Increased concentration of alpha- and gamma-endorphin in post mortem hypothalamic tissue of schizophrenic patients

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".

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.

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.

A Peptide Found in Schizophrenia and Autism Causes Behavioral Changes in Rats

In a previous study we showed that β-casomorphin-7 (β-CM7) is taken up by brain regions relevant to schizophrenia and autism. The present experiment was designed to find whether β-CM7 has any behavioral or analgesic effects in rats. About 65 seconds after treatment with different doses of β-CM7, rats became restless and ran violently, with teeth chattering and with rapid respiration. Seven minutes later, the rats became inactive with less walking, distancing themselves from the other rat in the same cage, and sitting in, or putting their head against, the corner of the cage. The sound response was reduced and social interaction was absent. One hour later, the rats showed hyperdefensiveness. The above behavioral effects of β-CM7 did not occur when rats were pretreated with naloxone (2 mg/kg, IP). The rats receiving saline did not show any behavioral changes throughout the 2 hour period of observation. β-CM7 also demonstrated analgesic effects, which could be blocked by naloxone. The results suggest that β-CM7 may play a role in behavioral disorders such as autism and schizophrenia.

β-Casomorphin Induces Fos-Like Immunoreactivity in Discrete Brain Regions Relevant to Schizophrenia and Autism

The induction of Fos-like immunoreactivity (FLI) was used to determine the brain localization affected by b-casomorphin-7 (b-CM7). Peripheral administration of human b-CM7 at different doses (5, 10 and 30 mg/kg, IV for 1 hour) to rats induced moderate to strong FLI in discrete brain regions including the nucleus accumbens, caudate putamen, ventral tegmental and median raphe nucleus, and orbitofrontal, prefrontal, parietal, temporal, occipital and entorhinal cortex. All of the above areas have been shown to be altered either functionally or anatomically in patients with schizophrenia, and most have been shown to be functionally abnormal in autism. Some of these brain areas are originators or components of dopaminergic, serotoninergic and GABA-ergic pathways, suggesting that b-CM7 can affect the function of all of these systems. The role of some other affected areas in emotional and motivated behavior, social adaptation, hallucinations and delusions suggests that b-CM7, which was found in high concentration in the CSF, blood and urine of patients with either schizophrenia or autism, may be relevant to schizophrenia and autism. Induction of FLI in the above brain areas by a moderate dose (10 mg/kg) of b-CM7 was attenuated significantly, or blocked, by pretreatment with naloxone (2 mg/kg, IP). It is concluded that human b-CM7 can cross the blood-brain barrier, activate opioid receptors and affect brain regions similar to those affected by schizophrenia and autism.

Reduced neuronal expression of insulin-degrading enzyme in the dorsolateral prefrontal cortex of patients with haloperidol-treated, chronic schizophrenia

Insulin-degrading enzyme (IDE) is a neutral thiol metalloprotease, which cleaves insulin with high specificity. Additionally, IDE hydrolyzes Abeta, glucagon, IGF I and II, and beta-endorphin. We studied the expression of IDE protein in postmortem brains of patients with schizophrenia and controls because: (1) the gene encoding IDE is located on chromosome 10q23-q25, a gene locus linked to schizophrenia; (2) insulin resistance with brain insulin receptor deficits/receptor dysfunction was reported in schizophrenia; (3) the enzyme cleaves IGF-I and IGF-II which are implicated in the pathophysiology of the disease; and (4) brain gamma-endorphin levels, liberated from beta-endorphin exclusively by IDE, have been reported to be altered in schizophrenia. We counted the number of IDE immunoreactive neurons in the dorsolateral prefrontal cortex, the hypothalamic paraventricular and supraoptic nuclei, and the basal nucleus of Meynert of 14 patients with schizophrenia and 14 matched control cases. Patients had long-term haloperidol treatment. In addition, relative concentrations of IDE protein in the dorsolateral prefrontal cortex were estimated by Western blot analysis. There was a significantly reduced number of IDE expressing neurons and IDE protein content in the left and right dorsolateral prefrontal cortex in schizophrenia compared with controls, but not in other brain areas investigated. Results of our studies on the influence of haloperidol on IDE mRNA expression in SHSY5Y neuroblastoma cells, as well as the effect of long-term treatment with haloperidol on the number of IDE immunoreactive neurons in rat brain, indicate that haloperidol per se, is not responsible for the decreased neuronal expression of the enzyme in schizophrenics. Haloperidol however, might exert some effect on IDE, through changes of the expression levels of its substrates IGF-I and II, insulin and beta-endorphin. Reduced cortical IDE expression might be part of the disturbed insulin signaling cascades found in schizophrenia. Furthermore, it might contribute to the altered metabolism of certain neuropeptides (IGF-I and IGF-II, beta-endorphin), in schizophrenia.

