Dihydroxyphenylacetic Acid Concentrations Research Articles

HIV-1 Tat and morphine interactions dynamically shift striatal monoamine levels and exploratory behaviors over time.

Despite the advent of combination anti-retroviral therapy (cART), nearly half of people infected with HIV treated with cART still exhibit HIV-associated neurocognitive disorders (HAND). HAND can be worsened by co-morbid opioid use disorder. The basal ganglia are particularly vulnerable to HIV-1 and exhibit higher viral loads and more severe pathology, which can be exacerbated by co-exposure to opioids. Evidence suggests that dopaminergic neurotransmission is disrupted by HIV exposure, however, little is known about whether co-exposure to opioids may alter neurotransmitter levels in the striatum and if this in turn influences behavior. Therefore, we assayed motor, anxiety-like, novelty-seeking, exploratory, and social behaviors, and levels of monoamines and their metabolites following 2 weeks and 2 months of Tat and/or morphine exposure in transgenic mice. Morphine decreased dopamine levels, but significantly elevated norepinephrine, the dopamine metabolites dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), and the serotonin metabolite 5-hydroxyindoleacetic acid, which typically correlated with increased locomotor behavior. The combination of Tat and morphine altered dopamine, DOPAC, and HVA concentrations differently depending on the neurotransmitter/metabolite and duration of exposure but did not affect the numbers of tyrosine hydroxylase-positive neurons in the mesencephalon. Tat exposure increased the latency to interact with novel conspecifics, but not other novel objects, suggesting the viral protein inhibits exploratory behavior initiation in a context-dependent manner. By contrast, and consistent with prior findings that opioid misuse can increase novelty-seeking behavior, morphine exposure increased the time spent exploring a novel environment. Finally, Tat and morphine interacted to affect locomotor activity in a time-dependent manner, while grip strength and rotarod performance were unaffected. Together, our results provide novel insight into the unique effects of HIV-1 Tat and morphine on monoamine neurochemistry that may underlie their divergent effects on motor and exploratory behavior.

3H]Dopamine Uptake through the Dopamine and Norepinephrine Transporters is Decreased in the Prefrontal Cortex of Transgenic Mice Expressing HIV-1 Transactivator of Transcription Protein.

Dysregulation of dopamine neurotransmission has been linked to the development of human immunodeficiency virus (HIV)-associated neurocognitive disorder (HAND). To investigate the mechanisms underlying this phenomenon, this study used an inducible HIV-1 transactivator of transcription (Tat) transgenic (iTat-tg) mouse model, which demonstrates brain-specific Tat expression induced by administration of doxycycline. We found that induction of Tat expression in the iTat-tg mice for either 7 or 14 days resulted in a decrease (∼30%) in the V max of [3H]dopamine uptake via both the dopamine transporter (DAT) and norepinephrine transporter (NET) in the prefrontal cortex (PFC), which was comparable to the magnitude (∼35%) of the decrease in B max for [3H]WIN 35,428 and [3H]nisoxetine binding to DAT and NET, respectively. The decreased V max was not accompanied by a reduction of total or plasma membrane expression of DAT and NET. Consistent with the decreased V max for DAT and NET in the PFC, the current study also found an increase in the tissue content of DA and dihydroxyphenylacetic acid in the PFC of iTat-tg mice after 7 days' administration of doxycycline. Electrophysiological recordings in layer V pyramidal neurons of the prelimbic cortex from iTat-tg mice found a significant reduction in action potential firing, which was not sensitive to selective inhibitors for DAT and NET, respectively. These findings provide a molecular basis for using the iTat-tg mouse model in the studies of NeuroHIV. Determining the mechanistic basis underlying the interaction between Tat and DAT/NET may reveal novel therapeutic possibilities for preventing the increase in comorbid conditions as well as HAND. SIGNIFICANCE STATEMENT: Human immunodeficiency virus (HIV)-1 infection disrupts dopaminergic neurotransmission, leading to HIV-associated neurocognitive disorders (HANDs). Based on our in vitro and in vivo studies, dopamine uptake via both dopamine and norepinephrine transporters is decreased in the prefrontal cortex of HIV-1 Tat transgenic mice, which is consistent with the increased dopamine and dihydroxyphenylacetic acid contents in this brain region. Thus, these plasma membrane transporters are an important potential target for therapeutic intervention for patients with HAND.

