Experiences with an outpatient relapse program (community reinforcement approach) combined with naltrexone in the treatment of opioid-dependence: effect on addictive behaviors and the predictive value of psychiatric comorbidity

BACKGROUND

There is increasing interest in naltrexone, an opiate antagonist, in the treatment of opiate addicts. The effects of naltrexone are often compromised by a lack of compliance and drop-out. The effects of this compound are probably more favorable when combined with a psychosocial intervention such as the Community Reinforcement Approach (CRA).

AIM

To explore the effects of a combination therapy (naltrexone plus CRA treatment) and the predictive value of sociodemographic and psychopathologic characteristics.

METHOD

Using a before-and-after design, heroine addicts (n = 24) receiving a combined naltrexone plus CRA treatment are compared with a group (n = 20) on methadone maintenance therapy (reference group).

RESULTS

Over a period of 6 months, 58% (14/24) did not relapse, after 1 year at least 55% (12/22) still met the initial goal of continuous abstinence. At baseline, the treatment group and the reference group were similar on nearly all variables except for the number of times clients were arrested. Within the treatment group, a comparison was made between the continuous abstinent and those who relapsed into frequent opioid use. Differences were significant in the cluster-B personality disorders and in polydrug users.

CONCLUSION

The combination of naltrexone plus intensive CRA in an outpatient setting appears to be promising. A high score on cluster-B and polydrug use is associated with relapse.

Twenty-four week maintenance treatment of cigarette smoking with nicotine gum, clonidine and naltrexone

This research study investigated the effect of nicotine gum, clonidine, and naltrexone, in the maintenance treatment of cigarette smoking. In a double blind study, 171 nicotine-dependent male subjects who met DSM-IV criteria for nicotine dependence and smoking 10 cigarettes or more per day, were allocated randomly to three equal groups of 57. Subjects received nicotine gum, clonidine, or naltrexone over a 24-week treatment period. The nicotine gum dose was 2 mg every 1 to 2 h for the first 6 weeks, 2 mg every 2 to 4 h for the next 3 weeks, and 2 mg every 4 to 8 h for the remaining 15 weeks. The clonidine dose was 0.4 mg and the naltrexone dose was 50 mg per day. Continuous abstinence rates were recorded weekly for 24 weeks from the quit date. The abstinence rates by treatment groups were 36.8% for the nicotine gum group, 19.3% for the clonidine group, and 5.3% for the naltrexone group,and all between groups differences were significant. These results support the efficacy and safety of nicotine gum and clonidine for smoking relapse prevention among Iranian nicotine-dependent patients, but call in question the utility of naltrexone treatment for smoking relapse prevention.

Use of oral and implantable naltrexone in the management of the opioid impaired physician

Doctors are at an increased risk for prescription drug use, particularly opioids and benzodiazpines. This use can interfere with work function and has major potential negative implications for patient safety. Oral naltrexone, an opioid antagonist, has been used as part of a management strategy for opioid dependent physicians. While some patients stabilize on oral naltrexone, others relapse to opioid use. An alternative method of naltrexone maintenance involves the injection or surgical insertion of a sustained release preparation of naltrexone. This approach dramatically improves compliance, removing the onus from the previously opioid impaired physician to use daily oral naltrexone. This article describes the cases of four opioid-impaired doctors who received naltrexone (either oral or implant) as part of their management. The authors conclude that monitoring daily oral naltrexone use and detecting early opioid relapse is difficult, placing both the opioid impaired physician and their patients at risk. In contrast, by using implantable naltrexone, compliance is assured and opioid abstinence can virtually be guaranteed for five months. It is argued that naltrexone implants offer a level of protection not achieved with any previous treatment. It is recommended that management should involve early and close collaboration between the treating doctor and the Medical Board, with initial treatment, ongoing monitoring and follow-up being a Medical Board requirement for registration.

Exposure to the opioid antagonist naltrexone throughout gestation alters postnatal heart development

The influence of endogenous opioid blockade by naltrexone during prenatal life on postnatal heart development was studied in rats. Pregnant Sprague-Dawley rats received daily injections of 50 mg/kg naltrexone (NTX) or saline throughout gestation; offspring were cross-fostered at birth to mothers not receiving NTX. In general, NTX-treated offspring weighed more than controls throughout preweaning life, whereas heart weights were often increased from age-matched controls up to 35 days. Biochemical analyses of nucleic acids and protein demonstrated that DNA and protein content were increased throughout development in NTX-treated animals relative to controls. Morphometric analyses revealed increases in total area of the heart and myocardial area in NTX-exposed rats relative to control levels. These data suggest that endogenous opioids function to regulate cardiac growth during the prenatal period, and that disruption of this process has long-term implication for cardiac biology.

