OP) caused an interoceptive discriminative stimulus (IDS) in rats similar to that produced by the anxiogenic drug pentylenetetrazol (PTZ). Rats were trained to discriminate PTZ (20 mg/kg) from saline, using a drug discrimination procedure. When appropriate lever selection was achieved, generalization tests were performed. Tests of various doses of PTZ showed that the drug exerts dose-dependent discriminative control over response. Two more generalization tests were conducted with 250 mg/kg of CPF and 76.8 mg/kg of LiCl for up to 9 days. Results revealed that CPF (250 mg/kg s.c.) produced a PTZ-like IDS that fully substituted for PTZ 24 h after injection and that subjective effects remain for at least 6 days. However, administration of LiCl did not produce any generalization to PTZ on any of the days tested. These results suggest that CPF shares a site of action, and perhaps functional properties, with PTZ that last for several days, are not due to general malaise and should be taken into account in the use of cholinesterase inhibitors in the treatment of different types of dementia.

Effects of GABA(A) compounds on mCPP drug discrimination in rats

Male Long-Evans rats were trained to discriminate mCPP (1.4 mg/kg, i.p.) from saline, using a two-lever, food-reinforced operant task. The GABA(A) antagonist, bicuculline (0.16-0.64 mg/kg), partially substituted for mCPP, whereas the benzodiazepine antagonist, flumazenil (1-10 mg/kg), and the benzodiazepine inverse agonist, Ro 15-4513 (0.25-2.5 mg/kg), failed to substitute for mCPP. Bicuculline produced no change in response rate, whereas Ro 15-4513 dose-dependently decreased responding. Flumazenil produced a small increase in response rates. Flumazenil (10 mg/kg), Ro 15-4513 (1.25 mg/kg), and the benzodiazepine agonists alprazolam (0.64 mg/kg) and diazepam (5 mg/kg) full agonist all failed to block the mCPP discriminative stimulus. When given in combination with mCPP, Ro15-4513 and alprazolam both produced lower response rates than did mCPP alone, whereas flumazenil and diazepam did not significantly alter response rates. These findings provide evidence that GABA(A) antagonists modulate the discriminative stimulus effects of mCPP, but that these effects are not mediated by activity at the benzodiazepine site.

Effects of hippocampal injections of a novel ligand selective for the alpha 5 beta 2 gamma 2 subunits of the GABA/benzodiazepine receptor on Pavlovian conditioning

Benzodiazepine pharmacology has led to greater insight into the neural mechanisms underlying learning and anxiety. The synthesis of new compounds capable of modulating responses produced by these receptors has been made possible by the development of an isoform model of the GABA(A)/benzodiazepine receptor complex. In the current experiment, rats were pretreated with several concentrations of the novel ligand RY024 (an alpha 5 beta 2 gamma 2 -selective benzodiazepine receptor inverse agonist) in the hippocampus and were trained in a Pavlovian fear conditioning paradigm. RY024 independently produced fear-related behavior prior to training and, at the highest concentration, decreased the strength of conditioning observed 24 h after training. These data provide further evidence for the involvement of hippocampal GABA(A)/benzodiazepine receptors in learning and anxiety.

GABA(A)-benzodiazepine receptor complex sensitivity in 5-HT(1A) receptor knockout mice on a 129/Sv background

Previous studies in 5-HT(1A) receptor knockout (1AKO) mice on a mixed Swiss Websterx129/Sv (SWx129/Sv) and a pure 129/Sv genetic background suggest a differential gamma-aminobutyric acid (GABA(A))-benzodiazepine receptor complex sensitivity in both strains, independent from the anxious phenotype. To further investigate these discrepancies, various GABA(A)-benzodiazepine receptor ligands were tested in different behavioral paradigms in 1AKO and wild type (WT) mice on a 129/Sv background. 1AKO and WT mice responded comparably to alprazolam, flumazenil, alcohol and pentylenetetrazol as measured in the stress-induced hyperthermia paradigm. In addition, sedative-anesthetic effects of pentobarbital measured via the righting reflex were similar and a selected dose of diazepam exerted similar anxiolytic effects in both genotypes in the elevated plus maze. In conclusion, 1AKO mice on a 129/Sv background have undisturbed GABA(A)-benzodiazepine receptor sensitivity in contrast to those described on a mixed Swiss Websterx129/Sv background. The anxious phenotype of 1AKO mice seems to occur independent of the GABA(A)-benzodiazepine receptor complex functioning.

