Neuropeptides, dopamine, and schizophrenia

Association between angiotensin-converting enzyme gene insertion/deletion polymorphism and cognition impairment in patients with schizophrenia

RATIONALE

Several lines of evidence indicate that an insertion/deletion (I/D) polymorphism in the angiotensin-converting enzyme gene (ACE) gene may be involved in the pathogenesis of schizophrenia and cognitive impairment. However, the relationship between ACE I/D polymorphism and cognitive impairment in patients with schizophrenia remains unclear.

OBJECTIVES

The aim of this study was to examine whether ACE gene I/D polymorphism contributed to cognitive impairment in Chinese patients with schizophrenia, and whether the association between clinical symptoms and cognitive impairment depended on different ACE genotypes.

METHODS

The ACE I/D polymorphism was genotyped in 928 schizophrenia patients and 325 healthy controls using a case-control design. The severity of psychopathological symptoms was assessed using the Positive and Negative Syndrome Scale (PANSS). Cognitive functioning was assessed by the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS).

RESULTS

There were significant differences in genotype and allele frequencies of the ACE I/D polymorphism between patients and healthy controls (both P < 0.01). After controlling for demographic characteristics, patients who are homozygous carriers of D and I performed worse on the RBANS attention index than heterozygous carriers (P = 0.009). In addition, attention index score was negatively correlated with PANSS negative symptom score in patients of all genotypes (all P < 0.05), and positively correlated with positive symptom score only in the I/I genotype (P = 0.005).

CONCLUSIONS

These findings suggest that ACE I/D gene variants play a role in susceptibility to schizophrenia, specific cognitive impairment and the association between clinical symptoms and cognitive impairment in schizophrenia patients.

Decreased plasma neuropeptides in first-episode schizophrenia, bipolar disorder, major depressive disorder: associations with clinical symptoms and cognitive function

Background

There is an urgent need to identify differentiating and disease-monitoring biomarkers of schizophrenia, bipolar disorders (BD), and major depressive disorders (MDD) to improve treatment and management.

Methods

We recruited 54 first-episode schizophrenia (FES) patients, 52 BD patients, 35 MDD patients, and 54 healthy controls from inpatient and outpatient clinics. α-Melanocyte Stimulating Hormone (α-MSH), β-endorphin, neurotensin, orexin-A, oxytocin, and substance P were investigated using quantitative multiplex assay method. Psychotic symptoms were measured using the Brief Psychiatric Rating Scale (BPRS) and Positive and Negative Syndrome Scale (PANSS), manic symptoms using the Young Mania Rating Scale (YMRS), and depressive symptoms using 17 item-Hamilton Depression Rating Scale (HAMD). We additionally measured cognitive function by using a battery of tests given to all participants.

Results

α-MSH, neurotensin, orexin-A, oxytocin, and substance P were decreased in the three patient groups compared with controls. Neurotensin outperformed all biomarkers in differentiating patient groups from controls. There were no significant differences for 6 neuropeptides in their ability to differentiate between the three patient groups. Higher neurotensin was associated with better executive function across the entire sample. Lower oxytocin and higher substance p were associated with more psychotic symptoms in FES and BD groups. β-endorphin was associated with early morning wakening symptom in all three patient groups.

Conclusion

Our research shows decreased circulating neuropeptides have the potential to differentiate severe mental illnesses from controls. These neuropeptides are promising treatment targets for improving clinical symptoms and cognitive function in FES, BD, and MDD.

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.

Dopamine in human follicular fluid is associated with cellular uptake and metabolism-dependent generation of reactive oxygen species in granulosa cells: implications for physiology and pathology

STUDY QUESTION

Is the neurotransmitter dopamine (DA) in the human ovary involved in the generation of reactive oxygen species (ROS)?

SUMMARY ANSWER

Human ovarian follicular fluid contains DA, which causes the generation of ROS in cultured human granulosa cells (GCs), and alterations of DA levels in follicular fluid and DA uptake/metabolism in GCs in patients with polycystic ovary syndrome (PCOS) are linked to increased levels of ROS.

WHAT IS KNOWN ALREADY

DA is an important neurotransmitter in the brain, and the metabolism of DA results in the generation of ROS. DA was detected in human ovarian homogenates, but whether it is present in follicular fluid and plays a role in the follicle is not known.

