Upregulation Of Dopamine Transporter Research Articles

Novel Dopamine Transporter Inhibitor, CE-123, Ameliorates Spatial Memory Deficits Induced by Maternal Separation in Adolescent Rats: Impact of Sex.

Maternal separation (MS) is a key contributor to neurodevelopmental disorders, including learning disabilities. To test the hypothesis that dopamine signaling is a major factor in this, an atypical new dopamine transporter (DAT) inhibitor, CE-123, was assessed for its potential to counteract the MS-induced spatial learning and memory deficit in male and female rats. Hence, neonatal rats (postnatal day (PND)1 to 21) were exposed to MS (180 min/day). Next, the acquisition of spatial learning and memory (Barnes maze task) and the expression of dopamine D1 receptor, dopamine transporter (DAT), and the neuronal GTPase, RIT2, which binds DAT in the vehicle-treated rats were evaluated in the prefrontal cortex and hippocampus in the adolescent animals. The results show that MS impairs the acquisition of spatial learning and memory in rats, with a more severe effect in females. Moreover, the MS induced upregulation of DAT and dopamine D1 receptors expression in the prefrontal cortex and hippocampus in adolescent rats. Regarding RIT2, the expression was decreased in the hippocampus for both the males and females, however, in the prefrontal cortex, reduction was found only in the females, suggesting that there are region-specific differences in DAT endocytic trafficking. CE-123 ameliorated the behavioral deficits associated with MS. Furthermore, it decreased the MS-induced upregulation of D1 receptor expression level in the hippocampus. These effects were more noted in females. Overall, CE-123, an atypical DAT inhibitor, is able to restore cognitive impairment and dopamine signaling in adolescent rats exposed to MS—with more evident effect in females than males.

Regulator of G protein signaling 6 (RGS6) is a critical modulator of reward behavior and dopamine signaling in the mesolimbic circuit

Spicer MM1,2, Weber MA3, Yang J1, Stewart AM6, Luo Z5, Yang J1, Narayanan NS3,4, and Fisher RA1,2,4. 1Department of Neuroscience & Pharmacology, 2Interdisciplinary Graduate Program in Molecular Medicine, 3Department of Neurology, 4Iowa Neuroscience Institute, 5Department of Pediatrics, Carver College of Medicine, University of Iowa, Iowa City, IA 52242 6Department of Biomedical Sciences, Florida Atlantic University Brain Institute, Florida Atlantic University, Boca Raton, FL 33431 Alcohol (EtOH) is the most commonly abused drug worldwide and chronic EtOH consumption often leads to development of dependence and abuse. EtOH dependence is characterized by progressive, neuroadaptive changes to the brain's reward system resulting from chronic EtOH exposure. The neurobiological mechanisms underlying EtOH-seeking behavior and dependence are not fully understood, resulting in limited therapeutics. Currently, abstinence remains the only effective way to prevent alcohol use disorders (AUDs). We previously discovered that loss of RGS6 in mice leads to reduced EtOH seeking and reward behaviors. GABAB and D2 autoreceptor (D2R) antagonism partially reduced EtOH seeking in RGS6-/- mice, whereas singular inhibition of the dopamine (DA) transporter (DAT) completely reversed this effect. Moreover, RGS6-/- mice exhibited reduced striatal DA content. These findings led us to hypothesize that RGS6 promotes mesolimbic DA neurotransmission by suppressing GPCR-Gαi/o-mediated upregulation of DAT. To investigate this possibility, we examined the effects of RGS6 loss on DAT expression in VTA cell bodies and synaptic terminals in the nucleus accumbens (NAcc). In addition, we examined the effects of RGS6 loss on mesolimbic neuronal activity and DA transmission using c-Fos staining and EtOH-induced release of DA from VTA neurons, respectively. We found robust RGS6 expression in VTA cell bodies and terminals, where its loss led to upregulated expression of DAT. Additionally, RGS6 loss reduced VTA neuronal activity as measured by c-Fos immunostaining. These findings suggest that RGS6 functions to promote EtOH seeking and reward behavior by promoting DA transmission in the mesolimbic circuit by suppressing GPCR-Gαi/o signaling, thereby promoting VTA neuronal activity and suppressing DAT upregulation.

