Withdrawal In Morphine-dependent Rats Research Articles

Modulation of morphine physical dependence and discriminative stimulus effects by ovarian hormones: Role of estradiol

Ovarian hormones influence the activity of endogenous opioids, and exogenous administration of estradiol reduces opioid intake and opioid seeking in animal models of opioid reward and reinforcement. The purpose of this study was to examine the effects of ovarian hormones on the discriminative stimulus effects of morphine and naloxone-precipitated opioid withdrawal. To this end, separate groups of ovariectomized female rats were trained to discriminate the stimulus effects of either 3.0 or 10 mg/kg morphine, and substitution tests were conducted with estradiol or progesterone alone and in combination with morphine. At the conclusion of discrimination testing, rats were treated chronically with estradiol, progesterone, or their combination, and challenged with naloxone to measure opioid-like withdrawal symptoms. Finally, the effects of estradiol, progesterone, and their combination were examined on naloxone-precipitated withdrawal in morphine-dependent rats. Neither estradiol nor progesterone substituted for the morphine discriminative stimulus, but estradiol significantly increased the potency of morphine in rats trained to discriminate 10 mg/kg but not 3 mg/kg morphine. When administered chronically, neither hormone nor their combination produced an opioid-like withdrawal syndrome following a naloxone challenge. Acute administration of estradiol, but not progesterone or a combination of estradiol and progesterone, significantly reduced naloxone-precipitated weight loss in morphine-dependent rats. These data indicate that estradiol influences the behavioral effects of morphine, possibly by increasing endogenous tone at mu opioid receptors.

The role of adenosine A1 receptors in the nucleus accumbens during morphine withdrawal.

Opioids are effective analgaesic agents, but serious adverse effects such as tolerance and withdrawal contribute to opioid dependence and limit their use. Opioid withdrawal is a common occurrence in human opiate addicts that is not life-threatening. Studies have shown that the mesocorticolimbic system, especially the nucleus accumbens, is an important region in drug addiction and adenosinereceptors play a modulatory role in the mechanism of action of drug dependence and withdrawal. The aim of this study was to investigate the effects of the selective A1 receptor agonist CPA (N6 -cyclopentyladenosine) on withdrawal symptoms, and the concentration of dopamine and noradrenaline in the nucleus accumbens and locomotor activity behaviour during naloxone-precipitated withdrawal in morphine-dependent rats. The local administration of CPA (1.5, 3.0, and 6.0mmol/L bilateral 250nL) into the nucleus accumbens decreased the Gellert-Holtzman withdrawal scale, and increased concentrations of dopamine and noradrenaline in the same region during naloxone-induced withdrawal. Our findings suggest that administration of the A1 receptor agonist significantly decreased withdrawal behaviours and increased dopamine and noradrenaline concentrations in opioid withdrawal in a dose-dependent manner. These results demonstrate that adenosine receptors should be examined as a potential mechanism that could be exploited for the treatment of morphine withdrawal.

Methocinnamox Produces Long-Lasting Antagonism of the Behavioral Effects of µ-Opioid Receptor Agonists but Not Prolonged Precipitated Withdrawal in Rats.

A novel µ-opioid receptor antagonist, methocinnamox (MCAM), attenuates some abuse-related and toxic effects of opioids. This study further characterized the pharmacology of MCAM in separate groups of rats using procedures to examine antinociception, gastrointestinal motility, and withdrawal in morphine-dependent rats. Antinociceptive effects of opioid receptor agonists were measured before and after MCAM (1-10 mg/kg) using warm water tail withdrawal and sensitivity to mechanical stimulation in inflamed paws (complete Freund's adjuvant). Before MCAM, morphine, fentanyl, and the κ-opioid receptor agonist spiradoline dose dependently increased tail-withdrawal latency from 50°C water; MCAM attenuated the antinociceptive effects of morphine and fentanyl, but not spiradoline. Morphine increased sensitivity to mechanical stimulation and decreased gastrointestinal motility, and MCAM blocked both effects. These antagonist effects of 10 mg/kg MCAM were persistent, lasting for 2 weeks or longer. Withdrawal emerged after discontinuation of morphine treatment or administration of 10 mg/kg MCAM or 17.8 mg/kg naloxone; other than the day of antagonist administration when withdrawal signs were greater in rats that received antagonist compared with rats that received vehicle, there was no difference among groups in directly observable withdrawal signs or decreased body weight. These results confirm that MCAM is a selective µ-opioid receptor antagonist with an exceptionally long duration of action, likely due to pseudoirreversible binding. Despite its sustained antagonist effects, the duration of withdrawal precipitated by MCAM is not different from that precipitated by naloxone, suggesting that the long duration of antagonism provided by MCAM could be particularly effective for treating opioid abuse and overdose. SIGNIFICANCE STATEMENT: The opioid receptor antagonist MCAM attenuates some abuse-related and toxic effects of opioids. This study demonstrates that MCAM selectively antagonizes multiple effects mediated by µ-opioid receptor agonists for 2 weeks or longer, and like naloxone, MCAM precipitates withdrawal in morphine-dependent rats. Despite this persistent antagonism, withdrawal signs precipitated by MCAM are not significantly different from signs precipitated by naloxone or occurring after discontinuation of morphine, suggesting that using MCAM for opioid abuse or overdose would not produce sustained withdrawal.