STUDY DESIGN, SIZE AND DURATION

We used human follicular fluid from patients undergoing in vitro fertilization (IVF), GCs from patients with or without PCOS and also employed mathematical modeling to investigate the presence of DA and its effects on ROS.

PARTICIPANTS/MATERIALS, SETTING AND METHODS

DA in follicular fluid and GCs was determined by enzyme-linked immunosorbent assay. GC viability, apoptosis and generation of ROS were monitored in GCs upon addition of DA. Inhibitors of DA uptake and metabolism, an antioxidant and DA receptor agonists, were used to study cellular uptake and the mechanism of DA-induced ROS generation. Human GCs were examined for the presence and abundance of transcripts of the DA transporter (DAT; SLC6A3), the DA-metabolizing enzymes monoamine oxidases A/B (MAO-A/B) and catechol-O-methyltransferase and the vesicular monoamine transporter. A computational model was developed to describe and predict DA-induced ROS generation in human GCs.

MAIN RESULTS AND ROLE OF CHANCE

We found DA in follicular fluid of ovulatory follicles of the human ovary and in GCs. DAT and MAO-A/B, which are expressed by GCs, are prerequisites for a DA receptor-independent generation of ROS in GCs. Blockers of DAT and MAO-A/B, as well as an antioxidant, prevented the generation of ROS (P < 0.05). Agonists of DA receptors (D1 and D2) did not induce ROS. DA, in the concentration range found in follicular fluid, did not induce apoptosis of cultured GCs. Computational modeling suggested, however, that ROS levels in GCs depend on the concentrations of DA and on the cellular uptake and metabolism. In PCOS-derived follicular fluid, the levels of DA were higher (P < 0.05) in GCs, the transcript levels of DAT and MAO-A/B in GCs were 2-fold higher (P < 0.05) and the DA-induced ROS levels were found to be more than 4-fold increased (P < 0.05) compared with non-PCOS cells. Furthermore, DA at a high concentration induced apoptosis in PCOS-derived GCs.

LIMITATIONS, REASONS FOR CAUTION

While the results in IVF-derived follicular fluid and in GCs reveal for the first time the presence of DA in the human follicular compartment, functions of DA could only be studied in IVF-derived GCs, which can be viewed as a cellular model for the periovulatory follicular phase. The full functional importance of DA-induced ROS in small follicles and other compartments of the ovary, especially in PCOS samples, remains to be shown.

WIDER IMPLICATIONS OF THE FINDINGS

The results identify DA as a factor in the human ovary, which, via ROS generation, could play a role in ovarian physiology and pathology. The results obtained in samples from women with PCOS suggest the involvement of DA, acting via ROS, in this condition.

STUDY FUNDING/COMPETING INTERESTS

This work was supported by a grant from DFG MA1080/17-3 and in part MA1080/19-1. There are no competing interests.

Dopamine induces Ca2+ signaling in astrocytes through reactive oxygen species generated by monoamine oxidase

Dopamine is a neurotransmitter that plays a major role in a variety of brain functions, as well as in disorders such as Parkinson disease and schizophrenia. In cultured astrocytes, we have found that dopamine induces sporadic cytoplasmic calcium ([Ca(2+)](c)) signals. Importantly, we show that the dopamine-induced calcium signaling is receptor-independent in midbrain, cortical, and hippocampal astrocytes. We demonstrate that the calcium signal is initiated by the metabolism of dopamine by monoamine oxidase, which produces reactive oxygen species and induces lipid peroxidation. This stimulates the activation of phospholipase C and subsequent release of calcium from the endoplasmic reticulum via the inositol 1,4,5-trisphosphate receptor mechanism. These findings have major implications on the function of astrocytes that are exposed to dopamine and may contribute to understanding the physiological role of dopamine.

An intron 1 polymorphism in the cholecystokinin-A receptor gene associated with schizophrenia in males

OBJECTIVE

To identify whether a genetic variation (rs1800857; IVS1-5T>C) in the neuropeptide cholecystokinin-A receptor (CCKAR) gene is a risk factor in the pathogenesis of schizophrenia.

METHOD

The variation was analysed in a case-control design comprising 508 patients with schizophrenia and 1619 control subjects. A possible functional impact of this variant on CCKAR protein synthesis through alterations in splicing was analysed in an exon-trapping assay.

