Assessment of Moroccan Cannabis sativa Seed Oil: Chemical Analysis and Evaluation of Antioxidant, Toxicological, and Antinociceptive Effects.

Cannabis sativa L. is a plant known locally as "El kif" of the Cannabaceae family. This study aimed to conduct a chemical analysis of Cannabis sativa seed oil (CSSO) and assess its acute toxicity, antioxidant properties, and analgesic effects. The chemical analysis was performed using gas chromatography and mass spectrometry (GC/MS) to identify its fatty acids (FAs) content. Antioxidant activity was evaluated in vitro using the DPPH (2,2-diphenyl-1-picrylhydrazyl) radical scavenging method and the FRAP (ferric reducing antioxidant power) method. Concurrently, acute toxicity, along with antinociceptive activity, was studied through three distinct animal models: writhing test, formalin test, and hot plate test. The results revealed that linoleic acid, oleic acid, α-linolenic acid, and palmitic acid were the main components of CSSO. The LD50 of CSSO was greater than 5 g/kg, indicating low toxicity. Additionally, CSSO exhibited a significant content of flavonoids and total polyphenols, along with notable antioxidant activity with values. The results indicated a significant increase in thermal stimulus latency, a reduction in the number of writhes induced by acetic acid, and a decrease in licking time in both phases of the formalin test. In conclusion, this study suggests promising results for CSSO emphasizing its potential as a therapeutic agent.

Chemical Investigation and Antinociceptive Activity Evaluation of Marrubium Vulgare L. Aqueous Extract.

Marrubium vulgare L. (Lamiaceae) has a long history of use in traditional herbal medicine for the treatment of respiratory tract infections, inflammatory conditions, and pain. This study aimed to investigate the chemical composition, acute toxicity, and antinociceptive effects of the aqueous extract from M. vulgare leaves (AEMV). Antioxidant activity was evaluated using DPPH and reducing power assays. The chemical composition of AEMV was determined through LC-MS/MS, and the levels of total phenolics, flavonoids, and condensed tannins were quantified. Acute oral toxicity was assessed in male Swiss mice with a single oral dose of AEMV (1, 2, 5 g/kg). The analgesic impact was examined through writhing, hot plate, and formalin tests. Our findings not only confirmed the safety of the extract in animal models but also revealed significant antioxidant activity in AEMV. High-performance liquid chromatography (HPLC) analysis identified important bioactive compounds, with marrubiin being a major component. Furthermore, AEMV demonstrated robust antinociceptive properties in all conducted tests, highlighting its potential as a valuable natural source of bioactive compounds suitable for a wide range of therapeutic applications.

Molecular docking of quercetin: a promising approach for the development of new anti-inflammatory and analgesic drugs.

The aim of this study is to investigate the antinociceptive, anti-inflammatory and antipyretic effects of quercetin. Additionally, molecular docking studies were conducted to evaluate potential interactions between quercetin and various molecular targets. Animal models were used to conduct a comprehensive pharmacological investigation of quercetin. Evaluation of analgesic activity revealed a reduction in the number of abdominal cramps during the twisting test and inhibition of pain during the second phase of the formaldehyde test. Additionally, evaluation of its anti-inflammatory activity showed a reduction in ear oedema. However, it is important to note that quercetin administration has not been shown to significantly reduce yeast-induced hyperthermia. The docking study revealed the high inhibitory potential of quercetin against the COX-2 receptor.

Modulation of Gut Microbiome in Ecstasy/MDMA-Induced Behavioral and Biochemical Impairment in Rats and Potential of Post-Treatment with Anacyclus pyrethrum L. Aqueous Extract to Mitigate Adverse Effects.

The use of illicit substances continues to pose a substantial threat to global health, affecting millions of individuals annually. Evidence suggests the existence of a 'brain-gut axis' as the involving connection between the central nervous system and gut microbiome (GM). Dysbiosis of the GM has been associated with the pathogenesis of various chronic diseases, including metabolic, malignant, and inflammatory conditions. However, little is currently known about the involvement of this axis in modulating the GM in response to psychoactive substances. In this study, we investigated the effect of MDMA (3,4-methylenedioxymethamphetamine, "Ecstasy")-dependence on the behavioral and biochemical responses, and the diversity and abundance of the gut microbiome in rats post-treated (or not) with aqueous extract of Anacyclus pyrethrum (AEAP), which has been reported to exhibit anticonvulsant activity. The dependency was validated using the conditioned place preference (CPP) paradigm, behavioral, and biochemical tests, while the gut microbiota was identified using matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS). The CPP and behavioral tests confirmed the presence of MDMA withdrawal syndrome. Interestingly, treatment with AEAP led to a compositional shift in the GM compared to the MDMA-treated rats. Specifically, the AEAP group yielded a higher relative abundance of Lactobacillus and Bifidobacter, while animals receiving MDMA had higher levels of E. coli. These findings suggest that A. pyrethrum therapy may directly modulate the gut microbiome, highlighting a potential target for regulating and treating substance use disorders.

