Effects of isatin on rotational behavior and DA levels in caudate putamen in Parkinsonian rats

Production of Indole and Indole-Related Compounds by the Intestinal Microbiota and Consequences for the Host: The Good, the Bad, and the Ugly

The intestinal microbiota metabolic activity towards the available substrates generates myriad bacterial metabolites that may accumulate in the luminal fluid. Among them, indole and indole-related compounds are produced by specific bacterial species from tryptophan. Although indole-related compounds are, first, involved in intestinal microbial community communication, these molecules are also active on the intestinal mucosa, exerting generally beneficial effects in different experimental situations. After absorption, indole is partly metabolized in the liver into the co-metabolite indoxyl sulfate. Although some anti-inflammatory actions of indole on liver cells have been shown, indoxyl sulfate is a well-known uremic toxin that aggravates chronic kidney disease, through deleterious effects on kidney cells. Indoxyl sulfate is also known to provoke endothelial dysfunction. Regarding the central nervous system, emerging research indicates that indole at excessive concentrations displays a negative impact on emotional behavior. The indole-derived co-metabolite isatin appears, in pre-clinical studies, to accumulate in the brain, modulating brain function either positively or negatively, depending on the doses used. Oxindole, a bacterial metabolite that enters the brain, has shown deleterious effects on the central nervous system in experimental studies. Lastly, recent studies performed with indoxyl sulfate report either beneficial or deleterious effects depending once again on the dose used, with missing information on the physiological concentrations that are reaching the central nervous system. Any intervention aiming at modulating indole and indole-related compound concentrations in the biological fluids should crucially take into account the dual effects of these compounds according to the host tissues considered.

DJ-1 Protein and Its Role in the Development of Parkinson's Disease: Studies on Experimental Models

DJ-1, also known as Parkinson's disease protein 7, is a multifunctional protein ubiquitously expressed in cells and tissues. Interacting with proteins of various intracellular compartments, DJ-1 plays an important role in maintaining different cellular functions. Mutant DJ-1 forms containing amino acid substitutions (especially L166P), typical of Parkinson's disease, are characterized by impaired dimerization, stability, and folding. DJ-1 exhibits several types of catalytic activity; however, in the enzyme classification it exists as protein deglycase (EC 3.5.1.124). Apparently, in different cell compartments DJ-1 exhibits catalytic and non-catalytic functions, and their ratio still remains unknown. Oxidative stress promotes dissociation of cytoplasmic DJ-1 dimers into monomers, which are translocated to the nucleus, where this protein acts as a coactivator of various signaling pathways, preventing cell death. In mitochondria, DJ-1 is found in the synthasome, where it interacts with the β ATP synthase subunit. Downregulation of the DJ-1 gene under conditions of experimental PD increases sensitivity of the cells to neurotoxins, and introduction of the recombinant DJ-1 protein attenuates manifestation of this pathology. The thirteen-membered fragment of the DJ-1 amino acid sequence attached to the heptapeptide of the TAT protein penetrating into the cells exhibited neuroprotective properties in various PD models both in cell cultures and after administration to animals. Low molecular weight DJ-1 ligands also demonstrate therapeutic potential, providing neuroprotective effects seen during their incubation with cells and administration to animals.

Participation of glutamatergic and nitrergic systems in the striatal dopamine release induced by isatin, a MAO inhibitor

Isatin is a biofactor with different biochemical and pharmacological properties whose effects attract much attention because it is an endogenous inhibitor of the monoamine oxidase in the brain. When exogenously administrated, isatin increases dopamine levels in intact and denervated striatum of rats, an effect that could indicate its potential as a therapeutic agent in Parkinson disease. However, the neurochemical mechanisms by which isatin increases dopamine in the striatum are poorly understood. In the present study, we evaluate the role of the glutamatergic and nitrergic systems in the isatin-induced dopamine release from rat striatum. Our findings show that the intrastriatal administration of 10 mM isatin significantly increases the in vivo release of dopamine (1,104.7% ± 97.1%), and the amino acids glutamate (428.7% ± 127%) and taurine (221% ± 22%) from rat striatum measured by brain microdialysis. The pretreatment with MK-801 (500 µM) or AP5 (650 µM) (glutamatergic NMDA receptors antagonists) significantly reduces the effect of isatin on dopamine release by 52% and 70.5%, respectively. The administration of the nitric oxide synthase inhibitors, L-NAME (100 µM) or 7-NI (100 µM) also decreases the isatin-induced dopamine release by 77% and 42%, respectively. These results show that isatin, in addition to increasing dopamine release, also increases glutamate levels, and possibly activates NMDA receptors and nitric oxide production, which can promote a further increase in the dopamine release.