Discrimination of a single dose of morphine followed by naltrexone: substitution of other agonists for morphine and other antagonists for naltrexone in a rat model of acute dependence

Rats were trained to discriminate 4-h pretreatment with 10 mg/kg morphine and 15-min pretreatment with 0.3 mg/kg naltrexone (morphine-->naltrexone) from pretreatment with saline and 0.3 mg/kg naltrexone (saline-->naltrexone). The discrimination seems to derive from interoceptive stimuli from antagonist-precipitated withdrawal from acute morphine dependence. The purpose of this study was to extend pharmacological characterization of the discrimination by testing opioid agonists other than morphine and antagonists other than naltrexone. Of seven mu-opioid agonists tested in place of morphine, only two (heroin and levorphanol) substituted completely for it; trials completed on the morphine-->naltrexone-appropriate lever increased as a function of agonist and naltrexone dose. Agonists with intrinsic efficacy higher (etorphine, fentanyl, and methadone) or lower (buprenorphine and meperidine) than that of morphine substituted only partially. However, when naltrexone was administered during continuous infusion of fentanyl or methadone via s.c. osmotic pump, rats responded as if they had received morphine-->naltrexone; discriminative responding correlated with global withdrawal scores. Rats responded primarily on the saline-->naltrexone-appropriate lever when naltrexone was administered after pretreatment with dextrorphan, the dextrorotatory isomer of levorphanol, or kappa-opioid agonists (5-alpha,7-alpha,8-beta)-(+)-N-methyl-N-[7-(1-pyrrolidinyl)-1-oxaspiro(4,5)dec-8-yl]-benzeneacetamide (U69,593) and spiradoline. Antagonists with no intrinsic efficacy at mu-opioid receptors (naloxone and diprenorphine) substituted completely for naltrexone, whereas those with some efficacy (nalorphine and levallorphan) substituted partially. Thus, morphine-->naltrexone-like stimulus control of behavior by drugs administered acutely requires pretreatment with certain mu-opioid agonists and a pure antagonist, is independent of agonist efficacy, and is stereoselective. Interoceptive stimuli from naltrexone-precipitated opioid withdrawal are more similar across morphine-like agonists during chronic dependence than they are during acute dependence.

Stress-limiting effect of dehydroepiandrosterone sulfate and its mechanism

Dehydroepiandrosterone sulfate prevented the increase in corticosterone level in rats induced by repeated exposure to stress. The mu-opioid receptor blocker naltrexone administered in a dose of 0.1 mg/kg 20 min before treatment with dehydroepiandrosterone sulfate abolished the effect of this agent. Dehydroepiandrosterone sulfate and naltrexone had no effect on rats after acute stress.

[Pharmacotherapy in heroin addiction: pharmacological approaches to remission stabilization and recurrence prevention]

After withdrawal arrest in many heroin addicts, they displayed the syndrome of anhedonia including affective disorders (depression, dysphoria, anxiety), dyssomnia and a pathologic craving for opiates. Anhedonia is often the cause for recurrence in heroine addiction, therefore, an appropriate treatment is an important aspect in recurrence prevention and remission stabilization. Since depression and drive for heroin are the key symptoms in anhedonia, we undertook the efficiency study of therapy (in anhedonia) by antidepressants belonging to the selective serotonin reuptake inhibitors (SSRI) and NMDA receptor antagonists, citalopram and memantine, respectively, which have a clinical antidepressant action and an experimental anti-addictive action. Both drugs were found to arrest effectively virtually all signs of anhedonia, however, their action on remission stabilization was rather moderate. It looked to be more promising to use, in remission stabilization, the uttermost antagonist of opiate receptors (naltrexone) blocking reliably all heroine effects. A double blind placebo-controlled study, undertaken by us, convincingly showed a significantly smaller number of relapses with naltrexone in heroin addicts. At the same time, the drug had no valuable effect on the anhedonia symptoms, which worsened the compliance entailing a poorer therapy efficiency. Finally, a combination of naltrexone (blocking the heroin action and reducing the recurrence rate) with SSRI antidepressants (effectively arresting the anhedonia symptoms and improving the compliance with naltrexone medication and remission quality) is a most promising approach to remission stabilization and recurrence prevention.

