Physical dependence on morphine, phenobarbital and diazepam in rats by drug-admixed food ingestion

Acupuncture Inhibits Morphine Induced-Immune Suppress via Antioxidant System

Objectives

A powerful analgesic called Morphine causes addiction behaviors and immune suppression as a potential oxidative stressor. Acupuncture showed to inhibit oxidative stress-induced hepatic damage, regulate reactive oxygen species, and attenuate morphine addiction behaviors. Therefore, we investigated the potential effects of acupuncture on morphine-induced immune suppression.

Materials and Methods

Rats received morphine intravenously through implanted catheters for 3, 7, or 21 days to determine the optimal condition for morphine-induced immune suppression. Second, we examined whether intravenous (iv.) or intraperitoneal (ip.) administration produced different results. Third, the effects of acupuncture in rats who received morphine for 21 days were investigated. Spleen and submandibular lymph node (S-LN) weights and natural killer (NK) cell activity were measured, and the white pulp diameter, total and cortical spleen thicknesses, and the number of lymphoid follicles in S-LNs were examined. The number of immunoreactive cells was also measured.

Results

Decreased organ weights and increased atrophic changes were observed as morphine-induced immune suppression. However, dose-dependent increased immune suppression was not observed between 5.0 mg/kg and 10.0 mg/kg of morphine. And, 3-day withdrawal did not affect. Similar histopathological findings were observed in 5.0 and 10.0 ip. rats when compared to equal dosages of iv., respectively. The morphine induced-immune suppression evidenced by spleen and left S-LN weights, splenic NK cell activities, histopathological findings, and the immunoreactive cell number were normalized by acupuncture.

Conclusion

These results indicate that acupuncture inhibits morphine-induced immune suppression, maybe via antioxidative action.

Mitragynine Attenuates Morphine Withdrawal Effects in Rats-A Comparison With Methadone and Buprenorphine

BACKGROUND

Opiate addiction is a major health problem in many countries. A crucial component of the medical treatment is the management of highly aversive opiate withdrawal signs, which may otherwise lead to resumption of drug taking. In a medication-assisted treatment (MAT), methadone and buprenorphine have been implemented as substitution drugs. Despite MAT effectiveness, there are still limitations and side effects of using methadone and buprenorphine. Thus, other alternative therapies with less side effects, overdosing, and co-morbidities are desired. One of the potential pharmacotherapies may involve kratom's major indole alkaloid, mitragynine, since kratom (Mitragyna speciosa Korth.) preparations have been reported to alleviate opiate withdrawal signs in self-treatment in Malaysian opiate addicts.

METHODS

Based on the morphine withdrawal model, rats were morphine treated with increasing doses from 10 to 50 mg/kg twice daily over a period of 6 days. The treatment was discontinued on day 7 in order to induce a spontaneous morphine abstinence. The withdrawal signs were measured daily after 24 h of the last morphine administration over a period of 28 abstinence days. In rats that developed withdrawal signs, a drug replacement treatment was given using mitragynine, methadone, or buprenorphine and the global withdrawal score was evaluated.

RESULTS

The morphine withdrawal model induced profound withdrawal signs for 16 days. Mitragynine (5-30 mg/kg; i.p.) was able to attenuate acute withdrawal signs in morphine dependent rats. On the other hand, smaller doses of methadone (0.5-2 mg/kg; i.p.) and buprenorphine (0.4-1.6 mg/kg; i.p.) were necessary to mitigate these effects.

CONCLUSIONS

These data suggest that mitragynine may be a potential drug candidate for opiate withdrawal treatment.

Morphine-Induced Dendritic Spine Remodeling in Rat Nucleus Accumbens Is Corticosterone Dependent

BACKGROUND

Chronic morphine treatments produce important morphological changes in multiple brain areas including the nucleus accumbens.

METHODS

In this study, we have investigated the effect of chronic morphine treatment at a relatively low dose on the morphology of medium spiny neurons in the core and shell of the nucleus accumbens in rats 1 day after the last injection of a chronic morphine treatment (5 mg/kg once per day for 14 days). Medium spiny neurons were labeled with 1,1' dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate crystal and analyzed by confocal laser-scanning microscope.

RESULTS

Our results show an increase of thin spines and a decrease of stubby spines specifically in the shell of morphine-treated rats compared with control. Since morphine-treated rats also presented an elevation of corticosterone level in plasma, we explored whether spine alterations induced by morphine treatment in the nucleus accumbens could be affected by the depletion of the hormone. Thus, bilaterally adrenalectomized rats were treated with morphine in the same conditions. No more alteration in stubby spines in the shell was detected in morphine-treated rats with a depletion of corticosterone, while a significant increase was observed in mushroom spines in the shell and stubby spines in the core. Regarding the thin spines, the increase observed with morphine compared with saline was lower in adrenalectomized rats than in nonadrenalectomized animals.

CONCLUSION

These results indicate that dendritic spine remodeling in nucleus accumbens following chronic morphine treatment at relatively low doses is dependent on corticosterone levels.

