Modification of quasi-morphine withdrawal with serotonin agonists and antagonists: evidence for a role of serotonin in the expression of opiate withdrawal

Behavioral effects of fatty acid amide hydrolase inhibition on morphine withdrawal symptoms

Chronic morphine exposure causes tolerance and dependence. The cessation of morphine consumption induces a withdrawal syndrome that may involve cannabinoids and is characterized by undesirable psychological and physical signs. The present study examined whether augmentation of the endocannabinoid system by inhibition of fatty acid amide hydrolase could suppress the morphine withdrawal syndrome in morphine-addicted rats. Morphine dependency was induced by 7 consecutive days of morphine injection. The morphine-addicted rats received URB597 (1, 0.5, 0.3, 0.1, 0.03 mg/kg), a fatty acid amide hydrolase inhibitor, before the precipitation of morphine withdrawal syndromes by naloxone. Withdrawal symptoms including jumping, teeth chattering, paw tremor, wet dog shakes, face grooming, penis licking, standing, rearing, sniffing and percent of weight loss were recorded during 30 min after naloxone injection. The results showed that the morphine withdrawal precipitated rats had significantly more withdrawal symptoms than naive control rats and the administration of URB597 (all doses except 0.03 mg/kg) reduced most of the morphine withdrawal symptoms. We conclude that the administration of URB597 modulated morphine withdrawal symptoms. This finding shows that endocannabinoids interact with the opioid system during the morphine withdrawal period and that potentiation of the endogenous cannabinoid system by URB597 may be a new target strategy for the management of morphine addiction.

Mu and kappa opioid receptor agonists antagonize icilin-induced wet-dog shaking in rats

Icilin is a cooling agent that precipitates vigorous wet-dog shakes in rats after acute i.p. administration. Recent research has emphasized the peripheral agonist properties (e.g. activation of transient receptor potential channels, TRPM8 and TRPA1) of icilin rather than its unusual and pronounced behavioral effects, often classified as quasi-morphine withdrawal. We tested selective opioid receptor agonists against icilin-induced wet-dog shakes in rats. Shaking was antagonized following s.c. pretreatment with the mu agonists, morphine (1, 2, 3 mg/kg) and buprenorphine (0.10 mg/kg) or the kappa agonists, nalfurafine (0.02, 0.04 mg/kg) and U50,488H (5 mg/kg). Pretreatment with ICI 204,448 (1, 5, 10 mg/kg), the peripherally directed kappa agonist, or the delta agonist, SNC 80 (0.30, 1, 3, 10 mg/kg), had no marked effect on the incidence of shaking. We conclude that (a) icilin can trigger shaking via interactions within the central nervous system and (b) mu and kappa opioid receptors are involved in suppressing this stimulant behavior.

Absence of quasi-morphine withdrawal syndrome in adenosine A2A receptor knockout mice

RATIONALE

Caffeine and other methylxanthines induce behavioral activation and anxiety responses in mice via antagonist action at A2A adenosine receptors. When combined with the opioid antagonist naloxone, methylxanthines produce a characteristic quasi-morphine withdrawal syndrome (QMWS) in opiate-naive animals.

OBJECTIVES

The aim of this study was to establish the role of A2A receptors in the quasi-morphine withdrawal syndrome induced by co-administration of caffeine and naloxone and in the behavioral effects of caffeine.

METHODS

We have used A2A receptor knockout (A(2A)R(-/-)) mice in comparison with their wild-type and heterozygous littermates to measure locomotor activity in the open field and withdrawal symptoms induced by caffeine and naloxone. Naïve wild-type and knockout mice were also examined for enkephalin and dynorphin mRNA expression by in situ hybridization and for mu-opiate receptor by ligand binding autoradiography to check for possible opiate receptor changes induced by A2A receptor inactivation.

