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.     

Assessment of precipitated abstinence in morphine- dependent rats

An experimental model is described for quantifying the precipitated abstinence syndrome in morphine-dependent rats. Male rats were made dependent on morphine by subcutaneous implantation of a morphine pellet and the abstinence syndrome precipitated by intraperitoneal injection of naloxone hydrochloride. A ranking system, based on the median effective dose of naloxone for abstinence signs, quantitatively related the incidence of certain precipitated signs to the dose of naloxone. The time course for the development of dependence was shown to be maximal 70–74 h after pellet implantation. Food or water deprivation for 48 h dissociated the body weight loss during abstinence from the behavioral signs of precipitated withdrawal. Ganglionic blockade did not significantly modify abstinence behavior. An evaluative procedure which ranks abstinence signs is proposed for quantifying physical dependence on morphine.     

Withdrawal-like symptoms in young and adult rats maternally exposed to methadone

Rats of 30, 45, 60 and 120 days of age, maternally exposed to methadone (5 mg/kg daily) during gestation and /or lactation, were evaluated on a variety of behavioral and physiological parameters related to drug withdrawal. Animals were tested before and after an acute injection of naloxone (10 mg/kg). Prior to maloxone injection, methadone-exposed rats were subnormal in body temperature at 30 days of age, hypoalgesic at 45 days, and weighed less than controls at 60 days. Additionally, and in contrast to control rats, methadone-exposed animals at most ages displayed head shake and wet-dog shake behaviors. After naloxone administration, methadone-exposed rats exhibited an increase in the mean number of head and wet-dog shakes over pre-injection levels. Although control rats injected with naloxone also demonstrated head shakes (at all ages) and wet-dog shakes (at 45 days), these behaviors were usually not of the magnitude as noted for methadone-exposed offspring receiving naloxone. Perturbations in body weight and hypothermia during development, along with head shake and wet-dog shake behaviors which were exacerbated following naloxone administration, suggest a protracted state of physical dependence/withdrawal and/or permanent damage as a result of perinatal exposure to methadone.     

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)     

A comparison of the cardiovascular and the behavioral changes following naloxone as measures of the degree of physical dependence on morphine in rats

Behavioral and cardiovascular changes evoked by naloxone (0.5 mg/kg) were evaluated in unrestrained rats made physically dependent by a constant infusion of morphine at increasing doses over 7 days. The relationship between the duration of morphine administration and the naloxone-induced cardiovascular changes was investigated to determine the reliability and sensitivity of blood-pressure measurements in assessing the degree of physical dependence produced in these animals. No significant behavioral or cardiovascular changes from preaddiction levels were observed during morphine infusion. Arterial pressure increased significantly in a dose- and time-dependent manner in response to naloxone injected on days 1, 3, 5, or 7 of the morphine infusion schedule. Heart rate changes which accompanied the increase in blood pressure, however, were similar in magnitude over the course of increasing physical dependence. The frequency of counted behavioral signs precipitated by naloxone over the same infusion schedule indicated a significant, progressive increase only for escape attempts, whereas withdrawal body shakes and writhing peaked early in the schedule and actually declined to very low frequencies by day 7. A high dose of morphine (50 mg/kg) was injected following naloxone-precipitated withdrawal in an attempts to reverse the abstinence symptoms. The only symptoms significantly inhibited by morphine were the increase in arterial pressure and the occurrence of diarrhea. These results indicate that the absolute increase in arterial blood pressure produced by naloxone in opiate-dependent animals may serve as a simple, objective, and sensitive measurement, along with traditional behavioral signs, in the assessment of narcotic dependence liability.     

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.     

拮抗触液核P物质对吗啡戒断大鼠行为学的影响

目的观察P物质(substance P,SP)在吗啡戒断大鼠触液核内的表达及拮抗触液核内SP对吗啡戒断行为学的影响,探讨触液核内SP在吗啡戒断中的作用。方法 SPF级SD♂大鼠2组,吗啡戒断-人工脑脊液组(A组)和吗啡戒断-SP抑制剂组(B组);两组均采用剂量递增法腹腔注射盐酸吗啡,建立大鼠吗啡依赖模型,在d4上午侧脑室注射霍乱毒素亚单位B-辣根过氧化物酶复合物(CB-HRP)逆行追踪触液神经元;B组d5上午在立体定位仪下侧脑室注射SP拮抗剂(D-Pro2、D-Phe7、D-Trp9)-SP,A组注射人工脑脊液作为对照组;d6上午腹腔注射纳络酮(5mg·kg-1)建立吗啡戒断模型;并进行戒断行为学评分、记录戒断总评分(total withdrawal scores,TWS),免疫荧光结合激光共聚焦显微镜观察SP的表达。结果 A组大鼠触液核内SP表达增加,B组显示,拮抗触液核内SP可减弱吗啡戒断样症状;两组TWS相比较,A组高于B组(P<0.01)。结论抑制触液核内SP能够减轻吗啡戒断症状,本研究首次证实触液核SP表达参与了吗啡躯体依赖的发展与纳洛酮药物催促戒断,这将有助于利用药理学手段干预阿片依赖寻找新方法。     

