Dopamine Metabolites Dihydroxyphenylacetic Acid Research Articles

Isotopic reinforcement of essential polyunsaturated fatty acids diminishes nigrostriatal degeneration in a mouse model of Parkinson's disease

Oxidative damage of membrane polyunsaturated fatty acids (PUFA) is thought to play a major role in mitochondrial dysfunction related to Parkinson's disease (PD). The toxic products formed by PUFA oxidation inflict further damage on cellular components and contribute to neuronal degeneration. Here, we tested the hypothesis that isotopic reinforcement, by deuteration of the bisallylic sites most susceptible to oxidation in PUFA may provide at least partial protection against nigrostriatal injury in a mouse model of oxidative stress and cell death, the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model. Mice were fed a fat-free diet supplemented with saturated acids, oleic acid and essential PUFA: either normal, hydrogenated linoleic (LA, 18:2n−6) and α-linolenic (ALA, 18:3n−3) or deuterated 11,11-D2-LA and 11,11,14,14-D4-ALA in a ratio of 1:1 (to a total of 10% mass fat) for 6 days; each group was divided into two cohorts receiving either MPTP or saline and then continued on respective diets for 6 days. Brain homogenates from mice receiving deuterated PUFA (D-PUFA) vs. hydrogenated PUFA (H-PUFA) demonstrated a significant incorporation of deuterium as measured by isotope ratio mass-spectrometry. Following MPTP exposure, mice fed H-PUFA revealed 78.7% striatal dopamine (DA) depletion compared to a 46.8% reduction in the D-PUFA cohort (as compared to their respective saline-treated controls), indicating a significant improvement in DA concentration with D-PUFA. Similarly, higher levels of the DA metabolite 3,4-dihydroxyphenylacetic acid (DOPAC) were detected in MPTP-exposure mice administered D-PUFA; however, saline-treated mice revealed no change in DA or DOPAC levels. Western blot analyses of tyrosine hydroxylase (TH) confirmed neuroprotection with D-PUFA, as striatal homogenates showed higher levels of TH immunoreactivity in D-PUFA (88.5% control) vs. H-PUFA (50.4% control) in the MPTP-treated cohorts. In the substantia nigra, a significant improvement was noted in the number of nigral dopaminergic neurons following MPTP exposure in the D-PUFA (79.5% control) vs. H-PUFA (58.8% control) mice using unbiased stereological cell counting. Taken together, these findings indicate that dietary isotopic reinforcement with D-PUFA partially protects against nigrostriatal damage from oxidative injury elicited by MPTP in mice.

Human prostaglandin H synthase (hPHS)-1- and hPHS-2-dependent bioactivation, oxidative macromolecular damage, and cytotoxicity of dopamine, its precursor, and its metabolites

The dopamine (DA) precursor l-dihydroxyphenylalanine (L-DOPA) and metabolites dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), and 3-methoxytyramine may serve as substrates for prostaglandin H synthase (PHS)-catalyzed bioactivation to free radical intermediates. We used CHO-K1 cells expressing human (h) PHS-1 or hPHS-2 to investigate hPHS isozyme-dependent oxidative damage and cytotoxicity. hPHS-1- and hPHS-2-expressing cells incubated with DA, L-DOPA, DOPAC, or HVA exhibited increased cytotoxicity compared to untransfected cells, and cytotoxicity was increased further by exogenous arachidonic acid (AA), which increased hPHS activity. Preincubation with catalase, which detoxifies reactive oxygen species, or acetylsalicylic acid, an inhibitor of hPHS-1 and -2, reduced the cytotoxicity caused by DA, L-DOPA, DOPAC, and HVA in hPHS-1 and -2 cells both with and without AA. Protein oxidation was increased in hPHS-1 and -2 cells exposed to DA or L-DOPA and further increased by AA addition. DNA oxidation was enhanced earlier and at lower substrate concentrations than protein oxidation in both hPHS-1 and -2 cells by DA, L-DOPA, DOPAC, and HVA and further enhanced by AA addition. hPHS-2 cells seemed more susceptible than hPHS-1 cells, whereas untransfected CHO-K1 cells were less susceptible. Thus, isozyme-specific, hPHS-dependent oxidative damage and cytotoxicity caused by neurotransmitters, their precursors, and their metabolites may contribute to neurodegeneration associated with aging.