Involvement of neuropeptide systems in schizophrenia: human studies

Neuropeptides are heterogeneously distributed throughout the digestive, circulatory, and nervous systems and serve as neurotransmitters, neuromodulators, and hormones. Neuropeptides are phylogenetically conserved and have been demonstrated to regulate numerous behaviors. They have been hypothesized to be pathologically involved in several psychiatric disorders, including schizophrenia. On the basis of preclinical data, numerous studies have sought to examine the role of neuropeptide systems in schizophrenia. This chapter reviews the clinical data, linking alterations in neuropeptide systems to the etiology, pathophysiology, and treatment of schizophrenia. Data for the following neuropeptide systems are included: arginine-vasopressin, cholecystokinin (CCK), corticotropin-releasing factor (CRF), interleukins, neuregulin 1 (NRG1), neurotensin (NT), neuropeptide Y (NPY), opioids, secretin, somatostatin, tachykinins, thyrotropin-releasing hormone (TRH), and vasoactive intestinal peptide (VIP). Data from cerebrospinal fluid (CSF), postmortem and genetic studies, as well as clinical trials are described. Despite the inherent difficulties associated with human studies (including small sample size, variable duration of illness, medication status, the presence of comorbid psychiatric disorders, and diagnostic heterogeneity), several findings are noteworthy. Postmortem studies support disease-related alterations in several neuropeptide systems in the frontal and temporal cortices. The strongest genetic evidence supporting a role for neuropeptides in schizophrenia are those studies linking polymorphisms in NRG1 and the CCKA receptor with schizophrenia. Finally, the only compounds that act directly on neuropeptide systems that have demonstrated therapeutic efficacy in schizophrenia are neurokinin receptor antagonists. Clearly, additional investigation into the role of neuropeptide systems in the etiology, pathophysiology, and treatment of schizophrenia is warranted.

Could schizophrenia be reasonably explained by Dohan's hypothesis on genetic interaction with a dietary peptide overload?

1. Dohan has proposed that schizophrenia is a genetic disposition which interacts with an overload of dietary proteins such as casein and gluten or gliadin. 2. A systematic attempt is made to see if this hypothesis is possible faced with aspects of schizophrenia that must be accounted for. 3. The authors conclusion is that it is possible, but more serious work in this field is urgently needed.

Remarkable beta-endorphinergic innervation of human cerebral cortex as revealed by immunohistochemistry

Beta-Endorphin immunoreactivity has been localized in 12 regions of the post mortem human cerebral cortex by using a polyclonal antiserum specifically recognizing the peptide. Cell bodies and proximal dendrites of certain cortical neurons (mostly interneurons) were densely populated with nerve endings immunoreactive for beta-endorphin. These 'endorphinoceptive' nerve cells were most abundantly present in the cingulate cortex as well as in the Gyri frontales superior and medius. In other cortical areas they appeared with much lower frequency (Gyri ambiens, semilunaris, parahippocampalis, temporalis). Our data show that the human cerebral cortex receives an endorphinergic innervation which might be of potential interest with regard to certain neuropsychiatric and neurodegenerative disorders.

Alterations in plasma dipeptidyl peptidase IV enzyme activity in depression and schizophrenia: effects of antidepressants and antipsychotic drugs

Recently, our laboratory reported that the activity of dipeptidyl-peptidase IV (DPP IV) was significantly lower in the peripheral blood of major depressed patients than in normal controls. The present study examines plasma DPP IV activity in 43 major depressed and 13 schizophrenic subjects versus 21 normal controls and the effects of antidepressants and antipsychotic drugs on plasma DPP IV activity. DPP IV activity was significantly lower in major depressed subjects than in normal controls and schizophrenic subjects. There was a trend towards higher DPP IV activity in schizophrenic patients than in normal controls. There were no significant effects of antidepressants or neuroleptics on plasma DPP IV activity in depressed and schizophrenic patients, respectively. There were no significant relationships between plasma DPP IV activity and plasma cortisol or immune-inflammatory markers, such as serum interleukin-6 (IL-6) or soluble IL-2 receptor. A significant and positive correlation was found between plasma DPP IV and prolyl endopeptidase (PEP) enzyme activity in the study group as a whole and in schizophrenic subjects. The results support the hypothesis that lower and higher plasma DPP IV activities are trait markers of major depression and schizophrenia, respectively. It is concluded that alterations in the enzyme activity of peptidases, such as DPP IV and PEP, play a role in the pathophysiology of major depression and schizophrenia.

