Possible antidepressive effects of opioids: action of buprenorphine

Baseline characteristics and treatment outcomes in prescription opioid dependent patients with and without co-occurring psychiatric disorder

BACKGROUND

Given the growing prevalence of prescription opioid dependence and the considerable rates of additional psychopathology in drug dependence, we examined the association between the presence of a co-occurring Axis I psychiatric disorder and sociodemographic and clinical characteristics in this secondary analysis of patients entering a treatment study for dependence on prescription opioids. Treatment outcomes were also compared.

METHODS

Patients dependent on prescription opioids participated in a multi-site, two-phase, randomized, controlled trial to assess different lengths of buprenorphine-naloxone pharmacotherapy and different intensities of counseling (Clinicaltrials.gov identifier: NCT00316277). Among the 653 participants entering the first phase of the trial, 360 entered the second phase, receiving 12 weeks of buprenorphine-naloxone treatment; they are reported here. Half of those participants (180/360) had a current co-occurring psychiatric disorder in addition to substance dependence.

RESULTS

Sociodemographic characteristics were similar overall between those with and without a co-occurring psychiatric disorder, but women were 1.6 times more likely than men to have a co-occurring disorder. On several clinical indicators at baseline, participants with a co-occurring disorder had greater impairment. However, they had better opioid use outcomes at the conclusion of 12 weeks of buprenorphine-naloxone stabilization than did participants without a co-occurring disorder.

CONCLUSIONS

Prescription opioid-dependent patients with a co-occurring psychiatric disorder had a better response to buprenorphine-naloxone treatment despite demonstrating greater impairment at baseline. Additional research is needed to determine the mechanism of this finding and to adapt treatments to address this population.

Patient characteristics associated with buprenorphine/naloxone treatment outcome for prescription opioid dependence: Results from a multisite study

BACKGROUND

Prescription opioid dependence is a growing problem, but little research exists on its treatment, including patient characteristics that predict treatment outcome.

METHODS

A secondary analysis of data from a large multisite, randomized clinical trial, the National Drug Abuse Treatment Clinical Trials Network Prescription Opioid Addiction Treatment Study (POATS) was undertaken to examine baseline patient characteristics (N=360) associated with success during 12-week buprenorphine/naloxone treatment for prescription opioid dependence. Baseline predictor variables included self-reported demographic and opioid use history information, diagnoses assessed via the Composite International Diagnostic Interview, and historical opioid use and related information from the Pain And Opiate Analgesic Use History.

RESULTS

In bivariate analyses, pre-treatment characteristics associated with successful opioid use outcome included older age, past-year or lifetime diagnosis of major depressive disorder, initially obtaining opioids with a medical prescription to relieve pain, having only used opioids by swallowing or sublingual administration, never having used heroin, using an opioid other than extended-release oxycodone most frequently, and no prior opioid dependence treatment. In multivariate analysis, age, lifetime major depressive disorder, having only used opioids by swallowing or sublingual administration, and receiving no prior opioid dependence treatment remained as significant predictors of successful outcome.

CONCLUSIONS

This is the first study to examine characteristics associated with treatment outcome in patients dependent exclusively on prescription opioids. Characteristics associated with successful outcome after 12 weeks of buprenorphine/naloxone treatment include some that have previously been found to predict heroin-dependent patients' response to methadone treatment and some specific to prescription opioid-dependent patients receiving buprenorphine/naloxone.

Mania precipitated by opioid withdrawal: a retrospective study

OBJECTIVE

Little evidence is available on the occurrence of mania following opioid withdrawal. This is the first report on clinical and demographic characteristics of mania precipitated by opioid withdrawal in a relatively large sample.

METHOD

In this study, we assessed the files of the patients admitted to a large referral psychiatric hospital during a 3-year period with a presentation of manic episode shortly after opioid withdrawal. Forty-five relevant cases (one woman) were found, including 28 patients with their first manic episode, and 17 patients with a previous history of bipolar disorder.

RESULTS

Most of the identified cases had a long history (mean = 11.8 years) of opium dependence (24 cases used only opium and 16 cases opium and other opioids) and had recently experienced an intense withdrawal (25 cases). These associations were present in both first-episode patients and those with recurrent episodes.

CONCLUSION

Emergence of mania following opioid withdrawal could be partly explained by mood stabilizing effects of opioids. Other than the type of opioid, it seems that the duration of use and withdrawal method might play a role. Caution should be used while detoxifying patients with a long history of opioid use.

Development of κ opioid receptor antagonists

κ opioid receptors (KORs) belong to the G-protein-coupled class of receptors (GPCRs). They are activated by the endogenous opioid peptide dynorphin (DYN) and expressed at particularly high levels within brain areas implicated in modulation of motivation, emotion, and cognitive function. Chronic activation of KORs in animal models has maladaptive effects including increases in behaviors that reflect depression, the propensity to engage in drug-seeking behavior, and drug craving. The fact that KOR activation has such a profound influence on behaviors often triggered by stress has led to interest in selective KOR antagonists as potential therapeutic agents. This Perspective provides a description of preclinical research conducted in the development of several different classes of selective KOR antagonists, a summary of the clinical studies conducted thus far, and recommendations for the type of work needed in the future to determine if these agents would be useful as pharmacotherapies for neuropsychiatric illness.

