Antipsychotic action of gamma-type endorphins: animal and human studies

Changes in puromycin-sensitive aminopeptidases in postmortem schizophrenic brain regions

We studied the distribution of puromycin-sensitive aminopeptidase (PSA) in well-defined human brain ares by Western immunoblot in an attempt to examine its possible role in schizophrenia. The schizophrenic brains were from suicide victims (n = 13) of either sex, with an age range of 30-60 yr (average 45). The controls were mostly victims of myocardial infarction (n = 12), of either sex and between 32 and 56 yr old (average 44). The brain regions were obtained within 48 h after death. After ultracentrifugation the PSA was quantified by Western blot analysis using a PSA antiserum. The distribution of the two most abundant antigens, MW 100 kDa (PSA-100) and 170 kDA (PSA-170), were compared. PSA-100 had peptidase activity, PSA-170 did not. PSA-100 was found in all of the region studied. In the control brain areas prefrontal cingulate and frontal cortices, thalamus, hippocampus, hypothalamus and outer globus pallidus contained significantly more PSA-100 than the corresponding areas from schizophrenic brain. PSA-170 was mostly found only in areas of schizophrenic brains. In three control brains, in one area of each, it could be detected, but the level in each of these regions was less than 30% of that in the corresponding schizophrenic area. PSA-170 was found in all the schizophrenic brains, in 20 of the 35 regions we studied, with parahippocampal cortex the highest (134 ng/g wet tissue) and frontal inferior cortex the lowest (9.3 ng/g wet tissue). It was not detectable in cerebral or cerebellar white matter. Our data show that the amounts and distribution of PSA-170, a protein of unknown function, is restricted mostly to schizophrenic brain areas. The difference is not due either to neuroleptic treatment of the patient or to the postmortem proteolysis of the brain samples.

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.

Subchronic treatment with the neuroleptic-like peptide desenkephalin-gamma-endorphin may decrease dopaminergic neurotransmission in the nucleus accumbens of rats

In rats, subchronic administration of desenkephalin-gamma-endorphin (DE gamma E) into the nucleus accumbens or subcutaneously for 10 days resulted in hypoactivity. Intra-accumbens administration caused a significant reduction in the nucleus accumbens tissue levels of the dopamine (DA) metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA). Systemic administration of DE gamma E decreased DOPAC and 5-hydroxyindoleacetic acid (5-HIAA) levels in nucleus accumbens tissue. Subchronic subcutaneous DE gamma E treatment reduced the basal release of [3H]DA from rat nucleus accumbens slices in vitro and the basal release of endogenous DA and DOPAC in vivo as assessed with on-line dialysis in the nucleus accumbens of freely moving rats. The DA agonist N,N-dipropyl-7-hydroxy-2-aminotetralin (DP-7-ATN) was equally effective in inhibiting [3H]DA release elicited by electrical stimulation from slices of subchronically DE gamma E and placebo treated rats. Administration of a small dose of apomorphine caused similar reductions of the in vivo release of DA and DOPAC in both placebo and DE gamma E treated rats. These results indicate that subchronic DE gamma E treatment may decrease dopaminergic neurotransmission in the nucleus accumbens. This effect is probably not due to alterations in the sensitivity of presynaptically located DA autoreceptors mediating DA release in vitro and in vivo.

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 brain and higher mental function

Critical evaluation of biological theories of psychiatric disorder requires an understanding of current concepts of higher mental function and its related biology. Both the nature of the topic and the rapidity of advances in the field make it difficult to obtain an updated synthesis. Part I of this paper attempts to provide that by reviewing current concepts of the mind/body relationship, emotion, arousal, attention, consciousness and motivation. Part II considers those concepts in relation to recent work on the structure and function of the reticular, limbic and anterior cerebral systems. It is concluded that the model of the limbic system as subserving emotional life could now perhaps be set aside in favour of the model of a core set of chemically identified neurons in the reticular system being necessary but not sufficient to subserve higher mental function whilst also subserving other integrating functions for which no mental terminology is required. The problem of developing an eclectic theory of higher mental function that will embrace these concepts is discussed.

Neuropeptides: animal behaviour and human psychopathology

Animal studies have demonstrated that neuropeptides modulate nervous system functions. It has been postulated that disturbances in neuropeptide systems may be aetiological factors in psychiatric and neurological disorders. Neuropeptides related to ACTH/MSH, including ORG 2766, increase motivation and attention and facilitate recovery processes after nerve damage. These peptides may be effective during the early stage of dementia. Vasopressin and related peptides improve memory processes in animals and humans. In addition, these peptides influence social behaviour, mood and addictive behaviour. The non-opioid gamma-type endorphins have neuroleptic-like activities in animals and antipsychotic effects in a category of schizophrenic patients. Peptides related to CCK have also been found to be effective in these patients. Some neuropeptides, e.g. TRH and PLG, have been reported to exert antidepressant effects. Further research may eventually produce neuropeptides with therapeutic action in psychiatric and neurological diseases.

Dopamine release in the nucleus accumbens of freely moving rats determined by on-line dialysis: effects of apomorphine and the neuroleptic-like peptide desenkephalin-gamma-endorphin

This study examined the effects of apomorphine, sulpiride, desenkephalin-gamma-endorphin (DE gamma E) and a combination of DE gamma E with apomorphine on the release of dopamine (DA) and its main metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in the nucleus accumbens of freely moving rats. A fully automated on-line brain dialysis system was used. A small dose of s.c. administered apomorphine induced a decrease in the output of DA and DOPAC. Sulpiride, infused into the nucleus accumbens, induced a 2-fold increase in the output of DA, DOPAC and HVA. DE gamma E hardly modified either the basal release of DA, DOPAC and HVA or the apomorphine-induced attenuation of the release of DA and DOPAC. These results indicate a dissociation between the behavioural effects of DE gamma E and its effect on the release of DA in vivo.

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

The concentrations of alpha-, beta- and gamma-endorphin were determined by radioimmunoassay in HPLC fractionated extracts of post mortem hypothalamic tissue obtained from schizophrenic patients and controls. The hypothalamic concentration of alpha- and gamma-endorphin was significantly higher in patients than in controls (+72.9% and +50.5% respectively). No difference was found in the concentration of beta-endorphin, the putative precursor of alpha- and gamma-endorphins. These results suggest a deviant metabolism of beta-endorphin in the brain of schizophrenic patients. Whether this phenomenon is related to the psychopathology, or is a consequence of ante mortem farmacotherapy, remains to be established.

The hypomotility elicited by small doses of apomorphine seems exclusively mediated by dopaminergic systems in the nucleus accumbens

The reduction of motor activity elicited in rats by a subcutaneous injection of a small dose of apomorphine was reversed by pretreatment of the nucleus accumbens with haloperidol (10 pg), sulpiride (10 pg) or desenkephalin-gamma-endorphin (DE gamma E) (100 pg or 10 ng). These doses of the compounds did not change motor activity in placebo-treated rats. Pretreatment of the nucleus caudatus with the same neuroleptics or DE gamma E did not diminish the effect of subcutaneously administered low doses of apomorphine. A small dose of apomorphine decreased motor activity when it was injected directly into the nucleus accumbens. This effect was dose dependently antagonized by subcutaneous pretreatment with DE gamma E. It is suggested that the hypoactivity elicited by small doses of apomorphine is exclusively mediated by dopaminergic systems in the nucleus accumbens.