A new approach for assessment of narcotic physical dependence using urinary sex-dependent low molecular weight proteins in male rats

Attempts have been made to examine the relationship between urinary excretion of sex-dependent low molecular weight proteins found only in male rats (LMWP) and morphine physical dependence. Chronic administration of morphine produced a dose-related decrease in urinary LMWP excretion, which was correlated to the intensity of withdrawal signs including body weight loss and abnormal behaviors recognized after naloxone challenge. Furthermore, a statistically high correlation was obtained between the decrease in urinary LMWP excretion and the loss of body weight precipitated by naloxone challenge. LMWP was identified immunologically in the livers, kidneys, and sera using an antibody against purified LMWP. The serum level of LMWP was increased rapidly following bilateral nephrectomy. After chronic treatment with morphine, the LMWP content in the livers, kidneys, and sera were decreased. These findings indicate that the decrease in urinary LMWP excretion induced by chronic administration of morphine can be a useful parameter to assess the development of physical dependence on narcotics on the peripheral level without requiring drug withdrawal and naloxone challenge. This decrease in urinary LMWP may be caused by the inhibition of LMWP synthesis in the liver.     

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.     

Pharmacodynamics and kinetics of loss of tolerance and physical dependence on morphine induced by pellet implantation in the rat.

The decay characteristics of tolerance and physical dependence on morphine induced by a pellet implantation procedure were determined in male Sprague-Dawley rats. Rats were implanted subcutaneously with 6 morphine pellets during a 7-day period. The pellets were removed, and at various times thereafter tolerance to the analgesic and hyperthermic effects of morphine was measured by determining the response in rats implanted with morphine and placebo pellets. Similarly, the physical dependence was assessed by monitoring withdrawal signs following an injection of naloxone. A high degree of tolerance developed to the analgesic and hyperthermic effects of morphine. Similarly, a high degree of physical dependence also developed as evidenced by a high incidence of jumping response, teeth chattering and production of fecal boli induced by injections of naloxone. In addition, loss of body weight and body temperature also occurred. The analgesic and hyperthermic response to morphine recovered very gradually. There was no significant difference in the analgesic and hyperthermic responses to morphine on day 4 after the pellet removal in rats implanted with morphine and placebo pellets. The decay of tolerance was linear with time for the analgesic effect (r = 0.98) and for the hyperthermic effect (r = 0.93). The change in symptoms of physical dependence on morphine with time depended on the specific symptom monitored. The average number of jumps and teeth chattering decreased with time in a linear fashion with r values of 0.98 and 0.99, respectively. However, the number of fecal boli and wet dog shakes increased linearly with time (r = 0.97). The recovery of loss of body weight was also linear with time. Thus, it is clear that fecal boli and wet dog shakes, which increase in number as the dependence decays, are signs of a low degree of dependence. The results suggest that different central or peripheral mechanisms may be operating in different withdrawal symptoms. These studies may prove to be useful when studying the mechanisms involved in the induction and reversibility of tolerance and dependence processes, and in long-term effects of opiates at a time when the tolerance and physical dependence is no longer evident.     

Induction of physical dependence in rats by short interval medication

Rats were intermittently medicated at one hour intervals through an implanted intravenous cannula. Physical dependence on morphine and codeine was developed rapidly and it was detectable with the maintenance dose as low as 9.6 mg/kg/day. Physical dependence on pentazocine was also developed with the maintenance dose of 96 mg/kg/day, but was not with 9.6 mg/kg/day. In the pentazocine-treated rats, body weight loss was observed after the abrupt withdrawal, and abstinence signs were precipitated by naloxone 1 mg/kg. Cross physical dependence between morphine and pentazocine was demonstrated. Pentazocine suppressed the abstinence signs of rats weakly dependent on morphine, and morphine suppressed those of pentazocine-dependent rats. ID-1229, a new benzomorphan analgesic, did not produce dependence in this test and did not suppress the abstinence signs of morphine- and pentazocine-dependent rats.     

