Effects of acute or chronic carbamazepine on experimentally-induced conflict in the rat

The effects of acutely or chronically administered carbamazepine were studied in rats submitted to the modified Geller-Seifter conflict test. Diazepam was used as a standard anxiolytic. The results showed an increase in punished response after carbamazepine, as observed with diazepam, leading to the suggestion of an anticonflicteffect for this drug. No tolerance to the antipunishmenteffect was seen after chronic carbamazepine administration.     

Increased sensitivity to benzodiazepine antagonists in rats following chronic treatment with a low dose of diazepam

The effects of benzodiazepine (BZ) antagonists on operant behavior were examined in rats chronically administered a low dose of diazepam (DZ). The low maintenance dose of DZ (5 mg/kg twice daily) was selected as more closely associated with its anxiolytic effects than the higher treatment doses previously used to study BZ dependence. Food-restricted rats were trained to press a lever for food reinforcement under a FR20 schedule of reinforcement prior to the start of DZ administration. Acute administration of DZ caused a dose-dependent reduction of response rates, with 5 mg/kg causing a 50% decrease. Rats treated chronically with DZ became tolerant to its rate-suppressant effects as shown by a 5-fold increase in the dose of DZ required to reduce FR20 response rates by 50%. The BZ antagonist flumazenil (formerly Ro 15-1788; 10–56 mg/kg) suppressed rates of responding in rats treated chronically with DZ. The suppression of operant responding was obtained when flumazenil was given up to 3 h, but not 18 h, after the last treatment with DZ. In contrast, only the highest dose of flumazenil (56 mg/kg) caused reductions of operant responding when given to rats treated with saline. The BZ antagonist CGS 8216 (3.3–33 mg/kg IP), given 10 min prior to the session, was similarly more potent and effective at suppressing operant responding in rats treated chronically with DZ than saline. This procedure may provide a model for the clinical problem of physical dependence to chronically-administered low, anxiolytic doses of BZ tranquilizers.     

Effects of diazepam on conflict behaviour and on plasma corticosterone levels in male and female rats

The anxiolytic properties of diazepam and its effects on plasma corticosterone levels were compared in male and female, water deprived rats exposed to the punished (0.8 mA) drinking procedure. The effects of diazepam on unpunished licking, tested under familiar or unfamiliar conditions, and on the lick latency were also studied and a comparison between the two sexes was made. Both punished and unpunished drinking were less in females than in males. In both sexes, a clear anticonflict effect, i.e. a much greater effect on punished than on unpunished drinking, was obtained with 2 and 4 mg/kg, but not with I mg/kg, of diazepam i.p. Plasma corticosterone levels were higher in water deprived females than in males. Following the punished and unpunished drinking procedure, plasma corticosterone levels were found to have decreased more in female than in male rats, especially after administration of 1 mg/kg of diazepam. Diazepam had similar anticonflict effects in rats of both sexes but had a greater suppressive effect on the plasma corticosterone levels in female rats. There was no correlation between the anxiolytic effects of diazepam and its effect on the plasma corticosterone levels. When testing was done under unfamiliar conditions, the latency to licking was greater in female than in male rats and diazepam (1, 2 and 4 mg/kg) increased this latency in both sexes. The results suggest sex differences in the neuroendocrine, but not in the anxiolytic, effects of diazepam.     

Behavioral analysis of diazepam-induced memory deficits: evidence for sedation-like effects

Rats were trained on a nonmatching-to-sample task with delays of 2, 5, and 10 min. Subsequently, performance was assessed in three groups of rats following treatment with saline or diazepam (2.0 mg/kg) administered acutely or tested chronically in six administrations. Relative to treatment with saline, diazepam produced a deficit in discrimination performance, which was greater in the acutely treated rats than in those treated chronically. The deficit was not dependent on the length of the delays. Diazepam-treated animals differed from controls in erring on trials in which they failed to investigate both test objects, failed to investigate the test object for a long enough period of time, and displaced the test object on the preferred side of the apparatus. The hypothesis that these effects represented a sedation-like reduction in behavioral variability was also supported by evidence of a diazepam-induced decrease in gross bodily activity, increase in inactivity, and increase in latencies to respond to objects. No support was found for the involvement of diazepam-induced changes in habituation, extinction, or reward effects.     

