Reduction Of Dopamine Research Articles

A synopsis on the role of tyrosine hydroxylase in Parkinson's disease.

Parkinson's disease (PD) is a common chronic progressive neurodegenerative disorder in elderly people. A consistent neurochemical abnormality in PD is degeneration of dopaminergic neurons in substantia nigra pars compacta, leading to a reduction of striatal dopamine (DA) levels. As tyrosine hydroxylase (TH) catalyses the formation of L-dihydroxyphenylalanine (L-DOPA), the rate-limiting step in the biosynthesis of DA, the disease can be considered as a TH-deficiency syndrome of the striatum. Problems related to PD usually build up when vesicular storage of DA is altered by the presence of either α-synuclein protofibrils or oxidative stress. Phosphorylation of three physiologically-regulated specific sites of N-terminal domain of TH is vital in regulating its kinetic and protein interaction. The concept of physiological significance of TH isoforms is another interesting aspect to be explored further for a comprehensive understanding of its role in PD. Thus, a logical and efficient strategy for PD treatment is based on correcting or bypassing the enzyme deficiency by the treatment with L-DOPA, DA agonists, inhibitors of DA metabolism or brain grafts with cells expressing a high level of TH. Neurotrophic factors are also attracting the attention of neuroscientists because they provide the essential neuroprotective and neurorestorative properties to the nigrostriatal DA system. PPAR-γ, a key regulator of immune responses, is likewise a promising target for the treatment of PD, which can be achieved by the use of agonists with the potential to impact the expression of pro- and anti-inflammatory cytokines at the transcriptional level in immune cells via expression of TH. Herein, we review the primary biochemical and pathological features of PD, and describe both classical and developing approaches aimed to ameliorate disease symptoms and its progression.

Pharmacological manipulation of peroxisome proliferator-activated receptor γ (PPARγ) reveals a role for anti-oxidant protection in a model of Parkinson's disease

Peroxisome proliferator-activated receptor γ (PPARγ) agonists have been shown to provide neuroprotection in a number of neurodegenerative diseases including Parkinson's disease and Alzheimer's disease. These protective effects are primarily considered to result from the anti-inflammatory actions of PPARγ, however, there is increasing evidence that anti-oxidant mechanisms may also contribute. This study explored the impact of the PPARγ agonist rosiglitazone and the PPARγ antagonist GW9662 in the MPP+/MPTP (1-methyl-4-phenylpyridinium/1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) model of Parkinson's disease, focussing on oxidative stress mechanisms. Rosiglitazone attenuated reactive oxygen species formation induced by MPP+ in SH-SY5Y cells concurrent with an upregulation of glutathione-S-transferase activity, but not superoxide dismutase activity. These responses were not attenuated by cotreatment with GW9662 suggesting that PPARγ activation is not required. The localisation of PPARγ in vivo to dopaminergic neurons of the substantia nigra pars compacta (SNpc) was established by immunohistochemistry and PPARγ levels were found to be upregulated 7days after MPTP treatment. The importance of PPARγ in protecting against MPTP toxicity was confirmed by treating C57BL6 mice with GW9662. Treatment with GW9662 increased MPTP-induced neuronal loss in the SNpc whilst not affecting MPTP-induced reductions in striatal dopamine and 3,4-dihdroxyphenylacetic acid. GW9662 also caused neuronal loss in the SNpc of saline-treated mice. The evidence presented here supports the role of anti-oxidant mechanisms in the protective effects of PPARγ agonists in neurodegenerative diseases, but indicates that these effects may be independent of PPARγ activation. It also demonstrates the importance of PPARγ activity for neuronal survival within the SNpc.

Voltammetric determination of dopamine and norepinphrine on a glassy carbon electrode modified with poly (L-aspartic acid)

A convenient and useful method for the voltammetric determination of dopamine (DA) and norepinphrine (NE) based on poly(L-aspartic acid) modified glassy carbon electrode (GCE) is reported in this paper. The modified electrode exhibits excellent electro-catalytic activities for the oxidation–reduction of DA and NE, as well as eliminating the interference of ascorbic acid (AA) and uric acid (UA). Factors influencing the detection processes are optimized and the kinetic parameters are calculated. Under the optimal conditions, the anodic peak currents of DA and NE are linear with their concentration and the detection limits (S/N = 3) are 1.0 × 10 − 9 mol L − 1 for DA and 4.31 × 10 − 9 mol L − 1 for NE, respectively. The practical application of this method is demonstrated by determining the concentration of NE and DA in injection which is commercially available with satisfactory results. Compared with other electrochemical methods, this method is simple, highly selective and sensitive.

