Two opposite effects of diazepam on fear by differential training in the CER-paradigm

Two groups of rats were trained in a CER paradigm. The conditioned stimulus was a sound, the unconditioned stimulus was an electric shock. Group 1 received conventional CER training before the effects of different doses of diazepam were studied. For Group 2 the shock was always and exclusively given contingent on pretreatment with diazepam. After prolonged training the compound thus became a discriminative stimulus complex (DSC) and produced response suppression during the CS. Group 2 was also challenged with various doses of diazepam. The results showed that diazepam acquired diametrically different properties in the two groups. Group 1 exhibited disinhibitory effects and Group 2 suppressive effects, which may reflect anxiolytic and anxiogenic properties, respectively.     

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.     

Pretreatment with diazepam suppresses the reduction in defensive freezing behavior induced by fluvoxamine in the conditioned fear stress paradigm in mice

The effects of the selective serotonin (5-hydroxytryptamine (5-HT)) reuptake inhibitor fluvoxamine, given alone or in combination with the benzodiazepine anxiolytic diazepam on the defensive freezing behavior of mice in the conditioned fear stress paradigm were examined. Fluvoxamine (5-20 mg/kg, i.p.) induced a dose-dependent reduction in freezing behavior. In contrast, while low doses of diazepam (0.125 and 0.25 mg/kg, i.p.) reduced the freezing behavior, such effects were not observed with high doses of diazepam (0.5 and 1 mg/kg, i.p.). In the combination study, fluvoxamine (20 mg/kg, i.p. ) did not reduce the freezing behavior in mice that had been pretreated with diazepam (0.125-1 mg/kg, i.p.). None of the doses of fluvoxamine and diazepam used in the present study had any effects on motor activity under non-stressed conditions. These results suggest that benzodiazepines may negatively influence the clinical efficacy of selective 5-HT reuptake inhibitors in the treatment of anxiety disorders.     

Effect of flumazenil and diazepam on transient actions in defensive burying elicited by the social interaction experience in rats

In the present work, we studied the effects of benzodiazepine (BZ) receptor antagonist, flumazenil, and of the agonist, diazepam, on social interaction-induced transient changes in defensive burying (DB). Enhanced defensive burying was observed after 1.5 min of social interaction experience, while a longer social interaction experience, 15 min, inhibited the expression of burying behavior. Defensive burying and social interaction paradigms have been used for the screening of compounds with anxiolytic potential and, more extensively, to study the neurobiology of anxiety. To elucidate the participation of the BZ receptor on transient changes induced by intervals of social interaction experience, its receptor antagonist, flumazenil (2.5, 5, and 10 mg/kg) was intraperitoneally injected (IP). Flumzenil enhanced in a dose-dependent manner, the blocking effect of the saline IP injection on facilitated DB in 1.5-min social interaction-experienced subjects. In addition, flumazenil enlarged in a dose-dependent manner the blocking effect of saline IP on defensive burying levels in animals exposed to social interaction experience for 15 min. To analyze the presumed participation of the BZ receptor mediating enhanced burying behavior levels in subjects exposed to 1.5 min of social interaction, a suboptimal dose of diazepam (0.25 mg/kg) was administered. Diazepam enhanced the saline IP elicited defensive burying reduction. Results are discussed in terms of the suggested BZ receptor mediation on transient changes in defensive burying elicited by social interaction experience.     

The effects of ethanol and diazepam on reactions to predatory odors

In a straight alley containing a cat odor stimulus rats show high rates of risk assessment, including flat back approach and stretch attend behaviors oriented toward the threat stimulus and contact with the stimulus. In this situation, diazepam (2.0 and 4.0 mg/kg) significantly reduced risk assessment measures (flat back approach + stretch attend), while not reliably altering control locomotion (curved back). In combination with earlier findings that the same doses of diazepam reliably increased risk assessment from a movement arrest baseline, these results strongly support a behavioral model of anxiety involving predictable nonmonotonic changes in risk assessment as a function of anxiety reduction. In comparison to diazepam, ethanol had less pronounced effects on the Cat Odor Test, as in earlier tasks of reactivity to potential threat. However, reliable dose x time interactions for risk assessment measures suggest ethanol effects similar to those of diazepam but most pronounced in initial stages in the test session.     