RESULTS

In males only, the risk variant, IVS1-5C, was associated with a significantly increased risk of schizophrenia. Carrying one risk allele was associated with an increased risk of 1.74 (Odds Ratio, OR) and homozygosity (CC) was associated with an OR of 3.19. The variation had no impact on protein synthesis of CCKAR.

CONCLUSION

This is the first report associating the CCKAR gene variant with schizophrenia specifically in men. Our study strengthens the conclusion that a CCKAR dysfunction could be involved in the aetiology of schizophrenia.

Neuropeptide and sigma receptors as novel therapeutic targets for the pharmacotherapy of depression

Among the most prevalent of mental illnesses, depression is increasing in incidence in the Western world. It presents with a wide variety of symptoms that involve both the CNS and the periphery. Multiple pharmacological observations led to the development of the monoamine theory as a biological basis for depression, according to which diminished neurotransmission within the CNS, including that of the dopamine, noradrenaline (norepinephrine) and serotonin systems, is the leading cause of the disorder. Current conventional pharmacological antidepressant therapies, using selective monoamine reuptake inhibitors, tricyclic antidepressants and monoamine oxidase inhibitors, aim to enhance monoaminergic neurotransmission. However, the use of these agents presents severe disadvantages, including a delay in the alleviation of depressive symptoms, significant adverse effects and high frequencies of non-responding patients. Neuroendocrinological data of recent decades reveal that depression and anxiety disorders may occur simultaneously due to hypothalamus-pituitary-adrenal (HPA) axis hyperactivity. As a result, the stress-diathesis model was developed, which attempts to associate genetic and environmental influences in the aetiology of depression. The amygdala and the hippocampus control the activity of the HPA axis in a counter-balancing way, and a plethora of regulatory neuropeptide signalling pathways are involved. Intervention at these molecular targets may lead to alternative antidepressant therapeutic solutions that are expected to overcome the limitations of existing antidepressants. This prospect is based on preclinical evidence from pharmacological and genetic modifications of the action of neuropeptides such as corticotropin-releasing factor, substance P, galanin, vasopressin and neuropeptide Y. The recent synthesis of orally potent non-peptide micromolecules that can selectively bind to various neuropeptide receptors permits the onset of clinical trials to evaluate their efficacy against depression.

Rubiscolin-6, a delta opioid peptide derived from spinach Rubisco, has anxiolytic effect via activating sigma1 and dopamine D1 receptors

Rubiscolin-6 (Tyr-Pro-Leu-Asp-Leu-Phe) is a delta opioid peptide derived from the large subunit of spinach d-ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). We previously reported that rubiscolin-6 had an analgesic effect and stimulated memory consolidation. Here we show that intraperitoneally (i.p.) or orally administered rubiscolin-6 has an anxiolytic effect at a dose of 10 mg/kg or 100 mg/kg, respectively, in the elevated plus-maze test in mice. The anxiolytic effects of rubscolin-6 after i.p. (10 mg/kg) and oral (100 mg/kg) administration were blocked by a delta opioid receptor antagonist, naltrindole (1 mg/kg, s.c.), suggesting that the anxiolytic activity of rubiscolin-6 is mediated by delta opioid receptor. The anxiolytic effect of rubiscolin-6 (10 mg/kg, i.p.) was also blocked by a dopamine D(1) antagonist, SCH23390 (30 microg/kg, i.p.), but not by a dopamine D(2) antagonist, raclopride (15 microg/kg, i.p.). The anxiolytic effect of rubiscolin-6 (10 mg/kg, i.p.) was blocked by sigma(1) receptor antagonist, BMY14802 (0.5 mg/kg, i.p.) or BD1047 (10 mg/kg, i.p.). Taken together, the anxiolytic effect of rubiscolin-6 is mediated by sigma(1) and dopamine D(1) receptors downstream of delta opioid receptor.

