Tolerance to competitive NMDA antagonists, but no crosstolerance with barbiturates

Neuroprotective effect of Clerodendrum serratum Linn. leaves extract against acute restraint stress-induced depressive-like behavioral symptoms in adult mice

Objective:

The objective of this study was to study the effect of ethanol extract of Clerodendrum serratum (EECS) Linn. on acute restraint stress (ARS)-induced depressive-like behavior and biochemical alterations in mice.

Materials and Methods:

Ethyl acetate and n-butanol fractions of EECS were analytically characterized for the flavonoid components, apigenin (API) and luteolin (LUT) by reverse-phase high-performance liquid chromatography. Behavioral tests, namely, forced-swim test and tail-suspension test were performed for assessing antidepressant-like effect and anxiolytic activity in mice. Oxidative stress parameters and biochemical alterations in mice brain tissue were also performed.

Statistical Analysis:

Expression of data was done as mean ± standard error of mean. The normally distributed data were subjected to two-way ANOVA followed by Dunnett's test. P < 0.05 was considered statistically significant.

Results:

The study showed that flavonoids, API and LUT were present in ethyl acetate and n-butanol fractions of EECS, which significantly reversed ARS-induced depressive-like behavior without affecting locomotion. EECS also attenuated oxidative damage caused by ARS. The level of norepinephrine and 5-hydroxytryptamine was also significantly restored by pretreatment with EECS for 7 days.

Conclusion:

EECS significantly alleviated ARS-induced depressive-like behavior without affecting locomotion.

Evaluation of the anxiolytic effect of Nepeta persica Boiss. in mice

The aim of the present study was to evaluate the anxiolytic effects of hydroalcoholic extract (HE) of Nepeta persica Boiss. (Lamiaceae) on the elevated plus-maze (EPM) model of anxiety. The extract of arial parts of the plant was administered intraperitoneally to male NMRI mice, at various doses, 30 min before behavioural evaluation. The HE extract of N. persica at the dose of 50 mg kg⁻¹ significantly increased the percentage of time spent and percentage of arm entries in the open arms of the EPM. This dose of plant extract affected neither animal's locomotor activity nor ketamine-induced sleeping time. The 50 mg kg⁻¹ dose of the plant extract seemed to be the optimal dose in producing the anxiolytic effects, lower or higher doses of the plant produce either sedative or stimulant effects. At 100 mg kg⁻¹, the plant extract increased the locomotor activity. These results suggested that the extract of N. persica at dose of 50 mg kg⁻¹ possess anxiolytic effect with less sedative and hypnotic effects than that of diazepam and causes a non-specific stimulation at 100 mg kg⁻¹.

Studies on the anti-inflammatory properties of Plantago erosa leaf extract in rodents

ETHNOPHARMACOLOGICAL RELEVANCE

Leaves of Plantago erosa ex Roxb are used traditionally in Northeast India in different illnesses which include wounds, cuts, bruises, insect bites, poison-ivy rashes, minor sores and snakebite, etc.

AIM OF THE STUDY

Plantago erosa is one of the commonly used medicinal plants in various inflammatory conditions in this region; however, due to paucity of scientific literature on its anti-inflammatory property, the present study was aimed at evaluating its anti-inflammatory activity in the leaves using in vivo models of inflammation.

MATERIALS AND METHODS

Different models like carageenan induced paw edema in rat and mice, formalin induced paw licking in rats and cotton pellet induced granuloma in rats were used for studying the anti-inflammatory activity in methanol extract of Plantago erosa (PEME) leaves.

RESULTS

The PEME at the oral doses from 300 to 600 mg/kg showed anti-inflammatory activity in various models. The extract (PEME) reduced carageenan induced paw edema in rat and mice, inhibited the formation of granulomatous tissue in cotton pellet induced granuloma after treatment and also decreased the reaction time in both early and late phases in formalin induced paw licking in rats.

CONCLUSION

The study evidently confirmed anti-inflammatory activity of PEME and thus supported the traditional claim. The anti-inflammatory activity could be attributed to the phytoconstituent (flavonoids, alkaloids and steroid) present in the methanol extract of the plant.

Evaluation of antianxiety and sedative effects of essential oil of Ducrosia anethifolia in mice

INTRODUCTION

We investigated the antianxiety and sedative effects of the essential oil of Ducrosia anethifolia. Boiss. (Apiaceae).

METHODS

We used elevated plus maze, spontaneous motor activity and ketamine-induced sleep tests in mice. In addition, the essential oil was analyzed by GC/MS. Twenty compounds were identified, and n-decanal (70.1%) and alpha-pinene (12.4%) constituted the major components.