Polychlorinated Biphenyls and Polybrominated Diphenyl Ethers Alter Striatal Dopamine Neurochemistry in Synaptosomes from Developing Rats in an Additive Manner

Polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) are widespread environmental contaminants associated with changes in behavior and neurochemical function in laboratory animals and behavioral deficits in children. PCBs and PBDEs are found in food, especially in seafood and dairy products, and coexposure to these contaminants is likely. We examined the effects of an environmentally relevant mixture of PCBs (Fox River Mix [FRM]) and a PBDE mixture (DE-71) alone and in combination on synaptosomal and medium dopamine (DA) levels and the levels of the DA metabolite 3,4-dihydroxyphenylacetic acid (DOPAC) in striatal synaptosomes derived from postnatal days (PND) 7, PND14, or PND21 rats. FRM elevated medium DA and reduced synaptosomal DA concentrations with greater potency than equimolar concentrations of DE-71. The effects of FRM, but not DE-71, were dependent on the age of the animals from which the synaptosomes were derived, with greater effects observed in synaptosomes from the youngest animals. We used Bliss' model of independence to assess the possible interaction(s) of a 1:1 mixture of FRM and DE-71 on synaptosomal DA function and found that the effects of the FRM/DE-71 mixture were additive. Furthermore, as for FRM alone, the effects of the FRM/DE71 mixture were greater in synaptosomes prepared from PND7 rats than in synaptosomes from PND14 and PND21 rats. Because the effects of these contaminants are additive, it is necessary to take into account the cumulative exposure to organohalogen contaminants such as PCBs and PBDEs during risk assessment.

Reserpine causes biphasic nociceptive sensitivity alteration in conjunction with brain biogenic amine tones in rats

The present study investigated the precise relationship between brain biogenic amine (dopamine, noradrenaline, and serotonin) tones and nociception. Nociceptive sensitivities to multimodal (muscle pressure, tactile, cold, and heat) stimuli were assessed in acute phase (up to 24 h after reserpine or tetrabenazine injection) and chronic phase (on day 2 or later) in rats. A single injection of reserpine (3 mg/kg s.c.) significantly decreased biogenic amines in the spinal cord (SC), thalamus (THA), and prefrontal cortex (PFC) in both acute and chronic phases, but significantly increased a dopamine metabolite 3,4-dihydroxyphenylacetic acid (DOPAC) in the SC and a serotonin metabolite 5-hydroxyindoleacetic acid (5-HIAA) in the SC and THA in acute phase. The content of all biogenic amine metabolites was at low level in chronic phase. Animals exhibited hypersensitivities to tactile and heat stimuli and hyposensitivity to muscle pressure stimulus in acute phase. In chronic phase, they manifested hypersensitivities to all modes of stimuli. Tetrabenazine (20 mg/kg i.p.) significantly decreased brain biogenic amines for a short time, although it did not significantly affect the nociceptive sensitivities. In conclusion, a single injection of reserpine causes a biphasic alteration of nociceptive sensitivities, which is in conjunction with the dynamic change of brain biogenic amine tones, in rats. Cold and heat hypersensitivities in addition to mechanical ones are induced by the reserpine treatment. Sustained modification of brain biogenic amine tones would be critical to induce a robust change in nociceptive sensitivities based on the different effects between reserpine and tetrabenazine.

