A method for computer control of morphine ingestion by rats

In this paper, we describe a method for controlling the administration of liquid diet and morphine to sixteen rats using a computer. Morphine ingestion treatment was performed with 6 feeding occasions per 24 hr, all experimental animals receiving similar drug doses. The amount of drug was individual and based on body weight at each feeding occasion. Control and experimental animals were kept under isocaloric conditions. Corrections of drug doses in order to compensate for changes in body weight were made every 24 hr. Sensors registered the exact time of complete drug and diet consumption and prevented overdistribution. Rats were administered 103 mg/kg b.wt. morphine during 24 hr. In another experiment rats were administered 191 mg/kg b.wt. morphine during 48 hr, and no weight loss or decrease in fluid diet intake was registered during the time of drug administration in either of the experiments. After exclusion of morphine from the fluid diet, the body weight loss was 6.1% and 8.3%, respectively, and the liquid diet intake decreased by 12.4 ml and 13.4 ml, respectively, compared with control animal intake. This demonstrates the induction of physical drug dependence. A major advantage of using computer-aided administration of morphine-admixed, fluid diet is the stepwise, small dose increments provided several times a day, resulting in higher drug dose per unit time when compared with ingestion procedures using one feeding occasion per day. The method enables rats to rapidly ingest large morphine doses under standardized conditions.     

Production of physical dependence in rats by drinking a morphine solution

The plasma concentrations of morphine and glucose, the body weight, and the severity of the naloxone-precipitated withdrawal syndrome were studied in female rats in which morphine dependence was induced by administration of the opiate, with or without sucrose, in their drinking water. It was found that sucrose encouraged the animals to consume more morphine and that the initial plasma concentrations of the opiate, as well as the rate of development of physical dependence, were higher than the group not given sucrose. Plasma glucose concentrations, maximum plasma morphine levels and the maximum severity of the naloxone-precipitated withdrawal syndrome were, however, not significantly different between the two groups. The findings suggest that both regimens of administering the opiate in drinking fluid are effective in inducing morphine dependence in rats; the addition of sucrose tends to speed up the development of physical dependence, probably by increasing intake of the opiate through consuming more sucrose solution.     

Concentration-ingestion relations of morphine-adulterated food and morphine solution

Four groups (n=16/group) of rats were given ad libitum access to morphine-adulterated food in one of four different concentrations (1, 2, 3, or 4 mg morphine HCl/g milled food). Half of the subjects in each group were given ad libitum water while the other half were provided with sucrose morphine (1 mg morphine HCl/ml 10% sucrose). Daily measures of body weight, food, liquid, caloric, and morphine intake were recorded for each animal. All eight treatment regimens were effective in inducing physical dependence on morphine as shown by: a) a preference for the morphinized food (1 and 2 mg/g groups) or, b) observable withdrawal signs in rats which failed to maintain their daily morphine intake (3 and 4 mg/g groups) in a subsequent choice test between plain food and morphine-adulterated food at the respective concentration. Caloric intake for all groups was similar to a non-drugged control group. It is concluded that opiate dependence can be achieved by adulterating both the food and liquid regimen of the rat with morphine.This study was Supported by NSF Research Grants B023365 and P2B0349 to K. A. Khavari. The authors thank Thomas Peters and Jan Westerman for their assistance with parts of this work.     

Morphine preference in rats previously morphine dependent

Morphine preference and tendency to relapse to morphine tolerance and dependence were studied in rats which were previously made morphine dependent. Tolerance to, and physical dependence on, morphine were initially produced by administration of increasing concentrations of morphine sulphate in 5% sucrose solution for 3 weeks. A test for drinking preference was performed 4 days after the rats had been successfully detoxified and showed no significant signs of morphine dependence. It was found that, while control animals drank only negligible amounts of morphine solution, previously morphine-dependent rats consumed significantly larger volumes of morphine solution and had recurrence of morphine tolerance and dependence. The present findings show that chronic administration of morphine in drinking fluid produces tolerance and physical dependence as well as addiction in rats; the latter definition is exemplified by these animals having a high tendency to relapse after successful drug withdrawal.     

