One-trial tolerance to the effects of chlordiazepoxide in the elevated plus-maze is not due to acquisition of a phobic avoidance of open arms during initial exposure

A single exposure to the elevated plus-maze (EPM) test of anxiety reduces or abolishes the anxiolytic-like efficacy of benzodiazepines. This phenomenon called one-trial tolerance has been suggested to represent the acquisition of a phobic-like response to the open arms during trial 1. The present study was designed to examine the effects of chlordiazepoxide (5 mg/kg, ip) on the behaviour of rats in a conventional EPM apparatus after previous exposure to a four-open-arm EPM, a four-enclosed arm EPM or a conventional EPM, as well as in naive rats. Chlordiazepoxide had clear-cut anxiolytic-like effects (increased percentage of time spent on the open arms) in a traditional EPM in naive rats and in animals previously exposed to a four-open-arm EPM. However, it was ineffective in rats previously exposed to a traditional or a four-closed-arm EPM. Thus, the phenomenon of one-trial tolerance does not depend upon initial open-arm experience.     

Anxiolytic activity of Indian Hypericum perforatum Linn: an experimental study

The putative anxiolytic activity of 50% ethanolic extract of Indian Hypericum perforatum (IHp) was investigated in rats using various experimental paradigms of anxiety viz. open field exploratory behaviour (OFB), elevated plus maze (EPM), elevated zero maze (EZM), novelty induced suppressed feeding latency (FL) and social interaction (SI) tests. Pilot studies indicated that single dose administration of IHp had little to no acute behavioural effects, hence the extract of IHp was administered orally at different dose levels once daily for three consecutive days, while lorazepam (LR) (0.5 mg/kg, i.p.) was administered acutely. IHp extract (100 and 200 mg/kg, p.o.) showed significant anxiolytic effects on all the paradigms of anxiety. The results indicate that IHp and LR induced a significant increase in open field ambulation and slight increase in rearings and activity in centre, whereas grooming and fecal droppings remain unchanged. In EPM, significant augmentation of open arm entries, open arm/closed arm entries ratio and time spent on open arms was noted in IHp treated rats. In EZM test, significant increase in time spent on open arms and entries in open arms were observed, whereas slight increase in head dips and stretched attend postures were also observed. IHp and LR significantly attenuated the novelty induced increase in feeding latency. IHp treated rats also showed significant increase in social interaction in the novel environment. The IHp extracts showed consistent and significant anxiolytic activity in all the tests. The effects induced by 50% ethanolic extract of IHp were less marked than those of lorazepam were.     

Anxiolytic activity of Indian Abies pindrow Royle leaves in rodents: an experimental study

Putative anxiolytic activity of ethanolic extract of Indian A. pindrow Royle leaf was investigated in rats using various experimental paradigms of anxiety viz. open field exploratory behaviour, elevated plus maze (EPM) and elevated zero maze (EZM) tests. Pilot studies indicated that single dose administration of extract had little to no acute behavioural effects, hence the extract was administered orally at different dose levels once daily for three consecutive days, while lorazepam (LR) (0.5 mg/kg, i.p.) was administered acutely. Ethanolic extract of A. pindrow (AP) leaves (50 and 100 mg/kg, p.o.) showed significant anxiolytic effects on all the paradigms of anxiety. The results indicate that AP and LR induced a significant increase in open field ambulation and slight increase in rearings and activity in center, whereas grooming and faecal droppings remain unchanged. In EPM, significant augmentation of open arm entries, and time spent on open arms was noted in AP treated rats. In EZM test, significant increase in time spent on open arms and entries in open arms was observed, whereas slight increase in head dips and stretched attend postures was also observed. The AP extract showed consistent and significant anxiolytic activity in all the tests. The effects induced by ethanolic extract of AP were less marked than those of lorazepam were.     

