Bidirectional effects of benzodiazepine binding site ligands in the passive avoidance task: differential antagonism by flumazenil and beta-CCt

Sedative-hypnotic, anxiolytic and possible side effects of Salvia limbata C. A. Mey. Extracts and the effects of phenological stage and altitude on the rosmarinic acid content

ETHNOPHARMACOLOGICAL RELEVANCE

Salvia limbata C. A. Mey. (Persian name: Maryam Goli-e-labeh dar) has been used for treating central nervous disorders such as insomnia, anxiety and depression in Persian traditional medicine. S. limbata is known for its pharmacological activities which could be at least in a part, upon the presence of rosmarinic acid (RA). However, the sedative-hypnotic effect, anxiolytic activity, possible side effects, and the mechanism of action of S. limbata extract has not yet been examined.

AIM OF THE STUDY

In the current study the sedative-hypnotic effect, anxiolytic activity, possible side effects, and the mechanism of action of S. limbata extracts were evaluated. Besides, the effects of altitude and phenological stage on the RA content of S. limbata were investigated.

MATERIALS AND METHODS

Sedative-hypnotic and anxiolytic effects were evaluated through the pentobarbital induced loss of righting reflex test and open field test, respectively. Flumazenil was used to reveal the mechanism of action. Possible side effects were investigated in the passive avoidance and grip strength tests. Besides, the effects of altitude and phenological stage (vegetative, flowering, and seed setting) on the RA content of S. limbata were evaluated using reversed-phase high-performance liquid chromatography (RP-HPLC).

RESULTS

Following behavioral tests, sedative-hypnotic and anxiolytic effects were observed. Since the observed effects were reversed by flumazenil and no side effect on the memory and muscle strength was reported, modulation of the α1-containing GABA-A receptors could be proposed as one of the involved mechanisms. According to the RP-HPLC analysis, harvesting S. limbata in the vegetative stage at the altitude of 2500 m led to the highest content of RA (8.67 ± 0.13 mg/g dry matter). Among different extract of the plant samples collected in the vegetative stage at the altitude of 2500 m, the hydroalcoholic extract showed the highest rosmarinic acid content.

CONCLUSION

The obtained results help to find the optimum situation to gain the highest content of RA as well as the pharmacological activity that could be economically important for the pharmaceutical industries.

The behavioral pharmacology of zolpidem: evidence for the functional significance of α1-containing GABA(A) receptors

RATIONALE

Zolpidem is a positive allosteric modulator of γ-aminobutyric acid (GABA) with preferential binding affinity and efficacy for α1-subunit containing GABA(A) receptors (α1-GABA(A)Rs). Over the last three decades, a variety of animal models and experimental procedures have been used in an attempt to relate the behavioral profile of zolpidem and classic benzodiazepines (BZs) to their interaction with α1-GABA(A)Rs.

OBJECTIVES

This paper reviews the results of rodent and non-human primate studies that have evaluated the effects of zolpidem on motor behaviors, anxiety, memory, food and fluid intake, and electroencephalogram (EEG) sleep patterns. Also included are studies that examined zolpidem's discriminative, reinforcing, and anticonvulsant effects as well as behavioral signs of tolerance and withdrawal.

RESULTS

The literature reviewed indicates that α1-GABA(A)Rs play a principle role in mediating the hypothermic, ataxic-like, locomotor- and memory-impairing effects of zolpidem and BZs. Evidence also suggests that α1-GABA(A)Rs play partial roles in the hypnotic, EEG sleep, anticonvulsant effects, and anxiolytic-like of zolpidem and diazepam. These studies also indicate that α1-GABA(A)Rs play a more prominent role in mediating the discriminative stimulus, reinforcing, hyperphagic, and withdrawal effects of zolpidem and BZs in primates than in rodents.

CONCLUSIONS

The psychopharmacological data from both rodents and non-human primates suggest that zolpidem has a unique pharmacological profile when compared with classic BZs. The literature reviewed here provides an important framework for studying the role of different GABA(A)R subtypes in the behavioral effects of BZ-type drugs and helps guide the development of new pharmaceutical agents for disorders currently treated with BZ-type drugs.

