The inhibitory effect of diazepam on conditioned defensive burying is reversed by picrotoxin

Participation of GABAA chloride channels in the anxiolytic-like effects of a fatty acid mixture

Human amniotic fluid and a mixture of eight fatty acids (FAT-M) identified in this maternal fluid (C12:0, lauric acid, 0.9 μg%; C14:0, myristic acid, 6.9 μg%; C16:0, palmitic acid, 35.3 μg%; C16:1, palmitoleic acid, 16.4 μg%; C18:0, stearic acid, 8.5 μg%; C18:1cis, oleic acid, 18.4 μg%; C18:1trans, elaidic acid, 3.5 μg%; C18:2, linoleic acid, 10.1 μg%) produce anxiolytic-like effects that are comparable to diazepam in Wistar rats, suggesting the involvement of γ-aminobutyric acid-A (GABA_A) receptors, a possibility not yet explored. Wistar rats were subjected to the defensive burying test, elevated plus maze, and open field test. In different groups, three GABA_A receptor antagonists were administered 30 min before FAT-M administration, including the competitive GABA binding antagonist bicuculline (1 mg/kg), GABA_A benzodiazepine antagonist flumazenil (5 mg/kg), and noncompetitive GABA_A chloride channel antagonist picrotoxin (1 mg/kg). The FAT-M exerted anxiolytic-like effects in the defensive burying test and elevated plus maze, without affecting locomotor activity in the open field test. The GABA_A antagonists alone did not produce significant changes in the behavioral tests. Picrotoxin but not bicuculline or flumazenil blocked the anxiolytic-like effect of the FAT-M. Based on the specific blocking action of picrotoxin on the effects of the FAT-M, we conclude that the FAT-M exerted its anxiolytic-like effects through GABA_A receptor chloride channels.

The aqueous crude extract of Montanoa frutescens produces anxiolytic-like effects similarly to diazepam in Wistar rats: involvement of GABAA receptor

ETHNOPHARMACOLOGICAL RELEVANCE

Cihuapatli is the Nahuatl name assigned to some medicinal plants grouped in the genus Montanoa, where Montanoa frutescens (Family: Asteraceae, Tribe: Heliantheae) is included. The crude extract from these plants has been used for centuries in the Mexican traditional medicine as a remedy for reproductive impairments and mood disorders. Experimental studies have systematically corroborated the traditional use of cihuapatli on reproductive impairments and sexual motivation, however, the effect on mood and "nervous" disorders, remains to be explored.

MATERIALS AND METHODS

The anxiolytic-like effect of aqueous crude extract of M. frutescens (25, 50 and 75 mg/kg) was investigated in male Wistar rats evaluated in the elevated plus-maze and compared with several doses of diazepam (1, 2 and 4 mg/kg) as a reference anxiolytic drug. Picrotoxin (1 mg/kg), a noncompetitive antagonist of the GABA(A) receptor, was used in experimental procedures to evaluate if this receptor could be involved in the anxiolytic-like effects produced by M. frutescens. To discard hypoactivity, hyperactivity, or no changes associated with treatments, which could interfere with the behavioral activity in the elevated plus-maze, rats were subjected to the open field test.

RESULTS

M. frutescens at 50 mg/kg showed anxiolytic-like activity similarly to 2 mg/kg of diazepam, without disrupts in general motor activity. The anxiolytic-like effect of M. frutescens detected in the elevated plus-maze was blocked by picrotoxin, indicating that GABA(A) receptors are involved in the modulation of this effect.

CONCLUSIONS

The results corroborate the use of M. frutescens in folk Mexican ethnomedicine as a potential anxiolytic agent and suggest that this effect is mediated by the GABA(A) receptors. Additionally, some sedative effects with high doses of M. frutescens were detected in the present study.

