Effect of p-chlorophenylalanine on diazepam withdrawal signs in rats

Lack of tolerance to anxiolysis and withdrawal symptoms in mice repeatedly treated with AC-5216, a selective TSPO ligand

AC-5216, a ligand for the translocator protein (18 kDa) (TSPO), produces anxiolytic-like effects in animal models of anxiety without causing the side effects normally associated with conventional benzodiazepines. This study aimed to investigate whether repeated administration of AC-5216 induces tolerance to anxiolytic-like effects of AC-5216 and produces withdrawal on abrupt cessation, and compare the results with those of diazepam. In the tolerance experiment, AC-5216 (0.1 mg/kg, p.o.) produced significant anxiolytic-like effects in both groups of mice pretreated with the vehicle and AC-5216 twice daily for 14 days. Diazepam (0.1 mg/kg, p.o.) also retained its anxiolytic effects in mice repeatedly treated with diazepam. In the withdrawal experiment, mice were orally treated with either AC-5216 (0.1, 1 or 10 mg/kg; twice daily) or diazepam (0.1, 1 or 10 mg/kg; twice daily) for 14 days, and examined, during a treatment withdrawal period, for anxiogenic-like effects in the social interaction test, and for body weight loss as indices of emotional and somatic withdrawal symptoms, respectively. In AC-5216-treated groups, neither anxiogenic-like effects nor body weight loss was observed upon treatment withdrawal at any of the doses tested. In contrast, in diazepam 1 mg/kg- and 10 mg/kg-treated groups, treatment withdrawal not only induced anxiogenic-like effects on the second day of the withdrawal period, but also decreased body weight gain and brought about body weight loss in mice. These findings indicate that AC-5216 when repeatedly administered does not induce tolerance to its anxiolytic-like effects or withdrawal symptoms.

Changes in GABAA receptor function and cross-tolerance to ethanol in diazepam-dependent rats

Changes in gamma-aminobutyric acidA (GABAA) receptor function and their relation to cross-tolerance to ethanol (EtOH) were studied in diazepam (DZP)-dependent rats. Physical dependence on DZP was induced in male Fischer rats by using the drug-admixed food method. The 38Cl- influx into cerebral cortical synaptoneurosomes induced by 10 microM GABA in DZP-withdrawn rats was significantly increased, compared with control and DZP-tolerant rats. Although enhancement of GABA-dependent 38Cl- influx by the addition of EtOH and flunitrazepam (FZ) was recognized in the control, there was no such effect of EtOH or FZ in the DZP-tolerant animals. On the other hand, GABA-dependent 38Cl- influx was enhanced by FZ in the withdrawn group. The addition of picrotoxin and bicuculline inhibited GABA-dependent 38Cl- influx in each group. The stimulatory effect of FZ on GABA-dependent 38Cl- influx was inhibited by the addition of Ro 15-1788 in the control group. However, such an inhibitory effect was not observed in the withdrawn group. The antagonistic effect of Ro 15-4513 on EtOH stimulation of GABA-dependent 38Cl- influx observed in the control was not recognized in the withdrawn group. In a [3H]FZ assay of binding to benzodiazepine (BZ) receptors, Bmax values were significantly increased in DZP-withdrawn animals, but decreased in the DZP-tolerant group, compared with the control. When [3H]muscimol binding was examined, the Kd of high-affinity sites of the GABAA receptor in withdrawn rats was significantly lower than in the control. In low-affinity binding sites, the values of Kd and Bmax were significantly decreased, compared with those in the control. The present study indicates that GABAergic transmission involving the regulation of GABA-dependent chloride channels is altered in DZP-dependent rats. Alterations of the GABAA/BZ/chloride channel complex function may be related to the cross-tolerance between BZ and EtOH.