The discriminative stimulus effects of pentylenetetrazol as a model of anxiety: recent developments

Pentylenetetrazol (PTZ), a GABA(A) receptor antagonist and prototypical anxiogenic drug, has been extensively utilized in animal models of anxiety. PTZ produces a reliable discriminative stimulus which is largely mediated by the GABA(A) receptor. Several classes of compounds can modulate the PTZ discriminative stimulus including 5-HT(1A), 5-HT(3), NMDA, glycine, and L-type calcium channel ligands. Spontaneous PTZ-lever responding is seen in trained rats during withdrawal from GABA(A) receptor compounds such as chlordiazepoxide and diazepam, and also ethanol, morphine, nicotine, cocaine, haloperidol, and phencyclidine. This effect is largely mediated by the GABA(A) receptor, which suggests that anxiety may be part of a generalized withdrawal syndrome mediated by the GABA(A) receptor. There are also important hormonal influences on PTZ. Corticosterone plays some role in mediation of its anxiogenic effects. There is a marked sex difference in response to the discriminative stimulus effects of PTZ, and estrogens appear to protect against its anxiogenic effects. Further work with the PTZ drug discrimination is warranted for characterization of anxiety during withdrawal, and the hormonal mechanisms of anxiety.

Effects of NG-nitro-L-arginine methyl ester, 7-nitro indazole, and agmatine on pentylenetetrazol-induced discriminative stimulus in Long-Evans rats

This study was undertaken to determine any role that nitric oxide (NO) may play in the discriminative stimuli produced by pentylenetetrazol (PTZ). The PTZ-induced discriminative stimulus is pharmacologically similar to anxiety in humans and is used in a behavioral assay of anxiety (the PTZ model of anxiety). In the present study, effects of L-N(G)-nitro arginine methyl ester (L-NAME), 7-nitroindazole (7-NI) and agmatine, NO synthase (NOS) inhibitors, on PTZ-induced discriminative stimulus were investigated in male Long-Evans rats (330-350 g). Rats were trained to discriminate PTZ (16 mg/kg) from saline using a two-lever, food-reinforced choice procedure (FR 10). The rats that met the training criteria were injected with L-NAME (15, 30, and 60 mg/kg), 7-NI (15 and 30 mg/kg), agmatine (20, 40, and 60 mg/kg), and saline or vehicle intraperitoneally before each test. They were tested for the PTZ-discrimination to determine if the NOS inhibitors produce discriminative stimulus similar to PTZ or if they block PTZ-induced discrimination. Treatment with the NOS inhibitory drugs neither substituted for PTZ nor altered the PTZ lever selection in any other way. These findings suggest that PTZ-induced discriminative stimulus may not be related to NO-mediated central mechanisms.

Non-human primate models for investigating fear and anxiety

Non-human primates exhibit similar physiological and behavioral responses to anxiety-inducing situations as humans and have, in fact, been successfully employed in both conditioned (i.e. conflict paradigms) and ethologically based tests of fear/anxiety (i.e. involuntary isolation, social interaction, human threat, predator confrontation). In the last decade, a renewed and growing interest in non-human primate models has resulted from the use of the small callitrichid species in behavioral pharmacology and neuroscience. This review focuses on the available non-human primate models for investigating fear/anxiety, addressing their advantages, shortcomings, and conceptual framework on which they are based. Lastly, a new ethologically based model to study anxiety and fear-induced avoidance in callitrichids--the marmoset predator confrontation test--is discussed.