Role of central histaminergic system in lorazepam withdrawal syndrome in rats

Effects of histaminergic agonists and antagonists were investigated on withdrawal signs in lorazepam-dependent rats. Physical dependence was developed by giving lorazepam admixed with the food in the following dose schedule (in mg/kg given daily x days): 10 x 4, 20 x 4, 40 x 4, 80 x 4, and 120 x 7. The parameters observed during the periods of administration of lorazepam and after its withdrawal were spontaneous locomotor activity (SLA), reaction time to pain, foot shock aggression (FSA), and audiogenic seizures. During the withdrawal period, the rats were divided into groups of 10 each. Control-withdrawal group did not receive any drug. The drugs (in mg/kg administered intramuscularly)--L-histidine (50), histamine-N-methyl (2), promethazine (10), pheniramine (10), astemizole (10), and thioperamide (1)--were given separately in other groups daily during the withdrawal period. The withdrawal signs in control group were hyperkinesia, hyperaggression, and audiogenic seizures. L-Histidine, precursor of histamine, and thioperamide, antagonist of H3 receptor, potentiated hyperkinesia, hyperaggression, and audiogenic seizures. Histamine-N-methyl, agonist of H3 receptor, and H1 receptor antagonists, promethazine and pheniramine, blocked all the withdrawal signs. Astemizole, a peripheral antagonist of H1 receptor, could not affect any withdrawal sign. It may be concluded that histamine H1 receptors are facilitatory and H3 receptors are inhibitory for benzodiazepine (BZD) withdrawal syndrome.

Effect of dopamine agonists and antagonists on the lorazepam withdrawal syndrome in rats

1. The effects of dopaminergic agonists and antagonists were investigated on withdrawal signs in lorazepam-dependent rats. Physical dependence was developed by giving lorazepam admixed with food in the following dose schedules: 10 x 4, 20 x 4, 40 x 4, 80 x 4 and 120 x 7 mg/kg, daily for x days. 2. The parameters observed during the periods of administration of lorazepam and after its withdrawal were spontaneous locomotor activity (SLA), reaction time to pain, foot shock aggression (FSA) and audiogenic seizures. 3. During the withdrawal period, rats were divided into groups of 10 rats each. One group did not receive any drug and served as the control withdrawal groups. Three other groups received, separately, one of the following dopamimetic drugs: (i) 200 mg/kg per day, i.m., L-dihydroxyphenylalanine (DOPA; +50 mg/kg per day, i.m., carbidopa); (ii) 2 mg/kg per day, i.m., amphetamine; or (iii) 1 mg/kg per day, i.m., apomorphine. The remaining groups received one of the following dopamine antagonists: (i) 0.1 mg/kg per day, i.m., SCH 23390; (ii) 0.5 mg/kg per day, i.m., haloperidol; (iii) 0.5 mg/kg per day, i.m., centbutindol; and (iv) either 1 or 20 mg/kg per day, i.m., clozapine. 4. The withdrawal signs observed in the control group were hyperkinesia, hyperaggression and audiogenic seizures. 5. L-Dihydroxyphenylalanine (+ carbidopa), amphetamine and apomorphine potentiated hyperaggression and audiogenic seizures. The dopamine D2 receptor antagonists haloperidol, centbutindol and clozapine (at 20 mg/kg, i.m.) blocked all withdrawal signs. The D1 receptor antagonist SCH 23390 inhibited hyperkinesia and hyperaggression. The D4 receptor antagonist clozapine (at 1 mg/kg, i.m.) had no effect on any of the withdrawal signs. 6. It may be concluded that dopamine D2 receptors exert a dominant facilitatory influence, with partial contribution of D1 receptors, on the benzodiazepine withdrawal syndrome.

Subsensitivity to mitochondrial diazepam binding inhibitor receptor agonist FGIN-1-27-induced antiseizure effect in diazepam-withdrawn mice

We investigated the role of the mitochondrial diazepam binding inhibitor receptor (MDR) in diazepam-withdrawal seizure. In chronically vehicle-treated mice, the potent and selective MDR agonist FGIN-1-27 (N,N-di-n-hexyl 2-(4-fluorophenyl)indole-3-acetamide: 30 microg/mouse, i.c.v.) markedly increased the threshold for pentylenetetrazole (PTZ)-induced seizure. The antiseizure effect of FGIN-1-27 was blocked by pretreatment with the selective MDR antagonist PK11195 (1-(2-chlorophenyl)-N-methyl-N-(1-methylpropyl)-3-isoquinolinecarboxa mide). In chronically diazepam-treated mice, the seizure threshold of PTZ was decreased during diazepam withdrawal, indicating withdrawal hyperexcitability. Interestingly, FGIN-1-27 (30 microg/mouse, i.c.v.) failed to increase the seizure threshold of PTZ in diazepam-withdrawn mice, in contrast to its effect in chronically vehicle-treated mice. These findings suggest that the sensitivity of MDR-mediated pathways in the brain may be decreased during diazepam withdrawal.