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

The ability of picrotoxin to reverse the effect of diazepam was studied using the conditioned defensive burying paradigm. Although picrotoxin alone had no detectable effect of the conditioned defensive burying response of rats, picrotoxin was able to reverse the usual inhibitory effect of diazepam on defensive burying. These results suggest that the anxiolytic effect of diazepam may depend upon the integrity of GABAergic neural systems.     

Behavioral effects of toluene are modulated by stimulus control

Behavior that is strongly controlled by environmental stimuli is less susceptible to disruption by certain chemicals than is such behavior not under strong external control. To determine whether toluene's effects can also be minimized by environmental stimuli, two varieties of a fixed consecutive number schedule were studied. With one, a lever press response was reinforced with milk only if preceded by a minimum of eight consecutive responses on a second lever, no cues indicating that the minimum number had been reached. With the other, a combination of lights and a tone served as a discriminative stimulus signaling the completion of the minimum response number. In an experiment studying these schedules separately, rats were exposed to toluene concentrations up to 3000 ppm for 4-hr periods immediately before their performance was tested. Toluene reduced the accuracy of both types of behavior in a concentration-related fashion. Clear differential effects occurred, with the signaled behavior, i.e., that under stronger stimulus control, showing less disruption by toluene. Similar results were produced after 2-hr exposures with a multiple schedule in which the signaled and unsignaled performances alternated within a single session. Response rate changes were observed at 560 ppm, but changes in rate were independent of effects on the accuracy of performance. The EC50 for significant behavior disruption was 1081 ppm for the unsignaled component of the multiple schedule; the EC10 was 480 ppm. No performance disruption was observed in the signaled component below 1780 ppm. The finding of differential sensitivity could be useful in guiding the development of more sensitive tests of performance impairment.     

The effects of two "anti-aggressive" compounds, an indenopyridine and a benzothiazepin, on shock-induced defensive fighting in rats.

1. An indenopyridine (YG19-256) and a benzothiazepin (thiazesim) were investigated in rats for possible effects on shock-induced defensive fighting, shock reactivity and locomotor activity. 2. YG19-256 significantly reduced aggression at the higher dose levels employed. Thiazesim produced no significant decrease in aggression at the dose levels used. 3. Neither compound produced any consistent effect on shock reactivity or locomotor activity.     

Cutaneous MMPs are differently modulated by environmental stressors in old and young mice

Skin is frequently exposed to pro-oxidative insults such as UV light, ozone (O(3)) and cigarette smoke (CS), which are able to deplete antioxidants and induce oxidation products affecting skin pathophysiology. Skin turnover and regeneration are largely dependent on extracellular matrix metabolism, which is under the control of matrix metalloproteinases, MMPs. The present study evaluated cutaneous MMPs activity upon environmental pollutants exposure and analyzed the response of old and young animals. For this purpose, SKH-1 hairless mice (8 weeks and 18 months old) were exposed for 6h/day to 0.25ppm of O(3) or to UV radiation (0.3 MED) or to CS for 4 days. Gelatin zymography revealed an increase of MMP-2 in both young and old animals, after exposure to pollutants, while MMP-9, undetectable in unexposed subjects, was strongly induced only in old mice. Casein zymography and Western blot analysis showed an increase of MMP-12 in the aged group after environmental stressors exposure. TIMP-1 and -2 expression levels did not change. The current study demonstrates the ability of certain environmental pollutants to affect the ECM turnover through modulation of specific MMPs, and confirms the higher susceptibility of old subjects to exogenous pro-oxidant insults.     

The effects of noradrenaline on rat's behaviour

Summary The behavioural effects of NA injected without narcosis into the lateral brain ventricle of the rats were studied with two different techniques. Rats were classified according their normal level of exploratory activity into three groups: high, medium and low. It was shown that NA in a dose of 10 g increased locomotor activity only in animals of low activity; a dose of 50 g increased locomotor activity in all the animals; and a dose of 200 g induced a complete abolition of locomotor activity and a stuporose syndrome lasting 2 hours. The evidence that NA in some experimental conditions increases locomotor activity of rats supports the hypothesis that NA regulates processes in the central nervous system which stimulate behaviour.     

