Enhanced detection of hyperactivity after drug withdrawal with a simple modification of the open-field apparatus

Prevention of glutamate excitotoxicity in lateral habenula alleviates ethanol withdrawal-induced somatic and behavioral effects in ethanol dependent mice

Ethanol withdrawal commonly leads to anxiety-related disorder, a central factor toward negative reinforcement leading to relapse. The lateral habenula (LHb), an epithalamic nucleus, has emerged to be critical for both reward and aversion processing. Recent studies have also implicated the hyperactivity of LHb, adding to the emergence of negative emotional states during withdrawal from addictive drugs. Herein, we have studied the effects of glutamate transporter inhibitor (PDC), GluN2B-containing NMDAR antagonist (Ro25-6981), and intracellular calcium chelator (BAPTA-AM) injection in LHb on ethanol withdrawal symptoms. We found that ethanol 4 g/kg 20 % w/v intragastric (i.g.) for 10 days followed by 24 h of withdrawal showed a significant increase in somatic signs characterized by vocalization, shaking, and scratching. It also increased locomotor activity and anxiety-like behavior, collectively showing expression of ethanol withdrawal symptoms. The intra-LHb administration of PDC (0.5 ng) worsened the effect of ethanol withdrawal, whereas Ro25-6981 (2 and 4 ng) and BAPTA-AM (6.5 and 13 ng) significantly reversed ethanol withdrawal-induced behavior evident by a decrease in somatic signs, locomotor activity, and anxiety-like behavior. Further, pretreatment of Ro25-6981 and BAPTA-AM reduced the neuronal loss, whereas PDC increased it compared to the vehicle-treated group, as evidenced by NeuN staining. Altogether, our results suggest that increased glutamate, GluN2B activation, and likely calcium increase indicative of glutamate excitotoxicity-induced neuronal loss in LHb possibly endorse the emergence of ethanol withdrawal symptoms, while their inhibition might help in alleviating the ethanol withdrawal symptoms.

Two New βN-Alkanoyl-5-Hydroxytryptamides with Relevant Antinociceptive Activity

In this work, we describe a new route for the synthesis and the antinociceptive effects of two new ^βN-alkanoyl-5-hydroxytryptamides (named C_20:0-5HT and C_22:0-5HT). The antinociceptive activities were evaluated using well-known models of thermal-induced (reaction to a heated plate, the hot plate model) or chemical-induced (licking response to paw injection of formalin, capsaicin, or glutamate) nociception. The mechanism of action for C_20:0-5HT and C_22:0-5HT was evaluated using naloxone (opioid receptor antagonist, 1 mg/kg), atropine (muscarinic receptor antagonist, 1 mg/kg), AM251 (cannabinoid CB1 receptor antagonist, 1 mg/kg), or ondansetron (5-HT3 serotoninergic receptor antagonist, 0.5 mg/kg) 30 min prior to C_20:0-5HT or C_22:0-5HT. The substances both presented significant effects by reducing licking behavior induced by formalin, capsaicin, and glutamate and increasing the latency time in the hot plate model. Opioidergic, muscarinic, cannabinoid, and serotoninergic pathways seem to be involved in the antinociceptive activity since their antagonists reversed the observed effect. Opioid receptors are partially involved due to tolerant mice demonstrating less antinociception when treated with both compounds. Our data showed a quicker and simpler route for the synthesis of the new ^βN-alkanoyl-5-hydroxytryptamides. Both compounds demonstrated significant antinociceptive effects. These new compounds could be used as a scaffold for the synthesis of analogues with promising antinociceptive effects.

Topical and systemic use of Joannesia princeps vell. LC seed oil in acute pain and inflammation induced by different agents

ETHNOPHARMACOLOGICAL RELEVANCE

Joannesia princeps (SOJP) has been used in folk medicine as anthelmintic treatment and cutaneous wound healing.

AIM OF THE STUDY

The purpose of this study is to evaluate the pharmacological activity of seed oil of Joannesia princeps, administered systemically and topically, on acute pain and inflammation.