In vivo and in vitro characterization of naltrindole-derived ligands at the κ-opioid receptor

Accumulating evidence supports a role for κ-opioid receptor antagonists in the treatment of mood disorders. Standard κ-antagonists have an unusual pharmacodynamic action, with a single injection blocking receptor signaling for several weeks. Here, we have characterized the κ-selective properties of two ligands, 5'-(2-aminomethyl) naltrindole (5'-AMN) and N-((Naltrindol-5-yl) methyl) pentanimidamide (5'-MABN), to identify whether modifications of the naltrindole side chain produces short-acting κ-antagonists. Opioid receptor binding affinity and activity were assessed using [(3)H]-diprenorphine binding, guanosine-5'-O-(3-[35S]-thio) triphosphate ([(35)S]-GTPγS) binding and isolated guinea-pig ileum. Pharmacodynamic profiles of 5'-AMN and 5'-MABN (1-10 mg/kg) were investigated using the tail-withdrawal assay and diuresis. Efficacy was also determined in depression- and anxiety-related behavioral paradigms in CD-1 mice. Both 5'-AMN and 5'-MABN had high affinity for κ-receptors (K (i) 1.36 ± 0.98 and 0.27 ± 0.08, respectively) and were revealed as potent κ-antagonists (pA(2) 7.43 and 8.18, respectively) and μ-receptor antagonists (pA(2) 7.62 and 7.85, respectively) in the ileum. Contrary to our hypothesis, in vivo, 5'-AMN and 5'-MABN displayed long-lasting antagonist effects in mice, reducing the antinociceptive actions of U50,488 (10 mg/kg) at 28 and 21 days post-injection, respectively. Interestingly, while 5'-AMN and 5'-MABN were not κ-selective, both compounds did show significant antidepressant- and anxiolytic-like effects at 7-14 days post-injection in mice.

Mood and anxiety disorders and their association with non-medical prescription opioid use and prescription opioid-use disorder: longitudinal evidence from the National Epidemiologic Study on Alcohol and Related Conditions

BACKGROUND

Non-medical use of prescription opioids represents a national public health concern of growing importance. Mood and anxiety disorders are highly associated with non-medical prescription opioid use. The authors examined longitudinal associations between non-medical prescription opioid use and opioid disorder due to non-medical opioid use and mood/anxiety disorders in a national sample, examining evidence for precipitation, self-medication and general shared vulnerability as pathways between disorders.

METHOD

Data were drawn from face-to-face surveys of 34 653 adult participants in waves 1 and 2 of the National Epidemiologic Survey on Alcohol and Related Conditions. Logistic regression models explored the temporal sequence and evidence for the hypothesized pathways.

RESULTS

Baseline lifetime non-medical prescription opioid use was associated with incidence of any mood disorder, major depressive disorder (MDD), bipolar disorder, any anxiety disorder and generalized anxiety disorder (GAD in wave 2, adjusted for baseline demographics, other substance use, and co-morbid mood/anxiety disorders). Lifetime opioid disorder was not associated with any incident mood/anxiety disorders. All baseline lifetime mood disorders and GAD were associated with incident non-medical prescription opioid use at follow-up, adjusted for demographics, co-morbid mood/anxiety disorders, and other substance use. Baseline lifetime mood disorders, MDD, dysthymia and panic disorder were associated with incident opioid disorder due to non-medical prescription opioid use at follow-up, adjusted for the same covariates.

CONCLUSIONS

These results suggest that precipitation, self-medication as well as shared vulnerability are all viable pathways between non-medical prescription opioid use and opioid disorder due to non-medical opioid use and mood/anxiety disorders.

Design and discovery of a selective small molecule κ opioid antagonist (2-methyl-N-((2'-(pyrrolidin-1-ylsulfonyl)biphenyl-4-yl)methyl)propan-1-amine, PF-4455242)

By use of parallel chemistry coupled with physicochemical property design, a series of selective κ opioid antagonists have been discovered. The parallel chemistry strategy utilized key monomer building blocks to rapidly expand the desired SAR space. The potency and selectivity of the in vitro κ antagonism were confirmed in the tail-flick analgesia model. This model was used to build an exposure-response relationship between the κ K(i) and the free brain drug levels. This strategy identified 2-methyl-N-((2'-(pyrrolidin-1-ylsulfonyl)biphenyl-4-yl)methyl)propan-1-amine, PF-4455242, which entered phase 1 clinical testing and has demonstrated target engagement in healthy volunteers.

Self-treatment: illicit buprenorphine use by opioid-dependent treatment seekers

Outpatient-based opioid treatment (OBOT) with buprenorphine is an important treatment for people with opioid dependence. No quantitative empirical research has examined rationales for use of illicit buprenorphine by U.S. opioid-dependent treatment seekers. The current study sequentially screened OBOT admissions (n = 129) during a 6-month period in 2009. This study had two stages: (a) a cross-sectional epidemiological analysis of new intakes and existing patients already receiving a legal OBOT prescription (n = 78) and (b) a prospective longitudinal cohort design that followed 76% of the initial participants for 3 months of treatment (n = 42). The primary aims were to establish 2009 prevalence rates for illicit buprenorphine use among people seeking OBOT treatment, to use quantitative methods to investigate reasons for this illicit use, and to examine the effect of OBOT treatment on illicit buprenorphine use behavior. These data demonstrate a decrease in illicit use when opioid-dependent treatment seekers gain access to legal prescriptions. These data also suggest that the use of illicit buprenorphine rarely represents an attempt to attain euphoria. Rather, illicit use is associated with attempted self-treatment of symptoms of opioid dependence, pain, and depression.