A single session of emotional stress produces anxiety in Wistar rats

The sensorial stimulation arising from a physically stressed (PS) subject may produce emotional stress in a witnessing partner (WP). Both members of the pair develop functional changes. We tested changes in locomotor activity (crossing) and in the defensive burying test in WP, and PS adult male Wistar rats having been submitted to a single 10 min session in a two-compartment cage. During this session, the WP rats received auditory and olfactory stimulation coming from a PS pair submitted to unavoidable electric footshocks (1 mA, dc, 0.5s, 0.5c/s, 10 min). This experiment was replicated in other groups pre-treated with vehicle or diazepam, and their urine was collected and analyzed by the static Head-Space and Gas Chromatography-Mass Spectrometry (HS-GC/MS) techniques. The WP group displayed a significantly higher crossing [F((2,45))=4.31, P<0.01] and more cumulative burying time [F((2,22))=4.73, P<0.01] than the control or PS groups. Diazepam (1mg/kg) reverted these changes. Our results indicate that the conspecific sensorial communication coming from the PS group produces anxiety probably mediated by 2-heptanone, since the HS-GC/MS analyses showed the highest amount of 2-heptanone in the urine from the PS group [F((2,42))=5.17, P<0.009].

Individual response profiles of male Wistar rats in animal models for anxiety and depression

Previous work has shown that systematic individual differences between male Wistar rats can be detected in tasks like the elevated plus-maze, or the open field. Here, we investigated whether individual profiles of anxiety, as measured with the plus-maze, may predict behavioral response profiles in other tasks where anxiety, aversion, or depressive behaviors are important. Male Wistar rats were initially screened: (A) in an open field; and (B) in an elevated plus-maze. Based on their plus-maze behavior, that is, the time spent in the open arms, the animals were divided into two subgroups with either 'low' or 'high' anxiety (LA or HA) levels. These subgroups were exposed to other experimental anxiety paradigms, namely object burying and two-way active avoidance, and an animal model of depression, the forced swim test. In the plus-maze, the percentage of time spent on, and the number of entries into the open arms were lower in HA than in LA rats. In the object burying task, HA rats showed more burying behavior of Tabasco-coated marbles, and in the active avoidance task, they showed slower acquisition of avoidance learning and higher escape latency as compared to LA rats. Finally, LA and HA rats behaved similarly in the forced swim test; however, the percentage changes of immobility time between test days 1 and 2 were negatively correlated to open field behavior, namely locomotor activity and center entries. On the other hand, the frequencies of rearing in the open field, which can also gauge functional differences between rats (for example responsiveness to novelty, psychomotor activation), were not substantially related to the behavioral profiles in the tests of anxiety and depression. These results show that individual differences of anxiety in the plus-maze can be predictive of behavior in other anxiety models, but not in forced swim test, indicating that they may be determined partly by similar functional and physiological mechanisms.

Excitotoxic lesions of the septum produce anxiolytic effects in the elevated plus-maze and the shock-probe burying tests

Our previous research has shown that electrolytic lesions of the posterior septum result in dramatic, antianxiety effects in two different animal models of anxiolytic drug action, i.e., a selective increase in open-arm activity in the elevated plus-maze test, and a selective abolition of defensive burying in the shock-probe burying test. Although these results suggest that posterior regions of the septum play an important role in the expression of anxiety in these tests, it is unclear whether destruction of septal nuclei themselves mediated these effects, since electrolytic lesions also destroy fibers of passage. Accordingly, in the present experiments, the anxiolytic effects of electrolytic lesions of the septum were compared to those of excitotoxic lesions, which preferentially destroy cell bodies, leaving fibers of passage intact. In the first experiment, both electrolytic and kainic acid lesions of the posterior septum produced complete anxiolytic effects in the elevated plus-maze (an increase in the percentage of open-arm entries and percentage of time in open arms), and partial anxiolytic effects in the shock-probe test (an increase in contact-induced probe shocks), compared to sham-lesioned controls. These antianxiety effects could not be attributed to an increase in general activity, or a decrease in reactivity to shock. In the second experiment, excitotoxic lesions of the posterior septum were produced by a more selective agent, quisqualic acid. Quisqualic acid, like electrolytic lesions, produced clear, anxiolytic effects in both the plus-maze and the shock-probe tests, compared to sham-lesioned control. Taken together, these results strongly suggest that cells originating in posterior regions of the septum mediate anxiety-related responses.

