Antinociceptive and antidepressant like effects of Securidaca longepedunculata root extract in mice

Journal of Ethnopharmacology 107 (2006) 234–239

Antinociceptive and antidepressant like effects of Securidaca longepedunculata root extract in mice R.A. Adebiyi a,∗ , A.T. Elsa b , B.M. Agaie c , E.U. Etuk a a

b

Department of Pharmacology, Usmanu Danfodiyo University, c/o P.O. Box 3542, Sokoto, Nigeria Department of Veterinary Medicine, Surgery and Theriogenology, Usmanu Danfodiyo University, Sokoto, Nigeria c Department of Veterinary Physiology and Pharmacology, Usmanu Danfodiyo University, Sokoto, Nigeria Received 12 October 2005; accepted 9 March 2006 Available online 27 March 2006

Abstract The aqueous root extract of Securidaca longepedunculata (polygalaceae) was investigated for possible antinociceptive and central nervous system (CNS) effects in mice. Three nociceptive models; acetic acid, formalin and tail-flick tests were used to study the antinociceptive activity. Rectal temperature test was employed as an adjunct to the nociceptive models. The extract at 200 and 400 mg/kg significantly and dose dependently reduced the nociception induced by the acetic acid and in the early phase of formalin test (P < 0.05). The extract exerted significant (P < 0.05) hypothermic effect in the 15 and 30 min of the rectal temperature test. The antinociceptive and hypothermic effects were partially reversed by naloxone (1 mg/kg). The tail-flick test produced an insignificant increase in tail-flick latency at 400 mg/kg after 60 min of the test, but significantly (P < 0.05) increase tail-flick latency in the 400 mg/kg group of animals pre-treated with naloxone (1 mg/kg) after 120 min of the test. The extract also produced a significant (P < 0.05) naloxone reversible antidepressant like effect in the forced swimming test (an animal model of depression). Collectively, these results suggest that the extract possess antinociceptive and antidepressant like effects with possible involvement of opioidergic pathways. The extract at limit dose of 2 g/kg body weight appeared to be safe in oral formulation. © 2006 Elsevier Ireland Ltd. All rights reserved. Keywords: Securidaca longepedunculata; Antinociception; Antidepressant; Opioid pathways

1. Introduction Securidaca longepedunculata (fresen), commonly known as violet tree (family: polygalaceae), is a shrub or a small 2–10 m high flowering savannah tree which is widely distributed in tropical Africa, and occurs naturally in the north western and south western parts of Nigeria. It is reported that in Nigeria and some other African countries like South Africa, the roots, stem bark, and leaves of Securidaca longepedunculata are used medicinally for treating a plethora of human and animal ailments (Neuwinger, 1964). This has earned the plant a popular vernacular name in the Hausa speaking north western part of Nigeria “Uwar magnum guna”, meaning mother of all medicines. The powdered roots are reportedly rubbed into scarification marks made on the forehead to treat headaches, and roots are chewed

∗

Corresponding author. Tel.: +234 8036043370; fax: +234 60 231514. E-mail address: [email protected] (R.A. Adebiyi).

0378-8741/$ – see front matter © 2006 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.jep.2006.03.017

to relieve toothache; powdered root of the plant has been applied externally to wounds and sores, and around the joints for relief of rheumatism (Watt and Breyer-Brandwijk, 1962). In north western states of Nigeria, fresh pungent root bark is reportedly applied topically over the incision with sharp object at the site of snake bite or scorpion stings, and the roots are also used to treat cold and meningitis (Hambali, 1990). Atawodi et al. (2003) reported that the methanol extract of Securidaca longepedunculata has some in vitro trypanocidal activities while methyl salicylate reportedly present in the volatile constituent is said to be responsible for the plant biocide effect against stored grain insects (Lognay et al., 2000). The basis for the traditional use of this herb in the management of painful and some central nervous system related conditions has not yet been scientifically verified to our knowledge. The present study therefore, is aimed at investigating possible antinociceptive effect of the aqueous root extract of Securidaca longepedunculata (SL) and to explore its possible mechanism of action using experimental models in mice. The activity on CNS was