Effects of 7-Methylxanthine on Deprivation Myopia and Retinal Dopamine Release in Chickens

Introduction: Intake of 7-methylxanthine (7-MX), an adenosine receptor (AR) antagonist, has been shown to inhibit school myopia in children and deprivation myopia in rhesus monkeys, but the underlying mechanisms are not known. Also retinal dopamine seems to be involved in the control of eye growth, and in the brain, ARs and dopamine receptors interact widely by heteromerization. We have studied whether 7-MX can inhibit deprivation myopia also in chickens and whether inhibition may involve the retinal dopamine system. Methods: 7-MX was applied by either tube-feeding (100 µg/g body weight, twice a day) or intravitreal injection (12.5 µg, every other day). Forty-eight 2-week-old chicks wore unilateral diffusers and were randomly assigned to either the tube-feeding group (involving 7-MX, vehicle [xanthan gum], or no feeding, for 13 days) or the intravitreal injection group (involving 7-MX, vehicle, or DMSO, for 8 days). Refractions (REs), ocular biometry (AL, VCD), and scleral and choroidal thickness (ChT) were measured before and after treatment. Dopamine and dihydroxyphenylacetic acid (DOPAC) content were determined in retina and vitreous by HPLC at the end of the experiments. Results: No matter how 7-MX was applied, it did not inhibit deprivation myopia in chicks. No significant differences were observed in RE, VCD, AL, and scleral fibrous layer thickness. Feeding 7-MX produced more choroidal thinning in the open contralateral eye compared to control eyes in the vehicle-fed group (–40 ± 14 vs. –1 ± 7 µm, unpaired t test, p < 0.05). DOPAC and dopamine concentration in vitreous and DOPAC concentration in retina did not change with 7-MX. Vitreal dopamine content was significantly decreased in deprived eyes in the groups fed with the vehicle xanthan gum (paired t test, p < 0.01) but not in 7-MX-treated eyes, perhaps indicating a small effect of 7-MX on dopamine. Conclusions: In our study, 7-MX had no effect on DM in chicks and only minor effects on ChT and retinal dopamine. It remains unclear whether 7-MX inhibits myopia through a retinal mechanism or whether it acts directly on choroid and sclera. In the latter case, the finding that myopia is suppressed in mammals but not birds might be explained by differences in scleral structure.

Effects of Kisspeptin-10 on Hypothalamic Neuropeptides and Neurotransmitters Involved in Appetite Control.

Besides its role as key regulator in gonadotropin releasing hormone secretion, reproductive function, and puberty onset, kisspeptin has been proposed to act as a bridge between energy homeostasis and reproduction. In the present study, to characterize the role of hypothalamic kisspeptin as metabolic regulator, we evaluated the effects of kisspeptin-10 on neuropeptide Y (NPY) and brain-derived neurotrophic factor (BDNF) gene expression and the extracellular dopamine (DA), norepinephrine (NE), serotonin (5-hydroxytriptamine, 5-HT), dihydroxyphenylacetic acid (DOPAC), and 5-hydroxyindoleacetic acid (5-HIIA) concentrations in rat hypothalamic (Hypo-E22) cells. Our study showed that kisspeptin-10 in the concentration range 1 nM–10 μM was well tolerated by the Hypo-E22 cell line. Moreover, kisspeptin-10 (100 nM–10 μM) concentration independently increased the gene expression of NPY while BDNF was inhibited only at the concentration of 10 μM. Finally, kisspeptin-10 decreased 5-HT and DA, leaving unaffected NE levels. The inhibitory effect on DA and 5-HT is consistent with the increased peptide-induced DOPAC/DA and 5-HIIA/5-HT ratios. In conclusion, our current findings suggesting the increased NPY together with decreased BDNF and 5-HT activity following kisspeptin-10 would be consistent with a possible orexigenic effect induced by the peptide.