The therapeutic role of naltrexone in negative symptom schizophrenia

1. Naltrexone (50 mg bid, p.o.) was administered in a double-blind fashion (with placebo control) to chronic schizophrenic patients who maintained their routine neuroleptic and anxiolytic therapy. 2. Both positive and negative symptom patients who received naltrexone improved with regard to symptoms involving deterioration and social withdrawal. No significant amelioration was recorded in subjects assuming placebo relative to the same psychopathological areas. 3. Favourable results were obtained mainly from patients affected by negative symptom schizophrenia. 4. Naltrexone may have acted by direct or indirect neurochemical mechanisms related to negative symptom schizophrenia.

Alterations in plasma prolyl endopeptidase activity in depression, mania, and schizophrenia: effects of antidepressants, mood stabilizers, and antipsychotic drugs

The activity of prolyl endopeptidase (PEP), a serine proteinase, has been found to be significantly lower in the blood of patients with major depression than in normal volunteers. The present study investigates plasma PEP activity in 25 major depressed, 10 manic, and 14 schizophrenic subjects versus 30 normal volunteers. It also examines the effects of antidepressants, valproate, and neuroleptic drugs on plasma PEP activity. PEP activity was significantly lower in major depressed subjects than in normal volunteers and in patients with mania and schizophrenia. In depressed subjects, plasma PEP activity was significantly increased during treatment with antidepressant drugs, such as fluoxetine. Plasma PEP activity was significantly increased in manic and schizophrenic subjects compared with normal volunteers. In manic subjects, short-term treatment with valproate had a significant suppressive effect on PEP activity. No significant effects of neuroleptics on PEP activity could be found in the schizophrenic patients. The results support the hypothesis that lower PEP activity could play a role in the pathophysiology of major depression, while increased PEP activity may be related to psychotic conditions, such as mania and schizophrenia.

Decreased urinary peptide excretion in schizophrenic patients after neuroleptic treatment

Six schizophrenic patients had their urinary peptide levels measured before and after 5 weeks of treatment with neuroleptic medications. For two patients, levels were also measured after a reduction in the neuroleptic dose. Because of the heterogeneity of peptide peaks with the same bioactivity, the overall peptide levels were compared to initial levels. A neuroleptic effect on peptide levels was demonstrated. Several research groups have reported enzyme induction caused by neuroleptics in vivo.

Behavioral studies on the putative gamma-type endorphin receptor using different antibodies

To investigate the significance of endogenous, neuroleptic-like gamma-type endorphins and their putative receptors, polyclonal and monoclonal antibodies against gamma-type endorphins, which may bio-inactivate the ligands for the receptors, and monoclonal anti-idiotype antibodies, which presumably bind to the receptors, were injected into the nucleus accumbens of the rat brain. The desenkephalin-gamma-endorphin-induced antagonism of the hypomotility response elicited by challenge with apomorphine injected into the nucleus accumbens was used as test system. Both the anti-desenkephalin-gamma-endorphin antibodies and anti-idiotype antibodies blocked the action of exogenous desenkephalin-gamma-endorphin. Thus, the anti-idiotype antibodies may serve as receptor antagonists. Chronic treatment (injection into the nucleus accumbens) with the anti-idiotype antibodies induced sustained hypermotility, decreased habituation and impaired passive avoidance behavior. In such treated animals local treatment with apomorphine did not elicit hypomotility. It is suggested that gamma-type endorphins influence the setpoint for feedback regulation in dopaminergic neurons equipped with gamma-type endorphin receptor systems.

Drugs and endogenous ligands compete for receptor occupancy

Dietary and endogenous ligands compete with drugs for receptor occupancy and therefore should be considered during therapeutic interventions and during pharmacokinetic/pharmacodynamic modeling. When disease is the result of an overabundance of these natural ligands, antibodies and/or their Fab fragments may be useful as therapeutic agents to reverse the effects of the natural ligands.