Differential role of the medial and lateral prefrontal cortices in fear and anxiety

In the rat, both the medial and lateral prefrontal cortices (PFC; mPFC and lPFC, respectively) have direct connections with limbic structures that are important in the expression of fear and anxiety. The present study investigated the behavioral effects of excitotoxic lesions of either the mPFC or the lPFC on conditioned and unconditioned fear paradigms. In both unconditioned fear paradigms (open field, elevated plus-maze), lesions of the mPFC decreased anxiety. In fear conditioning, lPFC lesions substantially increased freezing throughout the different phases of the experiment, whereas mPFC lesions increased freezing to contextual cues and showed reduced freezing to discrete cues. These results support the functional role of the PFC in mediating or modulating central states of fear and anxiety and suggest a functional dissociation between the lPFC and mPFC in their role in fear and anxiety.

Effects of ritanserin on ethanol withdrawal-induced anxiety in rats

This study investigated the ability of ritanserin, a 5-HT2 antagonist, to modify ethanol withdrawal (EW) symptoms in two animal models of anxiety: the elevated plus-maze (EPM) and the pentylenetetrazol (PTZ) discrimination assay. Long-Evans hooded rats were given a nutritionally balanced liquid diet containing 4.5% ethanol for 10 days. Twelve hours after removal of the ethanol diet, rats were tested in the EPM. A significant reduction in the open-arm activity and the number of total arm entries was observed, which is indicative of EW. Acute ritanserin (0.16-0.64 mg/kg, i.p., 60 min) had no effect on EW-induced anxiety-like behavior on the EPM. Ritanserin (0.08-0.64 mg/kg, i.p., b.i.d. 12 h) administered concurrently with the last 5 days of ethanol diet produced an increase in the time spent on the open arms of the EPM and reversed the EW-induced reduction in total arm entries. Rats trained to discriminate between saline and PTZ (an anxiogenic drug), selected the PTZ lever during EW. Chronic ritanserin (0.32 mg/kg, i.p., b.i.d. ) did not block PTZ lever responding during EW. On the rotorod, ritanserin (0.32 mg/kg, i.p.) increased the motor incoordination induced by ethanol. In conclusion, coadministration of ritanserin with ethanol prevented the development of EW-induced anxiety as measured by the EPM, but not in the PTZ drug discrimination.

The anxiolytic-like properties of two selective MAOIs, moclobemide and selegiline, in a standard and an enhanced light/dark aversion test

The present study was designed to investigate the putative anxiolytic effects of moclobemide (MOC), a reversible inhibitor of type A monoamine oxidase enzyme (RIMA) antidepressant, in an experimental model of anxiety in mice. The test selected was the light/dark aversion test. In the present investigation, an anxiogenic-like behavior was induced by light, alone as the stimulus (standard version of the test) or by pretreatment with a subconvulsant dose of pentylenetetrazole (PTZ) (15 mg/kg IP) 45 min before testing ("enhanced" version of the test). In mice, the effect of repeated administration for 2 weeks of MOC (0.5, 1, and 5 mg/kg IP) was compared with those of selegiline (SEL) (5, 10, and 20 mg/kg IP), an irreversible and selective MAO-B inhibitor. For comparative purpose, the chronic effect of an established reference anxiolytic, such as lorazepam (LOR) (0.025, 0.05, and 0.10 mg/kg IP), was also evaluated. Results demonstrated that PTZ-treated mice showed a decrease in the number of transitions as well as in the time spent in the lit area, when compared with vehicle controls, an effect characteristic of an anxiogenic response. This anxiogenic-like behavior was reduced by chronic administration of LOR as well as MOC, suggesting an anxiolytic-like effect (as shown in the "standard" version of the test). In addition, the increased aversion of mice for the light compartment of the light/dark box was significantly reduced compared to PTZ-treated mice or vehicle controls. SEL failed to significantly alter the anxiogenic-like behavior induced by subconvulsant doses of PTZ. These data provide additional evidence for the anxiolytic-like effects of MOC administered chronically in the mouse.