RESULTS

Caffeine increases locomotion and anxiety in wild-type animals, but it has no psychomotor effects in A(2A)R(-/-) mice. Co-administration of caffeine (20 mg/kg) and naloxone (2 mg/kg) resulted in a severe quasi-morphine withdrawal syndrome in wild-type mice that was almost completely abolished in A(2A)R(-/-) mice. Heterozygous animals exhibited a 40% reduction in withdrawal symptoms, suggesting that there is no genetic/developmental compensation for the inactivation of one of the A(2A)R alleles. A(2A)R(-/-) and wild-type mice have similar levels of striatal mu-opioid receptors, thus the effect is not due to altered opioid receptor expression.

CONCLUSIONS

Our results demonstrate that A2A receptors are required for the induction of quasi-morphine withdrawal syndrome by co-administration of caffeine and naloxone and implicate striatal A2A receptors and mu-opiate receptors in tonic inhibition of motor activity in the striatum.

Prenatal opiate withdrawal activates the chick embryo hypothalamic pituitary-adrenal axis and dilates vitelline blood vessels via serotonin(2) receptors

Opiate withdrawal during pregnancy may occur because of voluntary or forced detoxification, or from rapid cycling associated with exposure to short-acting "street" opiates. Thus, animal modeling of prenatal withdrawal and development of potential therapeutic interventions is important. Direct developmental effects of opiates and/or withdrawal can be studied using a chick model. In ovo administration of the long-acting opiate N-desmethyl-l-alpha-noracetylmethadol (NLAAM) induces opiate dependence in the chick embryo. We examined activation of the hypothalamic-pituitary-adrenal (HPA) axis (assessed via serum corticosterone) and hemodynamic changes (assessed as changes in apparent diameter of vitelline (extraembryonic) blood vessels) after chronic NLAAM exposure and naloxone (Nx)-precipitated withdrawal during late stages of embryogenesis. Nx-precipitated withdrawal increased corticosterone 2- to 4.5-fold and diameters of vitelline blood vessels by 15 to 45%. NLAAM exposure itself did not effect these measures. In a second set of experiments, isobutylmethylxanthine (IBMX), a phosphodiesterase inhibitor, was injected into eggs with embryos. IBMX similarly increased corticosterone and vitelline vessel diameter, with a similar time course and response magnitude. Previous studies found that serotonin(2) (5-HT(2)) receptors were involved in other withdrawal manifestations, so we determined whether they were likewise involved. Pretreatment with the 5-HT(2) antagonist ritanserin completely blocked HPA axis activation and vasodilation associated with both Nx-precipitated withdrawal and IBMX administration. This indicates that 5-HT(2) receptors, directly or indirectly, mediate these withdrawal manifestations in the chick embryo.

Embryonic "binge" cocaine exposure alters neural-immune and neural-endocrine interactions in young chickens: involvement of serotonin(2) receptors

As part of our characterization of the developmental consequences of prenatal cocaine exposure, cocaine was injected into eggs containing viable chicken embryos on embryonic day (E) 18 and the fever response to the endotoxin lipopolysaccharide (LPS) and a delayed-type hypersensitivity response to phytohemagglutinin (PHA) were assessed postnatally. E18 cocaine exposure did not affect basal body temperature. LPS induced a fever in the chicks at 4 h post-injection on post-hatch day (D) 4 and 2 h post-injection on D24. E18 cocaine exposure suppressed the peak LPS-induced fever by 50% at both ages. E18 cocaine exposure also suppressed the hypersensitivity reaction to an intradermal injection of PHA on D17, while having no effect on the response to a saline injection. To determine the importance of serotonin(2) (5-HT(2)) receptors in the developmental toxicity of cocaine, varying doses of the 5-HT(2) antagonist ritanserin were injected on E17 followed by cocaine on E18. Ritanserin, like cocaine, did not alter basal temperature, but it dose-relatedly attenuated or blocked cocaine's effect on LPS-induced fever on both D4 and D24. Ritanserin pretreatment was also able to block the blunted isolation stress response seen in D16 chicks following E18 cocaine exposure. Thus, late prenatal cocaine exposure significantly alters adaptive fever and hypersensitivity responses, and embryonic 5-HT(2) receptors played a mediating role in the fever effect.

