Dopamine and the action of opiates: a reevaluation of the dopamine hypothesis of schizophrenia. With special consideration of the role of endogenous opioids in the pathogenesis of schizophrenia

Opioid modulation of prefrontal cortex cells and circuits

Several neurochemical systems converge in the prefrontal cortex (PFC) to regulate cognitive and motivated behaviors. A rich network of endogenous opioid peptides and receptors spans multiple PFC cell types and circuits, and this extensive opioid system has emerged as a key substrate underlying reward, motivation, affective behaviors, and adaptations to stress. Here, we review the current evidence for dysregulated cortical opioid signaling in the pathogenesis of psychiatric disorders. We begin by providing an introduction to the basic anatomy and function of the cortical opioid system, followed by a discussion of endogenous and exogenous opioid modulation of PFC function at the behavioral, cellular, and synaptic level. Finally, we highlight the therapeutic potential of endogenous opioid targets in the treatment of psychiatric disorders, synthesizing clinical reports of altered opioid peptide and receptor expression and activity in human patients and summarizing new developments in opioid-based medications. This article is part of the Special Issue on "PFC circuit function in psychiatric disease and relevant models".

Methadone Withdrawal-Induced Psychosis: A Case Report

Methadone is a synthetic full µ-opioid receptor agonist and N-methyl-D-aspartate antagonist given to patients who have recently stopped using illicit opioids or are tapering off chronic opioid pain medication. Maintenance treatment with methadone is today the most widespread and effective way to treat opiate addiction, which achieves abstinence, decreases morbidity and mortality, improves quality of life, and reduces crime genesis, among other benefits. It is also approved by the Food and Drug Administration for treating moderate-to-severe pain that remains unresponsive to nonopioid medications. Patients sometimes abruptly discontinue the medication for several reasons and sometimes suffer distressing but non-life-threatening withdrawal symptoms. More common withdrawal symptoms include anxiety, agitation, rhinorrhea, nausea, and vomiting, like other opioid agonist medications. Psychosis has been reported in some rare cases of methadone withdrawal. However, more research is required because, although psychotic symptoms have been described in different case reports after the reduction or withdrawal of methadone, they have not been sufficient. This case report contributes to the literature on rare manifestations of psychosis in patients who abruptly discontinue the use of methadone.

Methadone Withdrawal-Related Psychosis in a Patient With Hormone-Dependent Breast Cancer: A Case Report

Methadone withdrawal usually presents as a classical opiate withdrawal syndrome, including symptoms such as restlessness, pupillary dilation, sweating, insomnia, irritability, sneezing, nausea, vomiting, and diarrhea. It rarely manifests as psychosis. Here, we discuss the case of a 43-year-old female with a history of long-term methadone use who presented with first-episode psychosis during methadone down-titration. She exhibited persecutory delusions and auditory hallucinations, unrelated to classical opiate withdrawal symptoms. Medical tests were unremarkable. The patient was diagnosed with first-episode psychosis and was involuntarily admitted to our psychiatric hospital. As she suffered from hormone-dependent breast cancer and presented paliperidone-induced hyperprolactinemia, we switched this drug to aripiprazole, a prolactin-sparing antipsychotic. Her psychotic symptoms remitted in six weeks, with no reintroduction of methadone. It remains unclear whether this presentation is attributable to a rare manifestation of withdrawal or methadone's antipsychotic properties, masking an underlying psychotic disorder. This case contributes to understanding psychosis emergence post-opioid withdrawal, underscoring the need for further investigation into withdrawal-related psychosis and opioid antipsychotic properties. It also prompts the discussion of antipsychotic treatment in patients with comorbid breast cancer, while evidence about hyperprolactinemia as a risk factor for breast cancer remains conflicting.

Psychiatric comorbidities and concurrent substance use among people who inject drugs: a single-centre hospital-based study

The management of people who inject drugs (PWID) is compounded by the presence of psychiatric comorbidities leading to frequent relapses and poor treatment outcomes. Early identification and treatment of psychiatric comorbidities should be included in the management to enhance treatment outcomes. The objective of this study was to estimate the prevalence of psychiatric comorbidities and concurrent substance use among opioid injectors. This hospital-based, cross-sectional study was conducted from March 2021 to August 2022. This study included opioid injectors of all ages and both sexes. The Mini International Neuropsychiatric Interview-7 (MINI-7) and WHO-ASSIST were used to determine psychiatric comorbidities and concurrent substance use, respectively. Both crude and adjusted odds ratios were calculated to assess associations among demographic variables, concurrent substance use and psychiatric comorbidities. Among the 328 opioid injectors, the overall prevalence of psychiatric comorbidities was 88.1%, with the majority (68.6%) having more than one comorbidity. The most common psychiatric comorbidities were panic disorder (41.2%), social anxiety disorder (40.5%), and antisocial personality disorder (39.3%). Concurrent use of alcoholic beverages doubled the risk of ASPD (odds ratio 2.14 (1.24-3.72)). Cocaine (odds ratio 2.36 (1.10-5.03)) and amphetamines (odds ratio 7.68 (2.21-26.65)) increased the risk of OCD. Daily heroin injections were negatively associated (odds ratio 0.18 (0.03-0.94)) with psychotic disorders. Younger age (adjusted odds ratio 0.20 (0.79-0.53)) and never married status (adjusted odds ratio 2.62 (1.06-6.47)) were the only significant variables in the regression analysis. In conclusion, opioid injectors had a higher prevalence of numerous psychiatric comorbidities. The most common comorbidity was anxiety disorders. Concurrent use of tobacco, cannabis, cocaine, inhalants, etc., greatly increased the risk of psychiatric comorbidities.

Reward processing in schizophrenia and its relation to Mu opioid receptor availability and negative symptoms: A [11C]-carfentanil PET and fMRI study

BACKGROUND

Reward processing deficits are a core feature of schizophrenia and are thought to underlie negative symptoms. Pre-clinical evidence suggests that opioid neurotransmission is linked to reward processing. However, the contribution of Mu Opioid Receptor (MOR) signalling to the reward processing abnormalities in schizophrenia is unknown. Here, we examined the association between MOR availability and the neural processes underlying reward anticipation in patients with schizophrenia using multimodal neuroimaging.

METHOD

37 subjects (18 with Schizophrenia with moderate severity negative symptoms and 19 age and sex-matched healthy controls) underwent a functional MRI scan while performing the Monetary Incentive Delay (MID) task to measure the neural response to reward anticipation. Participants also had a [11C]-carfentanil PET scan to measure MOR availability.

RESULTS

Reward anticipation was associated with increased neural activation in a widespread network of brain regions including the striatum. Patients with schizophrenia had both significantly lower MOR availability in the striatum as well as striatal hypoactivation during reward anticipation. However, there was no association between MOR availability and striatal neural activity during reward anticipation in either patient or controls (Pearson's Correlation, controls df = 17, r = 0.321, p = 0.18, patients df = 16, r = 0.295, p = 0.24). There was no association between anticipation-related neural activation and negative symptoms (r = -0.120, p = 0.14) or anhedonia severity (social r = -0.365, p = 0.14 physical r = -0.120, p = 0.63).

