The gerbil elevated plus-maze I: behavioral characterization and pharmacological validation.

Several neurokinin NK1 receptor antagonists currently being developed for anxiety and depression have reduced affinity for the rat and mouse NK1 receptor compared with human. Consequently, it has proven difficult to test these agents in traditional rat and mouse models of anxiety and depression. This issue has been overcome, in part, by using non-traditional lab species such as the guinea pig and gerbil, which have NK1 receptors closer in homology to human NK1 receptors. However, there are very few reports describing the behavior of gerbils in traditional models of anxiety. The aim of the present study was to determine if the elevated plus-maze, a commonly used anxiety model, could be adapted for the gerbil. Using a specially-designed elevated plus-maze, gerbils exhibited an 'anxious' behavioral profile similar to that observed in rats and mice, i.e., reduced entries into, and time spent exploring, an open, aversive arm. The anxiolytic drugs diazepam (0.03-3 mg/kg i.p.), chlordiazepoxide (0.3-10 mg/kg i.p.), and buspirone (0.3-30 mg/kg s.c.) increased open arm exploration and produced anxiolytic-like effects on risk-assessment behaviors (reduced stretch-attend postures and increased head dips). Of particular interest, the antidepressant drugs imipramine (1-30 mg/kg p.o.), fluoxetine (1-30 mg/kg, p.o.) and paroxetine (0.3-10 mg/kg p.o.) each produced some acute anxiolytic-like activity, without affecting locomotor activity. The antipsychotic, haloperidol, and the psychostimulant, amphetamine, did not produce any anxiolytic-like effects (1-10 mg/kg s.c). The anxiogenic beta-carboline, FG-7142, reduced time spent in the open arm and head dips, and increased stretch-attend postures (1-30 mg/kg, i.p.). These studies have demonstrated that gerbils exhibit an anxiety-like profile on an elevated plus-maze, and that the gerbil elevated plus-maze may have predictive validity for anxiolytics, and antidepressants with potential anxiolytic-like effects.     

Sodium phenobarbitone reverses the anxiogenic effects of compounds acting at three different central sites

Sodium phenobarbitone was tested for its ability to antagonise the anxiogenic effects of compounds acting at three different central sites. These compounds were: FG 7142, a beta-carboline which acts at the benzodiazepine binding site on the GABA-benzodiazepine receptor complex; pentylenetetrazole, which acts at the picrotoxinin site on the GABA-benzodiazepine receptor complex; and yohimbine which is an antagonist at the alpha 2-adrenoceptor. The experiments were carried out in two tests of anxiety using rats. In the social interaction test (the test arena was familiar and dimly lit), FG 7142 (5 mg/kg) and pentylenetetrazole (15 mg/kg) reduced the time spent in social interaction (indicating anxiogenic activity); these effects were reversed by sodium phenobarbitone (35 mg/kg). Sodium phenobarbitone (35 mg/kg) alone decreased locomotor activity as measured in the social interaction test, which was reversed by pentylenetetrazole (15 mg/kg). In the elevated plus-maze, FG 7142 (6.7 mg/kg) pentylenetetrazole (20 mg/kg) and yohimbine (4 mg/kg) reduced the percentage of open-arm entries and the percentage of time spent on the open arms (indicating anxiogenic activity); these effects were reversed by sodium phenobarbitone (35 mg/kg). Sodium phenobarbitone (35 mg/kg) alone significantly increased the percentage of open-arm entries and the percentage of time spent on the open arms (indicating anxiolytic activity). This study, together with previous studies using other clinically-effective anxiolytic drugs, suggests that the ability of a compound to antagonise the effects of anxiogenic agents may be a useful indirect means of predicting anxiolytic activity.     

Involvement of the GABA/benzodiazepine receptor in the axiolytic-like effect of nociceptin/orphanin FQ