Therapeutic armamentarium for treating depression

Depressive disorders are highly prevalent and are a leading cause of disability, morbidity, and mortality worldwide; however, they often remain undertreated or untreated. This article provides a broad overview of the many strategies for treating depression. More than 24 antidepressant medications and depression-focused psychotherapies are available as first-choice options for treating depression. When patients have not had a satisfactory treatment response, the 2 main strategies are switching to an alternative antidepressant therapy or adding a second antidepressant therapy. A large number of medication combinations have been reported in the literature, and some have been shown to be effective in controlled studies. Nonstandard alternatives to conventional antidepressant treatments include exercise, light therapy, sleep deprivation, and various complementary and alternative therapies. For more chronic and refractory forms of depression, various neuromodulation therapies are available or are being investigated. Because depressive disorders are common in primary care and other medical settings, medical practitioners should be aware of the therapeutic armamentarium available for treating depression.

Augmentation strategies in electroconvulsive therapy

Electroconvulsive therapy (ECT) is a highly effective treatment, but strategies to enhance therapeutic outcomes are occasionally needed. This review examines the evidence for approaches used for enhancing seizure production: hyperventilation, pretreatment with xanthines, and use of remifentanil or ketamine in ECT anesthesia. Hyperventilation may be a useful strategy to enhance seizure production, but its effects on ECT outcomes have not been systematically studied and require further research. Pretreatment with caffeine, theophylline or aminophylline (xanthines) prolongs the duration of ECT seizures but has not been clearly shown in controlled trials to increase efficacy. Caution is also warranted because their use may be associated with significant adverse effects. There are case reports of the usefulness of remifentanil in assisting seizure induction by reducing the dose of barbiturate anesthetic required, but there are no controlled data on whether it independently enhances efficacy outcomes. Preliminary evidence suggests that ketamine and ECT may have synergistic antidepressant effects, although this needs to be further examined in randomized controlled trials.

The Diverse Clinical Uses of Opioid Receptor Drugs

Opioid receptors are widely distributed throughout the nervous system. In addition to their central role in brain pathways mediating pain, endogenous opioid peptides function as neuromodulators and opioid systems are involved in many physiological functions. Opioid receptor drugs, including methadone (Dolophine ® ), buprenorphine (Buprenex ® , Subutex ® ), naltrexone (Revia ® ), naloxone (Narcan ® ), and buprenorphine/naloxone (Suboxone ® ), are the focus of this article. This class of drugs is likely to be further developed for the treatment of addictions and mood disorders.

Comorbid pain, depression, and anxiety: multifaceted pathology allows for multifaceted treatment

The care of patients who suffer from physical pain and a psychiatric illness is typically challenging because of the complex interplay of affective, behavioral, cognitive, and physical aspects of pain. Psychiatrists are often asked to evaluate patients with pain because of a concern for comorbid depression and anxiety, and fears of suicidality as a result of pain. This article reviews the pathophysiology of comorbid pain, anxiety, and depression, along with the treatment modalities (pharmacologic, psychotherapeutic, and "alternative") that may benefit all three conditions.

Pathways between nonmedical opioid use/dependence and psychiatric disorders: results from the National Epidemiologic Survey on Alcohol and Related Conditions

BACKGROUND

While nonmedical use of opioids and psychiatric disorders are prevalent in the population, little is known about the temporal ordering between nonmedical opioid use and dependence and psychiatric disorders.

METHOD

Data were gathered in a face-to-face survey of the United States conducted in the 2001-2002 (NESARC wave 1). Participants were household and group quarters residents aged 18 years and older (n=43,093). Cox proportional hazards models with time-dependent covariates were used to investigate potential pathways between lifetime nonmedical opioid use/dependence and psychiatric disorders.

RESULTS

Preexisting psychiatric disorders (mood disorders, major depressive disorder, bipolar I disorder, anxiety disorders, panic and generalized anxiety disorders) were associated with an increased risk of nonmedical opioid use, with hazard ratios ranging from 2.2[95% CI=1.6-3.1] (any anxiety disorder) to 3.1[95% CI=2.4-2.4] (bipolar I disorder). Preexisting nonmedical opioid use was associated with an increased risk of onset of psychiatric disorders, with hazard ratios ranging from 2.8[95% CI=2.2-3.6] (generalized anxiety disorder) to 3.6[95% CI=2.6-4.9] (bipolar I disorder), adjusted for demographics and other illegal drug use. Nonmedical use of opioids led to the development of dependence more often among individuals with preexisting psychiatric disorders, hazard ratios were particularly strong for generalized anxiety disorder (HR=10.8, 95% CI=4.9-23.7) and bipolar I disorder (HR=9.7, 95% CI=5.4-17.3). Preexisting opioid dependence resulting from nonmedical opioid use was associated with an increased risk of onset of psychiatric disorders, with hazard ratios ranging from 4.9[95% CI=3.0-7.9] (mood disorders) to 8.5[95% CI=4.5-16.0] (panic disorder), adjusted for demographics and alcohol and/or other illegal drug dependence.

CONCLUSIONS

Our findings support a general vulnerability to nonmedical opioid use and major psychopathologies, as well as evidence for a 'self-medication' model for dependence resulting from nonmedical opioid use with bipolar disorder and generalized anxiety disorder.

