Behavioral and biological effects of acute beta-endorphin injection in schizophrenic and depressed patients

The endogenous opioid system in the medial prefrontal cortex mediates ketamine's antidepressant-like actions

Recent studies have implicated the endogenous opioid system in the antidepressant actions of ketamine, but the underlying mechanisms remain unclear. We used a combination of pharmacological, behavioral, and molecular approaches in rats to test the contribution of the prefrontal endogenous opioid system to the antidepressant-like effects of a single dose of ketamine. Both the behavioral actions of ketamine and their molecular correlates in the medial prefrontal cortex (mPFC) are blocked by acute systemic administration of naltrexone, a competitive opioid receptor antagonist. Naltrexone delivered directly into the mPFC similarly disrupts the behavioral effects of ketamine. Ketamine treatment rapidly increases levels of β-endorphin and the expression of the μ-opioid receptor gene (Oprm1) in the mPFC, and the expression of gene that encodes proopiomelanocortin, the precursor of β-endorphin, in the hypothalamus, in vivo. Finally, neutralization of β-endorphin in the mPFC using a specific antibody prior to ketamine treatment abolishes both behavioral and molecular effects. Together, these findings indicate that presence of β-endorphin and activation of opioid receptors in the mPFC are required for the antidepressant-like actions of ketamine.

The endogenous opioid system in the medial prefrontal cortex mediates ketamine's antidepressant-like actions

Recent studies have implicated the endogenous opioid system in the antidepressant actions of ketamine, but the underlying mechanisms remain unclear. We used a combination of pharmacological, behavioral, and molecular approaches in rats to test the contribution of the prefrontal endogenous opioid system to the antidepressant-like effects of a single dose of ketamine. Both the behavioral actions of ketamine and their molecular correlates in the medial prefrontal cortex (mPFC) were blocked by acute systemic administration of naltrexone, a competitive opioid receptor antagonist. Naltrexone delivered directly into the mPFC similarly disrupted the behavioral effects of ketamine. Ketamine treatment rapidly increased levels of β-endorphin and the expression of the μ-opioid receptor gene (Oprm1) in the mPFC, and the expression of the gene that encodes proopiomelanocortin, the precursor of β-endorphin, in the hypothalamus, in vivo. Finally, neutralization of β-endorphin in the mPFC using a specific antibody prior to ketamine treatment abolished both behavioral and molecular effects. Together, these findings indicate that presence of β-endorphin and activation of opioid receptors in the mPFC are required for the antidepressant-like actions of ketamine.

The Role of Physical Exercise in Opioid Substitution Therapy: Mechanisms of Sequential Effects

It is generally accepted that chronic opioid use is associated with structural and functional changes in the human brain that lead to an enhancement of impulsive behavior for immediate satisfaction. Interestingly, in recent years, physical exercise interventions have been used as an adjunctive treatment for patients with opioid use disorders (OUDs). Indeed, exercise has positive effects on both the biological and psychosocial basis of addiction, modifying neural circuits such as the reward, inhibition, and stress systems, and thus causing behavioral changes. This review focuses on the possible mechanisms that contribute to the beneficial effects of exercise on the treatment of OUDs, with emphasis placed on the description of a sequential consolidation of these mechanisms. Exercise is thought to act initially as a factor of internal activation and self-regulation and eventually as a factor of commitment. This approach suggests a sequential (temporal) consolidation of the functions of exercise in favor of gradual disengagement from addiction. Particularly, the sequence in which the exercise-induced mechanisms are consolidated follows the pattern of internal activation-self-regulation-commitment, eventually resulting in stimulation of the endocannabinoid and endogenous opioid systems. Additionally, this is accompanied by modification of molecular and behavioral aspects of opioid addiction. Overall, the neurobiological actions of exercise in combination with certain psychological mechanisms appear to promote its beneficial effects. Given the positive effects of exercise on both physical and mental health, exercise prescription is recommended as a complement to conventional therapy for patients on opioid maintenance treatment.

The Opioid System in Depression

Opioid receptors are widely distributed throughout the brain and play an essential role in modulating aspects of human mood, reward, and well-being. Accumulating evidence indicates the endogenous opioid system is dysregulated in depression and that pharmacological modulators of mu, delta, and kappa opioid receptors hold potential for the treatment of depression. Here we review animal and clinical data, highlighting evidence to support: dysregulation of the opioid system in depression, evidence for opioidergic modulation of behavioural processes and brain regions associated with depression, and evidence for opioidergic modulation in antidepressant responses. We evaluate clinical trials that have examined the safety and efficacy of opioidergic agents in depression and consider how the opioid system may be involved in the effects of other treatments, including ketamine, that are currently understood to exert antidepressant effects through non-opioidergic actions. Finally, we explore key neurochemical and molecular mechanisms underlying the potential therapeutic effects of opioid system engagement, that together provides a rationale for further investigation into this relevant target in the treatment of depression.