Naloxone-precipitated withdrawal causes an increase in impulsivity in morphine-dependent rats

Opiate dependence is associated with increased impulsivity in both humans and animals. Although the state of withdrawal appears to contribute to this effect, a causal relationship has not been shown. Here, we test whether precipitating withdrawal in morphine-dependent rats through naloxone can cause increased impulsivity. Rats were trained on a delay discounting task and then randomly assigned to either a dependent group that received a nightly 30 mg/kg subcutaneous dose of morphine or a naive group that received nightly saline. Once dependence was established, 2-day test delay discounting curves were determined 1 h after three doses of naloxone (0, 0.25, 0.5 mg/kg). In dependent rats both doses of naloxone caused increased preference for the small reward at short delays. Naloxone had no effect on delay discounting in naive rats. We conclude that precipitating withdrawal in dependent rats can cause increased impulsivity.

The kappa-opioid receptor antagonist, nor-binaltorphimine (nor-BNI), decreases morphine withdrawal and the consequent conditioned place aversion in rats

Much data suggest that the binding of dynorphin-like peptides to kappa-opioid receptors (KORs) during the administration of and withdrawal from a variety of addictive drugs is aversive and serves to limit the reinforcing properties of those drugs and to enhance tolerance, withdrawal, and the probability of stress-induced relapse. In this study, we examined the role of KORs in mediating opioid withdrawal and its aversive consequences in rats. We found that selective blockade of KORs by i.p. administration of 20mg/kg nor-binaltorphimine (nor-BNI) 5h prior to naltrexone-precipitated withdrawal in morphine-dependent rats decreased feces excreted during a 30-min withdrawal session. More critically, this injection of nor-BNI decreased the subsequent conditioned place aversion (CPA) for the withdrawal chamber 2 days later. The subsequent finding that administration of nor-BNI 2h following withdrawal did not affect the CPA 2 days later suggested that nor-BNI reduced the CPA in the prior experiment because it reduced the aversive effects of withdrawal, not because it reduced the aversive/anxiogenic effects of the withdrawal chamber at the time of CPA testing. These data indicate that the binding of dynorphin-like peptides to KORs during opioid withdrawal serves to enhance withdrawal and its aversive consequences and suggest that selective KOR antagonists may be useful in reducing these aversive effects and consequent relapse.

Voluntary and forced exercises prevent the development of tolerance to analgesic effects of morphine in rats.

Morphine is widely used to treat chronic pain. However, its utility is hindered by the development of tolerance to its analgesic effects. Despite the renowned beneficial effects of physical exercise on cognitive functions and signs of morphine withdrawal in morphine-dependent rats, little is known about the roles of voluntary and forced exercises in tolerance to analgesic effect of morphine in rats. In this study, rats were injected with 10 mg/kg of morphine, once daily, SC over a period of 8 days of either voluntary or treadmill exercise. Following these injections, the percent of maximum possible effect (%MPE) of morphine was measured on the 1(st), 4(th), and 8(th) days by hot plate test. Both voluntary and forced exercises significantly increased pain threshold compared to the sedentary group (P<0.05). Voluntary and forced exercises also significantly increased potency of morphine compared to sedentary morphine group (P<0.05). Thus, we concluded that voluntary and forced exercises blocked the development of tolerance during 8 daily simultaneously treatments. When exercising rats were returned to sedentary conditions, sensitivity to the analgesic effects of morphine increased significantly and persisted during sedentary period in the exercising rats. In other words, %MPE of the exercising morphine-group increased significantly compared to saline group (P<0.05). Our results showed that voluntary and forced exercises may be possible methods for treating the development of tolerance to analgesic effect of morphine in rats.

