The pharmacology of benzodiazepine tolerance and withdrawal.
Explore the source record for details and available documents.
Animals↗
Biomedical subjects
S E File
Publications and source records attributed to S E File.
Usefulness of animal models with newer anxiolytics.
Explore the source record for details and available documents.
Animals↗
Low but not high doses of buspirone reduce the anxiogenic effects of diazepam withdrawal.
After 21 days of treatment with diazepam (2 mg/kg/day IP) rats were tested 24 h after the last injection in the social interaction and elevated plus-maze tests of anxiety. Compared with control-treated rats, they showed significant decreases in social interaction, in the % numbers of entries onto open arms of the plus-maze and in the % of time spent on the open arms, indicating an anxiogenic response on withdrawal from diazepam. Buspirone (200 micrograms/kg SC) significantly increased social interaction in diazepam withdrawn rats and in the plus-maze also this dose significantly reversed the anxiogenic effects of diazepam withdrawal. Buspirone (400 micrograms/kg SC) was without effect in the plus-maze, but buspirone (800 micrograms/kg SC) significantly decreased the % of time spent on open arms in control-treated rats, indicating an anxiogenic effect. In the social interaction test buspirone (800 micrograms/kg SC) was without significant effect. The contrasting effects of the 200 and 800 micrograms/kg doses are discussed in terms of the pre- and post-synaptic actions of buspirone. The findings are consistent with earlier proposals that the increased anxiety during benzodiazepine withdrawal is at least partly caused by an increased release of hippocampal 5-HT.
Animals↗
Diazepam withdrawal responses measured in the social interaction test of anxiety and their reversal by baclofen.
After 21 days of treatment with diazepam (0.5 or 2 mg/kg/day) rats were tolerant to the effects of diazepam to increase social interaction in the low light unfamiliar test condition of the social interaction test of anxiety. When they were tested 24 h after the last of 21 injections they showed significant decreases in social interaction, indicating an anxiogenic withdrawal response. However, the social interaction scores of rats tested 48 h after withdrawal from diazepam treatment were no longer different from those of the control group. The decreased social interaction, indicating increased anxiety, detected 24 h after withdrawal of diazepam (21 daily injections of 0.5 or 2 mg/kg), could be reversed by the usual daily diazepam dose (0.5 or 2 mg/kg, respectively) or by baclofen (0.5 or 1 mg/kg). Baclofen (2 mg/kg) was sedative in both control treated and diazepam-dependent rats, but was ineffective at reversing the decrease in social interaction seen after diazepam withdrawal. Possible sites of action mediating these effects of baclofen are discussed, and it is suggested that either post-synaptic GABAB sites in the hippocampus are involved or that the reversal of the decreased social interaction detected on withdrawal of diazepam treatment is due to a baclofen-mediated inhibition of 5-HT release in the hippocampus.
Animals↗
Effects of baclofen and nitrendipine on ethanol withdrawal responses in the rat.
Withdrawal of rats from 5 weeks of a liquid ethanol diet (10%), resulted in anxiogenic responses in the social interaction and elevated plus-maze tests of anxiety. The rats withdrawn from ethanol also showed increased aggression, tremor and rearing. Baclofen (1.25 and 2.5 mg/kg), but not nitrendipine (25-100 mg/kg), reversed the anxiogenic withdrawal responses, without having any effect in control animals and without having significant sedative effects. Baclofen reduced the enhanced aggression during withdrawal of ethanol, but this may have reflected a more general anti-aggressive action. Baclofen (2.5 mg/kg) reduced the withdrawal tremor. Nitrendipine (100 mg/kg) significantly reduced withdrawal tremor, but this dose was sedative, so this was likely to be a non-specific effect. It is proposed that the anxiogenic response during withdrawal of ethanol is due to a reduced GABA function, involving both GABAA and GABAB receptors.
Aggression↗
Sex differences in animal tests of anxiety.
To explore further the meaning of sexually dimorphic behavior in the open-field test, male and female hooded Lister rats were tested in three tests of anxiety. In the social interaction test, the social interaction scores of the female rats were lower and did not increase as readily following familiarization to the apparatus as those of the male rats. In the elevated plus-maze test, female rats showed a reduced aversion to the open arms compared to male rats; and in a modified Vogel conflict test, the punished licking rates of the female rats were lower than those of the male rats. It is concluded that the behavior of male and female rats differs in these tests, but that firm conclusions concerning sex differences in anxiety levels cannot be made because all three tests did not lead to predictions which were in the same direction. It is also suggested that cautious interpretation is necessary because these tests may measure different variables in male and female rats and they may not be valid tests of anxiety for female rats.