We investigated the mechanism underlying the anxiolytic actions of the neuropeptide nociceptin/orphanin FQ (N/OFQ) with an elevated plus-maze test. In mice, intracerebroventricular (i.c.v.) infusions of N/OFQ (0.1 and 0.32 nmol) led to an increase in time spent in the open arms (anxiolytic-like effects). A non-peptidyl N/OFQ receptor (NOP) antagonist, J-113397(1-{(3R,4R)-1-cyclooctylmethyl-3-hydroxymethyl-4-piperidyl}-3-ethyl-1,3-dihydro-2H-benzimidazol-2-one), (1.0 and 3.2 mg/kg, s.c.) blocked the increase induced by N/OFQ. On the other hand, a benzodiazepine receptor antagonist, flumazenil, (10 mg/kg, i.p.) and a GABAA receptor antagonist, (+)-bicuculline, (5.6 mg/kg, i.p.) also inhibited the increase induced by N/OFQ. In rats, microinfusions of N/OFQ (10 and 32 pmol) into the amygdala led to an increase in time spent in the open arms. However, intracranial infusions of N/OFQ (10-100 pmol) into the dorsal hippocampus did not affect the time spent in the open arms. These findings suggest that the anxiolytic-like effects of N/OFQ may be related to the GABA/benzodiazepine system in the amygdala.     

Neurological activities of lapachol and its furano derivatives from Kigelia africana

This study was carried out to investigate some neurological activities of lapachol and other chemical constituents isolated from Kigelia africana in male albino mice using elevated plus-maze (EPM) test, open-field test (OFT), and forced swimming test (FST). The anxiolytic-like and antidepressant effects of these constituents were compared to known active anxiolytic (diazepam, 2 mg/kg) and antidepressant (imipramine, 15 mg/kg) reference drugs. The compounds 1 [50 mg/kg, intraperitoneally (i.p.)] and 3 (100 mg/kg, i.p.) significantly increased the number of lines crossed in the OFT and the duration of immobility in the FST, indicating a possible antidepressant activity, but no significant effect was observed in the EPM test. The compound 4 (100 mg/kg, i.p.) significantly increased the time spent on the open arms, but the increase in number of open arms entries was not significant in the EPM test. Meanwhile, the duration of the immobility time was significant and quite close to that of the standard drug, imipramine used in the FST. The compound 5 (100 mg/kg, i.p.) substantially increased the time spent and entries into open arms of the EPM, and reduced the time spent and entries into closed arms, when compared with saline controls (P < 0.05). This compound also increased the exploratory activity of the mice as well as the swimming duration in the OFT and FST, respectively. These results indicate that among the compounds tested, quinones displayed significant anxiolytic and/or antidepressant effects at all doses tested. Kojic acid, a fungal metabolite whose structure was unambiguously confirmed by single-crystal X-ray studies, is also isolated for the first time from K. africana, suggesting that it is a possible taxonomic marker in the biogenesis of the quinone skeleton.     

Influence of acute or chronic calcium channel antagonists on the acquisition and consolidation of memory and nicotine-induced cognitive effects in mice

Nicotinic cholinergic receptors (nAChRs) form a heterogeneous family of ligand-gated ion channels found in the nervous system. The main objective of our research was to investigate the interaction between cholinergic nicotinic system and calcium homeostasis in cognitive processes using the modified elevated plus maze memory model in mice. The time each mouse took to move from the open arm to either of the enclosed arms on the retention trial (transfer latency, TL2) was used as an index of memory. Our results showed that a single injection of nicotine (0.035 and 0.175 mg/kg) shortened TL2 values, improving memory-related processes. Similarly, L-type calcium channel antagonists (CCAs), i.e., flunarizine, verapamil, amlodipine, nimodipine, nifedipine, and nicardipine (at the range of dose 5–20 mg/kg) administered before or after training, decreased TL2 value improving memory acquisition and/or consolidation. Interestingly, at the subthresold doses, flunarizine, nicardipine, amlodipine, verapamil, and bupropion, a nAChR antagonist, significantly reversed the nicotine improvement of memory acquisition, while flunarizine, verapamil, and bupropion attenuated the improvement of memory consolidation provoked by an acute injection of nicotine (0.035 mg/kg, s.c.). After subchronic administration (14 days, i.p.) of verapamil and amlodipine, two CCAs with the highest affinity for nAChRs, only verapamil (5 mg/kg) impaired memory acquisition and consolidation while both verapamil and amlodipine, at the subthresold, ineffective dose (2.5 mg/kg), significantly reversed the improvement of memory provoked by an acute injection of nicotine (0.035 mg/kg, s.c.). Our findings can be useful to better understand the interaction between cholinergic nicotinic receptors and calcium-related mechanisms in memory-related processes.     