Ethanol, but not the anxiolytic drugs buspirone and diazepam, produces a conditioned place preference in rats exposed to conditioned fear stress

The present study was designed to investigate the role of an anxiolytic effect in the development of a drug-associated place preference in rats exposed to conditioned fear stress, using the conditioned place-preference paradigm. The administration of a low dose of ethanol (300 mg/kg, IP) and the anxiolytic drugs, buspirone (1 and 2 mg/kg, IP) and diazepam (1.25 and 2.5 mg/kg, IP), did not produce a place preference in rats that were not exposed to conditioned fear stress. In rats that were exposed to conditioned fear stress, ethanol produced a significant place preference, while buspirone and diazepam failed to produce a place preference. In addition, ethanol, buspirone, and diazepam produced no place preference in rats treated with an anxiogenic dose of pentylenetetrazole (20 mg/kg, IP). A significant decrease in locomotor activity was observed in rats exposed to conditioned fear stress. Ethanol, but not buspirone and diazepam, significantly recovered or increased locomotor activity in rats exposed to conditioned fear stress. Further, the locomotor-stimulating effect of ethanol was markedly enhanced by repeated exposure to conditioned fear stress. These results suggest that the stimulating effect may be strongly related to the development of the rewarding effect of a low dose of ethanol under psychological stress, and that the conditioned place preference paradigm with conditioned fear stress may be useful for studying the rewarding mechanism of ethanol with regard to the interaction between ethanol and psychological stress.

The 5-HT1A receptor and its ligands: structure and function

An overview is presented on progress made in research on 5-HT1A receptors and their ligands since their discovery in 1983. Molecular biology has offered new tools, for example cloned 5-HT1A receptors, their mutants and chimeras to study structure and function. Many compounds, belonging to different chemical classes, display high affinity and selectivity for 5-HT1A receptors. The majority of these compounds are agonists or partial agonists, full antagonists are still scarce. Agonists and partial agonists are active in various animal models of anxiety and depression. Partial receptor agonists have been proven to be effective in general anxiety disorder and depression in man. Potential therapeutic applications for 5-HT1A receptor antagonists are evaluated, for example, in cognition disorders.

Animal models sensitive to anti-anxiety agents

Animal models of anxiety serve two primary purposes in psychopharmacological research. (i) The pharmacological profile observed in the model provides a basis which, depending on its predictive validity, permits an estimation of clinical activity. (ii) Insofar as the 'anxiety' occurring in the animal model is homologous to human anxiety disorders, it is possible to investigate the underlying cellular and molecular mechanisms. The most commonly used laboratory procedures for the identification of anxiolytic effects of drugs are described in this paper.

A primate model of anxiety

Pentylenetetrazol (PTZ; 30 mg/kg, i.m.) produced an acute anxiogenic effect on the behaviour of a social colony of rhesus monkeys acclimatized to laboratory conditions. The animals exhibited hypervigilance, aggressiveness, tachypnea, piloerection and frequent change of posture and also had raised plasma cortisol levels. These effects of PTZ were antagonized by benzodiazepines (diazepam; 1 mg/kg, i.v. and alprazolam; 0.05 mg/kg, p.o.). Non-benzodiazepine anxiolytic drug (buspirone; 10 mg/kg, p.o.) blocked the behavioural effects but not the rise in plasma cortisol concentration. On the other hand, pretreatment with hypnosedative (promethazine; 5 mg/kg, i.m.) or anticonvulsant (sodium valproate; 40 mg/kg, p.o.) agents did not attenuate the effects of PTZ indicating the specificity of its anxiogenic response. The model, thus, seems suitable for evaluation of potential anxiolytic agents.

A discriminative stimulus produced by 1-(3-chlorophenyl)-piperazine (mCPP) as a putative animal model of anxiety