Descending Facilitatory Pathways from the Rostroventromedial Medulla Mediate Naloxone-Precipitated Withdrawal in Morphine-Dependent Rats

Opioids produce analgesic effects, and extended use can produce physical dependence in both humans and animals. Dependence to opiates can be demonstrated by either termination of drug administration or through precipitation of the withdrawal syndrome by opiate antagonists. Key features of the opiate withdrawal syndrome include hyperalgesia, anxiety, and autonomic signs such as diarrhea. The rostral ventromedial medulla (RVM) plays an important role in the modulation of pain and for this reason, may influence withdrawal-induced hyperalgesia. The mechanisms that drive opiate withdrawal-induced hyperalgesia have not been elucidated. Here, rats made dependent upon morphine received naloxone to precipitate withdrawal. RVM microinjection of lidocaine, kynurenic acid (excitatory amino acid antagonist) or YM022 (CCK2 receptor antagonist) blocked withdrawal-induced hyperalgesia. Additionally, these treatments reduced both somatic and autonomic signs of naloxone-induced withdrawal. Spinal application of ondansetron, a 5HT3 receptor antagonist thought to ultimately be engaged by descending pain facilitatory drive, also blocked hyperalgesia and somatic and autonomic features of the withdrawal syndrome. These results indicate that the RVM plays a critical role in mediating components of opioid withdrawal that may contribute to opioid dependence. Perspective Manipulations targeting these descending pathways from the RVM may diminish the consequences of prolonged opioid administration-induced dependence and be useful adjunct strategies in reducing the risk of opioid addiction.

Effect of CCK-B receptor antagonist on [Ca~(2+)]i, CaM activity and CaMK II α expression in hippocampal neurons during naloxone-precipitated withdrawal in morphine-dependent rats

Objective To investigate the effect of CCK-B receptor antagonist CR-2945 on cytoplasmic free calcium concentration ([Ca~(2+)]i), calmodulin (CaM) activity and calmodulin-dependent protein kinase Ⅱα(CaMK Ⅱα) expression in hippocampal neurons during naloxone-precipitated withdrawal in morphine-dependent rats. Methods Forty-five adult male Wistar rats weighing 180-240 g were randomly divided into 9 groups ( n = 5 each):morphine dependence group ( group MD) , normal saline group ( group NS), naloxone-precipitated withdrawal group ( group NPW ) , nucleus accumbens group ( group NA ) , amygdale group ( group A), lateral cerebral ventricle group (group LCV) , abdominal cavity (acute) group (group AC A) , abdominal cavity (chronic) group (group ACC) and placebo group (group P). Morphine dependence was induced by increasing doses of subcutaneous injection of morphine for 5 d and subcutaneous injection of morphine 50 mg/kg at 8:00 on 6th day. In group NS, equal volume of normal saline was injected instead of morphine. In group NPW, intraperitoneal nalxone 5 mg/kg was injected 1 h after the last subcutaneous injection of morphine. In group NA, A and LCV, CR-2945 10μg was injected into nucleus accumbens, amygdale and lateral ventricle 1 h after the last subcutaneous injection of morphine, and then intraperitoneal naloxone 5 mg/kg was injected 30 min later. In group ACA, CR-2945 1 mg/kg was injected 1 h after the last subcutaneous injection of morphine, and then intraperitoneal naloxone 5 mg/kg was injected 30 min later. In group ACC, CR-2945 1 mg/kg was injected simultaneously with morphine injection for 6 d, and intraperitoneal naloxone 5 mg/kg was injected 30 min after the last administration. In group P, normal saline was used instead of CR-2945, and the other procedures were the same as those in group LCV. Rats were killed and hippocampus was isolated. [Ca~(2+)]i and CaM activity were measured by flow cytometry. CaMK Ⅱα expression was determined by Western blot. Results [Ca~(2+) ]i, and CaM activity were significantly increased and CaMK Ⅱα expression was up-regulated in group MD compared with group NS (P 0.05) . Conclusion CCK-B receptor antagonist CR-2945 can inhibit naloxone-precipitated withdrawal responses through increasing [Ca~(2+)]i and CaM activity and up-regulating CaMK Ⅱα expression in hippocampal neurons in morphine-dependent rats. Key words: Receptor; cholecystokinin B; Morphine dependence; Naloxone; Substance withdrawal syndrome; Hippocampus; Neurons; Calcium; Calmodulin; Calcium-calmodulin-dependent protein kinase type 2

