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.     

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.     

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.     

Induction of physical dependence on cyclazocine and pentazocine in the rat

Rats were treated for 24, 48 or 72 h with slow release (SR) emulsions of morphine (75, 100 and 150 mg/kg), cyclazocine (75, 100 and 150 mg/kg) or pentazocine (100, 200 and 400 mg/kg). At these times the degree of physical dependence was assessed by examining the abstinence behavior (jumps + wet shakes), changes in body temperature and body weight induced by naloxone (5 mg/kg). The effects of SR treatments on brain levels of noradrenaline (NA), dopamine (DA), homovanillic acid (HVA), 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) were also determined at these times. The results show that all three opiates induce physical dependence in the order of severity of morphine greater than cyclazocine greater than pentazocine. An elevation of 5-HT turnover also appears to be associated with the dependence produced by these opiates. These findings indicate that the increase in brain 5-HT metabolism is not a primary causative factor during opiate dependence, but occurs in response to some other process.     

Studies on the development of physical dependence on barbitone in the rat and rat atrium

The mechanisms underlying the development of barbitone dependence have been studied in the rat and in atrial preparations removed from dependent animals. Long-term oral administration to the rat of barbitone, alone or together with the analeptics bemegride or pentylenetetrazol, has shown that the intensity of the withdrawal syndrome generally parallels the degree of associated CNS depression. In addition, the overall relationship between the spontaneous or evoked (chemical or audiogenic) responses of representative drug-withdrawn rats and the inotropic responses of corresponding withdrawn atria to supramaximal nerve stimulation, noradrenaline or Ca2+ was reasonably good. It is proposed that the rat atrial preparation may provide a suitable model system for the study of barbitone dependence in the rat, especially in relation to Ca2+-dependent mechanisms, and that selective calcium antagonists may prove helpful in the management of barbiturate and similar types of drug dependence. The barbitone withdrawal syndrome has been described in terms of a membrane phase distribution hypothesis of drug action.     

Morphine analgesia, tolerance and physical dependence in the adrenalectomized rat

1. Adrenalectomy reduced the median antinociceptive dose (AD50) of morphine in male Sprague-Dawley rats. The antinociceptive effect was assessed by the tail-flick method of D'Amour & Smith (1941).2. Tolerance to the antinociceptive effect of morphine developed in adrenalectomized and sham-operated rats after chronic exposure to morphine. Development of tolerance did not significantly alter the increased sensitivity of adrenalectomized rats to the antinociceptive effect of morphine.3. Adrenal weights were not increased in rats rendered physically dependent on morphine by subcutaneous implantation of a morphine pellet. Withdrawal, induced by intraperitoneal injection of naloxone hydrochloride, 4 mg/kg, or by removal of the implanted pellet, resulted in a rapid increase in adrenal weight.4. In morphine-dependent animals, the incidence of abstinence signs and body weight loss during precipitated withdrawal did not appear to be significantly influenced by adrenalectomy or by corticosterone-pretreatment.     

Dihydroetorphine: physical dependence and stereotypy after continuous infusion in the rat

In a previous study in this laboratory, exposure of rhesus monkeys to intermittent, high doses of dihydroetorphine for 42 days did not evoke behavioral signs of physical dependence on this opioid either after it was abruptly withdrawn or after challenge with a high dose of naloxone. To investigate further the physical dependence capacity of this opioid, it was given by infusion to rats thereby exposing receptors chronically and continuously to this opioid. Abstinence expressed as body weight loss, irritability, and wet-dog shakes was observed after abrupt withdrawal of the low-dose regimen (5,10, 40 and 40 microg/kg per day for 4 days, respectively). The high-dose regimen (10, 20 and 80 microg/kg per day for 3 days, respectively) produced stereotypy and physical dependence. Although many reported molecular events and dependence studies suggest otherwise, dihydroetorphine's propensity to produce physical dependence, an important determinant of opioid abuse, is real.     