P.1.003 Brain-derived neurotrophic factor as a biomarker of clinical response in bipolar disorder: 16-week follow-up study

Simultaneous infusion of the selective 5-HT2A-receptor antagonist M100907, as well as asenapine, completely blocked the DOI-induced increase in dopamine and serotonin release and partially the increased noradrenaline release, indicating a similar mechanism by M100907 and asenapine. When given alone, infusion of M100907 or asenapine, in the concentrations used, did not affect monoamine release. Intracortical administration of the selective a2adrenoceptor agonist clonidine significantly decreased dopamine, noradrenaline and serotonin release in the mPFC (maximal effects; 61.0±8.0, 50.4±7.6, and 67.0±4.1% of baseline, respectively; p< 0.01–0.001). Simultaneous infusion of the a2-adrenoceptor antagonist idazoxan blocked the clonidine-induced reduction of dopamine and noradrenaline release. The effect of idazoxan on serotonin was less pronounced and not statistically significant. Simultaneous infusion of asenapine did not acutely block the clonidine-induced decrease in transmitter release. However, following termination of the clonidine infusion the transmitter release remained at a low level. During this interval, i.e. the following hour after the clonidine infusion, intracortical infusion of asenapine restored the catecholamine release to baseline level, indicating an a2-adrenoceptor blocking effect of asenapine which was somewhat delayed. When given alone, the infusion of idazoxan or asenapine, in the concentrations used, did not affect monoamine release. Our results propose that local application of asenapine in the mPFC indeed exhibits a pharmacological significant 5-HT2Aand, to a weaker extent, a2-receptor antagonistic activity. Whereas its 5-HT2A blocking property preferentially influenced the release of serotonin and dopamine but only to a lesser extent noradrenaline, blockage of a2-adrenoceptors preferentially influenced dopamine and noradrenaline release, albeit the effect was somewhat delayed. Thus, 5-HT2A-receptor antagonism and a2-adrenoceptor blockage induced by asenapine in the mPFC may contribute to enhance prefrontal monoamine release in vivo and, secondarily, its effect on positive and negative symptoms as well as pro-cognitive and antidepressant effects [1,2].

Nigrostriatal overabundance of α-synuclein leads to decreased vesicle density and deficits in dopamine release that correlate with reduced motor activity

α-Synuclein (α-syn) is a presynaptic protein present at most nerve terminals, but its function remains largely unknown. The familial forms of Parkinson's disease associated with multiplications of the α-syn gene locus indicate that overabundance of this protein might have a detrimental effect on dopaminergic transmission. To investigate this hypothesis, we use adeno-associated viral (AAV) vectors to overexpress human α-syn in the rat substantia nigra. Moderate overexpression of either wild-type (WT) or A30P α-syn differs in the motor phenotypes induced, with only the WT form generating hemiparkinsonian impairments. Wild-type α-syn causes a reduction of dopamine release in the striatum that exceeds the loss of dopaminergic neurons, axonal fibers, and the reduction in total dopamine. At the ultrastructural level, the reduced dopamine release corresponds to a decreased density of dopaminergic vesicles and synaptic contacts in striatal terminals. Interestingly, the membrane-binding-deficient A30P mutant does neither notably reduce dopamine release nor it cause ultrastructural changes in dopaminergic axons, showing that α-syn's membrane-binding properties are critically involved in the presynaptic defects. To further determine if the affinity of the protein for membranes determines the extent of motor defects, we compare three forms of α-syn in conditions leading to pronounced degeneration. While membrane-binding α-syns (wild-type and A53T) induce severe motor impairments, an N-terminal deleted form with attenuated affinity for membranes is inefficient in inducing motor defects. Overall, these results demonstrate that α-syn overabundance is detrimental to dopamine neurotransmission at early stages of the degeneration of nigrostriatal dopaminergic axons.