盐酸二氢埃托啡依赖性潜力的进一步探讨

盐酸二氢埃托啡(DHE)是一种新的强效麻醉性镇痛药,本文着重对DHE在啮齿类动物Do及舌下给药条件下的自然戒断,替代吗啡,催促戒断等方面的致依赖性潜力进行了研究,结果表明,DHE的致身体依赖性潜力确实较低;以DHE替代吗啡抑制阿片类戒断症状时舌下给药剂量低于po给药剂量;在一定剂量条件下DHE舌下给药可使实验动物对其产生身体依赖性。     

Eating pattern of morphine dependent rats

To analyze the drug ingestion patterns of rats in the course of dependence development while on the drug-admixed food (DAF) method, an automatic food intake measuring apparatus was developed. Rats were put on morphine-admixed food, and the food ingestion patterns were recorded with the apparatus in the course of dependence development, during drug withdrawal and at the time of challenge with levallorphan. The naive rats ate the regular diet intermittently at night, and the eating time of morphine-treated rats was longer than that of naive rats. The treated rats also exhibited a frequent eating behavior after 4--5 days on the morphine treatment. During morphine withdrawal, the animal gradually ate the regular diet at about 1-hour intervals, even after evolvement of abstinence signs. When the morphine-dependent rats were given levallorphan, they neither ate nor approached to the food for the first 2--3 hours, but after this time, showed abrupt increases in these activities. Thus, the drug intake pattern of rats in the course of morphine dependence development suggests a correlation between the stage of development of physical dependence and the stage when the animals frequently eat the drug-admixed food.     

Ibotenic acid lesion of the lateral hypothalamus increases preference and aversion thresholds for saccharin and alters the morphine modulation of taste

In a previous study we showed that bilateral ibotenic acid lesions of the lateral hypothalamus in rats induced an increase in gustatory preference thresholds for saccharin solutions and which were associated with body weight and daily water intake impairments. The first aim of the present study was an attempt to dissociate the body weight and water intake deficits from the increase in gustatory thresholds. For this purpose we compared the effect of simultaneous bilateral lesions of the lateral hypothalamus with the effect of successive lesions in which each unilateral destruction was separated by a 10-day interval. Rats injected with vehicle only (either simultaneously or successively) served as controls. The two types of lesion produced very similar deficits, namely permanent body weight and water intake decreases, as well as a shift to the right in gustatory preference-aversion functions for saccharin (two-bottle procedure). The second aim of the present study was to analyse the effect of morphine (2 mg/kg SC) on saccharin preference in both lesioned and control rats. It was observed that for moderate and high concentrations of the sweetener morphine increased preference for saccharin over water but this effect was similar in both groups of rats. However, with a low concentration of the sweetener (0.3 mM) morphine clearly induced an opposite effect in the two groups of rats: the significant preference for this concentration shown by the control rats after vehicle injection was converted to a neutral response, whereas the neutral response of the lesioned animals after vehicle injection was transformed by morphine to a significant preference for saccharin over water.(ABSTRACT TRUNCATED AT 250 WORDS)     

