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Characterization of anxiolytic and neuropharmacological activities of Silexan 891 3

Charakterisierung anxiolytischer und neuropharmakologischer Aktivitäten von Silexan

Zusammenfassung Silexan ist ein ätherisches Öl aus Blüten von Lavandula angustifolia mit bewährter kli-nischer Wirksamkeit bei der Behandlung von Angst-störungen. Ziel der vorliegenden Studie war es, die an-xiolytische Aktivität und die neuropharmakologischen Eigenschaften von Silexan an Ratten und Mäusen bei-derlei Geschlechts näher zu charakterisieren. Silexan (3, 10 und 30  mg/kg i.p.), Lorazepam (5  mg/kg p.o.) oder Diazepam (3  mg/kg p.o.) wurden einmal täglich für 7 aufeinanderfolgende Tage verabreicht. Die Experi-mente wurden 1  h nach der letzten Verabreichung der Medikamente bzw. des Vehikels durchgeführt. Alle drei Dosen von Silexan bewirkten eine signifikante und do-sisabhängige anxiolytische Aktivität in den verwendeten pharmakologischen Modellen (Open-Field-Test, Eleva-ted-Plus-Maze-Test, Elevated-Zero-Maze-Test, sozialer Interaktionstest, Neuheit-induzierte Hypophagie), die vergleichbar war mit der des Standardanxiolytikums Lorazepam. Silexan verstärkte außerdem die Pentobar-bital-induzierte Schlafzeit, hatte im Gegensatz zu Dia-zepam aber keinen signifikanten Effekt auf die Bewe-gungsaktivität und die muskuläre Koordination.

Schlüsselwörter: Lavandula angustifolia, Lavendelöl, Angststörungen, Pharmakologie

Summary Silexan is an essential oil produced from Lavandula angustifolia flowers with proven clinical ef-ficacy for the treatment of anxiety disorders. The pres-ent study was conducted to assess its anxiolytic activity and to screen for neuropharmacological properties in

rats and mice of either sex. Silexan (3, 10, and 30  mg/kg, intraperitoneally), lorazepam (5  mg/kg, p.o.), or di-azepam (3 mg/kg, p.o.) were administered once daily for 7 consecutive days. Experiments were conducted 1 h af-ter the last drug or vehicle administration. All the three doses of Silexan showed significant and dose-dependent anxiolytic activity in the used pharmacological models (open-field test, elevated plus-maze test, elevated zero-maze test, social interaction test, and novelty-induced suppressed feeding latency test), which was compara-ble to that of the standard anxiolytic agent lorazepam. In addition, Silexan amplified pentobarbital-induced sleeping time, but in contrast to diazepam was found to be devoid of any significant effect on locomotor activity and muscle-grip performance.

Keywords: Lavandula angustifolia, Lavender oil, Anxi-ety disorders, Pharmacology

Introduction

Different lavender species and their essential oils have been used in folk medicine for centuries for the treat-ment of pain, infection, relaxation, anxiety, or improve-ment of sleep quality by oral administration, inhalation or topical application [1, 2]. Silexan1 is an orally active essential oil preparation of selected quality produced from the flowering tops of Lavandula angustifolia Mill. by steam distillation. Therapeutic efficacy in the treat-ment of subsyndromal or generalized anxiety disorder, restlessness and agitation, neurasthenia, posttraumatic stress disorder, as well as somatization disorder has been demonstrated in a number of open label and placebo or reference-controlled clinical trials [3]. In Germany, Silexan has recently been approved for the treatment of restlessness in case of anxious mood.

1 Silexan is the active pharmaceutical ingredient of Lasea (W. Spitzner Arzneimittelfabrik GmbH, Ettlingen, Germany).

Wien Med Wochenschr (2013) 163:89–94DOI 10.1007/s10354-012-0164-2

Characterization of anxiolytic and neuropharmacological activities of SilexanVikas Kumar

Dr. V. Kumar () Neuropharmacology Laboratory, Department of Pharmaceutics, Indian Institute of Technology, Banaras Hindu University, Varanasi 221005, India e-mail: vikas.phe@iitbhu.ac.in

Received: 5 September 2012 / Accepted: 29 October 2012 / Published online: 30 January 2013© Springer-Verlag Wien 2013

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The development of Silexan to a modern herbal medicinal product has been based on traditionally known beneficial effects of diverse types of lavender oils. However, till now little detailed information on the phar-macological activity profile is available. Therefore, the experiments conducted under this project were designed to examine whether the therapeutically observed effects could as well be verified in some conventionally known animal models commonly used for discovering structur-ally and functionally novel anxiolytics. The observations made during this reverse pharmacology-based holistic approach add preclinical evidences in support of the therapeutic use of Silexan and suggest that further pre-clinical efforts to define its neuropsychopharmacological activity profile could be useful for more precisely defin-ing and understanding the entire therapeutic potential of Silexan.