Monoamine Oxidase Inhibitors: From Classic to New Clinical Approaches

Monoamine oxidases (MAOs) are involved in the oxidative deamination of different amines and neurotransmitters. This pointed them as potential targets for several disorders and along the last 70 years a wide variety of MAO inhibitors have been developed as successful drugs for the treatment of complex diseases, being the first drugs approved for depression in the late 1950s. The discovery of two MAO isozymes (MAO-A and B) with different substrate selectivity and tissue expression patterns led to novel therapeutic approaches and to the development of new classes of inhibitors, such as selective irreversible and reversible MAO-B inhibitors and reversible MAO-A inhibitors. Significantly, MAO-B inhibitors constitute a widely studied group of compounds, some of them approved for the treatment of Parkinson's disease. Further applications are under development for the treatment of Alzheimer's disease, amyotrophic lateral sclerosis, and cardiovascular diseases, among others. This review summarizes the most important aspects regarding the development and clinical use of MAO inhibitors, going through mechanistic and structural details, new indications, and future perspectives. Monoamine oxidases (MAOs) catalyze the oxidative deamination of different amines and neurotransmitters. The two different isozymes, MAO-A and MAO-B, are located at the outer mitochondrial membrane in different tissues. The enzymatic reaction involves formation of the corresponding aldehyde and releasing hydrogen peroxide (H₂O₂) and ammonia or a substituted amine depending on the substrate. MAO's role in neurotransmitter metabolism made them targets for major depression and Parkinson's disease, among other neurodegenerative diseases. Currently, these compounds are being studied for other diseases such as cardiovascular ones.

A Neuroprotective Dose of Isatin Causes Multilevel Changes Involving the Brain Proteome: Prospects for Further Research

Isatin (indole-2,3-dione) is an endogenous regulator, exhibiting a wide range of biological and pharmacological activities. At doses of 100 mg/kg and above, isatin is neuroprotective in different experimental models of neurodegeneration. Good evidence exists that its effects are realized via interaction with numerous isatin-binding proteins identified in the brain and peripheral tissues studied. In this study, we investigated the effect of a single dose administration of isatin to mice (100 mg/kg, 24 h) on differentially expressed proteins and a profile of the isatin-binding proteins in brain hemispheres. Isatin administration to mice caused downregulation of 31 proteins. However, these changes cannot be attributed to altered expression of corresponding genes. Although at this time point isatin influenced the expression of more than 850 genes in brain hemispheres (including 433 upregulated and 418 downregulated genes), none of them could account for the changes in the differentially expressed proteins. Comparative proteomic analysis of brain isatin-binding proteins of control and isatin-treated mice revealed representative groups of proteins sensitive to isatin administration. Control-specific proteins (n = 55) represent specific targets that interact directly with isatin. Appearance of brain isatin-binding proteins specific to isatin-treated mice (n = 94) may be attributed to the formation of new clusters of protein–protein interactions and/or novel binding sites induced by a high concentration of this regulator (ligand-induced binding sites). Thus, isatin administration produces multiple effects in the brain, which include changes in gene expression and also profiles of isatin-binding proteins and their interactomes. Further studies are needed for deeper insight into the mechanisms of the multilevel changes in the brain proteome induced by isatin. In the context of the neuroprotective action, these changes may be aimed at interruption of pathological links that begin to form after initiation of pathological processes.

Ubiquitin Subproteome of Brain Mitochondria and Its Changes Induced by Experimental Parkinsonism and Action of Neuroprotectors