A meta-analysis of the potential antidepressant effects of buprenorphine versus placebo as an adjunctive pharmacotherapy for treatment-resistant depression

BACKGROUND

Numerous reports have suggested that buprenorphine may have antidepressant effects. Many individuals with depressive disorders don't respond to first-line treatment and are classified with treatment-resistant depression (TRD). Novel therapies for depression are required to better treat this population. This meta-analysis of randomized placebo-controlled trials sought to evaluate the potential antidepressant effects of buprenorphine as an adjunctive pharmacological treatment for individuals with TRD.

METHODS

PubMed, Embase, CINAHL, Web of Science, and ClinicalTrials.gov databases were searched until June 2019 for original peer-reviewed reports of buprenorphine used for the treatment of depression. Standardized mean differences (SMD) were generated from random effects models. Risk of publication bias was assessed using a funnel plot. Potential sources of heterogeneity were explored in subgroup analyses.

RESULTS

In six studies that met inclusion criteria, depression symptom severity in individuals with TRD was not significantly decreased after an adjunctive intervention with buprenorphine when compared to placebo (SMD = -0.07, 95% CI: -0.21-0.06, p = 0.30). Five of the six studies utilized a combination of buprenorphine/samidorphan. In these studies, depression symptom severity was also not significantly reduced after intervention compared to placebo (SMD = -0.08, 95% CI: -0.21 - 0.05, p = 0.23).

LIMITATIONS

Five included studies were performed by the same research group with significant conflicts of interest.

CONCLUSIONS

This meta-analysis did not reveal a significant reduction in depression symptom severity in individuals with TRD after an adjunctive intervention with buprenorphine when compared to placebo. However, more optimal doses of buprenorphine (2 mg/day) and longer treatment lengths should be explored.

What we have learned from the Methadone Maintenance Treatment of Dual Disorder Heroin Use Disorder patients

Mental Disorders and Heroin Use Disorder (HUD) often co-occur and constitute correlated risk factors that the authors believe are best considered from a unitary perspective. In this article we review and discuss data collected by the V.P. Dole Research Group in Dual Disorder (V.P. Dole DD-RG) patients according to the following six discussion points: (1) Treatment of personality disorders during Methadone Maintenance Treatment (MMT); (2) Treatment of Mood Disorders during MMT; (3) Treatment of Anxiety Disorders during MMT; (4) Treatment of Psychotic Disorders during MMT; (5) Treatment of violence during MMT; (6) Treatment of Alcohol Use Disorder (AUD) during MMT. In treating Mood Disorder in HUD patients, we must bear in mind the interactions (potentiation and side effects) between psychopharmacology, used substances and agonist opioid medications; the use of psychiatric medications as an anti-craving drug, and the possible use of agonist and antagonist opioid medications in treating the other mental disorders. In treating chronic psychosis in HUD patients, we must consider the potentiation and side effects of antipsychotic drugs consequent on HUD treatment, worsening addiction hypophoria and inducing a more severe reward deficiency syndrome (RDS) in hypophoric patients. Violence and AUD during MMT can benefit from adequate dosages of methadone and co-medication with Sodium gamma-hydroxybutyrate (GHB). The experience of our V.P. Dole DD-RG suggests the following: (a) DD is the new paradigm in neuroscience in deepening our understanding of mental health; (b) To successfully treat DD patients a double competence is needed; (c) In managing DD patients priority must be given to Substance Use Disorder (SUD) treatment (stabilizing patients); (d) Antidepressant use is ancillary to SUD treatment; antipsychotic use must be restricted to acute phases; mood stabilizers must be preferred; any use of Benzodiazepines (BDZs) must be avoided.