Genetic differences in the development of physical dependence on pentobarbital in four inbred strains of rats

Fischer 344 (F344), Lewis (LEW), spontaneously hypertensive (SHR) and Wistar Kyoto (WKY) rats were chronically fed food containing pentobarbital on an escalating drug dosage schedule over a period of 47 days. During treatment, the growth curve in LEW, SHR and WKY rats was suppressed as compared with the respective controls. Motor incoordination was evaluated by a rotarod performance test. The ranking of the motor incoordination was as follows: WKY much greater than LEW greater than SHR greater than F344. After substitution of normal food for the pentobarbital-admixed food, various signs of pentobarbital withdrawal occurred. The withdrawal signs from pentobarbital in F344, LEW and SHR rats were mild as compared with those in WKY rats. The order of the severity of withdrawal signs in four inbred strains was parallel to that for motor incoordination. These results suggest that the differences between strains in withdrawal can be attributed to differences in the degree of chronic CNS depression produced by pentobarbital.     

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 yohimbine on morphine analgesia and physical dependence in the rat.

The effects of yohimbine on morphine analgesia and on the development of opiate physical dependence were studied to find out more about the involvement of alpha 2-adrenergic mechanisms in opioid actions. Male Sprague-Dawley rats (250-300 g) were used. The acute effect of morphine (5 mg/kg i.p.) in the tail-flick test was reduced significantly by pretreatment with a single dose of yohimbine (2 mg/kg i.p.). Alone yohimbine, produced a slight hyperalgesia. Animals treated with a sustained-release preparation of morphine (300 mg/kg s.c.) showed the same sensitivity to opiate analgesia 72 h later whether they were treated concomitantly with yohimbine or not, but they exhibited fewer withdrawal symptoms upon naloxone injection after yohimbine (2 or 4 mg/kg i.p. 24, 28, 48 and 52 h after the start of systemic morphine treatment). The results obtained confirm previous data on the effects of yohimbine on morphine analgesia and reveal the importance of alpha 2-adrenergic activation in the development of opioid physical dependence.     

Quantitative relationships among measures of morphine tolerance and physical dependence in the rat

The influence of treatment dose on a number of characteristics of opiate tolerance was studied in male Sprague-Dawley rats treated with daily intraperitoneal (IP) injections of morphine sulfate. Zero, 7.5, 15, 25 or 45 mg/kg/day was given for 34 consecutive days and the degree of morphine effect on four different tests was periodically assessed. Dose-related effects on tailflick latency (tail immersion test, 1.5 hr post injection), swimming test (2 hr post injection), and body weight gain revealed the development of tolerance; there was a non-dose-related hyperthermia (1.5 hr post injection) to which rapid sensitization occurred. All changes reached asymptote and the rate and extent of change varied with the test. Plots of log response vs test day for tailflick and swimming indicated an early steep component and a later less steep component of decline. Subsequent testing indicated that the log-dose/response (LDR) curves for tailflick latency and time to maximum hyperthermia shifted to the right by an amount dependent on the treatment dose; there was no change in the curve for hyperthermia duration. In high dose groups no further shift occurred, but the tailflick LDR curves became flattened. The tailflick LDR curve changes were replicated in rats treated for 24 days with 0, 8, 24, 48, 96, or 240 mg/kg/day. Subsequently, a constellation of withdrawal signs precipitated by naloxone HCl (1 mg/kg, IP) was measured. On the basis of the relation between treatment dose and the magnitude of the various measures, there was a parallel between analgesia tolerance and some, but not all, signs of physical dependence.     