MATERIALS AND METHODS

Male swiss mice were treated orally and topically with seed oil of Joannesia princeps in models of acute pain (acetic acid-induced abdominal writhing, formalin-induced licking behaviour and tail flick tests) and acute inflammation (carrageenan- and histamine-induced paw oedema; arachidonic acid-, capsaicin- and croton oil-induced ear oedema and air pouch tests), besides the open field model in the motor performance evaluation.

RESULTS

Seed oil of Joannesia princeps showed systemic action against acute pain in abdominal writhing test (37% and 56% inhibition in the number of writhes at doses of 30 and 100 mg/kg, respectively) and in the second phase of formalin-induced licking behaviour test (29%, 47 and 52% inhibition in the licking time at doses of 10, 30 and 100 mg/kg, respectively), as well as reducing croton oil-induced ear oedema by 72%, leukocyte recruitment and production of TNF-α and IL-6 in the air pouch tests. In addition, topical administration of SOJP inhibited carrageenan-induced paw oedema by 39% at dose of 500 μg/paw and inhibited histamine-induced oedema by 43 and 52% at doses of 300 and 500 μg/paw, respectively. SOJP also decreased croton oil-induced ear oedema by 67% at dose of 500 μg/paw and arachidonic acid-induced ear oedema by 63% at dose of 500 μg/paw, reducing the production of TNF-α, IL-1β and MIP2 in both. In addition, no adverse effects were observed at doses up to 2000 mg/kg.

CONCLUSIONS

Seed oil of Joannesia princeps presents antinociceptive and anti-inflammatory actions through its topical and systemic administration, promoted by inhibition of leukocyte recruitment and cytokine production (TNF-α, IL-1β, IL-6 and MIP-2).

Lilium davidii extract alleviates p‑chlorophenylalanine‑induced insomnia in rats through modification of the hypothalamic-related neurotransmitters, melatonin and homeostasis of the hypothalamic-pituitary-adrenal axis

CONTEXT

Lilium davidii var. unicolour Cotton (Lilium genus, Liliaceae) is an edible plant and a herb used in China to alleviate insomnia.

OBJECTIVE

To investigate the alleviating insomnia mechanism of L. davidii (LD).

MATERIALS AND METHODS

Wistar rats were intraperitoneally injected with p-chlorophenylalanine (PCPA) to establish an insomnia model. Rats were divided into six groups (n = 8): Control, PCPA, Estazolam (0.5 mg/kg), LD extract in low, medium and high doses (185.22, 370.44, 740.88 mg/kg). Serum hormone levels of the HPA axis, levels of 5-HT, NE and MT, and the expression of GABA_A and 5-HT1A receptors in hypothalamus were determined. Moreover, behavioural and pathological changes in the hypothalamus were evaluated.

RESULTS

After LD administration, body weight and brain coefficient increased by 2.74% and 8.22%, respectively, and the adrenal coefficient decreased by 25%, compared with PCPA group. Elevation of the serum hypothalamic-pituitary-adrenal (HPA) axis hormone CRH (11.24 ± 3.16 ng/mL), ACTH (565.87 ± 103.44 pg/mL) and CORT (44.28 ± 8.73 ng/mL) in the PCPA group was reversed after LD treatment. Furthermore, abnormal excitatory behaviour [5 min movement distance (2096.34 ± 259.51 cm), central exercise time (5.28 ± 1.08 s)] of insomnia rats in the PCPA group was also relieved. LD extract increased 5-HT and MT levels, reduced NE level in the hypothalamus, and upregulated the expression of GABA_A R and 5-HT1A. Moreover, LD extract may improve the pathology of neurons in the hypothalamus.

CONCLUSIONS

LD can be considered to develop health-care food or novel drugs to cope with the increasing number of insomniacs.