Comparing and combining naltrexone and acamprosate in relapse prevention of alcoholism: a double-blind, placebo-controlled study

BACKGROUND

Naltrexone and acamprosate have been shown to be effective in relapse prevention of alcoholism via different pharmacologic mechanisms. Since it remains uncertain whether both substances are equally efficient and whether a combination of both drugs potentiates the efficacy, we conducted the first published controlled study comparing and combining both compounds.

METHODS

After detoxification, 160 patients with alcoholism participated in a randomized, double-blind, placebo-controlled protocol. Patients received naltrexone, acamprosate, naltrexone plus acamprosate, or placebo for 12 weeks. Patients were assessed weekly by interview, self-report, questionnaires, and laboratory screening. Time to first drink, time to relapse, and the cumulative abstinence time were the primary outcome measures.

RESULTS

Naltrexone, acamprosate, and the combined medication were significantly more effective than placebo. Comparing the course of nonrelapse rates between naltrexone and acamprosate, the naltrexone group showed a tendency for a better outcome regarding time to first drink and time to relapse. The combined medication was most effective with significantly lower relapse rates than placebo and acamprosate but not naltrexone.

CONCLUSIONS

The results of this study support the efficacy of pharmacotherapeutic strategies in the relapse prevention of alcoholism. Naltrexone and acamprosate, especially in combination, considerably enhance the potential of relapse prevention.

Efficacy and safety of oral naltrexone treatment for pruritus of cholestasis, a crossover, double blind, placebo-controlled study

BACKGROUND/AIMS

To assess the efficacy and safety of naltrexone for the short and long term treatment of pruritus of cholestasis.

METHODS

Twenty patients with pruritus and cholestasis were included. A baseline pruritus score was obtained over 1 week. Patients were then randomized to receive 50 mg/day of naltrexone or placebo for 2 weeks. Subsequently, a 1-week washout period ensued and patients were crossed over to the other therapy for 2 additional weeks. Pruritus was assessed daily with a visual analogue scale (VAS) from 0 to 10. Patients whose pruritus decreased >50% of basal with naltrexone received naltrexone 50 mg/day for 2 additional months.

RESULTS

Mean basal VAS was similar in both groups. VAS showed greater and more significant changes with naltrexone than with placebo (P<0.0003). In nine out of 20 patients (45%) receiving naltrexone, pruritus decreased >50% compared to basal value, including five whose pruritus disappeared completely. No significant changes were observed in serum biochemistry. Most of the adverse events that occurred during the first 48 h of naltrexone therapy were consistent with opioid withdrawal-like phenomena and spontaneously disappeared 2 days after starting treatment.

CONCLUSIONS

Naltrexone can be considered as an alternative option to treat pruritus of cholestasis. In the current study, side effects were transient and did not require specific medication.

Characteristics, retention and readmissions of opioid-dependent clients treated with oral naltrexone

The aims of this study were to examine the retention rates of opioid-dependent clients treated with oral naltrexone and identify factors that influence retention in treatment of 981 opioid-dependent clients at a public out-patient clinic in Perth, Western Australia. The average retention period for all clients was 9.0 weeks. The factors associated with longer retention were being employed and referral source. Clients who were employed stayed significantly longer in treatment than unemployed clients. Clients referred from a private clinic were retained in treatment significantly longer than those referred from other sources (X = 10.3 vs. 5.9 weeks). While the majority (80.8%) had one admission to naltrexone treatment, 19.2% presented for readmission, some on three or more occasions in the study period. The median period between the end of the first episode of treatment and commencement of the second was 15.6 weeks. The median period between the end of the second episode of treatment and commencement of the third was 11.4 weeks. Those employed had a higher probability of being retained longer in treatment than those who were unemployed in subsequent treatment episodes. Clinicians should expect that initial retention in naltrexone is likely to be relatively short, and that a substantial proportion of clients will represent for further treatment.