State-dependent effects of atypical benzodiazepine-receptor agonists

The state-dependent effect of the BZ-receptor agonist diazepam (1.25-10 mg/kg), the partial agonist FG 8205 (0.5-4.0 mg/kg) and the BZ1-receptor agonist zolpidem (0.25-2 mg/kg) were investigated in rats. During daily sessions, animals were trained to acquire FR10 lever pressing for food reinforcement whilst under the influence of the agonists, using an operant technique. Forty-eight hours after the final training session under drug, their performance of the FR10 was evaluated during a test session, carried out following vehicle administration only. Neither diazepam, nor FG 8205 impaired acquisition of the task. In the group treated with 2 mg/kg zolpidem, six out of eight rats failed to learn within 20 sessions, but the smaller doses were without effect on acquisition. When drug treatment was withdrawn, there was evidence that all three of the agonists tested produced state-dependency. This was apparent in the form of longer latencies to obtain reinforcement and decreased lever pressing rates. The significance of these findings are discussed in the context of the relationship between the state-dependent effects of BZ-receptor agonists and their other properties, and the receptor subtypes which might underly these effects.

Tolerance and withdrawal after chronic lorazepam treatment in rats

The purpose of the study was to develop an animal model for benzodiazepine tolerance and dependence on the basis of oral administration, using lorazepam as the test drug. We have used the continuous measurement of locomotor activity in home cages to obtain a narrow estimation of the time course of withdrawal related hyperactivity as an observer-independent symptom. Acute administration of lorazepam (9.5-37.5 mg/kg body weight/day) resulted in the first week in a dose-dependent muscle relaxation on the accelerod and sedation in the open field. The most striking manifestation of sedation, however, was the decrease of nocturnal locomotor activity in home cages. After 5 weeks of administration tolerance to the sedative effect had developed. In a second study, using a lower dose range (2.5-9.5 mg/kg body weight/day), a decrease of nocturnal locomotor activity was also observed as was the development of tolerance. The latter can be partly explained by dispositional tolerance, i.e., decreased serum concentrations after administration of lorazepam for more than 2 weeks. Withdrawal of lorazepam in the experiment using high doses led to three symptoms, i.e., a decrease in food intake, loss of body weight and an increase in daytime locomotor activity. The decrease in food intake and the loss of body weight were maximal on the first day of withdrawal. The increase in the daytime locomotor activity was present in the high dose experiment only, with a maximum on days 2-3 and a duration of at least 1 week. The increase however, was not dependent on the dose previously administered. The symptoms 'loss of body weight' and 'decrease in food intake' appeared to be more sensitive in benzodiazepine withdrawal: they were dose dependently present over the whole dosage range (2.5-37.5 mg/kg body weight/day). It is concluded that the model represents a sensitive model to measure lorazepam tolerance and dependence in animals. Comparative studies with other benzodiazepines are in progress.

Genetic differences in the development of physical dependence upon diazepam in Lewis and Fischer 344 inbred rat strains

The purpose of the present study was to investigate physical dependence upon diazepam systematically in two inbred strains of rats, Lewis (LEW) and Fischer 344 (F344). Rats were chronically fed food containing diazepam on an escalating drug dosage schedule, from 1 and 2 to 12 mg/g of food, over a period of 30 days. During treatment, the growth curve in LEW and F344 rats was suppressed compared with the respective controls. Motor incoordination was evaluated by a rotarod performance test. The ranking of the motor incoordination during the final concentration of diazepam was as follows: F344 greater than LEW. After substitution of normal food for the diazepam-admixed food, various signs of diazepam withdrawal occurred 16-120 h later. These signs included vocalization, irritability, muscle rigidity, ear-twitching, Straub's tail, piloerection, fascicular twitch, tremor, convulsion, and death. The incidences of vocalization, ear-twitching, piloerection, and tremor in F344 were significantly higher than those in LEW rats. Furthermore, two of six F344 rats showed spontaneous convulsions and one rat died of convulsions. Overall withdrawal scores were significantly greater in F344 (16.0) than in LEW (6.3) rats. These results suggest that diazepam withdrawal severity is strongly influenced by genetic factors, and F344 rats are highly susceptible to dependence upon benzodiazepines.