The review summarizes the data of our research and published studies on the ubiquitination of brain mitochondrial proteins and its changes during the development of experimental parkinsonism and administration of the neuroprotector isatin (indole-2,3-dione) with special attention to the mitochondrial ubiquitin-conjugating system and location of ubiquitinated proteins in these organelles. Incubation of brain mitochondrial fraction with biotinylated ubiquitin in vitro resulted in the incorporation of biotinylated ubiquitin in both mitochondrial and mitochondria-associated proteins. According to the interactome analysis, the identified non-ubiquitinated proteins are able to form tight complexes with ubiquitinated proteins or their partners and components of mitochondrial membranes, in which interactions of ubiquitin chains with the ubiquitin-binding protein domains play an important role. The studies of endogenous ubiquitination in the total brain mitochondrial fraction of C57Bl mice performed in different laboratories have shown that mitochondrial proteins represent about 30% of all ubiquitinated proteins. However, comparison of brain subproteomes of mitochondrial ubiquitinated proteins reported in the literature revealed significant differences both in their composition and involvement of identified ubiquitinated proteins in biological processes listed in the Gene Ontology database. The development of experimental parkinsonism in C57Bl mice induced by a single-dose administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) resulted in a decrease in the total number of mitochondrial ubiquitinated proteins and increase in the number of oxidized mitochondrial proteins containing the ubiquitin signature (K-ε-GG). Comparison of ubiquitinated proteins associated with the mouse brain mitochondrial fraction and mouse brain mitochondrial proteins bound to the proteasome ubiquitin receptor (Rpn10 subunit) did not reveal any common proteins. This suggests that ubiquitination of brain mitochondrial proteins is not directly related to their degradation in the proteasomes. Proteomic profiling of brain isatin-binding proteins identified enzymes involved in the ubiquitin-conjugating system functioning. Mapping of the identified isatin-binding proteins to known metabolic pathways indicates their participation in the parkin (E3 ubiquitin ligase)-associated pathway (CH000000947). The functional links involving brain mitochondrial ubiquitinated proteins were found only in the group of animals with the MPTP-induced parkinsonism, but not in animals treated with MPTP/isatin or isatin only. This suggests that the neuroprotective effect of isatin may be associated with the impaired functional relationships of proteins targeted to subsequent degradation.

[The effect of neurotoxin MPTP administration to mice on the proteomic profile of brain isatin-binding proteins]

Isatin (indole-2,3-dione) is an endogenous indole found in the mammalian brain, peripheral organs and body fluids. It acts as a neuroprotector, which decreases manifestation of locomotor impairments in animal models of Parkinson's disease. A wide range of biological activity of isatin is associated with interaction of this regulator with numerous isatin-binding proteins. The aim of this study was to investigate the profile of brain isatin-binding proteins in mice with MPTP-induced Parkinsonism (90 min and seven days after administration of this neurotoxin). A single dose administration of MPTP (30 mg/kg, ip.) was accompanied by locomotor impairments in the open field test 90 min after administration; seven days after MPTP administration locomotor activity of mice significantly improved but did not reach the control level. Five independent experiments on proteomic profiling of isatin-binding proteins resulted in confident identification of 96±12 proteins. Development of MPTP-induced locomotor impairments was accompanied by a significant decrease in the number of isatin-binding proteins (63±6; n=5; p<0.01). Seven days after MPTP administration the total number of identified proteins increased and reached the control level (132±34; n=4). The profiles of isatin-binding proteins were rather specific for each group of mice: in the control group these proteins (which were not found in both groups of MPTP-treated mice) represented more than 70% of total proteins. In the case of MPTP treated mice this parameter was 60% (90 min after MPTP administration) and >82% (seven days after MPTP administration). The major changes were found in the groups of isatin-binding proteins involved into cytoskeleton formation and exocytosis, regulation of gene expression, cell division and differentiation and also proteins involved in signal transduction.

Characterization of acute intrastriatal effects of paraoxon on in vivo dopaminergic neurotransmission using microdialysis in freely moving rats

Paraoxon (POX) is an extremely neurotoxic organophosphorous compound (OP) which main toxic mechanism is the irreversible inhibition of cholinesterase. Although the cholinergic system has always been linked as responsible for its acute effects, experimental studies have suggested that the dopaminergic system also may be a potential target for OPs. Based on this, in this study, the acute intrastriatal effects of POX on dopaminergic neurotransmission were characterized in vivo using brain microdialysis in freely moving rats. In situ administration of POX (5, 25 and 50 nmol, 60 min) significantly increased the striatal dopamine overflow (to 435 ± 79%, 1066 ± 120%, and 1861 ± 332%, respectively), whereas a lower concentration (0.5 nmol) did not affect dopamine levels. Administration of POX (25 nmol) to atropine (15 nmol) pretreated animals, produced an increase in dopamine overflow that was ∼63% smaller than those observed in animals not pretreated. Administration of POX (25 nmol) to mecamylamine (35 nmol) pretreated animals did not significantly affect the POX-induced dopamine release. Our results suggest that acute administration of POX increases the dopamine release in a concentration-dependent way, being this release dependent on acetylcholinesterase inhibition and mediated predominantly by the activation of striatal muscarinic receptors, once the muscarinic antagonist atropine partially blocks the POX-induced dopamine release.