Dopamine induces apoptosis in young, but not in neonatal, neurons via Ca2+-dependent signal

Dopamine signaling plays a major role in regulation of neuronal apoptosis. During the postnatal period, dopamine signaling is known to be dramatically changed in the striatum. However, because it is difficult to culture neurons after birth, little is known about developmental changes in dopamine-mediated apoptosis. To examine such changes, we established the method of primary culture of striatal neurons from 2- to 3-wk-old (young) mice. Dopamine, via D(1)-like receptors, induced apoptosis in young, but not neonatal, striatal neurons, suggesting that the effect of dopamine on apoptosis changed with development. In contrast, although isoproterenol (Iso), a beta-adrenergic receptor agonist, increased cAMP production to a greater degree than dopamine, Iso did not increase apoptosis in striatal neurons from young and neonatal mice, suggesting a minor role of cAMP in dopamine-mediated apoptosis. Next, we examined the effect of dopamine on Ca(2+) signaling. Dopamine, but not Iso, markedly increased intracellular Ca(2+) in striatal neurons from young mice, and Ca(2+)-chelating agents abolished dopamine-induced apoptosis, suggesting that Ca(2+) played a major role in the dopamine-mediated apoptosis pathway. In contrast, dopamine failed to increase intracellular Ca(2+) in neonatal neurons, and the expression of PLC, which can increase intracellular Ca(2+) via D(1)-like receptor activation, was significantly greater in young than in neonatal striatal neurons. These data suggest that the developmental change in dopamine-mediated Ca(2+) signaling was responsible for differences between young and neonatal striatum in induction of apoptosis. Furthermore, the culture of young striatal neurons is feasible and may provide a new tool for developmental studies.

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.

Cannabis-associated psychosis: current status of research

Cannabis has been used for recreational, medicinal and religious purposes in different cultures since ancient times. There have been various reports of adverse effects due to or associated with cannabis consumption, including psychotic episodes. Historically, our understanding of these clinical observations has been significantly hindered by a lack of knowledge regarding their underlying neurobiological and pharmacological processes. However, the discovery of the endogenous cannabinoid system has allowed a greater understanding of these adverse effects to develop. From a clinical perspective, toxic or transient psychotic reactions to the administration of herbal cannabis preparations or specific cannabinoid compounds have to be differentiated from longer-lasting, persistent schizophrenia-like disorders associated with the use of cannabis/cannabinoids. The latter are most likely to be associated with a predisposition or vulnerability to schizophrenia. Interestingly, the recently suggested role of the endogenous cannabinoid system in schizophrenia not related to previous cannabinoid consumption introduces an additional perspective on the mechanism underlying cannabis-associated schizophrenia-like disorders, as well as on the effects of cannabis consumption in schizophrenia. At present, acute psychopharmacological treatment options for cannabis-associated transient and persistent schizophrenia-like psychotic episodes are similar and are based on the use of benzodiazepines and antipsychotics. However, new pharmacological strategies using the endogenous cannabinoid system as a primary target are under development. Long-term psychotherapeutic treatment options involve case management strategies and are mainly based on specialised psychotherapeutic programmes to encourage cannabis users to stop their use of the drug.

Endomorphin-1, an endogenous mu-opioid receptor agonist, improves apomorphine-induced impairment of prepulse inhibition in mice

The present study was designed to examine the effects of the endogenous mu-opioid receptor agonist endomorphin-1 on prepulse inhibition (PPI) in mice. Although apomorphine (1mg/kg) produced a marked decrease in PPI, endomorphin-1 (17.5 microg) had no marked effects on PPI or startle amplitude in normal mice. Endomorphin-1 (17.5 microg) inhibited the apomorphine (1mg/kg)-induced decrease in PPI. beta-Funaltrexamine (5 microg), a mu-opioid receptor antagonist, did not significantly antagonize the effects of endomorphin-1 (17.5 microg). Naloxonazine (35 mg/kg), a mu(1)-opioid receptor antagonist, antagonized the effects of endomorphin-1 (17.5 microg) on the apomorphine (1mg/kg)-induced decrease in PPI, whereas naloxonazine (35 mg/kg) itself was without significant effects on the apomorphine (1mg/kg)-induced decrease. These results suggest that endomorphin-1 alleviates the impairment of PPI resulting from the hyperactivity of dopaminergic neurotransmission through the mediation of mu(1)-opioid receptors.