Regional GABA/benzodiazepine receptor/chloride channel coupling after acute and chronic benzodiazepine treatment

GABA/benzodiazepine coupling was evaluated in 8 regions of rat brain by the ability of GABA to stimulate 0.5 nM [3H]flunitrazepam binding. Rats were treated acutely with diazepam (p.o) or chronically with flurazepam, offered in the drinking water for 4 weeks, and compared to a pair-handled vehicle-treated control group. Regional variations in GABA/benzodiazepine coupling were found in control membranes. GABA increased benzodiazepine binding maximally (40%) in cerebellum and medulla, and least (25%) in olfactory bulb. A significant decrease in the effect of GABA was found in cortex of chronically treated rats immediately after, but not 2 days following treatment. The Emax for GABA stimulation of [3H]flunitrazepam binding was significantly increased in medulla after acute treatment but was not altered after acute or chronic treatment in other brain areas evaluated. Treatment had no effect on the ability of bicuculline to inhibit [3H]flunitrazepam binding in cortex. Benzodiazepine/Cl- coupling in cortex or hippocampus of acutely and chronically treated rats, evaluated by the ability of Cl- to stimulate specific [3H]flunitrazepam binding, was not changed. The results support the hypothesis that a functional uncoupling of the benzodiazepine recognition site from the GABA receptor in cortex, but not from the anion recognition site, may play a role in tolerance development.     

Benzodiazepine antagonist, CGS-8216, in diazepam- or pentobarbital-dependent and non-dependent rats

CGS-8216, a benzodiazepine antagonist, was administered to rats acutely dosed with diazepam, and to rats chronically dosed with diazepam or pentobarbital. The effects of an acute dose of diazepam were antagonized by CGS-8216 but signs of precipitated abstinence were not observed. An apparent arousing effect was seen in non-dependent rats when CGS-8216 was administered after placebo, but no arousal was observed when Ro15-1788 was administered after placebo in non-dependent rats. A precipitated abstinence syndrome was elicited with CGS-8216 in rats chronically dosed with diazepam and was very similar to the abstinence syndrome precipitated by Ro15-1788 in diazepam-dependent rats. Like Ro15-1788, CGS-8216 elevated Precipitated Abstinence Scale (PAS) scores in a dose-related manner until a plateau was reached with 5 mg/kg. No signs of precipitated abstinence were observed when CGS-8216 was administered to rats dependent on phenobarbital.     

Differences in the development of tolerance to various benzodiazepines

Anticonvulsant, sedative and anxiolytic effects of the following benzodiazepines, administered chronically by the intraperitoneal route, were assessed: nitrazepam (NTZ), diazepam (DZ), oxazepam (OXZ), chlordiazepoxide (CDX) and temazepam (TMZ). The action of NTZ in tests for sedative, anticonvulsant and anxiolytic effects rapidly changed upon a repeated daily treatment, which suggests development of tolerance, while no tolerance developed to such effects of OXZ. The stimulating effect of DZ was found not earlier than after 5 weeks of chronic treatment, but no tolerance to the anxiolytic action was observed, and the anticonvulsant action was even potentiated. The stimulating action and tolerance to the anxiolytic effects of CDX and TMZ developed rapidly, but was accompanied with an only slight decrease in the anticonvulsant effect.     

Evidence that gaba mechanisms mediate the anxiolytic action of benzodiazepines: A study with valproic acid

Valproic acid and diazepam were tested for “anti-anxiety” activity in two animal tests known to predict the anxiolytic action of drugs. In one test, male hooded rats were trained to discriminate the “anxiomimetic” action of pentylenetetrazol from saline by responding on one of two levers for food reinforcement after pentylenetetrazol (1450 μmol/kg) injection and the other lever after saline injection. Once the pentylenetetrazol-saline discrimination was acquired, pretreatment with either diazepam (4.4–35.0 μmol/kg) or valproic acid (278–2220 μmol/kg) produced a dose-dependent antagonism of the “anxiomimetic” stimulus in this test. In the other test, male Wistar rats were trained to respond for milk reinforcement and to suppress those responses when the reinforcement was accompanied by the simultaneous delivery of foot shock. Treatment of these rats with diazepam (7–28 μmol/kg) or valproic acid (1110–2220 μmol/kg) antagonized the suppression of responding induced by the foot shock in a dose-dependent manner. In both tests, diazepam and valproic acid showed anxiolytic activity at doses which did not result in an overall suppression of responding. The demonstration of anxiolytic activity by the GABAmimetic drug, valproic acid, suggests that GABA mechanisms may mediate the anxiolytic action of benzodiazepines.     