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also investigated in order to examine the antinociceptive activity related to antidepressant action. The acute toxicity profile was also evaluated. 2. Materials and methods 2.1. Preparation of plant materials and extract The fresh roots of Securidaca longepedunculata were collected in the month of October 2004 from its natural habitat at Mekujera village in Rabah local government area of Sokoto, Nigeria. The plant was authenticated by Dr. B.L. Aliero of Biological Science Department, Usmanu Danfodiyo University (UDUS), Sokoto. A voucher specimen (NO.: D-OISL-4) was deposited at the Herbarium, Department of Biological Sciences, Botany Unit, UDUS. The clean roots cut into pieces were air-dried to constant weight and pulverized to a dry powder. About 250 g of the powder were macerated with 3 l of distilled water for 24 h. The liquid obtained by filtration was oven dried at a temperature of 55 ◦ C and the percentage yield of extract was calculated to be 15.04% (w/w). Appropriate concentrations of the extracts were made in distilled water and used in the experiments. 2.2. Phytochemical screening Standard screening test (Evans, 1999), were used in screening the extract for different constituents. The extract was screened using conventional protocol for the presence of alkaloids, saponins, flavonoids, tannins, glycosides, triterpenoids, and volatile oils. 2.3. Animals Swiss albino mice of either sex (bred in Animal Facility Unit, University of Jos, Jos, Nigeria) weighing 25–30 g were used. The animals were fed with standard mouse diet (Vital Feeds, Jos), had free access to water under well ventilated condition of 12 h light cycle. Animals were randomly assigned to the treatment groups (n = 6 or 5). The observer or rater in each test was blind to the experimental treatment. This study was carried out according to the organization for economic cooperation and development (OECD) principles on good laboratory practice (GLP), 2001. 2.4. Acute oral toxicity (limit test) The limit test dose of 2000 mg/kg was used as described by Organization for Economic Cooperation and Development guideline 425 (OECD, 2000) and Interagency Research Animal Committee (IRAC, 2004) recommendation. Five female mice, each sequentially dose at interval of 48 h were used for the test. Animals were observed individually for any sign of acute toxicity, morbidity or mortality during the first 24 h and daily there after, for a total of 14 days.

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2.5. Antinociceptive activity 2.5.1. Acetic acid-induced writhing test Siegmund et al. (1957) technique modified by Koster et al. (1959) was adopted. Animals were divided into eight groups (n = 6). Group I (control) received 0.9% saline water (10 ml/kg) orally (p.o.). Groups II and III received 200 and 400 mg/kg (p.o.) of aqueous extract of Securidaca longepedunculata, respectively. Groups IV and V received reference drugs; 250 mg/kg (p.o.) of acetylsalicylic acid and 10 mg/kg of morphine intraperitoneally (i.p.), respectively. Groups VI, VII, and VIII were each pre-treated with subcutaneous (s.c.) administration of naloxone (1 mg/kg) 15 min before administration of 10 mg/kg (i.p.) morphine, 250 mg/kg (p.o.) of acetylsalicylic acid and 400 mg/kg (p.o.) of the aqueous extract, respectively. The test was carried out 1 h after the oral treatment and 30 min after intraperitoneal administration by injecting intraperitoneally, 0.2 ml of 3% acetic acid solution to induce the characteristic writhings. The number of writhings occurring between 5 and 15 min after acetic acid injection was recorded. 2.5.2. Formalin-induced paw licking test The method used was that described by Hunskaar et al. (1985). The mice were divided into seven groups (n = 5). Group I (control) received 0.9% saline water (10 ml/kg) orally. Groups II and III received 200 and 400 mg/kg (p.o.) of the aqueous extract of Securidaca longepedunculata, respectively. Groups IV and V received reference drugs; 5 mg/kg (p.o.) of indomethacin and 10 mg/kg (i.p.) of morphine,1 respectively. Groups VI and VII were each pre-treated with naloxone (1 mg/kg, s.c.) 15 min before administration of morphine (10 mg/kg, i.p.) and 400 mg/kg (p.o.) of aqueous extract of Securidaca longepedunculata, respectively. The test was carried out 1 h after the oral treatment and 30 min after intraperitoneal administration by injecting 20 ␮l of 1% formalin into the dorsal surface of the left hind paw of the mice. Mice were observed immediately after the injection of formalin and the time spent licking the injected paw (licking time) was recorded for 5 min in the first instance (early phase). Twenty minutes after the beginning of the experiment, the licking time was also recorded for another 5 min [late phase]. 2.5.3. Tail-flick test The method earlier described by D’Amour and Smith (1941), and modified by Kulkarni (1980) and Lapa et al. (1997) was adopted. Animals were divided into seven groups (n = 5). Group I (control) received 0.9% saline water (10 ml/kg) orally. Groups II and III received 200 and 400 mg/kg (p.o.) of aqueous extract of Securidaca longepedunculata, respectively. Groups IV and V received reference drugs; 10 mg/kg (p.o.) of acetaminophen and 0.3 mg/kg (s.c.) of fentanyl, respectively. Groups VI and VII were each pre-treated with 1 mg/kg (s.c.) of naloxone, 15 min before administration of 0.3 mg/kg (s.c.) of fentanyl and 400 mg/kg (p.o.) of aqueous extract of Securidaca longepedunculata, respectively. The test was carried out 1 h after the oral and subcutaneous administration by placing the animal held in a suitable restrainer