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.

Modification of the effects of naloxone in morphine-dependent mice

Mice were rendered dependent on morphine by mixing morphine with their food (2 mg/g) for three days. Increasing doses of naloxone precipitated dose-dependent withdrawal reactions such as weight loss and jumping. These withdrawal reactions were antagonized by morphine pretreatment. Effects of morphine, such as increased locomotor activity, inhibition of intestinal transport, and analgesia were antagonized by naloxone in both non-dependent and dependent subjects. The antagonist actions of naloxone were increased in dependent subjects; lower doses of naloxone were sufficient to antagonize effects of morphine. The present results confirm earlier studies indicating that precipitation of withdrawal can be antagonized by morphine pretreatment suggesting that withdrawal reactions are due to actions of naloxone at the same receptor at which opioid agonists act. The increased antagonist potency of naloxone in dependent subjects extends earlier results obtained with analgesic effects to several other agonist effects of morphine and is consistent with the interpretation that exposure to an opioid agonist induces a change in the conformation of opioid receptors.

Intravenous self-administration of diazepam in rats

Diazepam 0.5-2.0 mg/kg per injection was self-administered intravenously by rats on a continuous reinforcement schedule in a dose-dependent manner over a 30 day period. The rates of diazepam self-administration were relatively stable after responding was established, in comparison with rats self-administering morphine 0.5 mg/kg per injection whose rates continued to increase. At a fixed ratio 4 or 8 schedule, higher maximum rates of responding were seen with diazepam than with morphine. During withdrawal, reductions in body weight tended to occur in a manner dependent on the preceding rates of diazepam self-administration and were possibly caused by physical dependence. These findings suggest that diazepam acts as an intravenous reinforcer in rats and that the procedure we describe is of use to predict the dependence liability of drugs considered to have only a weak potential for abuse.

Self-injection of diazepam in naive rats: effects of dose, schedule and blockade of different receptors

The present series of experiments had two main objectives: The first was to determine the conditions under which self-injection of the benzodiazepine diazepam would be optimal; the second was to identify neurochemical substrates which underlie the maintenance of diazepam self-administration. Data from the first experiment indicated that rats maintained on an FI-1 (Fixed Interval of 1 min) schedule of food delivery self-injected significantly more diazepam than rats not maintained on this schedule. Results from the second experiment demonstrated that the benzodiazepine antagonist Ro 15-1788, and the GABA antagonist bicuculline, significantly reduced diazepam self-administration, but the opiate antagonist naloxone was without effect. Data from the third experiment showed that the dopamine antagonist haloperidol also significantly reduced the rate of diazepam self-injection. Thus, these findings indicate that the acquisition of diazepam self-injection occurs under an FI-1 schedule of food delivery, which has been shown to be middly stressful, while its maintenance depends upon the functional integrity of benzodiazepine and GABA receptors and upon the activity of dopaminergic pathways.

Development of physical dependence on and tolerance to morphine in rats treated with morphine-admixed food

1. The development process of physical dependence on and tolerance to morphine has been explored in rats treated with morphine-admixed food (0.5 mg/g of food) during 1 to 7 days. 2. In the morphine-treated animals, body weight loss was observed after the abrupt morphine withdrawal. 3. Intensity and time course of the weight loss were correlated to the morphine treatment. 4. On the other hand, the morphine-treated rats showed abnormal behaviors, such as diarrhea, ptosis, teeth chattering, salivation, body shakes, vocalization, nose bleed, irritability, aggression, lacrimation and writhing upon naloxone injection. 5. Loss of body weight, measured 3 hours after naloxone injection, was also correlated to the duration of morphine treatment. 6. Tolerance to the analgesic effect of morphine developed within one day in rats treated with morphine-admixed food. 7. The drug-admixed food ingestion method has the advantage of rapidly inducing a high degree of physical dependence and tolerance without causing morbidity or lethality in animals. It also eliminates the need for excessive handling of animals.