Assaying multiple biochemical variables from the same tissue sample

Experiments often involve multiple analyses, such as assays of neurotransmitters and proteins, and this can require different initial sample preparations. Typically, this is accomplished by using different animals or different tissue samples from the same animal. Either approach renders comparisons between assays more variable and greatly increases the effort and/or cost. Using tissue collected from rat striatum and molecules of special relevance to studies of Parkinson's disease, we show that tissue sonication in water prior to aliquoting into the appropriate concentrated solutions (e.g. HClO 4 and lysis buffers) permits several types of measurements to be made from the same initial samples. Dopamine and its metabolite homovanillic acid, serotonin and its metabolite 5-hydroxyindoleacetic acid, tyrosine hydroxylase and its phosphorylation at Ser19 and Ser31, and the dopamine transporter were unaffected. However, phospho-Akt levels fell slightly and phospho-ERK1/2 tended to drop. We also present a simple technique to preserve phosphorylation state of proteins such as ERK1/2 by perfusing animals through the heart with a phosphatase inhibitor, NaF. Dopamine metabolite dihydroxyphenyl acetic acid (DOPAC) levels were raised with both techniques, however. The general principles reported here are likely to apply to other brain regions, facilitate multiple comparisons of variables, increase efficiency, and decrease costs.

TheGinkgo bilobaextract EGb 761®and its main constituent flavonoids and ginkgolides increase extracellular dopamine levels in the rat prefrontal cortex

Experimental and clinical data suggest that extracts of Ginkgo biloba improve cognitive function. However, the neurochemical correlates of these effects are not yet fully clarified. The purpose of this study was to examine the effects of acute and repeated oral administration of the standardized extract EGb 761((R)) on extracellular levels of dopamine, noradrenaline and serotonin (5-HT), and the dopamine metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in the prefrontal cortex (PFC) and striatum of conscious rats. Monoamines and their metabolites were monitored by the use of microdialysis sampling and HPLC with electrochemical or fluorescence detection. A single oral dose of EGb 761 (100 mg.kg(-1)) had no effect on monoamine levels. However, following chronic (100 mg.kg(-1)/14 days/once daily) treatment, the same dose significantly increased extracellular dopamine and noradrenaline levels, while 5-HT levels were unaffected. Chronic treatment with EGb 761 showed dose-dependent increases in frontocortical dopamine levels and, to a lesser extent, in the striatum. The extracellular levels of HVA and DOPAC were not affected by either acute or repeated doses. Treatment with the main constituents of EGb 761 revealed that the increase in dopamine levels was mostly caused by the flavonol glycosides and ginkgolide fractions, whereas bilobalide treatment was without effect. The present results demonstrate that chronic but not acute treatment with EGb 761 increased dopaminergic transmission in the PFC. This finding may be one of the mechanisms underlying the reported effects of G. biloba in improving cognitive function.

The CRF-like peptide urocortin greatly attenuates loss of extracellular striatal dopamine in rat models of Parkinson's disease by activating CRF 1 receptors

We have recently observed that the corticotrophin releasing factor (CRF) related peptide urocortin reverses key features of nigrostriatal damage in two paradigms of Parkinson's disease. Here we have studied whether these effects are supported by a retention of striatal basal and evoked extracellular dopamine and the receptor(s) that may mediate this effect. Fourteen days following stereotaxic injections of 6-hydroxydopamine (6-OHDA) or lipopolysaccharide (LPS) and urocortin, extracellular dopamine levels in striata ipsilateral to injection sites of 6-OHDA/LPS and urocortin treated rats were comparable with sham injected rats, whilst rats given 6-OHDA/LPS and vehicle had considerably lower dopamine levels. Striatal dopamine levels in animals where urocortin injection was delayed by seven days were only modestly decreased compared to animals receiving 6-OHDA/LPS and urocortin concomitantly. Additionally, the dopamine metabolites dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were also preserved in dialysates from urocortin treated rats. The effects of urocortin were entirely blocked by the non-selective CRF receptor antagonist α-helical CRF as well as the selective CRF 1 antagonist NBI 27914 and were not replicated by the selective CRF 2 ligand urocortin III. In the substantia nigra tissue dopamine changes mirrored those seen in striatal extracellular dopamine. Our data strongly suggest that urocortin is capable of maintaining adequate nigrostriatal function in vivo via CRF 1 receptors following. neurotoxic challenge.