Effect of sildenafil on anxiety in the plus-maze test in mice

Several studies have shown a role of nitric oxide/cyclic guanosine monophosphate signaling pathway in the regulation of anxiety. The effects of the phosphodiesterase (PDE) 5 inhibitors on anxiety are not fully understood. The aim of present study was to investigate the possible role of sildenafil, an inhibitor of cyclic GMP-specific phosphodiesterase, on anxiety in the plus-maze test in mice. Sildenafil at a dose of 0.5 mg/kg had no significant effect on the behavior in the plus-maze test but at doses of 1 and 3 mg/kg induced an anxiogenic effect. The combination of sildenafil (1 mg/kg, i.p.) and methylene blue (1 mg/kg, i.p.) abolished the anxiogenic-like effect of sildenafil. The combination of sildenafil (1 mg/kg, i.p.) and L-arginine (50 mg/kg, i.p.) decreased the percentage of time spent in open arms compared to saline-treated group. Diazepam at a dose of 2 mg/kg significantly increased the percentage of time spent in open arms (p < 0.05). Sildenafil at a dose of 3 mg/kg and the combination of L-arginine (50 mg/kg, i.p.) and sildenafil (1 mg/kg, i.p.) significantly decreased the locomotor activity (p < 0.05). These results suggest that a nitric oxide-cGMP pathway seems to play an important role in sildenafil-induced anxiogenic-like effect.     

Comparative effects of valproate,anxiolytic, or anxiogenic drugs on the light/dark aversion test

The potential anxiolytic-like effects of 200, 300, and 400 mg/kg i.p. of sodium valproate were evaluated in the light/dark aversion test in mice. For comparison, we included the reference anxiolytic drug, diazepam (2.5, 5.0, 10 mg/kg i.p.) as well as putative anxiolytics, i.e., clonidine (0.015, 0.030, 0.060 mg/kg i.p.), verapamil (5, 10, 20 mg/kg i.p.), or anxiogenic drugs, pentylenetetrazol (5, 10, 15 mg/kg i.p.). Results showed that control mice preferred the dark compartment where they spent approximately 70% of their time. After administration of 5 and 10 mg/kg i.p. of diazepam or 400 mg/kg i.p. of valproate, the increase in exploratory behavior in the lit area was associated with an increase both in the number of transitions and in the time spent in the lit area. Pretreatment with 0.030 and 0.060 mg/kg i.p. clonidine caused an increase in the time spent in the lit area. Verapamil had no significant effect on both measures of this test. Pentylenetetrazol, in doses which did not cause convulsions, was anxiogenic. In conclusion, these results in the light/dark aversion test are consistent with clinical data showing that valproate, a GABA-agonist, and clonidine, an α₂ adrenoceptor agonist, possess anxiolytic properties. © 1992 Wiley-Liss, Inc.     

Calcium channel antagonists suppress nicotine-induced place preference and locomotor sensitization in rodents

The influence of calcium channel antagonists on the behavioral sensitization to nicotine-induced hyperlocomotion and place preference was investigated. Locomotor sensitization in mice was produced by injecting nicotine (0.5 mg/kg, i.p.) for 5 consecutive days before placement in an apparatus in which locomotor activity was evaluated for 1 h. One week later, activity of mice was recorded after challenge with the same dose of nicotine. The L-type voltage-dependent calcium channel antagonists: nimodipine (5, 10 and 20 mg/kg, i.p.), verapamil (5, 10 and 20 mg/kg, i.p.) and diltiazem (5, 10 and 20 mg/kg, i.p.) were injected 15 min before each injection of nicotine (induction of sensitization) or acutely 15 min before a challenge nicotine injection (expression of sensitization). It was shown that the calcium channel blockers attenuated both the induction and expression of nicotine-induced locomotor sensitization in a dose-dependent manner. In the place preference paradigm, nicotine produced a place preference to the initially less-preferred compartment paired with its injections during conditioning (0.5 mg/kg, i.p., 4 drug sessions). Pretreatment with nimodipine (10 mg/kg, i.p.), verapamil (10 mg/kg, i.p.) and diltiazem (10 mg/kg, i.p.) blocked nicotine-induced place conditioning. These results suggest the common calcium-dependent mechanisms of nicotine-induced behavioral sensitization and place preference.     