CONCLUSIONS

Our data suggest reduced MOR availability in schizophrenia might not underlie striatal hypoactivation during reward anticipation in patients with established illness. Therefore, other mechanisms, such as dopamine dysfunction, warrant further investigation as treatment targets for this aspect of the disorder.

The implications of hypothalamic abnormalities for schizophrenia

Until a few years ago, the hypothalamus was believed to play only a marginal role in schizophrenia pathophysiology. However, recent findings show that this rather small brain region involved in many pathways found disrupted-in schizophrenia. Gross anatomic abnormalities (volume changes of the third ventricle, the hypothalamus, and its individual nuclei) as well as alterations at the cellular level (circumscribed loss of neurons) can be observed. Further, increased or decreased expression of hypothalamic peptides such as oxytocin, vasopressin, several factors involved in the regulation of appetite and satiety, endogenous opiates, products of schizophrenia susceptibility genes as well as of enzymes involved in neurotransmitter and neuropeptide metabolism have been reported in schizophrenia and/or animal models of the disease. Remarkably, although profound disturbances of the hypothalamus-pituitary-adrenal axis, hypothalamus-pituitary-thyroid axis, and the hypothalamus-pituitary-gonadal axis are typical signs of schizophrenia, there is currently no evidence for alterations in the expression of hypothalamic-releasing and inhibiting factors that control these hormonal axes. Finally, the implications of hypothalamus for disease-related disturbances of the sleep-wakefulness cycle and neuroimmune dysfunctions in schizophrenia are outlined.

The Relationship Between Antipsychotic Treatment and Plasma β-Endorphin Concentration in Patients with Schizophrenia

OBJECTIVE

Some studies indicate the presence of elevated opioid levels in cases of schizophrenia and their relationship with negative symptoms. The pathogenesis of schizophrenia may be associated with an imbalance in the modulatory effect of opioids on the dopaminergic system. The aim of the study was to identify the association between β-endorphin (BE) concentration and the outcome of short-term schizophrenia treatment.

METHODS

We examined 49 patients hospitalized due to exacerbation of schizophrenia symptoms and 47 controls without schizophrenia. The severity of psychopathological symptoms was evaluated using Positive and Negative Syndrome Scale (PANSS) at the onset of hospitalization, and after four, six and ten weeks of treatment. Patients were classified into negative (NEG) and mixed (M) psychopathological subtypes according to the PANSS composite index. Β-endorphin (BE) plasma concentrations were assessed in all participants; in patients on inclusion to the study and after six weeks of treatment.

RESULTS

The patients with schizophrenia demonstrated higher BE levels than controls. During six-week antipsychotic treatment, BE concentration significantly increased in both NEG (p=0.000) and M (p=0.007), and positive symptoms were effectively reduced. In the NEG group, the prevalence of negative symptoms decreased only transiently and returned to approximately baseline values after 10 weeks (p=0.268). In the M patients, the prevalence of negative symptoms increased gradually (p=0.001), with more severe positive and, notably, negative symptoms correlating with higher BE2 concentrations at the 10-week assessment (R= 0.47, p= 0.0135 vs R= 0.74, p=0.0000). In both NEG and M, a greater rise in BE2 level correlated with a lower composite index during treatment.

CONCLUSION

Patients with schizophrenia demonstrate higher BE levels compared to controls. These changes in BE concentration during antipsychotic treatment could reflect the interaction between dopaminergic transmission and endogenous opioids. A rise in BE level following effective antipsychotic therapy could be a potential predictor of persisting negative symptoms.

Daily heroin injection and psychiatric disorders: A cross-sectional survey among People Who Inject Drugs (PWID) in Haiphong, Vietnam

BACKGROUND

Psychiatric comorbidities are frequent among people who inject drugs, they are associated with a poorer prognosis and need to be addressed. Their interaction with daily heroin injection requires clarification.

METHODS

A cross-sectional survey was conducted among PWID recruited in the city of Haiphong, Vietnam, by respondent-driven sampling. The inclusion criteria were age 18 or older and current injection drug use, verified by skin marks and positive urine tests for heroin or methamphetamine. Data on socio-demographic characteristics, drug use, sexual behaviour and access to treatment were collected using face-to-face questionnaires by trained interviewers. PWID were screened by trained psychiatrists for depression, psychotic disorder and suicidality, using the MINI questionnaire.

RESULTS

418 participants were included in the analyses. All were injected heroin users, 21 % were diagnosed with a current major depressive disorder, 15 % with a current psychotic disorder and 12 % presented a suicide risk. In the bivariate analyses, regular meth use, cannabis use and ketamine use were positively associated with presenting at least one psychiatric condition while daily heroin injection and being currently treated with methadone were negatively associated. In the multivariate model, poly-substance use was positively associated with depression (methamphetamine and drinking in addition to heroin) and psychotic disorder (methamphetamine and/or hazardous drinking in addition to heroin) while daily heroin injection and current methadone treatment were negatively and independently associated with depression and psychotic syndrome.

CONCLUSIONS

Our survey confirms the burden of methamphetamine use and the protective effect of methadone but also a possible protective effect of daily heroin injection.

Opioidergic System and Functional Architecture of Intrinsic Brain Activity: Implications for Psychiatric Disorders

The opioidergic system and intrinsic brain activity, as organized in large-scale networks such as the salience network (SN), sensorimotor network (SMN), and default-mode network (DMN), play core roles in healthy behavior and psychiatric disorders. This work aimed to investigate how opioidergic signaling affects intrinsic brain activity in healthy individuals by reviewing relevant neuroanatomical, molecular, functional, and pharmacological magnetic resonance imaging studies in order to clarify their physiological links and changes in psychiatric disorders. The SN shows dense opioidergic innervations of subcortical structures and high expression levels of opioid receptors in subcortical-cortical areas, with enhanced or reduced activity with low or very high doses of opioids, respectively. The SMN shows high levels of opioid receptors in subcortical areas and functional disconnection caused by opioids. The DMN shows low levels of opioid receptors in cortical areas and inhibited or enhanced activity with low or high doses of opioids, respectively. Finally, we proposed a working model. Opioidergic signaling enhances SN and suppresses SMN (and DMN) activity, resulting in affective excitation with psychomotor inhibition; stronger increases in opioidergic signaling attenuate the SN and SMN while disinhibiting the DMN, dissociating affective and psychomotor functions from the internal states; the opposite occurs with a deficit of opioidergic signaling.