Precipitated abstinence in the diazepam-dependent rat

Physical dependence was produced in the rat by exposure to continuous release of diazepam from silastic capsule implants (recrystallized diazepam) or by dosing through a gastric fistula. The precipitated abstinence syndrome induced by the IV infusion of flumazenil was characterized by clonic and tonic-clonic seizures, retropulsion, digging, rearing, head, limb and body tremors, twitches and jerks of the body, and ear twitches. This abstinence syndrome differed both qualitatively and quantitatively from the milder syndrome induced in previous experiments by the intragastric administration of flumazenil in the diazepam-dependent gastric fistula rat. Capsule-implanted rats had free plasma and extraneuronal brain levels of diazepam, oxazepam, and nordiazepam in the 10(-3) and 10(-4) mg/ml range, and their brain: plasma ratios were not significantly different from 1. The diazepam capsules had a sustained release of over 28 days. These studies show that the capsule implantation technique is an efficacious way of maintaining plasma levels of diazepam and its metabolites, and producing a high level of physical dependence in the rat.

Effects of flunarizine and diltiazem on physical dependence on barbital in rats

The effects of flunarizine and diltiazem both on development of physical dependence on barbital and on barbital withdrawal signs in rats were examined using the drug-admixed food (DAF) method. Rats were chronically treated with barbital or barbital in combination with flunarizine (fixed at 1.5 mg/g of food) or diltiazem (fixed at 0.75 mg/g of food)-admixed food on the schedule of gradually increasing doses of barbital. Motor incoordination during the treatment was potentiated by coadministration of flunarizine, but not by coadministration of diltiazem. After the termination of drug treatment, the body weight loss and withdrawal scores were significantly suppressed in the group coadministered flunarizine, but not in that coadministered diltiazem. There were no significant differences in plasma barbital levels after the withdrawal between groups. In the substitution test, flunarizine (20 and 40 mg/kg, IP) significantly suppressed the body weight loss and withdrawal scores after the withdrawal, but diltiazem (20 mg/kg, IP) did not. These results indicated that flunarizine suppressed both the development of physical dependence on barbital and barbital withdrawal signs, mainly according to the suppression of convulsions, but not diltiazem, which is known to poorly penetrate into the brain. Therefore, the present findings suggest that central calcium channels may be involved in both the development of physical dependence on barbital and the appearance of barbital withdrawal signs.

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.

Sex differences in physical dependence on pentobarbital in four inbred strains of rats

1. In Lewis (LEW), Fischer 344 (F344), Spontaneously hypertensive (SHR) and Wistar Kyoto (WKY) rats, pentobarbital (PB)-induced sleep time was much longer in female than in male rats. 2. At the time of awakening, brain levels of PB were significantly higher in the female F344 than in the male rats, but there was no sex differences in other strains. 3. Each strain of rats was treated with PB-admixed food for 47 days. There were significant sex differences in mean drug intake of the SHR and LEW strains, but not the WKY and F344 strains during the final concentration. 4. Only female rats exhibited moderate to severe motor impairment by PB. 5. After PB treatment ended, various signs of PB withdrawal occurred in female, but not male, rats. These marked sex differences were observed in all four inbred strains. 6. The sex differences in physical dependence on PB may be due mainly to differences in rates of drug metabolism for the LEW, SHR and WKY rats, and to differences in CNS sensitivity for the F344 rats.

Effects of nor-binaltorphimine on the development of analgesic tolerance to and physical dependence on morphine

The effects of a highly selective kappa antagonist, nor-binaltorphimine (nor-BNI), on the development of tolerance to morphine analgesia and physical dependence on morphine were examined. Pretreatment with nor-BNI (5 mg/kg s.c.) 2 h prior to injection of morphine or a selective kappa agonist, U-50,488H, significantly antagonized the analgesic effect of U-50,488H, but not morphine analgesia in mice. The development of tolerance to morphine analgesia was significantly potentiated by pretreatment of mice with nor-BNI 2 h prior to morphine treatment during chronic morphine treatment for 5 days. Additionally, the pretreatment with nor-BNI during chronic treatment with the high dose of morphine for 5 days significantly potentiated the naloxone-induced body weight loss in morphine-dependent mice and rats. These findings suggest that inactivation of the kappa opioid system may potentiate the development of tolerance to morphine analgesia in mice and may aggravate the naloxone-precipitated body weight loss in morphine-dependent mice and rats.

Susceptibility to, tolerance to, and physical dependence on ethanol and barbital in two inbred strains of rats

1. Ethanol-induced sleep time was significantly longer in F344 than LEW rats. However, there is no difference in barbital-induced sleep time between F344 and LEW. 2. Development of tolerance to ethanol-induced motor impairment was slightly faster in F344 than in LEW rats. While, LEW rats more easily developed tolerance to the impairment by barbital in comparison with F344 rats. 3. F344 and LEW rats were chronically treated with liquid diet containing ethanol or with barbital-admixed food. After the termination of ethanol and barbital treatments, various withdrawal signs occurred in F344 rats, including tremor and convulsions, whereas LEW rats showed no convulsions. Withdrawal scores of ethanol and barbital were significantly higher in F344 than in LEW rats. 4. These results suggest that strain differences in physical dependence on ethanol and barbital may be mainly influenced by the susceptibility to ethanol and the development of tolerance to barbital, respectively.