Neurodegeneration and Motor Dysfunction in Mice Lacking Cytosolic and Mitochondrial Aldehyde Dehydrogenases: Implications for Parkinson's Disease

Previous studies have reported elevated levels of biogenic aldehydes in the brains of patients with Parkinson's disease (PD). In the brain, aldehydes are primarily detoxified by aldehyde dehydrogenases (ALDH). Reduced ALDH1 expression in surviving midbrain dopamine neurons has been reported in brains of patients who died with PD. In addition, impaired complex I activity, which is well documented in PD, reduces the availability of the NAD+ co-factor required by multiple ALDH isoforms to catalyze the removal of biogenic aldehydes. We hypothesized that chronically decreased function of multiple aldehyde dehydrogenases consequent to exposure to environmental toxins and/or reduced ALDH expression, plays an important role in the pathophysiology of PD. To address this hypothesis, we generated mice null for Aldh1a1 and Aldh2, the two isoforms known to be expressed in substantia nigra dopamine neurons. Aldh1a1−/−×Aldh2−/− mice exhibited age-dependent deficits in motor performance assessed by gait analysis and by performance on an accelerating rotarod. Intraperitoneal administration of L-DOPA plus benserazide alleviated the deficits in motor performance. We observed a significant loss of neurons immunoreactive for tyrosine hydroxylase (TH) in the substantia nigra and a reduction of dopamine and metabolites in the striatum of Aldh1a1−/−×Aldh2−/− mice. We also observed significant increases in biogenic aldehydes reported to be neurotoxic, including 4-hydroxynonenal (4-HNE) and the aldehyde intermediate of dopamine metabolism, 3,4-dihydroxyphenylacetaldehyde (DOPAL). These results support the hypothesis that impaired detoxification of biogenic aldehydes may be important in the pathophysiology of PD and suggest that Aldh1a1−/−×Aldh2−/− mice may be a useful animal model of PD.

Disease-Toxicant Interactions in Manganese Exposed Huntington Disease Mice: Early Changes in Striatal Neuron Morphology and Dopamine Metabolism

YAC128 Huntington's disease (HD) transgenic mice accumulate less manganese (Mn) in the striatum relative to wild-type (WT) littermates. We hypothesized that Mn and mutant Huntingtin (HTT) would exhibit gene-environment interactions at the level of neurochemistry and neuronal morphology. Twelve-week-old WT and YAC128 mice were exposed to MnCl2-4H2O (50 mg/kg) on days 0, 3 and 6. Striatal medium spiny neuron (MSN) morphology, as well as levels of dopamine (DA) and its metabolites (which are known to be sensitive to Mn-exposure), were analyzed at 13 weeks (7 days from initial exposure) and 16 weeks (28 days from initial exposure). No genotype-dependent differences in MSN morphology were apparent at 13 weeks. But at 16 weeks, a genotype effect was observed in YAC128 mice, manifested by an absence of the wild-type age-dependent increase in dendritic length and branching complexity. In addition, genotype-exposure interaction effects were observed for dendritic complexity measures as a function of distance from the soma, where only YAC128 mice were sensitive to Mn exposure. Furthermore, striatal DA levels were unaltered at 13 weeks by genotype or Mn exposure, but at 16 weeks, both Mn exposure and the HD genotype were associated with quantitatively similar reductions in DA and its metabolites. Interestingly, Mn exposure of YAC128 mice did not further decrease DA or its metabolites versus YAC128 vehicle exposed or Mn exposed WT mice. Taken together, these results demonstrate Mn-HD disease-toxicant interactions at the onset of striatal dendritic neuropathology in YAC128 mice. Our results identify the earliest pathological change in striatum of YAC128 mice as being between 13 to 16 weeks. Finally, we show that mutant HTT suppresses some Mn-dependent changes, such as decreased DA levels, while it exacerbates others, such as dendritic pathology.