Pharmacotherapy of schizophrenia: Mechanisms of antipsychotic accumulation, therapeutic action and failure

Schizophrenia is a multi-dimensional disorder with a complex and mostly unknown etiology, leading to a severe decline in life quality. Antipsychotic drugs (APDs) remain beneficial interventions in the treatment of the disorder, but vary significantly in binding profile, clinical effects and adverse reactions. The present review summarizes the main principles of APD mechanisms of action with a particular focus on recent findings in APD accumulation and its role in the therapeutic efficacy and treatment failure. High and low doses of APDs were shown to be effective in different dimensions of antipsychotic-like behaviour in rodent models. Efficacy of the APDs correlates with high dopamine D2 receptor occupancy, which occurs quickly after drug administration. However, onset and peak of action are delayed up to several days or weeks. APD accumulation via acidic trapping in synaptic vesicles is considered to underlie the time course of APD action. Use-dependent exocytosis, co-release with dopamine and serotonin and inhibition of ion channels impact on the neuronal transmission and determine effects of APDs. Disruption in accumulating properties leads to diminished APD effects. In addition, long-term APD administration at therapeutic doses leads to treatment failure both in animal models and in humans. APD failure was associated with treatment induced neuroadaptations, including a decline in extracellular dopamine levels, dopamine transporter upregulation, and altered neuronal firing. However, enhanced synaptic vesicle release has also been reported. APD loss of efficacy may be reversed through inhibition of the dopamine transporter or switching the administration regimen from continuous to intermittent. Thus, manipulating the accumulation properties of APDs, changes in the administration regimen and doses, or co-administration with dopamine transporter inhibitors may be considered to yield benefits in the development of new effective strategies in the treatment of schizophrenia.

Regulation of dopaminergic neuronal phenotypes by the estrogen-related receptor gamma ligand GSK4716 via the activation of CREB signaling

Midbrain dopaminergic (DAergic) neurotransmission plays a crucial role in regulating motor, cognitive, and emotional functions. The orphan nuclear receptor estrogen-related receptor gamma (ERRγ) is highly expressed in the adult brain and in the developing fetal brain. Our previous study showed the relevance of ERRγ in the regulation of the DAergic neuronal phenotype with the upregulation of dopamine synthesizing tyrosine hydroxylase (TH) and dopamine transporter (DAT) and the possibility that ERRγ could be a novel target for regulating DAergic neuronal differentiation. In this study, we examined whether ERRγ ligands could be small molecule regulators of DAergic phenotypes. The ERRγ agonist GSK4716 increased DAT and TH expression, and the ERRγ inverse agonist GSK5182 attenuated the retinoic acid-induced upregulation of DAT and TH in differentiated SH-SY5Y cells. We found that biphasic activation of the protein kinase A/cyclic AMP response element-binding (CREB) protein signaling pathway was involved in the GSK4716-induced increase in the DAergic phenotype in SH-SY5Y cells. CREB signaling activated as early as 3 h after GSK4716 treatment in an ERRγ-independent manner, but increased following ERRγ activation after 3 days. Protein kinase A inhibitor H-89 attenuated GSK4716-induced DAT and TH upregulation. In primary cultured DAergic neurons, GSK4716 increased neurite length and the number of DAT and TH-double-positive (DAT + TH+) neurons compared to that in control cells. These findings suggest that ERRγ ligands could serve as useful chemical tools for obtaining a better understanding of the regulation of DAergic phenotypes and might facilitate the development of small molecule therapeutics to treat DA-related neurological diseases.