1. This study compares behavioral responses to serotonergic (5HT) agonists and pentylenetetrazol (PTZ) in two behavioral paradigms used as animal models of anxiety. PTZ and mCPP were compared for behavioral effects in elevated plus-maze and interoceptive discriminative stimuli they produce. 2. PTZ is a known anxiogenic drug. The discriminative stimuli of mCPP were selected for comparison because this drug produces "anxiety" in human subjects and "anxiety-like" behaviors in rats, and is a potent agonist at 5HT1B/2C receptors and a partial agonist at 5HT2A receptors. 3. In rats trained to discriminate mCPP (1.4 mg/kg, training dose) from saline, PTZ substituted for the mCPP suggesting the "anxiety-like" properties of the mCPP stimulus. The mCPP stimulus was blocked in a dose-related manner by methysergide, a 5HT2A/2C antagonist but not by the anxiolytic diazepam. TFMPP (a 5HT agonist) and DOI (a 5HT2A/2C agonist) substituted for mCPP, but 1-NP (a 5HT1 agonist and 5HT2C/2A antagonist) did not. 4. In animals trained to discriminate PTZ (16 mg/kg) from saline, mCPP and DOI substituted for PTZ, while TFMPP and 1-NP do not. 5. In the elevated plus maze, time spent on the open arms was reduced by mCPP, DOI and PTZ but there was no significant dose effect of TFMPP, or 1-NP. 6. Methysergide blocked the "anxiety-like" behavior in the EPM. 7. These data suggest that the discriminative stimuli produced by mCPP are based upon its selective actions on 5HT receptors and their use in behavioral pharmacology may offer another tool in studying pharmacology of 5HT based anxiogenic and anxiolytic drugs.

Experimental anxiety and antidepressant drugs: the effects of moclobemide, a selective reversible MAO-A inhibitor, fluoxetine and imipramine in mice

Available evidence derived from behavioural and clinical studies indicates that antidepressant drugs may be effective as anxiolytic agents. In this connection, the present study was designed to assess the behavioural effects of three antidepressant drugs, i.e. imipramine (IMI), a non selective serotonin (5-HT) and noradrenaline re-uptake (NA) inhibitor, fluoxetine (FLU), a selective 5-HT re-uptake inhibitor (SSRI) and moclobemide (MOC), a reversible inhibitor of type A monoamine-oxidase enzyme (RIMA) on anxiety, exploratory and locomotor activities in mice. The experiments used two animal models which attempt to separate these three factors: the "light-dark aversion" test and the "open-field" test. Naive female CD1 mice were administered intraperitoneally (i.p.) 30 min before testing with IMI (10, 20 and 40 mg/kg) or FLU (5, 10 and 20 mg/kg) or MOC (1, 5 and 10 mg/kg) or vehicle. Results showed that IMI (10 and 20 mg/kg), FLU (10 and 20 mg/kg) and MOC (1, 5 and 10 mg/kg) significantly reduced the aversive behavior of mice for the lit area in the light/dark aversion test, suggesting an anxiolytic-like effect. In fact, vehicle controls preferred the dark box where they spent approximately 70% of their time, indicating that light serves as an anxiogenic stimulus. Importantly, the anxiolytic-like effects of these antidepressant drugs were not associated with any increase in locomotor activity. In summary, these data suggest that FLU and the new generation of RIMA, exemplified by MOC, in terms of probable efficacy and greater safety, are of interest as treatment for a broad spectrum of anxiety disorders.

The road to tranquility: the search for selective anti-anxiety agents

The earliest treatments of anxiety included cathartics and emetics, which were used to remove the excess of black bile (hence our word melancholia) thought to be responsible for the patient's demeanor. By the 1700s, physicians were prescribing drugs that are more selective for the CNS, chiefly opium and strengthening tonics. In the 1860s, cardioactive drugs such as atropine, aconite, and digitalis were assumed to counteract anxiety because it could be associated with tachycardia and/or melancholia. A little later, the emergence of laboratory animal models, culminating in the conditioned avoidance response, and also Freudian psychiatry, permitted the evolution of new definitions of anxiety, as well as the introduction of sedative agents such as KBr, chloral hydrate, and barbiturates for its treatment. The first somewhat selective anxiolytics, reserpine, meprobamate, and chlorpromazine, appeared in the early 1950s, while in 1959 the benzodiazepines were the first to prove more selective than all the others in a systematic battery of screening tests.