Hyponeophagia and arousal in rats: Effects of diazepam, 5-methoxy-N,N-dimethyltryptamine,d-amphetamine and food deprivation

A modified hyponeophagia test is described as an animal model of anxiety. The effects of 0, 0.3, 1.0, 3.0 and 10 mg/kg diazepam, given both acutely and for 7 days pretest, were assessed in rats. Acutely, diazepam reduced hyponeophagia over the dose range 0.3–3.0 mg/kg but 10.0 mg/kg produced sedation and large variability. Chronically, the dose-response relationships were monotonic and the maximal effect was increased, suggesting that differential tolerance occurs to the sedative, but not to the anxiolytic, effects of this drug. Increased food deprivation did not mimic benzodiazepine effects on hyponeophagia, and actually prolonged eating latency in rats treated with 5-methoxy-N,N-dimethyltryptamine (2.5 mg/kg), which does not support an interpretation of diazepam effects in terms of appetitive actions. An arousal hypothesis of hyponeophagia was proposed and supported by the antagonism of the sedative effects of 10.0 mg/kg diazepam by d-amphetamine (0.5 mg/kg). Although both male and female rats were used throughout, sex differences were few in these studies.     

The effect of doxepin on the central action of ethanol.

The effect of combined treatment with doxepin and ethanol was tested in mice, rats and rabbits. Doxepin was given in a single dose (5 or 10 mg/kg) or chronically (10 mg/kg/d for 21 days). Doxepin did not affect ethanol toxicity and ethanol-induced impairment of rota-rod performance, but potentiated ethanol-induced hypothermia (only acutely) and prolonged ethanol-induced sleep in mice. Given acutely it potentiated the inhibitory effect of ethanol on locomotor activity in mice, while given chronically it counteracted the ethanol-induced sedation. Doxepin did not interfere with ethanol-induced EEG effects in rabbits, and prevented the development of tolerance to hypothermic, but not to hypnotic effects of ethanol in rats. In general, the interference of doxepin with ethanol was more pronounced after single doses of the drug than after chronic treatment.     

The excitatory effect of ethanol: absence in rats, no tolerance and increased sensitivity in mice

Three questions related to ethanol's stimulating effect (ESE) were studied. The first referred to the reported absence of tolerance to ESE in mice. It was determined whether tolerance would develop if the period of ethanol treatment were extended significantly beyond those normally found in the literature. No evidence of tolerance to ESE was found over a 5-month period of treatment. The second issue related to the possibility that mice not only do not develop tolerance but actually become more responsive to ESE after chronic exposure. A dose of ethanol that acutely did not produce a significant activating effect did induce a marked excitation after the animals were chronically treated with ethanol. Finally, the issue was addressed of whether the absence of ESE in some strains of rats could in part be due to a masking effect by the depressant component of this drug. To test this possibility rats were treated with ethanol for a 4-month period. Tolerance to the depressant effect was observed but no ESE was detected.     

Effects of acute and chronic interactions of diazepam and d-Amphetamine on punished behavior of rats

Drinking of water-deprived rats was punished by delivery of either 0.03 or 0.1 mA shocks through the drinking tube during the last 5 of 7-s tone components during a 15-min daily exposure to water. These sessions consisted of 66 alternating components marked by the presence or absence of a tone. Drinking was not punished during the 33 components without tones or during the first 2 s of each tone. The baseline number of shocks accepted by the rats at 0.1 mA was less than half that at 0.03 mA. Acute diazepam markedly increased shocks delivered from the baseline values for both shock intensities, while acute d-amphetamine either had no effect or decreased the number of shocks accepted. The combination of acute diazepam and d-amphetamine caused a decrease in shock rates as compared to diazepam alone. Daily treatment with the combination of 10 mg/kg diazepam and 1 mg/kg d-amphetamine caused a gradual increase in punished responding over 25 days under either shock intensity. Gross observation of these rats after daily treatments indicated the development of hyperreactivity and a pattern resembling stereotyped behavior. At the end of the chronic treatment with the drug combination the shock rates were significantly greater than those caused by diazepam alone. Nevertheless, neither the effect of diazepam nor that of d-amphetamine, when administered singly after the period of chronic treatment with the combination, differed significantly from initial effect of the respective drugs on punished responding.     