Study on action mechanism of 1-(4-methoxy-2-methylphenyl)piperazine (MMPP) in acquisition, formation, and consolidation of memory in mice

In the present study, the mechanism of action of MMPP (1-(4-methoxy-2-methylphenyl) piperazine) in the acquisition (pretraining administration), formation (posttraining administration), and consolidation (pretest administration) of memory was assessed in the passive avoidance test using a short- and long-term memory protocol in mice. MMPP modified avoidance in the acquisition and formation of memory protocols but not in the consolidation protocol. Scopolamine (0.1 mg/kg i.p.), dizocilpine (0.003 mg/kg i.p.), and buspirone (0.1 mg/kg i.p.) completely inhibited MMPP-induced effects on memory acquisition and partially inhibited memory formation in the short-term but not long-term paradigm. This suggested that cholinergic, N-methyl-D-aspartate (NMDA) and 5-hydroxytryptamine-1A (5-HT1A ) receptors were implicated in the MMPP-induced improvements in memory. The sedative, anxiolytic, motor impairment, myorelaxant, and anticonvulsive (pentylenetetrazole-induced seizures) properties of MMPP were also assessed with the compound only showing a nondose-dependent myorelaxation. These results suggest that MMPP can enhance acquisition and formation, but not consolidation, of memory in short-term and long-term protocol via cholinergic, NMDA-glutamatergic, and 5-HT1A receptors.

The memory stages of a spatial Y-maze task are not affected by a low dose of ketamine/midazolam

Anesthetics, such as the ketamine/midazolam combination, are used in research with animals and in human clinical practice; thus, it is essential to clarify the potential effects of these anesthetics on memory. This study aimed to evaluate how a low dose of the ketamine/midazolam combination affects the acquisition, consolidation, or recall of a spatial memory task. Thirty-three adult male C57BL/6 mice were divided into four treatment groups: unanesthetized control animals and three groups of animals treated with 40 mg/kg of ketamine and 10mg/kg of midazolam administered in a single intraperitoneal injection. The different treatment groups received the same anesthetic dose at different time points, to study the acquisition, consolidation, and recall of spatial memory in the Y-maze task. The percentage of correct choices was measured. Six mice were killed 4 days and 12 days after anesthesia for histopathological analyses. There were no differences between treatment and control groups regarding the acquisition of spatial memory, measured as the slope of the learning curve, or in the percentage of correct choices in the consolidation or recall periods of the task. Similarly, no differences were detected between groups regarding the number of cells per square millimeter in the visual and retrosplenial cortex, in the dentate gyrus, and in the CA1 and CA3 regions of the hippocampus. Hence, a low dose of the ketamine/midazolam combination did not impair memory processes or brain integrity in adult mice, suggesting that this combination is unlikely to cause cognitive complications.

Effects of zolpidem on sedation, anxiety, and memory in the plus-maze discriminative avoidance task

RATIONALE

Zolpidem (Zolp), a hypnotic drug prescribed to treat insomnia, may have negative effects on memory, but reports are inconsistent.

OBJECTIVES

We examined the effects of acute doses of Zolp (2, 5, or 10 mg/kg, i.p.) on memory formation (learning, consolidation, and retrieval) using the plus-maze discriminative avoidance task.

METHODS

Mice were acutely treated with Zolp 30 min before training or testing. In addition, the effects of Zolp and midazolam (Mid; a classic benzodiazepine) on consolidation at different time points were examined. The possible role of state dependency was investigated using combined pre-training and pre-test treatments.

RESULTS

Zolp produced a dose-dependent sedative effect, without modifying anxiety-like behavior. The pre-training administration of 5 or 10 mg/kg resulted in retention deficits. When administered immediately after training or before testing, memory was preserved. Zolp post-training administration (2 or 3 h) impaired subsequent memory. There was no participation of state dependency phenomenon in the amnestic effects of Zolp. Similar to Zolp, Mid impaired memory consolidation when administered 1 h after training.

CONCLUSIONS

Amnestic effects occurred when Zolp was administered either before or 2-3 h after training. These memory deficits are not related to state dependency. Moreover, Zolp did not impair memory retrieval. Notably, the memory-impairing effects of Zolp are similar to those of Mid, with the exception of the time point at which the drug can modify consolidation. Finally, the memory effects were unrelated to sedation or anxiolysis.