Late embryonic ritanserin exposure fails to alter normal responses to immune system stimulation in young chicks

Prior studies in our laboratory have demonstrated that prenatal treatment with the serotonin2 (5-HT2) antagonist ritanserin is effective in blocking some of the lethal, dysmorphic, cardiovascular, and behavioral consequences of excessive direct or indirect stimulation of 5-HT2 receptors in the developing chicken. The efficacious dose range for ritanserin in these studies had very little or no effect on the above measures of toxicity when administered alone. In the present study, we extend our characterization of ritanserin's potential toxicity, or lack thereof, to include the normal behavioral and endocrine responses to immune system stimulation by the endotoxin lipopolysaccharide (LPS). LPS administration induces a syndrome collectively known as sickness behavior, manifest as altered thermoregulatory processes leading to fever, and increased serum concentrations of neuroendocrine hormones, including corticosterone. These survival-promoting responses to LPS were assessed in young chickens that had been treated with doses of ritanserin ranging from 0 to 2.7 mg/kg on embryonic day 17 (E17). When sickness behavior was assessed in 5-7-day-old chicks 1 h post-LPS injection, E17 ritanserin-treated subjects did not differ from controls. At 4-6 h post-LPS, 4-day-old chicks displayed a robust fever, and E17 ritanserin did not affect the magnitude of this response. Similarly, E17 ritanserin treatment failed to affect corticosterone concentrations 2 h post-LPS in 14-day-old chicks. Thus, ritanserin treatment during late embryogenesis, a time when it is effective against direct and indirect acting 5-HT2 agonists, failed to modify the survival promoting and beneficial interactions between the nervous, endocrine, and immune systems that are elicited following immunostimulation.

Modification of naloxone-induced withdrawal signs by dextromethorphan in morphine-dependent mice

In the present study the effect of dextromethorphan on naloxone-induced withdrawal signs in morphine-dependent mice was examined. In addition, the modulatory role of dopaminergic mechanisms upon the effect of dextromethorphan was investigated. Mice were rendered dependent on morphine by subcutaneous (s.c.) injections of morphine sulfate three times a day for 3 days, and withdrawal signs were induced by intraperitoneal (i.p.) administration of naloxone 2 h after the 10th injection of morphine sulfate on day 4. Dextromethorphan (20-50 mg/kg, i.p.) caused a significant decrease in withdrawal jumping, paw-shakes, grooming, burrows, writhing and diarrhea in morphine-dependent mice. The mixed dopamine D1/D2 receptor agonist apomorphine (0.5 and 1 mg/kg, s.c.) reduced the response induced by dextromethorphan. The effect of apomorphine was blocked by the dopamine D1 receptor antagonist SCH 23390 (R-(+)-8-chloro-2,3,4,5-tetrahydro-3-methyl-5-phenyl-1H-3-benzazepine-7- ol maleate) (0.5 and 1 mg/kg, i.p.) but not by the dopamine D2 receptor antagonist sulpiride (25 and 50 mg/kg, s.c.) nor the peripheral dopamine receptor antagonist domperidone (5 and 10 mg/kg, s.c.). These results suggest that the dopaminergic system(s) may in part mediate the suppressive action of the NMDA receptor antagonist dextromethorphan on naloxone-induced withdrawal signs in morphine-dependent mice.

Relationships between midembryonic 5-HT2 agonist and/or antagonist exposure and detour learning by chickens

The importance of serotonin (5-HT) as both a transmitter and a regulatory signal during development of many species is well established. The availability of 5-HT receptor subtype agonists and antagonists will enable pharmacological dissection of the importance of one or more of the 5-HT receptors for their involvement in the mediation of developmental insults by drugs that are less selective but include actions upon serotonergic function. Such insults include exposure to cocaine or opiate withdrawal, both of which are blocked or attenuated by 5-HT2 antagonists. The 5-HT2 receptor agonist dimethoxyiodophenylaminopropane (DOI), like cocaine, causes vasoconstriction during embryogenesis, herniated umbilici in hatchlings, and altered detour learning by young chickens after injection into eggs at late stages of embryogenesis. The 5-HT2 antagonist ritanserin (RIT) blocks or significantly attenuates these effects. This study describes an effect of DOI on posthatch detour learning when injected earlier during embryogenesis (i.e., on embryonic day 12, E12) which is opposite its effect when injected later (i.e., on E15). Both effects are blocked by an inactive dose of RIT (0.3 mg/kg egg) and by a higher dose of RIT (0.9 mg/kg egg), which itself retards posthatch detour learning following E12 injection. Thus, excessive stimulation or blockade of 5-HT2 receptors around midembryogenesis can cause a similar behavioral teratogenic outcome. The data are discussed in relation to the likelihood that potential use of 5-HT2 antagonists for treating pregnant women and their fetuses who are not at risk is nil.