Opposite effects of dopamine and serotonin on resting-state networks: review and implications for psychiatric disorders

Alterations in brain intrinsic activity-as organized in resting-state networks (RSNs) such as sensorimotor network (SMN), salience network (SN), and default-mode network (DMN)-and in neurotransmitters signaling-such as dopamine (DA) and serotonin (5-HT)-have been independently detected in psychiatric disorders like bipolar disorder and schizophrenia. Thus, the aim of this work was to investigate the relationship between such neurotransmitters and RSNs in healthy, by reviewing the relevant work on this topic and performing complementary analyses, in order to better understand their physiological link, as well as their alterations in psychiatric disorders. According to the reviewed data, neurotransmitters nuclei diffusively project to subcortical and cortical regions of RSNs. In particular, the dopaminergic substantia nigra (SNc)-related nigrostriatal pathway is structurally and functionally connected with core regions of the SMN, whereas the ventral tegmental area (VTA)-related mesocorticolimbic pathway with core regions of the SN. The serotonergic raphe nuclei (RNi) connections involve regions of the SMN and DMN. Coherently, changes in neurotransmitters activity impact the functional configuration and level of activity of RSNs, as measured by functional connectivity (FC) and amplitude of low-frequency fluctuations/temporal variability of BOLD signal. Specifically, DA signaling is associated with increase in FC and activity in the SMN (hypothetically via the SNc-related nigrostriatal pathway) and SN (hypothetically via the VTA-related mesocorticolimbic pathway), as well as concurrent decrease in FC and activity in the DMN. By contrast, 5-HT signaling (via the RNi-related pathways) is associated with decrease in SMN activity along with increase in DMN activity. Complementally, our empirical data showed a positive correlation between SNc-related FC and SMN activity, whereas a negative correlation between RNi-related FC and SMN activity (along with tilting of networks balance toward the DMN). According to these data, we hypothesize that the activity of neurotransmitter-related neurons synchronize the low-frequency oscillations within different RSNs regions, thus affecting the baseline level of RSNs activity and their balancing. In our model, DA signaling favors the predominance of SMN-SN activity, whereas 5-HT signaling favors the predominance of DMN activity, manifesting in distinct behavioral patterns. In turn, alterations in neurotransmitters signaling (or its disconnection) may favor a correspondent functional reorganization of RSNs, manifesting in distinct psychopathological states. The here suggested model carries important implications for psychiatric disorders, providing novel and well testable hypotheses especially on bipolar disorder and schizophrenia.

Reduced mu opioid receptor availability in schizophrenia revealed with [11C]-carfentanil positron emission tomographic Imaging

Negative symptoms, such as amotivation and anhedonia, are a major cause of functional impairment in schizophrenia. There are currently no licensed treatments for negative symptoms, highlighting the need to understand the molecular mechanisms underlying them. Mu-opioid receptors (MOR) in the striatum play a key role in hedonic processing and reward function and are reduced post-mortem in schizophrenia. However, it is unknown if mu-opioid receptor availability is altered in-vivo or related to negative symptoms in schizophrenia. Using [¹¹C]-carfentanil positron emission tomography (PET) scans in 19 schizophrenia patients and 20 age-matched healthy controls, here we show a significantly lower MOR availability in patients with schizophrenia in the striatum (Cohen's d = 0.7), and the hedonic network. In addition, we report a marked global increase in inter-regional covariance of MOR availability in schizophrenia, largely due to increased cortical-subcortical covariance.

The Role of Dynorphin and the Kappa Opioid Receptor in the Symptomatology of Schizophrenia: A Review of the Evidence

Schizophrenia is a debilitating mental illness that affects approximately 1% of the world's population. Despite much research in its neurobiology to aid in developing new treatments, little progress has been made. One system that has not received adequate attention is the kappa opioid system and its potential role in the emergence of symptoms, as well as its therapeutic potential. Here we present an overview of the kappa system and review various lines of evidence derived from clinical studies for dynorphin and kappa opioid receptor involvement in the pathology of both the positive and negative symptoms of schizophrenia. This overview includes evidence for the psychotomimetic effects of kappa opioid receptor agonists in healthy volunteers and their reversal by the pan-opioid antagonists naloxone and naltrexone and evidence for a therapeutic benefit in schizophrenia for 4 pan-opioid antagonists. We describe the interactions between kappa opioid receptors and the dopaminergic pathways that are disrupted in schizophrenia and the histologic evidence suggesting abnormal kappa opioid receptor signaling in schizophrenia. We conclude by discussing future directions.

The past and future of novel, non-dopamine-2 receptor therapeutics for schizophrenia: A critical and comprehensive review

Since the discovery of chlorpromazine in the 1950's, antipsychotic drugs have been the cornerstone of treatment of schizophrenia, and all attenuate dopamine transmission at the dopamine-2 receptor. Drug development for schizophrenia since that time has led to improvements in side effects and tolerability, and limited improvements in efficacy, with the exception of clozapine. However, the reasons for clozapine's greater efficacy remain unclear, despite the great efforts and resources invested therewith. We performed a comprehensive review of the literature to determine the fate of previously tested, non-dopamine-2 receptor experimental treatments. Overall we included 250 studies in the review from the period 1970 to 2017 including treatments with glutamatergic, serotonergic, cholinergic, neuropeptidergic, hormone-based, dopaminergic, metabolic, vitamin/naturopathic, histaminergic, infection/inflammation-based, and miscellaneous mechanisms. Despite there being several promising targets, such as allosteric modulation of the NMDA and α7 nicotinic receptors, we cannot confidently state that any of the mechanistically novel experimental treatments covered in this review are definitely effective for the treatment of schizophrenia and ready for clinical use. We discuss potential reasons for the relative lack of progress in developing non-dopamine-2 receptor treatments for schizophrenia and provide recommendations for future efforts pursuing novel drug development for schizophrenia.

Dysregulated mitochondrial and chloroplast bioenergetics from a translational medical perspective (Review)

Mitochondria and chloroplasts represent endosymbiotic models of complex organelle development, driven by intense evolutionary pressure to provide exponentially enhanced ATP-dependent energy production functionally linked to cellular respiration and photosynthesis. Within the realm of translational medicine, it has become compellingly evident that mitochondrial dysfunction, resulting in compromised cellular bioenergetics, represents a key causative factor in the etiology and persistence of major diseases afflicting human populations. As a pathophysiological consequence of enhanced oxygen utilization that is functionally uncoupled from the oxidative phosphorylation of ADP, significant levels of reactive oxygen species (ROS) may be generated within mitochondria and chloroplasts, which may effectively compromise cellular energy production following prolonged stress/inflammatory conditions. Empirically determined homologies in biochemical pathways, and their respective encoding gene sequences between chloroplasts and mitochondria, suggest common origins via entrapped primordial bacterial ancestors. From evolutionary and developmental perspectives, the elucidation of multiple biochemical and molecular relationships responsible for errorless bioenergetics within mitochondrial and plastid complexes will most certainly enhance the depth of translational approaches to ameliorate or even prevent the destructive effects of multiple disease states. The selective choice of discussion points contained within the present review is designed to provide theoretical bases and translational insights into the pathophysiology of human diseases from a perspective of dysregulated mitochondrial bioenergetics with special reference to chloroplast biology.