The anaesthetic combination of ketamine/midazolam does not alter the acquisition of spatial and motor tasks in adult mice

The ketamine/midazolam association of a dissociative with a sedative agent is used for the induction and maintenance of anaesthesia in laboratory animals. Anaesthesia may interfere with research results through side-effects on the nervous system, such as memory impairment. It is known that ketamine and midazolam affect cognition; however, their effects have not been clarified when used in a context of balanced anaesthesia. Thus, this study evaluated the effects of ketamine/midazolam on the acquisition of motor and of a spatial memory task in adult mice. Twenty-eight C57BL/6 adult male mice were divided into three groups: untreated control, treated with ketamine/midazolam (75 mg/kg / 10 mg/kg) and treated with midazolam (10 mg/kg) groups. Respiratory rate, heart rate and systolic pressure were measured every 5 min in the animals treated with ketamine/midazolam, as this was the only group that exhibited loss of the righting reflex. One day after treatment, animals were tested in the open field, rotarod and radial arm maze. There were no differences between treatments regarding open-field activity, rotarod performance or number of working and reference memory errors in the radial arm maze task. In conclusion, the learning process of spatial and motor tasks was not disrupted by the anaesthetic combination of ketamine/midazolam. These results suggest its safe use in adult mice in projects where acquisition of a spatial and motor task is necessary.

Synthesis and nootropic activity of some 2,3-dihydro-1H-isoindol-1-one derivatives structurally related with piracetam

Three 2,3-dihydro-1H-isoindol-1-ones structurally related with piracetam (=2-oxopyrrolidine-1-acetamide) have been synthesized and tested for their nootropic effects in the passive avoidance test in mice. Compounds (RS)-2, (R,R)-3, and (R,S)-3 were obtained in good yields in only two steps starting from methyl DL-phthaloylalanine. Compound (RS)-2 exhibited nootropic activity at lower doses than piracetam, used as reference drug, but it showed lower efficacy. Whereas diastereoisomers (R,R)-3 and (R,S)-3 were as potent as piracetam to revert amnesia induced by scopolamine, (R,S)-3 showed lower efficacy than (R,R)-3. Only (R,R)-3 showed myorelaxant effect at doses of 10 and 30 mg/kg; other compounds did not exhibit any anticonvulsant, sedative, myorelaxant, or impaired motor-coordination effect in mice. These synthesized 2,3-dihydro-1H-isoindol-1-one derivatives constitute a new kind of nootropic compounds.

Mismatch between changes in baicalein-induced memory-related biochemical parameters and behavioral consequences in mouse

Baicalein is one of the major flavonoids originally isolated from the roots of Scutellaria baicalensis Georgi (Labiatae). Reports on baicalein-induced changes in memory-related biochemical parameters including extracellular signal-regulated kinases (ERK), Akt, cAMP response element-binding protein (CREB), and brain-derived neurotrophic factor (BDNF) have been scarce, and the action of baicalein is controversial. Baicalein promotes phosphorylation of ERK under normal conditions; on the other hand, it inhibits phosphorylation of ERK extracellularly under oxidative conditions. In the present study, we observed that baicalein (20mg/kg, p.o.) as compared to vehicle significantly increased the expression of phosphorylated ERK (pERK), phosphorylated CREB (pCREB), and BDNF but did not increase phosphorylated Akt expression in the hippocampus of naive mice. Baicalein also significantly increased the expression of pERK and BDNF in the cortex of naive mice. However, baicalein had no effect on memory acquisition in the step-through passive avoidance task. On the contrary, baicalein (20mg/kg, p.o.) co-injected with flumazenil (10mg/kg, i.p.) significantly increased the retention latency in the passive avoidance task in comparison to the flumazenil-treated group, baicalein-treated group, and vehicle-treated control group. In addition, the number of platform crossings in the Morris water maze test during the probe trial session was significantly increased by co-administration of baicalein with flumazenil. Furthermore, the expressions level of BDNF was significantly increased in the baicalein with flumazenil-treated group compared to the baicalein- or flumazenil-treated groups in the hippocampus after an acquisition trial. These results suggest that the reasons why baicalein does not exert cognitive enhancement although it enhances the expression levels of pERK, pCREB, and BDNF are, in part, derived from its GABA(A) receptor agonistic property which is antagonized by flumazenil.