Striatal Dopamine Transporter Modulation After Rotigotine: Results From a Pilot Single-Photon Emission Computed Tomography Study in a Group of Early Stage Parkinson Disease Patients.

Several in vitro data have reported negative interference by dopamine-agonists on the expression of dopamine transporter (DAT), whereas the majority of imaging studies have shown that neither L-dopa nor dopamine-agonists interfere with DAT availability. As yet, there are no in vivo studies on DAT expression after treatment with rotigotine. We evaluated presynaptic nigrostriatal function in 8 patients with de novo Parkinson disease (age, 59 ± 6.2 years; male/female sex, 5/3) using 123-I- N-ω-fluoropropyl-2-β-carbomethoxy-3-β-(4-iodophenyl)nortropane (FP-CIT) single-photon emission computed tomography before and after 3 months of treatment with rotigotine (mean dose, 7.75 ± 1.98 mg). For data analysis, specific (left and right caudate, left and right putamen) to nonspecific (occipital cortex) binding ratios, putamen-to-caudate ratios, and asymmetry indices were calculated. After rotigotine, motor symptoms improved in all patients (Unified Parkinson Disease Rating Scale III mean score, 11.88 ± 2.59 vs 7.63 ± 1.92 on therapy; P = 0.0022). Striatal FP-CIT levels showed a significant improvement in every patient at the follow-up scan. Comparisons between before and after treatment in the whole group revealed a significant improvement in FP-CIT uptake in both caudate and putamen (P < 0.001 in each nucleus). Putamen-to-caudate ratio and asymmetry indices did not show any significant difference before and after treatment. Although the study population was small, we found DAT overexpression after chronic treatment with rotigotine, presumably related to its pharmacological profile. The DAT upregulation by rotigotine in an opposite direction with respect to early Parkinson disease compensatory mechanisms might reduce the risk of dyskinesia, but it could imply less motor benefit because of less stimulation by the dopamine itself on dopaminergic receptors.

Potential role of dopamine transporter in behavioral flexibility

Behavioral flexibility is subserved by the prefrontal cortex and the basal ganglia. Orbitofrontal cortex (OFC) and dorsomedial striatum (DMS) form a functional frontocorticostriatal circuit crucial for the mediation of flexibility during reversal learning via dopamine (DA) neurotransmission. The regulatory control in maintaining DA homeostasis and function is provided by the dopamine transporter (DAT), which therefore likely plays a significant role in controlling the influence of DA on cognitive processes. Here we used a gene knockout mouse model to investigate the role of DAT in the performance on the Attentional Set-Shifting Task (ASST) stages dependent upon the OFC and the DMS. Additionally, behavior of mice after repeated administration of selective DAT inhibitor, GBR 12909, was examined. The animals were treated with the inhibitor to elicit a compensatory DAT up-regulation following withdrawal. Learning was slower and the number of errors during reversal learning and intra-dimensional shift stages was higher in DAT+/- mutant mice than in WT mice. GBR 12909-treated mice had deficits in reversal stages of the ASST. Neuronal activation in the OFC and DMS during the ASST was examined with early growth response proteins 1 and 2 (egr-1, egr-2) immunohistochemistry. Density of egr-2 labeled cells in the OFC was lower in mutant mice than in wild-types during reversal learning and the expression of the egr-1 was lower in mutant mice in the OFC and DMS during reversal and intra-dimensional shift stages. Mice with decreased DAT levels displayed behavioral difficulties that were accompanied by a lower task-induced activation of neurons in brain regions involved in the reversal learning. Altogether, these data indicate the role of the DAT in the behavioral flexibility.

Essential Oils from the Medicinal Herbs Upregulate Dopamine Transporter in Rat Pheochromocytoma Cells.