Maternal para-chlorophenylalanine exposure modifies central monoamines and behaviors in the adult offspring

We reported a perspective animal model of neurodevelopmental disorders using rats prenatally exposed to an inhibitor of serotonin (5HT) synthesis, para-chlorophenylalanine (PCPA). Earlier, we demonstrated that prenatal exposure to PCPA caused fetal 5HT depletion and changes both in open field activity and in depression-related behavior, as well as impairments in spatial learning in the adult offspring (Vataeva et al., 2007). The present study revealed that prenatal PCPA treatment resulted in the offspring's significantly reduced anxiety-related behavior in the elevated plus-maze and reduced neophobia to intake fluids in a novel environment. These effects are accompanied by hedonic changes in the form of an appropriate increase in saccharin preference. We confirmed our earlier finding that prenatal PCPA exposure affected the open field locomotor activity. In the present study we have shown that the selective 5HT reuptake inhibitor (SSRI) paroxetine decreases locomotor activity in the prenatally PCPA-treated offspring. It was also found that in the PCPA-treated fetal brain, 5HT depletion was associated with a significant decrease in the level of dopamine (DA) metabolite dihydroxyphenylacetic acid (DOPAC) and with a reduction of DOPAC/DA and homovanillic acid (HVA)/DA ratios. An assay of adult offspring brain revealed that the prenatal PCPA produced different effects on monoamines in the studied brain structures. The relationships between behavioral abnormalities and alterations in brain monoamine levels consequent on the prenatal PCPA treatment are discussed.

Alterations in amphetamine‐stimulated dopamine overflow due to the Nurr1‐null heterozygous genotype and postweaning isolation

The nuclear receptor Nurr1 functions to regulate dopamine neurotransmission, as Nurr1-null heterozygous (+/-) mice have alterations in dopamine function and, when raised in isolation immediately after weaning, have disruptions in sensorimotor gaiting, a behavior altered in schizophrenia and modulated by dopamine neurotransmission. The goal of this study was to determine nigrostriatal and mesoaccumbens dopamine neurotransmission using microdialysis in +/- and wild-type (+/+) mice raised in groups or isolation. In the striatum, isolation significantly reduced amphetamine-stimulated dopamine overflow and levels of the dopamine metabolite 3,4-dihydroxyphenylacetic acid (DOPAC). The +/- genotype alone caused a small, nonsignificant reduction in basal dopamine levels but a significant reduction in basal DOPAC levels. In the nucleus accumbens shell, the +/- genotype elevated basal dopamine levels. Isolation had genotype specific effects, causing an elevation in amphetamine-stimulated dopamine overflow in +/- mice but a reduction in +/+ mice, resulting in a large difference in stimulated dopamine overflow when comparing the +/+ and +/- isolated mice. These data indicate that a deletion of a single allele of Nurr1, which produces only subtle changes alone, when coupled with a developmental stressor, can dramatically alter mesoaccumbens dopamine neurotransmission. These observations demonstrate how the combination of genetic predisposition and an environmental insult during development can cause dysfunction of dopamine neurotransmission and could contribute to diseases such as schizophrenia or attention deficit hyperactivity disorder.

PLASMA HOMOVANILLIC ACID LEVELS IN SCHIZOPHRENIC PATIENTS: CORRELATION WITH NEGATIVE SYPMTOMS

Andia, Isabel, Mercedes Zumárraga, Francisco Retuerto, Isabel Zamalloa and Ricardo Davila: Chronic neuroleptic treatment does not suppress the dynamic characteristics of the dopaminergic receptor D2 system. Prog. Neuro-Psychopharmacol. & Biol. Psychiat. 1994,18(1): 181–191.1.1. Rats were treated with either haloperidol(0.5 mg/kg) or haloperidol plus an anticholinergic drug (0.5 and 0.15 mg/kg/day respectively) for 3 days, 7 days and 16 months.2.2. Estimates made twenty hours after the last doses showed that haloperidol reduced the concentrations of the dopamine metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in the striatum and the olfactory tubercle.3.3. A challenge dose of either haloperidol or haloperidol plus an anticholinergic drug was administered to rats pretreated with haloperidol or haloperidol plus an anticholinergic drug; this challenge dose reversed the reduction in dopamine metabolites caused by neuroleptic administration.4.4. After sixteen months of haloperidol administration dopamine levels were reduced, but adding an anticholinergic drug to haloperidol treatment prevented this reduction in dopamine concentration.