Behavioral effects of sinomenine in murine models of anxiety

The present study was designed to investigate the putative anxiolytic-like effect of sinomenine in three experimental models of anxiety in male rats and mice. Use of the elevated plus-maze test revealed that sinomenine (20 and 40 mg/kg, p.o.) increased the percentage of open arm entries and diazepam (2 mg/kg, p.o.) increased the percentage of open arm entries, the percentage of time spent on open arms and total arm entries in mice. In the light/dark transition test, sinomenine (20 and 40 mg/kg, p.o.) increased time spent in the light area and diazepam (2 mg/kg, p.o.) increased time spent in the light area and the overall movements in mice. In the social interaction test, the sinomenine-treated animals significantly increased social interaction time in low light unfamiliar (7 mg/kg, p.o.) and high light unfamiliar conditions (7 and 14 mg/kg, p.o.) as well as diazepam (3 mg/kg, p.o.). Sinomenine (28 mg/kg, p.o.) can also decrease squares entered in rats in social interaction test under low light unfamiliar condition. In the open-field test, sinomenine (160 mg/kg) decreased squares entered in mice. Thus, these findings indicated that sinomenine exhibited anxiolytic-like effect.     

Role of free radicals in stress-induced neurobehavioural changes in rats

Effect of restraint stress (RS) and its modulation by antioxidants were evaluated on elevated plus maze (EPM) and open field (OF) tests in rats. Restraint stress (RS for 1 hr) reduced the number of open arm entries, as also the time spent on open arms indicating enhanced anxiogenic response in the EPM test as compared to normal non RS group of rats. Pretreatment with ascorbic acid (100 and 200 mg/kg) and alpha-tocopherol (30 and 60 mg/kg) attenuated these RS-induced effects. In the OF test, RS-reduced (a) ambulations; and (b) rearings, whereas an increase was seen in (a) latency of entry and (b) number of fecal boluses. The RS-induced changes in OF parameters were reversed after pretreatment with the antioxidants, (ascorbic acid and alpha tocopherol). Biochemical data showed that RS enhanced MDA levels in both serum and brain, and these were attenuated after pretreatment with the antioxidants. The pharmacological and biochemical results indicate that free radicals might be involved in such stress-induced neurobehavioural effects.     

Kaempferol from the leaves of Apocynum venetum possesses anxiolytic activities in the elevated plus maze test in mice

The present work evaluated the anxiolytic activity of an aqueous extract of Apocynum venetum L. (Apocynaceae) and bioguided its fractionation using the elevated plus maze (EPM) in mice as a model of anxiety. A single treatment of AV extract markedly increased the percentage time spent on the open arms of the EPM in two distinct concentration ranges of 22.5–30 and 100–125 mg/kg p.o., respectively, indicating a putative anxiolytic-like activity. Fractions showing anxiolytic effects in concentrations equal to 30 or 125 mg/kg of whole extract were antagonized using the benzodiazepine antagonist flumazenil (3 mg/kg i.p.) or the 5-HT_1A receptor antagonist WAY-100635 (0.5 mg/kg i.p.). All active fractions in a concentration equal to 125 mg/kg were effectively blocked by the benzodiazepine antagonist flumazenil, while the anxiolytic activities of fractions in the lower dose equivalent to 30 mg/kg of whole extract were inhibited by the 5-HT_1A receptor antagonist WAY-100635. Through further separation of AV fractions it was possible to isolate and characterize the flavonol kaempferol which showed an anxiolytic-like activity in concentrations from 0.02 to 1.0 mg/kg p.o. The anxiolytic activity of kaempferol was partially antagonized by concomitant administration of flumazenil, but not by WAY-100635. In conclusion, our study clearly demonstrates that AV extract possesses anxiolytic-like activity and that at least one of its flavonoids, kaempferol, can elicit the same kind of neuropharmacological activity.     

Anxiolytic effects of Equisetum arvense Linn. extracts in mice

The petroleum ether (PE), chloroform (CH), ethanol (ETH) and water extracts of E. arvense stems were evaluated for anti-anxiety activity in mice using elevated plus maze model. Ketamine induced hypnosis and actophotometer was used to evaluate sedative effect with various extracts in mice. The results were compared with standard drug diazepam. The ethanolic extract of E. arvense (50 and 100 mg/kg) significantly increased the time-spent and the percentage of the open arm entries in the elevated plus-maze model which was comparable to diazepam. Ethanolic extract (100 mg/kg) prolonged the ketamine-induced total sleeping time and decreased the locomotor activity in mice. The results suggest that the ethanolic extract of E. arvense seems to possess anxiolytic effect with lower sedative activity than that of diazepam. The results could be attributed to the flavonoid content of the ethanolic extract.     