The dopamine transporter (DAT) protein, a component of the dopamine system, undergoes adaptive neurobiological changes from drug abuse. Prevention of relapse and reduction of withdrawal symptoms are still the major limitations in the current pharmacological treatments of drug addiction. The present study aimed to investigate the effects of essential oils extracted from Elsholtzia ciliata, Shinchim, Angelicae gigantis Radix, and Eugenia caryophyllata, well-known traditional Korean medicines for addiction, on the modulation of dopamine system in amphetamine-treated cells and to explore the possible mechanism underlying its therapeutic effect. The potential cytotoxic effect of essential oils was evaluated in PC12 rat pheochromocytoma cells using cell viability assays. Quantification of DAT, p-CREB, p-MAPK, and p-Akt was done by immunoblotting. DAT was significantly reduced in cells treated with 50 μM of amphetamine in a time-dependent manner. No significant toxicity of essential oils from Elsholtzia ciliata and Shinchim was observed at doses of 10, 25, and 50 μg/mL. However, essential oils from A. gigantis Radix at a dose of 100 μg/mL and E. caryophyllata at doses of 50 and 100 μg/mL showed cytotoxicity. Treatment with GBR 12909, a highly selective DAT inhibitor, significantly increased DAT expression compared with that of amphetamine only by enhancing phosphorylation of mitogen-activated protein kinases (MAPK) and Akt. In addition, essential oils effectively induced hyperphosphorylation of cyclic-AMP response element-binding protein (CREB), MAPK, and Akt, which resulted in DAT upregulation. Our study implies that the essential oils may rehabilitate brain dopamine function through increased DAT availability in abstinent former drug users.

Upregulation of tumor necrosis factor-alpha in nucleus accumbens attenuates morphine-induced rewarding in a neuropathic pain model

Treatment of neuropathic pain with opioid analgesics remains controversial and a major concern is the risk of addiction. Here, we investigated this issue with spared nerve injury (SNI) model of neuropathic pain in rats and mice. SNI prevented conditioned place preference (CPP) induced by low dose (3.5mg/kg) of morphine (MOR), which was effective for anti-allodynia, but not by high dose (⩾5.0mg/kg) of MOR. Tumor necrosis factor-alpha (TNF-α) was upregulated in nucleus accumbens (NAcc) following SNI. The inhibitory effect of SNI on MOR-induced CPP was blocked by either genetic deletion of TNF receptor 1 (TNFR1) or microinjection of anti-TNF-α into the NAcc and was mimicked by intra-NAcc injection of TNF-α in sham rats. Furthermore, SNI reduced dopamine (DA) level and upregulated dopamine transporter (DAT) in the NAcc, but did not affect total tyrosine hydroxylase (TH) or phospho-TH (p-TH), a rate-limiting enzyme of catecholamine biosynthesis, in ventral tegmental area (VTA). Accordingly, the increase in DA reuptake but not decrease in its synthesis may lead to the reduction of DA level. Finally, the upregulation of DAT in the NAcc of SNI animals was again blocked by either genetic deletion of TNFR1 or NAcc injection of anti-TNF-α, and was mimicked by NAcc injection of TNF-α in sham animals. Thus, our data provided novel evidence that upregulation of TNF-α in NAcc may attenuate MOR-induced rewarding by upregulation of DAT in NAcc under neuropathic pain condition.

Telmisartan attenuates MPTP induced dopaminergic degeneration and motor dysfunction through regulation of α-synuclein and neurotrophic factors (BDNF and GDNF) expression in C57BL/6J mice