安定对大鼠开场行为活动和高钾诱发单胺递质释放的影响

急性ip安定3mg/kg显著抑制大鼠开场(OF)行为活动。慢性ip同一剂量安定15d,对OF抑制产生耐受。完成OF观察后,断头取脑,观察高K⁺诱发不同脑区单胺递质释放变化。整体急性ip安定3mg/kg产生与离体条件下9μmol/L安定相似的抑制高K⁺诱发单胺递质释放作用。慢性ip安定,对海马和杏仁核区高K~+诱发儿茶酚胺释放抑制作用产生显著耐受;未观察到对高K⁺诱发5-羟色胺抑制作用的耐受现象。     

Prevention of diazepam withdrawal syndrome by nifedipine-behavioural and neurochemical studies

Our studies aimed at investigating whether the dihydropyridine calcium antagonist, nifedipine, could prevent anxiogenic-like consequences of diazepam withdrawal in rats. Animals withdrawn from chronic diazepam (2 mg/kg/day i.p. for 2 weeks) drank significantly less water than did control rats in the unfamiliar arm of a Y maze. This anxiogenic-like effect could be prevented by acute administration of nifedipine (at 10 mg/kg i.p., but not at lower doses), which, on its own, did not change water intake in naive rats. Given chronically in combination with diazepam for the second half of a 2-week treatment with this drug, nifedipine (at the daily dose of 5 mg/kg i.p.) also suppressed the reduction of water intake normally observed on diazepam withdrawal. Biochemical measurements showed that acutely, as well as chronically, administered nifedipine increased 5-HT turnover in the hippocampus of diazepam-treated rats, thereby suggesting that the prevention of diazepam withdrawal-induced anxiogenic behaviour by the calcium antagonist might be underlain by serotoninergic mechanisms.     

A lack of tolerance to the anxiolytic effects of diazepam on the plus-maze: comparison of male and female rats

Rationale: The demonstration of tolerance to the anxiolytic effects of benzodiazepines remains inconsistent. Objectives: The present study tested the hypothesis that intact and gonadectomized male and female rats might exhibit differential tolerance to the anxiolytic effects of diazepam (DZ). Methods: Following acute (3 days) or chronic (3 weeks) DZ exposure, all animals were tested on the elevated plus-maze and immediately sacrificed for analysis of corticosterone, adrenocorticotropin hormone, estrogen and progesterone levels in serum. In experiment 2, following acute or chronic DZ exposure, animals were treated with a DZ challenge dose on the test day. Results: In experiment 1, both acute and chronic DZ treatment similarly enhanced percentage open arm time and entries, regardless of the hormonal status of the animal. The results of experiment 2 showed that both acute and chronic DZ-treated animals exhibited a significantly higher percentage open arm time than control animals after the DZ challenge dose, and males and females did not differ in their responses to DZ exposure. Conclusions: The findings from these experiments suggest that tolerance to the anxiolytic effects of DZ did not develop in males or females, and that the hormonal status of the animal does not significantly alter the anxiolytic effects of DZ following either acute or chronic exposure. Following plus-maze exposure, females had significantly higher corticosterone levels than males and acute DZ treatment diminished this stress response. Received: 23 February 1999 / Final version: 28 July 1999     

Does the increase in locomotion induced by ethanol indicate its stimulant or anxiolytic properties?

The responses of mice to low doses of acutely and chronically administered ethanol (2.0 g/kg) and diazepam (2.0 mg/kg) were observed in activity cages, the open field and the elevated plus-maze. After prolonged administration, ethanol significantly increased locomotion in the activity cages and the plus-maze. In the open field, an increase was only observed in the tests performed after 7 and 14 days of treatment. Ethanol increased the open-arm time in the plus-maze in all the tests, including after acute administration, suggesting an anxiolytic effect. Diazepam induced an anxiolytic effect after 14 days of daily injections but had no stimulant effect on locomotion. Moreover, after prolonged administration sensitization to the anxiolytic, but not to the stimulant effect, was observed. In short, the present paper's data support the hypothesis that the stimulant and anxiolytic effects of ethanol are probably being mediated by distinct mechanisms. Furthermore, these data support the hypothesis that drugs that lead to abusive use, such as ethanol, may act both as positive and negative reinforcement.     

Are there changes in sensitivity to 5-HT3 receptor ligands following chronic diazepam treatment?