Comparison of opiate agonists and their N-allyl derivatives in the production of physical dependence in the rat

The development of physical dependence to slow-release (SR) emulsions of various opiate agonists and their N-allyl derivatives was examined. Rats were injected SC with SR preparations of morphine (75 mg/kg), nalorphine (75 mg/kg), oxymorphone (75 mg/kg), naloxone (75 mg/kg), levorphanol (30 mg/kg), levallorphan (75 mg/kg) or dextrorphan (75 mg/kg), and behaviour was assessed for 24 h. Only morphone, oxymorphone and levorphanol induced signs typical of opiate intoxication lasting 12 h or more. After 24 h the rats were challenged with injections of naloxone (5 mg/kg IP) and withdrawal behaviour and changes in body temperature and body weight were estimated. Withdrawal symptoms were exhibited to varying degrees by all rats except those which had received naloxone SR. Only rats which were injected with the agonists exhibited both jumping and wetshake responses. Falls in body temperature and body weight appeared to be associated with withdrawal, but it was difficult to differentiate between the opiate agonists and their N-allyl derivatives. In other groups of rats, the brain levels of noradrenaline (NA), dopamine (DA), homovanillic acid (HVA), 5-hydroxytrypamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) were measured spectrofluorimetrically 24 h after administration of the SR preparations. Apart from levorphanol SR, which increased brain DA and HVA, none of the drugs affected the levels of NA, DA, HVA and 5-HT. However, all drugs significantly increased the brain levels of 5-HIAA. The opiate agonists increased the level of this metabolite to a significantly greater extent than their corresponding N-allyl derivative. It is concluded that opiate agonists induce a greater degree of physical dependence than their N-allyl derivatives. In addition, since dextrorphan is as effective as the agonists in producing several of these effects, it appears that changes in body temperature and body weight and alteration of the metabolism of brain 5-HT may not be causally related to the dependence process induced by opiates. Such modifications may be associated with the structure of the opiate molecule.     

Indomethacin facilitates acute tolerance to and dependence upon morphine as measured by changes in fixed-ratio behavior and rectal temperature in rats

The effects of indomethacin, a prostaglandin (PG) synthetase inhibitor, on acute tolerance to and dependence on morphine were investigated. Twelve mature, male Long-Evans rats were trained to lever press for food reinforcement on a fixed-ratio 30 schedule (FR 30 behavior) and have their rectal temperature taken. The experimental protocol began with taking the rat's temperature followed by a 30 minute behavioral session. Immediately after this session the animal was injected with indomethacin or its vehicle. Two-and-a-half hours later this procedure was repeated, except that morphine or saline was administered. After an additional 2.5 hours had elapsed, a 60 minute behavioral session occurred. Half-way through the session the rat was injected with morphine (tolerance), naloxone (dependence), or saline. Immediately after the session the rat's temperature was recorded. Indomethacin potentiated the acute tolerance to the behavioral suppressant and hyperthermic effects of morphine. Indomethacin pretreatment also greatly enhanced the capacity of naloxone to decrease temperature and suppress FR 30 behavior in morphine-treated rats. These effects were not due to indomethacin altering the acute effects of morphine or the amount of morphine in the brain. These data suggest that indomethacin is inhibiting synthesis of PGs which are important in morphine tolerance and dependence.     

Physical dependence potential of an enkephalin analog, EK-399, in rats

The physical dependence potential of Tyr-D-Met(O)-Gly-EtPhe-NHNHCOCH3.AcOH (EK-399), a novel enkephalin analog with a potent analgesic effect, was assessed in rats. The animals were given EK-399 (0.008, 0.032, 0.125, or 0.5 mg/kg), morphine (0.125, 0.5, or 2 mg/kg), pethidine (2 or 8 mg/kg), or pentazocine (2 or 8 mg/kg) every hour through an implanted intravenous cannula. After 3 days of treatment, precipitated withdrawal tests were conducted: naloxone (5 mg/kg) was administered subcutaneously. Rats treated with morphine showed withdrawal signs such as hyperirritability, salivation, diarrhea, and weight loss. Rats treated with pethidine, pentazocine, or EK-399 showed similar signs, but they were less evident than those in morphine-treated rats. In abrupt withdrawal tests after 7 days of treatment, rats treated with morphine, pethidine, or pentazocine showed weight loss, whereas rats treated with EK-399 showed little or no weight loss. In substitution tests, EK-399 suppressed the withdrawal signs in morphine-dependent rats, and vice versa. These results show that EK-399 has a morphine-like physical dependence potential that is weaker than that of morphine, pethidine, or pentazocine in rats.     