Anxiolytic effect of berberine on exploratory activity of the mouse in two experimental anxiety models: interaction with drugs acting at 5-HT receptors

The aim of this study was to assess the anxiolytic effect of berberine (abbrev. BER) using two experimental anxiety models in the mouse. In the black and white test of anxiety, berberine (100, 500 mg/kg) produced an increase in the first time entry, time spent in the white section, and total changes between two compartments. On the other hand, in the elevated plus-maze test, berberine (100, 500 mg/kg) produced an increase in the time spent and arm entries in the open arms, and a decrease in the time spent and arm entries in the closed arms. Berberine (500 mg/kg) decreased locomotor activity in mice. Furthermore, BER at 100, 500 mg/kg decreased concentrations of NE, DA and 5-HT, and increased the concentrations of VMA, HVA and 5-HIAA in the brain stem. BER also attenuated the anxiogenic effect of WAY-100635, 8-OH DPAT and DOI and enhanced the anxiolytic effect of BUS, p-MPPI and RIT in the elevated plus-maze. These results suggested that berberine at 100 mg/kg had a significant anxiolytic-like effect, which was similar to that observed with 1 mg/kg diazepam and 2 mg/kg buspirone. The anxiolytic mechanism of BER might be related to the increase in turnover rates of monoamines in the brain stem and decreased serotonergic system activity. Moreover, BER decreased serotonergic system activity via activation of somatodendritic 5-HT1A autoreceptors and inhibition of postsynaptic 5-HT1A and 5-HT2 receptors.     

Asparagus racemosus Attenuates Anxiety-Like Behavior in Experimental Animal Models

Asparagus racemosus Linn. (AR) is used worldwide as a medicinal plant. In the present study, the anxiolytic activity of standardized methanolic extract of root of AR (MAR) was evaluated in open-field test (OFT), hole-board, and elevated plus maze (EPM) tests. Rats received oral pretreatment of MAR in the doses of 50, 100, and 200 mg/kg daily for 7 days and then were evaluated for the anxiolytic activity in different animal models. Both MAR (100 and 200 mg/kg) and diazepam (1 mg/kg, p.o.) increased the grooming behavior, number of central squares crossed, and time spent in the central area during OFT. Further, MAR (100 and 200 mg/kg) increased the head-dip and head-dip/sniffing behavior, and decreased sniffing activity in hole-board test. Furthermore, MAR (100 and 200 mg/kg) increased the percentage entries and time spent to open arm in EPM test paradigm. The anxiolytic activity in the experimental models was similar to that of diazepam. MAR (100 and 200 mg/kg) enhanced the level of amygdalar serotonin and norepinephrine. It also increased the expression of 5-HT_2A receptors in the amygdala. In another set of experiment, flumazenil attenuated the anxiolytic effect of minimum effective dose of MAR (100 mg/kg) in OFT, hole-board, and EPM tests, indicating GABA_A-mediated mechanism. Moreover, the anxiolytic dose of MAR did not show sedative-like effect in OFT and EPM tests compared to diazepam (6 mg/kg, p.o.). Thus, the anxiolytic response of MAR may involve GABA and serotonergic mechanisms. These preclinical data show that AR can be a potential agent for treatment of anxiety disorders.     

Anxiolytic-like effects of sinapic acid in mice

Sinapic acid is a phenylpropanoid compound and is found in various herbal materials and high-bran cereals. With the exception of its antioxidant activities, the pharmacological properties of sinapic acid have been rarely reported. The purpose of this study was to characterize the putative anxiolytic-like properties of sinapic acid using an elevated plus-maze (EPM) and hole-board test. Control mice were orally treated with an equal volume of vehicle (10% Tween 80 solution), and positive control mice were treated with diazepam (1 mg/kg, i.p.). Sinapic acid (4 mg/kg, p.o.) significantly increased the percentages of time spent in the open arms of the EPM test (P<0.05). In the hole-board test, sinapic acid also significantly increased the number of head-dips at 4 mg/kg (P<0.05). In addition, the anxiolytic-like properties of sinapic acid examined in the EPM test were blocked by flumazenil or bicuculline, which are GABA(A) antagonists. Moreover, sinapic acid markedly potentiated GABA current in single cortical neurons in a dose-dependant manner, and reactive I(GABA) increased to 1.8 times at 1 muM of sinapic acid. These results suggested that sinapic acid is a prominent anxiolytic agent, and that its anxiolytic-like effects are mediated via GABA(A) receptors and potentiating Cl(-) currents.     

