Elevated Dopamine Concentrations Research Articles

Increased Concentrations of Dopamine in the Blood and the State of the Immune System in Practically Healthy Residents of the Northern Territories

The numerous effects of dopamine are predetermined by the fact that it, being a chemical precursor of noradrenaline, is secreted in nervous tissue, in the adrenal medulla, kidneys, intestines, and APUD cells (Apudocytes). The purpose of the work is to study the effectiveness of immune reactions at elevated concentrations of dopamine in the blood of practically healthy residents of the northern territories. The results of an immunological examination of 1064 practically healthy people aged 25-55 years living in the Arkhangelsk and Murmansk regions, as well as in the Nenets Autonomous Okrug, the Komi Republic and the Svalbard archipelago (Barentsburg) were analyzed. It was found that elevated concentrations of dopamine in peripheral venous blood were more often recorded in Arctic residents; during the polar day, dopamine concentrations are higher than in winter. Increased concentrations of dopamine in the blood of Northerners are associated with a decrease in the level of activated T cells with the transferrin receptor and IL-2, T-helper cells, as well as with increased concentrations of IL-1β, TNF-α, cortisol and thyroxine. An increase in dopamine concentration may be a consequence of a cytokine reaction in the nervous tissue to inhibit excessive receptor activity of cells by increasing the concentration of IL-10. The formation of an excess of both central hormones secreted by the pituitary gland and peripheral hormones at the same time is probably due to an increase in the sensitivity threshold of the hypothalamus, which is associated with an increase in the flow of interoceptive impulses of afferent systems.

Unveiling serotonergic dysfunction of obsessive-compulsive disorder on prefrontal network dynamics: a computational perspective.

Serotonin (5-HT) regulates working memory within the prefrontal cortex network, which is crucial for understanding obsessive-compulsive disorder. However, the mechanisms how network dynamics and serotonin interact in obsessive-compulsive disorder remain elusive. Here, we incorporate 5-HT receptors (5-HT1A, 5-HT2A) and dopamine receptors into a multistable prefrontal cortex network model, replicating the experimentally observed inverted U-curve phenomenon. We show how the two 5-HT receptors antagonize neuronal activity and modulate network multistability. Reduced binding of 5-HT1A receptors increases global firing, while reduced binding of 5-HT2A receptors deepens attractors. The obtained results suggest reward-dependent synaptic plasticity mechanisms may attenuate 5-HT related network impairments. Integrating serotonin-mediated dopamine release into circuit, we observe that decreased serotonin concentration triggers the network into a deep attractor state, expanding the domain of attraction of stable nodes with high firing rate, potentially causing aberrant reverse learning. This suggests a hypothesis wherein elevated dopamine concentrations in obsessive-compulsive disorder might result from primary deficits in serotonin levels. Findings of this work underscore the pivotal role of serotonergic dysregulation in modulating synaptic plasticity through dopamine pathways, potentially contributing to learned obsessions. Interestingly, serotonin reuptake inhibitors and antidopaminergic potentiators can counteract the over-stable state of high-firing stable points, providing new insights into obsessive-compulsive disorder treatment.

Development of a cellular model to study L-DOPA decarboxylase deregulation in the pathogenesis of schizophrenia