RESULTS

In elevated plus maze, Ducrosia anethifolia essential oil at doses of 25-200 mg/kg increased the percentage of open arm time and entries. Unlike diazepam, ducrosia anethifolia essential oil could not suppress spontaneous motor activity and did not alter ketamine-induced sleep parameters. These results are indicative of antianxiety effect of Ducrosia anethifolia essential oil without sedative effect.

Central nervous system depressant action of flavonoid glycosides

The pharmacological effects on the central nervous system (CNS) of a range of available flavonoid glycosides were explored and compared to those of the glycosides 2S-hesperidin and linarin, recently isolated from valeriana. The glycosides 2S-neohesperidin, 2S-naringin, diosmin, gossipyn and rutin exerted a depressant action on the CNS of mice following i.p. injection, similar to that found with 2S-hesperidin and linarin. We demonstrate in this work that these behavioural actions, as measured in the hole board, thiopental induced sleeping time and locomotor activity tests, are unlikely to involve a direct action on gamma-aminobutyric acid type A (GABA(A)) receptors. The corresponding aglycones were inactive, pointing to the importance of the sugar moieties in the glycosides in their CNS depressant action following systemic administration. The pharmacological properties of the flavonoid glycosides studied here, in addition to our previous results with hesperidin and linarin, opens a promising new avenue of research in the field.

Aspergillus mycotoxins and their effect on the host

Aspergillus fumigatus is known to produce various immunosuppressive mycotoxins including gliotoxin. However, none of these mycotoxins has been confirmed as being directly related to the pathogenesis of aspergilli. Recent studies have made substantial progress in the determination of mycotoxins as virulence factors. Gliotoxin was found to be produced much faster than previously believed under certain culture conditions, such as at 37 degrees C and under high oxygen content, which is close to the environment in the host. Gliotoxin was also found to be detectable in the sera of aspergillosis mice and of aspergillosis patients. Based on these findings, it is becoming evident that gliotoxin is produced in the infected organs of patients of aspergillosis at a significant level. In addition to these known mycotoxins, A. fumigatus produces many mycotoxins apparently different from known toxins. From the aspect of gene analysis, the deletion of laeA was found to block the expression of metabolic gene clusters such as sterigmatocystin, and the gene is also expected to be related to the production of gliotoxin. The significance of mycotoxins as virulence factors will hopefully be clarified in the near future.

Hydroalcohol extract and fractions ofStachys lavandulifolia vahl: effects on spontaneous motor activity and elevated plus-maze behaviour

The present study aimed to investigate the anxiolytic effects of four fractions of Stachys lavandulifolia Vahl. The aerial parts of the plant were extracted with petroleum ether (PF), ethyl acetate (EF), butanol (BF) and water (AF) and tested for spontaneous motor activity and elevated plus-maze (EPM) behaviour in mice. The hydroalcohol extract (HE) and different fractions of S. lavandulifolia were administered intraperitoneally to male Syrian mice, at various doses, 30 min before the behavioural evaluation. The HE of S. lavandulifolia (at 50 mg/kg) increased the percentage of time spent (39%) and the percentage of arm entries in the open arms (53%). The HE (50 mg/kg), PF (25 and 50 mg/kg), EF (25 and 50 mg/kg) and AF (50 mg/kg) of S. lavandulifolia significantly increased the percentage of time spent and the percentage of arm entries in the open arms. The BF up to a dose of 50 mg/kg had no significant effects on any of the measured parameters in the EPM. The spontaneous locomotor activity was significantly decreased in animals injected with each plant fractions, compared with that of saline. The EF and AF showed the least and the most reduction in the activity, respectively. The anxiolytic effects of EF, PF and AF could be related to their content of flavonoids, phenylpropanoids or terpenoids.

Anxiolytic effects of Echium amoenum on the elevated plus-maze model of anxiety in mice

The ethanolic extract of Echium amoenum flowers at the dose of 50 mg/kg increased the percentage of time-spent and the percentage of arm entries in the open arms of the elevated plus-maze (EPM) and decreased the percentage of time-spent in the closed arms of EPM. Moreover, it prolonged the ketamine-induced latency to sleep but had no significant effects on total sleeping time induced by ketamine. Also, the locomotor activity was affected but not to the same extent as observed for diazepam. These results suggested that the extract of E. amoenum seems to possess anxiolytic effect with lower sedative activity than that of diazepam.