The acoustic startle response as a measure of behavioral dependence in rats

A series of experiments was conducted to assess the sensitivity of the acoustic startle response to chronic morphine administration and naloxone-precipitated withdrawal. Rats were implanted with two subcutaneous pellets containing either 75 mg each of morphine or containing only placebo. In experiment 1, withdrawal induced by 0.05–0.2 mg/kg naloxone dose-dependently decreased the magnitude of the startle response. Physical dependence was confirmed by a naloxone-induced acute weight loss seen in morphine-implanted rats, but naloxone had no effect on startle or body weight in nondependent animals. In experiment 2, a modified procedure with fewer trials per session and fewer test days was employed. Naloxone (0.2 mg/kg) given 4–5 days after implantation induced large startle-response decreases in morphine-dependent rats while having no effect in placebo-implanted rats. Post-naloxone saline tests revealed no significant differences in startle between morphine and placebo groups. Startle scores were significantly higher in morphine-implanted rats than in placebo rats during a saline test given 3 days following pellet implantation. In a separate group of animals, however, acute IP injections of morphine from 0.3–10 mg/kg had no significant effect on startle amplitude. The effect of repeated pairings of withdrawal with the startle environment was assessed in experiment 3. Morphine-dependent rats startled significantly less if naloxone injections were given before the startle session than if they were administered 4 h later. Conditioned withdrawal effects, expressed during a final test session when all rats received saline, were observed for the body-weight measure but not for the startle response. These results suggest that the acoustic startle response may be a useful objective measure in evaluating physical dependence produced by substances of abuse.     

Aspects of abstinence after morphine ingestion

Sprague-Dawley male rats were intoxicated with morphine, using an ingestion method where exposed and control rats received equivalent amounts of calories and nutrients. The degree of physical dependence on morphine was demonstrated by studying and quantifying abstinence symptoms after withdrawal or after administration of opiate antagonists. The aims of the study were (1) to further enlighten the specificity and validity of the intoxication method concerning physical dependence, and (2) to determine whether some of the abstinence signs might be of value to facilitate quantitation of the degree of physical dependence on morphine, with diet and fluid intake being maintained under control. Withdrawn rats showed a decreased fluid diet intake and a body weight loss, the latter partly due to anorexia. Other mild abstinence signs were irritation, tremor and some motor excitation. The body weight loss during the first day of morphine withdrawal was proportional to the accumulated drug dose (between 25 and 300 mg morphine PO/kg b.wt.). However, prolonged morphine treatment on one dose (340 mg/kg b.wt.) did not reinforce the body weight changes caused by morphine withdrawal. The succeeding weight gain some days after morphine withdrawal was not entirely dependent on the amount of fluid diet intake. Methadone was shown to partially block the decrease in diet intake and the weight loss seen during morphine withdrawal. The naloxone-precipitated withdrawal symptoms were motor excitation, cholinergic signs, body weight loss, diarrhoea and decreased diet intake. The weight loss 2 hr after naloxone administration to long-term intoxicated rats was proportional to the naloxone dose.(ABSTRACT TRUNCATED AT 250 WORDS)     

Alterations in consummatory behavior following intracisternal injection of 6-hydroxydopamine

Intracisternal administration of two doses of 6-hydroxydopamine, one with pargyline pretreatment and one without, caused an initial disruption of consummatory behavior. In spite of measures to enhance recovery from these acute effects, 6-hydroxydopamine treated rats were found to maintain body weight at a lower level than control rats. Similar to controls, treated animals were found to drink water in the absence of food and to enhance water consumption in response to the administration of a hypertonic saline solution. However, unlike control rats, animals treated with 6-hydroxydopamine failed to increase food intake following insulin administration. Desoxycorticosterone acetate (DOCA) treatment enhanced saline preference in 6-hydroxydopamine treated rats, but the maximum volume of saline consumed was markedly less than the intake of control rats following DOCA treatment. While control rats drank a large volume of either a sucrose or a saline solution when substituted for water, 6-hydroxydopamine treated animals showed little increase in their intake of these solutions. Preferential deplition of norepinephine in brain did not alter consumption of a sucrose solution; however, depletion of dopamine produced a significant reduction in sucrose intake. These latter findings suggest that this deficit observed in the 6-hydroxydopamine treated rat involves interruption of dopaminergic pathways.     

The physical dependence liability of butorphanol: a comparative study with morphine.