Preference for cocaine by the weight pulling method in rats

The purpose of the present study is to show the efficiency of the weight pulling method in evaluating quantitatively the positive reinforcing effect of cocaine. Rats were trained to pull the weight in order to eat the drug-admixed food (DAF). The experiments began with the preexposure of the drug through the repetition of CFF schedule. The schedule consisted of one choice trial (C) between the intake of normal food and DAF followed by two consecutive forced trials (F), in which the rats were forced to take the DAF only. The study consisted of Experiment I, where cocaine concentration in DAF was varied while the period of cocaine preexposure was kept constant and Experiment II, where the period of preexposure was varied while the cocaine concentration was kept constant. Results show that the reinforcing effect of cocaine was dependent on cocaine intake. On the other hand, the reinforcing effect of cocaine was independent of cocaine preexposure period. The effect of cocaine on the drug-seeking behavior was evident on the first day of cocaine exposure. It is concluded that the weight pulling method is sufficient to evaluate quantitatively the reinforcing effects of cocaine in rats, and this method may be useful for the prediction of dependence potential in man.

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.

Enhancement of morphine withdrawal signs in the rat after chronic treatment with naloxone

Chronic treatment of rats with naloxone for 5 days increased the analgesic threshold (hot plate latency). Further, when rats were treated with morphine-admixed food for 3 days after the chronic naloxone treatment the withdrawal signs precipitated by naloxone were significantly greater in the naloxone-pretreated rats than in saline-pretreated rats. These results suggest that paradoxical analgesia and enhancement of the morphine withdrawal signs induced by chronic naloxone treatment may be associated mainly with up-regulation of mu- and delta-opioid binding sites in the central nervous system.

Preferences for opioids by the weight pulling method in rats

The preference for morphine and codeine was studied by means of the antagonistic conflict behavior between the positive drive of drug intake and the negative drive of weight pulling in rats. An apparatus was developed in which rats were compelled to pull the weight for the intake of drug-admixed food. The experiments began with the preadministration of the drug through the repetition of CFF schedule. The schedule consisted of one choice trial between the intake of normal food and drug-admixed food followed by two consecutive forced trials, in which the rats were forced to take the drug-admixed food only. In the test trial, the findings were that the rats which had already shown a drug seeking behavior toward morphine or codeine pulled weight to take each drug and that the reinforcing effects of these drugs on the drug seeking behavior depended on the treatment period of these drugs. The reinforcing effect of codeine was weaker than one of morphine. It is suggested that the reinforcing effects of these opioids can be evaluated quantitatively by the weight pulling method in rats.

A liquid diet model of chlordiazepoxide dependence in mice

Mice fed chronically (3 to 4 weeks) a liquid diet containing chlordiazepoxide (CDP) became physically dependent on the drug as demonstrated by the occurrence of withdrawal signs precipitated by injection of the benzodiazepine antagonist Ro15-1788 (5 to 25 mg/kg) or by omitting CDP from the diet (spontaneous withdrawal). Very low blood concentrations of CDP, but medium to high levels of the active metabolites N-desmethyl CDP and demoxepam were found during the period of CDP administration. The Ro15-1788-induced withdrawal signs appeared within 1 min after the injection of the antagonist and lasted for at least 10 min. Quantifiable withdrawal signs included tail lift, tremor, impaired movement and handling-induced seizures. Mice undergoing spontaneous withdrawal had milder withdrawal signs such as weight loss, in appetite and suppression of runway and head-dipping activities on day 1 or day 2 of withdrawal. These signs were also present in Ro15-1788-induced withdrawal. A long-lasting rebound increase in runway and head-dipping activities occurred several days after CDP withdrawal.

Effects of a selective kappa-opioid agonist, U-50,488H, on morphine dependence in rats

Rats were made dependent on morphine by mixing the drug with their only source of food. Naltrexone (0.5 mg/kg) injection precipitated a syndrome of withdrawal signs including weight loss. Pretreatment with the selective kappa agonist, U-50,488H (1.0, 30.0 or 10.0 mg/kg), generally had no effects on the signs of morphine withdrawal. In other subjects, U-50,488H was repeatedly administered (1.0, 3.0 or 10.0 mg/kg per 12 h) during the development of morphine dependence. In these subjects, the course of naltrexone-precipitated withdrawal was unchanged. These results suggest that agonist activity at kappa receptors is not sufficient to alter morphine dependence or withdrawal.

Dependence on phenobarbital but not pentobarbital using drug-adulterated food

A drug-adulterated food (DAF) method was used in an attempt to establish physical dependence on either pentobarbital or phenobarbital in male CF1 mice. The mice were acclimated to the control diet for four days and then assigned to treatment groups. Group I continued to receive the control diet; Group II received pentobarbital, 5 mg/g food, increased by 5 mg, daily, for 14 days; Group III received pentobarbital, 5 mg/g food, increased by 5 mg, daily, for 7 days; Group IV received pentobarbital, 10 mg/g food, increased by 10 mg, daily, for 7 days; Group V received phenobarbital at 2.5 mg/g food for 5 days and then 3.0 mg/g food for 2 days. During drug administration, all mice were monitored daily for signs of intoxication, change in body weight, and food consumption. At the end of the drug exposure period all mice received control diet and were observed for signs of withdrawal. Mice in Group II and Group IV demonstrated significant declines in body weight and food consumption and an apparent increase in the degree of intoxication but not signs of withdrawal. Group III mice demonstrated little sign of impairment during exposure to pentobarbital and no withdrawal syndrome was observed. Mice presented phenobarbital were found to exhibit a significant degree of intoxication and a withdrawal syndrome was demonstrated. The data suggest, with respect to the drug administration schedules used, that the DAF method was not suitable for the establishment of physical dependence on pentobarbital in mice.