Influence of changes in the effectiveness of blockade of the benzodiazepine-GABA ionophore complex on the reproduction of the amnestic memory trace in mice after preliminary administration of diazepam

A comparative analysis was carried out in experiments on mice, using the methodology of the conditioned passive avoidance reaction, of the effectiveness of the blockade of the BD-GABA ionophore complex and its individual components in the recovery of a memory trace following "psychogenic" amnesia developing against the background of preliminary activation of BD-receptors by diazepam. It was shown that an improvement in the reproduction of the conditioned reaction was observed on the second day under conditions of "neurochemical tuning" only with the blockade of the GABAA receptor by bicuculline. Flumazepil and picrotoxin did not elicit an improvement in the reproduction of the reaction. A similar relationship of the effectiveness of the pharmacological actions was observed on the 21st day after training and "psychogenic" amnesia. The facts presented permit the hypothesis that the development of "psychogenic" amnesia is determined by the functional state, which governs the possibility of retrieving the memory trace, of the mediator systems of the brain during learning and the amnestic influence.

Septal lesions inhibit fear reactions in two animal models of anxiolytic drug action

The role of the septum in anxiety was studied using two different animal models of antianxiety drug action; i.e., the shock probe-burying test and the elevated plus maze test. Antianxiety effects were observed in both paradigms (i.e., a decrease in probe burying, and an increase in open arm activity) after lesions of the entire septum, compared to sham-lesioned controls (Experiment 1). No differences between lesioned and sham-lesioned rats were found in general activity, shock reactivity, or handling reactivity at the time of the antianxiety tests. A second experiment showed that the antianxiety effects observed in the two paradigms were anatomically specific, since lesions of the posterior septum decreased both indices of anxiety (probe burying and open arm avoidance), whereas lesions of the anterior septum resulted in levels of anxiety that were comparable to those displayed by sham-lesioned controls. Taken together, these results provide convergent evidence that posterior regions of the septum play an important role in the control of anxiety in the rat.

Conditioned defensive burying as a model for identifying anxiolytics

Rats exposed to a presumably aversive stimulus such as electric shock respond by heaping litter on the source, a behavior known as conditioned defensive burying (CDB). Because some anxiolytics suppress this behavior, CDB has been proposed as a screening method for anxiolytics. We tested the effects of the conventional anxiolytics chlordiazepoxide (4-32 mg/kg) and meprobamate (75-125 mg/kg), the novel anxiolytic buspirone (8-64 mg/kg), the antidepressant imipramine (4-16 mg/kg), the opiate analgesic morphine (2-8 mg/kg), and the antipsychotic chlorpromazine (1-16 mg/kg) on CDB. Chlordiazepoxide, meprobamate, imipramine, and morphine significantly suppressed CDB, but chlordiazepoxide did so only at a dose that reduced general activity. Buspirone and chlorpromazine did not suppress CDB at doses that reduced activity. There were some methodological differences from previous studies. We conclude that the test as constituted in this study lacks drug-class specificity. The necessity of distinguishing between specific reduction of burying and general reduction of activity is emphasized.

Behavioural and neuropharmacological properties of the dibenzazepines, desipramine and lofepramine: studies on the olfactory bulbectomized rat model of depression

1. Lofepramine was compared with its major desipramine for its effects on adaptation to novel objects in the home cage (neophobia) and exploratory behaviours in both sham operated and olfactory bulbectomized rats. 2. In the test for neophobia (marble burying), the aversive response of bulbectomized rats differed from that of the sham operated animals, the bulbectomized rats showing a diminished aversive response. This response was unaffected by either antidepressant. 3. Of two tests for exploratory activity, the "open field" test clearly differentiated the bulbectomized rats treated with desipramine from those treated with lofepramine. In the lower doses used (1 and 10 mg/kg), only desipramine treatment significantly attenuated the hypermotility of the bulbectomized rats. In high doses (30 mg/kg), lofepramine also attenuated the hypermotility of the bulbectomized rats; this could have been due to the presence of high concentrations of the desipramine metabolite. In a non-stressful novel environment ('hole board'), neither drug significantly affected the behaviour of sham operated or olfactory bulbectomized rats. Neither antidepressant had noticeable anticholinergic properties as indicated by the number of faecal boli deposited. 4. Acute clonidine administration was found to attenuate the activity of rats in the 'open field' apparatus. This effect was attenuated following the chronic administration of desipramine but not lofepramine. It may be concluded that the pharmacological activity of lofepramine is independent of its metabolism to desipramine in vivo.