High Susceptibility to Experimental Myopia in a Mouse Model with a Retinal ON Pathway Defect

Nob mice share the same mutation in the Nyx gene that is found in humans with complete congenital stationary night blindness (CSNB1). Nob mutant mice were studied to determine whether this defect resulted in myopia, as it does in humans. Refractive development was measured in unmanipulated wild-type C57BL/6J (WT) and nob mice from 4 to 12 weeks of age by using an infrared photorefractor. The right eye was form deprived by means of a skull-mounted goggling apparatus at 4 weeks of age. Refractive errors were recorded every 2 weeks after goggling. The content of dopamine and the dopamine metabolite 3,4-dihydroxyphenylacetic acid (DOPAC) were measured by HPLC with electrochemical detection (HPLC-ECD) in retinas of nob and WT mice under light- and dark-adapted conditions. The nob mice had greater hyperopic refractive errors than did the WT mice under normal visual conditions, until 12 weeks of age when both strains had similar refractions. At 6 weeks of age, refractions became less hyperopic in the nob mice but continued to become more hyperopic in the WT mice. After 2 weeks of form deprivation (6 weeks of age), the nob mice displayed a significant myopic shift (~4 D) in refractive error relative to the opposite and control eyes, whereas WT mice required 6 weeks of goggling to elicit a similar response. As expected with loss of ON pathway transmission, light exposure did not alter DOPAC levels in the nob mice. However, dopamine and DOPAC levels were significantly lower in the nob mice compared with WT. Under normal laboratory visual conditions, only minor differences in refractive development were observed between the nob and WT mice. The largest myopic shift in the nob mice resulted after form deprivation, suggesting that visual pathways dependent on nyctalopin and/or abnormally low dopaminergic activity play a role in regulating refractive development. These findings demonstrate an interaction of genetics and environment in refractive development.

Effects of Postnatal Exposure to Methamphetamine on the Development of the Rat Retina

Since the development of different cell types in the retina occurs at different rates, it is possible that exposure to an exogenous substance may produce effects during one time period, but not during another. This study aims to analyze the effects of methamphetamine (METH) in the growth pattern of an experimental model as well as neurochemical and immunohistochemical parameters of the dopaminergic system of the rat retina. The three development stages chosen in this study are key markers in rat eye development. Rats were given 15 mg/kg body weight per day of METH as subcutaneous injections in 0.9% saline (3 mL/kg weight/day) from the day after birth PND 1 to PND 6, PND 13, and PND 29. Each daily dose was split into two. The control group was injected subcutaneously with saline. Both the schedule and volume for injecting saline in the control group were the same as for the METH-treated group. There were no significant differences in the total number of offspring per litter among treatment groups. All offspring had similar body weight at birth. Analysis of body weight on PND 1, showed that animals treated with METH had similar body weights to control-treated animals and females had smaller weights than males. For growth evolution, only litters with a sex ratio of four males and four females were used. Animals treated with METH had smaller body weights than the control-treated animals for all ages studied (PND 7, 14, and 30). Within the control group at PND 30, a significant difference was found in the body weight of females, which was lower when compared with males. For the postnatal model, 7 deaths occurred for the METH-exposed group. No deaths occurred in the control group in a total of 16 saline-injected litters comprising 186 pups. Although the levels of dopamine (DA) was within normal values for the postnatally exposed METH group when compared with its respective control group at PND 7 and 30, at PND 14 this was not the case: in this experimental group, the level of DA was lower than in the control group for both females and males. Support for this result was not evident from the TH immunoreactivity studies, probably because the methodology lacks the sensitivity to distinguish any mild effects, such as that observed in the postnatal model at PND 14. The level of the DA metabolite 3, 4-dihydroxyphenylacetic acid (DOPAC) remained unaffected at all ages studied, for both females and males. The results obtained in this study support the view that, during the critical periods in which the catecholamines can influence the development of neurones, METH transiently affects the pattern of the dopaminergic system in the developing retina.