Induction of physical dependence on pentobarbital by new infusion method in the rat

1. A new intermittent intravenous infusion method was developed for the induction of tolerance to and physical dependence on pentobarbital in rats. 2. Female and male rats were injected with pentobarbital (20 mg/kg/injection) through an implanted intravenous cannula. 3. The rats were allowed to receive an injection after the completion of a fixed amount of behavioral activity counted from the preceding injection, and therefore, the sedative and hypnotic effects of pentobarbital were used as an index in the determination of the injection intervals. 4. During pentobarbital treatment, the number of pentobarbital injections per day rapidly increased and stabilized (approximately 40: male, approximately 30: female) on the third to fifth day. 5. Upon withdrawal, the female and male rats who were maintained on pentobarbital administration of more than 30 and 40 injections/day for approximately 10 days manifested withdrawal signs which included spontaneous convulsion. 6. These results suggest that a new infusion method exists to produce a high degree of physical dependence in rats on a short-acting barbiturates, pentobarbital.

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.

Changes in locomotor-activity patterns as a measure of spontaneous morphine withdrawal: no effect of clonidine

The anti-withdrawal action of clonidine was studied in a model of spontaneous morphine withdrawal in rats. After withdrawal the behaviour of the animals was registered continuously for several days. In the initial phase of induction of dependence the locomotor activity was enhanced during daytime. Partial tolerance to this increase developed in the course of 3 weeks. In morphine withdrawn animals the activity decreased strongly at night, and this effect was maximal on the second night after removal of morphine. After four nights the nightly activity was restored. Treatment with clonidine (100 micrograms/kg s.c. twice daily) changed neither the observed decrease in nightly locomotor activity nor other withdrawal symptoms such as a decrease in food intake and loss of body weight. In non-dependent animals clonidine induced a biphasic effect in locomotor activity, i.e. a decrease in the first few hours of the night and an increase in the second part of the night. The latter can be interpreted as a rebound phenomenon occurring after only three injections. It was concluded that clonidine was not effective as an anti-withdrawal compound in a model for spontaneous morphine abstinence. The low incidence of symptoms relating to a hyperactive sympathetic system during spontaneous withdrawal may be an explanation for the absence of an effect of clonidine.

The concentration of morphine in serum of rats made dependent using a drug-admixed food method

The present study reports on the induction of physical dependence in rats using morphine-admixed food and addresses the question of the resulting concentration of morphine in serum. The stability of morphine in food is good, since no decrease in concentration could be observed. The concentration of morphine in serum during the experiment was measured using a radioimmunoassay technique. A correlation was found between the food intake during a 7-hour period and the concentration of morphine in the serum at the end of that period, both for a 1 g/kg and a 2 g/kg batch of morphine-admixed food. The concentration of morphine in serum was also found to be dose-related during a period of 6-23 days when the rats were fed for a prolonged period. After long-term administration of 1 g/kg morphine in food a steady-state level of about 0.5 mg/l serum was obtained. Similarly with 2 g/kg morphine in food a steady-state level of 0.8-1.1 mg/l serum was reached. After withdrawal of morphine the serum concentration of morphine dropped to 0.1 mg/l within 24 hours and to below the detection limit within 48 hours. During the withdrawal period sharp drops were noted in body weight (20%) and food intake (50%) after one day.

Sex differences in physical dependence on methaqualone in the rat

The establishment of, and sex differences in, physical dependence on methaqualone (MQ) in rats were studied by the drug-admixed food (DAF) method. Female and male rats were treated with MQ-admixed food on the same schedule of gradually increasing doses (0.5 and 1 to 6 mg of methaqualone/g of food). Only female rats showed hypothermia from MQ at 1 and 2 mg/g and motor incoordination from MQ at 4 and 6 mg/g of food. Moreover, after MQ withdrawal, severe withdrawal signs, including convulsions and death, were observed in female rats, but not in male rats. We also instituted a different schedule of graded increases in dose (1 and 2 to 10 and 12 mg/g of food) to develop physical dependence on MQ in male rats. Under this schedule male rats exhibited a hypothermia and severe motor incoordination from MQ 6 and 8 mg/g of food condition. After MQ withdrawal, various severe signs of MQ withdrawal occurred, including tremor, convulsions and death. These results demonstrate that severe physical dependence on MQ in both sexes can be established using the DAF method, and that there are marked sex differences in the physical dependence on MQ.