The Effect of Neurotoxin MPTP and Neuroprotector Isatin on the Profile of Ubiquitinated Brain Mitochondrial Proteins

Mitochondria are a crucial target for the actions of neurotoxins, causing symptoms of Parkinson's disease in various experimental animal models, and also neuroprotectors. There is evidence that mitochondrial dysfunction induced by the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) influences functioning of the ubiquitin-proteasomal system (UPS) responsible for selective proteolytic degradation of proteins from various intracellular compartments (including mitochondria) and neuroprotective effects of certain anti-Parkisonian agents (monoamine oxidase inhibitors) may be associated with their effects on the UPS. In this study, we have investigated the effect of the neurotoxin MPTP and neuroprotector isatin, and their combination on the profile of ubiquitinated brain mitochondrial proteins. The development of movement disorders induced by MPTP administration caused dramatic changes in the profile of ubiquitinated proteins associated with mitochondria. Pretreatment with the neuroprotector isatin decreased manifestations of MPTP-induced Parkinsonism, and had a significant impact on the profile of ubiquitinated mitochondrial proteins (including oxidative modified proteins). Administration of isatin alone to intact mice also influenced the profile of ubiquitinated mitochondrial proteins, and increased the proportion of oxidized proteins carrying the ubiquitination signature. These alterations in the ubiquitination of mitochondrial proteins observed within 2 h after administration of MPTP and isatin obviously reflect immediate short-term biological responses to these treatments.

Isatin, an endogenous nonpeptide biofactor: A review of its molecular targets, mechanisms of actions, and their biomedical implications

Isatin (indole-2,3-dione) is an oxidized indole. It is widely distributed in mammalian tissues and body fluids, where isatin concentrations vary significantly from <0.1 to > 10 µM. Isatin output is increased under conditions of stress. Exogenously administered isatin is characterized by low toxicity, mutagenicity, and genotoxicity in vivo. Cytotoxic effects of isatin on various cell cultures are usually observed at concentrations exceeding 100 µM. Binding of [³ H]isatin to rat brain sections is consistent with its physiological concentrations. Proteomic analysis of mouse and rat brain isatin-binding proteins revealed about 90 individual proteins, which demonstrated significant interspecies differences (rat versus mouse). Certain evidence exist that redox state(s) and possibly other types of posttranslational modifications regulate affinity of target proteins to isatin. Recent data suggest that interacting with numerous intracellular isatin binding proteins, isatin can act as a regulator of complex protein networks in norm and pathology. Physiological concentrations of isatin in vitro inhibit monoamine oxidase B and natriuretic peptide receptor guanylate cyclase, higher (neuroprotective) concentrations (50-400 μM) cause apoptosis of various (including malignant tumor) cell lines and influence expression of certain apoptosis-related genes. Being administered in vivo, isatin exhibits various behavioral effects; it attenuates manifestations of MPTP-induced parkinsonism and tumor growth in experimental animal models. © 2017 BioFactors, 44(2):95-108, 2018.

Ceruloplasmin is Involved in the Nigral Iron Accumulation of 6-OHDA-Lesioned Rats

Elevated iron levels in the substantia nigra (SN) participate in neuronal death in Parkinson's disease (PD), while the mechanisms underlying the increased iron are still unknown. Ceruloplasmin (CP), a ferroxidase, converts highly toxic ferrous iron to its non-toxic ferric form, which cooperated with ferroportin1 (FP1) facilitating the export of iron from cells. To elucidate if the abnormal expression of CP is involved in the nigral iron accumulation, here, we investigated CP expression in the SN of rats lesioned by 6-hydroxydopamine (6-OHDA). We showed that FP1 and CP colocalized in the rat SN. One day after 6-OHDA lesion, when there was a half reduction in the number of dopaminergic neurons, the iron level was increased compared with the normal rats; both the mRNA and protein expressions of CP decreased compared with the control. When rats began showing rotation behavior induced by apomorphine, usually after 6 weeks since 6-OHDA lesion, they are considered PD models. In these PD models, almost no dopaminergic neurons can be detected in the lesioned SN and nigral iron level was further increased. At this time point, a further decrease of CP was observed. These results show that FP1 and CP colocalize in the rat brain, indicating the coordinated actions of the two proteins in the cellular iron export, and suggest that decreased expression of CP in the SN is involved in the nigral iron accumulation of 6-OHDA-lesioned rats.

The effects of endogenous non-peptide molecule isatin and hydrogen peroxide on proteomic profiling of rat brain amyloid-β binding proteins: relevance to Alzheimer's disease?