Endothelins and dopamine levels in tears for assessment of neurovascular disorders in glaucoma

To estimate the possibility of detection of neurovascular ocular disorders in glaucoma by assessing the content of catecholamines and endothelins in lacrimal fluid. The study included 47 patients with primary open-angle glaucoma (POAG). Tear eluate was analyzed by high performance liquid chromatography (HPLC) for catecholamines concentrations, and enzyme-linked immunoassay (ELISA) was used for evaluation of endothelins content. Endothelin-1 (ET-1) and big endothelin (bET) content in tears of patients with POAG was higher than in healthy controls. Concentration of dopamine (DA) in tears was lower and concentrations of L-dioxyphenylalanine and dihydroxyphenylacetic acid had a tendency for decrease. Noradrenaline content was equal in patients with POAG and controls. Adrenaline was not detected in any tear samples. Multidirectional changes of endothelins and DA levels in tears of patients with POAG was found. The increased concentration of ET-1 and its precursor bET promote vasoconstriction and decrease of aqueous humor outflow. The decrease of DA concentration is typical for neurodegenerative processes. Estimation of DA and endothelins concentrations in tears can enable early detection of neurovascular disorders in glaucoma patients and help evaluate their severity.

Dopamine Responsiveness in the Nucl. Accumbens Shell and Parameters of the Heroin-Influenced Conditioned Place Preference in Rats

Previous evidence demonstrated that drug-induced extracellular dopamine (DA) concentrations in the nucl. accumbens shell (AcbSh) might underlie different vulnerabilities to heroin addiction in inbred mice strains. We investigated a potential role of the responsiveness of the DA system in the AcbSh with respect to the vulnerability to heroin-influenced conditioned place preference (CPP) in rats. Animals were randomly assigned to the heroin and saline (control) groups. Heroin-group rats were then reclassified into two groups according to the degree of heroin-induced CPP, high preference (HP) and low-preference (LP) ones. The levels of extracellular DA and dihydroxyphenyl acetic acid (DOPAC) were estimated dynamically by in vivo microdialysis. Compared with the saline group, extracellular DA and DOPAC concentrations in the heroin-treated groups were significantly higher 30 min after the last injection, but the DA level decreased sharply in these groups on days 1 and 3 and became lower than that of the saline group. Compared with LP-group rats, HP-rats displayed a higher heroin-induced increase in the DA concentration 30 min after the last heroin injection and higher DOPAC and DOPAC/DA ratios 14 days after such injection. These results suggest that differences in the DA system responsiveness in the AcbSh may determine individual differences in vulnerability to heroin addiction.

Asymmetry in the content of brain monoamines of BALB/c mice reared in social isolation conditions

The effects of long-term social isolation on the content and metabolism of dopamine and serotonin systems were studied in symmetrical brain structures of BALB/c male mice. With HPLC the contents of dopamine (DA), serotonin (5-HT) and their metabolites dihydroxyphenylacetic acid (DOPAC) and 5-hydroxyindolacetic acid (5-HIAA) were measured in the cortex, hippocampus and striatum of both the right and the left hemispheres of the brain in mice reared in groups and social isolation. The isolated mice were characterized by reduced level of DA in the left striatum and elevated level of 5-HIAA and ratio 5-HIAA/5-HT in the right striatum. In the hippocampus of isolated mice, the activation of both DA-ergic and 5-HT-ergic systems was observed, that is the high level of DA and DOPAC in the left hippocampus and the elevated level of 5-HT in both hemispheres and of 5-HIAA in the right hippocampus were registered. On the other hand, the reduction of both DA-ergic and 5-HT-ergic systems activity was shown to be in the right hemisphere. The decreased concentration of DOPAC and ratio DOPAC/DA in the right cortex were observed as well. As to 5-HT-ergic system, the reduced level of 5-HT in the both cortex of the hemispheres as well as 5-HIAA in the right hemisphere of isolated mice was determined. The phenomenon of interhemispheric asymmetry was revealed in the hippocampus only, which was characterized by the increased DA-ergic activity in the left hippocampus but not in the striatum and the cortex.