Dopaminergic modulation of neuronal excitability in the striatum and nucleus accumbens

The striatum and its ventral extension, the nucleus accumbens, are involved in behaviors as diverse as motor planning, drug seeking, and learning. Invariably, these striatally mediated behaviors depend on intact dopaminergic innervation. However, the mechanisms by which dopamine modulates neuronal function in the striatum and nucleus accumbens have been difficult to elucidate. Recent electrophysiological studies have revealed that dopamine alters both voltage-dependent conductances and synaptic transmission, resulting in state-dependent modulation of target cells. These studies make clear predictions about how dopamine, particularly via D1 receptor activation, should alter the responsiveness of striatal neurons to extrinsic excitatory synaptic activity.

Presynaptic dopamine D2-like receptors inhibit excitatory transmission onto rat ventral tegmental dopaminergic neurones

1. The effects of dopamine (DA) on non-NMDA glutamatergic transmission onto dopaminergic neurones in the ventral tegmental area (VTA) were examined in rat midbrain slices using the whole-cell patch-clamp technique. EPSCs in dopaminergic neurones evoked by focal stimulation within the VTA were reversibly blocked by 5 microM CNQX in the presence of bicuculline (20 microM), strychnine (0.5 microM) and D-amino-5-phosphonopentanoic acid (D-AP5, 25 microM). 2. Bath application of DA reduced the amplitude of EPSCs up to 65.1 +/- 9. 52% in a concentration-dependent manner between 0.3-1000 microM (IC50, 16.0 microM) without affecting the holding current at -60 mV measured using a Cs+-filled electrode. 3. The effect of DA on evoked EPSCs was mimicked by the D2-like receptor agonist quinpirole but not by the D1-like receptor agonist SKF 81297, and was antagonized by the D2-like receptor antagonist sulpiride (KB, 0.96 microM), but not by the D1-like receptor antagonist SCH 23390 (KB, 228.6 microM). 4. Dopamine (30 microM) reduced the mean frequency of spontaneous miniature EPSCs (mEPSCs) without affecting their mean amplitude, and the DA-induced effect on the mEPSCs was dependent on the external Ca2+ concentration. 5. These results suggest that afferent glutamatergic fibres which terminate on VTA dopaminergic neurones possess presynaptic D2-like receptors, activation of which inhibits glutamate release by reducing Ca2+ influx.

Cholecystokinin, beta-endorphin and vasoactive intestinal peptide in peripheral blood mononuclear cells of drug-naive schizophrenic patients treated with haloperidol compared to healthy controls

Cholecystokinin (CCK), beta-endorphin (BE), and vasoactive intestinal peptide (VIP) in peripheral blood mononuclear cells from 30 drug-naive schizophrenics compared to 22 healthy controls were studied. Patients were evaluated with the Brief Psychiatric Rating Scale (BPRS), the Scale for the Assessment of Positive Symptoms (SAPS) and the Scale for the Assessment of the Negative Symptoms (SANS) at baseline (TO), and after four weeks (T4) in nine patients who were subsequently treated with haloperidol (HL). Neuropeptide concentrations in peripheral blood mononuclear cells (PBMC) were measured at TO and, for the treated patients, at T4. There was a negative correlation between CCK and SANS baseline scores and a trend for patients who responded poorly to HL (i.e. patients with a prevalence of negative symptomatology) to have lower CCK basal values.

Coordinated expression of dopamine receptors in neostriatal medium spiny neurons

In recent years, the distribution of dopamine receptor subtypes among the principal neurons of the neostriatum has been the subject of debate. Conventional anatomical and physiological approaches have yielded starkly different estimates of the extent to which D1 and D2 class dopamine receptors are colocalized. One plausible explanation for the discrepancy is that some dopamine receptors are present in physiologically significant numbers, but the mRNA for these receptors is not detectable with conventional techniques. To test this hypothesis, we examined the expression of DA receptors in individual neostriatal neurons by patch-clamp and RT-PCR techniques. Because of the strong correlation between peptide expression and projection site, medium spiny neurons were divided into three groups on the basis of expression of mRNA for enkephalin (ENK) and substance P (SP). Neurons expressing detectable levels of SP but not ENK had abundant mRNA for the D1a receptor. A subset of these cells (approximately 50%) coexpressed D3 or D4 receptor mRNA. Neurons expressing detectable levels of ENK but not SP had abundant mRNA for D2 receptor isoforms (short and long). A subset (10-25%) of these neurons coexpressed D1a or D1b mRNAs. Neurons coexpressing ENK and SP mRNAs consistently coexpressed D1a and D2 mRNAs in relatively high abundance. Functional analysis of neurons expressing lower abundance mRNAs revealed clear physiological consequences that could be attributed to these receptors. These results suggest that, although colocalization of D1a and D2 receptors is limited, functional D1 and D2 class receptors are colocalized in nearly one-half of all medium spiny projection neurons.