Enzymatic transamination of d‐kynurenine generates kynurenic acid in rat and human brain

In the mammalian brain, the α7 nicotinic and NMDA receptor antagonist kynurenic acid is synthesized by irreversible enzymatic transamination of the tryptophan metabolite l-kynurenine. d-kynurenine, too, serves as a bioprecursor of kynurenic acid in several organs including the brain, but the conversion is reportedly catalyzed through oxidative deamination by d-amino acid oxidase. Using brain and liver tissue homogenates from rats and humans, and conventional incubation conditions for kynurenine aminotransferases, we show here that kynurenic acid production from d-kynurenine, like the more efficient kynurenic acid synthesis from l-kynurenine, is blocked by the aminotransferase inhibitor amino-oxyacetic acid. In vivo, focal application of 100 μM d-kynurenine by reverse microdialysis led to a steady rise in extracellular kynurenic acid in the rat striatum, causing a 4-fold elevation after 2 h. Attesting to functional significance, this increase was accompanied by a 36% reduction in extracellular dopamine. Both of these effects were duplicated by perfusion of 2 μM l-kynurenine. Co-infusion of amino-oxyacetic acid (2 mM) significantly attenuated the in vivo effects of d-kynurenine and essentially eliminated the effects of l-kynurenine. Thus, enzymatic transamination accounts in part for kynurenic acid synthesis from d-kynurenine in the brain. These results are discussed with regard to implications for brain physiology and pathology.

Prenatal lipopolysaccharide exposure increases anxiety-like behaviors and enhances stress-induced corticosterone responses in adult rats

Maternal infection during pregnancy may affect fetal brain development and lead to neurological and mental disorders. Previously, we used lipopolysaccharide [LPS, 33 μg/kg, intraperitoneal injection] exposure on gestation day 10.5 to mimic maternal bacterial infection in rats and found reduced dopaminergic and serotoninergic neurons in the offspring. In the present study, we examined the anxiety and stress responses of the affected offspring and the neurophysiological changes in their brains. Our results show that LPS rats displayed more anxiety-like behaviors and heightened stress responses. Dopamine (DA) in the nucleus accumbens and serotonin (5-HT) in the medial prefrontal cortex and the hippocampus were significantly reduced in LPS rats. Their glucocorticoid receptors in the dorsal hippocampus and the 5-HT(1A) receptors in the dorsal and ventral hippocampus were also reduced. In addition, chronic but not acute fluoxetine treatment reversed the behavioral changes and increased hippocampal 5-HT(1A) receptor expression. This study demonstrates that LPS exposure during a critical time of embryonic development could produce long-term reduction of DA and 5-HT and other neurophysiological changes; such alterations may be associated with the increases in stress response and anxiety-like behaviors in the offspring.

Methamphetamine-induced vascular changes lead to striatal hypoxia and dopamine reduction

Methamphetamine (meth) is a potent psychostimulant known to cause neurotoxicity. Clinical reports suggest meth abuse is a risk factor for Parkinson's disease. We investigated changes in the blood-brain barrier and cerebral vasculature as a mechanism underlying this risk in rats treated acutely and trained to self-administer meth. We observed blood-brain barrier leakage in rats treated acutely with meth. Hypoperfusion in the striatum was detected with acute and chronic meth treatment and was associated with hypoxia. This was correlated with reductions in striatal tyrosine hydroxylase in rats trained to self-administer meth. These findings suggest a new mechanism of meth-induced neurotoxicity involving striatal vasoconstriction resulting in hypoxia and dopamine reductions leading to an increased risk for Parkinson's disease for meth abusers.

Neuromelanin is an immune stimulator for dendritic cells in vitro

BackgroundParkinson's disease (PD) is characterized at the cellular level by a destruction of neuromelanin (NM)-containing dopaminergic cells and a profound reduction in striatal dopamine. It has been shown recently that anti-melanin antibodies are increased in sera of Parkinson patients, suggesting that NM may act as an autoantigen. In this study we tested whether NM is being recognized by dendritic cells (DCs), the major cell type for inducing T- and B-cell responses in vivo. This recognition of NM by DCs is a prerequisite to trigger an adaptive autoimmune response directed against NM-associated structures.ResultsMurine DCs were treated with NM of substantia nigra (SN) from human subjects or with synthetic dopamine melanin (DAM). DCs effectively phagocytized NM and subsequently developed a mature phenotype (CD86high/MHCIIhigh). NM-activated DCs secreted the proinflammatory cytokines IL-6 and TNF-α. In addition, they potently triggered T cell proliferation in a mixed lymphocyte reaction, showing that DC activation was functional to induce a primary T cell response. In contrast, DAM, which lacks the protein and lipid components of NM but mimics the dopamine-melanin backbone of NM, had only very little effect on DC phenotype and function.ConclusionsNM is recognized by DCs in vitro and triggers their maturation. If operative in vivo, this would allow the DC-mediated transport and presentation of SN antigens to the adaptive immune system, leading to autoimmmunity in susceptible individuals. Our data provide a rationale for an autoimmune-based pathomechanism of PD with NM as the initial trigger.