Ambient illuminance, retinal dopamine release and refractive development in chicks

Form deprivation and low illuminance of ambient light are known to induce myopia in chicks. Low concentrations of retinal dopamine, a light-driven neurohormone, was previously shown to be associated with form deprivation myopia. In the present study we examined the dependence of retinal dopamine release in chicks on illuminance during light–dark cycles and in continuous light, and the role of retinal dopamine release in illuminance dependent refractive development. Newly hatched chicks (n = 166) were divided into two experimental groups, a dopamine (n = 88) and a refraction group (n = 78). Both groups were further divided into six illumination groups for exposure of chicks to illuminances of 50, 500 or 10,000 lux of incandescent illumination (referred to throughout as low, medium, and high illuminance, respectively), either under a light–dark cycle with lights on between 7 AM and 7 PM or under continuous illumination. For the dopamine experiment, chicks were euthanized and vitreous was extracted on day 14 post-hatching at 7, 8 AM and 1 PM. Vitreal dihydroxyphenylacetic acid (DOPAC) and dopamine concentrations were quantified by high-performance liquid chromatography coupled to electrochemical detection. For the refraction experiment, chicks underwent refraction, keratometry and A-scan ultrasonography on days 30, 60 and 90 post-hatching, and each of those measurements was correlated with vitreal DOPAC concentration measured at 1 PM (representing the index of retinal dopamine release). The results showed that under light–dark cycles, vitreal DOPAC concentration was strongly correlated with log illuminance, and was significantly correlated with the developing refraction, corneal radius of curvature, and axial length values. On day 90, low vitreal DOPAC concentrations were associated with myopia (−2.41 ± 1.23 D), flat cornea, deep anterior and vitreous chambers, and thin lens. Under continuous light, vitreal DOPAC concentrations measured at 1 PM in the low, medium, and high illuminance groups did not differ from the concentrations measured at 8 AM. On day 90, low DOPAC concentrations were associated with emmetropia (+0.63 ± 3.61), steep cornea, and shallow vitreous chamber. We concluded that ambient light over a log illuminance range of 1.69–4 is linearly related to vitreal DOPAC concentration. Under both light–dark cycles and continuous light, the intensity of ambient light regulates the release of retinal dopamine. Refractive development is associated with illuminance dependent dopamine release.

Aging of the dopaminergic system and motor behavior in mice intoxicated with the parkinsonian toxin 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine

1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) intoxication of mice is a standard model of Parkinson's disease (PD). However, it does not reproduce functionally PD. Given the occurrence of PD during aging, symptoms might only be detected in MPTP-intoxicated mice after aging. To address this, mice injected with MPTP at 2.5 months were followed up to a maximum age of 21 months. There was no loss of dopamine cells with aging in control mice; moreover, the initial post-MPTP intoxication decrease in dopamine cell was no longer significant at 21 months. With aging, striatal dopamine level remained constant, but concentrations of the dopamine metabolites dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were markedly reduced in both groups. There was also a late impairment of fine motor skills. After MPTP intoxication, hyperactivity was immediately detected and it became greater than in control mice from 14 months of age; fine motor skills were also more impaired; both these symptoms were correlated with striatal dopamine, DOPAC and HVA concentrations. In bothgroups, neither motor symptoms nor dopamine changes worsened with age. These findings do not support the notion that PD develops with age in mice after MPTP intoxication and that the motor deficits seen are because of an aging process.