Diurnal patterns of dopamine release in chicken retina

The retinal dopaminergic system appears to play a major role in the regulation of global retinal processes related to light adaptation. Although most reports agree that dopamine release is stimulated by light, some retinal functions that are mediated by dopamine exhibit circadian patterns of activity, suggesting that dopamine release may be controlled by a circadian oscillator as well as by light. Using the accumulation of the dopamine metabolite dihydroxyphenylacetic acid (DOPAC) in the vitreous as a measure of dopamine release rates, we have investigated the balance between circadian- and light control over dopamine release. In chickens held under diurnal light:dark conditions, vitreal levels of DOPAC showed daily oscillations with the steady-state levels increasing nine-fold during the light phase. Kinetic analysis of this data indicates that apparent dopamine release rates increased almost four-fold at the onset of light and then remained continuously elevated throughout the 12 h light phase. In constant darkness, vitreal levels of DOPAC displayed circadian oscillations, with an almost two-fold increase in dopamine release rates coinciding with subjective dawn/early morning. This circadian rise in vitreal DOPAC could be blocked by intravitreal administration of melatonin (10 nmol), as predicted by the model of the dark–light switch where a circadian fall in melatonin would relieve dopamine release of inhibition and thus be responsible for the slight circadian increase in dopamine release. The increase in vitreal DOPAC in response to light, however, was only partially suppressed by melatonin. The activity of the dopaminergic amacrine cell in the chicken retina thus appears to be dominated by light-activated input.

Enhanced tail pinch-induced activation of catecholamine metabolism in the pericerulean area of RU 24722-treated rats

Our study was devoted to determine in freely moving rats whether the increase in tissue concentration of tyrosine hydroxylase (TH) elicited by a single administration of RU 24722 could modify the catecholaminergic reactivity of neuronal processes present in the rostrolateral part of the pericerulean area (r-lPCA) in response to tail pinch. Catecholaminergic activity was monitored by measuring in vivo the concentration of dopamine metabolite 3,4-dihydroxyphenylacetic acid (DOPAC) using microdialysis coupled to HPLC detection. In this study, the microdialysis probe was implanted at a sufficient distance from the lateral border of rostral nucleus locus ceruleus (LC) to avoid a large contribution of the noradrenergic cell bodies in the measurements performed. We first evidenced that DOPAC measured in the r-lPCA indicated the functional state of catecholaminergic metabolism in neuronal processes (dendrites and fibers) laying in this region. We also showed that the enhancement of TH protein concentration in the r-lPCA following RU 24722 treatment supported an increased in vivo catecholaminergic metabolism in this region. Furthermore, catecholaminergic metabolism response to tail pinch was potentiated in animals with greater TH tissue concentration. Thus, our study reveals that the modulation of both TH concentration and catecholaminergic metabolism in the r-lPCA may be critical in the functioning of cells and neuronal elements present in this region, notably in adaptive responses to noxious stimuli.

Repeated Exposure to the Abused Inhalant Toluene Alters Levels of Neurotransmitters and Generates Peroxynitrite in Nigrostriatal and Mesolimbic Nuclei in Rat