Neuroprotection of desferrioxamine in lipopolysaccharide-induced nigrostriatal dopamine neuron degeneration

Inflammation and iron accumulation in the substantia nigra (SN) are implicated in the pathogenesis of Parkinson's disease (PD). However, the relationship between neuroinflammation and iron mismanagement remain largely unknown. In the present study, an animal model induced by lipopolysaccharide (LPS) was used to evaluate iron concentration in the ventral midbrain with or without neuroinflammation. Furthermore, the iron chelator desferrioxamine (DFO) was used to explore its neuroprotective property against LPS-induced nigrostriatal degeneration. Adult C57BL/6 mice were treated with DFO (2.5 µg) commenced 3 days prior to or following microinjection of LPS into the striatum. Animal behavioral tests, as well as pathological and biochemical assays were performed to evaluate the nigrostriatal dopamine neuron degeneration and neuroprotective effects of DFO. Here, we report that the iron concentration in the ventral midbrain significantly increased following intrastriatal injection of LPS, and administration of DFO improved behavior deficits, attenuated dopamine (DA) neuron loss and striatal DA reduction, and alleviated microglial activation in the SN. These results suggest that DFO may possess neuroprotective effect against LPS-induced nigrostriatal dopamine neuron degeneration.

Asiaticoside: Attenuation of neurotoxicity induced by MPTP in a rat model of Parkinsonism via maintaining redox balance and up-regulating the ratio of Bcl-2/Bax

In this study, we investigated the neuroprotective effects of asiaticoside, a triterpenoid saponin isolated from the Chinese medicinal herb Centella asiatica, in the rats model of Parkinsonism induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Rats were first injected with MPTP. One day after surgery, asiaticoside was administered and the behavioral tests were assessed. On 14th day, the rats were sacrificed, substantia nigra (SN) and striatum were dissected, and then dopamine (DA) and its metabolites in striatum and malonyldialdehyde (MDA) contents, reduced glutathione (GSH) level and gene expression level in SN were estimated. Treatment with asiaticoside was found to protect dopaminergic neuron by antagonizing MPTP induced neurotoxicity and to improve locomotor dysfunction. Asiaticoside significantly attenuated the MPTP-induced reduction of dopamine in the striatum. The content of MDA was significantly decreased while the GSH level was significantly increased in asiaticoside-treated groups. In addition, asiaticoside increased the Bcl-2/Bax ratio. These results indicated that asiaticoside was effective in reversing MPTP induced Parkinsonism via its neuroprotective effects including antioxidant activity, maintaining the metabolic balance of DA, and increasing ratio of Bcl-2/Bax.

Increased spreading activation in depression

The dopaminergic system is implicated in depressive disorders and research has also shown that dopamine constricts lexical/semantic networks by reducing spreading activation. Hence, depression, which is linked to reductions of dopamine, may be associated with increased spreading activation. However, research has generally found no effects of depression on spreading activation, using semantic priming paradigms. We used a different paradigm to investigate the relationship between depression and spreading activation, one based on word frequencies. Our sample included 97 undergraduates who completed the BDI-II and the Controlled Oral Word Association test as well as the Animal Naming test. The results indicated that the group scoring within the depressed ranged evidenced greater spreading activation as compared to those who scored within the normal range on the BDI-II. The implications of these results as they relate to creativity in depression is discussed.

Brain cannabinoid CB2 receptors modulate cocaine's actions in mice

The presence and function of cannabinoid CB2 receptors in the brain have been subject to debate. We report here that systemic, intranasal or intra-accumbens local administration of JWH133, a selective CB2 receptor agonist, dose-dependently inhibits intravenous cocaine self-administration, cocaine-enhanced locomotion, and cocaine-enhanced accumbens dopamine (DA) in wild-type (WT) and CB1 receptor-knockout (CB1−/−), but not CB2−/−, mice. This inhibition is mimicked by GW405833, another CB2 receptor agonist with a different chemical structure, and is blocked by AM630, a selective CB2 receptor antagonist. Intra-accumbens JWH133 alone dose-dependently decreases, while intra-accumbens AM630 elevates, extracellular DA and locomotion in WT and CB1−/− mice, but not in CB2−/− mice. Intra-accumbens AM630 also blocks the reduction in cocaine self-administration and extracellular DA produced by systemic administration of JWH133. These findings, for the first time, suggest that brain CB2 receptors modulate cocaine’s rewarding and locomotor-stimulating effects, likely by a DA-dependent mechanism.