Excessive stimulation of serotonin2 (5-HT2) receptors during late development of chicken embryos causes decreased embryonic motility, interferes with hatching, and induces herniated umbilici

The existence and functional significance of 5-HT2 receptors in chicken embryos was studied by injecting the selective agonist dimethoxyiodophenylaminopropane (DOI), alone or in conjunction with the selective 5-HT2 antagonist ritanserin (RIT), into domestic chicken eggs with embryos of varying ages. DOI caused dose-dependent reductions in hatchability and herniated umbilici in hatchlings. These effects were observed after injection early, mid, or late during embryonic development, with evidence of the toxic effects of DOI being greater in older embryos, probably due to 5-HT2 receptor activation late in development, even after injecting DOI as early as on day 3 of embryogenesis. This is based upon the fact that embryos in eggs injected with DOI early continued to develop apparently normally, failing to hatch, often after pipping their shells. Additionally, those that hatched often did so with herniated umbilici, as did late-exposed embryos, indicating that DOI's effects upon this organ were most likely mediated during the prehatching period (i.e., days 18-20). The agonist's selectivity was confirmed by the capacity of RIT to dose dependently block both of these toxic effects of DOI. Reduced embryonic motility monitored on day 19, after injection of DOI on the evening of day 18, suggests that excessive activation of 5-HT2 receptors late during development of this species interferes with some normal embryonic behaviors and physiological changes necessary for inducing and/or maintaining the hatching process.

Nicotine attenuates naloxone-induced jumping behaviour in morphine-dependent mice

In the present study the effect of nicotine on naloxone-induced jumping behaviour in morphine-dependent mice was examined. In addition, the modulatory role of dopaminergic, adrenergic and cholinergic mechanisms upon the effect of nicotine were investigated. Animals were rendered dependent on morphine by subcutaneous (s.c.) injections of morphine sulfate 3 times a day for 3 days, and jumping behaviour was induced by intraperitoneal (i.p.) administration of naloxone 2 h after the tenth injection of morphine sulfate on day 4. Nicotine (0.001-2 mg/kg s.c.) caused a significant decrease in withdrawal jumping behaviour in morphine-dependent mice. The effect of nicotine was blocked by the central nicotinic antagonist mecamylamine (0.01-0.1 mg/kg i.p.) but not by the peripheral nicotinic antagonist hexamethonium (0.01 and 0.1 mg/kg i.p.) nor the muscarinic receptor antagonist atropine (2.5-10 mg/kg i.p.). The dopamine receptor antagonist SCH 23390 (R-(+)-8-chloro-2,3,4,5-tetrahydro-3-methyl-5- phenyl-1H-3-benzazepine-7-ol maleate) (0.01-0.5 mg/kg s.c.) reduced the response induced by nicotine. The dopamine receptor antagonist sulpiride (25 and 50 mg/kg s.c.) and the adrenoceptor antagonists phenoxybenzamine (5 and 10 mg/kg i.p.) and propranolol (5 and 10 mg/kg i.p.) were without an effect. The results indicate that the effect of nicotine on naloxone-induced jumping is mediated by central nicotinic receptors.