IntroductionSchizophrenia (SZ) is an inherited mental illness that affects 1% of the world’s population. Schizophrenia is a common functional psychosis with some unifying features that appears to have a universal distribution. Much of the research on SZ seeks to identify physiological, biochemical, or genetic features that differ between patients and healthy individuals. Biochemical factors represent an imbalance of certain biochemical substances in the brain, especially neurotransmitters. Early studies focused on the brain biochemistry of patients with SZ in terms of dysregulation of the neurotransmitter network. There is evidence that elevated dopamine concentrations are associated with positive symptoms (i.e., hallucinations, delirium) of the disease. For example, L-DOPA decarboxylase (DDC) is an enzyme involved directly in dopamine and serotonin synthesis and indirectly in noradrenaline synthesis. Therefore, the DDC gene can be considered a candidate gene for schizophrenia and its activity is a good candidate for functional analysis via epigenetic repression.ObjectivesWe aimed to create a cellular model with a deregulated DDC gene.MethodsWe constructed two lentiviral vectors, one expressing the dCas9-KRAB-MeCP2 repressor under the control of a synthetic tetracycline inducible promoter, and the other carrying a cassette expressing two sgRNAs with spacers against the DDC promoter. The SH-SY5Y cell line was sequentially stably transduced with both lentiviral constructs, and cells carrying both constructs were selected by the fluorescence of the GFP and RFP reporter proteins encoded in the lentiviral construct backbones.ResultsMethyl-sensitive real-time PCR followed by high-resolution fusion showed methylation of the DDC promoter. Correspondingly, real-time PCR showed a two-fold decrease in DDC expression in SH-SY5Y during tetracycline-induced expression of the CRISPR repressor.ConclusionsWe developed a cellular model to study the contribution of DDC deregulation to SZ-related molecular mechanisms.Disclosure of InterestNone Declared

Domestication and Feed Restriction Programming Organ Index, Dopamine, and Hippocampal Transcriptome Profile in Chickens

The domestication process exerts different phenotypic plasticity between slow- and fast-growing breeds of chicken. Feed restriction has a critical role in production performance, physiological plasticity, and stress response. Our study aimed to explore how feed restriction programed the organ index, dopamine, and hippocampal transcriptome profile between slow- and fast-growing chickens, which were fed either ad libitum (SA and FA), or feed restricted to 70% of ad libitum (SR and FR), for 30 days. Results showed that feed restriction influenced the brain organ index (P < 0.05), but not the organ index of the heart, liver, and spleen. The slow-growing breed tested had a higher brain organ index than the fast-growing breed (P < 0.05). Under feed restriction conditions, both the slow- and fast-growing breeds had significantly elevated dopamine concentrations (P < 0.05) compared to those fed ad libitum. In the GO term, upregulated genes in the FA group were enriched in the mitochondria, respiratory chain, and energy metabolism compared to the SA group (P < 0.05). Membranes and ribosomes were enriched in the cellular component between the SR and FR groups (P < 0.05). In the KEGG functional pathways, upregulated DEGs in the FR group were enriched in the cardiovascular disease category and neurodegenerative disease category compared to the FA group (P < 0.05). Downregulated DEGs in the FA group were enriched in the oxidative phosphorylation and neurodegenerative disease categories (Parkinson's disease and Huntington's disease) compared with the SA group (P < 0.05). Upregulated DEGs in the FR group were enriched in the cardiovascular disease category, neurodegenerative disease category, and energy metabolism than the SR group (P < 0.05). In conclusion, feed restriction had profound effects on the brain organ index and plasma dopamine in the slow- and fast-growing chickens. Feed restriction may result in issues relating to cardiovascular and neurodegenerative diseases in the fast-growing breed tested, but not in the slow-growing breed.

The effects of exercise treatment on learning and memory ability, and cognitive performance in diet-induced prediabetes animals

Changes associated with cognitive function in the high-fat high-carbohydrate diet-induced prediabetes animal model and effect of exercise remain unclear. Rats were randomly assigned to the following groups (n = 6): non-diabetic (ND), prediabetic (PD), intermittent exercising PD (PD + IE) and regular exercising PD (PD + RE). After exercise cessation, oral glucose tolerance (OGT), Novel Object Recognition Test (NORT) and Morris-Water Maze (MWM) tests were performed to assess cognitive function. After sacrifice, malonaldehyde, glutathione peroxidase, interleukin-1β and dopamine concentration in the prefrontal cortex (PFC) and hippocampus were measured. Impaired OGT response in PD animals was accompanied by poor performance on behavioural tasks. This was associated with increased oxidative stress markers and impaired dopamine neurotransmission as evidence by elevated dopamine concentration in the PFC and hippocampal tissue. Improved OGT response by exercise was coupled with improved performance on behavioural tasks, oxidative stress markers and increased interleukin-1β concentration. In regular exercise, this was further coupled with improved dopamine neurotransmission. Cognitive function was affected during prediabetes in animals. This was partly due to oxidative stress and impaired dopamine neurotransmission. Both intermittent and regular exercise improved cognitive function. This was partly mediated by improved glucose tolerance and oxidative stress as well as a subclinical increase in interleukin-1β concentration. In regular exercise, this was further mediated by improved dopamine neurotransmission.