In these studies, the physical dependence liability of butorphanol, a mixed 'agonist/antagonist' opioid analgesic, was compared to that of morphine. Male, Sprague-Dawley rats received i.c.v. infusions of saline (1 microliter/h), or an equimolar dose of butorphanol or morphine (52.3 nmol/h) for 3 days. The physical dependence liabilities of these two compounds were then compared by assessing both behavioral withdrawal signs and weight loss following naloxone-precipitated withdrawal. Body weight loss was also evaluated following abrupt (cessation of infusion) withdrawal from butorphanol or morphine. In animals receiving i.c.v. infusions of butorphanol or morphine, naloxone administration (5 mg/kg s.c.) induced an equivalent degree of body weight loss compared to saline-treated animals. In addition, the ED50 of naloxone to produce wet shakes, escape behavior, teeth chattering, urination and defecation was equivalent in rats receiving butorphanol or morphine. Infusions of butorphanol or morphine also produced an equivalent degree of weight loss in animals undergoing abrupt withdrawal. These results demonstrate then that a substantial degree of physical dependence had developed in rats which received a large dose of butorphanol.     

Morphine preference in individual rats after morphine ingestion

Individual differences in drug intake were investigated. Inbred Sprague-Dawley male rats were choice-tested after various periods of morphine ingestion. Nearly 10% of the rats showed more than 50% preference already after 4 days ingestion on 340 mg morphine/kg/day, while a further 10% had a mean preference less than 30% over 6 days of choice, even after as long as 38 days' treatment on this same dose. High morphine preference was stable for long choice periods. It was also found that a high morphine preference level in an individual rat persisted over several choice tests, even if the animals had been without morphine for several months. The ₂-agonist clonidine diminished high preference to the same extent as it diminished over-all morphine preference. There were no differences in food intake, body weight gain, severity of abstinence reactions, morphine serum levels, taste sensitivity tested with quinine, or learning the choice test behaviour comparing extremely high and low morphine preference rats. Thus, two subgroups of high and low morphine-ingesting rats were identified in the Sprague-Dawley strain.     

Withdrawal from chronic nicotine fails to produce a conditioned taste aversion to saccharin in rats

Sprague-Dawley rats were maintained on a daily regimen of nicotine, morphine or saline administration for 28 days. Following the discontinuation of the daily drug regimen, rats were given a choice of tap water or a saccharin-water solution. The rats previously receiving morphine drank significantly less saccharin-water solution than did the rats receiving nicotine or saline injections. The failure of the nicotine rats to display a conditioned aversion to the novel saccharin flavor suggests that nicotine did not produce a physiological withdrawal syndrome analogous to morphine withdrawal in this paradigm.     

18-Methoxycoronaridine: a potential new treatment for obesity in rats?

Rationale  Excessive eating often leads to obesity. Although a variety of neurotransmitters and brain regions are involved in modulating food intake, a role of accumbal dopamine is thought to be critical for several aspects of this behavior. Since 18-methoxycoronaridine (18-MC), a selective antagonist of α3β4 nicotinic receptors, was previously shown to alter dopamine release in the nucleus accumbens in response to chronic injections of cocaine and morphine, this drug could be a promising therapy for abnormal eating behavior. Objectives  Assess the effect of 18-MC on the consumption of sucrose (15%) vs. water in a self-administration paradigm and on the intake of freely available palatable fluids (i.e., 5% sucrose, 0.1% saccharin, and 0.6% saline solutions) as well as on water intake. Determine whether repeated administration of 18-MC (20 mg/kg i.p.) affects weight gain, food intake, and fat deposition in rats drinking 30% sucrose solution. Results  Acute administration of 18-MC (10–40 mg/kg i.p.) reduced operant responding for sucrose and decreased ad libitum ingestion of sucrose, saccharin, and saline. The highest dose of 18-MC also reduced consumption of water when palatable fluids were not available. In rats having unlimited access to sucrose (30%), chronic treatment with 18-MC (20 mg/kg i.p.) prevented sucrose-induced increases in body weight, decreased fat deposition, and reduced consumption of sucrose while not altering food intake. Conclusions  These data suggest that antagonism of α3β4 nicotinic receptors may be involved in the regulation of intake of palatable substances regardless of its caloric value and may participate in maintaining obesity.     