Acute effect of Copaifera reticulata Ducke copaiba oil in rats tested in the elevated plus‐maze: an ethological analysis

Objectives Copaiba oil oleoresin exuded from Copaifera reticulata Ducke (CRD) is commonly used in anti‐inflammatory, healing and anti‐tumoral folk medicines. The purpose of this study was to investigate the putative anxiolytic effect of acute administration of CRD. Methods CRD was administered (100, 400 and 800 mg/kg, p.o.) to male Wistar rats submitted to the elevated plus‐maze model of anxiety using an ethopharmacological analysis. Key findings In comparison with control rats, CRD increased the percentage of entries in the open arms over the entire dose range tested (vehicle, 33.6 ± 4.5; CRD 100 mg/kg, 44.67 ± 3.68; CRD 400 mg/kg, 47.2 ± 2.3; CRD 800 mg/kg, 50.7 ± 2.2) and the percentage of time spent in the open arms of the elevated plus‐maze at the highest dose (800 mg/kg) (vehicle, 26.4 ± 5.7; CRD 800 mg/kg, 52.0 ± 2.7). A standard anxiolytic, diazepam (3 mg/kg, p.o.), was used as a positive control. In a similar way, diazepam increased the percentage of entries and time spent in the open arms when compared with vehicle (% open entries: vehicle, 45.4 ± 1.3; diazepam, 50.7 ± 1.9; % time spent in open arms: vehicle, 28.2 ± 0.9; diazepam, 38.9 ± 1.2). Regarding ethological measures, CRD at the highest dose (800 mg/kg) reduced peeping out (anxiety‐related behaviour) (vehicle, 3.1 ± 0.6; CRD, 0.9 ± 0.2) and increased end‐arm activity (vehicle, 0.2 ± 0.2; CRD, 2.0 ± 0.4), indicating an enhanced tendency of the rats to explore actively the potentially dangerous areas of the maze. Diazepam decreased peeping out (vehicle, 3.3 ± 0.3; diazepam, 1.0 ± 0.2) and flat‐back approach (vehicle, 0.8 ± 0.2; diazepam, 0.2 ± 0.1) and increased end‐arm activity (vehicle, 0.3 ± 0.1; diazepam, 2.5 ± 0.3) and head‐dipping (vehicle, 8.2 ± 0.4; diazepam, 12.0 ± 0.5). Conclusions These data showed, for the first time, that acute treatment with CRD copaiba oil produced a dose‐dependent anxiolytic‐like effect over the dose range tested, on conventional and ethological parameters, without adversely affecting general activity levels.     

Anxiolytic-like profile of propofol, a general anesthetic, in the plus-maze test in mice

The present study was performed to investigate the effect of propofol on anxiety using the elevated plus-maze test. Groups of mice received propofol (20, 40, 60 mg/kg) or diazepam (2 mg/kg), caffeine (30 mg/kg), L-arginine (100 mg/kg), m-chlorophenylpiperazine (m-CPP, 2.5 mg/kg) and then were placed in an elevated plus-maze that was composed of two opposite closed arms and two opposite open arms. Propofol (20, 40, 60 mg/kg) and diazepam (2 mg/kg) significantly increased the percentage of time spent in the open arms compared to control. Caffeine (30 mg/kg) and m-CPP (2.5 mg/kg) decreased the percentage of time spent in the open arms and these effects were antagonized when propofol (40 mg/kg) was administered before the test. L-arginine (100 mg/kg) has also produced anxiogenic effect and this effect was not prevented by propofol. All drugs used in this study did not significantly change locomotor activity. These results suggest that propofol has anxiolytic effect in plus-maze test.     

Amphetamine-induced anxiety-related behavior in animal models

The purpose of this study was to examine the anxiety-related effects of acute and repeated amphetamine administration using the elevated plus maze (EPM) and light/dark box tests in mice. D-amphetamine (2 mg/kg ip, 30 min after injection) had a significant anxiogenic effect only in the EPM test, as shown by specific decreases in the percentage of time spent in the open arms as well as in the percentage of open arm entries. Tolerance to this anxiogenic action developed after 8 days of daily d-amphetamine administration (2 mg/kg, ip). An anxiolytic effect was observed after the ninth injection, i.e. there were specific increases in the percentage of time spent in the open arms and in the percentage of open arm entries. L-type voltage-dependent calcium channel antagonists: nimodipine (5, 10 and 20 mg/kg, ip), flunarizine (5, 10 and 20 mg/kg, ip), verapamil (5, 10 and 20 mg/kg, ip), and diltiazem (5, 10 and 20 mg/kg, ip) were also injected prior to an acute low dose of d-amphetamine or to each injection of subchronic d-amphetamine. Our results revealed that calcium channel blockers dose-dependently attenuated both an anxiogenic effect of d-amphetamine and the development of tolerance to this effect. Our results suggest that neural calcium-dependent mechanisms are involved in the anxiety-related responses to acute and subchronic amphetamine injection that may lead to addiction relapse in human users.     