The C-terminal amidated analogue of the substance P (SP) fragment SP 1–7 attenuates the expression of naloxone-precipitated withdrawal in morphine dependent rats

We previously demonstrated that intracerebroventricular (i.c.v.) administration of the substance P (SP) aminoterminal fragment SP 1–7 attenuates the expression of morphine withdrawal in the male rat. In this study we have used a synthetic analogue of this peptide, i.e. the SP 1–7 amide showing higher binding potency than the native heptapeptide, in a similar experimental set-up. Thus, Wistar male rats were made tolerant to morphine by daily injections of the opiate during 8 days. Following peptide administration (i.c.v.) and a subsequent naloxone challenge a variety of physical syndromes of withdrawal were recorded. We observed that the SP 1–7 amide potently and dose-dependently reduced several signs of reaction to morphine withdrawal. Interestingly, the effect of the peptide amide was significantly attenuated by the addition of the sigma agonist (+)-SKF-10047. We conclude that the SP 1–7 amide mimics the effect of the native SP fragment and that the mechanisms for its action involve a sigma receptor site.

Anatomically dissociable effects of dopamine D1 receptor agonists on reward and relief of withdrawal in morphine-dependent rats.

Chronic opiate administration induces neuroadaptations within the nucleus accumbens (NAc) and ventral tegmental area (VTA) that can contribute to dependence. We have shown that morphine dependence shifts the behavioral consequences of D1 dopamine (DA) receptor signaling: systemic administration of a D1 receptor agonist is rewarding and blocks naloxone-precipitated withdrawal signs in morphine-dependent rats, but has minimal effects in nondependent rats. These data suggest that D1 receptors acquire the ability to regulate reward and withdrawal in morphine-dependent rats. The brain regions involved in these effects are not known. Studies were designed to test the hypothesis that the nucleus accumbens shell (NASh) and the ventral tegmental area (VTA) are important sites for mediating the behavioral effects of D1 receptor activation in morphine-dependent rats. The effects of microinjecting the D1 receptor agonist SKF 82958 into the NASh or the VTA on place conditioning and somatic withdrawal signs were studied in morphine-dependent and nondependent rats. Intra-NASh microinjection of SKF 82958 (1 microg/side) established conditioned place preferences in morphine-dependent but not nondependent rats, but had no effect on naloxone-induced place aversions or somatic withdrawal signs. Intra-VTA microinjection of SKF 82958 (2 microg) did not establish place preferences under any conditions, but blocked naloxone-induced place aversions without effects on somatic withdrawal signs. There is an anatomical dissociation between D1 receptor-mediated reward and relief of withdrawal in morphine-dependent rats. When combined, the individual effects of D1 receptor activation in the NASh and VTA on the affective signs of precipitated morphine withdrawal resemble those seen with systemic administration.

Low dose naltrexone administration in morphine dependent rats attenuates withdrawal-induced norepinephrine efflux in forebrain

The administration of low dose opioid antagonists has been explored as a potential means of detoxification in opiate dependence. Previous results from our laboratory have shown that concurrent administration of low dose naltrexone in the drinking water of rats implanted with subcutaneous morphine pellets attenuates behavioral and biochemical signs of withdrawal in brainstem noradrenergic nuclei. Noradrenergic projections originating from the nucleus tractus solitarius (NTS) and the locus coeruleus (LC) have previously been shown to be important neural substrates involved in the somatic expression of opiate withdrawal. The hypothesis that low dose naltrexone treatment attenuates noradrenergic hyperactivity typically associated with opiate withdrawal was examined in the present study by assessing norepinephrine tissue content and norepinephrine efflux using in vivo microdialysis coupled to high performance liquid chromatography (HPLC) with electrochemical detection (ED). The frontal cortex (FC), amygdala, bed nucleus of the stria terminalis (BNST) and cerebellum were analyzed for tissue content of norepinephrine following withdrawal in morphine dependent rats. Naltrexone-precipitated withdrawal elicited a significant decrease in tissue content of norepinephrine in the BNST and amygdala. This decrease was significantly attenuated in the BNST of rats that received low dose naltrexone pre-treatment compared to controls. No significant difference was observed in the other brain regions examined. In a separate group of rats, norepinephrine efflux was assessed with in vivo microdialysis in the BNST or the FC of morphine dependent rats or placebo treated rats subjected to naltrexone-precipitated withdrawal that received either naltrexone in their drinking water (5 mg/L) or unadulterated water. Following baseline dialysate collection, withdrawal was precipitated by injection of naltrexone and sample collection continued for an additional 4 h. At the end of the experiment, animals were transcardially perfused and the brains were removed for verification of probe placement. Low dose naltrexone pre-treatment significantly attenuated withdrawal-induced increases of extracellular norepinephrine in the BNST, with a smaller effect in the FC. These findings suggest that alterations in norepinephrine release associated with withdrawal may be attenuated in forebrain targets of noradrenergic brainstem neurons that may underlie reduced behavioral signs of withdrawal following low dose naltrexone administration.