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with the whole tail extending out, at a distance of 10 cm, to a radiant heat provided by an infra-red radiation lamp (Phillips, 150 W-250 V, Holland). The withdrawal time of the tail from the radiant heat in seconds was noted as the reaction time or tailflick latency. Antinociceptive effect (i.e. tail-flick latency) was determined every 30 min from 1 up to 3 h after the administration of test doses. Only mice that showed initial nociceptive response within 20 s were selected for the experiment while cut off time for the response was set at 60 s to avoid tissue damage to the mice’s tail.

2.8. Statistical analysis All data were expressed as the mean ± standard error of the mean (S.E.M.). One-way analysis of variance (ANOVA) with subsequent Dunnett’s or Turkey Kramer t-test post hoc analysis was used to detect further differences between groups. Values of P < 0.05 were considered significant. All statistical analysis were carried out using the Instat statistical package (Graph pad software, Inc., USA). 3. Results

2.6. Rectal temperature test 3.1. Phytochemical screening The procedure used was that described by Kulkarni and Jain (1999). Animals were divided into seven groups (n = 5). Group I (control) received 0.9% saline water (10 ml/kg) orally. Groups II and III received 200 and 400 mg/kg (p.o.) of aqueous extract of Securidaca longepedunculata, respectively. Groups IV and V received reference drugs; 250 mg/kg (p.o.) of acetylsalicylic acid and 10 mg/kg (i.p.) of morphine, respectively. Groups VI and VII were each pre-treated with naloxone (1 mg/kg, s.c.), 15 min before administration of 10 mg/kg (i.p.) of morphine and 400 mg/kg (p.o.) of aqueous extract of Securidaca longepedunculata, respectively. The test was carried out 1 h after oral treatment or 30 min after intraperitoneal administration by inserting the thermister probe of a digital thermometer (U-MEC) to a depth of 2 cm into the rectum of the animals. The rectal temperature was recorded just before (0 min) the administration of test dose and at 15, 30, 60, 120, and 180 min after administration of test doses. The ambient temperature was 34.2 ± 2 ◦ C. 2.7. Forced swimming test (FST) The method used was essentially similar to that described by Porsolt et al. (1977). Animals were divided into six groups (n = 5). Group I (control) received 0.9% saline water (10 ml/kg) orally. Groups II, III, and IV received 100, 200, and 400 mg/kg (p.o.) of aqueous extract of Securidaca longepedunculata, respectively. Group V received reference drug; 50 mg/kg (p.o.) of imipramine. Group VI were pre-treated with naloxone (1 mg/kg, s.c.) 15 min before administration of 400 mg/kg (p.o.) of aqueous extract of Securidaca longepedunculata. Each animal was subjected to a pre-test followed by an actual test within 24 h. The animals were dosed three times at intervals within 24 h and the test was carried out 1 h after the third dose was given. The test was performed by dropping each animal individually into a glass cylinder, height 25 cm, diameter 10 cm containing 12 cm of water maintained at temperature of about 25 ◦ C and left there for 4 min. The animal initially actively seeks escape, and there after rapidly becomes immobile (i.e. floating in an upright position) and making only small movement to keep their head above water. The duration of immobility was recorded. Decrease in the duration of immobility during the FST was taken as a measure of antidepressant activity.