Examination of the potential antiepileptic activity of calcium antagonists with different sites of action

1. Calcium is proposed to play a role in the genesis of epileptic seizures, and a number of established antiepileptic drugs limit the transport of extracellular calcium into neuronal cells. 2. The aim of the present study was to explore the potential antiepileptic activity of three calcium antagonists: nifedipine (20 mg/kg i.p.), which blocks the calcium channel at its outer mouth; verapamil (30 mg/kg i.p.), which blocks the calcium channel at its inner mouth; and propyl-methylenedioxyindene (pr-MDI; 68, 100 and 120 mg/kg i.p.), which acts intracellularly to inhibit calcium mobilization from the endoplasmic reticulum. 3. In the maximal electroshock test, none of the calcium antagonists provided protection against tonic seizures in mice. Phenytoin (20 mg/kg i.p.), on the other hand, afforded complete protection. 4. In the pentylenetetrazol-induced seizure test, the order of effectiveness of the three calcium antagonists in attenuating the severity of the clonic and tonic seizures in mice was: nifedipine greater than verapamil greater than pr-MDI. All three calcium antagonists were less effective than ethosuximide (200 mg/kg i.p.). 5. These findings indicate that the calcium antagonists would be of no value in the treatment of grand mal epilepsy, while only those agents acting at the outer side of the membrane would have limited usefulness at best against petit mal seizures.     

Anxiolytic-like effect of asiaticoside in mice

The putative anxiolytic activity of asiaticoside was examined in male mice by using a number of experimental paradigms of anxiety, with diazepam being as a positive anxiolytic control. In the elevated plus-maze test, diazepam (1 and 2 mg/kg) or asiaticoside (5 or 10 mg/kg) increased the percentage of entries into open arms and of time spent on open arms. In the light/dark test, as with 1 mg/kg diazepam, asiaticoside (10 and 20 mg/kg) increased the time spent in the light area and the movement in the light area without altering the total locomotor activity of the animals. In the hole-board test, asiaticoside at 10 mg/kg significantly increased head-dipping counts and duration as well as diazepam (0.3 mg/kg). Thus, these findings indicated that asiaticoside exhibited an anxiolytic-like effect. Further studies will be required to assess the generality of present findings to other species and behavioural paradigms.     

Anxiolytic and sedative effects of dehydroeffusol from Juncus effusus in mice

Dehydroeffusol, a phenanthrene isolated from Juncus effusus L., possesses characteristic anxiolytic and sedative properties, as determined by an array of behavioral tests in mice. In the elevated plus-maze test, dehydroeffusol significantly increased the number of entries into the open arms and the time the mice spent in these arms in a dose-dependent manner, with a minimum effective dose of 2.5 mg/kg. Dehydroeffusol also significantly increased the head-dips of mice in the hole-board test in a dose-dependent manner, with a minimum effective dose of 5 mg/kg. Dehydroeffusol reduced mouse locomotion in the open-field test with a minimum effective dose of 5 mg/kg. In the rota-rod test, 1-5 mg/kg dehydroeffusol did not decrease the fall-down time of mice. The above results confirm that dehydroeffusol possesses anxiolytic and sedative properties and does not affect the general movement coordination of mice. This suggests that dehydroeffusol is a novel anxiolytic chemical derived from herbal medicines.     

Interaction between cannabinoid compounds and diazepam on anxiety-like behaviour of mice