Orally administered l-ornithine reduces restraint stress-induced activation of the hypothalamic-pituitary-adrenal axis in mice

In a previous study, we confirmed that orally administered l-ornithine can be transported into the brain of mice. In addition, orally administered l-ornithine, within a limited dose range, had an anxiolytic-like effect in the elevated plus-maze test. However, the mechanism by which orally administered l-ornithine reduced the stress response in mice is still unclear. Experiment 1 determined whether orally administered l-ornithine could reduce the stress-induced activation of hypothalamic-pituitary-adrenal axis. Mice were orally administered l-ornithine (0, 0.75, 1.5 and 3mmol/10ml/kg, p.o.), and restrained for 30min from 30min post administration. There was a significant decrease in the corticosterone levels in the group receiving 0.75mmol of l-ornithine compared to the control group. In Experiment 2, the effect of orally administered l-ornithine (0 and 0.75mmol/10ml/kg, p.o.) on endogenous monoamine release was investigated using in vivo microdialysis. Only the monoamines metabolites 5-hydroxyindoleacetic acid (5-HIAA), dihydroxyphenylacetic acid (DOPAC) and homovallinic acids (HVA) were detected in the present study. Dialysate concentrations of 5-HIAA, DOPAC and HVA were not significantly changed immediately after administration of l-ornithine and restraint stress. In conclusion, changes of corticosterone concentrations by orally administered l-ornithine were not related to alterations in brain monoamine metabolisms.

Effects of a novel mGlu2/3 receptor agonist prodrug, LY2140023 monohydrate, on central monoamine turnover as determined in human and rat cerebrospinal fluid

Accumulating evidence suggests that the primary symptoms of schizophrenia may be associated with altered central glutamate transmission. LY2140023 monohydrate is the methionine prodrug of the selective mGlu(2/3) receptor agonist LY404039 and is currently being assessed for the treatment of schizophrenia. The objective of this study was to evaluate the central pharmacological activity of LY2140023 monohydrate in preclinical and clinical studies. Effects on neurotransmitter/metabolite concentrations were assessed in male rats following single oral doses of LY2140023 monohydrate (microdiasylates from the prefrontal cortex), single intraperitoneal injection of LY404039 [cerebrospinal fluid (CSF)], or LY2140023 monohydrate dosed once daily for 7 days (CSF). A clinical study in 16 healthy subjects assessed the effects of LY2140023 monohydrate 40 mg orally twice daily for 14 days in lumbar CSF. Rat studies: Acute dosing with LY2140023 monohydrate resulted in significant dose-dependent increases in extracellular concentrations of dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), but not 5-hydroxyindoleacetic acid (5-HIAA), in the prefrontal cortex. LY2140023 monohydrate dosing for 7 days elevated the concentrations of HVA in CSF, while acutely dosed LY404039 increased the concentrations of DOPAC, HVA, and methoxy-hydroxyphenylglycol (MHPG), but not 5-HIAA. Clinical study: Significant increases were seen for DOPAC, HVA, 5-HIAA, and MHPG in the CSF of subjects receiving LY2140023 monohydrate, but not placebo. LY2140023 monohydrate and/or LY404039 dosing potently affected dopamine turnover and also significantly affected serotonin turnover in the human and rat central nervous systems. The measurement of biogenic amine metabolites such as DOPAC and HVA may serve as useful biomarkers of LY2140023 monohydrate and/or LY404039 central pharmacodynamic activity.

Concentration change of DA, DOPAC, Glu and GABA in brain tissues in schizophrenia developmental model rats induced by MK-801.