Materials and methods

Animals Adult Charles Foster albino rats (150 ± 10 g) and Wistar mice (20 ± 5 g), of either sex, were obtained from the Central Animal House of the Institute of Medical Sci-ences, Banaras Hindu University or elsewhere and were randomly distributed into different experimental groups. Animals were housed in groups of six in polypropylene cages at an ambient temperature of 25 ± 1 °C and 45–55 % relative humidity, with a 12:12  h light/dark cycle. Ani-mals were provided with commercial food pellets and water ad libitum unless stated otherwise. Behavioral experiments were conducted between 09.00 and 14.00 h. Animals were acclimatized for at least 1 week before using them for the experiments. “Principles of laboratory animal care” (NIH publication no. 85-23, revised in 1985) guidelines were followed.

Drug treatments Silexan was developed and supplied by Dr. Willmar Schwabe GmbH & Co. KG, Karlsruhe (Ger-many). It was provided as a liquid injectable solution at three different concentrations (1.5, 5, and 15 mg/ml) in a mixture of medium-chain triglycerides (Myritol 318 PH, Cognis, Monheim, Germany) and filled into clear glass septa vials. Vials were stored at room temperature away from light until use. The test article was adminis-tered intraperitoneally (i.p.) at doses of 3, 10, and 30 mg/kg in a volume of 2 ml/kg body weight once daily for 7 consecutive days. In deviation from the oral route of administration in humans, i.p. injection was deliber-ately chosen to avoid any possible interference or pref-erence due to the characteristic lavender odor. Control rats were treated with an equal volume of the vehicle (a mixture of medium-chain triglycerides). Experiments were conducted on day 7, 1 h after the last drug or vehicle administration. Lorazepam (5 mg/kg, p.o.) or diazepam (3 mg/kg p.o) were used as standard anxiolytic agents for comparison.

Anxiolytic activity

Open-field test The open-field apparatus was made of plywood and consisted of squares (61 × 61 cm). The entire apparatus was painted black except for 6 mm thick white lines, which divided the floor into 16 squares. Open-field was lighted by a 40 W bulb focusing onto the field from a height of about 100 cm. The entire room, except the open-field, was kept dark during the experiment. Each animal was centrally placed in the test apparatus for 5 min and the following behavioral aspects were noted [4]:

• Ambulation: this was measured in terms of the num-ber of squares crossed by the animal.

• Rearings: number of times the animal stand on its hind limbs.

• Self groomings: number of times the animal groom fa-cial region, and licks/washed/scratched various parts of its body.

• Activity in center: number of central squares crossed by the animal.

• Fecal droppings: number of fecal droppings excreted during the period.

Elevated plus-maze test The maze has two opposite arms, 50 × 10 cm, crossed with two enclosed arms of the same dimension and having 40 cm high walls. The arms are connected with a central square, 10 × 10  cm, giving the apparatus the shape of a plus sign. The maze was kept in a dimly lit room and elevated 50 cm above the floor. Naive rats were placed individually in the center of the maze, facing an enclosed arm. Thereafter, the number of entries and time spent on the open and enclosed arms was recorded during the next 5  min. An arm entry was defined, when all four paws of the rat were in the arm. A neutral “blind” observer made the observations [4].

Elevated zero-maze test The maze comprised of a black perspex annular platform (105 cm in diameter and 10 cm width) elevated 65  cm above the ground level, divided equally into four quadrants. The two opposite quadrants were enclosed by a black perspex wall (27  cm high) on both the inner and outer edges of the platform, while the remaining two opposite quadrants were surrounded by perspex “lip” (1 cm high) which served as a tactile guide to animals on these open areas. The apparatus was illu-minated by dim white light arranged in such a manner as to provide similar lux levels in open and enclosed quad-rants. Rats were placed on one of the enclosed quadrants for a 5 min test period. The maze was cleaned with 5 % ethanol/water solution and dried thoroughly between test sessions. During the 5 min test period, time spent on open arms, number of “head dips” over the edges of plat-form, and number of “stretched-attend postures” from closed to open quadrants were recorded. Animals were scored as being in the open area when all four paws were in the open quadrants and in the enclosed area only when all four paws had passed the open-closed divide [4].