Phytochemical analysis of the extract showed strong presence of saponins, alkaloids, and volatile oil, moderate presence of flavonoids and triterpenoids and absence of steroids, tannins, and glycosides. 3.2. Acute toxicity The limit dose of 2000 mg/kg did not cause any mortality or any sign of acute toxicity in any of the five mice tested. LD50 of the extract according to OECD guidelines is therefore greater than the limit dose tested. 3.3. Acetic acid-induced writhing Securidaca longepedunculata extract significantly (P < 0.05) and in a dose dependent manner increased the pain threshold as the number of writhes responses decreases during 20 min as compared to the control group (Table 1). The animals in group II treated with 200 mg/kg of the extracts produced an effect equal in magnitude to the mice in group IV that received acetylsalicyclic acid. However, animals in group V that received 10 mg/kg of morphine produced a 100% inhibition compared to 93.2% inhibition recorded for group III that received 400 mg/kg of the extract. Pretreatments with naloxone partially reversed the antinociceptive effect of animals in groups VI and VIII treated with morphine and 400 mg/kg of the extract respectively while animals in group Table 1 Effect of oral administration of aqueous root extract from Securidaca longepedunculata on acetic acid-induced nociception in mice Group

Treatment

Dose (mg/kg)

I II III IV V VI VII VIII

Control SL SL ASA Morphine Nal + morphine Nal + ASA Nal + SL

200 400 250 10 1 + 10 1 + 250 1 + 400

Writhings (No.) 7.30 ± ± * 0.50 ± * 2.50 ± * 0.00 ± 1.90 ± 2.40 ± 3.20 ± * 2.50

1.05 1.15 0.34 0.91 0.00 1.19 0.62 1.11

Inhibition (%) 65.80 93.20 65.80 100.00 73.90 67.10 56.20

Data are means ± S.E.M., n = 6. Nal, naloxone; ASA, acetylsalicyclic acid; SL, Securidaca longepedunculata. * P < 0.05 vs. control, ANOVA and Dunnett’s as a post hoc test.

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Table 2 Effect of oral administration of aqueous root extract from Securidaca longepedunculata on formalin-induced nociception in mice Group

Treatment

Dose (mg/kg)

I II III IV V VI VII

Control SL SL Indomethacin Morphine Nal + morphine Nal + SL

200 400 5 10 1 + 10 1 + 400

Licking time (s) early phase 53.67 35.83 * 29.50 34.50 * 6.17 35.67 45.50

± ± ± ± ± ± ±

Licking time (s) late phase

2.59 5.41 3.07 4.19 5.97 7.84 7.38

13.00 3.83 7.83 9.17 0.67 10.83 10.50

± ± ± ± ± ± ±

4.51 1.80 2.20 2.69 0.67 6.31 3.37

Inhibition (%) early phase

Inhibition (%) late phase

33.20 45.00 35.70 87.60 33.54 15.22

70.50 39.80 29.50 94.90 16.70 19.20

Data are means ± S.E.M., n = 6. Nal, naloxone; SL, Securidaca longepedunculata. * P < 0.05 vs. control, ANOVA and Dunnett’s as a post hoc test. Table 3 Effect of oral administration of aqueous root extract from Securidaca longepedunculata on tail flick reaction time in mice Group

I II III IV V VI VII

Treatment

Control SL SL ACP Fen Nal + Fen Nal + SL

Dose (mg/kg)