Endogenous opioid system dysregulation in depression: implications for new therapeutic approaches

The United States is in the midst of an opioid addiction and overdose crisis precipitated and exacerbated by use of prescription opioid medicines. The majority of opioid prescriptions are dispensed to patients with comorbid mood disorders including major depressive disorder (MDD). A growing body of research indicates that the endogenous opioid system is directly involved in the regulation of mood and is dysregulated in MDD. This involvement of the endogenous opioid system may underlie the disproportionate use of opioids among patients with mood disorders. Emerging approaches to address endogenous opioid dysregulation in MDD may yield novel therapeutics that have a low or absent risk of abuse and addiction relative to µ-opioid agonists. Moreover, agents targeting the endogenous opioid system would be expected to yield clinical benefits qualitatively different from conventional monaminergic antidepressants. The development of safe and effective agents to treat MDD-associated endogenous opioid dysregulation may represent a distinct and currently underappreciated means of addressing treatment resistant depression with the potential to attenuate the on-going opioid crisis.

Medications between psychiatric and addictive disorders

INTRODUCTION

Many epidemiological studies have revealed a frequent co-occurrence of psychiatric and substance use disorders. The term used in the literature to refer to this co-occurrence is dual diagnosis. The high prevalence of dual diagnosis has led physicians to observe the effects of medication prescribed to treat psychiatric disorders on the co-occurring substance use disorder and vice versa. The concept of medications between psychiatric and addictive disorders stems from these clinical observations, alongside which, however, it has developed from the observation that both psychiatric and substance use disorders share common neurobiological pathways and trigger common cognitive disorders. This has led researchers to develop medications on the basis of neurobiological and cognitive rationales.

MATERIAL AND METHOD

In our article, we review peculiar medications based on neurobiological and cognitive rationales and that have an impact in both psychiatric and addictive disorders.

RESULTS

We highlight how interesting these new prescriptions are for clinical observation and for the treatment of patients suffering from dual diagnosis.

CONCLUSION

We then go on to discuss the interest in them from the perspective of clinical practice and clinical research, in that the development of medications to treat dual diagnosis helps to further our knowledge of both psychiatric and substance use disorders.

Reconsidering anhedonia in depression: lessons from translational neuroscience

Anhedonia is a core symptom of major depressive disorder (MDD), the neurobiological mechanisms of which remain poorly understood. Despite decades of speculation regarding the role of dopamine (DA) in anhedonic symptoms, empirical evidence has remained elusive, with frequent reports of contradictory findings. In the present review, we argue that this has resulted from an underspecified definition of anhedonia, which has failed to dissociate between consummatory and motivational aspects of reward behavior. Given substantial preclinical evidence that DA is involved primarily in motivational aspects of reward, we suggest that a refined definition of anhedonia that distinguishes between deficits in pleasure and motivation is essential for the purposes of identifying its neurobiological substrates. Moreover, bridging the gap between preclinical and clinical models of anhedonia may require moving away from the conceptualization of anhedonia as a steady-state, mood-like phenomena. Consequently, we introduce the term "decisional anhedonia" to address the influence of anhedonia on reward decision-making. These proposed modifications to the theoretical definition of anhedonia have implications for research, assessment and treatment of MDD.

The role of beta-endorphin in the pathophysiology of major depression

A role for beta-endorphin (beta-END) in the pathophysiology of major depressive disorder (MDD) is suggested by both animal research and studies examining clinical populations. The major etiological theories of depression include brain regions and neural systems that interact with opioid systems and beta-END. Recent preclinical data have demonstrated multiple roles for beta-END in the regulation of complex homeostatic and behavioural processes that are affected during a depressive episode. Additionally, beta-END inputs to regulatory pathways involving feeding behaviours, motivation, and specific types of motor activity have important implications in defining the biological foundations for specific depressive symptoms. Early research linking beta-END to MDD did so in the context of the hypothalamic-pituitary-adrenal (HPA) axis activity, where it was suggested that HPA axis dysregulation may account for depressive symptoms in some individuals. The primary aims of this paper are to use both preclinical and clinical research (a) to critically review data that explores potential roles for beta-END in the pathophysiology of MDD and (b) to highlight gaps in the literature that limit further development of etiological theories of depression and testable hypotheses. In addition to examining methodological and theoretical challenges of past clinical studies, we summarize studies that have investigated basal beta-END levels in MDD and that have used challenge tests to examine beta-END responses to a variety of experimental paradigms. A brief description of the synthesis, location in the CNS and behavioural pharmacology of this neuropeptide is also provided to frame this discussion. Given the lack of clinical improvement observed with currently available antidepressants in a significant proportion of depressed individuals, it is imperative that novel mechanisms be investigated for antidepressant potential. We conclude that the renewed interest in elucidating the role of beta-END in the pathophysiology of MDD must be paralleled by consensus building within the research community around the heterogeneity inherent in mood disorders, standardization of experimental protocols, improved discrimination of POMC products in analytical techniques and consistent attention paid to important confounds like age and gender.