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Social interaction test The rats were first housed indi-vidually for 5 days before testing. The apparatus used for the test was a wooden box (60 × 60 × 35  cm) with a solid floor and placed in a dimly lit room. On day 6, the rats were placed individually in the box and given two 7.5 min familiarization sessions at a 2 h interval. On day 7, rats were paired on weight and sex basis and placed in the box for 7.5 min. During this time, total time spent by the rat pair in “social interaction”, including sniffing, following, grooming, kicking, boxing, biting, and crawl-ing under or over the partner, were recorded by a neutral “blind” observer [4].

Novelty-induced suppressed feeding latency test The test apparatus was a wooden box (60 × 60 × 35 cm) with a solid floor placed in a dimly lit room. The floor of the wooden box was covered with 2  cm layer of wooden chips, and laboratory chow pellets was evenly placed on the floor. A similar arrangement was made in the home cages of the rats. Food was removed from the home cage 48 h prior to testing, but water was provided ad libitum. Naive rats were placed individually in the test chamber and the latency to begin eating (defined as chewing of the pellet and not merely sniffing or playing with it), was recorded. If the rat had not eaten within 300 s, the test was termi-nated and latency score 300  s was assigned. A neutral “blind” observer made the observations [4].

General neuropharmacological screening

Potentiation of pentobarbital-induced sleeping time Pen-tobarbital (40 mg/kg, i.p. on day 7) was administered to control and drug-treated animals. Onset of sleep (loss of righting reflex) was noted and duration of sleep was mea-sured as the period between the loss of righting reflex and its return [5]. Silexan (3, 10 and 30 mg/kg, i.p. for 7 days) and diazepam (3 mg/kg, p.o. on day 7) were administered 45 min prior to pentobarbital injection.

Locomotor activity The spontaneous locomotor activ-ity was assessed with the help of a photoactometer [6, 7]. Each animal was observed for a period of 10 min in a square closed-field arena (30 × 30 × 30 cm) equipped with six photocells in the outer wall. Interruptions of photo-

cell beams (locomotor activity) were recorded by means of a 6 digits resettable counter. The rats were observed for locomotor activity in the apparatus, one at a time.

Effect on muscle-grip performance of mice Effect on motor coordination was examined on rota-rod appara-tus. Each animal was placed on a rotating rod (20 rpm) in a pretest session and only those animals, which stayed on the rod for not less than 3 min, were selected for the test session. The test session was performed on the same day as the pretest session. Fall-off time (when the mouse falls from the rotating rod) for each animal was noted before and after drug administration [4, 7]. Silexan (3, 10 and 30  mg/kg, i.p.) and diazepam (3  mg/kg, p.o.) were administered 45 min before the test session.

Statistical analysis The values are expressed as mean ± SD. Statistical significance of the differences between control and treated groups was calculated using Kruskal–Wallis one-way analysis of variance (ANOVA) followed by Mann–Whitney U-test (two tailed). p < 0.05 was considered to be significant.

Results

Anxiolytic activity of Silexan

Effect of Silexan on open-field exploratory behavior in rats All the three doses (3, 10, and 30  mg/kg, i.p.) of Silexan induced potent anxiolytic activity. There was a significant and dose-dependent increase in open-field ambulation, rearing, and self-grooming in comparison to vehicle-treated rats. Although activity in the center was significantly increased and fecal dropping was sig-nificantly reduced in comparison to vehicle-treated rats, a dose-dependent effect was not observed for these two parameters. Lorazepam also exhibited significant anxio-lytic effect and the effect was similar to that of Silexan. The data are summarized in Table 1.