Trihexyphenidyl Alters Its Host's Metabolism, Neurobehavioral Patterns, and Gut Microbiome Feedback Loop-The Modulating Role of Anacyclus pyrethrum.

Trihexyphenidyl (THP)-a synthetic anticholinergic medication used to manage parkinsonism and extrapyramidal symptoms-has gained significant clinical recognition. However, there is a critical gap in understanding its withdrawal effects. This study investigates the intricate interplay between gut microbiota and oxidative stress during THP withdrawal. Furthermore, it explores the therapeutic potential of Anacyclus pyrethrum (AEAP) for alleviating the associated adverse effects. This comprehensive research combines behavioral tests, biochemical analysis, gut microbiome assessment utilizing matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS), and oxidative stress measures. The results reveal that the chronic administration of THP leads to severe withdrawal syndrome, marked by heightened anxiety, depressive-like behaviors, increased cortisol levels, elevated oxidative stress, and gut dysbiosis. However, the administration of AEAP alongside THP shows a significant capacity to mitigate these deleterious effects. Co-treatment and post-treatment with AEAP increased bacterial density and diversity, promoting the proliferation of beneficial bacteria associated with improved gut health. Furthermore, AEAP administration reduced cortisol levels and exhibited potent antioxidant properties, effectively countering the THP-induced oxidative damage. This study highlights the withdrawal effects of THP and underscores the therapeutic potential of AEAP for managing these symptoms. The findings reveal its promising effects in alleviating behavioral and biochemical impairments, reducing oxidative stress, and restoring gut microbiota, which could significantly impact the clinical management of THP withdrawal and potentially extend to other substance withdrawal scenarios.

Antiarthritic and Anti-Inflammatory Properties of Cannabis sativa Essential Oil in an Animal Model.

Arthritis and inflammatory conditions require effective therapies, but conventional drugs have side effects. This study explored Cannabis sativa L. essential oil (CSEO) as a safer alternative. A chemical characterization of EO conducted via GC/MS showed the presence of sesquiterpene hydrocarbons (67.63%), oxygenated sesquiterpenes (25.91%), and oxygenated monoterpenes (0.99%). The study used three established inflammation induction tests: xylene-induced ear swelling, carrageenan-induced paw inflammation, and inflammation in the paw induced by Freund's complete adjuvant (CFA). Xylene triggered acute inflammation in the ear, while carrageenan-induced acute inflammatory responses through edema and immune-cell recruitment in the paw. CFA-induced arthritis simulated chronic inflammatory conditions. The obtained results demonstrated that treatment with CSEO significantly reduced ear weight in the xylene-induced ear-swelling test, indicating potential inhibition of neutrophil accumulation. In the carrageenan-induced paw inflammation test, CSEO reduced paw volume, suggesting interference with edema formation and leukocyte migration. In the CFA-induced paw inflammation test, CSEO decreased contralateral paw volume, restored body weight, and reduced C-reactive protein levels. Conclusion: this study provides compelling evidence supporting the antiarthritic and anti-inflammatory effects of CSEO. The findings indicate the therapeutic value of EO in the management of arthritis and inflammatory diseases while highlighting the need for further in-depth research to study the molecular mechanisms and validate their safety and efficacy for clinical applications. Preliminary data from this study suggests encouraging prospects for advancing the treatment and prevention of inflammation.

Antioxidant and Polyphenol-Rich Ethanolic Extract of Rubia tinctorum L. Prevents Urolithiasis in an Ethylene Glycol Experimental Model in Rats.