Repeated central administration of selegiline attenuated morphine physical dependence in rat

BackgroundLong-term exposure to opiates induces physical dependence; however, the neurobiological mechanisms of this phenomenon are not completely clear. The purpose of this study was to evaluate the effects of systemic and intracerebroventricular (icv) administration of selegiline (a selective inhibitor of monoamine oxidase B) on the morphine withdrawal syndrome in rats.MethodsTo this aim, adult male Sprague Dawley rats were selected randomly, and then growing doses of morphine were administered subcutaneously at an interval of 12 h for nine days with the intention of inducing dependency. Nine days after, only the morning dose of morphine was administered, followed by systemic or central injection of saline or selegiline. Later, naloxone was injected after 30 min and withdrawal signs recorded for a period of 60 min.ResultsResults showed failure of systemic administration of selegiline in changing the withdrawal symptoms; nevertheless, icv injection attenuated the withdrawal signs significantly.ConclusionIn conclusion we found that central administration of selegiline attenuated morphine withdrawal symptoms     

Antidiuretic effect of morphine in the rat: tolerance and physical dependence.

1 Injection of rats with morphine or methadone, before they received a water load equivalent to 5% of their body weight, produced a dose-dependent antidiuretic effect. Following the antidiuresis, urine was eliminated with kinetics similar to control untreated rats. 2 The antidiuretic effect of morphine or methadone was blocked by naloxone administered before the opiate, or reversed when given after the opiate. 3 Rats implanted with morphine pellets developed a marked degree of tolerance to the antidiuretic effect of morphine. Tolerance was also obtained on injection of three daily doses of morphine or methadone over two days. 4 Withdrawal symptoms were precipitated by naloxone in rats implanted with pellets of morphine; under these conditions the animals showed a marked reduction in urine production as compared to naive rats.     

The NMDA antagonist memantine attenuates the expression of opioid physical dependence in humans

RATIONALE: The serotonin system has an important role in the modulation of several processes relevant to psychiatry such as anxiety, affect, aggression, and drug abuse. This review summarizes the recent progress in elucidating the function of the serotonergic system using knockout mice. This review while not exhaustive, highlights recent findings of relevance to psychopharmacology. OBJECTIVES: To familiarize the reader with the technique and the findings from serotonergic knockout mice. METHODS: Information included in this review was drawn from our own experience in this field and relevant publications from other investigators. RESULTS: We have focused on three main themes that have emerged from studies with mice bearing single-gene mutations of serotonergic genes: anxiety, aggression, and drug abuse. Mice lacking the 5-HT1A have been found to be more anxious in several behavioral paradigms. Elevated levels of aggression have been reported in mice lacking the monoamine oxidase A and the 5-HT1B receptor genes. The mice lacking the 5-HT1B receptor have also been reported to exhibit an increased vulnerability to cocaine. The molecular basis of this enhanced vulnerability has been linked to compensatory changes in the nucleus accumbens. These results and their correlation with pharmacological studies will be discussed. CONCLUSION: Mice lacking key components of the serotonin system have provided us with important animal models of genetic vulnerability to conditions such as anxiety disorders, aggression, and drug abuse. Ongoing research with these mice may help elucidate the mechanistic functioning of this complex system.     

Tolerance and evidence of physical dependence to daily codeine injections in the rat

Core temperatures, measured by telemetry, and acquisition of food pellets on a continuous reinforcement schedule were recorded every 30 min in unrestrained male rats given saline for 5 days before and 5 days after 10 daily SC injections of codeine phosphate (200 mg/kg) at 08:00 hr. After the first codeine injection rats were immobile, slightly catatonic, breathed shallowly and had elevated core temperatures, loss of body weight and inhibition of feeding activity. As injections of codeine were repeated, the initial depressant signs decreased and the period of inhibited feeding was replaced by prolonged (greater than 8 hr) post-injection bouts of feeding activity (stimulated feeding) during daylight hours. Core temperatures remained elevated during this phase of drug-induced feeding activity. Mean body weight and 24-hr food intake remained below control levels over the 10-day codeine period as diurnal feeding patterns became reversed. On the first withdrawal day core temperatures declined and feeding patterns changed from those responses on the last codeine day as the rats lost body weight and were hyperirritable. As withdrawal continued core temperature and feeding patterns began to resemble those of the saline control period, body weights increased and hyperirritability subsided. In this study, tolerance and evidence of physical dependence to daily injections of codeine could be demonstrated in rats by continuous monitoring of their diurnal feeding and temperature responses.     