Telmisartan (TEL), an angiotensin type 1 receptor (AT1R) antagonist, has been reported to exert neuroprotective effect in animal models of Parkinson's disease (PD). However, its effect on motor functions, mutant protein α-synuclein (SYN) and neurotrophic factors (BDNF and GDNF) expression and their interrelation in PD has not yet been elucidated. In the present study, the effect of TEL on 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) induced motor dysfunctions and dopaminergic degeneration was ascertained through investigating the alterations in protein expression of dopamine transporter (DAT), tyrosine hydroxylase (TH) and SYN in C57BL/6J mouse. Further, the role of TEL on the gene expression of neurotrophic factors such as BDNF and GDNF and protein expression of vesicular monoamine transporter 2 (VMAT2) and Glial fibrillary acidic proteins (GFAP) were studied. In TEL treated mouse, strong negative correlation was observed between motor function and SYN, while a strong positive correlation was noted with BDNF and GDNF expression. TEL caused down-regulation of SYN, GFAP and up-regulation of DAT, TH, VAMT2, BDNF and GDNF expressions. Present data suggest that brain renin angiotensin system (RAS) plays a crucial role in motor function and in the regulation of key proteins such as SYN, BDNF and GDNF, DAT, TH, VMAT2 and GFAP in Parkinsonism. In conclusion, the present study shows that angiotensin type 1 receptor antagonists can ameliorate motor dysfunction and act as potential neuroprotective agent in the management of Parkinsonism.

Neural progenitor cells derived from adult bone marrow mesenchymal stem cells promote neuronal regeneration

AimIt is well known that neural stem/progenitor cells (NS/PC) are an ideal cell type for the treatment of central nervous system (CNS) disease. However, ethical problems have severely hampered fetal NS/PC from being widely used as a source for stem cell therapy. Recently, it has been demonstrated that autologous bone marrow mesenchymal stem cells (BMSC) can transdifferentiate into neural progenitor cells (NPC). The biological function of BMSC derived NPC (MDNPC) in neuronal systems remains unknown. In the present study, we aimed to investigate whether MDNPC can promote in vitro neural regeneration, a process comprising mainly the generation of neurons and neurotransmitters. Main methodsWe co-cultured BMSC, MDNPC or fetal NS/PC with PC12 cells and studied their roles on proliferation, neurite formation and dopamine release from PC12 cells. Furthermore, we also explored the mechanisms by which MDNPC regulate dopamine secretion from PC12 derived neural cells using Western blot. Key findingsWe found that both MDNPC and NS/PC had similar morphologies and there were no significant differences between MDNPC and NS/PC in promoting PC12 cell proliferation, neurite outgrowth, and dopamine release. We also demonstrated that NS/PC induced dopamine secretion was associated with an upregulation of dopamine transporter (DAT) levels. SignificanceIn summary, MDNPC were comparable to NS/PC in promoting neural regeneration, indicating that MDNPC are a promising candidate source of neural stem cells for the treatment of neurological diseases.

Involvement of estrogen receptors in the resveratrol-mediated increase in dopamine transporter in human dopaminergic neurons and in striatum of female mice

Treatment with resveratrol (RSV) has been shown to protect vulnerable neurons after various brain injuries and in neurodegenerative diseases. The mechanisms for the effects of RSV in brain are not fully understood, but RSV may affect the expression of various gene products. RSV is structurally related to the synthetic estrogen, diethylstilbestrol so the effects of RSV may be gender-specific. Here we studied the role of RSV in the regulation of dopamine transporter (DAT) in the striatum using male and female mice. The basic levels of DAT in the striatum showed no sex difference, but the levels increased significantly by RSV (20 mg/kg i.p.) in female but not in male mice. Pretreatment of mice with the selective estrogen receptor (ER), ERα- and ERβ antagonist ICI 182,780, led to a complete block of RSV effect on DAT protein levels, suggesting that ERs are involved in the up-regulation of DAT by RSV. Similar data was also obtained in culture using human MESC2.10 and mouse SN4741 dopaminergic cells after treatment with RSV. Data further showed that RSV specifically induced gene transcription of DAT in the dopaminergic cells. These results show that estrogen receptors are involved in the up-regulation of DAT by RSV in the dopaminergic neurons, demonstrating a sex-dependent effect of RSV in the brain that may be of clinical importance. This article is part of a Special Issue entitled ‘Post-Traumatic Stress Disorder’.