Treatment of kidney stones is based on symptomatic medications which are associated with side effects such as gastrointestinal symptoms (e.g., nausea, vomiting) and hepatotoxicity. The search for effective plant extracts without the above side effects has demonstrated the involvement of antioxidants in the treatment of kidney stones. A local survey in Morocco has previously revealed the frequent use of Rubia tinctorum L. (RT) for the treatment of kidney stones. In this study, we first explored whether RT ethanolic (E-RT) and ethyl acetate (EA-RT) extracts of Rubia tinctorum L. could prevent the occurrence of urolithiasis in an experimental 0.75% ethylene glycol (EG) and 2% ammonium chloride (AC)-induced rat model. Secondly, we determined the potential antioxidant potency as well as the polyphenol composition of these extracts. An EG/AC regimen for 10 days induced the formation of bipyramid-shaped calcium oxalate crystals in the urine. Concomitantly, serum and urinary creatinine, urea, uric acid, phosphorus, calcium, sodium, potassium, and chloride were altered. The co-administration of both RT extracts prevented alterations in all these parameters. In the EG/AC-induced rat model, the antioxidants- and polyphenols-rich E-RT and EA-RT extracts significantly reduced the presence of calcium oxalate in the urine, and prevented serum and urinary biochemical alterations together with kidney tissue damage associated with urolithiasis. Moreover, we demonstrated that the beneficial preventive effects of E-RT co-administration were more pronounced than those obtained with EA-RT. The superiority of E-RT was associated with its more potent antioxidant effect, due to its high content in polyphenols.

Trigonella foenum-graecum L. Sprouted Seed Extract: Its Chemical HPLC Analysis, Abortive Effect, and Neurodevelopmental Toxicity on Mice.

The Trigonella foenum-graecum L. seeds, in a dormant or sprouted state, have been largely investigated for their therapeutic activities such as being antidiabetic, antioxidant, cholesterol-lowering, and as a digestive enhancer too. Nevertheless, there are no studies evaluating the potential developmental toxicity of germinated grains despite the availability of numerous research studies demonstrating the teratogenicity effect of unsprouted seeds. Therefore, this research work was conducted to assess the impact of fenugreek sprouts on maternal and neurobehavioral developmental toxicities on mice. The lyophilized aqueous extract of germinated seeds was administered via oral gavage on a daily basis to five groups of mated female mice throughout pregnancy at doses of 200, 500, 800, and 1000 mg/kg/day and the control group was administered distilled water. Maternal reproductive toxicity was evaluated, and the surviving pups were assessed for their physical development, malformation, and neurobehavioral toxicity by using a battery of tests from birth to the 25th postnatal day. Additionally, the aqueous extract of germinated and ungerminated seeds was analyzed by high-performance liquid chromatography (HPLC) for a comparison of their major compounds. For pregnant treated female mice, no death and no intoxication symptoms have been registered during the test. However, the sprouts' extract has provoked a significant decrease in fertility, spontaneous abortion, pup's mortality, and neurobehavioral disorder in offspring. HPLC analysis reveals an increase in total phenolic compound concentration by the process of sprouting.

Salvia officinalis, Rosmarinic and Caffeic Acids Attenuate Neuropathic Pain and Improve Function Recovery after Sciatic Nerve Chronic Constriction in Mice.

The leaves of Salvia officinalis L. have a traditional reputation for the management of pain in Morocco. This study was conducted to investigate the curative effects of Salvia officinalis (SO) and its major constituents Rosmarinic (ROS) and Caffeic acids (CAF) on peripheral neuropathic pain in mice. Chronic constriction injury (CCI) was induced in mice, and neuropathic pain behaviors tests were evaluated by mechanical, chemical, thermal sensation tests and functional recovery of the sciatic nerve at different time intervals, i.e., (day 0, 1, 7, 14, and 21). Ethanolic extract of SO (100 and 200 mg/kg, p.o.), ROS (10 and 20 mg/kg, i.p.), CAF (30 and 40 mg/kg, i.p.), and CLOM (5 mg/kg, i.p., a positive control) was given for 21 days after surgery. Hematological and biochemical parameters were also measured as well as histopathological analysis. CCI produced significant development in mechanical and thermal hyperalgesia, cold allodynia, and rise in the sciatic functional index in mice. Chronic treatments with SO extract, ROS, CAF, and CLOM for 3 weeks significantly increased mechanical sensibility, cold, and thermal withdrawal latency and enhanced functional recovery of the injured nerve. The same treatments remarkably ameliorated hematological parameters and did not alter biochemical levels. The histopathological findings had revealed the protective effect of SO, ROS, and CAF against the CCI-induced damage. Our data support the use of SO in folk medicine to alleviate pain. Their main phenolic constituents could be promising antineuropathic compounds, which may be attributed to their biological activities including anti-inflammatory, antioxidant, and neuroprotective effects. SO leaves may be a good candidate to treat neuropathic pain.