Neurotoxic Dopamine Transporter Substrates Differentially Affect DAT Regulation, Uptake, and Reverse Transport

Synaptic action of the neurotransmitter dopamine (DA) is primarily terminated by reuptake into presynaptic dopaminergic neurons via dopamine transporters (DATs). DATs are integral plasmalemmal proteins whose reuptake function is tightly coordinated by interplay between the post translational modifications phosphorylation and palmitoylation. The psychostimulant amphetamine (AMPH) is a DAT substrate known to empty sequestered DA from vesicles and induce protein kinase C (PKC)‐dependent DAT phosphorylation, resulting in reverse transport of DA (efflux) greatly increased DA signaling. Elevated DA concentrations similar to those produced by AMPH create neurotoxic conditions as DA oxidation produces free radicals and hinders mitochondrial respiration, thus strict spatial and temporal control of cytosolic and synaptic DA is essential for neuronal health. DA induced oxidative stress is an important pathogenic mediator in Parkinson's disease (PD), and animal models of PD are generated by the neurotoxins 1‐methyl‐4‐phenylpyridinium ion (MPP+) and 6‐hydroxydopamine (6OHDA) which selectively target DAT‐expressing neurons, are translocated to the cytosol by DAT, and perturb the oxidative balance within the cell, producing nigrostriatal DA neuron death observed in PD. It is therefore intriguing to investigate DAT‐involved mechanisms in terms of PD etiology as atypical DAT function could contribute to DA oxidative stress and is hypothesized to play a role in other neurological disorders including attention deficit/hyperactivity disorder (ADHD) and addiction. DAT expression occurs around synaptic terminals, along axons, and on dendritic spines, and efflux via DATs located on dendrites in the substantia nigra has been shown to diminish dopaminergic signaling. It is possible, therefore, for aberrant regulation and localization of DA clearance and DAT‐mediated DA efflux to profoundly influence the excitability of neurons and play a significant role in neurodegeneration in the progression of PD. This is even more interesting in the light of recent studies revealing DAT polymorphisms in patients diagnosed with a psychiatric disorder or early onset PD that display an elevated basal DA efflux phenotype. In this study, we are investigating the effect of DAT substrates and PD‐inducing neurotoxins on DAT phosphorylation, palmitoylation, down‐regulation, and reverse transport to better understand aberrant DAT mechanisms which may contribute the onset of PD. Our findings thus far indicate MPP+ and 6OHDA differentially alter DAT function. 6OHDA inhibits basal and attenuates PMA‐induced DAT phosphorylation, does not significantly reduce DAT function, and decreases DA efflux. MPP+ does not change basal or PMA stimulated DAT phosphorylation yet it induces significant DA efflux which may be an additional means by which MPP+ produces neurodegeneration. This MPP+ induced efflux was not blunted by pretreatment with the PKC inhibitor bisindolylmaleimide (BIM). Although AMPH‐induced efflux was blunted after BIM treatment, significant efflux remained suggesting mechanisms independent of PKC mediated DAT phosphorylation for the stimulation of DA efflux.Support or Funding InformationSupported by the National Institute on Drug Abuse Grant DA 031991 JDF, P20 RR017699 (to U.N.D.) from the COBRE program of the National Center for Research Resources, and P20 RR016741 (to U.N.D.) from the INBRE program of the National Center for Research Resources.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Evidence from Impedance Spectroscopy that Elevated Dopamine Reduces Mitochondrial Membrane Potential