Opioid peptides and receptors in relation to affective illness. Effects of desipramine and lithium on opioid receptors in rat brain

A brief review is given of clinical and experimental evidence supporting the notion that opioid peptides and opioid receptors play a role for the regulation of mood and activity, and that they could be involved in the pathophysiology of affective illness and the action of antimanic and antidepressant treatment modalities. We have carried out in vitro and in vivo studies on the effects of desipramine and lithium on opioid receptors in rat brain. In vitro desipramine inhibited the binding of 3H-enkephalinamide to neuronal membranes (P2-fractions) through mechanisms not yet known. Treatment with desipramine in vivo (10 mg/kg body weight/day) caused a down-regulation of 3H-enkephalinamide binding in the basal ganglia and the hippocampus, while no effects could be observed in the cerebral cortex and the rest of the forebrain. In vitro addition of lithium inhibited enkephalin binding to opioid receptors through a reduction in the number of binding sites, while the affinity remained unchanged or was changed only slightly. Treatment with lithium in vivo for three weeks with lithium doses providing serum lithium concentrations of about 1 mM also caused a down-regulation in the number of opioid binding sites in the cerebral cortex, the hippocampus, and the basal ganglia, while no changes could be observed in affinity. The studies suggest that desipramine and lithium, both effective in the treatment of manic-depressive illness, may share certain actions on opioid receptors in the brain.

Correlates of extramedical use of OxyContin versus other analgesic opioids among the US general population

BACKGROUND

There has been substantial public and media attention regarding extramedical use of OxyContin, but few studies focus on the characteristics of extramedical OxyContin users and whether they differ from extramedical other opioid users.

METHODS

We used data from 8218 respondents who were past-year extramedical opioid analgesic users in the 2005 and 2006 National Survey of Drug Use and Health (NSDUH). We investigated differences in socio-demographic and psychiatric characteristics associated with past-year extramedical OxyContin use (n=1144) versus extramedical other opioid analgesics use (n=7074). Data on opioid sources was compared among past-month users. We also compared extramedical opioid users (n=8218) versus other drug users (n=16,214), and individuals with an analgesic disorder who had past-year extramedical OxyContin use (n=339) versus those with other opioid use (n=820).

RESULTS

Past-year opioid users were more likely than users of other illegal drugs to be more educated and have a past-year major depressive episode. Past-year OxyContin users were more likely than other opioid users to be 18-25 years old (aOR=1.9[1.1,3.2]), and have mental health and deviant behavior problems. Those with past-year analgesic disorder who used OxyContin were more likely to be younger, sell illegal drugs (aOR=2.5[1.5,4.2]), and use illegal drugs than those who used other opioids. Past-month OxyContin users were more likely than past-month other opioid users to buy analgesics from drug dealers/other strangers and obtain opioid analgesics from multiple sources.

CONCLUSION

Our findings point out differences between OxyContin and other opioid users that might help prevention specialists and assist efforts to curb opioid analgesics diversion.

Psychotherapeutic benefits of opioid agonist therapy

Opioids have been used for centuries to treat a variety of psychiatric conditions with much success. The so-called "opium cure" lost popularity in the early 1950s with the development of non-addictive tricyclic antidepressants and monoamine oxidase inhibitors. Nonetheless, recent literature supports the potent role of methadone, buprenorphine, tramadol, morphine, and other opioids as effective, durable, and rapid therapeutic agents for anxiety and depression. This article reviews the medical literature on the treatment of psychiatric disorders with opioids (notably, methadone and buprenorphine) in both the non-opioid-dependent population and in the opioid-dependent methadone maintenance population. The most recent neurotransmitter theories on the origin of depression and anxiety will be reviewed, including current information on the role of serotonin, N-Methyl d-Aspartate, glutamate, cortisol, catecholamine, and dopamine in psychiatric disorders. The observation that methadone maintenance patients with co-existing psychiatric morbidity (so called dual diagnosis patients) require substantially higher methadone dosages by between 20% and 50% will be explored and qualified. The role of methadone and other opioids as beneficial psychiatric medications that are independent of their drug abuse mitigating properties will be discussed. The mechanisms by which methadone and other opioids can favorably modulate the neurotransmitter systems controlling mood will also be discussed.

Opioids: from physical pain to the pain of social isolation

The opioid systems play an important role in mediating both physical pain and negative affects (eg, the pain of social isolation). From an evolutionary perspective, it is not surprising that the neurocircuitry and neurochemistry of physical pain would overlap with that involved in complex social emotions. Exposure to trauma as well as a range of gene variants in the opioid system may be associated with alterations in opioid systems function, with changes in reward processing, and with vulnerability to substance abuse. A role for interventions with opioid agents in depression and anxiety disorders has been suggested.

Do antidepressants cure or create abnormal brain states?

Moncrieff and Cohen argue that psychotropic drugs create abnormal states that may co-incidentally relieve symptoms of mental illness.

Mood and affect during detoxification of opiate addicts: a comparison of buprenorphine versus methadone

Twenty-six in-patients with Diagnostic and Statistical Manual version IV (DSM-IV) criteria for opioid dependence were selected at random to receive either a combination of an 11-day low-dose buprenorphine and a 14-day carbamazepine regimen (n = 14) or a combination of an 11-day methadone and a 14-day carbamazepine regimen (n = 12) in a double-blind, randomized 14-day in-patient detoxification treatment. Patients with buprenorphine and carbamazepine showed a significantly better psychological state after the first and second weeks of treatment. Above all, the buprenorphine-treated patients demonstrated a less marked tiredness, sensitiveness and depressive state as well as a more prominent elevated mood during the detoxification process. Seven non-completers (after 7 days: four of 12 = 33.3%; after 14 days: seven of 12 = 58.3%) were treated with methadone and carbamazepine and five non-completers (after 7 days: two of 14 = 14.3%; after 14 days: five of 14 = 35.7%) received buprenorphine and carbamazepine. The difference in the overall dropout rate after day 14 was not significant. The present study supports the hypothesis that the combination of buprenorphine and carbamazepine leads to a better clinical outcome than does a combination of methadone and carbamazepine in the detoxification of opioid addicts with additional multiple drug abuse. The buprenorphine and carbamazepine-regimen provides a more effective short-term relief of affective disturbances than does methadone and carbamazepine. No severe side effects occurred during the treatment period in both groups.