Mean increase in tail flick latency (second) after

200 400 10 0.3 1 + 0.3 1 + 400

60 min

90 min

120 min

37.20 ± 3.40 37.00 ± 3.91 44.20 ± 11.77 41.60 ± 6.50 54.50 ± 21.87 44.00 ± 9.24 39.60 ± 5.95

37.80 ± 9.86 33.20 ± 2.96 39.00 ± 5.61 30.80 ± 1.80 34.40 ± 8.40 34.40 ± 7.28 45.80 ± 6.90

42.60 30.20 31.20 34.80 27.40 51.6 * 59.80

± ± ± ± ± ± ±

150 min 1.91 3.31 4.53 5.13 2.79 10.21 9.37

44.40 44.20 29.80 24.00 33.00 45.00 54.40

± ± ± ± ± ± ±

180 min 5.24 19.77 4.79 1.67 3.02 0.58 5.20

34.20 25.60 35.80 36.40 29.60 * 59.20 49.00

± ± ± ± ± ± ±

5.65 2.11 2.67 6.11 4.46 5.34 2.43

Data are means ± S.E.M., n = 5. Nal, naloxone; ACP, acetaminophen; Fen, fentanyl; SL, Securidaca longepedunculata. * P < 0.05 vs. groups II and III, ANOVA and Turkey Kramer’s as a post hoc test.

3.5. Tail-flick latency

VII that received acetylsalicyclic acid pre-treated with naloxone remained largely unaffected.

Table 3 shows that the mice produced an insignificant (P > 0.05) increase in tail-flick latency in group III (400 mg/kg), group IV (acetaminophen) and group V (fentanyl), after 60 min of the test, though fentanyl group recorded the highest response. There was also partial reversal of the antinociception (shown by decrease in tail-flick latency) in group VI (fentanyl) and group VII (400 mg/kg) pre-treated with naloxone after 60 min of the test. However, at 120 min, there was significant (P < 0.05) increase in tail-flick latency in group VII pre-treated with naloxone before treatment with 400 mg/kg of the extract, and also at 180 min in group VI pre-treated with naloxone before treatment with fentanyl.

3.4. Formalin-induced paw licking Securidaca longepedunculata extract significantly (P < 0.05) at 400 mg/kg and dose dependently inhibited the early phase of the formalin response but could not effectively protect the mice against paw licking in the late phase (Table 2). Group V (morphine) showed greatest protection against paw licking in both phases. Indomethacin produced a result only comparable to group II (200 mg/kg) of the extract in the early phase. Pre-treatment with naloxone however partially reversed the antinociceptive effect in group VII (400 mg/kg of extract) in both phases.

Table 4 Effect of oral administration of aqueous root extract from Securidaca longepedunculata on rectal temperature of mice at ambient temperature Group

Treatment

Dose (mg/kg)

Mean decrease in rectal temperature (◦ C) after 0 min

I II III IV V VI VII

Control SL SL ASA Mor Nal + Mor Nal + SL

200 400 250 10 1 + 10 1 + 400

36.86 ± 0.18 37.96 ± 0.27 37.52 ± 0.17 37.32 ± 0.19 36.52 ± 0.26 36.58 ± 0.33 36.24 ± 0.36

15 min 38.08 ± ± * 34.90 ± 37.52 ± * 34.84 ± 36.58 ± 35.00 ± * 34.66

30 min 0.29 0.16 0.48 0.27 0.41 0.31 0.79

37.72 ± ± * 35.42 ± 37.74 ± * 34.46 ± 36.02 ± 34.80 ± * 34.72

0.09 0.72 0.49 0.29 0.33 0.51 0.79

60 min

120 min

180 min

37.06 ± 0.35 35.16 ± 0.82 35.72 ± 0.26 37.16 ± 0.27 35.12 ± 0.41 35.92 ± 0.25 35.18 ± 0.94

36.98 ± 0.26 35.34 ± 0.87 36.30 ± 0.61 37.14 ± 0.28 36.10 ± 0.38 36.78 ± 0.28 35.14 ± 0.84

37.43 ± 0.29 35.38 ± 0.66 36.78 ± 0.46 37.36 ± 0.38 36.50 ± 0.18 36.18 ± 0.22 35.28 ± 1.01

Data are means + S.E.M., n = 5. Nal, naloxone; SL, Securidaca longepedunculata; ASA, acetylsalicyclic acid; Mor, morphine. * P < 0.05 vs. control, ANOVA and Dunnett’s as a post hoc test.