Animals↗
Amnesia for dental procedures and mood change following treatment with nitrous oxide or midazolam.
Fifty-eight patients undergoing restorative dental treatment at Guy's Hospital had been previously allocated on the basis of clinical assessment, including that of their dental anxiety, to treatment under local anaesthetic alone or in combination with i.v. midazolam or inhalation nitrous oxide. They were tested before and after dental treatment to determine their memory of dental procedures and changes in mood and bodily symptoms. The patients allocated to the midazolam treatment had significantly higher pre-treatment scores on the Bond & Lader mood factors of "anxiety" and "discontent". All the groups showed significant pre- to post-treatment reductions in sweating, palpitations, restlessness, dry mouth, muscular tension, nausea, loss of appetite and upset stomach and the extent of these reductions were not different for the different treatments. Midazolam treatment resulted in significantly greater reductions in self-ratings of bodily symptoms of anxiety, shaking and trembling compared with the control (local anaesthetic) group. Nitrous oxide resulted in a significant reduction in irritability, compared with controls. Both midazolam and nitrous oxide significantly reduced the patients' memory of the dental procedures and the impairments in memory were independent of any changes in anxiety or sedation. Of the items remembered there were no differences between the groups in their ratings of how well explained, how pleasant or unpleasant, or how painful the procedures were.
Adult↗
Handling habituation and chlordiazepoxide have different effects on GABA and 5-HT function in the frontal cortex and hippocampus.
In slices of frontal cortex and hippocampus from rats that had been habituated to handling for 21 days, there was significantly less 20 mM K(+)-evoked release of [14C]GABA ([14C]gamma-aminobutyric acid) compared with rats naive to handling. Handling for 21 days also significantly increased the uptake of [14C]GABA into frontal cortex and hippocampus. The change in uptake in the hippocampus was independent of any changes in release and could account for the apparent change in evoked release; in the cortex there were no independent changes in uptake and K(+)-evoked release. When the changes in uptake were taken into account, there were no independent changes in basal release of GABA in either region. HPLC analysis showed the change in uptake was not due to differences between the groups in endogenous GABA concentrations. Acute administration of chlordiazepoxide (CDP 7.5 mg/kg i.p.) to handling naive rats also significantly reduced K(+)-evoked [14C]GABA release from the cortex and hippocampus, but basal release and GABA uptake were unchanged. Neither handling nor CDP administration significantly changed the K(+)-evoked [3H]5-HT release, however, the uptake of 5-HT and its basal release in both regions were both significantly and independently increased in animals habituated to handling, compared with handling naive animals. In the hippocampus, the endogenous 5-HT concentrations were significantly lower in the rats that had received 21 days of handling, compared with handling naive rats. In the cortex the endogenous 5-hydroxyindoleacetic acid concentrations were significantly lower in the group that had been handled for 21 days. Thus both the GABA and 5-HT systems were responsive to handling habituation.
Animals↗
Long-lasting effects on habituation and passive avoidance performance of a period of chronic ethanol administration in the rat.
Rats were fed a liquid diet to which an increasing concentration of ethanol was added over a period of 3 weeks; a concentration of 10% ethanol was then maintained for a further 4 weeks. The rats were then returned to a normal ad libitum diet of rat pellets. In order to assess the long-term effects of this ethanol diet, the performance of different groups of rats was assessed 3 and 5 months after the normal diet was resumed. At both times, the ex-ethanol-treated rats showed significantly impaired between-day habituation of exploratory head-dipping at holes that were empty, but normal between-day habituation of head-dipping at the hole with the same object underneath on all 3 days. The ex-ethanol-treated rats also showed a reduced response to the introduction of an object at a previously empty hole and, following this, a subsequent disruption of between-day habituation of head-dipping at this hole. Within-session habituation of head-dipping was unimpaired. There were no deficits in the acquisition or short-term retention of a passive avoidance response, but on retention testing 24 h after training the ex-ethanol-treated rats showed a decreased latency to enter the shocked compartment. On the trials 24 h and 48 h after training the rats tested 5 months after their ethanol treatment showed impaired extinction of the passive avoidance response.
