Anxiolytic effect of carbamazepine in the elevated plus-maze: possible role of adenosine

In order to extend previously reported observations with other animal models of anxiety, the effect of carbamazepine (CBZ) was presently measured in rats placed on the elevated plus-maze. Intraperitoneal injection of CBZ (5–40 mg/kg) increased the percentage of open arm entries as well as the percentage of time spent on the open arms of the maze, without affecting the total number of arm entries. This effect is characteristic of anxiolytic drugs. The inhibitor of adenosine neuronal uptake papaverine (5–40 mg/kg) caused a similar anxiolytic effect, whereas the adenosine receptor antagonist aminophylline (1–4 mg/kg) selectively decreased the percentage of open arm entries, indicative of an anxiogenic effect. Furthermore, the combination of an anxiogenic dose (4 mg/kg) of aminophylline with an anxiolytic dose (40 mg/kg) of CBZ resulted in cancellation of each other effects. Since reported neurochemical evidence shows that CBZ interacts with adenosine receptors, the present results provide preliminary support for a participation of this neurotransmitter in the anxiolytic action of CBZ.     

Decreased reactivity to anxiolytics caused by early protein malnutrition in rats

In order to investigate whether early malnutrition causes lasting changes in the reactivity to anxiolytic drugs, rat dams during lactation (21 days) and pups after weaning until the 49th day of life were fed on 8% casein diet (M rats), while their well-nourished controls received 25% casein (W rats). From day 50 on all animals ate the same balanced diet. Experiments started on the 91st day. Rats deprived for 22 hours drank water containing either 1.8% or 2.7% sodium chloride for 30 min in a test chamber, total intake being measured. Dose-effect curves for diazepam (0.5-5.0 mg/kg, IP), as well as for the nonbenzodiazepine anxiolytics ipsapirone (0.5-5.0 mg/kg), ritanserin (0.05-1.0 mg/kg) and isamoltane (2.5-20.0 mg/kg) were determined in M as well as in W rats. Diazepam and ipsapirone dose-dependently released drinking suppressed by either salt concentration in W rats, but caused little or no effect in M rats. Ritanserin and isamoltane were ineffective in both groups. These and previously reported results show that early protein malnutrition markedly reduces anticonflict effects of anxiolytics, indicating long-lasting impairment of neuronal systems underlying emotional behavior.     

Actions and some interactions of 5-HT1A ligands in the elevated X-maze and effects of dorsal raphe lesions

Effects of 5-HT_1A agonists and partial agonists on open/total arm entry ratio (OTR) have been examined in the elevated X-maze anxiety model. 8-OH-DPAT (0.05–0.2 mg/kg), RU 24969 (0.5–2.0 mg/kg) and BAY R 1521 (0.1–1.2 mg/kg) produced dose-dependent reductions in OTR, signifying anxiogenic effects. Buspirone reduced OTR only at doses (0.25–5.0 mg/kg) decreasing total entries; gepirone (0.1–5.0 mg/kg) was inactive. Ipsapirone (0.25–5.0 mg/kg) increased OTR and at 1.0 mg/kg antagonised the anxiogenic action of 8-OH-D-PAT, RU 24969 and BAY R 1531. Gepirone (2.5 mg/kg) failed to antagonise 8-OH-DPAT, but the dose was limited by its effect on total entries. The anxiogenic effect of a low dose of 8-OH-DPAT was also prevented byp-chlorophenylalanine (p-CPA) pretreatment and reversed to anxiolytic by 5,7-dihydroxytryptamine lesions of dorsal raphe, which spared median raphe. These lesions also abolished the anxiolytic effect of ipsapirone without affecting the anxiogenic response to yohimbine. This study provides preliminary evidence that 8-OH-DPAT may be capable of acting as an agonist and ipsapirone as an antagonist at a presynaptic site related to dorsal raphe which is separate from the site of action of yohimbine. 5-HT_1A agonists and partial agonists may have multiple sites and/or mechanisms of action in the elevated X-maze.     