The amyloid-β peptide is considered as a key player in the development and progression of Alzheimer’s disease (AD). Although good evidence exists that amyloid-β accumulates inside cells, intracellular brain amyloid-binding proteins remain poorly characterized. Proteomic profiling of rat brain homogenates, performed in this study, resulted in identification of 89 individual intracellular amyloid-binding proteins, and approximately 25% of them were proteins that we had previously identified as specifically binding to isatin, an endogenous neuroprotector molecule. A significant proportion of the amyloid-binding proteins (more than 30%) are differentially expressed or altered/oxidatively modified in AD patients. Incubation of brain homogenates with 70 µM hydrogen peroxide significantly influenced the profile of amyloid-β binding proteins and 0.1 mM isatin decreased the number of identified amyloid-β binding proteins both in control and hydrogen peroxide treated brain homogenates. The effects of hydrogen peroxide and isatin have been confirmed in optical biosensor experiments with purified glyceraldehyde-3-phosphate dehydrogenase, one of the known crucial amyloid-β binding proteins (also identified in this study). Data obtained suggest that isatin protects crucial intracellular protein targets against amyloid binding, and possibly favors intracellular degradation of this protein via preventing formation of amyloid-β oligomers described in the literature for some isatin derivatives.

Peptide hormone ghrelin enhances neuronal excitability by inhibition of Kv7/KCNQ channels

The gut-derived orexigenic peptide hormone ghrelin enhances neuronal firing in the substantia nigra pars compacta, where dopaminergic neurons modulate the function of the nigrostriatal system for motor coordination. Here we describe a novel mechanism by which ghrelin enhances firing of nigral dopaminergic neurons by inhibiting voltage-gated potassium Kv7/KCNQ/M-channels through its receptor GHS-R1a and activation of the PLC-PKC pathway. Brain slice recordings of substantia nigra pars compacta neurons reveal that ghrelin inhibits native Kv7/KCNQ/M-currents. This effect is abolished by selective inhibitors of GHS-R1a, PLC and PKC. Transgenic suppression of native Kv7/KCNQ/M-channels in mice or channel blockade with XE991 abolishes ghrelin-induced hyperexcitability. In vivo, intracerebroventricular ghrelin administration causes increased dopamine release and turnover in the striatum. Microinjection of ghrelin or XE991 into substantia nigra pars compacta results in contralateral dystonic posturing, and attenuation of catalepsy elicited by systemic administration of the D2 receptor antagonist haloperidol. Our findings indicate that the ghrelin/KCNQ signalling is likely a common pathway utilized by the nervous system.

Transplantation of mouse CGR8 embryonic stem cells producing GDNF and TH protects against 6-hydroxydopamine neurotoxicity in the rat

Embryonic stem cells (ESCs)-based therapies have been increasingly recognized as a potential tool to replace or support cells and their function damaged by the neurodegenerative process that underlies Parkinson's disease (PD). In this study, we implanted engineered mouse embryonic stem (ES) CGR8 cells, which stably co-express glial cell line-derived neurotrophic factor (GDNF) and tyrosine hydroxylase (TH), into striatum (Str) or both Str and substantia nigra (SN) of parkinsonian rats lesioned by 6-hydroxydopamine (6-OHDA). We found that cell transplantation into Str or both Str and SN rescued behavioral abnormalities and striatal DA depletion associated with 6-OHDA lesion. Our findings suggested that the profound functional impairment in nigrostriatal circuitry could be at least partially restored by ESCs-based expression of TH and GDNF, which may be developed into a useful tool for PD therapy.

L-type Cav1.2 calcium channel is involved in 6-hydroxydopamine-induced neurotoxicity in rats

Evidence suggested that L-type calcium channels may play a key role in the pathogenesis of dopaminergic neuron degeneration. In the present study, effects of L-type Cav1.2 calcium channel on 6-hydroxydopamine (6-OHDA)-induced neurotoxicity were investigated. By the semi-quantitative reverse transcription polymerase chain reaction (RT-PCR) studies, we showed that the expression of L-type Cav1.2 calcium channel α1 subunit mRNA increased in the substantia nigra (SN) of 6-OHDA-lesioned rats. Treatment with nifedipine could improve the apomorphine-induced rotation behavior in 6-OHDA-lesioned rats. Using high-performance liquid chromatography electrochemical detection, we also observed that nifedipine partly restored 6-OHDA-induced dopamine depletion in the striatum of rats. These results suggest that the L-type Cav1.2 calcium channel is associated with the development and progression of dopaminergic neuron degeneration.