Depressive symptoms during buprenorphine vs. methadone maintenance: findings from a randomised, controlled trial in opioid dependence

Research suggests that buprenorphine may possess antidepressant activity. The Beck Depression Inventory was completed at baseline and 3 months by heroin dependent subjects receiving either buprenorphine or methadone maintenance as part of a larger, pre-existing, double blind trial conducted by NDARC (Australia). Depressive symptoms improved in all subjects, with no difference between methadone and buprenorphine groups, suggesting no differential benefit on depressive symptoms for buprenorphine compared to methadone.

Buprenorphine: considerations for pain management

New effective analgesics are needed for the treatment of pain. Buprenorphine, a partial mu-opioid agonist which has been in clinical use for over 25 years, has been found to be amenable to new formulation technology based on its physiochemical and pharmacological profile. Buprenorphine is marketed as parenteral, sublingual, and transdermal formulations. Unlike full mu-opioid agonists, at higher doses, buprenorphine's physiological and subjective effects, including euphoria, reach a plateau. This ceiling may limit the abuse potential and may result in a wider safety margin. Buprenorphine has been used for the treatment of acute and chronic pain, as a supplement to anesthesia, and for behavioral and psychiatric disorders including treatment for opioid addiction. Prolonged use of buprenorphine can result in physical dependence. However, withdrawal symptoms appear to be mild to moderate in intensity compared with those of full mu agonists. Overdoses have primarily involved buprenorphine taken in combination with other central nervous system depressants.

Behavioral evidence for mu-opioid and 5-HT2A receptor interactions

Electrophysiological studies have demonstrated a physiological interaction between 5-HT2A and mu-opioid receptors in the medial prefrontal cortex. Furthermore, behavioral studies have found that phenethylamine hallucinogens induce head shakes when directly administered into the medial prefrontal cortex. The receptor(s) by which morphine suppresses head shakes induced by serotonin agonists have not been characterized. We administered mu-opioid receptor agonists and antagonists to adult male Sprague-Dawley rats prior to treatment with the phenethylamine hallucinogen 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI), which is known to induce head shakes via 5-HT2A receptors. The suppressant action of the moderately selective mu-opioid receptor agonist, buprenorphine (ID50 approximately 0.005 mg/kg, i.p.; a mu-opioid receptor partial agonist and kappa-opioid receptor antagonist) was blocked by naloxone and pretreatment with the irreversible mu-opioid receptor antagonist clocinnamox. Another mu-opioid receptor agonist fentanyl also suppressed DOI-induced head shakes. In contrast, a delta-opioid receptor agonist was without effect on DOI-induced head shakes. Thus, activation of mu-opioid receptors can suppress head shakes induced by hallucinogenic drugs.

The validity of animal models of predisposition to depression

Some animal models of depression, including the majority of the more recently introduced models, are better characterized as models of predisposition to depression. In the first part of this paper, we show that the basis for such a model could be either a procedure that increases the ease with which an analogue of major depression may be evoked, or a presentation analogous to dysthymia (chronic mild depression). We then consider how the concepts of predictive, face, and construct validity apply to such models. Next, we review the validity of the available models of predisposition to depression, which derive from genetics, genomics, developmental manipulations, and brain lesioning. Finally, we compare the performance of the different models, using a novel scoring system that formalizes the evaluation of animal models against each of the three sets of validation criteria.

Prodynorphin and kappa opioid receptor mRNA expression in the cingulate and prefrontal cortices of subjects diagnosed with schizophrenia or affective disorders

The present study examined the prodynorphin and kappa opioid receptor mRNA expression levels in the anterior cingulate and dorsolateral prefrontal cortices of subjects diagnosed with schizophrenia, bipolar disorder, or major depression as compared with normal controls without a psychiatric diagnosis. Multivariate analyses failed to reveal any differences in the mRNA expression levels between the four diagnostic groups, though a group trend (non-significant) was evident for the expression of the kappa opioid receptor and prodynorphin mRNAs in the prefrontal cortex. The mRNA expression levels were not associated with lifetime history of antipsychotic treatment or with suicide as a cause of death. The results, however, suggested an influence of certain drugs of abuse on the prodynorphin cortical mRNA expression. Prodynorphin mRNA expression levels were found to be elevated in individuals with a history of marihuana or stimulant use, but not alcohol. Overall, our data do not provide strong evidence for impaired prodynorphin or kappa opioid receptor mRNA levels in the dorsolateral prefrontal or cingulate cortices of schizophrenic, bipolar disorder, or major depressed subjects.

Opioid peptide receptor studies. 12. Buprenorphine is a potent and selective mu/kappa antagonist in the [35S]-GTP-gamma-S functional binding assay