Effects of benzodiazepine receptor partial inverse agonists in the elevated plus maze test of anxiety in the rat

The present series of experiments examined the effects of five benzodiazepine receptor (BZR) partial inverse agonists on the behaviour of rats on an elevated plus maze. The drugs were tested in a standard plus maze with 3-cm walls added to the open arms, as this has been shown to increase the sensitivity of the plus maze to anxiogenic-like drug effects (Jones and Cole 1995). The drugs tested were FG 7142 (0–100 mg/kg),-CCE (0–30 mg/kg), ZK 132 556 (0–100 mg/kg), ZK 90 886 (0–30 mg/kg) and Ro 15–4513 (0–30 mg/kg). In addition, to allow a comparison with previous studies, the effects of three reference substances, DMCM (0–2.5 mg/kg), pentylenetetrazol (PTZ; 0–30 mg/kg) and yohimbine (0–5 mg/kg), were also examined. These three reference compounds produced a dose-dependent reduction in the duration of open arm exploration and the total number of open arm entries, indicative of anxiogenic-like effects. DMCM produced significant effects at the doses of 1.25 and 2.5 mg/kg, PTZ at 30 mg/kg, and yohimbine at 5 mg/kg. The BZR partial inverse agonist FG 7142 (10, 30 and 100 mg/kg) also reduced the duration of open arm exploration and the total number of arm entries. The minimally effective dose resulted in a receptor occupancy of approximately 80%. Ro 15–4513 also produced anxiogenic-like effects, but only at a dose (30 mg/kg) that resulted in a receptor occupancy of approximately 95%. In contrast, the other BZR partial inverse agonists, ZK 132 553 and ZK 90 886, did not significantly reduce the duration of open arm exploration, even at doses that produced greater than 95% receptor occupancies.-CCE also did not reduce open arm exploration at any dose tested (0–30 mg/kg). The GABA shift, a biochemical index of intrinsic activity, indicates that these latter three compounds are more inverse agonistic than Ro 15–4513. In summary, these results demonstrate that not all BZR receptor partial inverse agonists have anxiogenic-like activity in the rat plus maze, and that the GABA shift, a biochemical index of intrinsic efficacy, does not predict which BZR partial inverse agonists are anxiogenic.     

Effects of DN-2327, a new anxiolytic,diazepam and buspirone on exploratory activity of the rat in an elevated plus-maze

In the present study, the effects of a new anxiolytic, DN-2327, were compared to those of diazepam and buspirone in rats in the elevated plus-maze test. Two indices of anxiety were obtained in this test: the number of entries into the open arms expressed as a percentage of the total number of arm entries and the percentage of time spent on the open arms. Both a typical anxiolytic, diazepam, at 2.5, 5 and 10 mg/kg, PO and a new anxiolytic, DN-2327, at 2.5 and 5 mg/kg, PO dose-dependently increased the two indices: the percentage of time spent on the open arms and the percentage of open-arm entries. On the other hand, pentylenetetrazol (PTZ) at 10 and 20 mg/kg, IP decreased the two indices dose dependently as did yohimbine at 1.5 and 3 mg/kg, IP. DN-2327 at 2.5 and 5 mg/kg, PO and diazepam at 5 and 10 mg/kg, PO dose dependently and significantly increased the two indices that were suppressed following administration of PTZ at 10 mg/kg, IP. The effects of both DN-2327, 5 mg/kg, PO, and diazepam, 10 mg/kg, PO, on the two indices were significantly antagonized by the benzodiazepine (BZD) receptor antagonist flumazenil, 20 mg/kg, IP. Buspirone (2.5–20 mg/kg, PO) did not affect either of the two responses but dose dependently decreased the number of rearings, although in the Vogel conflict test, the anti-conflict activity of buspirone was equipotent to that of diazepam and DN-2327 at the minimum effective dose (10 mg/kg, PO) of each drug. In conclusion, the present experiment revealed that the anxiolytic effect of DN-2327 in this test was clear, whereas buspirone showed no apparent effect.     