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.

Possible use of repeated cold stress for reducing fatigue in chronic fatigue syndrome: a hypothesis

BACKGROUND

Physiological fatigue can be defined as a reduction in the force output and/or energy-generating capacity of skeletal muscle after exertion, which may manifest itself as an inability to continue exercise or usual activities at the same intensity. A typical example of a fatigue-related disorder is chronic fatigue syndrome (CFS), a disabling condition of unknown etiology and with uncertain therapeutic options. Recent advances in elucidating pathophysiology of this disorder revealed hypofunction of the hypothalamic-pituitary-adrenal axis and that fatigue in CFS patients appears to be associated with reduced motor neurotransmission in the central nervous system (CNS) and to a smaller extent with increased fatigability of skeletal muscle. There is also some limited evidence that CFS patients may have excessive serotonergic activity in the brain and low opioid tone.

PRESENTATION OF THE HYPOTHESIS

This work hypothesizes that repeated cold stress may reduce fatigue in CFS because brief exposure to cold may transiently reverse some physiological changes associated with this illness. For example, exposure to cold can activate components of the reticular activating system such as raphe nuclei and locus ceruleus, which can result in activation of behavior and increased capacity of the CNS to recruit motoneurons. Cold stress has also been shown to reduce the level of serotonin in most regions of the brain (except brainstem), which would be consistent with reduced fatigue according to animal models of exercise-related fatigue. Finally, exposure to cold increases metabolic rate and transiently activates the hypothalamic-pituitary-adrenal axis as evidenced by a temporary increase in the plasma levels of adrenocorticotropic hormone, beta-endorphin and a modest increase in cortisol. The increased opioid tone and high metabolic rate could diminish fatigue by reducing muscle pain and accelerating recovery of fatigued muscle, respectively.

TESTING THE HYPOTHESIS

To test the hypothesis, a treatment is proposed that consists of adapted cold showers (20 degrees Celsius, 3 minutes, preceded by a 5-minute gradual adaptation to make the procedure more comfortable) used twice daily.

IMPLICATIONS OF THE HYPOTHESIS

If testing supports the proposed hypothesis, this could advance our understanding of the mechanisms of fatigue in CFS.

Salivary cortisol during opiate dependence and withdrawal

Seventeen inpatients (14 men, three women) with opiate dependence and polysubstance misuse participated in a longitudinal study of salivary cortisol secretion during and after lofexidine detoxification treatment. Both opiate withdrawal symptoms and salivary cortisol were measured every morning for up to 25 days. Results were compared with a control group of 10 normal volunteers. There was an 80% reduction in withdrawal symptom severity between the first 12 days and the subsequent 12 days of treatment. Salivary cortisol fell from a mean of 22.3 nm/l over days 1-12 to 18.5 nm/l during days 13-25, a reduction of 17%. Salivary cortisol concentration correlated significantly with withdrawal symptom severity. Salivary cortisol levels remained significantly higher than controls for the duration of the study. The study supports a role for hypothalamo-pituitary-adrenal (HPA) activation in opiate withdrawal. The contribution of persistant dysregulation of the HPA, found in this study, to the vulnerability for relapse after abstinence has been achieved, is discussed.

Naltrexone augmentation of neuroleptics in schizophrenia

This study was conducted to determine whether the addition of naltrexone to ongoing neuroleptic treatment would facilitate the reduction in positive or negative symptoms in patients with schizophrenia. Twenty-one patients meeting DSM-III criteria for schizophrenia were enrolled; all patients had been stabilized for at least 2 weeks on their dosage of neuroleptic medicine before entering the study. Patients were randomized to receive either placebo or naltrexone 200 mg/day for 3 weeks in addition to their neuroleptic. Patients randomized initially into the placebo arm were crossed over to receive naltrexone in a single-blind fashion for 3 additional weeks. All patients were rated weekly with the Brief Psychiatric Rating Scale (BPRS). Fifteen patients received placebo and six received naltrexone in the first 3 weeks. No significant effects of naltrexone on total BPRS scores or BPRS subscale scores were observed. Patients who received naltrexone on a single-blind basis at the end of the placebo-controlled trial demonstrated a transient exacerbation in negative symptoms as reflected by the total BPRS score and the BPRS Withdrawal-Retardation subscale score. Repeated-measures analysis of variance (ANOVA) on the BPRS total score of the subsequent treatment with naltrexone showed a trend for a significance in the drug by time effect. Repeated-measures ANOVA on the BPRS Withdrawal-Retardation subscale of the subsequent treatment with naltrexone showed a significant drug by time effect. The current data failed to indicate a clinical benefit when naltrexone was added to the neuroleptic regimen. Other potential applications of naltrexone in schizophrenia are addressed.