Periadolescent exposure to cannabinoids alters the striatal and hippocampal dopaminergic system in the adult rat brain

In a previous work, we have shown that chronic administration of the cannabinoid agonist CP 55,940 (CP) during periadolescence increases cocaine self-administration in adult female rats, while it produces no such effect in males (Higuera-Matas et al., 2008). To extend these findings, we have analysed here the brains of the rats used as subjects in this previous work to evaluate the impact of the interaction between CP exposure and cocaine self-administration on dopaminergic parameters. We evaluated the levels of the dopamine transporter (DAT), and the D1- (D1R) and D2-type (D2R) dopaminergic receptors, as well as tyrosine hydroxylase (TH) mRNA in dopaminergic areas of the adult, cocaine self-administered, rat brain that had been chronically exposed to CP or vehicle (VH) during periadolescence. Control groups with CP/VH exposure and no self-administration experience were also included. In adult females, CP administration induced an up-regulation of DAT in the caudate-putamen that was maintained after cocaine self-administration. In males, CP induced an increase in the D1Rs content in the nucleus accumbens shell, which was not evident after cocaine self-administration. CP also reduced the expression of D2Rs in CA1 irrespective of sex. Finally, an increase in D1Rs was observed in the substantia nigra following cocaine self-administration. These findings suggest that a dopaminergic component modulated by cannabinoids may underlie the enhanced cocaine self-administration previously observed in adult female rats.

Reduced D2-mediated signaling activity and trans-synaptic upregulation of D1 and D2 dopamine receptors in mice overexpressing the dopamine transporter

The dopamine transporter (DAT) regulates the temporal and spatial actions of dopamine by reuptaking this neurotransmitter into the presynaptic neurons. We recently generated transgenic mice overexpressing DAT (DAT-tg) that have a 3-fold increase in DAT protein levels which results in a 40% reduction of the extracellular DA concentration in the striatum. The aim of this study was to examine the effect of this reduction in dopaminergic tone on postsynaptic responses mediated by dopamine receptors. We report here that DAT-tg mice have increased levels of striatal D1 (30%) and D2 (~ 60%) dopamine receptors with D1 receptor signaling components not significantly altered, as evidenced by unaffected basal or stimulated levels of phospho-GluR1 (Ser845) and phospho-ERK2. However, the novel D2 mediated Akt signaling is markedly altered in DAT-tg animals. In particular, there is a 300% increase in the basal levels of phospho-Akt in the striatum of DAT-tg, reflecting the reduced extracellular dopamine tone in these animals. This increase in basal pAkt levels can be pharmacologically recapitulated by partial dopamine depletion in WT mice treated with the selective tyrosine hydroxylase inhibitor alpha-methyl-para-tyrosine (α-MPT). Behaviorally, DAT-tg animals demonstrate an augmented synergistic interaction between up-regulated D1 and D2 receptors, which results in increased climbing behavior in transgenic mice after stimulation with either apomorphine or a co-administration of selective D1 and D2 receptor agonists. In sum, our study reveals that hypodopaminegia caused by up-regulation of DAT results in significant alterations at postsynaptic receptor function with most notable dysregulation at the level of D2 receptor signaling.