Background: Recent studies suggest that elevated dopamine concentrations reduce mitochondrial membrane potential, potentially contributing to neurological or other disorders. Changes in average membrane potential of suspended cells or organelles can be monitored in real time by measuring impedance of the suspension as a labelfree assay. Methods/Results: Here we report on measurements of frequency- and time-dependent electrical impedance of mitochondrial suspensions in the presence of various substrates, including dopamine. We find that, during succinateinduced state-2 respiration, addition of either trifluoromethoxy carbonylcyanide phenylhydrazone (FCCP), a known mitochondrial uncoupler (depolarizer), or dopamine at high concentrations cause similar increases in impedance, consistent with a drop in mitochondrial membrane potential. Conclusion: Our results provide further evidence that dopamine reduces mitochondrial membrane potential, albeit less severely than FCCP, possibly by generating free radicals that partially perforate the mitochondrial inner membrane and/or reduce activity of respiratory complexes. These results suggest that prolonged excess dopamine can impair ATP production, with possible implications in some neurological disorders and suggesting the need for care in the use of dopamine to treat Parkinson’s disease or heart failure.

The fast-off hypothesis revisited: A functional kinetic study of antipsychotic antagonism of the dopamine D2 receptor

Newer, “atypical” antipsychotics carry a lower risk of motor side-effects than older, “typical” compounds. It has been proposed that a ~100-fold faster dissociation from the dopamine D2 receptor (D2R) distinguishes atypical from typical antipsychotics. Furthermore, differing antipsychotic D2R affinities have been suggested to reflect differences in dissociation rate constants (koff), while association rate constants (kon) were assumed to be similar. However, it was recently demonstrated that lipophilic accumulation of ligand in the cell interior and/or membrane can cause underestimation of koff, and as high-affinity D2R antagonists are frequently lipophilic, this may have been a confounding factor in previous studies. In the present work, a functional electrophysiology assay was used to measure the recovery of dopamine-mediated D2R responsivity from antipsychotic antagonism, using elevated concentrations of dopamine to prevent the potential bias of re-binding of lipophilic ligands. The variability of antipsychotic kon was also reexamined, capitalizing on the temporal resolution of the assay. kon was estimated from the experimental recordings using a simple mathematical model assumed to describe the binding process. The time course of recovery from haloperidol (typical antipsychotic) was only 6.4- to 2.5-fold slower than that of the atypical antipsychotics, amisulpride, clozapine, and quetiapine, while antipsychotic kons were found to vary more widely than previously suggested. Finally, affinities calculated using our kon and koff estimates correlated well with functional potency and with affinities reported from radioligand binding studies. In light of these findings, it appears unlikely that typical and atypical antipsychotics are primarily distinguished by their D2R binding kinetics.

Elevated dopamine concentration in light-adapted zebrafish retinas is correlated with increased dopamine synthesis and metabolism.

Probing zebrafish (Danio rerio) retinal cryostat sections, collected either 8h into the light or dark cycle, with an antibody against tyrosine hydroxylase (TH) identified a single population of immunopositive cells in the inner retina. However, the observed labeling patterns were not identical in both sets of tissues - label intensity was brighter in light-adapted tissue. This difference was quantified by probing western blots of retinal homogenates with the same TH antibody, which showed that TH expression increased by 42% in light-adapted tissue. High-performance liquid chromatography with electrochemical detection revealed that the concentrations of both dopamine and 3,4-dihydroxyphenylacetic acid (DOPAC) are also elevated in light-adapted zebrafish retinal tissue. Dopamine levels increased by 14% and DOPAC levels increased by 25% when measured in retinal homogenates harvested during the light cycle. These results indicate that dopamine levels in zebrafish retina are significantly increased in light-adapted tissue. The increase in dopamine content is correlated with an increase in both TH and DOPAC, suggesting that changes in dopamine concentration are due to light-adaptive changes in the synthesis, release and metabolism of dopamine. Dopamine concentration is elevated in lighted-adapted zebrafish retinas. This increase is correlated with an increase in both tyrosine hydroxylase (TH) and DOPAC (3,4-dihydroxyphenylacetic acid), suggesting that changes in dopamine concentration are due to light-adaptive changes in the synthesis, release and metabolism of dopamine. This is applicable to studies examining retinal mutants, the role of dopamine in disease or visual system development.