Anxiolytic effects of Stachys lavandulifolia Vahl on the elevated plus-maze model of anxiety in mice

Interest in alternative medicine and plant-derived medications that affect the "mind" is growing. The aim of the present study was to investigate the effects of a hydroalcoholic extract and essential oil of Stachys lavanduifolia Vahl on the elevated plus-maze (EPM) model of anxiety. The Stachys lavandulifolia extract or its essential oil was administered intraperitoneally to male TO mice, at various doses, 30 min before the behavioral evaluation. The extract of Stachys lavandulifolia at the dose of 100 mg/kg increased the percentage of time spent and the percentage of arm entries in the open arms of the EPM and decreased the percentage of time spent and the percentage of arm entries in the closed arms of the EPM. The plant extract at doses lower than 100 mg/kg had no significant effects on any of the parameters measured on the EPM. This dose of the plant extract prolonged the ketamine-induced sleeping time, and decreased the locomotor activity in mice. These results suggested that the extract of Stachys lavandulifolia possessed anxiolytic effect with relatively lower sedative activity than diazepam. The essential oil of Stachys lavandulifolia, however, at doses of up to 100 mg/kg did not have any significant effects on the mice behaviour on the EPM.

Decrement in operant performance produced by NMDA receptor antagonists in the rat: tolerance and cross-tolerance

Current perspectives on the clinical use of NMDA receptor antagonists infer repeated administration schedules for the management of different pathological states. The development of tolerance and cross-tolerance between different NMDA receptor antagonists may be an important factor contributing to the clinical efficacy of these drugs. The present study aimed to characterize the development of tolerance and cross-tolerance to the ability of various site-selective NMDA receptor antagonists to produce a decrement of operant responding (multiple extinction 9 s fixed-interval 1-s schedule of water reinforcement). Acute administration of D-CPPen (SDZ EAA 494; 1-5.6 mg/kg), dizocilpine (MK-801; 0.03-0.3 mg/kg), memantine (0.3-17 mg/kg), ACEA-1021 (10-56 mg/kg), and eliprodil (1-30 mg/kg) differentially affected operant responding. Both increases and decreases in response rates and accuracy of responding were observed. Repeated preexposure to D-CPPen (5.6 mg/kg, once a day for 7 days) attenuated a behavioral disruption produced by an acute challenge with D-CPPen or ACEA-1021, but potentiated the effects of dizocilpine, memantine, and eliprodil. Based on the present results, one can suggest that the repeated administration of a competitive NMDA receptor antagonist differentially affects the functional activity of various sites on NMDA receptor complex.

Chronic blockade of N-methyl-D-aspartate receptors alters gamma-aminobutyric acid type A receptor peptide expression and function in the rat

Chronic in vivo or in vitro application of GABA(A) receptor agonists alters GABA(A) receptor peptide expression and function. Furthermore, chronic in vitro application of N-methyl-D-aspartate (NMDA) agonists and antagonists alters GABA(A) receptor function and mRNA expression. However, it is unknown if chronic in vivo blockade of NMDA receptors alters GABA(A) receptor function and peptide expression in brain. Male Sprague-Dawley rats were chronically administered the noncompetitive NMDA receptor antagonist MK-801 (0.40 mg/kg, twice daily) for 14 days. Chronic blockade of NMDA receptors significantly increased hippocampal GABA(A) receptor alpha4 and gamma2 subunit expression while significantly decreasing hippocampal GABA(A) receptor alpha2 and beta2/3 subunit expression. Hippocampal GABA(A) receptor alpha1 subunit peptide expression was not altered. In contrast, no significant alterations in GABA(A) receptor subunit expression were found in cerebral cortex. Chronic MK-801 administration also significantly decreased GABA(A) receptor-mediated hippocampal Cl- uptake, whereas no change was found in GABA(A) receptor-mediated cerebral cortical Cl- uptake. Finally, chronic MK-801 administration did not alter NMDA receptor NR1, NR2A, or NR2B subunit peptide expression in either the cerebral cortex or the hippocampus. These data demonstrate heterogeneous regulation of GABA(A) receptors by glutamatergic activity in rat hippocampus but not cerebral cortex, suggesting a new mechanism of GABA(A) receptor regulation in brain.