Pyrethroid pesticide-induced alterations in dopamine transporter function

Parkinson's disease (PD) is a progressive neurodegenerative disease affecting the nigrostriatal dopaminergic pathway. Several epidemiological studies have demonstrated an association between pesticide exposure and the incidence of PD. Studies from our laboratory and others have demonstrated that certain pesticides increase levels of the dopamine transporter (DAT), an integral component of dopaminergic neurotransmission and a gateway for dopaminergic neurotoxins. Here, we report that repeated exposure (3 injections over 2 weeks) of mice to two commonly used pyrethroid pesticides, deltamethrin (3 mg/kg) and permethrin (0.8 mg/kg), increases DAT-mediated dopamine uptake by 31 and 28%, respectively. Using cells stably expressing DAT, we determined that exposure (10 min) to deltamethrin and permethrin (1 nM-100 microM) had no effect on DAT-mediated dopamine uptake. Extending exposures to both pesticides for 30 min (10 microM) or 24 h (1, 5, and 10 microM) resulted in significant decrease in dopamine uptake. This reduction was not the result of competitive inhibition, loss of DAT protein, or cytotoxicity. However, there was an increase in DNA fragmentation, an index of apoptosis, in cells exhibiting reduced uptake at 30 min and 24 h. These data suggest that up-regulation of DAT by in vivo pyrethroid exposure is an indirect effect and that longer-term exposure of cells results in apoptosis. Since DAT can greatly affect the vulnerability of dopamine neurons to neurotoxicants, up-regulation of DAT by deltamethrin and permethrin may increase the susceptibility of dopamine neurons to toxic insult, which may provide insight into the association between pesticide exposure and PD.

Differential up-regulation of striatal dopamine transporter and α-synuclein by the pyrethroid insecticide permethrin

The effects of permethrin on striatal dopaminergic biomarkers were assessed in this study. Retired breeder male C57 B1/6 mice were given an ip dose of permethrin (0.1–200 mg/kg) at 7-day intervals, over a 2-week period (Days 0, 7, and 14). Animals were then sacrificed 1 day ( t = 1), 14 days ( t = 14), or 28 days after the last treatment ( t = 28). Dopamine transporter (DAT) protein as assayed by Western blotting was increased to 115% in the 0.8 mg/kg group over that of control mice at t = 1 ( P < 0.05). At t = 14, this value increased to 140% of control, and declined slightly to 133% of control at t = 28. The mice given the 1.5 mg/kg dose displayed a significant increase in DAT protein only at t = 28, to 145% of controls. Thus, upregulation of the DAT at low doses of PM is variable 24 h after treatment, and seems to stabilize by t = 28. The threshold dose for increasing DAT expression in Western blots by t = 28 was 0.2 mg/kg permethrin. [ 3H]GBR 12935, used to assay DAT binding, followed the same trend as that for the Western blotting data for 0.8 and 1.5 mg/kg doses of permethrin over the 4 weeks posttreatment. At 200 mg/kg permethrin, DAT protein was unchanged vs controls ( t = 1), but had significantly increased by t = 14 and continued to increase at t = 28, suggesting that the reduced dopamine transport at this dose was due to nerve terminal stress and that recovery had occurred. The protein α-synuclein was also significantly induced at the 1.5 mg/kg dose at t = 1; however, unlike DAT up-regulation, this effect had declined to control values by t = 14. Maximal induction of α-synuclein protein occurred at a dose of 50 mg/kg permethrin. These data provide evidence that the pyrethroid class of insecticides can modulate the dopaminergic system at low doses, in a persistent manner, which may render neurons more vulnerable to toxicant injury.

Long-term methamphetamine-induced decreases of [(11)C]WIN 35,428 binding in striatum are reduced by GDNF: PET studies in the vervet monkey.

The effects of glial cell line-derived neurotrophic factor (GDNF) pretreatment on methamphetamine (METH)-induced striatal dopamine system deficits in the vervet monkey were characterized with [(11)C]WIN 35,428 (WIN)-positron emission tomography (PET). WIN, a cocaine analog that binds to the dopamine transporter (DAT), was used to provide an index of striatal dopamine terminal integrity. In two subjects, GDNF (200 microg/40 microl) was injected into the caudate and putamen unilaterally vs. saline contralaterally. After 1-2 weeks, + and -GDNF striatal WIN-PET binding values were equivalent as calculated by multiple time graphic analysis, suggestive of an absence of unilateral DAT up-regulation. Three other subjects (n = 3) received GDNF injections into the caudate and putamen unilaterally and one week later, were administered METH HCl (2 x 2 mg/kg; i.m., 24 hours apart; a neurotoxic dosage for this species). At 1 week post-METH, WIN-PET studies showed that mean WIN binding was decreased by 72% in the +GDNF and by 92% in the -GDNF striatum relative to pre-drug assessment values. Thus, GDNF pretreatment reduced the extent of METH-induced decreases in WIN binding. Subsequent WIN-PET studies (1.5-9-month range) showed a protracted recovery of WIN binding in each striatum, indicative of long-term but partially reversible METH neurotoxicity. Further, at each time point, WIN binding remained relatively higher in the +GDNF vs. -GDNF striatum. These results provide further evidence that the adult non-human primate brain remains responsive to exogenously administered GDNF and that this pharmacotherapy approach can counteract aspects of neurotoxic actions associated with methamphetamine.