Effect of opioid agonist-antagonist interaction on morphine dependence in rats

Morphine dependence was induced by treatment with morphine-admixed food (0.25mg/g of food) for 7 days. Withdrawal was precipitated by injecting naloxone (0.5mg/kg, s.c.). Rats treated with morphine exhibited body weight loss upon the naloxone injection. When morphine-dependent rats were injected subcutaneously with morphine, codeine, meperidine and pentazocine 30 min before the naloxone injection, these drugs significantly suppressed the naloxone-precipitated loss of body weight in a dose-dependent manner. However, body weight loss induced through coadministration of naloxone and Mr-2266 BS were not suppressed by morphine pretreatment. These results suggest that opioids protect against naloxone-precipitated loss of body weight, and that mu and kappa opiate receptors play an important role in the protection against naloxone-precipitated withdrawal.

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.

Circadian rhythm of the liver of male rats dosed with phenobarbital--I. Organ weight, cellular structures, glycogen contents and mitotic activity

The circadian rhythm of the liver, namely organ weight, cellular structures (by light-microscopy), glycogen content (by periodic acid-Schiff (PAS) reaction) and mitotic activity, was studied in 166 male Sprague-Dawley rats orally treated daily at 0800-0900 with 70 (study 1) or 50 (study 2) mg/kg phenobarbital (PB) for 7 days. Thereafter, eight (study 1) or five (study 2) rats each were studied at 4-hr intervals at 1000, 1400, 1800, 2200, 0200, 0600 and 1000 through till the following day. The lighting schedule in the colony was 12:12, light:dark (light from 0600 to 1800). The liver weight was raised in PB-treated rats at all times of the day compared to controls and showed a distinct circadian rhythm with a peak at 1000 and a minimum at 2200 in PB-treated rats and the controls. The circadian rhythm of cellular structures was closely related to the hepatic glycogen content which was in good agreement with the controls, but at 1400 and 1800 the glycogen particles were more distinctly diminished in the enlarged centrilobular hepatocytes of PB-treated rats. The mitotic activity of hepatocytes was markedly increased in rats treated with PB but showed the same circadian rhythm as controls with a peak at 1000.

Substitution of chlordiazepoxide for ethanol in alcohol-dependent mice

Alcohol dependence was induced in C57BL/6J mice by administration of a liquid diet containing ethanol. These mice showed alcohol withdrawal signs when the alcohol diet was withdrawn. However, when the alcohol diet was substituted with three liquid diets containing different amounts of chlordiazepoxide (CDP; 0.4, 1 and 2 mg/ml), the alcohol withdrawal signs were fully suppressed by CDP. The CDP diet administration was continued for 14-24 days. At termination of the diet treatment, the mice showed CDP withdrawal signs. Similar signs, but much more short-lived, can be precipitated by injection of the benzodiazepine receptor antagonist, RO-15-1788. The results are consistent with the hypothesis that alcohol-dependent mice are cross-dependent on CDP. This report constitutes the first experimental demonstration of cross-dependence between ethanol and CDP. The reverse phenomenon, namely, CDP-dependent mice being cross-dependent on ethanol, remains to be investigated.

Sex differences in the induction of physical dependence on pentobarbital in the rat

Sex differences in physical dependence on sodium pentobarbital in the rat were studied by the drug-admixed food (DAF) method. With male rats, the concentration of pentobarbital in the food was gradually increased from 2 to 30 mg/g over a period of 50 days. The final level of drug intake was approximately 1.7 g/kg/day. At pentobarbital concentrations of 20 and 22 mg/g of food, sedation and mild muscle relaxation were observed. At the highest drug concentration, 30 mg/g of food, marked muscle relaxation was noted. With female rats, the concentration of pentobarbital in the food was gradually increased from 1 to 16 mg/g over a period of 47 days. The final level of intake was approximately 1.0 mg/kg/day. At drug concentrations of 12 and 14 mg/g, sedation and mild muscle relaxation appeared. At 16 mg/g, female rats showed marked muscle relaxation similar to that of the male rats. To produce severe loss of muscle tone, the male rats required twice as much pentobarbital as the female rats. After substitution of normal food for the pentobarbital-admixed food, various signs of pentobarbital withdrawal occurred in both sexes. These signs included vocalization, irritability, muscle rigidity, tremors and convulsions. Onset of withdrawal was more rapid in the females, and the maximum weight loss was greater, 8.0% compared to 3.8% in the males. Physical dependence on pentobarbital was easily developed in both sexes by the DAF method. There was a marked sex difference in withdrawal which we attribute to sex differences in drug metabolizing enzyme activity.