延胡索甲素与左旋延胡索乙素抗吗啡躯体依赖和精神依赖的作用研究

目的 观察并比较延胡索甲素(corydaline,Cor)与左旋延胡索乙素(l-tetrahydropalmatine,l-THP)抗吗啡躯体依赖和精神依赖的作用。方法 SD大鼠随机分为对照组、模型组、Cor组、l-THP组。连续递增sc吗啡9 d后,纳洛酮促瘾,制备吗啡依赖大鼠催促戒断模型,促瘾前30 min ip Cor(40、80 mg/kg)或l-THP(5.0、10.0 mg/kg),观察大鼠戒断症状和体质量的降低;应用旷场实验,观察Cor(5、10 mg/kg)和l-THP(2.5、5.0 mg/kg)对吗啡诱导的大鼠自发活动的影响、对吗啡连续递增给药致大鼠行为敏化效应的影响,以及Cor(10、20、40 mg/kg)和l-THP(2.5、5.0、10.0 mg/kg)对大鼠自发活动的影响。结果 Cor(40、80 mg/kg)、l-THP(5.0 mg/kg)对吗啡催促戒断症状无显著改善作用,10 mg/kg l-THP显著改善大鼠戒断症状(P<0.05);Cor和l-THP对吗啡降低大鼠体质量效应有改善趋势,但差异不显著;Cor 40 mg/kg以下剂量、l-THP 10 mg/kg以下剂量对大鼠自发活动无显著影响;Cor(5、10 mg/kg)和l-THP(2.5、5.0 mg/kg)均可显著降低吗啡诱发的大鼠高活动性行为、行为敏化的形成(P<0.05、0.01)。结论 Cor和l-THP对吗啡所致的大鼠躯体依赖和精神依赖均有不同程度的调节作用,l-THP的起效剂量明显低于Cor。     

可乐定对吗啡依赖小鼠催促戒断后行为的影响

目的:研究吗啡依赖小鼠在纳洛酮催促戒断时可乐定治疗对稽延性戒断症状相关行为的影响。方獉法獉:采用剂量递增法使小鼠对吗啡产生依赖;每天sc盐酸吗啡3次,共3d,剂量由50mg·kg-1逐步上升到125mg·kg-1。d4sc注射50mg·kg-1吗啡1h后,可乐定治疗组小鼠ig0.6mg·kg-1可乐定,对照组ig等体积的去离子水;sc吗啡2h后各组小鼠均ip5mg·kg-1的纳洛酮进行催促戒断,观察30min内小鼠的跳跃反应和体重变化。在催促戒断后5h和24-30h通过洞板试验、悬尾试验、十字迷宫试验和自发活动试验,观察小鼠的探究行为、抑郁样行为、焦虑行为及活动性。部分小鼠在第一次戒断后10h及次日重新给予吗啡(100-125mg·kg-1)使之再次产生依赖,在d6依d4操作进行二次戒断,但不给予可乐定治疗。结果:在催促戒断试验中,可乐定可以显著降低吗啡依赖小鼠的跳跃次数和体重减轻(P<0.01);催促戒断5h后,可乐定组小鼠在洞板试验中的探洞次数比对照组少(P<0.01);在悬尾试验中的不动时间比对照组长(P<0.01);在十字迷宫试验中进入开臂的时间和次数与对照组比较差异无显著性;在自发活动试验中,前5min自发活动计数低于对照组(P<0.01),但30min内活动量与对照组比较差异无显著性;催促戒断24-30h后,两组之间的各项行为学指标差异均无显著性;在二次戒断实验中,可乐定组小鼠跳跃次数高于对照组(P<0.05),但两组小鼠体重变化差异无显著性。结论:用于拮抗吗啡依赖小鼠急性戒断症状的可乐定对戒断后的抑郁样行为有加重趋势,对焦虑行为没有影响;可乐定上述作用的行为药理学机制可能是抑制逃脱动机。     

Induction of physical dependence on and tolerance to ethanol in rats fed a new nutritionally complete and balanced liquid diet

Rats offered a nutritionally balanced and complete liquid diet containing 35% of energy as ethanol, 12% as fat, 21% as protein, and the balance as carbohydrate consumed greater than 9 g/kg ethanol after 10 days. Rats displayed signs of physical dependence and tolerance while showing a net gain in weight. Physical dependence was indicated by severe intensity of the following signs during withdrawal from ethanol: Muscle rigidity; tail tremors; caudal tremors; and general tremors. Severity of these signs reached a maximum intensity by 19 h after withdrawal of ethanol. Tolerance was assessed by performance on a moving belt after injection of an IP challenge dose of ethanol. Tolerance was exhibited by chronically treated rats as measured by significantly reduced time off the belt after 7 days. Concentrations of ethanol in blood were documented on selected mornings and were observed to increase. These data suggest that physical dependence and tolerance can be induced through voluntary consumption of ethanol by rats and without nutritional compromises or weight loss.     