Behavioral and neural analysis of GABA in the acquisition, consolidation, reconsolidation, and extinction of fear memory

The current review systematically documents the role of gamma-amino-butyric acid (GABA) in different aspects of fear memory-acquisition and consolidation, reconsolidation, and extinction, and attempts to resolve apparent contradictions in the data in order to identify the function of GABA(A) receptors in fear memory. First, numerous studies have shown that pre- and post-training administration of drugs that facilitate GABAergic transmission disrupt the initial formation of fear memories, indicating a role for GABA(A) receptors, possibly within the amygdala and hippocampus, in the acquisition and consolidation of fear memories. Similarly, recent evidence indicates that these drugs are also detrimental to the restorage of fear memories after their reactivation. This suggests a role for GABA(A) receptors in the reconsolidation of fear memories, although the precise neural circuits are yet to be identified. Finally, research regarding the role of GABA in extinction has shown that GABAergic transmission is also disruptive to the formation of newly acquired extinction memories. We argue that contradictions to these patterns are the result of variations in (a) the location of drug infusion, (b) the dosage of the drug and/or (c) the time point of drug administration. The question of whether these GABA-induced memory deficits reflect deficits in retrieval is discussed. Overall, the evidence implies that the processes mediating memory stability consequent to initial fear learning, memory reactivation, and extinction training are dependent on a common mechanism of reduced GABAergic neurotransmission.

The differential role of alpha1- and alpha5-containing GABA(A) receptors in mediating diazepam effects on spontaneous locomotor activity and water-maze learning and memory in rats

The clinical use of benzodiazepines (BZs) is hampered by sedation and cognitive deterioration. Although genetic and pharmacological studies suggest that alpha1- and alpha5-containing GABA(A) receptors mediate and/or modulate these effects, their molecular substrate is not fully elucidated. By the use of two selective ligands: the alpha1-subunit affinity-selective antagonist beta-CCt, and the alpha5-subunit affinity- and efficacy-selective antagonist XLi093, we examined the mechanisms of behavioural effects of diazepam in the tests of spontaneous locomotor activity and water-maze acquisition and recall, the two paradigms indicative of sedative- and cognition-impairing effects of BZs, respectively. The locomotor-activity decreasing propensity of diazepam (significant at 1.5 and 5 mg/kg) was antagonized by beta-CCt (5 and 15 mg/kg), while it tended to be potentiated by XLi093 in doses of 10 mg/kg, and especially 20 mg/kg. Diazepam decreased acquisition and recall in the water maze, with a minimum effective dose of 1.5 mg/kg. Both antagonists reversed the thigmotaxis induced by 2 mg/kg diazepam throughout the test, suggesting that both GABA(A) receptor subtypes participate in BZ effects on the procedural component of the task. Diazepam-induced impairment in the declarative component of the task, as assessed by path efficiency, the latency and distance before finding the platform across acquisition trials, and also by the spatial parameters in the probe trial, was partially prevented by both, 15 mg/kg beta-CCt and 10 mg/kg XLi093. Combining a BZ with beta-CCt results in the near to control level of performance of a cognitive task, without sedation, and may be worth testing on human subjects.

The melanin-concentrating hormone1 receptor antagonists, SNAP-7941 and GW3430, enhance social recognition and dialysate levels of acetylcholine in the frontal cortex of rats