Toluene, a volatile hydrocarbon found in a variety of chemical compounds, is misused and abused by inhalation for its euphorigenic effects. Toluene's reinforcing properties may share a common characteristic with other drugs of abuse, namely, activation of the mesolimbic dopamine system. Prior studies in our laboratory found that acutely inhaled toluene activated midbrain dopamine neurons in the rat. Moreover, single systemic injections of toluene in rats produced a dose-dependent increase in locomotor activity which was blocked by depletion of nucleus accumbens dopamine or by pretreatment with a D2 dopamine receptor antagonist. Here we examined the effects of seven daily intraperitoneal injections of 600 mg/kg toluene on the content of serotonin and dopamine in the caudate nucleus (CN) and nucleus accumbens (NAC), substantia nigra, and ventral tegmental area at 2, 4, and 24 h after the last injection. Also, the roles of nitric oxide, peroxynitrite, and the production of 3-nitrosotyrosine (3-NT), in the CN and NAC were assessed at the same time points. Toluene treatments increased dopamine levels in the CN and NAC, and serotonin levels in CN, NAC, and ventral tegmental area. Measurements of the dopamine metabolite dihydroxyphenylacetic acid (DOPAC) further suggested a change in transmitter utilization in CN and NAC. Lastly, 3-NT levels also showed a differential change between CN and NAC, but at different time points post-toluene injection. These results point out the complexity of action of toluene on neurotransmitter function following a course of chronic exposure. Changes in the production of 3-NT also suggest that toluene-induced neurotoxicity may mediate via generation of peroxynitrite.

Modulation of dopamine release by the nicotinic agonist epibatidine in the frontal cortex and the nucleus accumbens of naive and chronic nicotine treated rats

The effect of the nicotinic acetylcholine receptors (nAChRs) agonist (±)epibatidine on the modulation of dopamine (DA) release was investigated by microdialysis in vivo in the frontal cortex and the nucleus accumbens of naive and chronic nicotine-treated awake rats. (±)Epibatidine (2.5 μg/kg, s.c.), contrary to (−)nicotine (0.5 mg/kg, s.c.), decreased the extracellular concentrations of DA in the brain of naive rats. Subchronic nicotine treatment (0.45 mg/kg, s.c., twice daily for 7 days) attenuated the (±)epibatidine induced decrease in the DA level. The extracellular concentrations of the DA metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were elevated by (±)epibatidine administration in both naı̈ve and subchronic treated rats. The findings suggest that the decrease in DA extracellular concentrations induced by the high affinity nAChRs agonist (±)epibatidine might be due to inactivation of nAChRs, which can be overcome by subchronic treatment with nicotine. Different mechanisms in modulation of DA release appears to be involved in the rat brain by (±)epibatidine compare to (−)nicotine.

Maternal exposure to diphenhydramine during the fetal period in rats: Effects on physical and neurobehavioral development and on neurochemical parameters

Previous research from our laboratory suggested that the administration of antihistaminics (H 1 receptor antagonists) to pregnant Wistar rats throughout pregnancy altered brain sexual differentiation and dopaminergic physiology of the offspring. In the present study, we assessed the effects of 20 mg/kg diphenhydramine (DPH) administration to pregnant rats during the fetal period of pregnancy [Gestation Days (GDs) 16–21], a critical period for brain sexual differentiation and central nervous system (CNS) maturation. Maternal body weight and water and food consumption were measured during pregnancy and offspring physical and behavioral development were evaluated during lactation. Offspring open-field behavior was assessed at 21 and 100 days of age. After the final open-field test, male and female sexual behavior, stereotypy following an apomorphine challenge, striatal content of dopamine (DA), the dopamine metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanilic acid (HVA), serotonin (5-HT) and the serotonin metabolite 5-hydroxyindolacetic acid (5-HIAA) were assessed. There were no significant treatment-related changes in maternal reproductive parameters, but DPH treatment decreased maternal body weight gain during the treatment period. Offspring physical parameters were not altered in the treated group, and no significant treatment-related changes were found in female open-field measures, sexual behavior or in striatal neurochemical measurements. However, delayed testis descent and altered patterns of sexual behavior occurred in male offspring accompanied by increased striatal DA, decreased striatal DOPAC as well as reduced DOPAC/DA, HVA/DA and 5-HIAA/5-HT ratios. Taken together, these data suggest that exposure to DPH during the fetal period of rat development altered postnatal CNS maturation and sexual development of male offspring via changes in striatal bioamine systems.