Effect of mazindol on extracellular dopamine concentration in human brain measured by PET

Mazindol, an appetite suppressant, inhibits the reuptake of dopamine in the synaptic cleft. It has been considered that mazindol might enhance dopamine transmission in the human brain. However, there has been no study that investigated the extracellular dopamine concentration in vivo. Using positron emission tomography (PET), we aimed to measure the effect of mazindol on the extracellular dopamine concentration and to evaluate how mazindol affects the dopamine system in the healthy human brain. Eleven healthy individuals (six males, five females, age 30.9 ± 4.9 years) were enrolled in this study. Each participant was scanned with [(11)C]raclopride on 1 day without any medicine as baseline condition, and on another day with mazindol as drug condition. In the drug condition, participants took mazindol 0.5 mg (N = 5) or 1.5 mg (N = 6) 2 h before the PET scan. Plasma concentrations of mazindol were measured before the injection of [(11)C]raclopride, and urine concentrations of mazindol were measured after the scan. After taking mazindol, the calculated decrease in binding potential (ΔBP) in the striatum was 1.74 % for 0.5 mg and 8.14 for 1.5 mg, and the correlation with the blood concentration of mazindol was significant (P = 0.0016, R (2) = 0.69). ΔBP was not significantly correlated with the urine concentration of mazindol (P = 0.84, R (2) = 0.005). Mazindol increased the extracellular concentration of dopamine in the human brain, and its effect was dose dependent. A single administration of mazindol, even at usual dosage, elevated dopamine concentration similarly to other addictive drugs, suggesting that the risk of dependence may increase with the mazindol dose.

Effects of the histamine H1 receptor antagonist and benztropine analog diphenylpyraline on dopamine uptake, locomotion and reward

Diphenylpyraline hydrochloride (DPP) is an internationally available antihistamine that produces therapeutic antiallergic effects by binding to histamine H1 receptors. The complete neuropharmacological and behavioral profile of DPP, however, remains uncharacterized. Here we describe studies that suggest DPP may fit the profile of a potential agonist replacement medication for cocaine addiction. Aside from producing the desired histamine reducing effects, many antihistamines can also elicit psychomotor activation and reward, both of which are associated with increased dopamine concentrations in the nucleus accumbens (NAc). The primary aim of this study was to investigate the potential ability of DPP to inhibit the dopamine transporter, thereby leading to elevated dopamine concentrations in the NAc in a manner similar to cocaine and other psychostimulants. The psychomotor activating and rewarding effects of DPP were also investigated. For comparative purposes cocaine, a known dopamine transporter inhibitor, psychostimulant and drug of abuse, was used as a positive control. As predicted, both cocaine (15mg/kg) and an equimolar dose of DPP (14mg/kg) significantly inhibited dopamine uptake in the NAc in vivo and produced locomotor activation, although the time-course of pharmacological effects of the two drugs was different. In comparison to cocaine, DPP showed a prolonged effect on dopamine uptake and locomotion. Furthermore, cocaine, but not DPP, produced significant conditioned place preference, a measure of drug reward. The finding that DPP functions as a potent dopamine uptake inhibitor without producing significant rewarding effects suggests that DPP merits further study as a potential candidate as an agonist pharmacotherapy for cocaine addiction.