Effects of 5-HT receptor antagonists on morphine-induced tolerance in mice

The effect of 5-HT receptor antagonists on tolerance to morphine antinociception was studied in mice. Slow release morphine suspension was injected subcutaneously (s.c.) in order to produce tolerance. When different doses of morphine (3, 6 and 9 mg/kg) were administered on the 4th day after injection of slow-release morphine suspension, tolerance to the test doses of morphine was observed. The tolerance obtained was decreased by pretreatment with the non-selective 5-HT receptor antagonist methysergide (1 and 2 mg/kg) or the 5-HT2 receptor antagonist ritanserin (1 and 2 mg/kg). When the 5-HT receptor antagonists were used on the 2nd and 3rd day after injection of slow-release morphine suspension or on the 4th day (60 min before last dose of morphine), a maximum reduction in morphine tolerance was observed on the 3rd day. Pretreatment of animals with metergoline (1 and 2 mg/kg) or mianserin (1 and 2 mg/kg) also decreased the tolerance to morphine. It may be concluded that at least a 5-HT2 receptor mechanism is involved in tolerance to morphine antinociception.

Effects of trazodone and m-chlorophenylpiperazine (m-CPP) on acute dependence in mice

The antidepressant trazodone and its main metabolite, m-CPP, having an antiserotoninergic and serotoninergic activity respectively, were studied in an acute dependence model in mice, to establish whether 5-hydroxytryptaminergic systems are involved in the manifestations of acute opiate dependence and in its development. When drugs were administered 15 min before naloxone, all signs of abstinence decreased, with the exception of teeth chattering that was increased by m-CPP and unaffected by trazodone. When injected 15 min before morphine, jump episodes were decreased by the highest doses of both drugs, while teeth chattering was decreased by m-CPP only. When administered 1 h before morphine, trazodone increased paw and head shakes and mCPP decreased teeth chattering and both left the other signs unaffected. Serotoninergic systems seem to have a significant role in events involved in the withdrawal syndrome and a minor one in those leading to the development of dependence.

Long-term effects of neonatal exposure to isobutylmethylxanthine. II. Attenuation of acute morphine withdrawal in mature rats

An acute model of morphine withdrawal was used to determine if neonatal exposure to 3-isobutyl-1-methylxanthine (IBMX) would cause alterations in the expression of withdrawal in the adult rat. IBMX induces a quasi-morphine withdrawal syndrome (QMWS), which is almost identical to true morphine withdrawal both behaviorally and neurochemically. Transient IBMX treatment during infancy (on days 7-10 of life) caused an attenuated suppression of fixed ratio (FR) responding during acute morphine withdrawal in adulthood; however, there appeared to be no attenuation of withdrawal-induced hypothermia. The attenuated behavioral response was not due to an altered ability to express withdrawal, as these rats did not react differently to various doses of IBMX plus naloxone (i.e., varying severities of quasi-morphine withdrawal) in adulthood. Coadministration of the serotonin (5-HT) antagonist mianserin with IBMX in the neonate prevented the effects of IBMX. Both the mianserin-treated and the IBMX plus mianserin-treated groups had increased levels of [3H]naloxone binding in brainstem, while IBMX treatment alone apparently had no significant effect. None of the neonatal drug treatments affected [3H]naloxone binding in frontal cortex. Thus, the long-term effects of IBMX on the opioid withdrawal response cannot be explained by changes in the number of opioid binding sites (labelled with [3H]naloxone) within the brain. The results indicate that exposure to a methylxanthine, and thus quasi-morphine withdrawal, during development results in long-lasting alterations of a system which is involved in opioid withdrawal. Because coadministration of mianserin prevented the effects of IBMX, 5-HT and 5-HT2 receptors are implicated in these effects.

Long-term effects of neonatal exposure to isobutylmethylxanthine. I. Retardation of learning with antagonism by mianserin