Flumazenil blockade of anxiety following ethanol withdrawal in rats

In previous research, the drug flumazenil has been categorized both as a pure benzodiazepine antagonist and as a benzodiazepine partial agonist. The following studies used an elevated plus maze to test whether flumazenil would exert any antianxiety action in rats. While chlordiazepoxide (3.0 mg/kg), ethanol (0.75 g/kg), and the atypical benzodiazepine zolpidem (1.0 mg/kg) all significantly increased time spent on the open arms and percent open arm entries, flumazenil (1–10 mg/kg) alone did not produce any anxiolytic effects on the maze. Withdrawal from chronic ethanol treatment led to a decrease in open arm time and percent open arm entries. Flumazenil (3.0 mg/kg) blocked these changes, suggesting that the effects of flumazenil are at least partially dependent upon the levels of stress or anxiety in the subjects. An anxiolytic action of flumazenil was not seen following the central administration of the neuropeptide corticotropin-releasing factor (CRF), which reduced open arm time on the elevated plus maze. These results support the hypothesis that the mechanism of action for flumazenil effects on the anxiety observed during ethanol withdrawal involves antagonism of an endogenous benzodiazepine inverse agonist, rather than activity as a partial agonist or blockade of CRF-mediated effects. Received: 30 September 1996/Final version: 23 December 1996     

Age and anxiety: Increased anxiety,decreased anxiolytic,but enhanced sedative,response to chlordiazepoxide in old rats

The effects of chlordiazepoxide (7.5 mg/ kg) were assessed on the performance of young (3 months) and old (12 months) hooded Lister rats in the elevated plus-maze test of anxiety. In young animals chlordiazepoxide significantly increased the percentage of entries onto open arms and the percentage of time spent on the open arms of the plus-maze, measures that reflect its anxiolytic action. In the young animals this dose of chlordiazepoxide did not change the total number of arm entries, a measure that reflects its sedative action. However, in the old animals the only significant effect was a reduction in total arm entries. The effects of ageing on performance in the plus-maze was assessed by testing rats at 3, 6, 9 and 12 months of age. Between 9 and 12 months the rats showed a significant decrease in the percentage of entries onto open arms and in the percentage of time spent on the open arms, indicating an increase in this measure of anxiety. Thus it seems that old rats might have an increase in their baseline measures of anxiety, coupled with a reduced anxiolytic response to benzodiazepines.     

Bidirectional effects of benzodiazepine binding site ligands in the elevated plus-maze: differential antagonism by flumazenil and beta-CCt

Recent research using genetically modified mice has pointed to the specific contribution of individual receptor subtypes to the various effects of benzodiazepines. The aim of this study was to examine the relative significance of alpha(1)-containing GABA(A) receptors in the effects of modulators at the benzodiazepine site in the elevated plus-maze (EPM) under dim red light in rats. We tested the effects of the non-selective antagonist flumazenil (0-20.0 mg/kg), the preferential alpha(1)-subunit selective antagonist beta-carboline-3-carboxylate-t-butyl ester (beta-CCt, 0-30.0 mg/kg), the non-selective agonist midazolam (0-2.0 mg/kg), the preferential alpha(1)-subunit selective agonist zolpidem (0-2.0 mg/kg) and the non-selective inverse agonist methyl 6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate (DMCM, 0-2.0 mg/kg). The influence of flumazenil (10.0 mg/kg) and beta-CCt (30.0 mg/kg) on the effects of both kinds of agonists were also examined. The standard spatio-temporal parameters reflecting anxiety (percentage of open arm entries and time) and locomotion (closed and total arm entries) were analyzed. beta-CCt did not affect behavior, while flumazenil at the highest dose (20.0 mg/kg) decreased indices of open arm activity and total arm entries. Midazolam at the dose of 1.0 mg/kg significantly increased the percentage of open arm time, whereas at 2.0 mg/kg both anxiety-related parameters were increased. In contrast to the open arm entries, the open arm time was independent of the decreased closed arm entries, observed at 2.0 mg/kg. Flumazenil abolished these effects, whereas beta-CCt partially potentiated the anxiolytic actions of midazolam. Zolpidem significantly increased both open-arm indices at 1.0 mg/kg, but the effect was dependent on the decreased closed arm entries. The selectivity of the anxiolytic-like effects of zolpidem was further checked under brighter white illumination. In these settings, the influence on anxiety-related, but not activity-related parameters, was absent. All of the activity-related effects of midazolam and zolpidem were mainly counteracted by both antagonists. DMCM produced significant anxiogenic effects at 1.0 mg/kg (open arm time) and 2.0 mg/kg (both parameters). beta-CCt (30.0 mg/kg) and flumazenil at higher dose (20.0 mg/kg) antagonized the effects of DMCM. The results indicate the anxiolytic effects of a non-selective benzodiazepine site agonist involve a predominant role of subunits other than alpha(1), whereas the behavioral indices of the anxiolytic-like properties of an alpha(1)-selective ligand, if observed, depend on the experimental settings and the changes in locomotor activity, and hence were behaviorally non-specific. The present results generally correspond well to the behavioral findings with the genetically modified mice. On the other hand, the relative significance of the alpha(1)-subunit in the anxiogenic effects of DMCM could not be clearly deduced.     