Effect of Artemisia herba-alba consumption during pregnancy on fertility, morphological and behaviors of mice offspring.

ETHNOPHARMACOLOGICAL RELEVANCE: Pregnant women prefer herbal medicines more than pharmaceutical drugs due to the cultural belief that herbs are more suffer during pregnancy for an accurate foetus development. Artemisia herba-alba (Asteraceae) is one of the most used plants in the Mediterranean region to treat various diseases including diabetes, hypertension, spasmodic dysphonia and some bacterial infection. AIM OF THE STUDY: The present study aimed to investigate the effect of Artemisia herba-alba consumption during pregnancy on fertility, physical and behavior developments of mice offspring from birth-to-weaning days. MATERIALS AND METHODS: Female pregnant mice were divided into three groups and orally administrated with 80 and 150 mg/kg/day of the methanol extract of Artemisia h.a respectively, during the entire period of gestation. At birth, total fertility rate was counted. Body development; neuromotor reflex and behavior were also examined in mice offspring RESULTS: Artemisia h.a (Aha) exposure significantly decreased the fertility ratio in both Aha-treated groups and increased the weight and length of mice offspring in 80 mg/kg/day Aha-exposed group. Moreover, Aha administration prolonged the time of completing the reflex response of surface righting, negative geotaxis, cliff avoidance and jumping test of mice offspring in Aha-exposed groups. CONCLUSION: The present study provides strong evidence that discourage the use of Artemisia h.a during gestation period.

Intracerebroventricular administration of cigarette smoke condensate induced generalized seizures reduced by muscarinic receptor antagonist in rats.

Tobacco smoking is considered the greatest risk factor for early death caused by noncommunicable diseases. Currently, there are more than one billion tobacco smokers in the world predisposed to many diseases including heart attack, stroke, cancer, and premature birth or birth defects related to the consumption of cigarettes. However, studies on the association between tobacco smoking and seizures or epilepsy are insufficient and not well documented. In the present study, the authors examined the convulsive effects of the intracerebroventricular administration of cigarette smoke condensate (CSC, 2µl/Rat) in rats and compared it with the intensity of seizures in the kainic acid (KA)-induced seizure model of epilepsy. The role of the cholinergic system was also investigated by testing the effect of the muscarinic acetylcholine receptors (mAChRs) antagonist atropine (2ml/kg) on CSC-induced seizures. The results indicate that a central injection of CSC produces an epileptic behavior similar to that induced by KA, the similarities include the following parameters: time latency of seizures, latency and duration of tonic-clonic seizures, duration of seizures, survival, and tonic-clonic rate. However, a pretreatment with atropine reduced seizures and all their parameters.

Comparative study of the antitumor effect of natural monoterpenes: relationship to cell cycle analysis

Monoterpenes have been identified as responsible of important therapeutic effects of plant-extracts. In this work, we try to compare the cytotoxic effect of six monoterpenes (carvacrol, thymol, carveol, carvone, eugenol and isopulegol) as well as their molecular mechanisms. The in vitro antitumor activity of the tested products, evaluated against five tumor cell lines, show that the carvacrol is the most cytotoxic monoterpene. The investigation of an eventual synergistic effect of the six natural monoterpenes with two anticancer drugs revealed that there is a significant synergy between them (p<5%). On the other hand, the effect of the tested products on cell cycle progression was examined by flow cytometry after DNA staining in order to investigate the molecular mechanism of their cytotoxic activity. The results revealed that carvacrol and carveol stopped the cell cycle progression in S phase; however, thymol and isopulegol stopped it in G0/G1 phase. Regarding carvone and eugenol, no effect on cell cycle was observed.