Motor impairment produced by ethanol and site-selective NMDA receptor antagonists in mice: tolerance and cross-tolerance

Current perspectives on clinical use of N-methyl-D-aspartate (NMDA) receptor antagonists infer acute and repeated administration schedules for management of different pathological states. Development of tolerance and cross-tolerance between different antagonists may significantly affect their clinical effectiveness. Since ethanol was repeatedly demonstrated to act as NMDA receptor antagonist, ethanol use may also have its impact on the effects of NMDA receptor ligands. Using the rotarod test in mice, the present study evaluated development of tolerance and cross-tolerance between ethanol (3.2 g/kg, p.o.), competitive NMDA receptor antagonist, D-CPPene (5.6 mg/kg, i.p.), and low-affinity NMDA receptor channel blocker, memantine (30 mg/kg, i.p.), that were administered for seven days once a day after the daily rotarod training session. Acute tests with ethanol (0.3, 1, 1.7, 3.2 g/kg), D-CPPene (0.3, 1, 3, 5.6 mg/kg) and memantine (1, 3, 10, 30 mg/kg) revealed that (a) each of these drugs dose-dependently disrupted rotarod performance in drug-naive mice; (b) in ethanol- and D-CPPene-treated mice, tolerance was observed to ethanol and D-CPPene but not to memantine; moreover, effects of memantine were even more pronounced in D-CPPene-treated subjects; and (c) repeated memantine administration decreased acute motor impairing effects of ethanol, D-CPPene and memantine. Thus, the history of ethanol use or abuse may influence pharmacological activity of NMDA receptor antagonists and this effect is dependent on type of the NMDA receptor antagonist applied.

Morphine tolerance and dependence in mice with history of repeated exposures to NMDA receptor channel blockers

Mice were subjected to two successive treatment protocols: first with NMDA receptor channel blockers (14 days, once a day) and second with morphine (5 mg/kg, 8 days, once a day). Treatment with the higher doses of dizocilpine (1 mg/kg), memantine (30 mg/kg), and MRZ 2/576 (30 mg/kg) upon discontinuation revealed only minor behavioral abnormalities attributable to the state of withdrawal. Following repeated administration of low-dose morphine, tolerance to morphine analgesia developed in mice preexposed to dizocilpine (1 mg/kg but not 0.3 mg/kg) but not memantine (10 and 30 mg/kg), MRZ 2/579 (10 and 30 mg/kg), or saline. There were no signs of morphine dependence in any treatment group. Overall, the present study found only minor effects of the subchronic administration of high doses of NMDA receptor channel blockers, suggesting that clinical use of NMDA receptor channel blockers such as memantine will not be accompanied by increased propensity to induction of morphine tolerance and dependence.

Effects of oral administration of the competitive N-methyl-D-aspartate antagonist, CGP 40116, on passive avoidance, spatial learning, and neuromotor abilities in mice

The effects were investigated of the potent competitive N-methyl-D-aspartate (NMDA) receptor antagonist CGP 40116[D-(E)-2-amino-4-methyl-5-phosphono-3-pentenoic acid] on the performance of mice in water maze and passive avoidance tasks, and in wire suspension, rotarod, and cage activity tests. The drug was administered per os (p.o.) in its anticonvulsant dose range. CGP 40116 dose-dependently impaired passive avoidance learning when given before, but not when given after training. The antagonist (5, 10, and 20 mg/kg, administered 4 h before each training session) dose-dependently affected water maze acquisition, and impaired retention test performance in both hidden- and visible-platform water maze tasks. In addition, the drug dose-dependently decreased swimming speed during water maze acquisition. Repeated administration of CGP 40116 (20 mg/kg, p.o.) persistently decreased cage activity and wire suspension test performance, whereas motor coordination and equilibrium on the rotarod apparatus remained unimpaired. In our administration protocol, no tolerance was found to the effects of the drug on passive avoidance learning and neuromotor abilities. The parallel effects of CGP 40116 on memory and motor performance are discussed, and it was concluded that the antagonist impairs neuromotor abilities and also induces memory impairments which cannot be entirely reduced to motor interference.

The effects of repeated administration of diazepam, MK-801 and CGP 37849 on rat behavior in two models of anxiety

The effects of repeated administration of diazepam, MK-801 and CGP 37849 on rat behavior in the Vogel conflict test, and in the open field test of neophobia, were studied in rats. The drugs were given at doses active acutely, for 5 days, the last dose was administered 30 or 60 min prior to testing. It appeared that diazepam and MK-801 treated animals showed clear-cut signs of behavioral tolerance and motor sensitization, respectively. CGP 37849 was characterized by the best pharmacological profile, in that on repeated administration the drug not only retained its anxiolytic-like potency in the Vogel test, but even enhanced rat exploratory behavior in a new environment, independently of changes in animal motor activity. Repeated injections of the examined agents did not cause any significant modifications in monoamine levels and their turnover rates, in the striatum and limbic forebrain. It is concluded that the new class of competitive NMDA receptor antagonists, exemplified by CGP 37849, is the most promising candidate for clinical trials in anxiety disorders.