Rapid induction and quantitation of morphine dependence in the rat by pellet implantation

Four schedules of subcutaneous morphine pellet implantation were developed to render rats rapidly physically dependent on morphine. The schedules included implantation of four morphine pellets over a 3-day period (schedule 1), six morphine pellets over a 3-day period (schedule 2), six pellets over a 7-day period (schedule 3), and ten pellets over a 10-day period (schedule 4). Each morphine pellet contained 75 mg of morphine base. The degree of morphine dependence was quantitated by determining the median effective dose (ED₅₀) of naloxone required to induce the stereotyped jumping response. Hypothermia and weight loss, during abrupt and naloxone-induced withdrawal, were also measured. Rats on schedule 4 exhibited a high degree of dependence on morphine as evidenced by an extremely low naloxone ED₅₀ for the precipitated withdrawal jumping response, whereas schedules 1 and 2 produced a low degree of dependence as shown by high naloxone ED₅₀'s. Further evidence for a high degree of physical dependence on morphine is schedule 4 rats was indicated by their greater loss in body weight and greater hypothermic response after abrupt and after naloxone precipitated withdrawal compared with these responses in the rats in the other three schedules. A correlation was found to exist between naloxone ED₅₀ for the jumping response, body weight loss, and hypothermia observed during naloxone-induced withdrawal in morphine-dependent rats. These studies suggest that the implantation of four morphine pellets in the rat produces a mild degree of dependence and that caution should be exercised when making generalized conclusions about the biochemical correlations involved when four or less number of pellets, each containing 75 mg of morphine base, are used to induce morphine dependence in the rat.     

Ethopharmacological analysis of naloxone-precipitated morphine withdrawal syndrome in rats: a newly-developed “etho-score”

The intensity of opiate withdrawal syndrome in rats is usually quantified on the basis of selected physical signs or global scores. However, the selection criteria of signs and scores have not been subjected to an ethological discussion, hence they appear to be somewhat arbitrary. The objectives of this study were thus: i) to analyse the rat's behaviour during the nalox-one-precipitated morphine withdrawal syndrome, ii) to evaluate the validity of classic methods, and iii) to design a new etho-score. Ten rats were implanted with morphine pellets (75 mg×2, SC), all receiving different naloxone doses following a within-subject design (0, 0.01, 0.05, 0.1, 0.5, 1 mg/kg SC). Twenty unexperienced rats and 20 with placebo pellets were injected with either saline or naloxone. Behaviour was videotaped and later analysed by computer-based ethological techniques. The ethogram encompassed 16 patterns displayed by rats during morphine withdrawal. Frequency, duration and latency of each pattern was measured, and a cluster analysis allowed discerning the structure of behaviour. Several physical signs and the Gellert-Holtzman score were also evaluated. The data revealed that writhing responses linearly changed in a dose-related fashion, and mastication was also enhanced after naloxone. Wet-dog shakes and jumping changed following an U-shaped curve. Significant changes in weight loss were found to be dose-dependent, and highly correlated to diarrhea. Learning effects were found to reliably affect exploration, writhing responses and some physical signs. The Gellert-Holtzman score was gradually enhanced after naloxone, being affected by learning as well. Naloxone affected lying and self-care responses in placebo rats. To sum up, the data indicated that: i) classic signs are useful, although most of them are disrupted by high naloxone or affected by learning effects, ii) the Gellert-Holtzman score was validated in this study, and iii) mastication and weight loss are good indicators of naloxone-precipitated morphine withdrawal, representing the basis of an etho-score which is herein proposed.     

The physical dependence liabilities of oxybutynin and morphine in rats

The anticholinergic/antispasmodic agent oxybutynin does not induce physical dependence in rats when administered by oral gavage twice daily for 40 days; nor did challenge with naloxone precipitate withdrawal signs in these (oxybutynin-treated) animals. In contrast, morphine treatment resulted in a high degree of physical dependence as evidenced by the withdrawal signs noted after treatment was halted. Challenge with naloxone also induced severe withdrawal signs in morphine-treated rats. Withdrawal signs characterised by squealing, teeth chattering and "wet-dog" shakes were seen in one from five morphine-treated rats challenged with oxybutynin.