Physiology of beta-endorphins. A close-up view and a review of the literature

When an endogenous morphine, beta-endorphin was discovered ten years ago, the fact that this morphine is present in the brain and many other tissues suggested to neurobiologists that these peptide opiates play a role which goes beyond that of a simple modulator of the perception of pain. beta-endorphin is a neurohormone which is secreted by the pituitary gland and reaches all tissues present in the body by diffusion. Many laboratories have investigated variations in serum levels of beta-endorphin under widely varying physiological or pathological conditions. Many references to these studies in the literature have thus demonstrated that beta-endorphins play a role in certain behavioural patterns (stress, alcoholism), in obesity, diabetes and psychiatric diseases. In fact, the activity of beta-endorphins would appear to have an interesting role to play and are a promising feature in the treatment of cerebral aging; in this field, beta-endorphins act not only as neuroregulators of other neurotransmitting substances but also, via calcium channels, exert an effect on the walls of cerebral arterioles. In situ, the role of beta-endorphins at the ionic channel level has been studied using the patch-clamp technique. In 1991, E Neher and B Sakmann received the Nobel Medicine and Physiology Prize for this work. beta-endorphin, which may be the "missing link" between the neuron and the wall of the arteriole, must be considered as being a fundamental neurotransmitter in the same way as well-known substances such as noradrenaline, acetylcholine, serotonin, dopamine and the GABAergic system are also neurotransmitters.

Effects of stress on opioid receptor binding in the rat central nervous system

The endogenous opioid peptides are known to play a significant role in the modulation and/or mediation of numerous environmental or experimental stressors. However, the specific opioid peptide(s) and receptor type(s) involved, under what physiologic conditions they are engaged and within which regions of the CNS is not well understood. We therefore examined the effects of both a chronic and an acute stressor-90-h water deprivation and a single 20-min foot shock on opioid receptor binding in 17 specific rat brain nuclei. [3H]DSTLE (Tyr-D-Ser-Gly-Phe-Leu-Thr) and [3H]DAGO(Tyr-D-Gly-Phe-NMe-Phe-Gly-ol) were used to label delta and mu receptors, respectively. Foot shock induced profound antinociception as measured by tail-flick latency which outlasted the stressor by several minutes. However, only the septum responded with a decrease in [3H]DAGO binding to this type of stress-induced analgesia. No other alterations in either [3H]DAGO or [3H]DSTLE binding were seen in response to foot shock. In contrast, water deprivation induced increases in [3H-DAGO] binding in the septum as well as increases in [3H]DSTLE binding in the caudate and accumbens nuclei. Moreover, the presumptive mild stress of handling in the foot shock control group was sufficient to decrease mu or delta receptor binding in seven out of 17 brain regions investigated (including the frontal cortex and olfactory tubercle where both mu and delta binding were increased) when compared to unhandled deprivation control animals. These changes in opioid receptor binding may have been the result of alterations in treatment-induced peptide release, receptor regulation, or interactions with other released neurotransmitter ligand/receptor complexes.(ABSTRACT TRUNCATED AT 250 WORDS)

Neuropeptides as psychotropic drugs

Neuropeptides are endogenous substances present in nerve cells and involved in nervous system functions. Neuropeptides are synthetized in large precursor proteins and several are formed in the same precursor. Neuropeptides affect learning and memory processes, social, sexual and maternal behavior, pain and addiction, body temperature, food and water intake e.a. In addition, neuropeptides possess trophic influences on the nervous system, neuroleptic-like andpsychostimulant-like activities. Disturbances in classical neurotransmitter activity as found in Parkinson's disease, psychoses, and dementia, may also be caused by disturbances in neuropeptide activity. In fact, alterations in the concentration of a number of neuropeptides in schizophrenia, depression, and dementia have been found. Much work has been done during the last decade on the influence of neuropeptides in schizophrenia, autism, depression, and in various disorders associated with memory disturbances. These studies concern neuropeptides related to adrenocorticotropic hormone (ACTH) and melanocyte stimulating hormone (MSH), vasopressin- and endorphin-type neuropeptides, thyrotropic releasing hormone (TRH), and the C-terminal part of oxytocin Pro-Leu-Gly-NH2 (PLG). Several of these exert positive effects but in not more than 25% the response is clinically relevant. This may have to do with the severity of the disease and its chronicity. The modest effects may also be caused by the poor bioavailability of peptides and insufficient pharmacotherapeutic experience regarding dose, and duration of treatment.