Cross talk between nitric oxide and ERK1/2 signaling pathway in the spinal cord mediates naloxone-precipitated withdrawal in morphine-dependent rats

Our recent study has shown activation of spinal extracellular signal-regulated kinase-1 and -2 (ERK1/2), a member of the mitogen-activated protein kinase (MAPK) family, contributes to naloxone-precipitated withdrawal and withdrawal-induced spinal neuronal sensitization in morphine-dependent rats. However, the mechanism and significance of the spinal ERK1/2 activation during morphine dependence and withdrawal remain unknown. In this study, we reported that intrathecal (i.t.) pretreatment with either the non-selective nitric oxide synthase (NOS) inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME), neuronal NOS (nNOS) inhibitor 7-nitro indazole (7-NI), or the inducible NOS (iNOS) inhibitor aminoguanidine (AG), could reduce morphine withdrawal-induced increase of phospho-ERK1/2 (pERK1/2) expression in the rat spinal cord. On the other hand, attenuation of the spinal ERK phosphorylation by the MAPK kinase (MEK) inhibitor U0126 also could inhibit the increase of nNOS and iNOS expression in the spinal cord of morphine withdrawal rats. Inhibitory expression of pERK1/2 by i.t. NOS inhibitor L-NAME, 7-NI or AG and of nNOS and iNOS by i.t. U0126 in the spinal cord were accompanied by decreased scores of morphine withdrawal and the inhibited spinal Fos protein (a maker for neuronal excitation or activation) expression induced by morphine withdrawal. These findings suggest cross talk between nitric oxide (NO) and the ERK1/2 signaling pathway mediates morphine withdrawal and withdrawal-induced spinal neuronal sensitization in morphine-dependent rats.

Ionotropic glutamatergic neurotransmission in the ventral tegmental area modulates ΔFosB expression in the nucleus accumbens and abstinence syndrome in morphine withdrawal rats

The present study sought to assess whether the blockade of ionotropic glutamate receptors in the ventral tegmental area could modulate morphine withdrawal in morphine-dependent rats and the expression of stable ΔFosB isoforms in the nucleus accumbens during morphine withdrawal. Rats were injected (i.p.) with increasing doses of morphine for 1 week to develop physical dependence, and withdrawal was then precipitated by one injection of naloxone (2 mg/kg, i.p.). Abstinence signs such as jumping, wet-dog shake, writhing posture, weight loss, and Gellert-Holtzman scale score were recorded to evaluate naloxone-induced morphine withdrawal. Two ionotropic glutamate receptor antagonists, dizocilpine (MK-801) and 6, 7-dinitroquinnoxaline-2, 3-dione (DNQX), were microinjected unilaterally into the ventral tegmental area 30 min before naloxone precipitation. A second injection of naloxone (2 mg/kg i.p.) was given 1 h after the first naloxone injection to sustain a maximal level of withdrawal so that the expression of stable ΔFosB isoforms in the nucleus accumbens could be measured. This would enable determination of the correlation between the MK-801 or DNQX-induced decrease in somatic withdrawal signs and the change in neuronal activity in the nucleus accumbens. The results showed that both MK-801 and DNQX significantly alleviated all symptoms of morphine withdrawal except for weight loss and reduced the expression of stable ΔFosB isoforms within the nucleus accumbens. These data suggest that ionotropic glutamatergic neurotransmission in the ventral tegmental area regulates the levels of stable ΔFosB isoforms in the nucleus accumbens, which play a very important role in modulating opiate withdrawal.