The placebo effect on mood and behavior: the role of the endogenous opioid system

Evidence from clinical and experimental studies has shown that placebos influence mood and behavior, that endogenous opioids are involved in the placebo effect, and that the endogenous opioid system is related to psychological events. Recent studies have also demonstrated that the endogenous opioid system is closely connected with other neurotransmitter systems in the brain. The author suggests that the interaction between the endogenous opioid system and different neurotransmitter systems in the brain mediates the placebo effect on mood and behavior of both healthy and sick people.

Pharmacological validation of the chronic mild stress model of depression

Chronic exposure to mild unpredictable stress has previously been found to depress the consumption of palatable sweet solutions, and this effect was reversed by chronic treatment with a variety of antidepressant drugs. The present study reports three experiments examining the effects in this model of further antidepressant agents, a number of non-antidepressants, and some compounds of indeterminate clinical status. Male Wistar rats were exposed sequentially to a variety of mild stressors, which continued throught the experiments. Drug treatments commenced after 3 weeks of stress, by which time intake of a 1% sucrose solution (measured in a 1-h weekly test) was significantly depressed. No drug effects were seen after 1 week of treatment. Normal levels of sucrose drinking were seen following chronic (3-5 weeks) of treatment with the antidepressants imipramine (10 mg/kg per day), brofaromine (20 mg/kg per day), and buspirone (5 mg/kg per day). Positive effects were also seen following chronic treatment with atropine (1 mg/kg per day) and mepyramine (5 mg/kg per day). d-Amphetamine (1 and 3 mg/kg per day), the neuroleptics haloperidol and chlorprothixene (1 mg/kg per day), and morphine (administered at doses rising to 110 mg/kg per day) were ineffective; amphetamine (3 mg/kg) and morphine decreased sucrose intake in control animals. No inferences can be drawn from the effects of atropine and mepyramine, which are of indeterminate clinical status; data from the other seven agents tested support the hypothesis that the chronic mild stress model responds appropriately to antidepressant and non-antidepressant agents.

Effects of morphine, naloxone and their interaction in the learned-helplessness paradigm in rats

The aim of this study was to investigate the possible involvement of the mu-opioid system on the learned-helplessness paradigm, an experimental model of depression, in rats. In this test, rats were first exposed to inescapable foot-shocks (IS); 48 h later, they were submitted to a daily shuttle-box session (30 trials) for 3 consecutive days. Avoidance responses, escape failures and animal activity during each intertrial interval were recorded. Twice daily injections of morphine (0.25-8 mg/kg per day, SC), a mu-opioid agonist, reduced the increased escape failures induced by IS, as did tricyclic antidepressants. Significantly higher intertrial activity was observed in rats treated with morphine (2-8 mg/kg per day) compared with their associated control groups. Naloxone (1 and 2 mg/kg, IP), a mu-opioid antagonist, injected 10 min before each shuttle-box session impaired escape behavior in non-stressed rats and worsened the escape deficit induced by IS. Morphine-induced improvement of escape behavior and increase in intertrial activity were clearly reversed by a low inactive dose of naloxone (0.5 mg/kg). These results suggest that mu-opioid receptor mediation is involved in the deleterious effects of uncontrollable stress.

Inadequate treatment response to des-enkephalin-gamma-endorphin compared with thioridazine and placebo in schizophrenia

The possibility of an involvement of peptidergic systems in schizophrenia has been under investigation for a number of years. Studies of the efficacy of des-tyr-gamma-endorphin were equivocal; more recent studies with des-enkephalin-gamma-endorphin have reported some activity but the peptide has only been investigated as an adjunct to neuroleptic medication, apart from one very small active reference comparator study. In the multicentre study reported here, 96 patients suffering from schizophrenia (DSM-III with a current exacerbation if chronic) were allocated randomly to double-blind treatment with either des-enkephalin-gamma-endorphin (DE-gamma-E) (Org 5878) 10 mg given as a once daily intramuscular injection for 4 weeks, thioridazine 400 mg orally in 2 divided doses or placebo using a double-dummy technique to preserve blindness. There was a significant advantage for thioridazine compared with placebo registered on all measures at weeks 3 and 4. There was no difference between DE-gamma-E and placebo. There was a significant difference between thioridazine and DE-gamma-E at weeks 3 and 4 registered on the MSS and at week 3 registered on the BPRS. The lack of efficacy of DE-gamma-E suggests that the theories that the endorphins have an important role in schizophrenia have to be revised. The need for well designed placebo controlled studies for assessing efficacy in schizophrenia is emphasized.