The grasping response in rats: interaction between gamma-type endorphins and haloperidol

gamma-Type endorphins mimic neuroleptics in inducing a grasping response in rats. It was studied whether the haloperidol-induced grasping response was altered after blockade of gamma-type endorphin activity in the rat brain. To achieve this blockade rats were injected i.c.v. with gamma-endorphin antiserum or with a monoclonal anti-idiotype desenkephalin-gamma-endorphin antibody, which may bio-inactivate the gamma-type endorphins or block the putative receptors for gamma-type endorphins, respectively. The results showed that both treatments attenuated the haloperidol-induced grasping response, particularly 3 h after haloperidol treatment. The influence of these antibodies appeared to be specific, since other sera were without effect. Thus there may be an interaction between the endogenous gamma-type endorphin activity and the haloperidol-induced grasping response.

The relationship of tardive dyskinesia to positive schizophrenia

Investigations aimed at identifying the clinical characteristics that discriminate Tardive dyskinesia (TD) from non-TD patients have yielded disparate findings. A number of studies have suggested that TD may be a feature of negative schizophrenia. In particular, the association of TD with high prevalence of "soft" neurological signs, cognitive deficits, and abnormal brain morphology on CT scan in some patients, have led several investigators to propose that negative schizophrenia may be a risk factor for TD. The neurochemical profile of TD, however, is not consistent with this hypothesis. In the following communication, we present our studies which suggest that TD is specific to and an intergral part of positive schizophrenia. The data suggest that schizophrenic patients with predominant positive symptoms may be at increased risk for the development of TD. In addition, we present evidence linking TD with left cerebral hemispheric dysfunction. By comparison, we provide evidence that negative schizophrenia is related to diencephalic damage, and discuss its relevance to negative schizophrenia and to Parkinsonism. We also provide evidence that negative schizophrenia may be a risk factor for acute drug-induced dystonia. Thus, these findings are consistent with our model that negative schizophrenia is a risk factor for Parkinsonism, whereas positive schizophrenia is related to TD. In analogy with the positive/negative dichotomy of schizophrenia, we propose that TD could be considered a "positive," where Parkinsonism a "negative" movement disorder.

The relationship of negative schizophrenia to parkinsonism

The positive-negative distinction of schizophrenia has emerged as a valid means of clarifying its heterogeneity. Despite evidence that the two symptom classes may reflect different dimensions of the disease, there is presently no integrated model for understanding of the pathophysiology of these symptoms and their co-occurrence in schizophrenia. We propose that negative phenomena of schizophrenia may be a variant of Parkinsonism. This view is supported by the overlap with Parkinsonism in terms of clinical features, neurochemistry, pharmacology, as well as neuroradiological and neuropathological aspects. As such, negative symptoms may be a manifestation of disease of the basal ganglia and constitute the core pathology in schizophrenia. Positive symptoms, conversely, may reflect an "accessory" process related to a compensatory increase in striatal and limbic dopamine activity following an injury to the dopaminergic system. In the present communication we present a series of studies that support the association of negative schizophrenia and Parkinsonism. Based on this evidence, we suggest that schizophrenic patients with prominent negative symptoms might be managed like patients with Parkinson's disease, namely, with dopaminergic drugs and MAO-B inhibitors. Finally, the association of negative schizophrenia with Parkinsonism raises the possibility that adrenal medullary tissue transplantation, which may benefit a selected group of Parkinsonian patients, may be a future promising therapy for refractory negative schizophrenia.

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.

Endogenous opiates: 1988

This paper is the eleventh installment in our annual review of the research during the past year involving the endogenous opiate system. It is concerned with nonanalgesic and behavioral studies of the opiate peptides that were published during 1988. The specific topics this year include stress; tolerance and dependence; eating; drinking; gastrointestinal, renal, and hepatic functions; mental illness; learning, memory, and reward; cardiovascular responses; respiration and thermoregulation; seizures and other neurological disorders; electrical activity; locomotor activity; sex, pregnancy, and development; immunology and cancer; and other behavior.