High tryptophan diet reduces extracellular dopamine release via kynurenic acid production in rat striatum

At endogenous brain concentrations, the neuroinhibitory tryptophan metabolite kynurenic acid (KYNA) is a preferential antagonist of the α7 nicotinic acetylcholine receptor (α7nAChR). In the present study, male Wistar rats were fed a high tryptophan diet (adding 0.1-1.5% tryptophan) for 24 h to examine (i) the effect of increased tryptophan on extracellular dopamine (DA) and KYNA levels and (ii) to determine any possible interactions between DA and KYNA. Brain KYNA levels were dose-dependently increased by tryptophan intake, and these increase were consistent with kynurenine (KYN), the precursor to KYNA, levels in the brain, plasma and liver. Administration of the 1.5% tryptophan added diet reduced the extracellular DA level to 60%, and increased the extracellular KYNA to 320% in the striatum. The DA reduction was attenuated through inhibiting KYNA synthesis with 2-aminoadipic acid. These results indicate that a high tryptophan diet can induce KYNA production and suppress DA release. One possible mechanism is that as more KYN is metabolized from the high doses of tryptophan in the liver and released into the blood stream, KYNA production in astrocytes is enhanced and the increased extracellular KYNA inhibits DA release by blocking α7nAChRs. Dietary manipulation of KYNA formation in astrocytes may offer a unique strategy to modulate DA.

Effects of Zingerone [4-(4-Hydroxy-3-Methoxyphenyl)-2-Butanone] and Eugenol [2-Methoxy-4-(2-Propenyl)Phenol] on the Pathological Progress in the 6-Hydroxydopamine-Induced Parkinson’s Disease Mouse Model

Parkinson's disease (PD) is characterized by progressive degeneration of dopaminergic neurons in the nigrostriatal system and dopamine (DA) depletion in the striatum. The most popular therapeutic medicine for treating PD, 3-(3,4-Dihydroxyphenyl)-L-alanine (L-DOPA), has adverse effects, such as dyskinesia and disease acceleration. As superoxide (·O(2)(-)) and hydroxyl radical (·OH) have been implicated in the pathogenesis of PD, free radical scavenging and antioxidants have attracted attention as agents to prevent disease progression. Rodents injected with 6-hydroxydopamine (6-OHDA) intracerebroventricularly are considered to be a good animal model of PD. Zingerone and eugenol, essential oils extracted from ginger and cloves, are known to have free radical scavenging and antioxidant effects. Therefore, we examined the effects of zingerone and eugenol on the behavioral problems in mouse model and on the DA concentration and antioxidant activities in the striatum after 6-OHDA administration and L-DOPA treatment. Daily oral administration of eugenol/zingerone and injection of L-DOPA intraperitoneally for 4 weeks following a single 6-OHDA injection did not improve abnormal behaviors induced by L-DOPA treatment. 6-OHDA reduced the DA level in the striatum; surprisingly, zingerone and eugenol enhanced the reduction of striatal DA and its metabolites. Zingerone decreased catalase activity, and increased glutathione peroxidase activity and the oxidized L-ascorbate level in the striatum. We previously reported that pre-treatment with zingerone or eugenol prevents 6-OHDA-induced DA depression by preventing lipid peroxidation. However, the present study shows that post-treatment with these substances enhanced the DA decrease. These substances had adverse effects dependent on the time of administration relative to model PD onset. These results suggest that we should be wary of ingesting these spice elements after the onset of PD symptoms.