Evaluation of the in vitro and in vivo anticancer properties of Moroccan propolis extracts

This investigation aimed to evaluate the in vitro and in vivo antitumor potential of a Moroccan propolis extracts. For in vitro assays, three mammalian tumor cell lines were used: BSR (hamster renal adenocarcinoma), Hep-2 (human laryngeal carcinoma) and P815 (murin mastocytoma). The propolis ethanolic extract as well as the ethyl acetate extract, exert an in vitro cytotoxic activity in dose-dependent manner. The IC50 values were ranging from 15 µg/mL to 38 µg/mL. This activity depends not only on the extract's chemical composition (analysed by HPLC/ESI-MS), but also on the target tumor cells. Interestingly, the cytotoxic effect of these extracts on the normal human peripheral blood mononuclear cells (PBMC) was weak when compared to that induced on tumor cells. On the other hand, oral route treatment of P815 tumor-bearing mice (DBA2/P815) with propolis ethanolic extract (5 mg per mouse every fourth day, five times for group A, and 2.5 mg per mouse every fourth day, five times for group B) significantly reduced the tumor volume (1.2 cm³ for group A and 2.7 cm³ for group B at the 22nd day after tumor graft). These effects are statistically significant as compared to those obtained with the control untreated mice (tumor volume 3.5 cm³ at day 22).

Comparative study of the anti-inflammatory and antinociceptive effects of two varieties of Punica granatum.

CONTEXT: Studies have shown that pomegranate, Punica granatum Linn. (Lythraceae), has remarkable biological and medicinal properties. OBJECTIVE: This work aimed to explore and compare the analgesic and anti-inflammatory activities of the methanol extract (MoE) obtained from fruit peels of two varieties of pomegranate: Amrouz (MoEA) and Sefri (MoES). MATERIALS AND METHODS: Antinociceptive activity of MoEA and MoES was examined using four models of pain. The extracts were administered by the intraperitoneal route (i.p.) in writhing (50, 100 and 150 mg/kg) and formalin tests (25, 50 and 100 mg/kg) and by intra-cerebroventricular injection (i.c.v.) in hotplate and tail-immersion tests (10, 25 and 50 µg/3 µl/rat). anti-inflammatory activity was studied using the hind paw egg albumin test (50, 100 and 150 mg/kg, i.p.). RESULTS: In the writhing test, the index of pain inhibition (IPI) was 52% for MoEA (150 mg/kg, i.p.) and 29% for MoES (150 mg/kg, i.p.). In the formalin test, the IPI of early and late phase were, respectively, 75% and 82% for MoEA (100 mg/kg, i.p.) and 8% and 63% for MoES (100 mg/kg, i.p.). In the hotplate and tail-immersion test, MoEA and MoES increased in a dosedependent manner the reaction latency to the thermal stimuli. MoEA seems to be more potent than MoES. Only the analgesic effect of MoEA was partially inhibited by pretreatment with naloxone. Both extracts exerted a significant anti-inflammatory effect. DISCUSSION AND CONCLUSIONS: The results demonstrated that P. granatum contains active constituents, which possess antinociceptive and anti-inflammatory activity, justifying its popular uses.

Prenatal exposure to tobacco extract containing nicotinic alkaloids produces morphological and behavioral changes in newborn rats.

Tobacco exposure is not only a health concern for adults but has also been shown to exert deleterious effects on the health of the fetus, newborn, child, and adolescent. Decreased cognitive function, lower Intellectual Quotient (IQ) and deficits in learning and memory in children have been associated with maternal smoking during pregnancy. In this study, we have studied the effect of a tobacco plant extract on the growth and development in the rat. The extract contained relative proportions of alkaloids, including nicotine, purified by chemical separation. Pregnant rats received oral doses of either control (NaCl) or tobacco extract during the entire gestational period. Offspring length and body weight were measured. Each day, the offspring were observed for the following physical parameters: hair growth, incisor eruption and eye opening. The day of appearance of these developments was recorded. Before weaning, the offspring were examined to test their cliff avoidance response (6 postnatal day (PN)), surface righting reflex (05, 07, 13 postnatal day), swimming development (10, 12 postnatal day), negative geotaxis response (7,9,13 and 17 postnatal day) and jumping down choice cage (15, 17 postnatal day). Administration of tobacco extract to dams during the entire gestation period affects behavior and development in pups. The observed effects were a delay in opening eyes, incisor eruption and hair appearance, behavioral developments and an alteration in the rate of success behavior. However, in the jumping down choice cage test there was no difference compared to control animals. The results suggest that tobacco extract has a significant effect on the development of behavioral patterns, orientation and motor coordination and function. They also suggest significant growth retardation and teratogenic effects.