地西泮对大鼠脑缺血再灌注损伤的保护作用

目的：研究地西泮对脑缺血再灌注损伤的保护作用。方法：用四动脉结扎法制造大鼠全脑缺血再灌注模型。动物随机分成伪手术组、再灌注组、尼莫地平２ｍｇ／ｋｇ组、地西泮２ｍｇ／ｋｇ组及４ｍｇ／ｋｇ组共５组。于缺血前、再灌注前及再灌注过程中各ｉｖ给药一次。结果：地西泮使缺血再灌注造成的脑水份含量增加，丙二醛含量增高，脑组织乳酸脱氢酶含量减少及脑钙升高向正常方向逆转（Ｐ＜０．０１），并且可以有效改善再灌期间脑电图的变化（Ｐ＜０．０５），减轻锥体细胞的坏死情况。结论：地西泮对脑缺血再灌注损伤有保护作用     

Differential effects of naloxone and diprenorphine on defensive behaviour in rats

Two opiate antagonists, naloxone and diprenorphine, were used to examine the proposed involvement of endogenous opioid mechanisms in the modulation of shock-induced defensive behaviour patterns in rats. Naloxone was found to exert a biphasic influence on defensive fighting, with small dose (0.1 mg/kg) facilitation and large dose (10 mg/kg) inhibition. This compound also induced a dose-dependent inhibitory effect on shock-elicited threat whilst facilitated escape/avoidance behaviour was observed with the largest doses only. None of these influences could be attributed to alterations in electric shock thresholds. In contrast to the effects of naloxone, diprenorphine (0.1–10 mg/kg) was largely ineffective in modifying shock-induced defensive behaviour. These data suggest that endogenous opioid mechanisms may not be involved in the effects of naloxone on defensive fighting and cast some doubt upon the general hypothesis of the involvement of endorphins in the regulation of innate defence patterns.     

The effects of diazepam on the behavioral structure of the rat's response to pain in the hot-plate test: anxiolysis vs. pain modulation

The aim of the present study was to evaluate, by means of quantitative and multivariate analyses, the effects of diazepam on the behavioral structure of the rat's response to pain in the hot-plate test as well as whether such changes are associated with drug-induced effects on anxiety and/or nociception. To this purpose, ten groups of male Wistar rats were intraperitoneally injected with saline, diazepam (0.25, 0.5 and 2 mg/kg), FG-7142 (1, 4 and 8 mg/kg) or morphine (3, 6 and 12 mg/kg). The mean number and mean latency to first appearance were calculated for each behavioral component. In addition, multivariate cluster and adjusted residual analyses based on the elaboration of transition matrices were performed. Three main behavioral categories were identified: exploratory (walking, sniffing), primary noxious-evoked (hind paw licking, front paw licking, shaking/stamping) and escape (climbing, jumping). Although no significant modifications in the latencies of the primary noxious-evoked components were induced by treatment with diazepam or FG-7142, significant effects were provoked by morphine treatment. Multivariate analyses showed that diazepam-induced anxiolysis redirected the rat's behavior toward a more purposeful and effective escape strategy. In contrast, the high level of anxiety induced by FG-7142 caused the behavioral structure to become disorganized and not purposefully oriented. Changes in the organization of behavioral components were observed in morphine-treated animals and mainly consisted of modifications in the primary noxious-evoked and escape components. The findings suggest that the effects of diazepam on the structure of the rat's response to pain in the hot-plate test are more likely attributable to anxiolysis than pain modulation.     

The effects of yohimbine and amphetamine on fear expression and extinction in rats

Rationale

Psychostimulants, such as yohimbine and amphetamine, can enhance learning and memory. Extinction of conditioned fear involves new learning, so we asked whether psychostimulants could enhance this learning. Previous work suggests that yohimbine facilitates extinction, using freezing as a fear measure. However, psychostimulant-induced alterations in locomotion can confound freezing measurements. Furthermore, the effects of amphetamine on fear extinction have never been examined.

Objective

We evaluated the effectiveness of yohimbine and amphetamine in enhancing fear extinction. In addition to freezing, we measured bar-press suppression, which is less sensitive to changes in locomotion. We asked: Do psychostimulants reduce fear during extinction training when drug is present? Does learning extinction with psychostimulants result in better extinction retention?