To explore the related neurobiochemical mechanism by comparing the concentration change of dopamine (DA), dihydroxy-phenyl acetic acid (DOPAC), glutamate (Glu), and γ-aminobutyric acid (GABA) in the brain tissues in schizophrenia (SZ) developmental model rats and chronic medication model rats. A total of 60 neonatal male Spragur-Dawley (SD) rats were randomly assigned to 3 groups at the postnatal day 6: an SZ developmental rat model group (subcutaneous injection with MK-801 at the postnatal day 7-10, 0.1 mg/kg, Bid), a chronic medication model group (intraperitoneal injection at the postnatal day 47-60, 0.2 mg/kg,Qd), and a normal control group (injection with 0.9% normal saline during the corresponding periods). DA, DOPAC, Glu, and GABA of the tissue homogenate from the medial prefrontal cortex (mPFC) and hippocampus were examined with Coularray electrochemic detection by high performance liquid chromatogram technique. The utilization rate of DA and Glu was calculated. Compared with the normal control group, the concentration of DA and DOPAC in the mPFC and the hippocampus in the SZ developmental model group significantly decreased (P<0.05), and the GABA concentration and Glu utilization rate in the mPFC also decreased (P<0.05). Compared with the chronic medication model group, the DA concentration of the mPFC in the SZ developmental group decreased (P<0.05), and the DOPAC concentration and the utility rate of DA in the hippocampus also decreased (P<0.01, P<0.05, respectively). The activities of DA, Glu and GABA system decrease in the mPFC and the DA system function reduces in the hippocampus of SZ developmental rats.

Differential effects of caffeine on dihydroxyphenylacetic acid concentrations in various rat brain dopaminergic structures

The behavioural and neurochemical effects of caffeine were examined in rats. The intraperitoneal administration of different doses of caffeine significantly decreased DOPAC concentrations in striatum, hypothalamus and frontal cortex, but increased them in nucleus accumbens. These observations suggest that the effects of caffeine on the central nervous system (cns) are at least partially mediated through an interaction with the dopaminergic system.

P01-191 - Biological support to distinguish between congruent and incongruent symptoms in psychotic bipolar i patients

IntroductionMany authors support the idea that Mood Incongruent Psychosis is a subtype of affective illness, although no clear definition or etiopathogenic basis of the congruent or incongruent subtype has been found.AimsIn this study we intend to evaluate clinical and biological differences between Psychotic Bipolar I patients who have mood congruent or mood incongruent psychotic symptoms.MethodsThe study has been carried out in 80 Psychotic Bipolar I Patients before, and after, four weeks of treatment with Olanzapine plus Lithium. We studied the correlation between the plasma concentration, before treatment, of the dopamine metabolite 3,4 Dihydroxyphenylacetic acid (DOPAC) and the clinical response to treatment.ResultsThe most remarkable result found was that Clinical Improvement after 28 days of treatment correlated positively with the initial concentration of DOPAC, but ONLY in the subgroup of patients with congruent psychotic symptoms.ConclusionsFrom our results it seems that the Congruence and Incongruence of psychosis in bipolar I patients can provide a basis to objectively divide these patients. Both groups can be distinguished based on the relationship established between their concentration of DOPAC before treatment and their clinical response to the pharmacological treatment.Supported byUniversidad del País Vasco Grant N° EHU 09/21 and Fondo de Investigación Sanitaria and Feder Founds Grant N° 09/01760.

Nicotinic Ligands Modulate Ethanol-Induced Dopamine Function in Mice

The aim of the present study was to examine the effects of two neuronal nicotinic acetylcholine receptor ligands on acute ethanol-induced dopamine (DA) function in the C57BL/6J mouse ventral striatumusing an ex vivo assay and high-performance liquid chromatography coupled with electrochemicaldetection. Acute systemic injection of ethanol (2.5 g/kg) significantly increased the DA and dihydroxyphenylacetic acid (DOPAC) content in the ventral striatum. Pretreatment with lobeline (1 or 10 mg/kg) inhibited the ethanol-induced increase in the tissue DA and DOPAC content in the ventral striatum. Similarly, pretreatment with cytisine (0.5 or 3 mg/kg) also reduced the ethanol-induced increase in the tissue DA and DOPAC content in the ventral striatum. However, when given alone lobeline or cytisine did not produce significant effect on the DA or DOPAC content in the ventral striatum compared with controls. These findings provide evidence that lobeline and cytisine modulate ethanol-induced DA function by targeting nicotinic acetylcholine receptors in the ventral striatum, a reward-relevant brain region implicated in ethanol dependence.