Effect of pentobarbital dependence on adenylate cyclase activity and calmodulin levels in rat cerebral cortex

The effect of calcium (Ca2+) on the adenylate cyclase activity and calmodulin level of cerebral cortex was determined in pentobarbital dependent rats and age matched controls. Female Sprague-Dawley rats were made dependent and maintained on pentobarbital by eating a mixture of pentobarbital and rat chow (350 mg pentobarbital/30 g chow). Ca2+ activated then inhibited the adenylate cyclase activity associated with a 20,000 X g particulate fraction from pentobarbital dependent and age matched control rats. The values for one-half maximal stimulation and inhibition by Ca2+ did not differ significantly in either cortical preparation. However, the ability of Ca2+ to activate adenylate cyclase from pentobarbital dependent animals was significantly decreased (p less than 0.05) when compared to control animals. Pentobarbital (10(-4) - 10(-3) added to particulate fractions from naive control rats did not alter the ability of Ca2+ to activate adenylate cyclase. The calmodulin levels in the particulate fraction from pentobarbital dependent animals (30.2 +/- 6.7 ng calmodulin/mg protein) did not differ significantly when compared to control (33.0 +/- 4.7 ng/mg). By contrast, the calmodulin levels (37.9 +/- 5.9 ng/mg) in the 20,000 X g supernatant from cortex of pentobarbital dependent animals was significantly greater than the level in the supernatant from control animals (28.6 +/- 2.6 ng/mg). The ability of forskolin, dopamine, GTP or forskolin plus GTP (all at a concentration of 100 microM) to activate adenylate cyclase was significantly decreased in particulate preparations from pentobarbital dependent animals. In summary, our data show that alterations in calmodulin levels and a decreased responsivity of adenylate cyclase occur in animals physically dependent on pentobarbital.

Time course for development of benzodiazepine tolerance and physical dependence

Chronic benzodiazepine treatment elicits adaptive responses in the CNS, seen behaviorally as functional tolerance and physical dependence. Experiments are described in which a radioreceptor assay is used to follow benzodiazepine activity in CSF samples during daily flurazepam treatment of cats. Tolerance is evident even after the second dose, despite increasing CSF drug activity, showing a large and rapidly developing functional tolerance. Other studies are discussed which also show tolerance within 24 hours of initiating benzodiazepine treatment. In contrast, a spontaneous withdrawal syndrome is usually seen only after prolonged treatment with high doses. However, physical dependence can also be studied by precipitating abstinence with a benzodiazepine antagonist, such as Ro15-1788. Cats were treated daily with flurazepam, then Ro15-1788 was given and abstinence signs were recorded. Abstinence could be precipitated 24 hours after beginning treatment, and dependence was nearly maximal after 7 days. Dependence developed during treatment with as little as 0.5 mg/kg flurazepam, which is near threshold for any behavioral response. Chronic diazepam caused the same dependence as flurazepam. Thus, the development of tolerance and physical dependence both show a remarkably rapid adaptation of the CNS in response to benzodiazepines.

Effects of combined alcohol and benzodiazepine: a review

Both human and animal studies relating to the combined effects of alcohol and benzodiazepine (BZD) are reviewed. Although the combination of alcohol and BZD is sometimes associated with drug-induced deaths, drug overdoses and traffic accidents or fatalities, epidemiological information is lacking on the true extent of the combined abuse and on the patterns and prevalence of use of these two drugs. Since BZD are widely used for the short- and long-term treatment of alcoholics, these patients are deemed more at risk of developing BZD or alcohol/BZD dependence than the general population. There is a dire need for large-scale controlled studies concerning the efficacy of BZD in the long-term treatment of alcoholics. Compared to men, women are at a higher risk as far as the potential for BZD addiction is concerned, since they tend to use BZD more often. Epidemiologic studies on the patterns of use of BZD, alcohol or alcohol/BZD in pregnant women are called for. Animal models are also needed to ascertain whether prenatal exposure to both alcohol and BZD can impart long-lasting behavioral changes in the progeny. It is possible that BZD can exacerbate the damaging prenatal effects of alcohol.

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.

Diazepam and pentobarbital dependence in the rat

Diazepam (100-133 mg/kg/day), administered chronically through a gastric fistula, and pentobarbital (ca 692 mg/kg/day), administered chronically in food, were studied for their dependence producing properties in Sprague-Dawley female rats. The diazepam abstinence syndrome was apparent 10 to 20 hours after withdrawal, persisted for over 60 hours and consisted of poker tail, explosive awakenings, digging in sawdust, jerks, tremors, wet dog shakes, hostility, decreased food and water consumption and weight loss. The pentobarbital abstinence syndrome came on rapidly peaking within 10 hours and was largely over by 16 hours. The pentobarbital abstinence syndrome differed from diazepam's by the presence of grand mal, clonic and atypical convulsions. Diazepam completely and in a dose related way suppressed the diazepam abstinence syndrome. Similarly pentobarbital suppressed the pentobarbital abstinence syndrome. The signs which could be suppressed in a dose related manner were different for the diazepam and pentobarbital abstinence syndromes. Diazepam only partially suppressed the pentobarbital abstinence syndrome and pentobarbital only partially suppressed the diazepam abstinence syndrome. These data indicate that diazepam and pentobarbital produce different types of dependencies in the rat and are not equivalent in suppressing signs of abstinence.

Effect of p-chlorophenylalanine on diazepam withdrawal signs in rats

The effect of p-chlorophenylalanine (PCPA), a specific serotonin (5-HT) depleter, on diazepam withdrawal signs was studied. Rats were made dependent on diazepam by the chronic administration of this drug in the diet. At the time of diazepam withdrawal, the animals were treated with PCPA (200 mg/kg, IP) or the corresponding vehicle (control). After diazepam withdrawal, the maximal body weight losses of control and PCPA-treated animals were 4.1% and 9.0%, respectively. In naive animals, PCPA did not cause any change in body weight. These results suggest that depletion of central 5-HT by PCPA may potentiate the severity of diazepam withdrawal signs.