Caffeine and a selective adenosine A2A receptor antagonist induce sensitization and cross-sensitization behavior associated with increased striatal dopamine in mice

BackgroundCaffeine, a nonselective adenosine A1 and A2A receptor antagonist, is the most widely used psychoactive substance in the world. Evidence demonstrates that caffeine and selective adenosine A2A antagonists interact with the neuronal systems involved in drug reinforcement, locomotor sensitization, and therapeutic effect in Parkinson's disease (PD). Evidence also indicates that low doses of caffeine and a selective adenosine A2A antagonist SCH58261 elicit locomotor stimulation whereas high doses of these drugs exert locomotor inhibition. Since these behavioral and therapeutic effects are mediated by the mesolimbic and nigrostriatal dopaminergic pathways which project to the striatum, we hypothesize that low doses of caffeine and SCH58261 may modulate the functions of dopaminergic neurons in the striatum.MethodsIn this study, we evaluated the neuroadaptations in the striatum by using reverse-phase high performance liquid chromatography (HPLC) to quantitate the concentrations of striatal dopamine and its metabolites, dihydroxylphenylacetic acid (DOPAC) and homovanilic acid (HVA), and using immunoblotting to measure the level of phosphorylation of tyrosine hydroxylase (TH) at Ser31, following chronic caffeine and SCH58261 sensitization in mice. Moreover, to validate further that the behavior sensitization of caffeine is through antagonism at the adenosine A2A receptor, we also evaluate whether chronic pretreatment with a selective adenosine A2A antagonist SCH58261 or a selective adenosine A1 antagonist DPCPX can sensitize the locomotor stimulating effects of caffeine.ResultsChronic treatments with low dose caffeine (10 mg/kg) or SCH58261 (2 mg/kg) increased the concentrations of dopamine, DOPAC and HVA, concomitant with increased TH phosphorylation at Ser31 and consequently enhanced TH activity in the striatal tissues in both caffeine- and SCH58261-sensitized mice. In addition, chronic caffeine or SCH58261 administration induced locomotor sensitization, and locomotor cross-sensitization to caffeine was observed following chronic treatment of mice with SCH58261 but not with DPCPX.ConclusionsOur study demonstrated that low dosages of caffeine and a selective adenosine A2A antagonist SCH58261 elicited locomotor sensitization and cross-sensitization, which were associated with elevated dopamine concentration and TH phosphorylation at Ser31 in the striatum. Blockade of adenosine A2A receptor may play an important role in the striatal neuroadaptations observed in the caffeine-sensitized and SCH58261-sensitized mice.

The protective effect of the insulin against paraquat-induced PC12 cells

Objective To observe dopamine (DA) D2R protein expression in the cultured PC 12 cells and the effect of insulin on the survival rate,morphology,and DA of paraquat (PQ)-induced PC12 cells. Methods Immunoprecipitate Western blotting method was performed to observe DA D2R protein expression in PC 12 cells,MTT assay was used to analyze the changes in viability and morphology of PC 12 ceils which were exposed to different concentrations of PQ and insulin. Results (1) DA D2R protein was expressed in PC 12 ceils. (2) Normal PCI2 cells bodies showed fusiform shape and the synapses were in-tegrity. The cells which were exposed to the 600 μmol/L PQ became ball-like, vacuolar degeneration oc-urred,and the synapse became shorter or disappeared. But the morphology of PC12 cells had a little difference between the normal PC12 and the insulin groups,except that the cells were fusiform shape or a-nomalism but not round shape,and the synapses grew. (3) With the increase of the concentration of PQ, the viability of the cells was decreased. Insulin increased the viability of the ceils which were exposed to 600 μmol/L PQ. Insulin elevated DA concentration both in the normal PC12 cells and those exposed to 600 μmol/L PQ,but there was no significant difference ( P > 0.05 ). Conclusion Insulin could protect the PC12 dopaminergic neurons from injury induced by PQ. Key words: Parkinson's disease; Paraquat; Insulin; PC12 cells

Regulation of Monoamine Oxidase A by Circadian-Clock Components Implies Clock Influence on Mood