Materials and methods

Rats received fear conditioning on day 1 followed by partial extinction training on days 2 and 3. Yohimbine (1.0, 2.0, or 5.0 mg/kg, i.p.), amphetamine (1.0 mg/kg, i.p.), or vehicle were injected prior to extinction on day 2.

Results

Yohimbine dose-dependently reduced freezing during extinction training on day 2, whereas bar-press suppression was reduced at the highest dose only. When tested drug-free, yohimbine-treated rats showed equivalent levels of freezing and suppression to controls. Amphetamine also decreased freezing during extinction, but did not decrease suppression. During the drug-free test, there was no difference between amphetamine-treated rats and controls in either measure.

Conclusions

Although yohimbine and amphetamine are capable of decreasing freezing, neither drug strengthened retention of fear extinction. Based on these rodent findings, psychostimulants may not be suitable adjuncts to extinction-based therapies for the treatment of anxiety disorders.

     

The effects of acute treatment with escitalopram on the different stages of contextual fear conditioning are reversed by atomoxetine

Rationale  

Although the antidepressant and anxiolytic effects of selective serotonin reuptake inhibitors and serotonin–noradrenaline reuptake inhibitors are well-documented, less is known about their cognitive effects.     

Effects of diazepam and zolpidem on EEG beta frequencies are behavior-specific in rats

A pharmacological dissociation of the relation between electroencephalographic (EEG) activity and behavior has been described for the benzodiazepines. While a decrease in high frequency EEG activity is associated with a decrease in arousal in drug-free conditions, sedative benzodiazepines increase beta activity. Non-benzodiazepine GABA(A) receptor modulators can increase beta activity as well. To further study the relationship between rat behavior and EEG under GABA(A) receptor modulation, EEG effects of diazepam (2.5 mg/kg) and zolpidem (2.5 mg/kg) were studied during different behaviors. Both drugs modulate the GABA(A) receptor, albeit that zolpidem shows alpha(1) subunit selectivity while diazepam is non-selective. A detailed analysis of rat open field behavior was made with a distinction of 25 behavioral elements. The EEG was segmented according to each behavioral element and a corresponding power spectrum calculated. Both diazepam and zolpidem increased EEG beta frequencies, characteristic for the benzodiazepines. However, the beta and gamma increase was specific for active behavior and not for inactivity. Interestingly, diazepam and zolpidem seemed to amplify, rather than dissociate, the relation between behavior and the EEG. It is hypothesized that the large increase in beta-3/gamma activity caused by diazepam and zolpidem is a compensatory mechanism that allows for behavioral activation, despite pharmacologically induced sedation.     

Behavioral and brain temperature responses to salient environmental stimuli and intravenous cocaine in rats: effects of diazepam

Rationale While diazepam is an effective anxiolytic and somnolent drug in humans, its physiological and behavioral effects in animals are often variable. Differences in basal activity state (basal arousal) may be important in determining both this response variability and the pattern of drug influence on behavioral and physiological responses to natural arousing stimuli and other drugs. Objectives To evaluate the changes in brain, muscle, and skin temperatures, and in locomotion induced in rats by several arousing stimuli and intravenous (i.v.) cocaine; and to assess how these responses are modulated by diazepam at a relatively low dose (1 mg/kg, i.p.). Materials and methods Male rats were implanted with thermal probes in the nucleus accumbens (NAcc), temporal muscle, and subcutaneously, and equipped with a chronic i.v. catheter. They were exposed to 1-min tail-pinch, 1-min social interaction with another male and cocaine (1 mg/kg, i.v.) after administration of diazepam or saline. Results While the injection of either diazepam or saline resulted in similar locomotor activation and temperature responses, diazepam decreased basal brain and muscle temperatures for about 3 h; the temperature-decreasing effect of diazepam was oppositely related to basal brain temperature (r = −0.51). After diazepam, rats also showed weaker temperature and locomotor responses to both arousing stimuli; the effect was stronger for tail-pinch and for absolute temperature increases than relative changes. Although diazepam significantly decreased cocaine-induced locomotor activation, it had virtually no effects on cocaine-induced temperature responses in all locations. Conclusions In accordance with the “law of initial values”, the temperature-increasing effects of all tested arousing stimuli and temperature-decreasing effect of diazepam depend upon basal brain temperature. The greatest temperature effects are seen with arousing stimuli at low basal arousal (increases) and with diazepam at high basal arousal (decreases). This is a likely explanation for the variability seen with the physiological and behavioral effects of diazepam in animals.     