Effects of NMDA Receptor Blockade During the Early Development Period on the Retest Performance of Adult Wistar Rats in the Elevated Plus Maze

The elevated plus maze (EPM) is an animal model of anxiety used to test the effects of anxioselective drugs. The loss of the anxiolytic effect of drugs during the second exposure to the EPM is called the “one trial tolerance” (OTT) phenomenon. The present study was designed to investigate the relationship between the OTT phenomenon and N-methyl-d-aspartate (NMDA) receptor blockade in the early developmental period of rats. NMDA receptor blockade was accomplished using MK-801 treatment given between postnatal days 20–30. Beginning on postnatal day 20, the rats were subcutaneously injected with MK-801 twice a day at the nape of the neck for a period of 10 days (0.25 mg/kg). Increased open arm exploration was observed in MK-801-treated rats during trial 1 (p = 0.001) and trial 2 (p = 0.003). The rats spent less time in the closed arms as compared to the saline animals in trial 1 (p = 0.006), and this time decreased further in trial 2 (p = 0.02). The fecal boli of the MK-801 group was decreased in trial 1 as compared to the saline group (p = 0.01), but was not significantly different in trial 2 (p = 0.08). In conclusion, NMDA receptor blockade using MK-801 produced an anxiolytic-like effect in trials 1 and 2. Furthermore, OTT was not affected by NMDA receptor blockade.     

Oleuropein reduces anxiety-like responses by activating of serotonergic and neuropeptide Y (NPY)-ergic systems in a rat model of post-traumatic stress disorder

Post-traumatic stress disorder (PTSD) is a stress-related mental disorder caused by traumatic experiences. This psychopathological response to traumatic stressors induces anxiety in rats. Oleuropein (OLE), a major compound in olive leaves, reportedly possesses several pharmacological properties, including anti-cancer, anti-diabetic, and anti-atherosclerotic and neuropsychiatric activities. However, the anxiolytic-like effects of OLE and its mechanism of action in PTSD are unclear. The present study used several behavioral tests to examine the effects of OLE on symptoms of anxiety in rats after a single prolonged stress (SPS) exposure by inhibiting the hypothalamic-pituitary-adrenal axis. Male Sprague Dawley rats received OLE (10, 50 and 70?mg/kg, i.p., once daily) for 14 days after SPS exposure. Daily OLE (70?mg/kg) administration significantly increased the number and duration of open arm visits in the elevated plus maze (EPM) test, reduced the anxiety index and grooming behavior in the EPM test, and increased the time spent and number of central zone crossings in the open field test. OLE also blocked the SPS-induced decrease in hippocampal serotonin and neuropeptide Y expression in hippocampus. These findings suggest that OLE has anxiolytic-like effects on behavioral and biochemical symptoms similar to those observed in patients with PTSD.     

Effect of a herbal psychotropic preparation, BR-16A (Mentat), on performance of mice on elevated plus-maze.

Effect of BR-16A on various parameters of anxiety and transfer latency (TL) was studied in mice using elevated plus-maze. BR-16A (50-500 mg/kg) reduced the percentage of time spent in open arms and the percent preference of open arms for the first arm entry following acute as well as chronic drug administration. The total number of arm entries and the percentage of open arm entries remained unaffected. In combination with FG 7142 (10 mg/kg), BR-16A (100-500 mg/kg) further reduced the exploration of open arms. BR-16A reversed scopolamine (0.3 mg/kg)-induced delay in TL on 1st day. The reversal effect of BR-16A was enhanced by aniracetam (50 mg/kg). The data suggest anxiogenic and nootropic actions of BR-16A.     

Antidepressant- and Anxiolytic-Like Effects of New Dual 5-HT1A and 5-HT7 Antagonists in Animal Models