Characterization of the Antinociceptive Activity from Stevia serrata Cav

Background: Stevia serrata Cav. (Asteraceae), widely found in Guatemala, is used to treat gastrointestinal problems. The aim of this study was to demonstrate the antinociceptive and anti-inflammatory effects of the essential oil (EO) and the mechanism of action. Methods: EO was tested in chemical (capsaicin- and glutamate-induced licking response) or thermal (hot plate) models of nociception at 10, 30 or 100 mg/kg doses. The mechanism of action was evaluated using two receptor antagonists (naloxone, atropine) and an enzyme inhibitor (L-NAME). The anti-hyperalgesic effect was evaluated using carrageenan-induced nociception and evaluated in the hot plate. Results: All three doses of EO reduced licking response induced by glutamate, and higher doses reduced capsaicin-induced licking. EO also increased area under the curve, similar to the morphine-treated group. The antinociceptive effect induced by EO was reversed by pretreatment of mice with naloxone (1 mg/kg, ip), atropine (1 mg/kg, ip) or L-NAME (3 mg/kg, ip). EO also demonstrated an anti-hyperalgesic effect. The 100 mg/kg dose increased the latency time, even at 1 h after oral administration and this effect has been maintained until the 96th hour, post-administration. Conclusions: Our data suggest that essential oil of S. serrata presents an antinociceptive effect mediated, at least in part, through activation of opioid, cholinergic and nitrergic pathways.

Shuangxia decoction alleviates p-chlorophenylalanine induced insomnia through the modification of serotonergic and immune system

As a Traditional Chinese Medicine (TCM), Shuangxia Decoction (SXD) has been used to treat insomnia in oriental countries for more than thousands of years and it presents remarkable clinical effects. However, its active pharmacological fraction and the mechanism of sedative-hypnotic effects have not been explored. In this paper, we investigated active pharmacological fraction and revealed the detailed mechanisms underlying the sedative-hypnotic effects of SXD. It showed that SXD water extract compared to ethanol extract possessed better sedative effects on locomotion activity in normal mice and increased sleep duration in subhypnotic dose of sodium pentobarbital-treated mice. SXD alleviated p-chlorophenylalanine (PCPA) -induced insomnia by increasing the content of 5-HT in cortex [F (4, 55) = 12.67], decreasing the content of dopamine (DA) and norepinephrine (NE). Furthermore, SXD enhanced the expression of 5-HT_1A and 5-HT_2A receptors in hypothalamic and reduced serum levels of IL-1,TNF-α [F (5, 36) = 15.58]. In conclusion, these results indicated that SXD produced beneficial sedative and hypnotic bioactivities mediated by regulating the serotonergic and immune system.

Evaluation of the antinociceptive and anti-inflammatory activities of piperic acid: Involvement of the cholinergic and vanilloid systems

Piperin is the active compound of black pepper (Piper nigrum). From the piperine was obtained the molecule of the piperic acid (PAC). The objective of this study was to evaluate the antinociceptive and anti-inflammatory of the compound. The antinociceptive effects of PAC were evaluated by abdominal writhing, formalin, capsaicin and tail-flick tests; while the anti-inflammatory effects were evaluated by paw oedema and air pouch tests, and in vitro COX inhibition assay. The possible action mechanism of PAC was evaluated using naloxone, L-NAME, glibenclamide and atropine in tail flick test and by Cholinesterase activity assay and production of TNF-α and IL-1β. PAC significantly reduced the nociceptive effects induced by acetic acid or formalin in mice. PAC also demonstrated an antinociceptive effect in the tail-flick model. The muscarinic receptor antagonist, atropine reduced the antinociceptive effect of PAC in the tail-flick model. PAC was able to inhibit capsaicin-induced nociception, showing involvement of TRPV1. The compound did not alter the motor capacity of the animals, not interfering in the nociceptive response. PAC also showed anti- inflammatory activity by inhibiting the formation of carrageenan-induced paw oedema, leukocyte migration, and cytokine production / release. Atropine reduced the activity of PAC on leukocyte migration, and cytokine production. The compound showed to be able to reduce the cytokine production stimulated by capsaicin. PAC inhibited the COX activity. The results presented suggest that the possible cholinomimetic action and vanilloid agonist of the piperic acid may be responsible by antinociceptive and anti- inflammatory effects; these effects are devoid of toxicity.