Melanin-concentrating hormone (MCH)1 receptors are widely expressed in limbic structures and cortex. Their inactivation is associated with anxiolytic and antidepressive properties but little information is available concerning cognition. This issue was addressed using the selective antagonists, SNAP-7941 and GW3430, in a social recognition paradigm in rats. The muscarinic blocker, scopolamine (1.25 mg/kg s.c.), reduced social recognition, an action dose-dependently blocked by SNAP-7941 and GW3430 (0.63-10.0 and 20.0-80.0 mg/kg i.p., respectively) which did not themselves display amnesic properties. Further, in a protocol where a spontaneous deficit was induced by a prolonged inter-session delay, SNAP-7941 and GW3430 dose-dependently enhanced social recognition. In dialysis studies, SNAP-7941 (0.63-40.0 mg/kg i.p.) and GW3430 (10.0-40.0 mg/kg i.p.) elevated extracellular levels of acetylcholine (ACh) in the frontal cortex (FCX) of freely moving rats. The SNAP-7941 effect was specific, as it did not increase levels of ACh in ventral and dorsal hippocampus: moreover, it did not modify levels of noradrenaline, dopamine, serotonin and glutamate in FCX. Active doses of SNAP-7941 and GW3430 corresponded to doses (2.5-40.0 and 10.0-80.0 mg/kg i.p., respectively) exerting anxiolytic properties in Vogel conflict and ultrasonic vocalization tests, and antidepressant actions in forced swim, isolation-induced aggression and marble-burying procedures. In contrast to SNAP-7941 and GW3430, the benzodiazepine, diazepam, decreased social recognition and dialysate levels of ACh, while the tricyclic, imipramine, reduced social recognition and failed to enhance cholinergic transmission. In conclusion, at anxiolytic and antidepressant doses, SNAP-7941 and GW3430 improve social recognition and elevate extracellular ACh levels in FCX. This profile differentiates MCH1 receptor antagonists from conventional anxiolytic and antidepressant agents.

Pharmacological Properties of DOV 315,090, an ocinaplon metabolite

Background

Compounds targeting the benzodiazepine binding site of the GABA_A-R are widely prescribed for the treatment of anxiety disorders, epilepsy, and insomnia as well as for pre-anesthetic sedation and muscle relaxation. It has been hypothesized that these various pharmacological effects are mediated by different GABA_A-R subtypes. If this hypothesis is correct, then it may be possible to develop compounds targeting particular GABA_A-R subtypes as, for example, selective anxiolytics with a diminished side effect profile. The pyrazolo[1,5-a]-pyrimidine ocinaplon is anxioselective in both preclinical studies and in patients with generalized anxiety disorder, but does not exhibit the selectivity between α₁/α₂-containing receptors for an anxioselective that is predicted by studies using transgenic mice.

Results

We hypothesized that the pharmacological properties of ocinaplon in vivo might be influenced by an active biotransformation product with greater selectivity for the α₂ subunit relative to α₁. One hour after administration of ocinaplon, the plasma concentration of its primary biotransformation product, DOV 315,090, is 38% of the parent compound. The pharmacological properties of DOV 315,090 were assessed using radioligand binding studies and two-electrode voltage clamp electrophysiology. We report that DOV 315,090 possesses modulatory activity at GABA_A-Rs, but that its selectivity profile is similar to that of ocinaplon.

Conclusion

These findings imply that DOV 315,090 could contribute to the action of ocinaplon in vivo, but that the anxioselective properties of ocinaplon cannot be readily explained by a subtype selective effect/action of DOV 315,090. Further inquiry is required to identify the extent to which different subtypes are involved in the anxiolytic and other pharmacological effects of GABA_A-R modulators.

PWZ-029, a compound with moderate inverse agonist functional selectivity at GABA(A) receptors containing alpha5 subunits, improves passive, but not active, avoidance learning in rats

Benzodiazepine (BZ) site ligands affect vigilance, anxiety, memory processes, muscle tone and epileptogenic propensity through modulation of neurotransmission at GABA(A) receptors containing alpha1, alpha2, alpha3 or alpha5 subunits, and may have numerous experimental and clinical applications. The ability of non-selective BZ site inverse agonists to enhance cognition, documented in animal models and human studies, is clinically not feasible due to potentially unacceptable psychomotor effects. Most investigations to date have proposed the alpha1 and/or alpha5 subunit-containing GABA(A) receptors as comprising the memory-modulating population of these receptors. The novel ligand PWZ-029, which we synthesized and characterized electrophysiologically, possesses in vitro binding selectivity and moderate inverse agonist functional selectivity at alpha5-containing GABA(A) receptors. This ligand has also been examined in rats in the passive and active avoidance, spontaneous locomotor activity, elevated plus maze and grip strength tests, primarily predictive of the effects on the memory acquisition, basal locomotor activity, anxiety level and muscle tone, respectively. The improvement of task learning was detected at the dose of 5 mg/kg in the passive, but not active avoidance test. The inverse agonist PWZ-029 had no effect on anxiety or muscle tone, whereas at higher doses (10 and 20 mg/kg) it decreased locomotor activity. This effect was antagonized by flumazenil and also by the lower (but not the higher) dose of an agonist (SH-053-R-CH3-2'F) selective for GABA(A) receptors containing the alpha5 subunit. The hypolocomotor effect of PWZ-029 was not antagonized by the antagonist ss-CCt exhibiting a preferential affinity for alpha1-subunit-containing receptors. These data suggest that moderate negative modulation at GABA(A) receptors containing the alpha5 subunit is a sufficient condition for eliciting enhanced encoding/consolidation of declarative memory, while the influence of higher doses of modulators at these receptors on motor activity shows an intricate pattern whose relevance and mechanism await to be defined.