Ethological evaluation of the effects of acute and chronic buspirone treatment in the murine elevated plus-maze test: comparison with haloperidol

Buspirone is renowned for its highly inconsistent effects in animal models of anxiety. In the present study, the effects of acute (0.63–5.0 mg/kg) and chronic (1.25–5.0 mg/kg, daily, 15 days) buspirone treatment on the behaviour of mice in the elevated plus-maze test were assessed using a recently developed ethological scoring method. On acute administration, a selective reduction in risk assessment behaviours was observed at 1.25 mg/kg; these mild anxiolytic-like effects were maintained at higher doses (2.5–5.0 mg/kg) which also reduced measures of general activity. Similar, though more potent, effects were observed with chronic administration; the lowest dose tested (1.25 mg/kg) reduced open arm entries and total stretch attend postures while higher doses profoundly reduced all major indices of anxiety (traditional and novel) and, concomitantly, suppressed total entries and rearing. Acute administration of haloperidol (0.0125–0.1 mg/kg) appeared to mimic the behavioural suppressant effects of buspirone without selectively affecting anxiety-related measures at any dose. It is suggested that the anti-anxiety and behavioural suppressant profile of buspirone may reflect combined action at 5-HT_1A and D₂ receptors, respectively. Results are discussed in relation to the utility of risk assessment as a sensitive index of anxiety in models based upon unconditioned behaviour.     

A re-evaluation of the role of alpha 2-adrenoceptors in the anxiogenic effects of yohimbine,using the selective antagonist delequamine in the rat.

1. The acute behavioural effects of the alpha2-adrenoceptor antagonists, yohimbine, idazoxan and delequamine (RS-15385-197) were compared in two tests of exploratory behaviour in the rat, operated in tandem. These were the elevated X-maze test (5 min) and a modified holeboard test (12 min), which comprised a holeboard arena with a small roof in one corner as a ''refuge''. Rats were first placed into this corner, thus enabling measurements of initial emergence latency and the number of forays. The experiments were always done with a concomitant vehicle control group, with 10-12 rats per group, and with the treatment blinded. 2. In order to validate the tests, the effects of representatives of four classes of psychoactive agents were examined, viz. picrotoxin (anxiogenic), chlordiazepoxide (anxiolytic), (+)-amphetamine (stimulant) and diphenhydramine (sedative). The modified holeboard tended to be more sensitive than the measurement of total arm entries in the elevated X-maze at detecting drug effects on exploratory behaviour, but unlike the X-maze it could not clearly identify each class of agent. Thus, picrotoxin (5 mg kg(-1), i.p.) reduced total arm entries and open arm exploration in the X-maze (P<0.02) and suppressed most measures of activity in the holeboard (P<0.05); chlordiazepoxide (7.5 mg kg(-1), i.p.) increased total arm entries and open arm exploration (P<0.02) in the X-maze, without clear-cut effects in the holeboard; (+)-amphetamine (1 mg kg(-1), i.p.) had no significant effects in the X-maze, but increased most holeboard activities (P<0.05), and diphenhydramine (30 mg kg(-1), i.p.) reduced total arm entries in the X-maze (P<0.002) and hole exploration in the holeboard (P<0.05).     

A comparison between Dark Agouti and Sprague-Dawley rats in their behaviour on the elevated plus-maze, open-field apparatus and activity meters, and their response to diazepam