Chemical composition and antiproliferative activity of essential oil from aerial parts of a medicinal herb Artemisia herba-alba

Artemisia herba-alba Asso., Asteraceae, is widely used in Morrocan folk medicine for the treatment of different health disorders. However, no scientific or medical studies were carried out to assess the cytotoxicity of A. herba-alba essential oil against cancer cell lines. In this study, eighteen volatile compounds were identified by GC-MS analysis of the essential oil obtained from the plant's aerial parts. The main volatile constituent in A. herba-alba was found to be a monoterpene, Verbenol, contributing to about 22 percent of the total volatile components. The essential oil showed significant antiproliferative activity against the acute lymphoblastic leukaemia (CEM) cell line, with 3 µg/mL as IC50 value. The anticancer bioactivity of Moroccan A. herba-alba essential oil is described here for the first time.

Evaluation of the analgesic effect of alkaloid extract of Peganum harmala L.: possible mechanisms involved.

The seeds of Peganum harmala L. (Pgh) (Zygophyllaceae) have been used in Moroccan traditional medicine for treatment of a various diseases and to relieve dolorous process. The major objective of this paper was to investigate the mechanism of the analgesia induced by alkaloid extract of Peganum harmala. In the present work, the antinociceptive action was assayed in several experimental models in mice: writhing, formalin, and hot plate tests. The alkaloid extract (12.5 and 25mg/kg) and in a dose-dependent manner significantly reduced the nociception by acetic acid intraperitoneal injection (p<0.001). In the formalin test, the extract also significantly reduced the painful stimulus in both phases of the test (p<0.001). Treatment with the extract when given by (i.p. or i.c.v.) or with morphine (10mg/kg, i.p.) produced a significant increase of the reaction time in hot plate test. These result showed that the alkaloid extract of Pgh contains active analgesic principles acting both centrally and peripherally. Furthermore, this antinociceptive effect has been avoided by naloxone at a dose of 1mg/kg in the first phase of formalin and hot plate tests indicating that this extract act partly through an opioid-mediated mechanism. In conclusion, the alkaloid extract of Peganum harmala seems to have both central and peripheral antinociceptive activities which may be mediated by opioid receptors.

Prophylaxis effect of Trigonella foenum graecum L. seeds on renal stone formation in rats.

Despite considerable progress in medical therapy, there is no satisfactory drug to treat kidney stones. Therefore, the current study aimed to look for an alternative by using Trigonella foenum graecum (Tfg) on nephrolithiasic rats as a preventive agent against the development of kidney stones, which is commonly used in Morocco as a phytotherapeutic agent. The inhibitory effect of the aqueous extract of Tfg seeds was examined on the formation of calcium oxalate renal stones induced by ethylene glycol (EG) with ammonium chloride. At the end of the experiment all kidneys were removed and examined microscopically for possible crystal/stone locations and the total calcium amount in the renal tissue was evaluated. The blood was recovered to determine the levels of calcium, phosphorus, creatinine and urea. The results showed that the amount of calcification in the kidneys and the total calcium amount of the renal tissue in rats treated with Tfg were significantly reduced compared with the untreated group. Consequently, Tfg may be a useful agent in the treatment of patients with calcic urolithiasis.

No tolerance to the antinociceptive action of calcitonin in rats and mice.

The involvement of a central opioid mechanism in the antinociceptive effect of calcitonin is still a matter of controversy. Since a major characteristic of the effects of opioids is tolerance to repeated treatments, we investigated the effects of acute and chronic (over 7 days) calcitonin injections on pain sensitivity in rats and mice. We examine the effect of single and repeated intraventricular (0.15 UI) and intraperitoneal (2.5, 5 and 20 IU/kg) injection of salmon calcitonin using respectively a tail flick test in rats and the writhing test in mice. The results showed that repeated injection of calcitonin produces a stronger antinociceptive effect than the single injection effect. The antalgic effect, evaluated in the writhing test, is dose-dependent. In both tail-immersion and writhing tests, repeated administration of calcitonin produced a long-lasting antinociceptive effect. These data suggest therefore that the tolerance does not develop after repeated treatment with calcitonin in both rat and mouse. These results support the hypothesis that an important component of the antinociceptive effects of calcitonin is not mediated by an opioid mechanism.