The aim of this study was to further characterize pharmacological properties of two phenylpiperazine derivatives: 1-{2-[2-(2,6-dimethlphenoxy)ethoxy]ethyl}-4-(2-methoxyphenyl)piperazynine hydrochloride (HBK-14) and 2-[2-(2-chloro-6-methylphenoxy)ethoxy]ethyl-4-(2- methoxyphenyl)piperazynine dihydrochloride (HBK-15) in radioligand binding and functional in vitro assays as well as in vivo models. Antidepressant-like properties were investigated in the forced swim test (FST) in mice and rats. Anxiolytic-like activity was evaluated in the four-plate test in mice and elevated plus maze test (EPM) in rats. Imipramine and escitalopram were used as reference drugs in the FST, and diazepam was used as a standard anxiolytic drug in animal models of anxiety. Our results indicate that HBK-14 and HBK-15 possess high or moderate affinity for serotonergic 5-HT₂, adrenergic α₁, and dopaminergic D₂ receptors as well as being full 5-HT_1A and 5-HT₇ receptor antagonists. We also present their potent antidepressant-like activity (HBK-14—FST mice: 2.5 and 5 mg/kg; FST rats: 5 mg/kg) and (HBK-15—FST mice: 1.25, 2.5 and 5 mg/kg; FST rats: 1.25 and 2.5 mg/kg). We show that HBK-14 (four-plate test: 2.5 and 5 mg/kg; EPM: 2.5 mg/kg) and HBK-15 (four-plate test: 2.5 and 5 mg/kg; EPM: 5 mg/kg) possess anxiolytic-like properties. Among the two, HBK-15 has stronger antidepressant-like properties, and HBK-14 displays greater anxiolytic-like activity. Lastly, we demonstrate the involvement of serotonergic system, particularly 5-HT_1A receptor, in the antidepressant- and anxiolytic-like actions of investigated compounds.     

Antidepressant- and anxiolytic-like activities of an oil extract of propolis in rats

PurposePropolis biological effects are mainly attributed to its polyphenolic constituents such as flavonoids and phenolic acids that were recently described in the chemical composition of an extract of propolis obtained with edible vegetal oil (OEP) by our group. The aim of this study was to evaluate the effect of OEP on the behavior of rats.Materials and methodsAn in vivo open field (OF), elevated Plus-maze (EPM), and forced swimming (FS) tests were performed to evaluate locomotor activity, anxiolytic- and antidepressant effects of the extract. Besides, oxidative stress levels were measured in rat blood samples after the behavioral assays by evaluation of the Trolox equivalent antioxidant capacity (TEAC) and nitric oxide levels.ResultsOEP increased locomotion in the OF test (50 mg/kg) and central locomotion and open arm entries in the OF and EPM tests (10–50 mg/kg) and decreased the immobility time in the FS test (10–50 mg/kg). Moreover, OEP reduced nitric oxide levels in response to swim stress induced in rats.ConclusionOEP exerted stimulant, anxiolytic and antidepressant effects on the Central Nervous System and antioxidant activity in rats, highlighting propolis as a potential therapeutic compound for behavior impairment of anxiety and depression.     

Modulation of elevated plus maze behavior after chronic exposure to the anabolic steroid 17alpha-methyltestosterone in adult mice

Exposure to supraphysiological doses of androgens may disrupt affective components of behavior. In this study, behavior of adult C57Bl/6 male mice was studied after exposure to the anabolic androgenic steroid (AAS) 17alpha-methyltestosterone (17alpha-meT; 7.5 mg/kg) via a subcutaneous osmotic pump for 17 days. Controls received vehicle implants (0.9% NaCl + 30% cyclodextrine). On day 15, experimental animals were challenged with an ethanol (EtOH) injection (i.p.; 1 g/kg) while controls received saline injections. Five minutes after the injection, animals were tested in an automated elevated plus maze (EPM) or in automated activity chambers. In addition, injection-free animals were tested for ethanol consumption on day 16 after an overnight water deprivation period. Whereas chronic exposure to 17alpha-meT did not modulate open arm behavior, EtOH-exposed animals made more entries into the open arms than controls (P < 0.05). A significant reduction of risk assessment behaviors (rearing, flat approach behavior, and stretch attended posture) over the EPM was noted for EtOH-exposed animals whereas a reduction in stretch attended postures was observed among 17alpha-meT-exposed animals. Locomotor activity, and light-dark transitions in activity chambers remained unaltered. Exposure to AAS did not modulate EtOH consumption. Our data suggest that exposure to a supraphysiological dose of 17alpha-meT has minimal effects on exploratory-based anxiety.     