Alcoholism↗
A theory of benzodiazepine dependence that can explain whether flumazenil will enhance or reverse the phenomena.
Repeated administration of benzodiazepines (BDZs) produces dependence in man and animals and this is reflected in the phenomena of tolerance and withdrawal responses. In BDZ-dependent animals the BDZ-receptor antagonist flumazenil (Ro 15-1788) reverses the increased anxiety and decreased seizure threshold seen when benzodiazepine treatment is withdrawn. In contrast are reports that flumaenil enhances BDZ-withdrawal responses. Indirect influences on the direction of flumazenil's effects on anxiety are the duration and dose of BDZ treatment, whether tolerance has developed to its anxiolytic effect and whether there is an anxiogenic response on drug withdrawal. However, we conclude that the crucial factor is the anxiety level of the animal: when this is high flumazenil becomes anxiolytic; when this is low flumazenil is anxiogenic. These bidirectional effects of flumazenil can be seen in drug-naive and BDZ-dependent animals. We propose a theory of benzodiazepine dependence that can account for anxiogenic responses on drug withdrawal and for flumazenil's bidirectional effects; central to this theory is the assumption that flumazenil normalises the benzodiazepine receptor, returning it to a baseline state. Thus it is whether an animal's score lies above or below this baseline that will determine the direction of flumazenil's effect. The clinical implications of this theory are discussed. We suggest that during the development of benzodiazepine dependence, two independent adaptive biochemical mechanisms are triggered: one underlying the development of tolerance to the anxiolytic responses, the other underlying the incidence of increased anxiety on drug withdrawal. It is only changes in the latter that are induced by the administration of flumazenil.
Animals↗
Changes in seizure threshold and aggression during chronic treatment with three anticonvulsants and on drug withdrawal.
Sodium phenobarbitone (20 and 70 mg/kg) had a significant anticonvulsant action against pentylenetetrazole-induced seizures, which persisted for 21 days of treatment. On drug withdrawal there was a significant decrease in seizure threshold below control level 24-48 h after the last dose of 70 mg/kg. Phenytoin (40 mg/kg) had a significant anticonvulsant action after 7 days of treatment and this persisted for 21 days of treatment. On drug withdrawal there was a significant decrease in seizure threshold 48 h after the last dose. Lorazepam (0.1 mg/kg) had a significant anticonvulsant action, but the group tested after 21 days of treatment did not differ from the controls, indicating that tolerance had developed to this effect; on drug withdrawal there was a decrease in seizure threshold from 24 to 72 h. The only drug to increase aggressive behaviour was sodium phenobarbitone (70 mg/kg); this reached significance after 14 and 21 days of treatment and occurred 8 h after drug administration; 0.5 h after drug administration phenobarbitone (70 mg/kg) abolished aggressive behaviour. After 7 days of treatment phenobarbitone (70 mg/kg) increased social behaviour 0.5 h after administration and this was still increased after 21 days of treatment. On drug withdrawal, there were no changes in aggressive behaviour, but there were significant decreases in social behaviour 24 and 48 h after phenobarbitone (70 mg/kg) withdrawal and 24, 48 and 72 h after lorazepam (0.1 mg/kg) withdrawal.
Aggression↗
One-trial tolerance to the anxiolytic effects of chlordiazepoxide in the plus-maze.
Chlordiazepoxide (CDP 7.5 mg/kg) had a significant anxiolytic effect in rats tested on the plus-maze for the first time. On a second trial the control scores did not change, but those of the CDP group did and they no longer differed from controls. Rats previously tested undrugged or after flumazenil (4 mg/kg) also failed to show an anxiolytic response to CDP. Thus this phenomenon of one-trial tolerance depended on prior experience with the plus-maze. It also depended on CDP acting at the benzodiazepine receptors on trial 2, since the joint administration of CDP and flumazenil on trial 2 reversed the phenomenon.
Animals↗
Characterisation of the phenomenon of "one-trial tolerance" to the anxiolytic effect of chlordiazepoxide in the elevated plus-maze.