The circadian clock has been implicated in addiction and several forms of depression [1, 2], indicating interactions between the circadian and the reward systems in the brain [3-5]. Rewards such as food, sex, and drugs influence this system in part by modulating dopamine neurotransmission in the mesolimbic dopamine reward circuit, including the ventral tegmental area (VTA) and the ventral striatum (NAc). Hence, changes in dopamine levels in these brain areas are proposed to influence mood in humans and mice [6-10]. To establish a molecular link between the circadian-clock mechanism and dopamine metabolism, we analyzed the murine promoters of genes encoding key enzymes important in dopamine metabolism. We find that transcription of the monoamine oxidase A (Maoa) promoter is regulated by the clock components BMAL1, NPAS2, and PER2. A mutation in the clock gene Per2 in mice leads to reduced expression and activity of MAOA in the mesolimbic dopaminergic system. Furthermore, we observe increased levels of dopamine and altered neuronal activity in the striatum, and these results probably lead to behavioral alterations observed in Per2 mutant mice in despair-based tests. These findings suggest a role of circadian-clock components in dopamine metabolism highlighting a role of the clock in regulating mood-related behaviors.

Proteasomal inhibition and apoptosis regulatory changes in human isolated lymphocytes: The synergistic role of dopamine

Abnormal deposition of protein aggregates and increased susceptibility to apoptotic cell death may result from defects in the activity of the ubiquitin-proteasome system (UPS); neurotoxicity related to UPS defects seems to require dopamine to be fully expressed. The aim of this study was to investigate the pro-apoptotic effects caused by proteasomal activity inhibition, as well as the synergistic effect of dopaminergic stimulation in human lymphocytes isolated from healthy volunteers. Cells were incubated 20 h at 37 degrees C, with: (1) lactacystin, (2) increasing concentrations of dopamine or (3) mixture of dopamine and lactacystin. Activities of proteasome 20S and pro-apoptotic caspases-3 and -9 and levels of anti-apoptotic Bcl-2 were measured with fluorimetric or immunochemical assays, while a "DNA diffusion" assay was used to determine the apoptosis. Incubation of lymphocytes with lactacystin, which caused reduction of proteasomal activity, was associated with activation of caspases. A clear, dose-dependent reduction of proteasomal activity was also seen in the presence of increasing doses of dopamine, which was accompanied by a slight dose-dependent increase of caspases activities and Bcl-2 levels. Both effects on proteasome and caspase activities were enhanced when cells were simultaneously exposed to lactacystin and elevated concentrations of dopamine. Apoptosis was detected in all treated samples, but not in controls, without significant differences among the treatment groups; however, the association of dopamine and lactacystin induced a clear reduction in the number of cells being analyzed, pointing to marked cytotoxicity. Our data confirm the potentiation of cytotoxicity related to proteasome inhibition, in the presence of dopaminergic stimulation.

Increase of postsynaptic dopaminergic transmission by presynaptic actions of cocaine

Cocaine is believed to modify dopaminergic transmission by blocking reuptake thereby increasing the concentration in the synaptic cleft. The elevated dopamine concentrations at the synapse can affect both post- and presynaptic dopamine receptors. Since the former receptor mediates the functional effects of dopamine while the latter suppresses subsequent release of dopamine, it is unclear whether cocaine would enhance or diminish dopamine's influences. Results of the present study indicated that the primary functional result of cocaine is to enhance dopamine's postsynaptic effects.

Neurotensin and cholecystokinin microinjected into the ventral tegmental area modulate microdialysate concentrations of dopamine and metabolites in the posterior nucleus accumbens

Neurotensin and cholecystokinin, neuropeptides which coexist with dopamine in many ventral tegmental neurons, were microinjected into the ventral tegmental area during in vivo microdialysis in the posterior nucleus accumbens. Neurotensin significantly elevated concentrations of dopamine and its metabolites at doses of 10 pmol, 1 nmol, and 10 nmol, while cholecystokinin significantly elevated dopamine metabolite concentrations only at a dose of 10 nmol. These data suggest that neurotensin potently mediates the release of dopamine from the mesolimbic pathway via direct actions on the cell body.