Naltrexone infusion inhibits the development of preference for a high-sucrose diet

We hypothesized that the opioid antagonist naltrexone would inhibit the redevelopment of a preference for a high-sucrose diet after an abstention period from this diet. Rats that chose between a starch or sucrose diet for 10 days preferred the sucrose diet. Rats were then given access to the starch diet alone for another 10-day period. A miniosmotic pump containing saline or naltrexone was then implanted (70 microg/h; 1.7 mg/day) for approximately 10 days. During the saline infusion, 77% of the total energy came from the sucrose diet, whereas during the naltrexone infusion, 33% of the total energy came from the sucrose diet. We repeated this study in another group of rats but did not restrict the sucrose diet. In this case naltrexone failed to decrease preference for the sucrose diet. Thus naltrexone infusion inhibited redevelopment of a preference for a sucrose diet after a period of restriction to a starch diet for 10 days but had no effect on preference if both diets were present throughout the study.

Using naltrexone implants in the management of the pregnant heroin user

OBJECTIVES

To describe the case history and associated obstetric and neonatal outcomes of eight women who had their heroin dependency managed over pregnancy by naltrexone implant (two x 1.8 g of naltrexone embedded in poly-DL-lactide acid) treatment.

METHOD

Case data on maternal management associated with naltrexone implant were collected at the Australian Medical Procedures Research Foundation, Perth, Australia and three Perth hospitals.

RESULTS

Despite earlier instability on oral naltrexone and repeated relapses back to dependent heroin use these women, following treatment with naltrexone implant, remained heroin free throughout their pregnancies. Neonatal and obstetric outcomes were unremarkable.

CONCLUSIONS

This case series provides preliminary evidence that the pregnant heroin user can be managed by naltrexone implant without obvious risk to the mother or developing foetus. Importantly, the current case series suggests that the pregnant woman who finds it difficult to stabilise on oral naltrexone maintenance and returns to dependent heroin use may be managed using implantable naltrexone, thereby removing from her the onus for daily naltrexone medication compliance. The authors conclude that naltrexone implant may represent an important procedure for managing the pregnant heroin dependent patient who finds it difficult to shift away from her heroin use patterns. These preliminary findings require confirmation using a much larger controlled study.

Combined blockade of both micro - and kappa-opioid receptors prevents the acute orexigenic action of Agouti-related protein

Agouti-related protein (AgRP) is an endogenous antagonist at the melanocortin 3 and 4 receptor in the hypothalamus. Central administration of AgRP produces a robust increase in food intake, and this effect can be blocked by administration of nonspecific opioid receptor antagonist. Such results implicate opioid receptors as critical to mediating the effects of AgRP. To determine which opioid receptor subtype is critical, we first determined the highest i3vt (administered into the third ventricle) dose of two specific opioid antagonists, nor-Binaltorphine or beta-funaltrexamine, that did not influence food intake on their own. Then, rats were pretreated with either of these two antagonists before i3vt AgRP and access to a high-fat diet. For neither the kappa- nor the micro -specific antagonist was there any effect to block the effects of AgRP on food intake. However, administration of both the kappa- and micro -receptor antagonists does significantly reduce the effect of AgRP. The current results implicate opioid receptors as critical downstream mediators of the potent effects of AgRP to increase food intake but indicate that either micro - or kappa-receptor activation is sufficient for AgRP's effect.

The role of opioid systems on orthodontic tooth movement in cholestatic rats

Endogenous opioids have been reported to accumulate in the plasma of cholestatic subjects. Another report showed that human osteoblast-like cells, MG-63, express 3 types of opioid receptors. In our laboratory we noticed that orthodontic tooth movement (OTM) is enhanced in cholestatic rats. Therefore, we suggest a possible role of opioid systems in bone remodeling and raising the rate of OTM in cholestatic conditions. To investigate this hypothesis, rat models were established and divided into 5 study groups. An orthodontic appliance, consisting of a 5 mm nickel-titanium closed coil spring, was ligated between the maxillary right incisor and first molar of each rat to deliver an initial force of 60 g. The bile duct ligated (BDL) group underwent a bile duct ligation operation and received orthodontic appliance 7 days after surgery. Another group underwent a sham operation and orthodontic appliances were inserted just as in the BDL group protocol. Surgery was performed the BDL + naltrexone group and orthodontic appliances were inserted 7 days after surgery. This group received daily subcutaneous injections of naltrexone HCI (an opioid antagonist) at 20 mg/kg at 24-hour intervals from the day of force application until the end of the study period. Another group, the naltrexone group, received naltrexone injections like the BDL + naltrexone group. A fifth control group neither underwent surgery nor received injections. Orthodontic tooth movement was measured 14 days after appliance insertion. The bile duct ligated group showed significantly increased OTM compared to all other study groups (P < .001). The difference between the OTM in the BDL + naltrexone and control groups was insignificant. This study suggests a role for opioid systems in OTM in cholestasis conditions.