Identification of a missense mutation and several polymorphisms in the proenkephalin A gene of schizophrenic patients

Schizophrenia is a complex and severe disorder of unknown cause and pathophysiology. In this study, we examined the opioid hypothesis for schizophrenia at the molecular level, focusing on the dopamine-regulated proenkephalin A gene (chromosome 8q11.23-q12). We have screened 150 schizophrenic patients for sequence variations within the promoter region, entire coding sequence, and 3'-untranslated region. We find one sequence change in a conserved amino acid that may be of functional significance. This mutation was found in a single schizophrenia patient but not in controls. Although several new, race-specific polymorphisms were identified, all other sequence changes appeared to be common polymorphisms, unlikely to contribute to the etiology of schizophrenia.

Increases in cortical neuropeptide Y and somatostatin concentrations following haloperidol-depot treatment in rats

The concentrations of neuropeptide Y (NPY) and somatostatin (SS) have been said to be altered in the brain and cerebrospinal fluid of schizophrenic patients. This alteration could result from the neuroleptic treatment. Therefore, it is of interest to evaluate effects of long-term treatment with neuroleptics on the peptide concentrations in the brain. Haloperidol (HPD) is one of the most frequently used neuroleptics for the treatment of schizophrenia. We determined regional brain levels of NPY and SS following HPD administration in the rat. A single intraperitoneal injection of HPD, at a dose of 1 mg/kg, did not affect peptide levels in the brain regions studied. Four weeks after an intramuscular deposit injection of HPD decanoate, 50 mg/kg, NPY concentrations were increased in a number of areas of the cerebral cortex. SS content was also significantly increased in the lateral prefrontal cortex and anterior cingulate cortex. Both peptide levels were decreased in the striatum. These results suggest that the reduction found in these peptides' levels in the cerebral cortex of the brain from schizophrenic patients may not be the consequence of HPD treatment and that these peptides' levels might be increased in the cerebral cortex of the brain of schizophrenic patients following the treatment with HPD.

Modulation of calcium currents by a D1 dopaminergic protein kinase/phosphatase cascade in rat neostriatal neurons

In rat neostriatal neurons, D1 dopamine receptors regulate the activity of cyclic AMP-dependent protein kinase (PKA) and protein phosphatase 1 (PP1). The influence of these signaling elements on high voltage-activated (HVA) calcium currents was studied using whole-cell voltage-clamp techniques. The application of D1 agonists or cyclic AMP analogs reversibly reduced N- and P-type Ca2+ currents. Inhibition of PKA antagonized this modulation, as did inhibition of PP1, suggesting that the D1 effect was mediated by a PKA enhancement of PP1 activity directed toward Ca2+ channels. In a subset of neurons, D1 receptor-mediated activation of PKA enhanced L-type currents. The differential regulation of HVA currents by the D1 pathway helps to explain the diversity of effects this pathway has on synaptic integration and plasticity in medium spiny neurons.

Are neostriatal dopamine receptors co-localized?

The postsynaptic effects of dopamine in the neostriatum are mediated by five G-protein-coupled receptors. The extent to which these receptors are co-localized in neostriatal neurons has become controversial. This debate has far-reaching implications for treatment strategies in disorders of dopaminergic signaling, such as Parkinson's disease and schizophrenia. This review examines the molecular and cellular evidence for and against co-localization, including new information derived from single-cell mRNA amplification and patch-clamping of isolated neurons. It is concluded that this evidence is largely consistent with co-localization of functionally significant receptors of the D1 and D2 families in the majority of neostriatal efferent neurons. This conclusion has important implications for parallel processing models of the neostriatum.