Previous studies have suggested that cannabinoidergic system is involved in anxiety. However, a complete picture of cannabinoid association in the anxiety is still lacking. In the present study, we investigated the possible interaction between cannabinoidergic and GABAergic systems in the anxiety-like behaviour of mice. Intraperitoneal (i.p.) administration of the cannabinoid receptor agonist WIN55212-2 (0.25-5 mg/kg), the endocannabinoid transport inhibitor AM404 (0.25-2 mg/kg) and diazepam (0.25-8 mg/kg) dose dependently exhibited an anxiolytic effect evaluated in terms of increase in the percentage of time spent in the open arms in the elevated plus maze (EPM) test. Administration of certain fixed-ratio combinations (3:1 and 1:1) of WIN55212-2 and diazepam produced a synergistic anxiolytic effect, while the 1:3 combination produced an additive effect. In hole-board test, administration of certain ratios of WIN55212-2-diazepam combination significantly altered the animal behaviour compared to groups that received each drug alone. Co-administration of AM404 (1 and 2 mg/kg) and diazepam (0.5 mg/kg) abolished the anxiolytic effect of the former drug in EPM and the latter in hole-board test, respectively. The combination of an ineffective dose of the fatty acid amide hydrolase (FAAH) inhibitor, URB597 (0.3 mg/kg, i.p.) on anxiety-related responses with an ineffective dose of diazepam (0.25 mg/kg, i.p.) led to a synergistic effect. Co-administration of the CB1 receptor antagonist, AM251 (5 mg/kg) and an effective dose of diazepam (2 mg/kg, i.p.) attenuated diazepam-induced elevation of percentage of time spent in open arm, while lower dose of AM251 (0.5 mg/kg) failed to inhibit diazepam-induced anxiolytic effect. Taken together, the present study showed that co-administration of exogenous cannabinoids and diazepam produce additive or synergistic effect at different combinations. Moreover, it has been shown that enhancement of the function of endocannabinoids could increase the anxiolytic effect of diazepam.     

Anxiogenic-like action of caerulein,a CCK-8 receptor agonist,in the mouse: influence of acute and subchronic diazepam treatment

Summary Effects of caerulein, a cholecystokinin octapeptide (CCK-8) receptor agonist, on exploratory activity of mice were investigated. Exploratory and locomotor activity of animals were measured using elevated plus-maze and open field tests. The systemic administration of caerulein at nonsedative doses (100 ng/kg-1 µkg i. p.) resulted in a significant decrease in the exploratory activity of mice. This effect was completely blocked by proglumide, a CCK-8 antagonist (15 mg/kg i. p.), indicating the participation of CCK-8 receptors. Acute treatment with low doses (0.1–0.75 mg/kg i. p.) of diazepam did not attenuate the anxiogenic-like effect of caerulein, but at more high doses of diazepam the coadministration depressed locomotor activity in mice. After subchronic diazepam treatment (2.5 mg/kg once a day, 10 days, i.p.) tolerance was developed toward the sedative effect of diazepam, and 72 h after withdrawal of the drug the animals showed increased anxiety in the plus-maze test. 30 min after the last injection procedure the anxiogenic-like effect of caerulein (500 ng/kg i. p.) on exploration was absent in both diazepam or vehicle groups. However, 72 h after the last pretreatment injection caerulein (500 ng/kg i. p.) reduced significantly the exploratory activity in control group, whereas it was inactive after diazepam withdrawal. The results obtained in this study support the hypothesis that endogenous CCK-8 an CCK-8 receptors are involved in the neurochemistry of anxiety and the anxiolytic action of benzodiazepine tranquillizers. Send offprint requests to: J. Harro at the above address     

Adenosine A1 receptors modulate the anxiolytic-like effect of ethanol in the elevated plus-maze in mice

The anxiolytic property of ethanol is generally accepted to be an important motivational factor for its consumption and the development of alcohol dependence. Recent studies suggest that adenosine receptors mediate important actions of ethanol, such as motor incoordination and hypnotic effects. In addition, several lines of evidence support the involvement of adenosine in anxiety. The aim of the present study was to evaluate the role of adenosine receptors in the anxiolytic-like effect of ethanol in mice. The effects of acute administration of the adenosine receptor antagonists caffeine (nonselective), 8-cyclopentyl-1,3-dipropylxanthine (DPCPX, adenosine A1 receptor antagonist) and 4-(2-[7-amino-2-[2-furyl][1,2,4]triazolo-[2,3-a][1,3,5]triazin-5-yl-amino]ethyl)phenol (ZM241385, adenosine A(2A) receptor antagonist), together with the adenosine A1 receptor agonist 2-chloro-N6-cyclopentyladenosine (CCPA), and their interaction with ethanol in the elevated plus-maze test in mice were studied. The highest doses of caffeine (30.0 mg/kg, i.p.) and DPCPX (6.0 mg/kg, i.p.) produced an anxiogenic-like effect, while CCPA administration (0.25 mg/kg, i.p.) showed an anxiolytic-like activity. The prior administration of "non-anxiogenic" doses of caffeine (10.0 mg/kg, i.p.) and DPCPX (3.0 mg/kg, i.p.), but not ZM241385 (1.0 mg/kg, i.p.), significantly reduced the anxiolytic-like effect of ethanol (1.2 g/kg, i.p.). Moreover, anxiolytic-like response was observed by the co-administration of "non-anxiolytic" doses of CCPA (0.125 mg/kg) and ethanol (0.6 g/kg). These results reinforce the involvement of adenosine in anxiety and suggest that the activation of adenosine A1 receptors, but not adenosine A(2A) receptors, mediate the anxiolytic-like effect induced by ethanol in mice.     