RATIONALE: Preliminary unpublished studies in our laboratory suggested that the behaviour of Sprague-Dawley (SD) and Dark Agouti (DA) rats was markedly different on both the elevated plus maze and in the open-field apparatus. We wished to confirm and extend this initial finding. OBJECTIVE: The study was designed to examine the behaviour of SD and DA rats in the elevated plus maze, open-field apparatus and automated activity meters. The response of both strains on the elevated plus maze following diazepam (1 mg/kg and 1.5 mg/kg) administration was subsequently investigated. RESULTS: DA rats showed markedly greater anxiety-like behaviour than SD rats in both the plus maze and open field, with fewer percentage open/total arm entries and percentage time spent on open/total arms in the plus maze and fewer crossings in the open field. Acute handling plus administration of vehicle abolished this difference in anxiety levels, with DA rats showing similar open-arm behaviour to that of SD rats. Both strains demonstrated a clear anxiolytic response to diazepam (1 mg/kg) in terms of percentage time spent on the open arms, but only SD rats had a statistically significant increase in percentage open-arm entries compared with vehicle-injected control animals. CONCLUSIONS: While the high level of anxiety-like behaviour of DA rats versus SD rats could prove useful in future ethological studies on anxiety, the fact that acute handling decreased the anxiety-like behaviour on the elevated plus maze may limit the value of this strain for the study of putative anxiolytic drugs.     

Anxiolytic effect of cannabidiol derivatives in the elevated plus-maze

• 1.1. In order to assess the presence of anxiolytic properties in cannabidiol (CBD) derivatives HU-219, HU-252 and HU-261, these drugs were tested in rats submitted to the elevated plus-maze model of anxiety.
• 2.2. Additional groups received diazepam or CBD. HU-219 (0.03-1 mg/kg) and CBD (5 mg/kg) significantly increased the percentage of open arm entries without changing the total number of entries, an anxiolytic-like effect.
• 3.3. Both HU-252 and HU-261 increased the percentage of time spent in open arms and the total number of entries, but only at the dose of 1 mg/kg.
• 4.4. Diazepam (2.5 mg/kg) increased both the percentage of entries and time spent on open arms and the total number of entries.
• 5.5. The results confirm previous findings with CBD and indicate that its derivative HU-219 may possess a similar anxiolytic-like profile.
• 6.6. Results from HU-252 and HU-261 are less apparent and suggest that the compounds may increase general exploratory activity in a limited range of doses.

     

The pharmacology of VA21B7: an atypical 5-HT3 receptor antagonist with anxiolytic-like properties in animal models

VA21B7 (3-[2-(4-piperonylpiperazinyl) indolyl] carboxaldehyde) was synthesized as a potential 5-HT₃ receptor antagonist. Even though VA21B7 showed a higher affinity towards 5-HT₃ receptors as compared to other receptors studied, it was not a potent 5-HT₃ receptor antagonist either in the periphery or in the brain. In a simple animal model of anxiety such as the two-compartment box in mice, a remarkable anxiolytic-like effect was found at doses of 2–500 µg/kg IP and also at low oral doses, in the microgram range. These drug doses did not produce any significant effect on spontaneous motor activity of mice. The anxiolytic profile of VA21B7 was further explored using other models of anxiety in rats such as the elevated plus-maze and punished-drinking. VA21B7 was compared with standard 5-HT₃ receptor antagonists such as ondansetron, tropisetron and granisetron, with the 5-HT_1A agent buspirone and with diazepam. In the plus-maze, VA21B7 showed an anxiolytic-like profile after doses of 0.25–0.5 mg/kg IP or 2–4 mg/kg PO which did not modify the number of total entries into the open and closed arms of the maze. Diazepam, granisetron and tropisetron were also effective in this test but not ondansetron and buspirone. VA21B7 was also able to release suppressed behaviour in the punished-drinking test. The dose-response curve was bell-shaped with a peak at 2–4 mg/kg. At variance with other studies, 5-HT₃ receptor antagonists also increased the number of shocks taken in this test and the dose-response curve was also bell-shaped. VA21B7 was not anticonvulsant like diazepam, its anxiolytic action in the light/dark test was not flumazenil-sensitive and there was no rebound anxiogenic effect on withdrawal from chronic VA21B7 treatment for 15 consecutive days. Moreover, VA21B7 was not amnesic like the benzodiazepines but low doses of 2–4 mg/kg reduced the memory deficits induced in rats by scopolamine. Much higher doses were necessary to decrease spontaneous motor activity in rats. Since VA21B7 appears to be well tolerated in rodents at high doses, we think that it is of potential interest as an anxiolytic in humans.     

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.     