Antihyperalgesic effect of [(±)-(2,4,6-cis)-4-chloro-6-(naphthalen-1-yl)-tetrahydro-2H-pyran-2-yl]methanol: participation of the NO/cGMP/KATP pathway and κ-opioid receptor

The present study used behavioral analyses to investigate the involvement of the NO/cGMP/KATP pathway, serotoninergic, and opioid systems in the antinociceptive action of [(±)-(2,4,6-cis)-4-chloro-6-(naphthalen-1-yl)-tetrahydro-2H-pyran-2-yl]methanol (CTHP) in mice. Oral administration of CTHP (1, 5, 10, and 30 mg/kg) exerted effects at higher doses in chemical models of nociception (the acetic acid writhing and formalin tests) as well as a thermal model (the tail-flick test). It was also found that pretreatment with L-N-nitroarginine methyl ester (nonselective nitric oxide synthase inhibitor), 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (selective inhibitor of nitric oxide-sensitive guanosyl cyclase), glibenclamide (selective ATP-sensitive K channel blocker), naloxone (nonselective opioid receptor blocker), and nor-binaltorphimine (selective κ-opioid receptor blocker), but not methylnaltrexone (peripheral μ-opioid receptor blocker) or naltrindole (selective δ-opioid receptor blocker), reversed the antinociceptive effect of CTHP. In addition, CTHP induced the development of tolerance in the tail-flick test: the tolerance appeared later compared with morphine, and was only observed with a higher dose. Taken together, the present study showed that the systemic administration of CTHP reduced pain induced by chemical and thermal stimuli. We also suggest that the possible mechanisms include the involvement of the NO/cGMP/KATP pathway and the κ-opioid receptor.

In vivo Study on Depressant Effects and Muscle Coordination Activity of Galphimia glauca Stem Methanol Extract

BACKGROUND

Galphimia glauca is an evergreen shrub found across peninsular India, belonging to family Malpighiaceae.

OBJECTIVE

The objective of this study was to assess the in vivo depressant effects and muscle coordination activity of G. glauca stem methanol extract (GGSME).

MATERIALS AND METHODS

The stem methanol extract was administered in Swiss albino mice in 1 day to study the central nervous system (CNS) depressant and muscle coordination activity employing animal models such as sodium pentobarbital-induced sleep test, hole-board test, open field test, pentylenetetrazole (PTZ)-induced convulsions, picrotoxin-induced convulsions, grip strengthening test in mice, and Rota-rod test.

RESULTS

The LD₅₀ of GGSME was found to be >2000 mg/kg body weight (b.w.). Mice treated with stem methanol extract at 100, 200, and 400 mg/kg, b.w. doses extended the sleeping time induced by sodium pentobarbital (40 mg/kg. b.w., i.p.). The stem methanol extract at 400 mg/kg dose showed a significant (P ≤ 0.001) dose-dependent decrease in the number of rears and head dipping number in the hole-board test. The extract exhibited a significant (P ≤ 0.001) effect on the ambulatory behavior of mice in the open field test and also extended the onset of seizures induced by PTZ (90 mg/kg b.w., i.p.) and picrotoxin (10 mg/kg, b.w., i.p.). The extract also exhibited significant (P ≤ 0.001) effects on muscle coordination in rota-rod and grip strengthening test in mice.

CONCLUSION

The study results conclude that the GGSME has a potential CNS depressant and muscle relaxant effects compared to the standard drugs.