The novel nicotinic receptor antagonist N,N′-dodecane-1,12-diyl- bis-3-picolinium dibromide decreases nicotine-induced dopamine metabolism in rat nucleus accumbens

The current study examined the effect of the novel nicotinic acetylcholine receptor antagonist, N, N′-dodecane-1,12-diyl- bis-3-picolinium dibromide (bPiDDB), on nicotine-induced dopamine metabolism in rat nucleus accumbens, striatum and medial prefrontal cortex. Acute nicotine (0.5 mg/kg, s.c.) produced an increase in the content of dihydroxyphenylacetic acid (DOPAC) in nucleus accumbens, but not in striatum or medial prefrontal cortex. Pretreatment with bPiDDB (1 or 3 mg/kg, s.c.) dose-dependently inhibited the nicotine-induced increase in DOPAC content in nucleus accumbens. These results indicate that bPiDDB inhibits the nicotine-induced increase in DOPAC in reward-relevant brain region targeting nicotinic acetylcholine receptors.

Blockade of NMDA receptors in the prefrontal cortex increases dopamine and acetylcholine release in the nucleus accumbens and motor activity

The present study investigates the effects of injections of a specific N-methyl-D-aspartic acid (NMDA) antagonist 3-[(R)-2-carboxypiperazin-4-yl]-propyl-1-phophonic acid (CPP) into the prefrontal cortex (PFC) on the extracellular concentrations of dopamine and acetylcholine in the nucleus accumbens (NAc) and on motor activity in the freely moving rat. Sprague-Dawley male rats were implanted with guide cannulas into the medial PFC and NAc to perform bilateral microinjections and microdialysis experiments. Spontaneous motor activity was monitored in the open field. Injections of CPP (1 microg/0.5 microL) into the PFC produced a significant increase of the baseline extracellular concentrations of dopamine (up to 130%), dihydroxyphenylacetic acid (DOPAC; up to 120%), homovanillic acid (HVA; up to 130%), and acetylcholine (up to 190%) in the NAc as well as motor hyperactivity. In the NAc, perfusion of the NMDA and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) glutamate antagonists CPP (50 microM)+6,7-dinitroquinoxaline-2,3-dione (DNQX; 50 microM) through the microdialysis probe blocked acetylcholine release, but not DOPAC and HVA increases produced by CPP injections into the PFC. Also, increases in motor activity produced by prefrontal injections of CPP were significantly reduced by bilateral injections into the NAc of a mixed D1/D2 antagonist, flupenthixol (5 and 25 microg/0.5 microL). Injections into the NAc of the muscarinic antagonist scopolamine (1 and 10 microg/0.5 microL) further increased, and of the nicotinic antagonist mecamylamine (1 and 10 microg/0.5 microL) did not change, the increases in motor activity produced by prefrontal CPP injections. These results suggest that the dysfunction of NMDA receptors in the PFC could be a key factor in the neurochemical and motor effects associated with corticolimbic hyperactivity.

Nicotine effects on learning in zebrafish: the role of dopaminergic systems

Nicotine improves cognitive function in a number of animal models including rats, mice, monkeys, and recently, zebrafish. The zebrafish model allows higher throughput and ease in discovering mechanisms of cognitive improvement. To further characterize the neural bases of nicotine effects on learning in zebrafish, we determined changes in dopaminergic systems that accompany nicotine-enhanced learning. Nicotine improved learning and increased brain levels of dihydroxyphenylacetic acid (DOPAC), the primary dopamine metabolite. There was a significant correlation between choice accuracy and DOPAC levels. The nicotinic antagonist mecamylamine blocked the nicotine-induced increase in DOPAC concentrations, in line with our previous finding that mecamylamine reversed nicotine-induced learning improvement. Dopamine systems are related to learning in zebrafish; nicotine exposure increases both learning rates and DOPAC levels; and nicotinic antagonist administration blocks nicotine-induced rises in DOPAC concentrations. Rapid cognitive assessment of drugs with zebrafish could serve as a useful screening tool for the development of new therapeutics for cognitive dysfunction.