Alcohol, anxiolytics and social stress in rats

The main objective was to compare the anxiolytic-like profiles of alcohol, diazepam and gepirone along the stress intensity gradient which characterizes consecutive phases of a social confrontation. The acute social stress situation consisted of initially placing the experimental rat as an intruder into the homecage of a resident while the resident was not present, termed the "anticipatory" phase, thereafter permitting brief physical agonistic interactions with the re-introduced resident until the intruder was forced into a submissive supine posture and emitted ultrasonic vocalizations (USV), and eventually exposing the intruder to the resident's threats for 1 h, while being shielded from potential injurious attacks. The hyperthermia, measured via telemetry, in the "anticipatory" phase prior to defeat and in reaction to threats, was decreased by alcohol, gepirone and diazepam; alcohol and gepirone were also effective in attenuating "anticipatory" tachycardia. Alcohol, like gepirone and diazepam, also decreased defensive responses and ultrasonic vocalizations in the "anticipatory" phase of the confrontation, but none of these drugs affected defensive reactions to threats which immediately followed defeat. Gepirone had no systematic sedative effects throughout the confrontation; infact, it dose-dependently reduced the stress-induced suppression of locomotor activity during the "anticipatory" phase. In contrast, at higher doses, alcohol as well as diazepam had marked sedative effects as evidenced by several behavioral parameters (i.e. lie, crouch, walk). The anxiolytic-like profile of hyperthermia, tachycardia, USV and defensive behavior in the "anticipatory" phase of the confrontation by alcohol, gepirone and diazepam contrasted with the lack thereof during the more intense reactive phase. This differential pattern of effects appears to be relevant to the clinical distinctions between anticipatory anxiety and other affective disturbances.

Defeat engenders pentylenetetrazole-appropriate responding in rats: antagonism by midazolam

Defeat and the threat of defeat by an aggressive conspecific is stressful and may engender an anxiety- or fear-like state in animals; the present experiment investigated whether defeat generalized to the discriminative stimulus properties of PTZ and how benzodiazepine receptors were involved in this generalization. Separate groups of male Long-Evans rats (Rattus norvegicus) were trained to discriminate 20 mg/kg pentylenetetrazole (PTZ) or 0.4 mg/kg midazolam (MDZ) from saline in a two-choice drug-discrimination task. After establishing stimulus control, PTZ- and MDZ-trained rats were exposed to an aggressive conspecific which resulted in defeat, as defined by the display of defensive and submissive postures as well as audible and ultrasonic vocalizations. Administration of saline after defeat resulted in greater than 80% PTZ lever selection in 15 out of 25 PTZ-trained rats; this effect was attenuated through pretreatment with MDZ (1 mg/kg). Furthermore, short-term defeat substitution for the PTZ discriminative stimulus was not accompanied by long-term changes in the post-defeat generalization curves for PTZ and MDZ when compared to pre-defeat generalization curves. Nor did defeat alter the antagonism of PTZ by diazepam (2.5 mg/kg) or MDZ by flumazenil (10 mg/kg). In order further to characterize the necessary features for defeat substitution for the PTZ discriminative stimulus, exposure to a threatening conspecific was also attempted by PTZ-trained rats protected from physical contact with a wire mesh cage. In these tests, saline continued to engender greater than 50% PTZ lever responding in 15 of 25 rats.(ABSTRACT TRUNCATED AT 250 WORDS)

An animal model for measuring behavioral responses to anxiogenic and anxiolytic manipulations

A method for measuring behavioral responses of rats to both anxiolytic and anxiogenic manipulations, the open field drink test (OFDT), is described. This method utilizes the concept that in the open field, appetitive behavior is reduced because of the ambient level of fear experienced in such an environment. For the OFDT, rats were given restricted access to water for 1 h per day for 3 days, and then their behavior was assessed in an open field that contained a water spout at its center. Use of the open field permitted a number of measures to be taken; of these, "time spent drinking" was most sensitive in detecting differences. Three experiments showed that the OFDT: a) permitted dissociation between behavioral responses to an anxiolytic (diazepam) and an anxiogenic (FG7142) drug, b) detected a dose-response relationship for an anxiolytic drug (diazepam), and c) detected behavioral responses to environmental manipulations designed to increase fear (presence of an olfactory cue from rats that had received foot shock). Advantages of this test over previously described methods are outlined, and several guidelines are provided to aid investigators in using this behavioral test.