Interacting Neural Processes of Feeding, Hyperactivity, Stress, Reward, and the Utility of the Activity-Based Anorexia Model of Anorexia Nervosa

Anorexia nervosa (AN) is a psychiatric illness with minimal effective treatments and a very high rate of mortality. Understanding the neurobiological underpinnings of the disease is imperative for improving outcomes and can be aided by the study of animal models. The activity-based anorexia rodent model (ABA) is the current best parallel for the study of AN. This review describes the basic neurobiology of feeding and hyperactivity seen in both ABA and AN, and compiles the research on the role that stress-response and reward pathways play in modulating the homeostatic drive to eat and to expend energy, which become dysfunctional in ABA and AN.

Mitochondria, Chloroplasts in Animal and Plant Cells: Significance of Conformational Matching

Many commonalities between chloroplasts and mitochondria exist, thereby suggesting a common origin via a bacterial ancestor capable of enhanced ATP-dependent energy production functionally linked to cellular respiration and photosynthesis. Accordingly, the molecular evolution/retention of the catalytic Q_o quinol oxidation site of cytochrome b complexes as the tetrapeptide PEWY sequence functionally underlies the common retention of a chemiosmotic proton gradient mechanism for ATP synthesis in cellular respiration and photosynthesis. Furthermore, the dual regulatory targeting of mitochondrial and chloroplast gene expression by mitochondrial transcription termination factor (MTERF) proteins to promote optimal energy production and oxygen consumption further advances these evolutionary contentions. As a functional consequence of enhanced oxygen utilization and production, significant levels of reactive oxygen species (ROS) may be generated within mitochondria and chloroplasts, which may effectively compromise cellular energy production following prolonged stress/inflammationary conditions. Interestingly, both types of organelles have been identified in selected animal cells, most notably specialized digestive cells lining the gut of several species of Sacoglossan sea slugs. Termed kleptoplasty or kleptoplastic endosymbiosis, functional chloroplasts from algal food sources are internalized and stored within digestive cells to provide the host with dual energy sources derived from mitochondrial and photosynthetic processes. Recently, the observation of internalized algae within embryonic tissues of the spotted salamander strongly suggest that developmental processes within a vertebrate organism may require photosynthetic endosymbiosis as an internal regulator. The dual presence of mitochondria and functional chloroplasts within specialized animal cells indicates a high degree of biochemical identity, stereoselectivity, and conformational matching that are the likely keys to their functional presence and essential endosymbiotic activities for over 2.5 billion years.

Mitochondria and chloroplasts shared in animal and plant tissues: significance of communication

Mitochondria have long been recognized as the main source of energy production for the eukaryotic cell. Recent studies have found that the mitochondria have a variety of dynamic functions aside from the production of energy. It communicates bidirectionally with other organelles in order to modulate its energy balance efficiently, as well as maintain homeostasis, ultimately prolonging its own and the cell’s longevity. The mitochondria achieves this level of regulation via specific and common bidirectional chemical messengers, especially involving the endoplasmic/sarcoplasmic reticulum (ER/SR), deoxyribonucleoside triphosphates (dNTP’s), ATP and the generation of reactive oxygen species (ROS). Its communication network is also involved in stress associated events. In this regard, the activation of the Bax family proteins and the release of cytochrome c occurs during cellular stress. The communication can also promote apoptosis of the cell. When mitochondrial abnormalities cannot be dealt with, there is an increased chance that major illnesses like type 2 diabetes, Alzheimer’s disease, and cancer may occur. Importantly, functioning chloroplasts can be found in animals, suggesting conserved chemical messengers during its evolutionary path. The dynamic capacity of mitochondria is also noted by their ability to function anaerobically. Indeed, this latter phenomenon may represent a return to an earlier developmental stage of mitochondria, suggesting certain disorders result from its untimely appearance.

Behavioral effects of food-derived opioid-like peptides in rodents: Implications for schizophrenia?

Dohan proposed that an overload of dietary peptides, such as those derived from wheat gluten and milk casein, could be a factor relevant to the development or maintenance of schizophrenia (SZ) symptoms in at least a subset of vulnerable individuals. Rodent behavioral models may offer insight into the plausibility of Dohan's exorphin hypothesis by providing a means to directly study the effects of such peptides. Accordingly, a review of the literature on the behavioral effects of food-derived opioid-like peptides in rodents was undertaken. Studies using a variety of behavioral tests to examine the effects of several classes of food-derived opioid-like peptides were identified and reviewed. Peptides derived from casein (β-casomorphins; BCMs, n=19), spinach (rubiscolins; RCs, n=4), and soy (soymorphins; SMs, n=1) were behaviorally active in various paradigms assessing nociception, spontaneous behavior, and memory. Surprisingly, only a single study evaluating a gluten-derived peptide (gliadorphin-7; GD-7, n=1) was identified and included in this review. In conclusion, food-derived peptides can affect rodent behavior, but more studies of GDs using diverse behavioral batteries are warranted. Assuming they occur in sufficient quantities during protein digestion and can access central opioid receptors (which entails crossing both the gastrointestinal and blood-brain barriers intact), these peptides may affect human behavior. Although BCMs and GDs may not be directly pathogenic in SZ, documented associations of casein and gluten sensitivity with SZ justify increased patient screening and dietary intervention where necessary.

Lack of association between the G-660C polymorphism in the dopamine transporter gene (SLC6A3) and schizophrenia in the Iranian population

BACKGROUND:

Dopaminergenic system plays an essential role in the plasticity of the human brain. The dopamine transporter gene (SLC6A3) mediates active reuptake of dopamine from synapsis, terminates dopamine signals, and therefore, is implicated in a number of dopamine-related disorders like psychosis. Variations in the form of single nucleotide polymorphisms in the core promoter of the SLC6A3 gene are reported to be involved in the pathogenesis of schizophrenia. In this study, we also attempted to establish the possible role of the polymorphism G-660C in the SLC6A3 gene promoter in schizophrenia in a case-control study.

MATERIALS AND METHODS:

The allele and genotype frequency were analyzed in an Iranian cohort of 200 unrelated patients and 200 controls using polymerase chain reaction and restriction fragment length polymorphism.

RESULTS:

The genotype frequency for case and control groups was GG 100%, GC 0%, CC 0%, and GG 100%, GC 0%, CC 0%, respectively. The C allele was failed in both groups.

CONCLUSION:

Our data suggest clearly that there is no association between the -660G/C polymorphism and outcome of schizophrenia in the Iranian population.