SUMMARY

Anxiety is implicated in the number of psychiatric disordersIn vivo depressant activity is studied employing animal models like Sodium pentobarbital-.induced sleep test, Hole-board test, Open field test, Pentylenetetrazole induced convulsions and Picrotoxin-induced convulsions tests.Muscle coordination activity is studied employing animal models like Grip strengthening test in mice and Rota-.rod test.The GABAergic system plays a significant role in CNS depressant and muscle relaxant effects.The study proves the traditional claims of the plant used in the treatment of phobia, panic, stress, anxiety and it is as well used in producing a calming effect on the nerves. Abbreviations Used: WHO: World Health Organization; CNS: Central nervous system; GGSME: Galphimia glauca stem methanol extract; IAEC: Institutional Animal Ethics Committee; OECD: The Organization for Economic Co-operation and Development; PTZ: Pentylenetetrazole; REM: Rapid eye movement; GABA: γ-aminobutyric acid; AMPA: α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor; b.w: Body weight; i.p: Intraperitoneal; p.o: per oral.

Central Antinociceptive and Mechanism of Action of Pereskia bleo Kunth Leaves Crude Extract, Fractions, and Isolated Compounds

Pereskia bleo (Kunth) DC. (Cactaceae) is a plant commonly used in popular medicine in Malaysia. In this work, we evaluate the antinociceptive effect of P. bleo leaf extracts and isolated compounds in central antinociceptive model. Ethanol extract (E), hexane (H), ethyl acetate (EA), or butanol (B) fractions (30, 50, or 100 mg/kg, p.o.), sitosterol (from hexane) and vitexin (from ethyl acetate), were administered to mice. Antinociceptive effect was evaluated in the hot plate and capsaicin- or glutamate-induced licking models. Morphine (1 mg/kg, p.o.) was used as reference drug. Naloxone (1 mg/kg, i.p.), atropine (1 mg/kg, i.p.), and L-nitro arginine methyl ester (L-NAME, 3 mg/kg, i.p.) were administered 30 min earlier (100 mg/kg, p.o.) in order to evaluate the mechanism of the antinociceptive action. Higher dose of B developed an effect significantly superior to morphine-treated group. Naloxone prevented the antinociceptive effect of all fractions. L-NAME demonstrated effect against E, EA, and B. In all fractions, sitosterol and vitexin reduced the licking time after capsaicin injection. Glutamate-induced licking response was blocked by H, EA, and B. Our results indicate that Pereskia bleo fractions, sitosterol and vitexin, possessed a central antinociceptive effect. Part of this effect is mediated by opioid receptors and nitrergic pathway.

Design, synthesis and in vivo evaluation of sodium 2-benzyl-chloromalonates as new central nervous system depressants

This work describes the design, synthesis and in vivo evaluation of new central nervous system depressing agents that show low levels of acute toxicity, high solubility in water, anxiolytic and hypnotic effects without sleep deprivation.

Antinociceptive esters of N-methylanthranilic acid: Mechanism of action in heat-mediated pain

Recently, we identified a new natural antinociceptive alkaloid ternanthranin, isopropyl N-methylanthranilate (ISOAN), from the plant species Choisya ternata Kunth (Rutaceae). In this work we concentrated on the elucidation of its mechanism of action in comparison with two other esters of this acid (methyl (MAN) and propyl (PAN)). Mice orally pre-treated with ISOAN, MAN or PAN (at 0.3, 1 and 3mg/kg) were less sensitive to chemical or thermal stimuli in different nociception models (formalin-, capsaicin- and glutamate-induced licking response, tail flick and hot plate). All compounds (1 and 3mg/kg) showed significant activity in the peripheral nociception models, as well as a dose-dependent spinal antinociceptive effect in the tail flick model. We observed that glibenclamide was able to reverse the antinociceptive effect of ISOAN in the hot plate model suggesting the involvement of K(+)ATP channels. The antinociceptive effect of MAN and PAN may be related to adrenergic, nitrergic and serotoninergic pathways. In addition, the antinociception of PAN was reverted by naloxone implying that the opioid pathway participates in its activity. The cholinergic and cannabinoid systems were found not be involved in the onset of the antinociceptive effects of any of the esters. In conclusion, isopropyl, methyl and propyl N-methylanthranilates produced significant peripheral and central antinociception at doses lower than that of morphine, the classical opioid analgesic drug, without causing toxicity.