Long-term methamphetamine-induced decreases of [11C]WIN 35,428 binding in striatum are reduced by GDNF: PET studies in the vervet monkey

The effects of glial cell line-derived neurotrophic factor (GDNF) pretreatment on methamphetamine (METH)-induced striatal dopamine system deficits in the vervet monkey were characterized with [11C]WIN 35,428 (WIN)-positron emission tomography (PET). WIN, a cocaine analog that binds to the dopamine transporter (DAT), was used to provide an index of striatal dopamine terminal integrity. In two subjects, GDNF (200 μg/40 μl) was injected into the caudate and putamen unilaterally vs. saline contralaterally. After 1–2 weeks, + and –GDNF striatal WIN-PET binding values were equivalent as calculated by multiple time graphic analysis, suggestive of an absence of unilateral DAT up-regulation. Three other subjects (n = 3) received GDNF injections into the caudate and putamen unilaterally and one week later, were administered METH HCl (2 × 2 mg/kg; i.m., 24 hours apart; a neurotoxic dosage for this species). At 1 week post-METH, WIN-PET studies showed that mean WIN binding was decreased by 72% in the +GDNF and by 92% in the –GDNF striatum relative to pre-drug assessment values. Thus, GDNF pretreatment reduced the extent of METH-induced decreases in WIN binding. Subsequent WIN-PET studies (1.5–9-month range) showed a protracted recovery of WIN binding in each striatum, indicative of long-term but partially reversible METH neurotoxicity. Further, at each time point, WIN binding remained relatively higher in the +GDNF vs. –GDNF striatum. These results provide further evidence that the adult non-human primate brain remains responsive to exogenously administered GDNF and that this pharmacotherapy approach can counteract aspects of neurotoxic actions associated with methamphetamine. Synapse 35:243–249, 2000. © 2000 Wiley-Liss, Inc.

Protein Kinase A Activity May Kinetically Upregulate the Striatal Transporter for Dopamine

The neuronal dopamine transporter (DAT) plays a key role in terminating dopaminergic chemical neurotransmission; thus, the study of the regulation of DAT activity is important in defining parameters relevant to the control of dopaminergic neurotransmission. Interpretation of the results from previous work of this laboratory suggests that occupation of presynaptic autoreceptors increases DAT activity. Second messenger signaling related to kinetic upregulation of DAT has not been examined previously. However, others have shown that protein kinase C activity may downregulate DAT activity, whereas protein kinase A has shown variable results. Herein it is shown that protein kinase A activity mediates the kinetic upregulation of DAT. Quinpirole increased DAT activity that was blocked by sulpiride and the protein kinase A selective inhibitor H-89. Brief incubations with forskolin and 8-bromo-cAMP (8-Br-cAMP) were found to stimulate striatal DAT activity by increasing the Vmax of transport without affecting the Km. Exposures >15 min had no effect. The 8-Br-cAMP-stimulated increases in DAT activity were blocked by pre-exposure to H-89. Thus, second messenger signaling via the cAMP cascade may mediate kinetic upregulation of DAT. Kinetic analyses of the results suggest that either insertion of DAT into the membrane or activation of pre-existing DAT within the membrane mediates the regulation.