Neuropharmacological and molecular docking studies of xanthones from Swertia corymbosa

Anxiety represents a public health problem consistently found to be the most prevalent class of mental disorders among people of all ages. Xanthones possess many biological properties, including neuroprotective, antioxidant or antidepressant-like. In this study, we aimed to investigate anxiolytic-like antidepressant and anticonvulsant properties of isolated xanthones from Swertia corymbosa. We evaluated anxiolytic-like activity of compounds 1–3 in the mouse elevated plus maze (EPM) and open field test (OF). We examined the influence on locomotor activity in mouse to determine if the effect observed in the actophotometer specific. We used step-through rotarod tests to evaluate the motor function and muscle grip. Compounds 1–3 significantly induced an increase in the number of entries into open arms and a decrease in time spent into closed arms at the dose of 50?mg/kg body weight (BW). The compounds also induced increase of rearing and decrease grooming at the doses of 25 and 50?mg/kg BW during the OF test. In addition, compounds induced a significant increase of time taken to enter at the center of the experimental set at the dose of 50?mg/kg BW during the open field test. The compounds 1–3 significantly delayed the onset as well as decreased the pentylenetetrazole and isoniazid-induced seizure tests. Compound 3 pretreatment significantly improved survivals in pentylenetetrazole and isoniazid-induced seizure tests. In silico studies reveal its possible mechanism of action shed on light to develop novel drugs against CNS disorders.     

Anxiolytic-like effect of succinic acid in mice

The putative anxiolytic activity of succinic acid was examined in male mice by using a number of experimental paradigms of anxiety and compared with that of the known anxiolytic compound diazepam. Use of the elevated plus-maze test revealed that diazepam (1.0, 2.0 and 4.0 mg/kg, PO) or succinic acid (3.0 or 6.0 mg/kg, PO) increased the percentage of entries into open arms and of time spent on open arms. In novel food consumption test, succinic acid (3.0, 6.0, and 12.0 mg/kg, IP) caused significant increases in food intake during 5 min when compared with the vehicle. In the stress-induced hyperthermia test, 40 min after drug administration rectal temperature was measured, succinic acid at dose of 1.5 mg/kg, inhibited stress-induced hyperthermia. Thus, these findings indicated that, in contrast with diazepam, succinic acid exhibits anxiolytic-like effect.     

Anxiolytic and antidepressant-like activity of a standardized extract from Galphimia glauca

An infusion prepared with aerial parts from Galphimia glauca has been widely used in Mexican traditional medicine as a remedy for nervous excitement. The sedative activity of a methanolic extract from this plant has been demonstrated by neuropharmacological tests. This effect was attributed to the nor-secotriterpene named galphimine B (GB). In the present work, the anxiolytic and antidepressant-like effects of G. glauca methanolic extract (standardized on GB content, 8.3mg/g) were assayed by using the elevated plus-maze, light-dark test and the forced swimming paradigm, on ICR albino mice. This extract, administered orally, three times (24, 18 and 1h before the test), and in different doses (125, 250, 500, 1,000 and 2,000 mg/kg) was able to increase significantly (p<0.05) the number of entries, as well as the time spent in the open arms of the elevated plus-maze, indicating an anxiolytic-like effect. A similar effect was observed in the light-dark paradigm test, the time spent in the light box was increased in treated mice. Nevertheless, this treatment was unable to change any parameter in the forced swimming test. Altogether, these results suggest an anxiolytic-like effect to the methanolic standardized extract of G. glauca on ICR inbred mice.     

Augmentation of the NO-cGMP cascade induces anxiogenic-like effect in mice.

Several studies have reported the anxiolytic-like effects of various nitric oxide synthase inhibitors in distinct animal models. However, in the context of anxiety, the possible involvement of cyclic GMP, believed to be one of the main targets of NO, remains obscure. Cyclic GMP is degraded by the specific phosphodiesterases in the brain. Therefore, we studied the effect of the selective phosphodiesterase type 5 inhibitor sildenafil in the mouse elevated plus-maze test of anxiety and in the open field test of locomotion. We found that sildenafil (0.05-10 mg/kg i.p.) alone did not affect the behavior of animals in the plus-maze or open field tests, but the anxiogenic beta-carboline DMCM given in a subconvulsive dose (2 mg/kg i.p.) decreased the time spent on open arms in the elevated plus-maze. Treatment with the NO precursor L-arginine (200 mg/kg i.p.) did not modify the behavior of animals in the plus-maze, however, when sildenafil (1 mg/kg i.p.) was administered in combination with L-arginine (200 mg/kg i.p.), both the time spent on the open arms and the percentage of open arm visits were significantly decreased. We conclude that augmentation of the NO-cGMP cascade induces anxiogenic-like effect in mice.