Immunobiologic and antiinflammatory properties of a bark extract from Ampelozizyphus amazonicus Ducke

Ampelozizyphus amazonicus is used in the treatment and prevention of malaria. The effect of an aqueous extract from this plant (SART) on the immune response was investigated by measuring immunoglobulin production induced by immunization with the antigen TNP-Ficoll in Plasmodium chabaudi-infected mice. SART treatment increased antigen-specific IgM and IgG levels in TNP-Ficoll-immunized mice. The B cell response during malarial infection was also modified by SART. There was an increase in total serum IgM and IgG and a decrease in the percentage of splenic plasma cells (CD138+ cells) in P. chabaudi-infected, SART-treated animals. SART (1, 3 or 10 mg/kg, p.o.) and the reference drug dexamethasone (5 mg/kg) were also tested in carrageenan-induced leukocyte migration to the subcutaneous air pouch (SAP). All SART doses significantly reduced leukocyte migration into the SAP. The protein concentration resulting from extravasation into the peritoneum was also significantly reduced. Our data indicate that SART possesses immunomodulatory properties, inducing an in vivo modification of the B lymphocyte response and anti-inflammatory properties, which are partly due to a reduction in cell migration and are most likely due to an inhibition of the production of inflammatory mediators. Preliminary HPLC-ESI-MS/MS analysis of SART shows a complex saponin profile with deprotonated molecule [M-H]⁻ ions in the range of m/z 800–1000.

Convolutamydine A and synthetic analogues have antinociceptive properties in mice

Convolutamydine A, an oxindole that originated from a marine bryozoan, has several biological effects. In this study, we aimed to investigate the antinociceptive effects of convolutamydine A and two new synthetic analogues. Convolutamydine A and the two analogues were given orally to assess their ability to induce antinociceptive effects. Formalin-induced licking response, acetic acid-induced contortions, and hot plate models were used to characterize the effects of convolutamydine A and its analogues. Convolutamydine A (4,6-bromo-3-(2-oxopropyl)-3-hydroxy-2-oxindole), compound 1 (3-(2-oxopropyl)-3-hydroxy-2-oxindole), and compound 2 (5-bromo-3-(2-oxopropyl)-3-hydroxy-2-oxindole) caused peripheral antinociceptive and anti-inflammatory effects in the acetic acid-induced contortions and the formalin-induced licking models. Supraspinal effects were also observed in the hot plate model and were similar to those obtained with morphine. The peripheral effects were not mediated by the cholinergic or opioid systems. The antinociceptive effects of convolutamydine A seem to be mediated by all three systems (cholinergic, opioid, and nitric oxide systems), and the mechanism of action of compounds 1 and 2 involved cholinergic and nitric oxide-mediated mechanisms. Convolutamydine A and its analogues (compounds 1 and 2) showed good antinociceptive ability after systemic administration in acute pain models. The antinociceptive action mediated by cholinergic, opioid, and nitric oxide systems could explain why convolutamydine A, compound 1, and compound 2 retained their antinociceptive effects. The doses used were similar to the doses of morphine and were much lower than that of acetylsalicylic acid, the classical analgesic and anti-inflammatory drug. In conclusion, convolutamydine A and the two analogues demonstrated antinociceptive effects comparable to morphine's effects.