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Table 5 Antidepressant effect of oral administration of aqueous root extract from Securidaca longepedunculata on forced swimming in mice Group

Treatment

Dose (mg/kg)

Decrease in immobility duration (min) Pre-test

I II III IV V VI

Control SL SL SL Imip Nal + SL

1.80 2.00 1.40 2.00 2.02 1.50

100 200 400 50 1 + 400

± ± ± ± ± ±

Test 0.20 0.32 0.25 0.32 0.17 0.16

2.00 1.40 1.09 * 0.51 * 0.83 1.48

± ± ± ± ± ±

0.31 0.40 0.25 0.17 0.07 0.14

Data are means ± S.E.M., n = 5. Nal, naloxone; SL, Securidaca longepedunculata; Imip, imipramine. * P < 0.05 vs. control, ANOVA and Dunnett’s as a post hoc test.

3.6. Rectal temperature Securidaca longepedunculata extract produced significant (P < 0.05) decrease in rectal temperature similar to those of group V (morphine) after 15 and 30 min of the test (Table 4). Acetylsalicyclic acid did not produce any change in rectal temperature throughout the duration of the experiment. Pre-treatment with naloxone partially reversed the decease in rectal temperature in group VII (400 mg/kg) while it completely reversed the decrease in rectal temperature in group VI (morphine). 3.7. Forced swimming test Securidaca longepedunculata extract produced a significant (P < 0.05) and dose dependent decrease in the duration of immobility of the mice at the highest dose of 400 mg/kg compared to imipramine (50 mg/kg) (Table 5), while pre-treatment of group VI (400 mg/kg) with naloxone reversed the decrease in duration of immobility of the mice. 4. Discussion The result of the acetic acid-induced writhing test showed that the extract possess significant antinociceptive activity. Acetic acid-induced writhing assay is widely used for the evaluation of peripheral antinociceptive activity (Gene et al., 1998). The method has been associated with increased level of prostaglandin in the peritoneal fluids (Derardt et al., 1980). Therefore, the result of the acetic acid-induced writhing suggests that the mechanism of action of antinociception of the extract may be linked partly to the cyclo-oxygenase enzymes. This is further corroborated by the fact that over 90% of the volatile constituent in the extract is said to contain methyl salicylate (Jayasekara et al., 2002), a classical non-steroidal anti-inflammatory drug (NSAID). Opioid antagonist, naloxone, partially blocked the antinociceptive effect of the extract in this model, suggesting that opioid receptors may also be involved in its antinociceptive action. Formalin injection into the hind paw produces an immediate noxious stimulus by inducing tissue damage, thus providing a model for inescapable acute pain. The extract significantly inhibited the early phase of paw licking of the formalin injected hind paw in this study. In formalin test, there is a distinctive biphasic nociceptive response termed early and late phases. Drugs that act