The effect of long-term repeated exposure to 3,4-methylenedioxymethamphetamine on cardiovascular and thermoregulatory changes

3,4-Methylenedioxymethamphetamine (MDMA, "ecstasy") disrupts thermoregulation in rats and can lead to life-threatening hyperthermia in humans. MDMA administration can also lead to long-term neurotoxicity in animals and possibly humans. The purpose of the current study was to extend previous results on the acute effects of MDMA on behavioral thermoregulation to a repeated dosing regime, simulating regular weekend use of ecstasy, on measures of thermoregulation and heart rate (HR). Sprague-Dawley rats with telemetry implants were administered 40 micromol/kg MDMA on three consecutive days each week for 1 or 6 weeks before being confined to an elevated ambient temperature (TA) (HOT; 30+/-1 degrees C) or an area at room temperature (ROOM; 21.5+/-1.5 degrees C) for 30 min. After the final drug administration, rats were placed in a thermal gradient for 4 h to allow behavioral thermoregulation. HOT rats showed higher core temperature (TC), HR, and locomotor activity than ROOM rats during confinement to a set TA (P<0.001). HR responses to MDMA over 6 weeks at both TAs progressively decreased with repeated dosing (P<0.05). TC was significantly higher in both 6-week groups compared to the 1-week groups (P<0.05) at the end of time in the gradient. Cortical concentrations of dihydroxyphenylacetic acid (DOPAC; P<0.05) and 5-hydroxyindole acetic acid (5-HIAA; P<0.001) decreased significantly irrespective of TA, while concentrations of dopamine and 5-HT did not change. Long-term treatment with MDMA resulted in apparent tolerance to the effects of the drug on HR, dysregulation of TC in thermal gradient, and depletion of cortical DOPAC and 5-HIAA.

Biomarkers to detect central dopamine deficiency and distinguish Parkinson disease from multiple system atrophy

Objective Biomarkers are increasingly important to diagnose and test treatments of neurodegenerative diseases such as Parkinson disease (PD). This study compared neuroimaging, neurochemical, and olfactory potential biomarkers to detect central dopamine (DA) deficiency and distinguish PD from multiple system atrophy (MSA). Methods In 77 PD, 57 MSA, and 87 control subjects, radioactivity concentrations in the putamen (PUT), caudate (CAU), occipital cortex (OCC), and substantia nigra (SN) were measured 2 h after 6-[ 18F]fluorodopa injection, septal myocardial radioactivity measured 8 min after 6-[ 18F]fluorodopamine injection, CSF and plasma catechols assayed, or olfaction tested (University of Pennsylvania Smell Identification Test (UPSIT)). Receiver operating characteristic curves were constructed, showing test sensitivities at given specificities. Results PUT:OCC, CAU:OCC, and SN:OCC ratios of 6-[ 18F]fluorodopa-derived radioactivity were similarly low in PD and MSA ( p < 0.0001, p < 0.0001, p = 0.003 compared to controls), as were CSF dihydroxyphenylacetic acid (DOPAC) and DOPA concentrations ( p < 0.0001, each). PUT:SN and PUT:CAU ratios were lower in PD than in MSA ( p = 0.004; p = 0.005). CSF DOPAC correlated positively with PUT:OCC ratios ( r = 0.61, p < 0.0001). Myocardial 6-[ 18F]fluorodopamine-derived radioactivity distinguished PD from MSA (83% sensitivity at 80% specificity, 100% sensitivity among patients with neurogenic orthostatic hypotension). Only PD patients were anosmic; only MSA patients had normal olfaction (61% sensitivity at 80% specificity). Conclusions PD and MSA feature low PUT:OCC ratios of 6-[ 18F]fluorodopa-derived radioactivity and low CSF DOPAC and DOPA concentrations, cross-validating the neuroimaging and neurochemical approaches but not distinguishing the diseases. PUT:SN and PUT:CAU ratios of 6-[ 18F]fluorodopa-derived radioactivity, cardiac 6-[ 18F]fluorodopamine-derived radioactivity, and olfactory testing separate PD from MSA.