A study on drug dependence using fast acting drugs]

Physical dependence on narcotics is induced in laboratory animals by intermittent parenteral administration (2 approximately 3 times daily). However, inducing of dependence on pethidine has been unsuccessful using the parenteral method. Recently, it has been reported that physical dependence on pethidine can be induced by continuous infusion methods (5.6). In the present experiment, pethidine was administered to rats (n=5 approximately 6) by ingestion of pethidine-admixed food preparations (0.5 approximately 4.0 mg/g of feed). The results indicated that (a) when rats are allowed free access to two food preparations (0.5 mg/g vs. 1 mg/g of food) for 7 weeks, spontaneous intake ratios of food (1 mg/g of food) gradually increased from 15% to 30% after 3 weeks. (b) Abrupt withdrawal for 48 hr after a 10 day administration period (2 mg/g of food on day 1 approximately 3 and 4 mg/g of food on day 4 approximately 10) resulted in a loss of body weight in the next 24 hr, and the prewithdrawal level of body weight was recovered in 48 hr. (c) The time course of body weight and food intake during the first 24 hr withdrawal period demonstrated the characteristic pattern of abstinence syndrome of pethidine, viz. early onset (12 approximately 13 hr) and rapid recovery (within 48 hr), as compared to morphine withdrawal. (d) Suppression of pethidine abstinence of both a single injection of morphine (10 mg/kg, s.c.) and substitution for morphine-admixed food was also realized. (e) When levallorphan (5 mg/kg, s.c.) was administered to both pethidine and morphine dependence rats, the maximal decrease in body weight was less than that in morphine dependent rats. These data indicate that pethidine possesses about one fifth the dependence liability of morphine and the maximal abstinence syndrome appears within 24 hr after withdrawal. Conclusively, application of a drug-admixed food preparation in drug dependence tests in rats has proven to be a useful method, particularly in the case of pethidine-like drugs which rapidly disappear from the blood.     

Antidepressive effects of the κ-opioid receptor agonist salvinorin A in a rat model of anhedonia

Salvinorin A (SalvA), the hallucinogenic derivative of the plant Salvia divinorum, is a selective κ-opioid receptor agonist that may also have antidepressant properties. Chronic mild stress (CMS) was applied to male and female Long-Evans rats to model anhedonia common in depression. The progressive loss in preference for a sucrose solution over plain water, a measure of anhedonia, and locomotor activity were monitored for 7 weeks. Because antidepressant medications often modify reproductive functions, endocrine glands and hormone-sensitive tissues were assessed at necropsy after the conclusion of the behavioral protocol. Three weeks of CMS exposure led to a decrease in sucrose preference. CMS was continued for 3 additional weeks and animals were randomly assigned to treatment with 1 mg SalvA/kg body weight or to a vehicle control group. The results indicate that SalvA reversed anhedonia whereas control animals continued to show a suppressed preference for the sucrose solution. In addition, no change in sucrose preference was observed in nonstressed rats that were exposed to the same dosage of SalvA. The results indicate that SalvA is an effective antidepressant agent when administered chronically to rats showing symptoms of depression similar to those observed in humans.     

Early housing experience modifies morphine self-administration and physical dependence in adult rats

Male Sprague-Dawley rats were raised from weaning in one of three housing conditions: one, two or four per housing unit. At 60 days of age, animals were moved to individual cages and tested in the open field. Following a baseline period in which animals were allowed to adapt to their new housing condition, animals had their water replaced with a $\text{0.8}\text{mg}\text{ml}$ morphine sulfate solution. Following 12 days of access to the drug, animals were injected with naloxone and abstinence precipitated. While no differences were found in body weight among the three groups of animals at 60 days of age, significant differences in open field behavior were noted. Animals that were raised in groups were found to be more active in the open field than animals raised in isolation. Early housing experience was also found to modify later morphine consumption and physical dependence. Animals raised in isolation exhibited a trend to start drinking morphine sooner and experienced less severe withdrawal symptoms following naloxone administration than group-raised animals.     