Increased ethanol intake in prodynorphin knockout mice is associated to changes in opioid receptor function and dopamine transmission

The purpose of this study was to examine the role of the prodynorphin gene in alcohol sensitivity, preference and vulnerability to alcohol consumption. Handling-induced convulsion (HIC) associated to alcohol, alcohol-induced loss of righting reflex (LORR), hypothermic effects in response to acute ethanol challenge, blood ethanol levels (BELs), conditioned place preference, voluntary ethanol consumption and preference, tyrosine hydroxylase (TH), dopamine transporter (DAT) and proenkephalin (PENK) gene expression, and µ-, δ- and κ-opioid agonist-stimulated [S(35) ]- guanosine 5'-triphosphate-binding autoradiography were studied in prodynorphin knockout (PDYN KO) and wild-type (WT) mice. There were no differences in HIC, LORR or the decrease in body temperature in response to acute ethanol challenge between PDYN KO and WT mice. PDYN KO mice presented higher BEL, higher ethanol-conditioned place preference and more ethanol consumption and preference in a two-bottle choice paradigm than WT mice. These findings were associated with lower TH and higher DAT gene expression in the ventral tegmental area and substantia nigra, and with lower PENK gene expression in the caudate-putamen (CPu), accumbens core (AcbC) and accumbens shell (AcbSh) in PDYN KO. The functional activity of the µ-opioid receptor was lower in the CPu, AcbC, AcbSh and cingulate cortex (Cg) of PDYN KO mice. In contrast, δ- and κ-opioid receptor-binding autoradiographies were increased in the CPu and Cg (δ), and in the CPu, AcbC and Cg (κ) of PDYN KO. These results suggest that deletion of the PDYN gene increased vulnerability for ethanol consumption by altering, at least in part, PENK, TH and DAT gene expression, and µ-, δ- and κ-opioid receptor functional activity in brain areas closely related to ethanol reinforcement.

Relative food preference and hedonic judgments in schizophrenia

There is a well-documented disruption of the neural network associated with reward evaluation in schizophrenia. This same system is involved in coding the incentive value of food in healthy individuals, but few studies to date have examined anhedonia and its relation to food hedonicity and preference in schizophrenia. Relative preference and hedonic food ratings were examined in schizophrenia patients and healthy controls. In the relative preference task, subjects viewed photographs of food items and selected the one that they most preferred. Hedonic ratings were obtained by asking subjects how much they liked the food stimulus on a scale of 1-5. There were no overall response time differences between the two groups in the relative preference task, but schizophrenia patients showed subtle differences in their hedonic ratings of foods compared with control subjects. Schizophrenia patients gave more positive hedonic ratings for food than did controls, and the use of fewer positive ratings was associated with increased anhedonia, particularly with loss of sexual interest. These results suggest that while making relative preference judgments may be intact, hedonic values attached to food may be altered in schizophrenia, and they may be related to dysfunction in more basic vegetative systems.

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.

Developmental changes in the mRNA expression of neuropeptides and dopamine and glutamate receptors in neonates and adult rats after ventral hippocampal lesion

BACKGROUND

The neurodevelopment of hippocampus and prefrontal cortex are known to influence different functions in normal and pathological conditions including cognition and sensorimotor functions. The neonatal lesion of the ventral hippocampus (VH) in rats has been established as an animal model of schizophrenia and is used to study postpubertal changes in behavior and neurobiology. In order to investigate whether early VH lesion in rats alters the expression of genes implicated in schizophrenia pre- and post-puberty, we studied the mRNA expression of neuropeptides (substance P, dynorphin and enkephalin), dopamine D1, dopamine D2, and NMDA (subunits NR1 and NR2A) receptors in this animal model.

METHODS

Rat pups were lesioned at postnatal day 7 by injecting ibotenic acid into the VH bilaterally, and then sacrificed at age 35 (pre-puberty) and 65 (post-puberty) days. Another group of adult rats had the same lesion in the VH, to independently assess the effects of the lesion on the expression of genes, and then sacrificed at week 4 and 8 post lesion. Sham groups were injected with cerebrospinal fluid using the same procedure. Brains were removed and sectioned to study the mRNA expression using in situ hybridization (ISH).

RESULTS

The main results are the postpubertal onset of increased NR1 mRNA expression in all cortical regions and decreased dopamine D2 receptor, substance P and enkephalin mRNA expression in the striatum only in rats lesioned as neonates. These changes were not observed in the adult group with VH lesion.

CONCLUSIONS

Our results demonstrate that the postpubertal behavioral changes in this animal model (and possibly schizophrenia) are related to postpubertal onset of changes in the development of functions and interactions of the dopamine and glutamate receptors in the mesocortical system.

Effects of bisphenol-A and other endocrine disruptors compared with abnormalities of schizophrenia: an endocrine-disruption theory of schizophrenia

In recent years, numerous substances have been identified as so-called "endocrine disruptors" because exposure to them results in disruption of normal endocrine function with possible adverse health outcomes. The pathologic and behavioral abnormalities attributed to exposure to endocrine disruptors like bisphenol-A (BPA) have been studied in animals. Mental conditions ranging from cognitive impairment to autism have been linked to BPA exposure by more than one investigation. Concurrent with these developments in BPA research, schizophrenia research has continued to find evidence of possible endocrine or neuroendocrine involvement in the disease. Sufficient information now exists for a comparison of the neurotoxicological and behavioral pathology associated with exposure to BPA and other endocrine disruptors to the abnormalities observed in schizophrenia. This review summarizes these findings and proposes a theory of endocrine disruption, like that observed from BPA exposure, as a pathway of schizophrenia pathogenesis. The review shows similarities exist between the effects of exposure to BPA and other related chemicals with schizophrenia. These similarities can be observed in 11 broad categories of abnormality: physical development, brain anatomy, cellular anatomy, hormone function, neurotransmitters and receptors, proteins and factors, processes and substances, immunology, sexual development, social behaviors or physiological responses, and other behaviors. Some of these similarities are sexually dimorphic and support theories that sexual dimorphisms may be important to schizophrenia pathogenesis. Research recommendations for further elaboration of the theory are proposed.

Sensorimotor gating and attentional set-shifting are improved by the mu-opioid receptor agonist morphine in healthy human volunteers

Prepulse inhibition (PPI) of the acoustic startle response (ASR) has been established as an operational measure of sensorimotor gating. Animal and human studies have shown that PPI can be modulated by dopaminergic, serotonergic, and glutamatergic drugs and consequently it was proposed that impaired sensorimotor gating in schizophrenia parallels a central abnormality within the corresponding neurotransmitter systems. Recent animal studies suggest that the opioid system may also play a role in the modulation of sensorimotor gating. Thus, the present study investigated the influence of the mu-opioid receptor agonist morphine on PPI in healthy human volunteers. Eighteen male, non-smoking healthy volunteers each received placebo or 10 mg morphine sulphate (p.o.) at a 2-wk interval in a double-blind, randomized, and counterbalanced order. PPI was measured 75 min after drug/placebo intake. The effects of morphine on mood were measured by the Adjective Mood Rating Scale and side-effects were assessed by the List of Complaints. Additionally, we administered a comprehensive neuropsychological test battery consisting of tests of the Cambridge Neuropsychological Test Automated Battery and the Rey Auditory Verbal Learning Test. Morphine significantly increased PPI without affecting startle reactivity or habituation. Furthermore, morphine selectively improved the error rate in an attentional set-shifting task but did not influence vigilance, memory, or executive functions. These results imply that the opioid system is involved in the modulation of PPI and attentional set-shifting in humans and they raise the question whether the opioid system plays a crucial role also in the regulation of PPI and attentional set-shifting in schizophrenia.