Ro 15-1788, CGS 8216, picrotoxin, and pentylenetetrazol: do they antagonize anxiolytic drug effects through an anxiogenic action?

Recent evidence suggests that agents that inhibit GABAergic function, particularly at sites on the GABA/benzodiazepine receptor complex, have intrinsic anxiogenic properties. The present experiments further characterize the behavioral effects of these receptor complex inhibitors, using the "defensive burying" test, which is reasonably selective for anxiolytics. Putative blockers of the GABA-receptor coupled chloride channel, picrotoxin and pentylenetetrazol, and the benzodiazepine receptor antagonists Ro 15-1788 and CGS 8216 each blocked the anxiolytic effect of chlordiazepoxide. However, these compounds failed to exert significant anxiogenic effects in the burying test. These findings suggest that different animal models of anxiolytic drug effects are not equally sensitive to the possible anxiogenic effects of drugs that act at the GABA/benzodiazepine receptor complex.

The effects of diazepam on "fear" reactions in rats are modulated by environmental constraints on the rat's defensive repertoire

The simultaneous effects of diazepam on three shock-induced reactions in rats were studied in order to determine the reliability of these behaviors as indices of anxiolytic drug action. Rats were injected with 1 mg/kg of diazepam or vehicle, placed in a 2-compartment chamber containing bedding material, and shocked with 1, 2, or 6 mA when they first touched a wire-wrapped prod attached to one end of the chamber. Diazepam-treated animals displayed significantly less burying behavior, but paradoxically, they also displayed more passive avoidance behavior and fewer exploratory side-transitions than vehicle-injected controls. Defensive burying behavior tended to be negatively correlated with passive avoidance behavior and positively correlated with exploratory side transitions. When the "competitive" relationship between defensive burying and passive avoidance was eliminated by testing rats in a 2-compartment chamber not containing bedding material, diazepam produced a significant suppression of passive avoidance and a significant increase in exploratory side-transitions, compared to control. Taken together, these results suggested that the validity of any single behavioral model of anxiolytic drug action might vary as a function of environmental constraints on the subjects' defensive repertoire.

GABA and the behavioral effects of anxiolytic drugs

Much recent research has shown that benzodiazepine binding sites in the central nervous system are associated with GABA receptors. It is therefore possible that the pharmacological and therapeutic effects of benzodiazepines and drugs with similar profiles are mediated through GABAergic mechanisms. In this paper the evidence is considered for a possible involvement of GABA in the behavioral effects of anxiolytic drugs. There are a number of reports that the behavioral actions of anxiolytics can be antagonised by GABA antagonists such as bicuculline or picrotoxin but there are many contradictory findings and these drugs are difficult to use effectively in behavioral studies. In general, GABA agonists do not exert anxiolytic-like behavioral effects after systemic injection but intracerebral administration of muscimol has been shown to produce benzodiazepine-like actions. Although a number of questions remain unanswered, current evidence does not provide strong support for a role for GABA in the behavioral effects of anxiolytic drugs.

Evidence that tolerance develops to the anxiolytic effect of diazepam in rats

The development of tolerance to the anxiolytic effect of diazepam was studied using suppression of defensive burying as an animal model of anxiolytic action. Although tolerance to the suppressive effect of diazepam was not apparent after chronic administration of diazepam when the rats were tested with a low-intensity shock, anxiolytic tolerance was detected under exactly the same drug regimen when the rats were tested with somewhat higher intensity shocks: under the latter conditions, chronically treated rats buried significantly more than acutely treated rats. Furthermore, this tolerance effect did not appear to depend upon the injection environment, the control vehicle, or the strain of rat; under each of these experimental variations rats chronically treated with diazepam buried significantly more than acutely treated rats when they had received a moderately high intensity shock. These results suggested that tolerance to the anxiolytic effects of benzodiazepines may be detectable when the stimuli eliciting anxiety are relatively intense.