Pharmacological mechanisms involved in the antinociceptive effects of dexmedetomidine in mice

Dexmedetomidine (DEX) is a α₂ -adrenoceptor (α₂ -AR) agonist used as an anesthetic adjuvant and as sedative in critical care settings. Typically, α₂ -AR agonists release nitric oxide (NO) and subsequently activate NO-GMPc pathway and have been implicated with antinociception. In this study, we investigate the pharmacological mechanisms involved in the antinociceptive effects of DEX, using an acetic acid-induced writhing assay in mice. Saline or DEX (1, 2, 5, or 10 μg/kg) was intravenously injected 5 min before ip administration of acetic acid and the resulting abdominal constrictions were then counted for 10 min. To investigate the possible mechanisms related to antinociceptive effect of DEX (10 μg/kg), the animals were also pretreated with one of the following drugs: 7-nitroindazole (7-NI; 30 mg/kg ip); 1H-[1,2,4] oxadiazole [4,3-a] quinoxaline-1-one (ODQ; 2.5 mg/kg, ip); yohimbine (YOH; 1 mg/kg, ip); atropine (ATRO; 2 mg/kg, ip); glibenclamide (GLIB; 1 mg/kg, i.p.) and naloxone (NAL; 0.2 mg/kg, ip). A rotarod and open-field performance test were performed with DEX at 10 μg/kg dose. DEX demonstrated its potent antinociceptive effect in a dose-dependent manner. The pretreatment with 7-NI, ODQ, GLIB, ATRO, and YOH significantly reduced the antinociceptive affects of DEX. However, NAL showed no effecting DEX-induced antinociception. The rotarod and open-field tests confirmed there is no detectable sedation or even significant motor impairment with DEX at 10 μg/kg dose. Our results suggest that the α₂ -AR and NO-GMPc pathways play important roles in the systemic antinociceptive effect of DEX in a murine model of inflammatory pain. Furthermore, the antinociceptive effect exerted by DEX appears to be dependent on KATP channels, independent of opioid receptor activity.

Antinociceptive action of (±)-cis-(6-ethyl-tetrahydropyran-2-yl)-formic acid in mice

The objective of this study was to investigate spinal and supraspinal antinociceptive effects of a new synthetic compound, (+/-)-cis-(6-ethyl-tetrahydropyran-2-yl)-formic acid (tetrahydropyran derivative). Its activity was compared with those from morphine. In peripheral models of inflammation and hyperalgesia, tetrahydropyran derivative significantly reduced nociceptive effect induced by acetic acid or formalin in mice. Tetrahydropyran derivative developed antinociceptive effect on the tail-flick and hot-plate tests with a long-acting curve maintaining the effect for 4 h longer than morphine. The opioid receptor antagonist naloxone totally reverted tetrahydropyran derivative effects on both models. Morphine as well as tetrahydropyran derivative induced tolerance and sedation in mice. However, tetrahydropyran derivative-induced tolerance had its onset retarded and the sedative activity was lower when compared to that induced by morphine. These results indicate that this new substance develops an antinociceptive activity and may be used in the future as a substitute for traditional opioids.

Anxiety-like behaviors following chronic ethanol exposure

Rodent models of ethanol withdrawal-induced anxiety have been used to explore the neurobiology underlying withdrawal and to evaluate the utility of therapeutic agents aimed at reducing withdrawal severity. Of the many tests of anxiety-like behavior, the elevated plus maze, light/dark box, and open field are the most commonly used. In general, ethanol withdrawal decreases most or all of the individual behaviors recorded in these tasks, indicating the occurrence of an anxiogenic-like effect of withdrawal in rodents, although these effects of withdrawal have not always been found. Potential problems with interpreting the effects of withdrawal as being indicative of an anxiety-like state include the effects of withdrawal on motivation to explore an apparatus, non-specific effects of withdrawal on locomotion, and the use of test parameters that have not been pharmacologically validated. For example, most of the published studies interpreted as having shown increased anxiety-like behavior during ethanol withdrawal have also observed concurrent decreases in locomotion. At a minimum, a given test of anxiety-like behavior during withdrawal should be responsive to the dose and duration of ethanol exposure that was used to produce physical dependence, and should not non-specifically decrease locomotion. In addition, standard anxiolytic drugs should ameliorate the anxiogenic-like effects of withdrawal, preferably in multiple tests of anxiety-like behavior.