Activation of the spinal ERK signaling pathway contributes naloxone-precipitated withdrawal in morphine-dependent rats

Extracellular signal-regulated kinase (ERK), a mitogen-activated protein kinases (MAPK), transduces a broad range of extracellular stimuli into diverse intracellular responses. Recent studies have showed that ERK activation in the supraspinal level involved in the development of drug dependence, especially in psychological dependence. In this study, we reported that the spinal ERK signaling pathway was activated by chronic morphine injection. There was a further increase in ERK activation after naloxone-precipitated withdrawal. Furthermore, attenuation of the spinal ERK phosphorylation by intrathecal a MAPK kinase (MEK) inhibitor U0126 or knockdown of the spinal ERK by antisense oligonucleotides not only decreased the scores of morphine withdrawal, but also attenuated withdrawal-induced allodynia, which were accompanied by decreased ERK phosphorylation in the spinal cord. The spinal ERK inhibition or knockdown also reduced morphine withdrawal-induced phosphorylation of cAMP response element binding protein (CREB), which is one of the important downstream substrates of ERK pathway, and Fos expression. The involvement of the spinal ERK in morphine withdrawal was supported by our finding that intrathecal N-methyl- d-aspartate receptor antagonist MK-801 or protein kinase C inhibitor chelerythrine chloride suppressed withdrawal-induced ERK activation in the spinal cord and attenuated morphine withdrawal symptoms. These findings suggest activation of the spinal ERK signaling pathway contributes naloxone-precipitated withdrawal in morphine-dependent rats.

Opiate Withdrawal-Induced Fos Immunoreactivity in the Rat Extended Amygdala Parallels the Development of Conditioned Place Aversion

Low doses of naloxone have been shown to affect the motivational aspects of opiate withdrawal in morphine-dependent rats. Conditioned place aversion to opiate withdrawal is one of the most sensitive of motivational indices of opiate withdrawal and is thought to be mediated by the basal forebrain. Expression of the transcription factor Fos is known to increase during opiate withdrawal, but its presence during low-dose antagonist-precipitated withdrawal has not previously been established. In order to determine if there is a relationship between withdrawal-induced neuronal activity and conditioned place aversion, immunocytochemical localization of Fos was examined in the basal forebrain of opiate-dependent animals receiving one of several doses of naloxone (0, 3.25, 7.5, 15, 30, or 1000 μg/kg). In separate groups of opiate-dependent animals, naloxone doses of 3.25 - 30 μg/kg were paired with a specific chamber in a single-pairing conditioned place aversion paradigm. Significant increases in both immunocytochemical detection of Fos and conditioned place aversion were seen at doses ≥ 7.5 μg/kg. The shell of the nucleus accumbens and central nucleus of the amygdala were most sensitive to low doses, thus supporting the hypothesis that the extended amygdala plays a role in opiate-induced condition place aversion.

Conditioning and opiate withdrawal.

The amygdala links neutral stimuli with the agony of overcoming drug addiction. The habitual behaviour of many opiate addicts means that the aversive symptoms of drug withdrawal are frequently experienced in specific environments1. Stimuli in these environments acquire some of the negative affective properties of opiate withdrawal through pavlovian conditioning, and subsequent exposure to these stimuli alone can then elicit a conditioned withdrawal response that is often associated with drug craving, drug seeking, and relapse back to compulsive drug use after a long abstinence1,2. We show here that selective excitotoxic lesions of the basolateral amygdala, part of the limbic forebrain, prevent the development of conditioned withdrawal in morphine-dependent rats.

210. CRF 1 receptor antagonists as novel putative antidepressants and anxiolytics

There is considerable evidence that CRF hypersecretion occurs in patients with major depression and to a lesser extent in certain anxiety disorders. These findings have led to the study of CRF1 receptor antagonists as a putative novel class of antidepressants/anxiolytic. This presentation will summarize the effects of a CRF1 receptor antagonist in a variety of well-characterized preclinical models predictive of clinical efficacy. The main findings we have recently obtained with a novel CRF1 receptor antagonist include: 1) attenuation of the ACTH and corticosterone response in the rate after exposure to swim stress; 2) attenuation of naltrexone-precipitated withdrawal in morphine dependent rats; 3) anxiolytic activity in rats in the open field paradigm; 4) attenuation of flumazanil-precipitated withdrawal in lorazepam-dependent rats; 5) increased time that rhesus monkeys spend in affiliative behaviors. These data suggest that CRF1 receptor antagonists may not only possess antidepressant and anxiolytic activity, but may be useful in treatment of opiate and benzodiazepine withdrawal.