N-Desmethylclozapine, a major clozapine metabolite, acts as a selective and efficacious delta-opioid agonist at recombinant and native receptors

The present study examined the effects of N-desmethylclozapine (NDMC), a biologically active metabolite of the atypical antipsychotic clozapine, at cloned human opioid receptors stably expressed in Chinese hamster ovary (CHO) cells and at native opioid receptors present in NG108-15 cells and rat brain. In CHO cells expressing the delta-opioid receptor (CHO/DOR), NDMC behaved as a full agonist both in stimulating [(35)S]GTPgammaS binding (pEC(50)=7.24) and in inhibiting cyclic AMP formation (pEC(50)=6.40). NDMC inhibited [(3)H]naltrindole binding to CHO/DOR membranes with competition curves that were modulated by guanine nucleotides in an agonist-like manner. Determination of intrinsic efficacies by taking into consideration both the maximal [(35)S]GTPgammaS binding stimulation and the extent of receptor occupancy at which half-maximal effect occurred indicated that NDMC had an efficacy value equal to 82% of that of the full delta-opioid receptor agonist DPDPE, whereas clozapine and the other clozapine metabolite clozapine N-oxide displayed much lower levels of agonist efficacy. NDMC exhibited poor agonist activity and lower affinity at the kappa-opioid receptor and was inactive at mu-opioid and NOP receptors. In NG108-15 cells, NDMC inhibited cyclic AMP formation and stimulated the phosphorylation of extracellular signal-regulated kinase 1/2 by activating the endogenously expressed delta-opioid receptor. Moreover, in membranes of different brain regions, NDMC stimulated [(35)S]GTPgammaS binding and regulated adenylyl cyclase activity and the effects were potently antagonized by naltrindole. These data demonstrate for the first time that NDMC acts as a selective and efficacious delta-opioid receptor agonist and suggest that this unique property may contribute, at least in part, to the clinical actions of the atypical antipsychotic clozapine.

Food intake and reward mechanisms in patients with schizophrenia: implications for metabolic disturbances and treatment with second-generation antipsychotic agents

Obesity is highly prevalent among patients with schizophrenia and is associated with detrimental health consequences. Although excessive consumption of fast food and pharmacotherapy with such second-generation antipsychotic agents (SGAs) as clozapine and olanzapine has been implicated in the schizophrenia/obesity comorbidity, the pathophysiology of this link remains unclear. Here, we propose a mechanism based on brain reward function, a relevant etiologic factor in both schizophrenia and overeating. A comprehensive literature search on neurobiology of schizophrenia and of eating behavior was performed. The collected articles were critically reviewed and relevant data were extracted and summarized within four key areas: (1) energy homeostasis, (2) food reward and hedonics, (3) reward function in schizophrenia, and (4) metabolic effects of the SGAs. A mesolimbic hyperdopaminergic state may render motivational/incentive reward system insensitive to low salience/palatability food. This, together with poor cognitive control from hypofunctional prefrontal cortex and enhanced hedonic impact of food, owing to exaggerated opioidergic drive (clinically manifested as pain insensitivity), may underlie unhealthy eating habits in patients with schizophrenia. Treatment with SGAs purportedly improves dopamine-mediated reward aspects, but at the cost of increased appetite and worsened or at least not improved opiodergic capacity. These effects can further deteriorate eating patterns. Pathophysiological and therapeutic implications of these insights need further validation via prospective clinical trials and neuroimaging studies.

Psychosis related to methadone withdrawal

We present two cases of typical psychosis related to methadone withdrawal. The two cases, appearing in the adult age, are not related to previous personal or familiar psychiatric illness and do not show the classical symptoms of methadone withdrawal. The appearance of this type of case is an experience repeated in different groups of researchers. In the line of previous investigators, we propose an alteration of neuromodulation in central opiate-dopamine system.

Personality measures in former heroin users receiving methadone or in protracted abstinence from opiates

OBJECTIVE

Methadone Maintenance Therapy (MMT) and detoxification to abstinence are among the most common treatment options for opiate-dependent patients. This paper compares personality traits in detoxified former heroin users and those on MMT in order to assess their relevance to treatment selection.

METHOD

Twenty-six formerly heroin-dependent subjects receiving MMT (MM), 33 formerly heroin-dependent subjects withdrawn from MMT (MW), and 43 healthy controls were compared on the Millon Clinical Multiaxial Inventory-II (MCMI-II) and the Temperament and Character Inventory (TCI).

RESULTS

On the TCI, MM patients had higher novelty seeking and lower self-directedness scores than controls. Both MM and MW subjects scored higher than controls on multiple MCMI-II scales. MW but not MM subjects scored higher than controls on two Cluster A Scales and the delusional disorder scale.

CONCLUSION

Schizophrenia-spectrum pathology in former opiate users may be greater than previously recognized and could potentially be relevant to treatment selection.

Reward deficiency syndrome: genetic aspects of behavioral disorders

The dopaminergic and opioidergic reward pathways of the brain are critical for survival since they provide the pleasure drives for eating, love and reproduction; these are called 'natural rewards' and involve the release of dopamine in the nucleus accumbens and frontal lobes. However, the same release of dopamine and production of sensations of pleasure can be produced by 'unnatural rewards' such as alcohol, cocaine, methamphetamine, heroin, nicotine, marijuana, and other drugs, and by compulsive activities such as gambling, eating, and sex, and by risk taking behaviors. Since only a minority of individuals become addicted to these compounds or behaviors, it is reasonable to ask what factors distinguish those who do become addicted from those who do not. It has usually been assumed that these behaviors are entirely voluntary and that environmental factors play the major role; however, since all of these behaviors have a significant genetic component, the presence of one or more variant genes presumably act as risk factors for these behaviors. Since the primary neurotransmitter of the reward pathway is dopamine, genes for dopamine synthesis, degradation, receptors, and transporters are reasonable candidates. However, serotonin, norepinephrine, GABA, opioid, and cannabinoid neurons all modify dopamine metabolism and dopamine neurons. We have proposed that defects in various combinations of the genes for these neurotransmitters result in a Reward Deficiency Syndrome (RDS) and that such individuals are at risk for abuse of the unnatural rewards. Because of its importance, the gene for the [figure: see text] dopamine D2 receptor was a major candidate gene. Studies in the past decade have shown that in various subject groups the Taq I A1 allele of the DRD2 gene is associated with alcoholism, drug abuse, smoking, obesity, compulsive gambling, and several personality traits. A range of other dopamine, opioid, cannabinoid, norepinephrine, and related genes have since been added to the list. Like other behavioral disorders, these are polygenically inherited and each gene accounts for only a small per cent of the variance. Techniques such as the Multivariate Analysis of Associations, which simultaneously examine the contribution of multiple genes, hold promise for understanding the genetic make up of polygenic disorders.