Discriminative stimulus properties of the benzodiazepine receptor inverse agonist methyl-6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate (DMCM)

The purpose of this study was to determine whether rats could be trained to discriminate the stimulus properties of the benzodiazepine (BZ) receptor inverse agonist DMCM from saline in a conditioned taste aversion paradigm. On a drug trial, water-deprived rats were injected with DMCM (0.55-0.6 mg/kg IP), allowed access to a 0.25% saccharin solution for 30 min, and then injected with LiCl. On non-drug trials, saline injections bracketed the drinking period. Conditioned controls were treated similarly with DMCM and saline on drug and non-drug trials, but received injections of saline instead of LiCl. At the completion of training, CMCM produced a 69% reduction of saccharin consumption on drug trials, compared with 23% for conditioned controls. The stimulus properties of DMCM were then measured by its ability to reduce the preference for saccharin over water in a two-bottle choice test. DMCM reduced saccharin preference in rats that received discrimination training from 68% to 19%, but did not alter saccharin preference in conditioned controls. Other compounds with varying activity at BZ receptors were evaluated for their ability to substitute for the discriminative stimulus effects of DMCM. Two BZ receptor inverse agonists, beta-CCE (10-18 mg/kg) and FG 7142 (3.2-18 mg/kg), substituted completely for DMCM. Partial substitution for DMCM was shown by the BZ receptor antagonist CGS 8216 (3.2-10 mg/kg) and the non-BZ convulsant pentylenetetrazol (10-20 mg/kg). The BZ receptor agonists chlordiazepoxide (0.32-5.0 mg/kg), diazepam (0.32-10 mg/kg), and alprazolam (0.1-3.2 mg/kg) and the BZ receptor antagonist flumazenil (1.0-32 mg/kg) failed to substitute for the DMCM stimulus. Pretreatment with flumazenil (1.0 mg/kg) blocked the stimulus effects of the training dose of DMCM and produced a shift to the right of the DMCM generalization curve. The pattern of compounds that substituted for the DMCM stimulus and the blockade of that stimulus by flumazenil indicate that the stimulus properties of DMCM are associated with its effects as a BZ receptor inverse agonist.

Effects of chlordiazepoxide, buspirone and the 5-HT3 receptor antagonist, BRL 46470, on the behaviour of oestrous and dioestrous female mice when encountering male partners

Ethological procedures were employed to examine the differences in behaviour between oestrous and dioestrous control mice, and to investigate the changes to behavioural responsiveness in oestrous and dioestrous mice induced by treatment with the anxiolytic compounds, chlordiazepoxide (CDP, 21.5 mg/l), buspirone (12.8 mg/l) and the 5-HT3 receptor antagonist, BRL 46470 (40 micrograms/l). Compounds were given in drinking fluid for 6-8 days prior to behavioural observations (average daily intake: CDP--5 mg/kg; buspirone--2.5 mg/kg; BRL 46470--10 micrograms/kg). Behaviour of the females was examined in the "approach-avoidance" situation of 5 min encounters with an unfamiliar male in a neutral cage. Oestrous controls spent more time in social investigation, sniffing of the substrate and scanning than dioestrous controls and spent less time in digging and exploration. Each of the anxiolytic compounds, CDP, buspirone and BRL 46470, significantly raised the duration of social investigation both in oestrous and dioestrous females. Each of these compounds also increased the duration of "digging" by oestrous females, and duration of the social element "investigate" in dioestrous females. Effects on the occurrence of other individual elements within each behavioural category depended on the anxiolytic compound administered and the stage of the ovarian cycle at the time of testing. There were few significant differences between the behaviour of the male partners in each group. It is concluded that in this paradigm both oestrous and dioestrous females are sensitive to the enhancement of social investigation by anxiolytic compounds and that the use of female mice in this test situation may provide a potentially useful method in drug screening.