We utilized the [(35)S]-GTP-gamma-S functional binding assay to determine the selectivity of opioid receptor agonists in guinea pig caudate membranes. The study focused on two opioid agonists used for treating opioid-dependent patients: methadone and buprenorphine. Selective antagonists were used to generate agonist-selective conditions: TIPP + nor-BNI to measure mu receptors, CTAP + nor-BNI to measure gamma receptors and TIPP + CTAP to measure kappa receptors. The assay was first validated with opioid agonists of known subtype specificity (DAMGO for mu, SNC80 for delta, and U69, 593 for kappa receptors). Methadone-stimulated [(35)S]-GTP-gamma-S binding was mu-specific and less potent and efficacious than etorphine (K(d) = 1,537 nM vs. K(d) = 7.8 nM). Buprenorphine failed to stimulate [(35)S]-GTP-gamma-S binding but inhibited agonist-stimulated [(35)S]-GTP-gamma-S binding. The antagonist-K(i) values (nM) of buprenorphine at mu, delta, and kappa receptors were 0.088 nM, 1.15 nM, and 0.072 nM, respectively. The antagonist-K(i) values (nM) of naloxone at mu, delta, and kappa receptors were 1.39 nM, 25.0 nM, and 11.4 nM, respectively. Autoradiographic studies showed that buprenorphine failed to stimulate [(35)S]-GTP-gamma-S binding in caudate-level rat brain sections but blocked DAMGO-stimulated [(35)S]-GTP-gamma-S binding. In cells expressing the cloned rat mu receptor, buprenorphine was a partial agonist and potent mu antagonist. Administration of buprenorphine to rats produced a long-lasting (>24 h) decrease in mu and kappa2 receptor binding and attenuated mu-stimulated [(35)S]-GTP-gamma-S binding. Viewed collectively, these data indicate that, in this assay system, buprenorphine is a potent mu and gamma receptor antagonist. The clinical implications remain to be elucidated. Synapse 34:83-94, 1999. Published 1999 Wiley-Liss, Inc.

Desipramine, amantadine, or fluoxetine in buprenorphine-maintained cocaine users

The clinical efficacy of promising cocaine anti-craving medications was examined in combination with buprenorphine. Twenty-one opioid-dependent cocaine abusers were enrolled in a double-blind, 12-week trial in which they received on a daily basis buprenorphine (8 mg, s.l.) plus either desipramine (150 mg, p.o.), amantadine (300 mg, p.o.), or fluoxetine (60 mg, p.o.). Urine samples and self-reported drug use were obtained 1-3 times/week. The order of greatest patient retention across the 12 weeks was desipramine (83.3%) > amantadine (66.7%) > fluoxetine (20.0%). The desipramine and amantadine groups appeared to have greater increases in opioid- and cocaine-free urines than the fluoxetine group. These results suggest that desipramine and amantadine may facilitate greater opioid and cocaine abstinence than fluoxetine.

Buprenorphine treatment of refractory depression

Opiates were used to treat major depression until the mid-1950s. The advent of opioids with mixed agonist-antagonist or partial agonist activity, with reduced dependence and abuse liabilities, has made possible the reevaluation of opioids for this indication. This is of potential importance for the population of depressed patients who are unresponsive to or intolerant of conventional antidepressant agents. Ten subjects with treatment-refractory, unipolar, nonpsychotic, major depression were treated with the opioid partial agonist buprenorphine in an open-label study. Three subjects were unable to tolerate more than two doses because of side effects including malaise, nausea, and dysphoria. The remaining seven completed 4 to 6 weeks of treatment and as a group showed clinically striking improvement in both subjective and objective measures of depression. Much of this improvement was observed by the end of 1 week of treatment and persisted throughout the trial. Four subjects achieved complete remission of symptoms by the end of the trial (Hamilton Rating Scale for Depression scores < or = 6), two were moderately improved, and one deteriorated. These findings suggest a possible role for buprenorphine in treating refractory depression.

Opioid peptide receptor studies. 3. Interaction of opioid peptides and other drugs with four subtypes of the kappa 2 receptor in guinea pig brain

Using guinea pig, rat, and human brain membranes depleted of mu and delta receptors by pretreatment with the site-directed acylating agents BIT (mu selective) and FIT (delta selective), previous studies from our laboratory resolved two subtypes of the kappa 2 binding site, termed kappa 2a and kappa 2b. In more recent studies, we used 6 beta-[125Iodo]-3,14-dihydroxy-17-cyclopropylmethyl-4,5 alpha-epoxymorphinan ([125I]IOXY) to characterize multiple kappa 2 binding sites in rat brain. The results indicated that [125I]IOXY, like [3H]bremazocine, selectively labels kappa 2 binding sites in rat brain membranes pretreated with BIT and FIT. In the rat brain, using 100 nM [D-Ala2-MePhe4,Gly-ol5]enkephalin to block [125I]IOXY binding to the kappa 2b site, we resolved two subtypes of the kappa 2a binding site. In the present study we examined the binding of [125I]IOXY to the kappa 2 receptors of guinea pig brain. As observed in rat brain, [125I]IOXY, under appropriate assay conditions, selectively labels kappa 2 binding sites. Quantitative binding studies readily demonstrated the presence of kappa 2a and kappa 2b binding sites. The kappa 2a binding sites were selectively assayed using 5 microM [Leu5]enkephalin to block [125I]IOXY binding to the kappa 2b sites, and kappa 2b sites were selectively assayed using 5 microM (-)-(1S,2S)-U50,488 to block [125I]IOXY binding to the kappa 2a sites. Under these conditions, two subtypes of the kappa 2a site were resolved with high (kappa 2a-1) and low (kappa 2a-2) affinity for nor-BNI (Ki values = 0.88 and 476 nM) and CI977 (Ki values = 17.5 and 95,098 nM). Similarly, two subtypes of the kappa 2b site were observed with high (kappa 2b-1) and low (kappa 2b-2) affinity for [D-Ala2-MePhe4,Gly-ol5]enkephalin (DAMGO) (Ki values = 97 and 12,321 nM) and alpha-neoendorphin (Ki values = 33 and 5308 nM). Two-site models were also resolved in the presence of 100 microM 5'-guanylyimidodiphosphate (GppNHp). We carried out detailed ligand selectivity analysis of the multiple kappa 2 binding sites. Most test agents were either nonselective or selective for the kappa 2a-1 site. Nalbuphine was moderately selective for the kappa 2a-2 site. Similarly, although most test agents were either nonselective or selective for the kappa 2b-1 site, butorphanol, and the delta antagonists naltrindole, naltriben, and 7-benzylidene-7-dehydronaltrexone were moderately selective for the kappa 2b-2 site.(ABSTRACT TRUNCATED AT 400 WORDS)