The effects of diazepam on cognitive processing

The study was designed to investigate the effects of diazepam on cognitive processing, and in particular to look at whether or not the drug reduces the bias towards the processing of threatening information shown by anxious subjects. Forty anxious female subjects were randomly and blindly allocated to two treatment groups; 10 mg diazepam or a placebo. Each subject was tested before and after treatment on a colour-naming task designed to measure selective attention towards both stressor-related and generally threatening material. It was found that the subjects showed a cognitive bias favouring the processing of threatening information, but that diazepam did not reduce this interference effect. This suggests that diazepam does not have a direct effect on cognitive aspects of anxiety.     

The anticonvulsant effects of diazepam and phenobarbital in prekindled and kindled seizures in rats

The effects of various doses of diazepam (0.5–4 mg/kg) and phenobarbital (7.5–60 mg/kg) were determined on prekindled and kindled amygdaloid seizures in the same rats. Diazepam was ineffective against the prekindled focal seizures, but demonstrated profound and statistically significant control of the kindled seizures. In the kindled state, diazepam reduced the afterdischarge duration and seizure rank score to prekindled levels. Only the largest sedating dose of phenobarbital produced a reduction of both prekindled afterdischarge duration and seizure rank score. Against the kindled seizure, phenobarbital showed a marked and statistically significant increase in effectiveness in all but the smallest dose tested. The afterdischarge duration of kindled seizures was reduced to prekindled levels by 15–60 mg/kg of phenobarbital, while seizure rank score was reduced to prekindled levels by 30 and 60 mg/kg phenobarbital. The effects of two doses of diazepam (0.5 and 2.5 mg/kg) and phenobarbital (7.5 and 30 mg/kg) were tested against prekindled and kindled pentylenetetrazol (PTZ)-induced seizures. Preliminary work with 3 doses of pentylenetetrazol (30, 40 and 60 mg/kg) demonstrated that repeated doses of 30 mg/kg readily kindled seizures without the significant mortality seen with larger doses. Both diazepam and phenobarbital were less effective against seizures kindled with 30 mg/kg pentylenetetrazol compared to prekindled seizures. The comparative lack of effect that was seen with diazepam and phenobarbital against the pentylenetetrazol kindled seizure at doses associated with control of the kindled amygdaloid seizure may reflect an underlying difference in the pathogenesis of kindling between these seizure models. Further, the lack of suppression of the prekindled amygdaloid afterdischarge duration by large doses of diazepam, in contrast to large doses of phenobarbital, may also reflect differences between the mechanisms of action of these two drugs. This paradigm provides a model for testing the effectiveness of anticonvulsants during the progressive development of various epileptogenic seizures.     

The effects of diazepam on brain 5-HT and 5-HIAA in stressed and unstressed rats

Diazepam, administered to rats at a high dose (25 mg/kg PO) has been shown to have no effect on the plasma corticosterone response to the stress of an elevated open platform. It did however, reduce the plasma corticosterone in rats repeatedly exposed to the apparatus. Diazepam-withdrawal from stress-habituated rats increased plasma corticosterone (p less than 0.01) whereas withdrawal of diazepam from unstressed rats had no effect on plasma corticosterone. It is concluded that this effect of diazepam-withdrawal may reflect the development of dependence upon the drug. Significant effects were not observed following the administration of a lower non-selective dose (5 mg/kg PO) of diazepam and, therefore, it is not clear whether dependence to its sedative, rather than the anxiolytic properties have been measured. Acute diazepam (25 mg/kg) increased (p less than 0.05) hippocampal 5-hydroxyindoleacetic acid; its withdrawal from unstressed rats after 40 days reduced (p less than 0.01) hypothalamic 5-hydroxytryptamine. There was no evidence that the effects of diazepam or its withdrawal on plasma corticosterone in stressed rats were associated directly with changes in brain 5-hydroxyindoles.