In the elevated plus-maze test of anxiety the scores of control animals remain stable over repeated tests. However, a single prior exposure to the plus-maze renders an animal insensitive to the anxiolytic effects of chlordiazepoxide. This phenomenon of "one-trial tolerance" persisted even when the two trials were separated by as much as 2 weeks. It has previously been shown that the drug state of the animal on trial 1 is not important to the development of the phenomenon, but one-trial tolerance did not develop if a very high dose (75 mg/kg) of chlordiazepoxide was given on trial 1; it is suggested that this is due to the amnesic effects of the drug. The learning on trial 1 was not specific to a particular plus-maze and tolerance could be observed even when the maze on trial 1 was made from different material. The crucial experience on trial 1 was experience of an open arm of the maze. Whereas tolerance could be obtained as a result of a previous plus-maze experience, there was no evidence of an anxiogenic withdrawal response when rats were tested the following day undrugged. The phenomenon of one-trial tolerance is explained within our recently proposed two-factor theory of benzodiazepine dependence; it is suggested that one-trial tolerance provides a method for studying the mechanism underlying the development of tolerance to anxiolytic effects, independently from the mechanism underlying the development of withdrawal responses.
Animals↗
Effects of sodium phenobarbital on motor activity and exploration in the mouse: development of tolerance and incidence of withdrawal responses.
Sodium phenobarbital (20 mg/kg) was without significant effect on exploratory head-dipping, but a higher dose (70 mg/kg) significantly reduced the number of head-dips and the time spent head-dipping 0.5 and 8 hr after acute administration. Tolerance developed rapidly, i.e., by day 7 of treatment, to these reductions. Both doses of phenobarbital significantly increased locomotor activity, the increase was more marked for the 70 mg/kg dose and for this dose was greater 8 hr after administration than 0.5 hr. No tolerance developed over 21 days of treatment to the increase in locomotor activity 0.5 hr after drug administration; some tolerance did develop by day 14 to the increase detected 8 hr after drug administration, but this is likely to be metabolic. After 21 days of treatment, sodium phenobarbital was withdrawn. Twenty-four hours after the last dose of 70 mg/kg there was a significant reduction in the time spent head-dipping; there was also significant reduction in locomotor activity, which peaked 48 hr after the last dose.
Animals↗
A comparison of the effects of diazepam and scopolamine in two positively reinforced learning tasks.
In a helical maze scopolamine (0.5 and 1 mg/kg) significantly impaired the ability of rats to acquire a spatial learning task using reference memory. In contrast, diazepam (0.5-2 mg/kg) did not impair acquisition of this task and the only effect of diazepam (4 mg/kg) was likely to be secondary to sedative effects. Diazepam (0.5-4 mg/kg) did not impair 8-day retention of the helical maze. In a test of working and reference memory in which spatial processing was minimised, scopolamine (0.5 and 1 mg/kg) significantly impaired acquisition and increased the number of reference memory errors. Diazepam (1 and 4 mg/kg) did not impair acquisition of this task, but when a delay was interposed in the middle of a trial the diazepam-treated rats were slower to complete the task than the controls and made more errors of both working and reference memory. In contrast, when the rats were tested with a change of context, the diazepam-treated rats completed the task more quickly than the controls and made fewer errors of both working and reference memory.
Animals↗
Interactions of anxiolytic and antidepressant drugs with hormones of the hypothalamic-pituitary-adrenal axis.
Changes in hormones of the hypothalamic-pituitary-adrenal (HPA) axis in patients suffering from anxiety and depressive disorders are reviewed, and the changes that occur when animals are exposed to test situations used preclinically to model anxiety or depression. The effects of exogenous administration of HPA hormones both clinically and in animal tests is discussed and the effects of clinically used anxiolytics and antidepressants on hormones of the HPA axis. The final section discusses stress-induced changes in the CNS.
Animals↗
The history of benzodiazepine dependence: a review of animal studies.
This article provides a historical review of the animal literature relating to the development of tolerance to the behavioral effects of benzodiazepines, and the incidence of biochemical and behavioral changes that result from termination of benzodiazepine treatment (spontaneous withdrawal responses). It charts the slow emergence of a pertinent animal literature and highlights conclusions that were prevalent in 1963 (at the introduction of diazepam), 1973 (at the introduction of lorazepam), 1980 and the present day. For 25 years the animal literature has lagged behind the clinical literature, but recent studies into the neurochemical mechanisms of benzodiazepine dependence and possible treatments for withdrawal responses suggest that, at last, animal experiments may be about to make a substantial contribution.
Alcoholism↗