Neurotoxic (+)-methamphetamine treatment in rats increases brain-derived neurotrophic factor and tropomyosin receptor kinase B expression in multiple brain regions

Methamphetamine (MA) is an abused stimulant which can result in cognitive deficits and monoamine depletions. Animal models of neurotoxic MA exposure show reductions in dopamine, serotonin, and their associated transporters. MA abuse can result in long-term attention, working memory, and executive function deficits in humans and deficits in route-based egocentric learning, novel object recognition, and novel odor preference in rodents. MA has also been shown to affect brain-derived neurotrophic factor (BDNF) in humans and rodents. This experiment examined the effects of a MA binge dosing regimen (10 mg/kg×4 at 2 h intervals, s.c.) in Sprague–Dawley rats on BDNF, tropomyosin receptor kinase B (TrkB), and tyrosine hydroxylase (TH) mRNA expression, and plasma corticosterone. Tissues were collected 1, 7, and 24 h following the last MA dose. Expression of BDNF and TrkB mRNA was analyzed using in situ hybridization with cRNA probes. Frontal, parietal, and entorhinal cortical BDNF mRNA expression were increased by MA exposure at all time-points. Increases in BDNF mRNA were also seen in the hippocampal CA1, prefrontal cortex (PFC), piriform cortex, and locus coeruleus but only at specific times. TrkB mRNA expression was modified in several subregions of the hippocampus as well as in PFC and striatum. TH mRNA was increased at the 1 h time-point in the substantia nigra pars compacta with no differences noted at the other times. Corticosterone levels were increased at all three time-points. The findings suggest that BDNF and its receptor may be upregulated as a compensatory mechanism after MA exposure.

Effects of the genotoxic agent 5-bromo-2′-deoxyuridine with or without pre-pubertal gonadectomy on brain monoamines and their metabolites in female rats

A nucleotide analog 5-bromo-2′-deoxyuridine (BrdU) is a genotoxic compound. Previous studies have demonstrated that prenatal treatment of rodents with BrdU affects the development of cortical neurons, reduces dopamine levels, and elevates serotonin (5-HT) levels in the striatum in adult male offspring from BrdU-treated dams. Moreover, prenatal BrdU-treated rats show locomotor hyperactivity in both males and females. This study investigated sexual dimorphism in the effect of prenatal BrdU on monoamine metabolism. Sprague–Dawley rats were treated with BrdU on gestational days 9–15 (50 mg/kg, i.p.) and monoamine metabolism was examined in female rats at 10 weeks of age. The influence of pre-pubertal gonadectomy on the effects of BrdU was also investigated. BrdU-treated females showed elevations of dopamine and 5-HT levels in the striatum; reductions in dopamine, dihydroxyphenylacetic acid, or homovanillic acid (HVA) in the hypothalamus or the midbrain; and elevated HVA and 5-HT in the hippocampus. Pre-pubertal gonadectomy had a suppressive effect on striatal dopamine levels in prenatal BrdU-treated females. The present data indicate sexual dimorphic effects of prenatal BrdU-treatment in striatal dopamine metabolism but not in serotonergic metabolism and suggest a contribution of the increasing gonadal hormones that accompany puberty to this sex difference.

The effect of freezing and extraction upon striatal dopaminergic function

Determinations of striatal dopamine (DA) and 3,4-dihydroxyphenylacetic acid (DOPAC) concentrations were compared under conditions where tissue was either frozen followed by extraction (FE) or extracted followed by freezing (EF). In Experiment 1, these determinations were performed at 0 (control), 0.5, 1 or 2 h postmortem. In Experiment 2, these two protocols were compared at 0 (control), 0.5 or 72 h after a neurotoxic regimen of methamphetamine. In Experiment 3, potassium-stimulated DA release from superfused striatal tissue was compared between frozen and fresh tissue. The results from the 0 h (control) groups of Experiments 1 and 2 revealed that FE results in significant reductions in DA concentrations as compared with the EF procedure. However, FE diminishes the time-dependent reductions in striatal DA and increases in DOPAC present in the EF group, as obtained under conditions of natural (Experiment 1) or neurotoxin-induced (Experiment 2) degradation. Potassium-stimulated DA release from superfused striatal tissue is significantly decreased when measured from frozen versus fresh tissue. While freezing seems to produce an initial detrimental effect upon measuring striatal DA concentrations and potassium-stimulated release, there appears to be a capacity for preservation of striatal DA and diminution in DOPAC production by freezing when tissue is undergoing degradation. Such results demonstrate the significance of the protocol used for determination of neurotransmitters in postmortem tissue and suggest a potential means for diminishing the adverse effects of insult to striatal tissue that may result from conditions like stroke and exposure to neurotoxins.