Administration of 1-(3-chlorophenyl)-biguanide (mCPB), a 5-HT₃ receptor agonist (1 and 10 mg/kg IP), was found to be significantly anxiogenic in vehicle treated rats tested in the plus-maze, while having no significant effect in rats withdrawn for 24 h from 21 days diazepam treatment (2 mg/kg/day), suggesting a decreased agonist action at 5-HT₃ receptors following withdrawal from chronic diazepam treatment. In the social interaction test, diazepam withdrawn rats showed a significant decrease in social interaction when compared to the chronic vehicle treated group. This anxiogenic response was reversed by low doses of zacopride (0.0001–0.01 mg/kg IP); in the vehicle treated animals 0.1 mg/kg was significantly anxiogenic. The overall pattern of results with zacopride is explained by suggesting that the anxiogenic effects of high doses of zacopride are detectable at low levels of 5-HT function and are due to an agonist action of the S-isomer in the rat at 5-HT₃ receptors. The anxiolytic action of low doses is attributed to the R-isomer acting at the R-zacopride binding site and is enhanced in conditions of high 5-HT function, e.g. in the diazepam withdrawn rats. If this hypothesis is correct, then we would predict the R-isomer alone would be more effective in reversing the anxiogenic effects of diazepam withdrawal than the racemate, used here.     

Chronic handling modifies the anxiolytic effect of diazepam in the elevated plus-maze

Rats treated for 3 days with diazepam demonstrated a clear anxiolytic action of the drug as assessed in the elevated plus-maze. However, in a chronic experiment, in which all rats were handled for 28 days, no anxiolytic effect of diazepam could be shown either in rats treated for 3 days or in those treated for 28 days. These results suggest that there is an interaction between handling and the anxiolytic effect of diazepam.     

Similarities and differences between d-ALA2 MET5 enkephalin amide and morphine in the induction of tolerance to their effects on catalepsy and on dopamine metabolism in the rat brain

Summary Rats were made tolerant to morphine or to DALA, a synthetic analogue of met-enkephalin, by prolonged exposure to these compounds. Tolerance was assessed by evaluating the resistance of the treated rats to present catalepsy after an acute dose of the opiates. Both morphine and DALA induced tolerance and cross-tolerance to the cataleptic effect. Acute administration of morphine and DALA increased the concentration of DOPAC in striatum, limbic area and s.nigra of control rats. This increase was not present when morphine was given acutely to chronically morphine-treated rats, indicating that these animals were tolerant to this effect. Chronically morphine-treated rats given DALA presented partial tolerance to the biochemical effect of the peptide in limbic area and in s.nigra but not in striatum, indicating that only in certain areas was crosstolerance produced by chronic morphine. When DALA was administered at different doses to chronically DALA treated rats, the peptide induced rise in DA catabolite was similar to that produced in control animals, so clearly there was no tolerance to this biochemical effect. In these animals cross tolerance to morphine's effect on DA metabolism was present in s.nigra but not in the other two areas, indicating that s.nigra is particularly sensitive to opiate-induced tolerance on DA metabolism.Supported by CNR-ROME Grant no. CT81.00258.04     

Effect of Chronic Diazepam Treatment on Footshock-Induced Ultrasonic Vocalization in Adult Male Rats

Abstract: Rats were tested in the footshock-induced ultrasonic vocalization model of anxiety. The ultrasounds were recorded 1–11 min. after 10 inescapable 0.6 mA footshocks each of 1 sec. duration. Repeated administration of benzodiazepines in the clinic has been reported to be accompanied by development of tolerance and withdrawal anxiety. The present study examined whether the ultrasonic vocalization model could reflect these two side effects. Diazepam 4.6 or 8.8 μmol/kg (1.3 or 2.5 mg/kg, subcutaneously) administered twice a day (8 a.m. and 4 p.m.) abolished the vocalization after acute administration and after 3 weeks of treatment. Hence, no tolerance developed to the anxiolytic effect of diazepam. When the rats were tested 24 and 48 hr after the last doses of diazepam there were no significant differences from the control group, i.e. no apparent withdrawal anxiety. Instead, the control groups developed tolerance to the shock regimen during the chronic experiments. This was examined further by daily testing of a group of naive rats for 13 days. The findings indicated that there is a limitation in number of test sessions before tolerance to the model develops. In conclusion, the results of the present study contribute to the many contradictory and by no mean unequivocally findings in the literature. It indicates that substantial prediction of anxiolytic effects as well as unwanted side effects cannot be made from one single test model.