Mode of antagonistic action of levallorphan in morphine-dependent rats and assessment of physical dependence liability

The antagonistic mode of levallorphan in rats dependent on morphine or codeine was studied from the viewpoints of the doses of morphine and the lengths of administration and also from the standpoint of timing of the challenge. In morphine-dependent rats on morphine-admixed food (60--100 mg/kg/day) for 1, 3 and 6 weeks, the rate of maximum weight loss on application of levallorphan (2 mg/kg, s.c.) did not correlate with the length of morphine treatment. The rate of weight loss on single application of levallorphan 0, 6, 12 or 24 hours after withdrawal or morphine was lower with the passage of time after the withdrawal. Rats which were given levallorphan 3 times in succession, i.e., at 0, 5 and 10 hours after morphine withdrawal showed such a pattern of weight loss that the first application of levallorphan resulted in 7% loss, while with the second and third applications there was little weight loss. Despite the continued withdrawal, the animals began to gain body weight as early as 14 hour, and body weight was totally recovered before the withdrawal in 24 hour. In conclusion, it is advisable to challenge with levallorphan at 0 hour of withdrawal to obtain qualitative and reproducible results. In addition, the application of levallorphan to morphine-dependent rats at adequate intervals provides for the early recovery of abstinence signs.

Experimental dependence on barbiturates. II. Relationship between drug levels in serum and brain and the development of dependence in rats

Feeding rats on food containing phenobarbital (PhB) (1 AND 2 mg/g) for 13 consecutive days resulted in the inhibition of motor coordination (by rotarod test) for 7 days, followed by a gradual decrease in the inhibition. PhB level in the serum reached a peak on the third day of feeding and then gradually decreased. PhB level in the brain, unlike that in the serum, gradually increased up to the seventh day and then decreased until the thirteenth day of feeding. Thus, alterations of the inhibited rotarod performance were depended on PhB level in the brain rather than on that in the serum. PhB level in the serum increased parallel to the graded increment in dosage from 0.5 and 1.0 mg/g to 4.0 mg/g, while that in the brain did not increase above the level on the seventh day of feeding on 1 and 2 mg/g food but remained relatively stable. PhB-dependent rats ate small amounts of drug-containing food incessantly day and night, and PhB levels in the serum and brain remained high and stable throughout the day. These phenomena suggest that the development of dependence on PhB is more intimately correlated with the length of application of the drug than with the magnitude of its dosage.

Preference for morphine and drug-seeking behavior in morphine dependent rats

We have already reported that morphine pretreated rats prefered morphine-admixed food during choice trials with the two cup method. In the present work, we utilized both the five and two cup methods and observed the preference for morphine in rats forcedly pretreated with the drug and the increasing rate of preference for the drug in rats where the feeding time was limited. In morphine pretreated rats, preference rate for morphine was 61.2 +/- 3.0% with the five cup method and 61.8 +/- 3.3% with the two cup method during the choice trials. In rats that were limitedly treated with morphine, each preference rate for morphine during choice trials rapidly increased in the five cup method, i.e. 5.5 leads to 14.4 leads to 31.7 leads to 43.6 leads to 61.2%, and the preference rate for morphine stabilized at approximately 60 percent. Findings with the two cup method were similar. After the preference for morphine was stabilized at the 60 percent level, morphine was given subcutaneously and it was found that the preference rate was dependent on the dose injected. When the drug-admixed concentration was changed from 1 mg/g food to 0.5 and 2 mg/g food, the preference rate changed in parallel with the concentration. When the number of food cups containing morphine-admixed food was changed from 1/5 to 2/5, 3/5 and 4/5 food cup, the preference rate was not effected. These studies clearly demonstrate drug-seeking behavior in rats. In the process of preference for morphine, morphine treatment enhances spontaneous intake of morphine-admixed food.

Experimental barbiturate dependence. I. Barbiturate dependence development in rats by drug-admixed food (DAF) method

A method for testing a rat's physical-dependence liability to sedaditive-hypnotic agents and for evaluating that dependence was studied by using the method. Rats received phenobarbital- or barbital-admixed food on a graded-increase dosage schedule over 30-40 days. Manifestations of CNS-suppressing action of either drug (e.g., systemic muscle relaxation, motor incoordination, staggering gait, and ptosis) persisted day and night during the drug medication. Twenty-four to 48 h after withdrawal of either drug, abstinence symptoms (e.g., muscle fasciculation, nuchal twitching, vocalization, increased irritability, ataxia, hyperthermia, and clonic-tonic and grand mal-type convulsions) were evidenced in all animals (N = 6), some of which died after convulsions. These withdrawal signs in rats were classified and found to be closely correlated with the magnitude of weight loss during the withdrawal. The calssification provides a basis for quantitatively assessing physical-dependence liability. The data obtained in the present study suggest that rats, like dogs and monkeys, are suitable experimental animals for tests in early stages of dependence liability, and that the administration of drug-admixed food is a useful method of developing dependence on both barbiturate and morphine-type drugs.