Addiction and schizophrenia

Epidemiologic studies in the general population and those based on the clinical assessment of schizophrenic populations have revealed a high degree of overlap between schizophrenia and addictive disorders. The abuse of psychoactive substances (including alcohol) throughout life is so frequent (50%) that the possibility of a specific link inevitably arises. Various hypotheses have been suggested to explain the high co-morbidity between schizophrenia and addiction: 1) The social-environmental hypothesis has been developed but studies have provided poor evidence to validate it. 2) The possible shared biological vulnerability between schizophrenia and addictions led researchers to explore common genetic determinants and study the involvement of the dopaminergic and opioid systems in the aetiology of both schizophrenia and the abuse of and dependence on psychoactive drugs. 3) Finally, the theory of self-medication suggests that schizophrenics may be attempting to counter the deficit linked to their disorders by using the substances they take or their dependency-type behaviour to cope with their emotional problems. The clinical profile of schizophrenic addicts does seem to display some distinctive features, such as the high level of depressive co-morbidity, very high nicotine and alcohol dependence, with a very poor prognosis. These patients are difficult to manage; the possibility of pharmacologic interactions between the substances they are taking and neuroleptic medication calls for prudence, and their compliance is also poor. Addictive disorders in schizophrenics are currently a topic of active research intended to lead to identifying specific treatments. The early identification of addictive disorders in schizophrenics should make it possible to limit their development and improve the prognosis.

The atypical neuroleptics clozapine and olanzapine differ regarding their antinociceptive mechanisms and potency

Using the mouse tail-flick assay, we evaluated the antinociceptive effect and the interaction with the opioid, adrenergic, and serotonergic systems of the two "atypical" neuroleptic agents clozapine and olanzapine. Clozapine induced a potent antinociceptive effect in a dose-dependent manner with ED50 of 8.7 mg/kg. This effect was antagonized by the nonselective opioid antagonist naloxone (p < 0.05), implying an opioid mechanism of action involved in clozapine-induced antinociception. Further evaluation demonstrated the involvement of micro1-, micro2-, kappa1- opioid receptor subtypes and of alpha2-adrenoreceptors in clozapine antinociception but not the serotonin receptors. Olanzapine induced a weak antinociceptive effect. The highest effect found was a 50% antinociception following an injection of 10 mg/kg. As the olanzapine dose increased beyond 10 mg/kg, latencies declined almost back to baseline. Yohimbine (an alpha2-adrenoreceptor antagonist) significantly reduced olanzapine's antinociceptive effect almost completely (to 10%; p < 0.05), while both naloxone and metergoline (a nonselective 5-HT receptor antagonist) reduced it only partially. These results indicate the possible involvement of the alpha2-adrenoreceptors in olanzapine antinociception and to a less extent the involvement of opioid and serotonergic receptors. Although both clozapine and olanzapine are dibenzodiazepines with similar "atypical" antipsychotic properties, it seems that they differ notably not only regarding their hematological side effects, but regarding their interaction with the opioid system as well.

Continuous infusion of clozapine increases mu and delta opioid receptors and proenkephalin mRNA in mouse brain

The biochemical mechanisms involved in the actions of the atypical antipsychotic clozapine are still unclear. Because elevated levels of enkephalin in certain areas of the central nervous system may be necessary for antipsychotic activity, we have examined the effect of clozapine on certain receptors and mRNA transcripts involved in the opioid peptidergic system. Clozapine was infused continuously into mice for 21 days and the density of mu and delta opioid receptors was measured in the brains by quantitative receptor autoradiography, and the level of proenkephalin mRNA and dopamine D1 and D2 receptor mRNA were measured by in situ hybridization histochemistry. The results showed that continuous infusion of clozapine increased the density of D1 but not D2 receptors. However, it failed to alter the levels of either D1 or D2 dopamine receptor mRNA. By contrast, clozapine increased the density of mu and delta opioid receptors and increased the levels of proenkephalin mRNA. These results indicate that continuous treatment with clozapine increases opioid peptidergic activity in mouse brain and suggest that alteration of peptidergic activity as well as alteration of dopaminergic activity may be involved in its antipsychotic action.

Histopathology and evaluation of potentiation of morphine-induced antinociception by intrathecal droperidol in the rat

Clinical studies have indicated that a low dose of the dopamine D2-receptor antagonist droperidol given epidurally potentiate the antinociceptive effect of epidural morphine. The present study was conducted in order to evaluate this drug interaction in a rat model. Rats were given morphine and droperidol intrathecally in several combinations of doses. It was found that droperidol had no antinociceptive effect by itself, nor in combination with morphine. It was also shown that droperidol and morphine exert no histopathological effects on the rat spinal cord. This discrepancy between clinical findings and experimental pain studies suggests different modes of action of droperidol in the two situations.

Possible involvement of dopaminergic mechanisms in the antimigraine action of flunarizine

Flunarizine, a calcium antagonist widely used in the prophylactic treatment of migraine, may interfere with dopaminergic systems. Flunarizine therapy can in fact induce extrapyramidal side effects and can increase basal as well as stimulated prolactin levels. To better define the mechanism of flunarizine action in migraine, we studied prolactin and growth hormone responses to thyrotropin releasing hormone and sulpiride in 13 female migraineurs before and after 60 days of flunarizine therapy. The treatment did not modify basal prolactin and growth hormone levels, but prolactin response to thyrotropin releasing hormone was enhanced. A paradoxical increase of growth hormone to thyrotropin releasing hormone observed before therapy was blunted after flunarizine treatment. These data indicate a modulatory action of flunarizine on dopaminergic systems which might to some extent explain the antimigraine action of this drug.

Interactions of naloxone with morphine, amphetamine and phencyclidine on fixed interval responding for intracranial self-stimulation in rats

Rats were implanted with stimulating electrodes aimed at the medial forebrain bundle-lateral hypothalamus (MFB-LH) and were trained to lever-press for brain self-stimulation on a fixed interval: 60 s schedule of reinforcement. The effects of graded doses of naloxone (0.1-30 mg/kg), morphine (0.3-5.6 mg/kg), naloxone plus morphine, d-amphetamine (0.03-1.0 mg/kg), naloxone plus d-amphetamine, phencyclidine (0.3-5.6 mg/kg), and naloxone plus phencyclidine were tested. Naloxone produced a significant decrease in rates at 30 mg/kg. Naloxone (0.1-1.0 mg/kg) plus morphine blocked the dose-dependent decrease produced by morphine alone. In contrast, naloxone (1.0-10 mg/kg) plus d-amphetamine attenuated the graded increase in response rates produced by d-amphetamine. Naloxone (1.0-10 mg/kg) plus phencyclidine did not reliably change the increase in response rates produced by phencyclidine alone. The use of the fixed interval schedule of brain self-stimulation to study these drug interactions is novel, and further demonstrates that the highly reinforcing aspects of brain stimulation, known to be influenced by dopamine, may also be modulated by the endogenous opiate system.