Alteration in the brain content of substance P (1–7) during withdrawal in morphine-dependent rats

Previous studies have shown that substance P (SP) may modulate the abstinence reaction to opioid withdrawal. Its N-terminal fragment SP 1–7 may inhibit the intensity of the withdrawal reactions in morphine dependent mice. This study was designed to determine whether the endogenous concentrations of the SP 1–7 fragment in the brain are affected during naloxone-precipitated withdrawal in the male rat. The amounts of the peptide was assessed by a specific radioimmunoassay in extracts of discrete brain regions (including the cerebral cortex, hippocampus, hypothalamus, nucleus accumbens, striatum, substantia nigra, ventral tegmental area and the spinal cord) during morphine tolerance and withdrawal. The results indicated that the concentrations of SP 1–7 were significantly elevated in the ventral tegmental area both in morphine tolerant rats and during naloxone-precipitated withdrawal. During morphine withdrawal significant increases in the peptide concentration were also observed in the hypothalamus and the spinal cord. It was concluded that the enhanced content of SP 1–7 may also indicate the involvement of the SP system during opioid withdrawal in the rat. The enhanced production of SP 1–7 may reflect an increased release and/or metabolism of SP, which, in turn, counteracts the withdrawal.

CB1 cannabinoid receptor antagonist-induced opiate withdrawal in morphine-dependent rats.

Recent reports have provided evidence of a link between the endogenous brain cannabinoid system and the endogenous central opioid systems. Here we report that the selective CB1 receptor antagonist SR 141716A induced behavioral and endocrine alterations associated with opiate withdrawal in morphine-dependent animals in a dose-dependent manner and that naloxone induced an opiate withdrawal syndrome in animals made cannabinoid-dependent by repeated administration of the potent cannabinoid agonist HU-210. Additionally CB1 and mu-opioid receptor mRNAs were co-localized in brain areas relevant for opiate withdrawal such as the nucleus accumbens, septum, dorsal striatum, the central amygdaloid nucleus and the habenular complex. These results suggest that CB1 cannabinoid receptors may play a role in the neuroadaptive processes associated with opiate dependence, and they lend further support for the hypothesis of a potential role of cannabinoid receptors in the neurobiological changes that culminate in drug addiction.

P.5.043 Impulsive behaviour with and without alcoholism: Clinical correlates and personality characteristics

The present study sought to assess whether the blockade of ionotropic glutamate receptors in the ventral tegmental area could modulate morphine withdrawal in morphine-dependent rats and the expression of stable ΔFosB isoforms in the nucleus accumbens during morphine withdrawal. Rats were injected (i.p.) with increasing doses of morphine for 1 week to develop physical dependence, and withdrawal was then precipitated by one injection of naloxone (2 mg/kg, i.p.). Abstinence signs such as jumping, wet-dog shake, writhing posture, weight loss, and Gellert-Holtzman scale score were recorded to evaluate naloxone-induced morphine withdrawal. Two ionotropic glutamate receptor antagonists, dizocilpine (MK-801) and 6, 7-dinitroquinnoxaline-2, 3-dione (DNQX), were microinjected unilaterally into the ventral tegmental area 30 min before naloxone precipitation. A second injection of naloxone (2 mg/kg i.p.) was given 1 h after the first naloxone injection to sustain a maximal level of withdrawal so that the expression of stable ΔFosB isoforms in the nucleus accumbens could be measured. This would enable determination of the correlation between the MK-801 or DNQX-induced decrease in somatic withdrawal signs and the change in neuronal activity in the nucleus accumbens. The results showed that both MK-801 and DNQX significantly alleviated all symptoms of morphine withdrawal except for weight loss and reduced the expression of stable ΔFosB isoforms within the nucleus accumbens. These data suggest that ionotropic glutamatergic neurotransmission in the ventral tegmental area regulates the levels of stable ΔFosB isoforms in the nucleus accumbens, which play a very important role in modulating opiate withdrawal.