Hypercortisolism after opioid discontinuation in rapid detoxification of heroin addicts

Long-term opioid consumption can induce hypoadrenalism through impairment of the hypothalamic-pituitary-adrenal axis. Results of the present study showed that, in heroin addicts, saliva cortisol concentrations varied according to the amount of recently consumed heroin and the time elapsed since the last self-administration. Hypercortisolism was observed either after abrupt withdrawal of heroin or the last dose of methadone. Post-detoxification hypercortisolism was still present on day 16 after the last opioid consumption, whereas it was not observed in abstinent addicts for a mean period of 4 months. During detoxification treatment, mean AUC8-24 cortisol in saliva of clonidine or guanfacine-treated patients was significantly higher than that in methadone-treated patients. It may be hypothesized that elevated cortisol levels may account for untoward effects of adrenergic agonist therapy which, in turn, may represent an added risk factor for relapse during detoxification. Further studies are necessary to correlate the severity of withdrawal symptoms to cortisol levels in opioid addicts detoxified with alpha 2-adrenergic agonist substitution.

Clinical and biochemical aspects of depressive disorders: II. Transmitter/receptor theories

The present document is the second of three parts in a review that focuses on recent data from clinical and animal research concerning the biochemical bases of depressive disorders, diagnosis, and treatment. Various receptor/transmitter theories of depressive disorders are discussed in this section. Specifically, data supporting noradrenergic, serotonergic, cholinergic, dopaminergic, GABAergic, and peptidergic theories, as well as interactions between noradrenergic and serotonergic, or cholinergic and catecholaminergic systems are presented. Problems with the data and future directions for research are also discussed. A previous publication, Part I of this review, dealt with the classification of depressive disorders and research techniques for studying the biochemical mechanisms of these disorders. A future publication, Part III of this review, discusses treatments for depression and some of the controversies in this field.

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.

Loss of the cortisol response to naltrexone in Alzheimer's disease

The administration of a single dose of the opiate antagonist naltrexone (NT) was accompanied by significant elevations in plasma cortisol in normal elderly subjects; in contrast, the cortisol response to NT was absent in individuals of comparable age with Alzheimer's disease (AD). The differential effect of AD on the cortisol response was not accompanied by a significant group difference in plasma prolactin in response to NT administration. Furthermore, this differential cortisol response to NT was not associated with any evident differences in age, sex ratio, plasma levels of naltrexone or its major metabolite beta-naltrexol, or with differences in measures of nonspecific stress, such as plasma free MHPG, pulse, or blood pressure, between the two groups. The absence of the well-characterized cortisol response to NT in AD, together with other reports of abnormal responses to other pharmacological challenges, suggests that neuroendocrine abnormalities might be an important concomitant and possibly a central contributor to the pathophysiology of Alzheimer's disease.

Clinical relevance of endorphins in psychiatry

1. 13 years after the discovery of endorphins, the relationships between these peptides and mental illness remain unclear. 2. Current concepts are controversial and convincing hypotheses have not been elaborated yet. 3. Endorphin measurements in CSF or serum of psychiatric patients did not strongly support that schizophrenia or depression is related to a deficit or an excess of these peptides. Moreover, treatment with endorphins or opiate antagonists did not result in a distinct change of psychiatric symptoms. Recently, research focused on the relationship between endorphins and addictive behavior, but substantial evidence for clinical relevance is still missing. 4. The physiological relevance of many newly discovered endorphins is barely known and several subtypes of the opiate receptor have been found. Thus, it will still require a substantial effort in basic and clinical studies before, if at all, endorphins turn out to be helpful in the treatment of mental illness.