Selective labeling of kappa 2 opioid receptors in rat brain by [125I]IOXY: interaction of opioid peptides and other drugs with multiple kappa 2a binding sites

Recent studies from our laboratory resolved two subtypes of the kappa 2 binding site, termed kappa 2a and kappa 2b, using guinea pig, rat, and human brain membranes depleted of mu and delta receptors by pretreatment with the site-directed acylating agents BIT (mu-selective) and FIT (delta-selective). 6 beta-Iodo-3,14-dihydroxy-17-cyclopropylmethyl-4,5 alpha-epoxymorphinan (IOXY), an opioid antagonist that has high affinity for kappa 2 sites, was radioiodinated to maximum specific activity (2200 Ci/mmol) and purified by high pressure liquid chromatography and used to characterize multiple kappa 2 binding sites. The results indicated that [125I]IOXY, like [3H]bremazocine, selectively labels kappa 2 binding sites in rat brain membranes pretreated with BIT and FIT. Using 100 nM [D-Ala2-MePhe4,Gly-ol5]enkephalin to block [125I]IOXY binding to the kappa 2b site, two subtypes of the kappa 2a binding site were resolved, both in the absence and presence of 50 microM 5'-guanylyimidodiphosphate. Viewed collectively, these results provide further evidence for heterogeneity of the kappa opioid receptor, which may provide new targets for drug design, synthesis, and therapeutics.

The opioid system in neurologic and psychiatric disorders and in their experimental models

Evidence from experimental and clinical studies suggests the involvement of the endogenous opioid system in several neurologic and psychiatric disorders (Alzheimer's, Huntington's and Parkinson's diseases, drug-induced movement disorders, Gilles de la Tourette syndrome, stroke, ischemia, brain and spinal cord injury, epilepsy, schizophrenia and affective disorders). However, its involvement is rather a secondary one, perhaps being a severe consequence of a primary, nonopioid disturbance. Thus, treatment of an opioidergic manifestation of a disorder of nonopioidergic origin is necessarily symptomatic and targets only the restoration of the opioid system; such treatment may be beneficial in ameliorating the clinical symptoms of the disorder.

Depressive symptoms during buprenorphine treatment of opioid abusers

Among 40 opioid addicts treated as outpatients with sublingual buprenorphine (2-8 mg daily) for a month, depressive symptoms significantly decreased in the 19 who were depressed at intake to treatment.

Chronic electroconvulsive shock and neurotransmitter receptors--an update

Electroconvulsive shock (ECS) produces many neurochemical alterations which may be related to its efficacy in the treatment of different psychiatric disorders. This review focuses particularly on experimental findings of CNS receptor changes in animals following chronic ECS and relates them to neurotransmitter and behavioral changes. Also, the pharmacological effect of other antidepressant treatment are compared. Possible mechanisms of action are discussed.

Involvement of beta-endorphin and mu-opioid receptors in mediating the aversive effect of lithium in the rat

The role of beta-endorphin and mu-opioid receptors in mediating the motivational effect of lithium was examined by use of an unbiased place-preference conditioning procedure. Administration of lithium to drug-naive rats resulted in a dose-related aversion for the drug-associated place. Radiofrequency lesions of the medio-basal arcuate hypothalamus, which markedly reduced the levels of immunoreactive beta-endorphin in the hypothalamus, abolished the lithium-induced aversion. However, suppression of circulating beta-endorphin levels by chronic dexamethasone treatment was without effect. Infusion of the opioid antagonist, naloxone, throughout the conditioning procedure at a dose (0.5 mg/kg per h) that blocks mu- but not kappa-opioid receptors, resulted in the complete abolition of the lithium-induced place aversion. These data demonstrate an involvement of endogenous opioidergic systems in the motivational effect of lithium and indicate that the aversive properties of this drug result from its interactions with beta-endorphin and mu-opioid receptors in the CNS.

The effect of chronic imipramine and electroconvulsive shock treatment on [3H]DADLE binding to cortical membranes of rats pretreated with chronic reserpine or 6-hydroxydopamine

Repetitive electroconvulsive shock treatment (for 8 days) or chronic administration of imipramine (10 mg/kg/day IP for 14 or 21 days) elevated the density of opioid delta receptors in the cerebral cortex of the rat. Electroconvulsive shock treatment produced a similar effect in rats treated subchronically with reserpine or receiving intraventricularly 6-hydroxydopamine, but these manipulations of central catecholamines prevented the action of imipramine.

Opioid receptors in the brain of the rat following chronic treatment with desipramine and electroconvulsive shock

The effect of chronic administration of electroconvulsive shock and the antidepressant drug desipramine on binding to opioid receptors was studied in the cerebral cortex, the basal ganglia and the hippocampus of the forebrain of the rat. In vitro, desipramine inhibited the binding of enkephalinamide to opioid receptors through a reduction in the number of binding sites, whereas the affinity was unchanged or only slightly decreased. In vivo desipramine, injected daily (10 mg/kg) for three weeks, did not change the number of opioid binding sites in the forebrain of the rat. Chronic electroconvulsive shock, given twice a week for three weeks, had no effect on the number of opioid binding sites in the forebrain of the rat. The data do not support the hypothesis of shared effects of lithium, tricyclic antidepressants and electroconvulsive shock on the opioid peptide-opioid receptor systems.