Effects of central administration of gonadotropin-releasing hormone agonists and antagonist on elevated plus-maze and social interaction behavior in rats

The correlation between neuronal mechanism of anxiety and neuroanatomic expression/neuromodulatory role of gonadotropin-releasing hormone (GnRH), points to a role of GnRH in the modulation of anxiety. Therefore, we investigated the influence of GnRH agonists and antagonist on the anxiety-like behavior of rats in the elevated plus-maze and social interaction tests. GnRH agonists, leuprolide [100 or 200 ng/rat, intracerebroventricularly (i.c.v.)] or 6-D-tryptophan luteinizing hormone-releasing hormone (400 ng/rat, i.c.v.), significantly increased percentage of open arms entries, time spent in open arms, and time spent in social interaction. The observed anxiolytic effect of these agents was comparable with diazepam (0.5-1.0 mg/kg, intraperitoneally). Treatment with a GnRH antagonist [pGlu-D-Phe-Trp-Ser-Tyr-D-Ala-Leu-Arg-Pro-Gly-NH2, (100 ng/rat, i.c.v.)], significantly reduced percentage of open arm indices and decreased time spent in social interaction, indicating an anxiogenic-like effect. Further, castrated rats exhibited anxiogenic-like behavior in these tests, which was significantly attenuated by leuprolide (200 ng/rat, i.c.v.) or 6-D-tryptophan luteinizing hormone-releasing hormone (400 ng/rat, i.c.v.), indicating the noninvolvement of peripheral sex hormone in their anxiolytic-like effect, at least in castrated rats. In conclusion, this study indicated a putative role of GnRH in the control of anxiety, and further adds to the importance of investigating the possible role of the hypothalamus-pituitary-gonadal axis in regulating the anxiety-related disorders arising out of hypothalamus-pituitary-adrenal axis dysregulation.     

Anxiogenic activity of Myristica fragrans seeds.

In the present study, the n-hexane extract of Myristica fragrans (MF) seeds, acetone-insoluble part of the n-hexane extract (AIMF) and trimyristin (TM) were assessed for their anxiogenic activity. The MF (10 and 30 mg/kg), AIMF (30, 100, and 300 mg/kg), and TM (10, 30, and 100 mg/kg) administered intraperitoneally exhibited anxiogenic activity in elevated plus-maze (EPM) paradigm. The open-field test and hole-board test were also used to assess anxiogenic activity of AIMF and TM. In the EPM test, MF, AIMF, and TM decreased the time spent by mice in the open arm and the entries in the open arm. Further, the effect of diazepam (1 mg/kg i.p.), serotonin 5-HT3 receptor antagonist, ondansetron (1 mg/kg i.p.), and 5-HT1A receptor agonist, buspirone (1 mg/kg i.p.), on the occupancy in open arm and entries in open arm was significantly reduced by TM. In the open-field test, AIMF as well as TM reduced the number of rearing and locomotion. Both TM and AIMF reduced the number of head pock in the hole-board test. Inhibition of anxiolytic activity of ondansetron (5-HT3 receptor antagonist), buspirone (5-HT1A receptor agonist), and diazepam [acting on gamma-aminobutyric acid (GABAA) receptor] suggests a nonspecific anxiogenic activity of TM and also a link between 5-HT and GABA systems in the anxiogenic activity of TM.     

Calcium-channel antagonists inhibit marble-burying behavior in mice

In the present study, we examined the effects of calcium-channel antagonists on marble-burying behavior, which is an animal model of obsessive-compulsive disorder. Amlodipine (10 mg/kg, i.p.), cilnidipine (10 mg/kg, i.p.), nilvadipine (3 and 10 mg/kg, i.p.), and flunarizine (30 mg/kg, i.p.) significantly inhibited marble-burying behavior in mice. These results suggest that calcium channels may be involved in the marble-burying behavior.