Multiple hormonal responses to morphine: relationship to diagnosis and dexamethasone suppression

Plasma cortisol, prolactin (PRL), growth hormone (GH), and thyroid stimulating hormone (TSH) responses to intravenous morphine (0.1 mg/kg body weight) were investigated in five healthy women and 22 female psychiatric inpatients (eight with major depression, 12 with schizophrenia and two with personality disorders) during a 120 min period. The results were also related to a subsequent dexamethasone suppression test (DST). Morphine caused a strong and progressive decline in plasma cortisol which was uniform in controls, depressed, and nondepressed patients. DST nonsuppressors had significantly higher cortisol levels during the entire period, but the same response to morphine. Morphine strongly stimulated PRL secretion, which was found to be significantly smaller in patients than in controls, but no difference was seen between depressed and nondepressed subjects. GH and TSH showed only minor and variable changes after morphine, with no overall significant differences. The data in this study do not support the assumption of a major alteration in opiate receptor responsivity either in depression or in DST nonsuppressor patients insofar as the regulation of the adrenal, thyroid, GH and PRL hormone secretion is concerned.

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.

beta-Endorphin: intranasal administration increases the serum prolactin level in monkey

Human beta-endorphin has been administered by nasal spray technique at a dose of 0.02 mg per kg in female bonnet monkeys. A significant increase of serum prolactin levels was observed within 30 min and maintained up to 60 min. In the same dose, intravenous injections of the hormone caused a marginal increase of prolactin levels only after 60 min. It was concluded that administration of beta-endorphin by nasal spray is more effective than the intravenous injection.

Endogenous opioid regulation of hypothalamo-pituitary-adrenal axis activity in schizophrenia

We utilized a naloxone challenge strategy to investigate the functioning of the endogenous opioid system (EOS) in schizophrenia. Patients with schizophrenia, who were on neuroleptic medication or drug-free, demonstrated a significantly larger serum cortisol response to opioid blockade by naloxone than did age- and sex-matched normal controls. Patients, but not normal controls, also demonstrated an inverse relationship between baseline cortisol and the magnitude of the response. This enhanced cortisol response is consistent with tonic hyperactivity of the EOS in schizophrenia.

Enkephalin analogue in schizophrenia. Double blind cross-over trial

In a double blind, cross-over study 10 chronic schizophrenic patients with productive symptoms in spite of neuroleptic treatment received the methionine-enkephalin analogue FK 33-824 2 mg i.m. daily for 7 consecutive days. Ratings performed by the Brief Psychiatric Rating Scale did not show any significant differences between FK 33-824 and the active placebo pentobarbital. The clinical condition of one patient worsened during and after the administration of FK 33-824. It is suggested that this might be due to a dopamine stimulating effect. The discrepancy between the findings of the present and a previous open study is discussed. The present study does not support the hypothesis of dysfunction of the endorphin system in schizophrenia.

Hormonal effects of high dose naloxone in humans

Utilizing a double-blind crossover design, the hormonal effects of high dose, 2 mg/kg, were compared to low dose, 0.4 mg (approx. 5 micrograms/kg), naloxone administration in physically healthy humans. A significant naloxone dose effect on plasma cortisol levels was found (p less than 0.001), but no significant effect on plasma or serum levels of prolactin, follicle stimulating hormone, luteinizing hormone, norepinephrine or epinephrine. These results confirm involvement of the endogenous opioid system (EOS) in the tonic regulation of the hypothalamicpituitary-adrenal axis, but fail to find evidence of EOS involvement in the regulation of adrenal medullary function or the gonadotrophic axis in man. The results are however consistent with a continuing action of naloxone as an EOS antagonist even at high doses in man.

Endogenous opiates and schizophrenia: directions in clinical research

In the past decade both basic and clinical research on endogenous opiates has involved many aspects of medicine. This review focuses on the clinical literature that relates physiology and pathophysiology of the endogenous opiates to schizophrenia. Three major investigative approaches are described and their results evaluated. These approaches are described and their results evaluated. These approaches include assays of endogenous opiates in the context of clinical illness and use of exogenous opiates as well as exogenous opiate antagonists in the treatment of clinical illness. Current understanding at both the basic science and clinical research levels does not allow firm conclusions about the role of endogenous opiates in schizophrenia; however, the evolution of the growing understanding is used by the author to provide a speculative hypothesis.

Brain peptides: what, where, and why?

Within the past decade, a large number of peptides have been described within the vertebrate central nervous system. Some of these peptides were previously known to be present in nonneural vertebrate tissues, as well as in lower species, in which they may serve as primitive elements of intercellular communication prior to the development of neuronal or endocrine systems. In vertebrates, these peptides are thought to have neurotransmitter or neuromodulatory roles and appear to be involved in the regulation of a number of homeostatic systems, although the mechanisms of their actions are still unclear.