Pharmacokinetics of (Me)Arg-Lys-Pro-Trp-tert-Leu-Leu-OEt and (Me)Arg-Lys-Pro-Trp-tert-Leu-Leu administered intravenously to beagle dogs

The pharmacokinetics of two analogues (NT-1 and NT-2) of the smallest active fragment of neurotensin were investigated in beagle dogs after intravenous (iv) administration at the doses of 0.1 and 0.5 mg/kg for NT-1 and of 0.25 and 0.5 mg/kg for NT-2. After iv administration of these two drugs, the plasma levels decreased with time with a biexponential pattern, and linear kinetic behavior was observed. The pharmacokinetic parameters (mean +/- standard error of mean) after iv administration of NT-1 at 0.1 mg/kg were as follows: the half-life of the distribution phase (t1/2 alpha) was 0.29 +/- 0.11 h, the half-life of the terminal phase (t1/2 beta) was 1.99 +/- 0.41 h, total plasma clearance (CL) was 33.2 +/- 6.3 mL/h/kg, steady-state volume of distribution (Vdss) was 57.1 +/- 2.8 mL/kg, and mean residence time (MRT) was 2.20 +/- 0.55 h. The t1/2 alpha, t1/2 beta, CL, Vdss, and MRT values after iv administration of NT-2 at 0.25 mg/kg were 0.11 +/- 0.02 h, 0.58 +/- 0.04 h, 257.3 +/- 17.2 mL/h/kg, 180.3 +/- 4.6 mL/kg, and 0.71 +/- 0.04 h, respectively. After iv administration of NT-1, NT-2 was detected in the plasma. It was confirmed from this result that NT-1 was metabolically hydrolyzed to NT-2 in the body of beagle dog.

Two types of neurone in the rat ventral tegmental area and their synaptic inputs

1. Intracellular recordings were made from 241 ventral tegmental neurones in slices of rat midbrain. Seventy-seven per cent of neurones were hyperpolarized by dopamine (principal cells); 16% were hyperpolarized by opioid peptides (secondary cells). 2. Most principal cells fired spontaneously (1-3 Hz) with a threshold of -53 mV; most secondary cells did not fire spontaneously. Action potentials of principal cells were longer (0.9 ms) than those of secondary cells (0.5 ms). 3. Focal electrical stimulation within the ventral tegmental area evoked a biphasic synaptic potential, depolarization followed by hyperpolarization, with a duration of about 200 ms. Experiments with receptor antagonists showed that the depolarizing component resulted from activation of both N-methyl-D-aspartate (NMDA) and non-NMDA receptors and the hyperpolarizing component resulted from activation of GABAA receptors. 4. A later hyperpolarizing synaptic potential developed after a latency of 50 ms, reached its peak in 250 ms and had a duration of about 1 s. It reversed polarity at -108 mV (external potassium concentration was 2.5 mM), was blocked by phaclofen (30 microM-1 mM) or 2-hydroxysaclofen (100-300 microM). In some cells, a phaclofen-resistant component remained that was increased by cocaine and blocked by sulpiride (1 microM). 5. It is concluded that the ventral tegmental area contains two types of neurone having properties similar to those in the substantia nigra. The cells receive synaptic inputs mediated by excitatory amino acids acting at NMDA and non-NMDA receptors, GABA acting at GABAA and GABAB receptors, and dopamine acting at D2 receptors.

Reduced concentrations of galanin, arginine vasopressin, neuropeptide Y and peptide YY in the temporal cortex but not in the hypothalamus of brains from schizophrenics

Postmortem investigations were performed in brains from 14 schizophrenic patients and 21 controls matched for age and autopsy latency. Concentrations of galanin, delta-sleep-inducing peptide (DSIP), corticotropin-releasing factor (CRF), arginine vasopressin (AVP), neuropeptide Y (NPY) and peptide YY (PYY) were determined in the hypothalamus and grey matter from the temporal cortex. A significant positive correlation between age and the concentrations of galanin and CRF was found in the controls. No sex differences were found except a higher mean of CRF in the hypothalamus of the women. In the temporal cortex of the schizophrenic brains, galanin, AVP, NPY and PYY were significantly reduced. DSIP reduction only bordered on significance. CRF was not reduced. Comparing neuroleptic-treated vs non-treated schizophrenics, the treatment factor could not explain the reduced concentrations of neuropeptides in the temporal lobe. A comparison of controls with schizophrenics showed no significant differences in hypothalamic neuropeptide concentrations.