Pregnant women regularly ingest the methylxanthines, caffeine and theophylline, during pregnancy and lactation. Also, theophylline is used to treat apnea in premature infants. In this study, rat pups were treated with 3-isobutyl-1-methylxanthine (IBMX), on days 7-10 of life. Transient IBMX treatment during infancy caused a retardation of acquisition of a delayed reinforced autoshaped lever touch response in adulthood. Treated rats required more trials to learn the task, but did not show altered exploratory activity in the operant chambers. Coadministration of the serotonin (5-HT) antagonist mianserin with IBMX was able to attenuate significantly the effects of IBMX in both males and females, even though mianserin treatment alone caused an apparent learning deficit in the males. The results indicate that 5-HT and 5-HT receptors are important during development for normal expression of a specific cognitive function later in life. Furthermore, a 5-HT system appears to play a role in the mechanism whereby perinatal methylxanthine exposure could lead to learning impairments or other undesirable behavioral consequences. The use of IBMX in developing rats may also offer a model for studying the long-term consequences of the expression of opioid withdrawal during the neonatal period, since this agent induces a quasi-morphine withdrawal syndrome (QMWS) in mature rats. It is of interest that mianserin can block or attenuate effects of both quasi- and true morphine withdrawal.

The serotonin2 antagonist ritanserin blocks quasi-morphine withdrawal at a time when mianserin is no longer effective

A quasi-morphine withdrawal syndrome (QMWS), produced in opiate-naive rats with an injection of isobutylmethylxanthine (IBMX) and the opioid antagonist naloxone, allows one to study the expression of opiate withdrawal in the absence of the acute or chronic effects of opiates and the adaptive processes termed dependence. The allegedly selective and long-acting serotonin2 (5-HT2) antagonist ritanserin attenuated the QMWS-induced suppression of fixed ratio (FR) operant responding, which is a sensitive measure of the expression of a QMWS. When administered 30 min prior to precipitation of the QMWS, the lowest dose of ritanserin tested (0.158 mg/kg) was the most effective in blocking the expression of withdrawal; however, there was not complete reversal of the behavioral suppression. Acutely, the two higher doses of ritanserin tested (2.5 and 10 mg/kg) suppressed responding when given alone. This may have masked their ability to attenuate a QMWS. At a dose of 2.5 mg/kg, ritanserin completely blocked the QMWS-induced suppression of responding 24 h post-administration, at a time when its actions at other receptors (e.g., alpha 2) have dissipated. At an equivalent dose, the shorter-acting 5-HT2 antagonist mianserin was unable to attenuate the QMWS-induced suppression of FR operant responding 24 h post-administration. The 5-HT2 antagonists reportedly produce a paradoxical down-regulation of 5-HT2 binding sites upon chronic treatment, rather than the expected supersensitivity. Chronic treatment with ritanserin (2.5 mg/kg/day for 7 days), but not mianserin (same regimen), attenuated a QMWS 24 h after the final injection, thus supporting with a functional measure, the down-regulation of such binding sites by ritanserin.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence of single dose opioid dependence in 12- to 14-day-old chicken embryos

We have previously reported that chicken embryos injected with a single dose of methadone (Meth) on day 3, 7 or 11 of embryogenesis fail to show dependence on day 14, measured as a significant overshoot in motility above baseline after challenge with the opioid antagonist naloxone (Nx). Constant infusion of Meth from day 7 to 14 also failed to produce evidence of dependence on day 14. To address the question of whether the 14-day-old embryo is capable of expressing withdrawal, isobutylmethylxanthine (IBMX), a compound that produces quasi-opioid withdrawal, was injected directly into the embryo, resulting in a significant increase in motility. To determine whether the 14-day-old embryo could also express true opioid withdrawal, the embryos were injected with various doses of Meth or morphine (Morph), followed at different time intervals by injections of varying doses of Nx. A high dose of Morph followed 24 hours later by a low dose of Nx produced evidence of withdrawal, as did a low dose of Meth followed 1 hour later by a higher dose of Nx, U50488H, a selective kappa agonist, had no effect on motility in the 14-day-old embryo, suggesting that the decrease in motility seen after Meth was not mediated by a kappa receptor. Pretreatment with the irreversible mu antagonist, beta-funaltrexamine (B-FNA), blocked the decrease in motility seen after Meth and also prevented the overshoot in motility when Nx was given 1 hour post-Meth. We were also able to demonstrate dependence/withdrawal in the 12-day-old embryo, but higher doses of both Meth and Nx were required.(ABSTRACT TRUNCATED AT 250 WORDS)