Outcomes of naltrexone maintenance following ultra rapid opiate detoxification versus intensive inpatient detoxification

Relapse rates of 30 opiate-addicted social service clients who were given a 9-month course of naltrexone after being rapidly detoxified using naltrexone + clonidine under anesthesia were compared to 33 similar clients detoxified in a 30-day intensive inpatient detoxification but not given naltrexone. Both groups had the same counseling aftercare. Telephone follow-up of 26 of the intensive inpatient detoxification clients and 24 of the rapidly detoxified clients found no significant differences (p = .62) in relapse rates, with 34% of respondents returning to regular opiate use 13.4 (+/- 3.8) months after detoxification. Naltrexone maintenance and counseling following rapid detoxification may be as effective as intensive inpatient detoxification and counseling.

Design of naltrexone-loaded hydrolyzable crosslinked nanoparticles

A hydrolyzable crosslinker (N,O-dimethacryloylhydroxylamine (MANHOMA)) was synthesized by a modified method and was characterized using 1H-NMR, FTIR, and melting point determination. Naltrexone-loaded nanoparticles were prepared by copolymerization of poly(ethylene glycol)1000 monomethyl ether mono methacrylate (PEO-MA), methyl methacrylate (MMA) and N,O-dimethacryloylhydroxylamine (MANHOMA) in 0.4% poly(vinyl alcohol) aqueous solution. The nanoparticles were characterized by FTIR, particle size determination and transmission electron microscope (TEM). The TEM photomicrographs of the nanoparticles show a crosslinked core surrounded by a ring formed by the polyethylene glycol tail of PEO-MA. The loading efficiency of the nanoparticles and in vitro drug availability from the nanoparticles were investigated. The naltrexone-loaded hydrolyzable crosslinked nanoparticles were able to sustain the release of naltrexone for different periods of time, depending on the monomer feed composition.

[Opioid detoxication under general anesthesia]

Antagonist-precipitated opioid detoxification under general anaesthesia has been used extensively since its introduction in 1988. The use of antagonists was believed to shorten the detoxification period. Administration to opioid dependents is followed by a violent activation of the adrenergic system, which results in the development of an acute withdrawal syndrome in the patient. This is usually treated with clonidine. To reduce the subjective discomfort, the procedure is conducted under anaesthesia. From the existing literature, one may conclude that despite more than ten years of development there is currently no sufficient evidence of the effectiveness of antagonist-precipitated opioid detoxification under general anaesthesia conducted under modern anaesthesiological management. Randomised, clinical trials are necessary to document the advantages of this detoxification method as compared to conventional treatment.

Neuroimmunotherapy of untreatable metastatic solid tumors with subcutaneous low-dose interleukin-2, melatonin and naltrexone: modulation of interleukin-2-induced antitumor immunity by blocking the opioid system

OBJECTIVES

The preliminary applications of the psychoneuroimmunological knowledges to the treatment of human diseases have confirmed the possibility to amplify IL-2-dependent anticancer immunity by the pineal hormone melatonin (MLT) or by opioid antagonist, such as naltrexone (NTX), which act by activating TH1 lymphocytes or suppressing TH2 lymphocytes, respectively. At present, however, there are no data about the immunobiological effects of a concomitant administration of both MLT and NTX on IL-2-induced anticancer immunity. This preliminary study was carried out to evaluate whether the association of NTX may further enhance the lymphocytosis induced by the neuroimmunotherapy with IL-2 plus MLT.

MATERIALS & METHODS

The study included 14 consecutive untreatable metastatic solid tumor patients. According to a cross-over randomized study, the patients were treated during two consecutive immunotherapeutic cycles at 21-day intervals with IL-2 plus MLT alone or with IL-2 plus MLT plus NTX. IL-2 was injected subcutaneously at 3 MIU/day for 6 days/week for 4 weeks, MLT was given orally at 20 mg /day in the evening every day, and NTX was given orally at 100 mg in the morning every next day. For the immune evaluation, venous blood samples were drawn before the onset of treatment and at weekly intervals.

RESULTS

Lymphocyte mean number significantly increased after both IL-2 plus MLT and IL-2 plus MLT plus NTX. However, the concomitant administration of NTX induced a significantly higher increase in lymphocyte mean number with respect to that achieved with IL-2 plus MLT alone. In contrast, the increase in eosinophil mean number was significantly higher on IL-2 plus MLT alone.