Effect of Silexan on elevated plus-maze test in rats Silexan exhibited anxiolytic activity in this model as indicated by a significant and dose-dependent increase in time spent

Table 1. Effect of Silexan on open-field exploratory behavior in rats

Treatment Dose (mg/kg) Ambulation (N) Rearing (N) Self grooming (N) Activity in centre (N) Fecal droppings (N)

Vehicle – 33.17 ± 3.66 8.67 ± 1.21 6.67 ± 1.37 4.17 ± 0.75 2.83 ± 0.75

Silexan 3 41.33 ± 4.13* 11.17 ± 1.47* 8.67 ± 1.21* 6.67 ± 1.21* 1.83 ± 0.98

Silexan 10 49.83 ± 3.43***,$ 12.83 ± 1.17*** 10.50 ± 1.05*** 6.83 ± 1.47*** 1.33 ± 0.82*

Silexan 30 56.17 ± 3.97***,$$ 15.67 ± 1.21***,$$,¥¥ 11.33 ± 1.21***,$ 7.83 ± 1.17*** 1.50 ± 0.55*

Lorazepam 5 55.83 ± 4.49*** 15.33 ± 0.82*** 12.33 ± 0.82*** 7.33 ± 1.51*** 1.50 ± 0.55*

N = 6 in each groupValues are mean ± SD*p < 0.05 and ***p < 0.001 compared with vehicle$p < 0.01 and $$p < 0.001 compared with Silexan (3 mg/kg)¥¥p < 0.01 compared with Silexan (10 mg/kg)

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on open arms and decrease in time spent in enclosed arms. However, significant but dose-independent changes were observed in entries made on open and closed arms. Lorazepam also exhibited significant anxio-lytic effect (see Table 2).

Effect of Silexan on elevated zero-maze test in rats Silexan-treated rats showed distinct reduction of anxiety as indi-cated by significant and dose-dependent increase in time spent on open arms. Entries in open arms, number of head dips, and stretched-attend postures also increased significantly; however, a dose-dependent effect was not observable for these parameters. Lorazepam also exhib-ited significant anxiolytic effect and the effect was similar to that of Silexan. The results are shown in Table 3.

Effect of Silexan on social interaction test in rats More time spent by the rat pair in “social interaction”, includ-ing sniffing, following, grooming, kicking, boxing, biting, and crawling under or over the partner is indicative of anxiolytic activity. Rats treated with all the three doses of Silexan showed significant and dose-dependent increase of social interaction time in comparison to vehicle-treated rats. Similar results were obtained with standard anxiolytic drug lorazepam used for comparison. The data are collected in Table 4.

Effect of Silexan on novelty-induced suppressed feeding latency test in rats Rats treated with Silexan took signifi-cantly less time in a dose-dependent manner to start eat-ing chow pellets compared with vehicle-treated rats. This indicates anxiolytic effect of Silexan. As shown in Table 5, similar results were obtained with lorazepam.

General neuropharmacological screening of Silexan

Potentiation of pentobarbital-induced sleeping time All the three doses of Silexan induced significant and dose-dependent potentiation of pentobarbital-induced sleep-ing as indicated by early onset of loss of righting reflex and delayed gain of such reflex in comparison to vehicle-

Table 2. Effect of Silexan on elevated plus-maze test in rats

Treatment Dose (mg/kg) Time spent (s) Entries (N)

Enclosed arms Open arms Enclosed arms Open arms

Vehicle – 247.67 ± 9.22 48.17 ± 3.37 9.67 ± 1.37 5.17 ± 0.98

Silexan 3 204.50 ± 4.51*** 93.33 ± 5.16** 6.33 ± 1.03*** 8.33 ± 1.03**

Silexan 10 186.83 ± 4.75***,$$ 109.83 ± 6.82**,$$ 5.83 ± 1.17*** 11.33 ± 2.16***

Silexan 30 179.83 ± 4.40***,$$ 119.83 ± 5.19**,$$,¥ 4.83 ± 0.75*** 12.67 ± 0.82***

Lorazepam 5 176.17 ± 6.97*** 123.17 ± 3.06** 4.17 ± 1.47*** 12.33 ± 1.63***

N = 6 in each groupValues are mean ± SD**p < 0.01 and ***p < 0.001 compared with vehicle$$p < 0.001 compared with Silexan (3 mg/kg)¥p < 0.05 compared with Silexan (10 mg/kg)

Table 3. Effect of Silexan on elevated zero-maze test in rats

Treatment Dose (mg/kg) Time spent on open arms (s) Head dips (N) Stretched-attend posture (N) Entries on open arms (N)