CART peptide increases the mesolimbic dopaminergic neuronal activity: a microdialysis study

The effects of cocaine-and amphetamine-regulated transcript (CART) peptide on extracellular concentrations of dopamine metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), in the shell region of the nucleus accumbens (AcbSh) were determined by microdialysis in conscious rats. Intracerebroventricular injections of various doses (0.1–5 μg/5 μl/rat) of CART 55–102 elicited dose-dependent increases of extracellular DOPAC and HVA concentration in the AcbSh, suggesting that CART 55–102 peptide has a psychostimulant-like effect via activation of the mesolimbic dopaminergic system.

Stress-induced increase of cortical dopamine metabolism: attenuation by a tachykinin NK 1 receptor antagonist

The present study examined the potential role of tachykinin NK 1 receptors in modulating immobilisation stress-induced increase of dopamine metabolism in rat medial prefrontal cortex. In agreement with previous studies, 20 min immobilisation stress significantly increased medial prefrontal cortex dopamine metabolism as reflected by the concentration of the dopamine metabolite dihydroxyphenylacetic acid (DOPAC). Pretreatment with the high affinity, selective, tachykinin NK 1 receptor antagonist (3( S)-(2-methoxy-5-(5-trifluoromethyltetrazol-1-yl)-phenylmethyl amino)-2( S)-phenylpiperidine) (( S)-GR205171, 10 mg/kg, s.c.), a dose that in ex vivo binding studies extensively occupied rat brain tachykinin NK 1 receptors for approximately 60 min, significantly attenuated the stress-induced increase of mesocortical DOPAC concentration without affecting cortical DOPAC levels per se. In contrast, pretreatment of animals with the less active enantiomer ( R)-GR205171 (10 mg/kg, s.c.), which demonstrated negligible tachykinin NK 1 receptor occupancy ex vivo, failed to affect either basal or stress-induced DOPAC concentration in medial prefrontal cortex. Furthermore, pretreatment of animals with the benzodiazepine/GABA A receptor antagonist, flumazenil (15 mg/kg, i.p.), did not affect the ability of ( S)-GR205171 to attenuate the increase of medial prefrontal cortex DOPAC concentration by acute stress. Results demonstrate that the selective tachykinin NK 1 receptor antagonist, ( S)-GR205171, attenuated the stress-induced activation of mesocortical dopamine neurones by a mechanism independent of the benzodiazepine modulatory site of the GABA A receptor.

Cerebrospinal fluid 3,4-dihydroxyphenylacetic acid level after tolcapone administration as an indicator of nigrostriatal degeneration

The development of reliable biological markers of nigrostriatal degeneration has important implications from both experimental and clinical viewpoints, since such biomarkers could be used for diagnostic and monitoring purposes in models of parkinsonism as well as in Parkinson’s disease patients. In this study, levels of the dopamine metabolite 3,4-dihydroxyphenylacetic acid (DOPAC) were measured in the cerebrospinal fluid (CSF) of normal and parkinsonian squirrel monkeys in order to assess their reliability as indicators of nigrostriatal injury. In particular, we tested the hypothesis that these measurements may become more accurate by inhibiting catecholamine-O-methyltransferase (COMT) activity and therefore blocking the conversion of DOPAC to homovanillic acid. Oral administration of the COMT inhibitor tolcapone (2 doses of 15 mg/kg each with a 4-h interval) significantly reduced enzyme activity in the monkey brain. Tolcapone treatment enhanced CSF DOPAC concentrations in unlesioned animals (by approximately four times) as well as monkeys rendered parkinsonian after severe nigrostriatal dopaminergic injury caused by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Importantly, however, COMT inhibition greatly magnified the differences in CSF DOPAC levels between control and parkinsonian monkeys, since MPTP-induced DOPAC depletion was 35% in the absence vs >60% in the presence of tolcapone. Thus, tolcapone administration enhances the detection of DOPAC in the CSF and, by doing so, improves the reliability of CSF DOPAC as a marker of nigrostriatal degeneration.