CONCLUSIONS

This preliminary study shows that the association of NTX further amplifies the lymphocytosis obtained by IL-2 plus MLT. Since the lymphocytosis represents the most important favourable prognostic variable predicting the anticancer efficacy of IL-2 immunotherapy, it is probable that a cancer neuroimmunotherapy with IL-2 plus both MLT and NTX to activate TH1 and suppress TH2 cells respectively, may deserve more promising results in the treatment of human neoplasms according to the psychoneuroimnunological knowledge.

Involvement of endogenous opioid systems in nociceptin-induced spinal antinociception in rats

The present study investigates the involvement of opioid receptors in the antinociceptive effects of nociceptin in the spinal cord of the rat. Intrathecal administrations of 5 and 10 nmol of nociceptin significantly increase the withdraw response latencies to noxious thermal and mechanical stimulations. This nociceptin-induced antinociceptive effect is significantly attenuated by intrathecal injection of (Nphe(1))nociceptin(1-13)-NH(2), a selective antagonist of the nociceptin receptor (opioid receptor-like receptor ORL1), indicating an ORL1 receptor-mediated mechanism. This antinociceptive effect is also significantly attenuated by intrathecal injections of naloxone (a nonselective opioid receptor antagonist), naltrindole (a selective delta-opioid receptor antagonist), and beta-funaltrexamine (a selective mu-opioid receptor antagonist) in a dose-dependent manner, but not by the selective kappa-opioid receptor antagonist norbinaltorphimine. Since it is unlikely that nociceptin acts by direct binding to opioid receptors, these results suggest a possible interaction between the nociceptin/ORL1 and opioid systems in the dorsal horn of the rat spinal cord.

Serum naltrexone and 6-beta-naltrexol levels from naltrexone implants can block very large amounts of heroin: a report of two cases

The maximum dose of heroin that is blocked by customary doses of oral naltrexone (NTX) and its active metabolite 6-beta-naltrexol (6BNT) is unknown, particularly at trough serum levels which show much interindividual variation and can be low. NTX has only once been tested formally against opiate equivalents of more than 25 mg of diamorphine. Increasing interest in long-acting implantable NTX preparations makes it important to have objective information about blocking activity at various blood levels of NTX and 6BNT. Two cases are described in which NTX and 6BNT levels as low as 2.8 and 9.0 ng/ml, respectively, were sufficient to block doses of pure diamorphine as high as 500 mg.

A new neuroimmunotherapeutic strategy of subcutaneous low-dose interleukin-2 plus the long-acting opioid antagonist naltrexone in metastatic cancer patients progressing on interleukin-2 alone

OBJECTIVES

Recent advances in knowledge of Psychoneuroimmunology have shown that several neuroactive substances, including neurohormones and neuropeptides, may exert immunomodulatory effects. However, despite the great variety of potential neuroimmune interactions, at present we may recognize two major neuroendocrine systems exerting a physiological neuroimmunomodulatory function, consisting of the pineal gland and the brain opioid system, provided by immunostimulatory and immunosuppressive effects, respectively. Recent in human studies have demonstrated the possibility to amplify the biological activity of IL-2, the major anticancer cytokine, by pineal indoles.

MATERIALS & METHODS

The present study was carried out to draw some preliminary in human results on the possible immunomodulatory effects of the inhibition of the brain opioid activity by a long-acting opioid antagonist, naltrexone (NTX). The study was performed in 10 metastatic renal cell cancer patients, who had progressed on a previous immunotherapeutic cycle with IL-2 alone. Patients were treated with the same doses of IL-2 (6 million lU/day subcutaneously for 6 days/week for 4 weeks) plus an oral administration of NTX at a dose of 100 mg every 2 days.

RESULTS

The clinical response consisted of a partial response in 1 and a stable disease in 5 patients, whereas the other 4 patients progressed. Therefore, the percent of non-progressive disease was 6/10 (60%). Moreover, mean lymphocyte increase achieved during IL-2 plus NTX was significantly higher (P<0.05) than that obtained during the previous treatment with IL-2 alone.

CONCLUSIONS

This study shows that a blockade of the brain opioid system, which plays a physiological immunosuppressive role, may improve the anticancer effects of IL-2 in humans.