Repeated naloxone administration in schizophrenia: a phase II World Health Organization Study

In the context of a previous WHO collaborative study, six research centers reported that naloxone (0.3 mg/kg) produced significant improvement in symptomatology in neuroleptic-treated patients. In the current Phase II WHO study, repeated (4 days) naloxone (0.3 mg/kg) administration was performed in schizophrenic patients (n = 43) from five WHO collaborating centers using a double-blind, placebo-controlled design. Both naloxone and placebo administrations were associated with significant reductions in symptoms. Naloxone, however, was not superior to placebo. These data are discussed in relation to endorphin hypotheses of schizophrenia.

Fluphenazine treatment reduces CSF somatostatin in patients with schizophrenia: correlations with CSF HVA

CSF somatostatin and homovanillic acid (HVA) were measured in 14 schizophrenic patients while they were drug-free and during chronic fluphenazine treatment. CSF somatostatin was significantly reduced and CSF HVA was significantly elevated (p less than 0.002) during fluphenazine treatment. There was a trend toward correlation between CSF somatostatin and CSF HVA in the 14 schizophrenic patients when drug-free (r = 0.49, p less than 0.07) and fluphenazine-treated (r = 0.47, p less than 0.08). When examined in a larger group (n = 46) of drug-free schizophrenics, this relationship was highly significant (r = 0.59, p less than 0.001). These clinical data are consistent with preclinical evidence indicating a functional interaction between CNS somatostatin and dopamine systems.

Unidirectional uptake of enkephalins at the blood-tissue interface of the blood-cerebrospinal fluid barrier: a saturable mechanism

The cellular uptake at the blood-tissue interface of the blood-cerebrospinal fluid (CSF) barrier to tyrosyl-3,5-[3H]enkephalin-[5-L-leucine] (abbreviated to Leu-enkephalin) and of its synthetic analogue D-alanine2-tyrosyl-3,5-[3H]enkephalin-[5-D-leucine] (abbreviated to D-Ala2-D-Leu5-enkephalin) was studied in the isolated perfused choroid plexuses from the lateral ventricles of the sheep, using the rapid (less than 30 s), single circulation, paired-tracer dilution technique, in which D-[14C]-mannitol serves as an extracellular marker. Cellular uptake of peptides was estimated by directly comparing venous dilution profiles of [3H] and [14C] radioactivities in the absence and presence of unlabelled peptide, the N-terminal amino acid (L-tyrosine), the typical L-transport system substrate, 2-aminobicyclo(2,2,1)heptane-2-carboxylic acid (BCH) and the inhibitor of aminopeptidase activity, bacitracin. The cellular uptake of both enkephalins was strongly (65-76%) but not completely inhibited by the addition of 5 mM unlabelled peptide to the bolus; the self-inhibition was significantly higher for D-Ala2-D-Leu5-enkephalin than for Leu-enkephalin. The addition to the bolus of L-tyrosine (5 mM), BCH (10 mM) or bacitracin (2 mM) reduced the 3H-radioactivity uptake by the choroid plexus of both enkephalins by 20-40%, the degree of inhibition being greater for [3H]-Leu-enkephalin than for its analogue. It is concluded that during single passage of enkephalins through the choroid plexus circulation, unidirectional uptake at the blood-tissue interface of the blood-CSF barrier consists of two components; a saturable component, which represents uptake of the intact peptide by the choroid epithelium, and a non-saturable component, which reflects enzymatic degradation of peptide in the blood and/or at the barrier, with a liberation of the N-terminal tyrosyl residue. Higher penetration of the blood-CSF barrier by D-Ala2-D-Leu5-enkephalin can be attributed to its greater resistance to hydrolysis.

CY 208-243: a unique combination of atypical opioid antinociception and D1 dopaminomimetic properties

Here we describe the potent antinociceptive action of the indolophenanthridine, CY 208-243, which has high affinities to the dopamine D1 binding and the opioid sites as well as to the 5-HT1A site. The antinociceptive action was comparable to that of morphine in most, but not all models of nociception, nevertheless, basic differences exist in its overall profile. Antagonism of CY 208-243's antinociceptive action was only possible with either high doses of naloxone or not at all and no cross-tolerance with morphine in CY 208-243 tolerant rats occurred. The biochemical basis for dependence liability may be absent and no opioid activity was observed in cultured hippocampal cells. Physical dependence did not occur after programmed administration in the rhesus monkey, nor did CY 208-243 cause respiratory depression in the rat (rather a stimulation). Lack of generalization in fentanyl-trained rats strongly suggests that CY 208-243 lacks opioid-like subjective cues. The coexistence of D1 dopaminergic and atypical opioid agonist properties represents a unique pharmacodynamic combination which is not shared with any other analgesic, and may provide safe and innovative pain therapy.

Preliminary evaluation of manassantin A, a potential neuroleptic agent from Saururus cernuus

Manassantin A (MNS-A), a novel dineolignan isolated from Saururus cernuus was evaluated for its central depressant effects. Intraperitoneal (IP) administration of MNS-A to mice at nontoxic doses caused a decrease in spontaneous motor activity and inhibition of amphetamine-induced stereotypy, with an ED50 of 0.21 +/- 0.02 mg/kg for its antiamphetamine activity. Doses of MNS-A up to the LD50 did not produce catalepsy and ptosis as were observed with haloperidol used as a reference drug. The compound caused a dose-dependent hypothermia, while haloperidol was not very effective in this test. Potentiation of pentobarbital-sleeping time was observed to be of comparable degree with both drugs. In spite of the higher toxicity (acute LD50 5.4 +/- 0.2 mg/kg, IP) than that shown by haloperidol, the somewhat selective neuroleptic profile of MNS-A makes it an interesting candidate for more detailed studies.

Estrogen treatment to ovariectomized rats modifies morphine-induced behavior

Two weeks after surgery, ovariectomized (OVX) rats were treated for 3 days with either 17 beta-estradiol (10 or 100 micrograms/kg, SC, per day) or the oil vehicle. They were then tested for morphine-induced hyperactivity (4 mg/kg, IP), analgesia and catalepsy (15 and 20 mg/kg, IP) 24 or 72 hr after the last steroid or oil injection. Estradiol treatment did not affect the locomotion or the sensitivity to nociceptive stimuli of OVX rats and did not induce a cataleptic state in animals. Estradiol- (100 micrograms/kg) treated OVX rats exhibited attenuated morphine-induced hyperlocomotion regardless of the time that had elapsed after estradiol treatment cessation, attenuated morphine-induced catalepsy at 24 hr after estradiol treatment and unaltered morphine-induced analgesia. OVX rats treated with a lower estradiol dose (10 micrograms/kg) exhibited significantly increased morphine-induced analgesia and slightly increased catalepsy. The results show that the sensitivity of brain opiate systems controlling some of the behavioral effects of morphine is modified following estradiol treatment to OVX rats.