primarily on the central nervous system inhibited both phases equally while peripherally acting drugs inhibit the late phase (Shibata et al., 1989). The early phase is said to be probably a direct result of stimulation of nociceptors in the paw and said to reflect centrally mediated pain while the late phase is said to be due to inflammation occurring following the release of serotonin, histamine, bradykinnin, and prostaglandins (Tjolsen et al., 1992). The result of the formalin test may therefore suggest that the extract possess central antinociceptive effect in acute nociceptive model but weak peripheral antinociceptive properties. Naloxone, also partially reversed the antinociceptive effect of the extract in both phases, and this may also suggest the involvements of opioid receptors in its action in this model too. The tail-flick test is considered selective for opioid-like analgesic compound (Janssen et al., 1963). However, tail-flick test in this study produced an insignificant increase in tail-flick latency. The significant late response increase in tail-flick latency after 120 and 180 min in the groups pre-treated with naloxone (i.e. fentanyl and 400 mg/kg group) may be because the antagonistic effect of naloxone had waded off since it has a duration of action of about 1–2 h while there may be accumulation or stimulation of endogenous opioid-like substances with subsequent production of increased antinociception. However, the result of this test suggests that the extract of Securidaca longepedunculata did not behave effectively as an opioid receptor agonist. It is possible that the extract present different central mechanism of action in this model. The extract at doses tested (200 and 400 mg/kg) exerted a significant hypothermic effect similar to that of morphine after 15 and 30 min of the test. Anatomically, A- delta and C- nerve fibre present in the nerve roots and afferent peripheral nerves are known to conduct pain and temperature impulses through the dorsal horn root (Carpenter and Mackey, 1992). Hypothermia is one of the principal pharmacological effects of opioid agonist like morphine and it is thought that opioids act directly on temperature control centre in the hypothalamus to produce this change (Smith et al., 1995). The hypothermic effect of the extract was partially reversed by naloxone, thus providing further evidence for involvement of opioid receptors in the temperature/pain pathways of the extract action. The result of the forced swimming test clearly showed that the extract produced significant and dose dependent antidepressant like effect on the mice. The antidepressant effect was reversed by

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naloxone, and this may also suggests involvement of opioidergic pathway in the antidepressant action. Studies have shown that analgesia by antidepressant can be inhibited by naloxone and enhanced by enkephalinase inhibitors (Gray et al., 1998). This probably suggests that the chemical constituent of the extract contain an antidepressant compound or the constituent of the extract may be simply behaving like an enkephalinase enzymes inhibitor. Chemically, apart from the methyl salicylate reportedly present in the volatile constituents of the extract, the plant has also been claimed to produce several other secondary metabolites, the major ones being sapogenins, including presenegenin; indole alkaloid securinine and some ergot alkaloids (Van Wyk et al., 1997). At present, it is not clear which of the chemical constituents of the plant may be responsible for the observed pharmacological effects of the extract seen in the present study. The result of the limit test (oral acute toxicity) could be an indication that the extract has some level of safety margin in oral formulation or low acute toxicity going by OECD guideline, this further justify its wide application in various communities coupled with lack of any reported serious side effect with the traditional use of the plant. 5. Conclusion This study has shown that the aqueous root extract of Securidaca longepedunculata (Polygalaceae) possess antinociceptive and antidepressant like effects with evidence of possible involvement of opioid receptors in it actions. These findings support the use of Securidaca longepedunculata roots in traditional medicine for the treatment of some painful and central nervous system disorders and also confirmed the presence of biologically active principles whose activities may need further investigation. The plant extract at doses tested also appear to present varied/or different central and peripheral mechanism of action which may worth further elucidation and evaluation. Acknowledgements The authors are grateful for the technical assistance of Rabi Ibrahim, Zulkarnaini Liman, and Ahmed Muazu. References Atawodi, S.E., Bulus, T., Ibrahim, S., Ameh, D.A., Noka, J., Mamman, M., Galadima, M., 2003. In vitro trypanocidal effect of methanol extract of some Nigerian Savannah Plants. African Journal of Biotechnology 2, 317–321. Carpenter, R.L., Mackey, D.C., 1992. Local anaesthetic. In: Barash, P.G., Cullen, B.F., Stoelting, R.R. (Eds.), Clinical Anaesthesia, second ed. J.B. Lippincott, Philadelphia, pp. 509–541. D’Amour, F.E., Smith, D.C., 1941. A method for determining loss of pain sensation. Journal of Pharmacology and Experimental Therapeutics 72, 74–79. Derardt, R., Jougney, S., Delevalcee, F., Falhout, M., 1980. Release of prostaglandins E and F in an algogenic reaction and its inhibition. European Journal of Pharmacology 51, 17–24.

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