Effects of naltrexone pellet implantation on morphine tolerance and physical dependence in the rat

• 1.1. The effect of naltrexone pellets containing either 10 or 30 mg of naltrexone base on the development of tolerance and physical dependence on morphine was assessed in male Sprague-Dawley rats. Tolerance-dependence on morphine was induced by s.c. implantation of six morphine pellets, each containing 75 mg morphine base for 7 days.
• 2.2. Naltrexone pellet implantation blocked the development of tolerance to the analgesic and hyperthermic effects of morphine. Similarly, naltrexone pellet implantation reversed morphine withdrawal-induced body weight loss. The effect of pellets containing 10 and 30 mg naltrexone did not differ.
• 3.3. The effect of naltrexone (10 mg) pellet implantation on various signs of naltrexone-precipitated withdrawal such as body weight loss, hypothermia and increases in urinary and fecal output was investigated. Naltrexone pellet implantation did not alter the naltrexone-precipitated withdrawal-induced body weight loss. Concurrent naltrexone pellet implantation blocked the naltrexone-precipitated withdrawal-induced hypothermia, increased fecal and urinary output in morphine-dependent rats.
• 4.4. These results indicate that a single pellet of 10 mg of naltrexone can effectively block morphine tolerance and physical dependence in the rat. Such a procedure may be useful in studying biochemical, endocrinological and immunological mechanisms involved in opioid addiction processes.

     

The production of morphine tolerance and physical dependence by the oral route in the rat

A method for the chronical administration of morphine by the oral route is discussed and compared with the production of physical dependence to morphine by injection. The method recommends the administration of Morphine HCl dissolved in a 45% sucrose syrup and given orally for 4 weeks. The initial concentration of morphine in the syrup was 1 mg/ml and was increased weekly up to 4 mg/ml at the end of the experiment. This procedure rendered the animals physically dependent on morphine as observed by drug withdrawal, when abstinence symptoms were easily identified.     

Assessment of morphine-type physical dependence liability: A screening method using the rat

The effects of centrally acting drugs on body weight changes during 8-h periods in the daytime were studied in the rat in attempts to relate those effects with morphine-type physical liability. Repeated administration of drugs which have morphine-type physical dependence liability altered the prevailing pattern of continuous body weight decrease during the observation period in control animals to an initial increase and subsequent decrease. Withdrawal of these drugs following chronic drug treatment caused a precipitous loss of body weight. Such a body weight loss was further enhanced by the administration of naloxone. In chronically morphine-treated animals, substitution for morphine with a single dose of a test drug caused an increase in body weight or attenuated the loss of body weight due to morphine withdrawal when the test drug has physical dependence liability. Drugs may be classified according to their effects on body weight changes into several groups, each with different physical dependence liability. It is concluded that physical dependence liability of centrally acting drugs can be predicted simply, inexpensively and objectively, by their effects on the pattern of daily body weight changes.     

Increased dihydropyridine-sensitive calcium channels in rat brain may underlie ethanol physical dependence

Ethanol physical dependence can be viewed as a state of latent hyperexcitability in brain which is exposed on withdrawal of the drug. This hyperexcitability may reflect an increased sensitivity to Ca2+ of central neurones. Dihydropyridine (DHP) binding sites which represent a subtype of neuronal Ca2+-channel, are increased in brains from ethanol-dependent rats as are functional effects of the DHP Ca2+-channel activator, BAYK8644. These effects are reversed by DHP Ca2+ inhibitors, which also prevent the ethanol physical withdrawal syndrome. These results suggest that an increase in DHP-sensitive Ca2+-channels on central neurons may represent the molecular basis for ethanol physical dependence.