Behavioral changes and cholinesterase activity of rats acutely treated with propoxur

Early assessment of neurological and behavioral effects is extremely valuable for early identification of intoxications because preventive measures can be taken against more severe or chronic toxic consequences. The time course of the effects of an oral dose of the anticholinesterase agent propoxur (8.3 mg/kg) was determined on behaviors displayed in the open-field and during an active avoidance task by rats and on blood and brain cholinesterase activity. Maximum inhibition of blood cholinesterase was observed within 30 min after administration of propoxur. The half-life of enzyme-activity recovery was estimated to be 208.6 min. Peak brain cholinesterase inhibition was also detected between 5 and 30 min of the pesticide administration, but the half-life for enzyme activity recovery was much shorter, in the range of 85 min. Within this same time interval of the enzyme effects, diminished motor and exploratory activities and decreased performance of animals in the active avoidance task were observed. Likewise, behavioral normalization after propoxur followed a time frame similar to that of brain cholinesterase. These data indicate that behavioral changes that occur during intoxication with low oral doses of propoxur may be dissociated from signs characteristic of cholinergic over-stimulation but accompany brain cholinesterase activity inhibition.

Repeated characterization of alcohol withdrawal reactions in rats chronically exposed to an alcohol liquid diet

1. Rats given a 10-% (v/v) alcohol liquid diet over long periods of time reach high blood alcohol levels of more than 200 mg/dl over several weeks. 2. Repeated discontinuation of the alcohol intake resulted, each time within 8 hr, in several withdrawal reactions including a reduction in exploratory behaviour and tremorogenic activity. 3. The inhibition of exploratory activity was measured in a neutral two-chamber model, both in terms of the number of transits into the open area as well as the time spent in the open space. The differences in exploration remained over the 4 successive withdrawal tests. 4. Rats in alcohol withdrawal were also consistently less active than control animals in the tremor cages equipped with a piezofilm floor, and this despite the presence of a clearly visible tremor in the hindpaws when lifted up. 5. Alcohol withdrawal rats revealed a more frequent tremor activity than controls after a challenge with 5 mg/kg harmine. This effect was independent of the length of the tremor bursts used to quantify harmine-induced tremor starting from the second withdrawal period onwards. 6. With a dose of 10 mg/kg harmine, ceiling effects were reached in both the alcohol withdrawal and control rats and differences between the two groups were only present during the first exposures. 7. Overall, these results indicate that it is possible to quantify some withdrawal reactions at repeated time intervals of alcohol cessation in rats chronically exposed to a 10-% alcohol liquid diet. As a consequence, these withdrawal reactions can be studied in a more systematic way.

The effects of GABAergic drugs on grooming behaviour in the open field

In a previous study it was demonstrated that sodium valproate, a drug that increases GABA cerebral concentrations, decreases grooming in the open field. This effect was not modified by morphine or naloxone. To provide evidence for the participation of the GABA system in the expression of grooming, other GABAergic drugs were acutely administered to rats before the test in the open field. The drugs, in the doses tested, did not modify locomotion, rearing, freezing or defaecation. Aminooxiacetic acid 10 mg/kg, barbital 60 mg/kg, baclofen 1.5 mg/kg, clonazepam 0.1 mg/kg, sodium valproate 150 mg/kg and 4,5,6,7-tetrahydroxi-azolo-5,4c-pyridine-3-ol (THIP) 0.75 mg/kg were the lowest doses to decrease the frequencies of grooming. The estimated ED50 to suppress grooming behaviour in the open field were 1.75 mg/kg baclofen, 52 mg/kg barbital, 0.86 mg/kg clonazepam and 1.0 mg/kg THIP. The decrease in grooming produced by the lowest effective doses of aminooxiacetic acid, clonazepam, sodium valproate and THIP was antagonized by concomitant administration of picrotoxin 1 mg/kg or bicuculline 1 mg/kg. The effects of baclofen and barbital on grooming were not modified by the antagonists. It is concluded that the GABA system, through GABA A and GABA B receptors may play a role in the expression of novelty-induced grooming behaviour.