The relationship of plasma cortisol and beta-endorphin immunoreactivity to surgical stress and postoperative analgesic requirement

It has been hypothesized that the endogenous opioid (endorphin) system is related to biologic stress responses. We have used general surgery as a naturalistic model for studying stress response in humans. Abdominal surgery, but not anesthesia induction, was associated with significant increases in plasma beta-endorphin immunoreactivity and cortisol. Both hormones decreased significantly during post-operative morphine administration. Baseline and mean surgery levels of plasma beta-endorphin immunoreactivity showed an inverse relationship with post-operative analgesic requirement. These data support involvement of the endorphin system in human stress response and in human endogenous analgesic mechanisms. Findings also support the concept that baseline or psychologically stimulated levels of arousal may also be an important determinant in the physiology of stress response and pain perception.

High-dose naloxone affects task performance in normal subjects

Increasing intravenous doses of naloxone (0.3 mg/kg, 1 mg/kg, and 2 mg/kg) were administered to normal subjects. Naloxone at 2 mg/kg, but not at lower doses, impaired aspects of memory as measured by a verbal learning task which assessed the direct free recall and recognition of presented versus non-presented words of a single category (effortful processing) and the monitoring of the frequency of such presentations (automatic processing). At the same time "working" memory was left unaffected. The results suggest a role for the opioid system in some memory processes in man.

Endorphins in the cerebrospinal fluid of psychiatric patients

In this paper we have reported the results of studies in psychiatric patient groups using the strategy of measuring opioid activity and beta-endorphin (ir) in CSF. Our findings do not lend support to the notion of excess endorphin activity in schizophrenia, but rather suggest the possibility of a decrease in endogenous opioid activity in some schizophrenic patients. In affectively ill patients our data suggest that there may be a relative change in endogenous opioid system activity across state change in manic-depressive illness. Who also found a relationship between nurses' ratings of anxiety and CSF opioid activity in depressed patients, although it is unknown whether this directly relates to the pathophysiology of this symptom, or is related to stress response. The relationship between CSF opioid activity and HPA axis activity, as reflected by urinary free cortisol excretion, supports the notion of important physiologic relationships between these systems and raises the issue of a role for the endogenous opioid system in the abnormal activation of this system in depression. Finally, the finding of increased CSF opioid activity in anorexia nervosa patients when a minimum weight coupled with data relating endogenous opioids to eating behavior raises interesting questions regarding a possible involvement of the endogenous opioid system involvement in this illness.

Endogenous opiates: 1981

This paper is the fourth of an annual series reviewing the research concerning the endogenous opiate peptides. This installment covers only work published during 1981 and attempts to provide a comprehensive, but not exhaustive, survey of the area. Previous papers in the series have dealt with research done before 1981. Topics concerning endogenous opiates reviewed here include a delineation of their receptors, their distribution, their precursors and degradation, behavioral effects resulting from their administration, their possible involvement in physiological responses, and their interactions with other peptides and hormones. Due to the burgeoning literature in this field, the comprehensive nature of this review in the future will be limited to considerations of behavioral phenomena related to the endogenous opiates.

Response of plasma beta-endorphin immunoreactivity to d-amphetamine and placebo in schizophrenic patients

The response of plasma beta-endorphin (ir) to infusions of randomly assigned d-amphetamine (20 mg) and placebo was studied in eight schizophrenic patients. Although there was no statistically significant difference between the response to d-amphetamine and placebo, significant increases in plasma beta-endorphin (ir) levels were observed following each infusion. Although heterogeneity in beta-endorphin (ir) response was observed, individual differences did not relate to clinical variables such as abnormalities on computed tomography or "process-reactive" distinctions. An excessive beta-endorphin response to placebo in schizophrenia is discussed.

Physiological effects of high dose naloxone administration to normal adults

The intravenous bolus administration of high doses of the opioid receptor antagonist naloxone (in the mg./kg. range) to normal adults produced dose-dependent increases in systolic blood pressure and respiratory rate. No significant alterations in other physiological processes were found although there were trends for increases in oral temperature and pulse rate with increasing dose. These results suggest the involvement of an endogenous opioid system in the tonic regulation of human systolic blood pressure and respiration and the probable inadequacy of doses of naloxone previously utilized in human studies to effect complete blockade of endogenous opioid systems.