Vehicle – 73.83 ± 4.83 6.83 ± 1.17 7.50 ± 1.05 7.33 ± 1.21

Silexan 3 87.33 ± 3.56* 10.17 ± 1.47*** 10.50 ± 1.87* 10.67 ± 1.37*

Silexan 10 103.67 ± 4.13***,$$ 12.50 ± 1.87*** 11.17 ± 1.17*** 11.67 ± 1.86***

Silexan 30 113.17 ± 4.79***,$$,¥ 12.83 ± 2.32*** 11.17 ± 1.47*** 12.17 ± 1.47***

Lorazepam 5 110.17 ± 7.19*** 15.17 ± 2.48*** 11.50 ± 2.17*** 12.33 ± 1.97***

N = 6 in each groupValues are mean ± SD*p < 0.05 and ***p < 0.001 compared with vehicle$$p < 0.001 compared with Silexan (3 mg/kg)¥p < 0.05 compared with Silexan (10 mg/kg)

Table 4. Effect of Silexan on social interaction test in rats

Treatment Dose (mg/kg) Social interaction time (s)

Vehicle – 166.33 ± 5.68

Silexan 3 181.83 ± 2.32***

Silexan 10 184.67 ± 5.85***

Silexan 30 192.50 ± 2.35***,$

Lorazepam 5 203.83 ± 6.43***

N = 6 in each groupValues are mean ± SD***p < 0.001 compared with vehicle$p < 0.01 compared with Silexan (3 mg/kg)

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treated rats. Similar observations were obtained with the standard drug diazepam. The results are summarized in Table 6.

Effect of Silexan on locomotor activity of rats Silexan-treated rats did not show any significant alteration of locomotor activity in terms of light beam interruption when compared with vehicle-treated rats. However, diaz-epam-treated rats showed significant reduction of pho-toactometer counts due to sedative action (see Table 7).

Effect of Silexan on muscle-grip performance of mice Treatment of Silexan did not cause ataxia in mice as fall-off time did not change significantly, whereas mice treated with diazepam showed muscle incoordina-

tion and fall-off time decreased significantly. The results are summarized in Table 8.

Discussion

Lavender oils have been found to exert calming and local anesthetic property and the ability to affect autonomic neurotransmission [8, 9]. They have widely been used as a popular herbal remedy for the treatment of stress and mild anxiety by oral administration, inhalation, or topi-cal application. Silexan is a herbal preparation, which contains a quality-selected and well-defined essential oil prepared from the flowering tops of Lavandula angusti-folia by steam distillation [10]. The efficacy and safety of the item in anxiety disorders has been demonstrated in several randomized, controlled clinical trials as well as open pilot studies [3]. In Germany, Silexan has recently been registered for the oral treatment of subsyndromal anxiety and tension.

On the basis of these facts, the present study was planned to investigate anxiolytic activity of Silexan using different validated behavioral models in rodents. The open-field test for anxiety is a conflict-based model, where anxiety is expressed by animals in response to a novel and inexperienced environment. The anxiety in this model is expressed as a decrease in ambulation and exploration, freezing, rearing, and grooming behavior and increased autonomic functions expressed as higher frequency of defecation [4]. In this experiment, all the three doses of Silexan showed significant and dose-dependent anxiolytic activity.

The elevated plus maze (EPM) is a commonly used nonconditioned model of anxiety in rats and mice, which utilizes the animals’ naturally occurring anxiety-related behaviors and it shows bidirectional sensitivity to anx-iolytic and anxiogenic agents [8]. Silexan exhibited anx-iolytic activity in EPM as indicated by a significant and dose-dependent increase in time spent on open arms. In addition, significant but not dose-dependent changes were observed with respect to entries into open and closed arms. Similar observations were also found in the elevated zero-maze test.

Table 6. Effect of Silexan on pentobarbital-induced sleep-ing time in rats

Treatment Dose (mg/kg) Onset of sleep (min) Duration of sleep

(min)

Vehicle – 5.33 ± 1.03 83.17 ± 6.91

Silexan 3 3.50 ± 0.55** 112.33 ± 9.93***

Silexan 10 3.17 ± 0.75*** 124.33 ± 5.89***,$

Silexan 30 2.83 ± 0.75*** 127.33 ± 6.62***,$$

Diazepam 3 2.17 ± 0.41*** 136.83 ± 4.79***

N = 6 in each groupValues are mean ± SD**p < 0.01 and ***p < 0.001 compared with vehicle$p < 0.05 and $$p < 0.01 compared with Silexan (3 mg/kg)

Table 5. Effect of Silexan on novelty-induced suppressed feeding latency test in rats

Treatment Dose (mg/kg) Latency time (s)