Psychotomimesis mediated by kappa opiate receptors

The kappa opioid agonists are analgesics that seem to be free of undesired morphine-like effects. Their dysphoric actions observed with the kappa agonist cyclazocine are thought to be mediated by an action at sigma-phencyclidine receptors. The benzomorphan kappa agonist MR 2033 is inactive at sigma-phencyclidine receptors. In male subjects, the opiate-active (-)-isomer, but not the (+)-isomer, elicited dose-dependent dysphoric and psychotomimetic effects that were antagonized by naloxone. Thus, kappa opiate receptors seem to mediate psychotomimetic effects. In view of the euphorigenic properties of mu agonists, our results imply the existence of opposed opioid systems affecting emotional and perceptual experiences.

Buprenorphine as new treatment for heroin dependence

Dr. Jasinski suggested years ago that on the basis of some preliminary findings buprenorphine could hold promise for the treatment of heroin dependence (D. Jasinski, J.S. Pevnick and J.D. Griffith, Arch. Gen. Psychiatry, 35 (1978) 501)). No significant report has been published to confirm that assumption, and no treatment program seems to have started on that ground. Buprenorphine is now available in several countries including Belgium. We tried to devise a treatment program for heroin addicts combining chemotherapy with sublingual buprenorphine and psychotherapy. The interim results of this treatment program--initiated in 65 heroin addicts and undertaken by 34 of them for periods varying from 2 to 17 months--seem sufficiently promising to pursue our research.

The effects of the acute administration of buprenorphine hydrochloride on the release of anterior pituitary hormones in the rat: evidence for the involvement of multiple opiate receptors

Multiple opiate receptor agonists and antagonists have been found to produce different patterns of anterior pituitary hormone release. The present studies examined the pattern of anterior pituitary hormone release produced by buprenorphine. The effects of the kappa agonist ethylketocyclazocine on thyroid stimulating hormone release were also examined. Following buprenorphine, serum levels of corticosterone and luteinizing hormone were not changed while growth hormone release was stimulated in a dose-dependent manner. Prolactin release was stimulated after the lowest dose of buprenorphine while the highest dose induced a fall in serum prolactin. Similar biphasic effects on thyroid stimulating hormone were seen after either buprenorphine or ethylketocyclazocine. The results provide support for the role of multiple opiate receptors in opiate-induced changes in anterior pituitary hormone release.

Antidepressants and endogenous opioid peptide systems

The influence of antidepressants on the brain and pituitary content of immunoreactive beta-endorphin (ir-beta E) and dynorphin (ir-DYN) was studied in rats. Chronic administration of the first and second generation antidepressants imipramine, citalopram and rolipram, and of the antidepressant neuroleptics levomepromazine and chlorprothixene elevated the level of ir-beta E in the hypothalamus. Imipramine and levomepromazine also increased the level of ir-DYN in this tissue. Imipramine administered chronically potentiated stress-induced as well as morphine analgesia. The results obtained suggest that chronic antidepressants enhance the brain opioid system activity and increase the sensitivity of opiate receptors.

Effect of electroconvulsive treatment on cerebral opioid receptors in the rat: changes in delta but not mu receptors

The rats subjected to repetitive electroconvulsive treatment (ECT; 8 electroshocks within 9 days) the density of specific 3H-D-Ala2, D-Leu5-enkephalin (3H-DADLE) binding sites in the cortical membranes was enhanced by approx. 60%, while the density of specific 3H-naloxone binding sites remained unchanged. In the striatum of rats subjected to ECT the specific binding of 3H-DADLE was reduced by 15%, and no change in 3H-naloxone binding was observed. The density of specific binding sites for either radioligand in the rest of brain remained unaffected by ECT. The results suggest that ECT affects specifically the opioid delta receptors in some brain areas.

Increase in rat cortical [3H]naloxone binding site density after chronic administration of antidepressant agents

Given chronically, the first and second generation antidepressants imipramine and citalopram, and antidepressant neuroleptics levomepromazine and chlorprothixene, elevated moderately but significantly (by 15-30%) the density of [3H]naloxone binding sites in rat cerebral cortical membranes. There were only small non-significant changes in Kd values.

Enkephalins and Endorphins. Clinical, pharmacological and therapeutic implications

During the past 8 years there has been substantial progress in our understanding of the structure, distribution and action of endogenous opioid peptides. Currently, there appear to be 2 groups of peptides; those derived from beta-lipotropin and an enkephalin-related group. Some of these peptides have been shown to be distributed widely in the central nervous system and in endocrine tissues. The activity of the peptides probably occurs at several receptors but only 1 relatively specific (mu-receptor) antagonist, naloxone, is well studies. Although there have been many clinical studies of the action of opioids in man, no novel therapeutic applications have yet been established in clinical practice. Of the many areas of involvement attributed to opioids, those of analgesia, reproductive endocrinology, opiate dependence, and certain as yet undefined subtypes of major psychoses seem reasonably promising. Speculation surround opioid involvement in other disorders such as spinal trauma, septic shock, alcohol dependence, "functional' gastrointestinal disease, diabetes and asthma is of considerable interest but is supported by less clinical evidence. It seems that as research in opioids advances, the putative physiological opioid "spheres of influence' widen. At the same time, opioid mechanisms of action are being revealed to be more subtle and complex than previously thought. As a consequence, the expectations of rapid therapeutic application of opioid peptides and their antagonists are being modified and refined and realistic research strategies applied. In view of the work reviewed in this paper it seems reasonable to expect that such work will pay dividends in the not too distant future.