Antianxiety effect of cannabidiol in the elevated plus-maze

In order to assess the presence of anxiolytic properties in cannabidiol (CBD) the drug was tested in an elevated plus-maze model of anxiety, in rats. Doses of 2.5, 5.0 and 10.0 mg/kg significantly increased the entry ratio (open/total number of entries), an anxiolytic-like effect. CBD at a dose of 20.0 mg/kg was no longer effective. None of the doses of CBD used changed total number of entries, a measure of total exploratory activity. Diazepam (2.0 mg/kg) also caused an anxiolytic-like effect in this model. These results indicate that CBD causes a selective anxiolytic effect in the elevated plusmaze, within a limited range of doses.     

Anxiolytic activity of ginkgolic acid conjugates from Indian Ginkgo biloba

Ginkgolic acid conjugates (GAC) (6-alkylsalicylates, namely n-tridecyl-, n-pentadecyl-, n-hepta- decyl-, n-pentadecenyl- and n-heptadecenylsalicylates) isolated from the leaves of Indian Ginkgo biloba Linn., (IGb) were tested for their putative role in anxiety in rats. Elevated plus maze, open-field behaviour, novelty-induced feeding latency and social interaction were the rodent behavioural models used in this study. GAC (0.3 and 0.6 mg/kg, each, PO) on single acute administration, showed dose-related changes in the behaviour. GAC (0.6 mg/kg) and DZ augmented open arm entries, the open arm/closed arm entries ratio and increased time spent in the open arm on the elevated plus maze. In the open field, GAC (0.6 mg/kg) and DZ significantly increased ambulation and reduced the immobility time. EGb 761 showed a similar profile. GAC (0.6 mg/kg) and DZ significantly attenuated the increased latency to feed in novel environment. By contrast, EGb 761 and Ginkocer further augmented feeding latency. None of the drugs tested showed any significant effect in the social interaction test. GAC showed consistent and significant anxiolytic activity in all the variables investigated. By contrast, EGb 761 and Ginkocer, which are devoid of GAC, did not evoke significant activity. However, increased rearing and decreased immobility time only in open field behaviour shown by EGb 761 may be due to some antianxiety activity of a lesser degree. Our observations suggest that GAC may be the active constituents of Ginkgo biloba responsible for the anxiolytic activity. Received: 5 May 1997/Final version: 23 August 1997     

Trial 2 in the elevated plus-maze: a different form of fear?

A factor analysis of the scores from rats given two trials in the elevated plus-maze showed that four independent factors emerged. Measures of anxiolytic activity on trial 1 (number of open arm entries and time spent on open arms) loaded on factor 1, measures of anxiolytic activity on trial 2 loaded on factor 2, the measure of general activity (number of closed arm entries) on both trials loaded on factor 3, and a measure of decision time (time spent in central square) for both trials loaded on factor 4. The independence of trials 1 and 2 anxiety measures raises the possibility that the state of anxiety/fear on the second trial in the plus-maze is qualitatively different from that on trial 1. This difference is reflected in the loss of anxiolytic action of diazepam (2 mg/kg) on trial 2. However, this occurs only when the trials are short (5 min); when they are longer (10 min) diazepam retains anxiolytic efficacy. It is concluded that during a brief (5 min) trial in the plus-maze rats acquire a specific phobic anxiety, which is relatively resistant to benzodiazepines. With a longer exposure to the plus-maze this form of fear extinguishes.     

Identification of anxiolytic ingredients in ginseng root using the elevated plus-maze test in mice

Ginseng root has been widely used for the management of anxiety and emotional instability, but there is little experimental evidence supporting these clinical applications. We pharmacologically identified the anxiolytic components in ginseng root, using the elevated plus-maze test. Male ICR albino mice and the following drugs were used: diazepam (0.5, 1 and 1.5 mg/kg, p.o.); red ginseng powder (300, 600 and 1200 mg/kg, p.o.); crude saponin and non-saponin ginseng fractions (50, 100 and 200 mg/kg, i.p., for each preparation); and pure ginsenoside Rb1, Rg1, and Ro (2.5, 5 and 10 mg/kg, i.p., for each preparation). Ginseng powder and crude saponin ginseng fraction significantly increased the frequency and duration of open arm entries. Among the three types of pure ginsenoside, only ginsenoside Rb1 significantly increased both the frequency and duration of open arm entries. Our results clearly indicate that ginsenoside Rb1 is one of the active anxiolytic components of ginseng root.