Matricaria chamomilla extract inhibits both development of morphine dependence and expression of abstinence syndrome in rats

The effect of Matricaria chamomilla (M. chamomilla) on the development of morphine dependence and expression of abstinence was investigated in rats. The frequencies of withdrawal behavioral signs (paw tremor, rearing, teeth chattering, body shakes, ptosis, diarrhea, and urination) and weight loss induced by naloxone challenge were demonstrated in morphine-dependent rats receiving M. chamomilla extract or saline. The withdrawal behavioral manifestations and weight loss were inhibited significantly by chronic co-administration of M. chamomilla extract with morphine. Administration of a single dose of M. chamomilla before the naloxone challenge in morphine-dependent animals abolished the withdrawal behavioral manifestations. The dramatic increase of plasma cAMP induced by naloxone-precipitated abstinence was prevented by chronic co-administration of M. chamomilla extract with morphine. These results suggest that M. chamomilla extract inhibits the development of morphine dependence and expression of abstinence syndrome.     

Prevention by the 5-HT3 receptor antagonist, ondansetron, of morphine-dependence and tolerance in the rat.

1. The effect of ondansetron, a selective 5-hydroxytryptamine3 (5-HT3) receptor antagonist, was studied in morphine-addicted rats. Morphine-dependence and tolerance, induced by drinking increasing concentrations of morphine sulphate in 5% sucrose solution for 3 weeks, were demonstrated by the naloxone-precipitated withdrawal syndrome and tail flick response to a thermal noxious stimulus (water at 50 degrees C), respectively. 2. Morphine-dependence, assessed by naloxone precipitated withdrawal, was undetectable by the 6th day, when the animals drank only tap water for 7 days after the 3-week induction period. 3. When detoxified rats were offered sucrose and morphine solutions for 10 days, the recurrence of opiate solution preference with relapse to dependence and tolerance was observed. 4. Giving ondansetron (0.1 or 1 microgram kg-1; i.p.; twice daily) on the 14th day of, or 7 days prior to, the 3-week induction period reduced dependence and tolerance seen during the 3-week morphine induction and the 10-day drinking preference periods. 5. 5-Hydroxytryptamine2 (5-HT2) receptor antagonism by cyproheptadine (100 or 250 micrograms kg-1; i.p.; twice daily) did not influence morphine-dependence and tolerance. 6. These findings suggest that ondansetron may be useful for treating opiate addiction and lowering the recidivism rate.     

Social behavior of juvenile rats after in utero exposure to morphine: dose-time-effect relationship.

In the present study, the effects of morphine exposure in utero on social behavior in juvenile male rats was investigated. Pinning, a measure for play behavior, and social grooming of the offspring were measured at postnatal day 21. The subjects were offspring of Wistar rat dams given sc. injections of 1 or 10 mg/kg body weight morphine HCl daily from gestational days 8 (GD8)-GD 21 and control dams injected daily with saline. Pinning and social grooming of the morphine-treated offspring were significantly elevated compared to saline controls. The doses of morphine used neither affected the gestation of pregnant mother rats nor sensorimotor development of the juvenile rats. Prenatal exposure to morphine of 10 mg/kg daily increased both pinning and social grooming, prenatal exposure to a lower dose of 1 mg/kg increased pinning behavior but not social grooming in the offspring. To study the importance of the gestational period, offspring of dams given 10 mg/kg body weight morphine HCl from GD8-GD15 and saline from GD16-parturition or morphine from GD16-parturition and saline from GD8-GD15 was tested. Pinning was only increased when morphine exposure occurred during the third week of gestation, social grooming was increased when morphine exposure had been in the second week of gestation. Subcutaneous administration of 1 mg/kg naltrexone 1 h before the test significantly decreased play behavior in control rats, but not in animals prenatally exposed to morphine. From these experiments we conclude that the long term effect of in utero exposure to morphine on play behavior is established by affecting the endogenous opioid system.