Alterations in food intake elicited by GABA and opioid agonists and antagonists administered into the ventral tegmental area region of rats

Food intake is significantly increased following administration of mu-selective opioid agonists into the ventral tegmental area (VTA) region acting through multiple local opioid receptor subtypes. Since GABA receptor agonists in the VTA region are capable of eliciting feeding, the present study investigated whether feeding elicited by the mu-selective opioid agonist [D-Ala(2), NMe(4), Gly-ol(5)]-enkephalin (DAMGO) in the VTA region was altered by pretreatment into the same site with equimolar doses of either GABA(A) (bicuculline) or GABA(B) (saclofen) antagonists, and further, whether pretreatment with either general opioid or selective GABA receptor antagonists decreased feeding elicited by GABA(A) (muscimol) or GABA(B) (baclofen) agonists in the VTA region. DAMGO-induced feeding in the VTA region was dose-dependently decreased following pretreatment with either GABA(A) or GABA(B) antagonists in the absence of significant alterations in food intake by the antagonists per se. However, the presence of short-lived seizures following bicuculline in the VTA region suggests that this ingestive effect was caused by nonspecific actions. In contrast, GABA(B) receptors are involved in the full expression of mu-opioid agonist-induced feeding in this region since saclofen failed to elicit either seizure activity or a conditioned taste aversion. Pretreatment with naltrexone in the VTA region reduced intake elicited by baclofen, but not muscimol. Finally, baclofen-induced feeding was significantly reduced by saclofen, but not bicuculline, pretreatment in the VTA region. Therefore, possible coregulation between GABA(B) and opioid receptors in the VTA region, as suggested by immunocytochemical evidence, is supported by these behavioral effects upon ingestion.

Differential involvement of mu-opioid receptors in the rostral versus caudal nucleus accumbens in the reinforcing effects of heroin in rats: evidence from focal injections of beta-funaltrexamine

RATIONALE

The nucleus accumbens is a diverse and heterogeneous structure along its rostrocaudal axis. The influence of specific subpopulations of mu-opioid receptors within the NAcc in heroin self-administration has not been documented.

OBJECTIVES

This study was undertaken to investigate the involvement of subregions of the NAcc in heroin self-administration in rats.

METHODS

Male rats were trained to self-administer heroin and then given beta-FNA, an irreversible mu-opioid receptor antagonist, into either the rostral or caudal portion of the NAcc.

RESULTS

beta-FNA (0.25-2.5 nmol) attenuated heroin self-administration in a dose-responsive manner when given into the caudal but not rostral NAcc. The number of infusions of 18 microg of heroin self-administered was increased by 50-100%. This effect persisted for up to 17 days following administration of the highest dose. These doses of beta-FNA were found to decrease [(3)H]DAMGO binding in a dose-responsive manner and the effect was confined to the NAcc, as nearby structures such as the caudate putamen and olfactory tubercles were unaffected. The effect of beta-FNA (2.5 nmol) administration into the caudal NAcc was also assessed on the dose-effect curve for heroin. This dose apparently shifted the dose-effect curve to the right initially, followed by an apparent upward shift for up to 17 days after beta-FNA administration.

CONCLUSIONS

The caudal portion of the NAcc and its output sites merit further investigation regarding the reinforcing effects of heroin.

The neuropeptide FF analogue, 1DMe, reduces in vivo dynorphin release from the rat spinal cord

Intrathecal infusion of the neuropeptide FF analogue, [D-Tyr1, (NMe)Phe3]neuropeptide FF (1DMe; 0.1 microm-0.1 mm) in anaesthetized rats produced a concentration-dependent decrease in the spinal outflow of dynorphin A (1-8)-like material, which persisted for at least 90 min after treatment with 10 microm-0.1 mm of the compound. Co-administration of d-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH2 (CTOP; 1 microm) to block spinal micro-opioid receptors did not modify this effect, whereas naltrindole (10 microm) totally prevented it and nor-binaltorphimine (10 microm) reduced the post-effect. These data suggest that 1DMe triggers the release of endogenous opioids that stimulate mainly delta-opioid receptors, and secondarily kappa-opioid receptors, thereby exerting a negative influence on dynorphin A (1-8)-like material outflow. Because dynorphin has pronociceptive properties, such a decrease in spinal dynorphin A (1-8)-like material release might underlie the long-lasting antinociceptive effects of intrathecally administered neuropeptide FF and analogues.