Vehicle – 183.67 ± 6.25

Silexan 3 164.33 ± 9.48***

Silexan 10 155.50 ± 7.87***

Silexan 30 144.33 ± 5.01***,$$

Lorazepam 5 135.83 ± 5.12***

N = 6 in each groupValues are mean ± SD ***p < 0.001 compared with vehicle$$p < 0.001 compared with Silexan (3 mg/kg)

Table 7. Effect of Silexan on locomotor activity of rats

Treatment Dose (mg/kg) Photoactometer count (N)

Vehicle – 214.83 ± 15.64

Silexan 3 230.50 ± 17.97

Silexan 10 222.17 ± 9.79

Silexan 30 228.33 ± 11.55

Diazepam 3 163.50 ± 17.38***

N = 6 in each groupValues are mean ± SD***p < 0.001 compared with vehicle

Table 8. Effect of Silexan on muscle-grip performance of mice

Treatment Dose

(mg/kg)

Fall-off time before drug

treatment (s)

Fall-off time after drug

treatment (s)

Vehicle – 191.83 ± 5.53 194.17 ± 5.46

Silexan 3 194.83 ± 8.06 195.00 ± 8.28

Silexan 10 195.00 ± 6.39 197.83 ± 5.80

Silexan 30 199.50 ± 9.48 201. 00 ± 8.72

Diazepam 3 193.33 ± 10.58 106.33 ± 4.41***

N = 6 in each groupValues are mean ± SD ***p < 0.001 compared with vehicle

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Conventional anxiolytics increase the social interac-tion and decrease the feeding latency respectively in the social interaction and novelty-induced suppressed feed-ing latency test in a novel environment [11]. Rats treated with all the three doses of Silexan showed significant and dose-dependent increase of social interaction time in comparison to vehicle-treated rats. Similarly, rats treated with Silexan took significant less time to start eating chow pellets compared with control animals.

Lorazepam also induced significant anxiolytic effects which were qualitatively similar to that of Silexan in the different test models. Thus, overall findings of the study reveal significant and dose-dependent anxiolytic activity of Silexan.

The pentobarbital-induced sleeping time test is a tool to check for central nervous system (CNS) activity, espe-cially, hypnotic and tranquilizing properties of drugs. The loss of righting reflex is a measure of duration of pentobarbital-induced sleeping time. All the three doses of Silexan potentiated pentobarbital-induced sleep-ing time in a significant and dose-dependent manner in comparison to vehicle-treated rats. Similar observa-tions were obtained with the standard drug diazepam. A potentiation of barbiturate-induced sleeping time in mice by a lavender oil has also been reported previously [12]. Although Silexan enhanced pentobarbital-induced sleeping time, it seems to be devoid of an intrinsic seda-tive potential since Silexan-treated rats did not show any significant alteration of locomotor activity. This is in strong contrast to diazepam, which caused a pronounced reduction of photoactometer counts due to a sedative action.

The rota-rod test or muscle-grip performance test is used to assess muscle-relaxant potential as well as neu-romuscular effects of drugs. CNS suppressive drugs such as benzodiazepines are active in this test as they show ataxia in treated rats. Treatment with Silexan did not cause ataxia in mice as fall-off time did not change sig-nificantly, whereas mice treated with diazepam showed muscle incoordination and fall-off time decreased significantly.

Similar results have previously been reported by Nöld-ner and Luderer [13]. Following repeated oral adminis-tration of Silexan to rats in a dose range between 3 and 30  mg/kg, they observed a statistically significant inhi-bition of the immobility time in the forced swimming test. Anxiolytic effects were seen at the same doses in mice using the light-dark-box and the EPM. Since the pentobarbital-induced sleeping time was prolonged, it is suggested that Silexan has anxiolytic and antidepressant properties and could as well modify the sleeping profile, which is frequently disturbed in affective disorders.

Thus, on the basis of these and previous findings, it can be concluded that Silexan possesses potent anxio-lytic activity without a sedating action and no deleterious

effect on muscle coordination in rodents. These obser-vations strongly support the therapeutic use of Silexan in anxiety disorders and suggest that further preclinical efforts to define its neuropsychopharmacological activ-ity profile as well as molecular mode(s) of action will be useful to more precisely defining and understanding its entire therapeutic potential.

Conflict of interest The investigations were financially supported by Dr. Will-mar Schwabe GmbH & Co. KG, Karlsruhe (Germany).

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