Neurobiology of memory and anxiety: from genes to behavior

Interaction of anxiety and memory represents an essential feature of CNS functioning. This paper reviews experimental data coming from neurogenetics, neurochemistry, and behavioral pharmacology (as well as parallel clinical findings) reflecting different mechanisms of memory-anxiety interplay, including brain neurochemistry, circuitry, pharmacology, neuroplasticity, genes, and gene-environment interactions. It emphasizes the complexity and nonlinearity of such interplay, illustrated by a survey of anxiety and learning/memory phenotypes in various genetically modified mouse models that exhibit either synergistic or reciprocal effects of the mutation on anxiety levels and memory performance. The paper also assesses the putative role of different neurotransmitter systems and neuropeptides in the regulation of memory processes and anxiety, and discusses the role of neural plasticity in these mechanisms.

The ameliorating effect of oroxylin A on scopolamine-induced memory impairment in mice

Oroxylin A is a flavonoid and was originally isolated from the root of Scutellaria baicalensis Georgi., one of the most important medicinal herbs in traditional Chinese medicine. The aim of this study was to investigate the ameliorating effects of oroxylin A on memory impairment using the passive avoidance test, the Y-maze test, and the Morris water maze test in mice. Drug-induced amnesia was induced by administering scopolamine (1 mg/kg, i.p.) or diazepam (1 mg/kg, i.p.). Oroxylin A (5 mg/kg) significantly reversed cognitive impairments in mice by passive avoidance and the Y-maze testing (P<.05). Oroxylin A also improved escape latencies in training trials and increased swimming times and distances within the target zone of the Morris water maze (P<.05). Moreover, the ameliorating effects of oroxylin A were antagonized by both muscimol and diazepam (0.25 mg/kg, i.p., respectively), which are GABA(A) receptor agonists. Furthermore, oroxylin A (100 microM) was found to inhibit GABA-induced inward Cl(-) current in a single cortical neuron. These results suggest that oroxylin A may be useful for the treatment of cognitive impairments induced by cholinergic dysfunction via the GABAergic nervous system.

Benzodiazepine site inverse agonists and locomotor activity in rats: bimodal and biphasic influence

Benzodiazepine site inverse agonists may increase or decrease locomotor activity in rodents, depending on the experimental settings. We have compared the behavioral responses to environmental novelty of rats treated with the non-selective inverse agonist DMCM (2 mg/kg) and the alpha1-subunit affinity-selective inverse agonist 3-EBC (15 mg/kg). The behavior in spontaneous locomotor assay (during 45 min) and elevated plus maze (EPM) was automatically recorded. In the EPM, general activity-related parameters were similarly decreased, whereas only DMCM inhibited open-arm activity. In the locomotor assay, both compounds depressed locomotion in the first 15 min and activity in the central zone of the chamber. However, the influence of 3-EBC was less pronounced. The alpha1-subunit selective antagonist beta-CCt (15 mg/kg) attenuated locomotor depression, but not the central-zone avoidance elicited by DMCM. When habituated to the chamber, DMCM-treated animals emitted a plateau phase of activity, which disappeared by adding beta-CCt. Hence, inhibition of activity in exposed areas may be mediated by non-alpha1-subunits, whereas both alpha1 and non-alpha1-subunits may participate in suppression of activity in more protective areas of an apparatus. Hyperlocomotion in habituated animals may depend primarily on the alpha1-subunit. Moreover, the bimodal influence of inverse agonists on locomotion can be biphasic, observable in the same experiment.