Effects of neurotensin on regional brain concentrations of dopamine, serotonin and their main metabolites

The effects of neurotensin, 7.5 or 30 μg, on concentrations of DA, DOPAC, (HVA), serotonin 5-HT and 5-HIAA were measured in 8 regions of the rat brain either 5 or 30 min following intracerebroventricular administration. Regions examined included the frontal cortex, striatum, nucleus accumbens, amygdala, septum, hypothalamus, ventral tegmentum and substantia nigra. Results indicate that both doses of neurotensin significantly elevated concentrations of dopamine in the striatum and amygdala 5 min following injection. The effects of the peptide on DOPAC and HVA were more pervasive and enduring, with significant increases in metabolite levels occurring in both mesolimbic and nigrostriatal terminal regions. In order to assess effects on turnover of dopamine, the ratios of each metabolic to dopamine concentrations were examined. Results indicate that, while the DOPAC DA ratio was elevated in many regions, the HVA DA ratio was increased in all regions examined. The effects of neurotensin on serotoninergic parameters were less pervasive and more variable, with both increases and decreases in 5-HT and 5-HIAA concentrations being observed. The effects of the peptide on 5-HIAA 5-HT were limited to the nucleus accumbens, where this ratio was increased, and the ventral tegmentum, where 5-HIAA 5-HT was decreased. These findings reveal that the effects of the neurotensin on dopaminergic transmission are more widespread than previously reported in that all major dopamine pathways are affected by the peptide. Also, the observed changes in the ratios of both DOPAC and HVA to DA suggest that neurotensin enhances the turnover of this transmitter.

Neurochemical effects of cyclopiazonic acid in chickens.

Chickens dosed (per os) with cyclopiazonic acid (CPA) at 0.5, 5.0, and 10 mg/kg body weight showed significant (P less than or equal to 0.05) increases in brain dopamine and serotonin concentrations 96 hr after dosing. The increases coincide with significant decreases in homovanillic acid and subtle increases of dihydroxyphenylacetic acid and 5-hydroxyindoleacetic acid concentrations. The elevated dihydroxyphenylacetic acid and 5-hydroxyindoleacetic acid concentrations may be related to the elevated concentrations of dopamine and serotonin, respectively. The observed changes in neurotransmitter/metabolite concentrations 96 hr after dosing parallel elimination of CPA from the birds skeletal muscles; however, they do not correlate with the significant weight losses in these birds at 48 and 96 hr after dosing. The brain weights of the treated birds were statistically insignificant from their respective controls, although increases in brain weight-body weight ratio within treatments and with time correlated with CPA toxicity. No significant changes were observed in dopamine, dihydroxyphenylacetic acid, homovanillic acid, serotonin, and 5-hydroxyindoleacetic acid concentrations among the treatments at 3, 24, and/or 48 hr after dosing.

Analysis of Brain Indoleamines and Catecholamines associated with Burn-induced Anorexia

Guinea pigs subjected to a full-thickness 30% body surface flame burn significantly reduced food intake and lost weight for 5 days thereafter. Comparison of brain monoamine changes in burned, pair-fed control, and freely feeding control groups revealed normal levels of norepinephrine and elevated concentrations of dopamine in burned animals compared to the pair-fed control group. Levels of the serotonin precursor, tryptophan, and metabolite, 5-hydroxyindoleacetic acid, were also increased in burned compared to pair-fed animals, suggesting increased activity of indoleamine neurons. Although brain catecholamine levels were not correlated with food intake, significant negative correlations between food consumption and tryptophan, serotonin, and 5-hydroxyindoleacetic acid were observed. These data suggest that aberrations in indoleamine and possible catecholamine neurotransmitter systems may be involved in the mediation of burn-induced anorexia.