The inhibitory effect of diazepam on defensive burying: anxiolytic vs. analgesic effects

The hypothesis that analgesic mechanisms might account for the suppressive effect of diazepam on defensive burying was tested in four experiments. In the first experiment, 1 mg/kg of diazepam had no appreciable effect on rat's latency to escape from a painful heat stimulus, but reliably suppressed defensive burying behavior. There was no significant relationship between the diazepam-treated rats' latency to escape and their duration of burying. Rats in Experiment 2 were injected with diazepam during a delay between shock and testing, so that they could not be experiencing the putative analgesic effect of diazepam during the shock. In spite of this, diazepam produced a significant suppression of burying compared to saline control. In the next experiment, the effect of diazepam on defensive burying was assessed in the complete absence of painful stimulation by exposing the rats to a novel stimulus known to elicit burying behavior. Diazepam suppressed burying behavior to the novel stimulus in a dose-dependent fashion. Finally, the ability of 10 mg/kg of naloxone to reverse the suppressive effect of 1 mg/kg of diazepam was assessed in Experiment 4. Naloxone failed to reverse the suppressive effect of diazepam and had no significant effect on defensive burying by itself, suggesting that the modulating influence of diazepam on rats' defensive burying behavior did not depend upon endogenous opiate mechanisms. Taken together, the results of the four experiments did not support the view that benzodiazepines produce their anxiolytic effects through analgesic mechanisms.

Animal models for the study of anti-anxiety agents: a review

Animal models for the study of anxiolytic agents are reviewed and evaluated according to pharmacological and behavioral criteria. Although there are important exceptions, in general, most early animal models have not provided a reliable basis for identifying compounds with potential anxiolytic action, or for delineating the mechanisms of anxiolytic drug action. The possibility that phylogenetically 'prepared' forms of defensive learning might serve as a basis for the study of anxiolytic agents is introduced.

Chlordiazepoxide-induced hyperphagia in rats: lack of effect of GABA agonists and antagonists

Because of the evidence that benzodiazepine binding sites are associated with GABA receptors in the central nervous system, it has been suggested that the behavioural effects of benzodiazepines may be mediated by GABAergic mechanisms. In order to investigate this hypothesis in relation to the hyperphagia produced by benzodiazepines, the effects of chlordiazepoxide were compared with those of the GABA agonists progabide and muscimol and the GABA antagonists picrotoxin and bicuculline. In rats adapted to a 22 h/day food deprivation schedule chlordiazepoxide produced a dose-related increase in food intake. Neither progabide nor muscimol produced a similar effect after IP injection, nor did these drugs potentiate the effects of a dose of chlordiazepoxide. Picrotoxin and bicuculline, each given at a sub-convulsant dose, did not affect quantities of food consumed and also did not antagonise the effect of chlordiazepoxide. These results provide no evidence for the hypothesis that chlordiazepoxide-induced hyperphagia in rats is mediated by GABAergic mechanisms.

Anti-conflict and depressant effects by GABA agonists and antagonists, benzodiazepines and non-gabergic anticonvulsants on self-stimulation and locomotor activity

Rats were injected systemically with different classes of gabergic agent in order to investigate gabergic involvement in limbic output. Agonists differed one from another in their effects on variable-interval self-stimulation: clonazepam (in repeatedly-tested rats), chlordiazepoxide and pentobarbitone had a strongly biphasic action, low doses being facilitatory and high doses depressant, whereas other agonists including valproate and 3-APS (homotaurine) were uniformly depressant. The facilitatory effects of the benzodiazepines were dramatically enhanced by GABA antagonists (picrotoxin or pentylenetetrazol) even though antagonists on their own produced a dose-dependent depression that was not reversible by other anticonvulsant drugs. Ventral tegmental electrode placements yielded generally similar results. Depression of self-stimulation observed on initial exposure to clonazepam was reversed by repeated self-stimulation testing in the drugged state but not by repeated daily injections without testing. Locomotor activity (under conflict-free conditions) was unaffected or was depressed both by agonists and by antagonists. Thus, the facilitation of self-stimulation by chlordiazepoxide, pentobarbitone and clonazepam appears to be accounted for in terms of non-gabergic anti-conflict activity by these agents. Self-stimulation and locomotor changes following systemic administration did not disclose facilitatory effects attributable to gabergic efferents from limbic dopamine areas.