Mitochondrial disfunction in Parkinson's disease

Mitochondrial structural and functional abnormalities in Parkinson's disease and experimental animal models of this pathology are described. Special attention is paid to the inactivation of mitochondrial enzymes, mutations in mitochondrial and nuclear DNA, and genomic and proteomic research of mitochondrial proteins in Parkinson's disease and experimental parkinsonism of animals.

Up-regulation of divalent metal transporter 1 in 6-hydroxydopamine intoxication is IRE/IRP dependent

Iron plays a key role in Parkinson's disease (PD). Increased iron content of the substantia nigra (SN) has been found in PD patients, and divalent metal transporter 1 (DMT1) has been shown to be up-regulated in the SN of both MPTP-induced PD models and PD patients. However, the mechanisms underlying DMT1 up-regulation are largely unknown. In the present study, we observed that in the SN of 6-hydroxydopamine (6-OHDA)-induced PD rats, DMT1 with the iron responsive element (IRE, DMT1+IRE), but not DMT1 without IRE (DMT1-IRE), was up-regulated, suggesting that increased DMT1+IRE expression might account for nigral iron accumulation in PD rats. This possibility was further assessed in an in vitro study using 6-OHDA-treated and DMT1+IRE-over-expressing MES23.5 cells. In 6-OHDA-treated MES23.5 cells, increased iron regulatory protein (IRP) 1 and IRP2 expression was observed, while silencing of IRPs dramatically diminished 6-OHDA-induced DMT1+IRE up-regulation. Pretreatment with N-acetyl-L-cysteine fully suppressed IRPs up-regulation by inhibition of 6-OHDA-induced oxidative stress. Increased DMT1+IRE expression resulted in increased iron influx by MES23.5 cells. Our data provide direct evidence that DMT1+IRE up-regulation can account for IRE/IRP-dependent 6-OHDA-induced iron accumulation initiated by 6-OHDA-induced intracellular oxidative stress and that increased levels of intracellular iron result in aggravated oxidative stress. The results of this study provide novel evidence supporting the use of anti-oxidants in the treatment of PD, with the goal of inhibiting iron accumulation by regulation of DMT1 expression.

Ferroportin1 and hephaestin are involved in the nigral iron accumulation of 6-OHDA-lesioned rats

Elevated iron levels in the substantia nigra (SN) participate in neuronal death in Parkinson's disease (PD). While the mechanisms underlying the increased iron are still unknown, some iron transport proteins may be involved. The nigral iron accumulation could be a result of either increased import or decreased export. The mechanisms of iron import have received considerable attention, but little is known about iron export mechanisms. Ferroportin1 (FP1) and hephaestin (HP), two newly discovered iron export proteins, cooperate in the iron export in the gut. Here, we investigated their expression in the SN of rats lesioned by 6-hydroxydopamine (6-OHDA). Using immunofluorescence, we showed that FP1 and HP were both expressed on astrocytes, microglia, oligodendrocytes and neurons in the SN. By immunohistochemistry, we showed that 1 day after 6-OHDA lesion, the expression of the two proteins decreased compared with the control. When rats began showing rotation behaviour induced by apomorphine, usually 6 weeks after 6-OHDA lesion, they are considered PD models. In these PD models, a further decrease in the two proteins was observed. Reverse transcriptase-polymerase chain reaction showed that the mRNA levels of FP1 and HP decreased 1 day after 6-OHDA lesion compared with the control, and further decrease was also observed in the PD model rats. These results show for the first time that FP1 and HP co-localize in the rat brain, and suggest that decreased expression of these transporters in the SN can account for the increased iron levels.

Controlled cortical impact injury affects dopaminergic transmission in the rat striatum

The therapeutic benefits of dopamine (DA) agonists after traumatic brain injury (TBI) imply a role for DA systems in mediating functional deficits post-TBI. We investigated how experimental TBI affects striatal dopamine systems using fast scan cyclic voltammetry (FSCV), western blot, and d-amphetamine-induced rotational behavior. Adult male Sprague-Dawley rats were injured by a controlled cortical impact (CCI) delivered unilaterally to the parietal cortex, or were naïve controls. Amphetamine-induced rotational behavior was assessed 10 days post-CCI. Fourteen days post-CCI, animals were anesthetized and underwent FSCV with bilateral striatal carbon fiber microelectrode placement and stimulating electrode placement in the medial forebrain bundle (MFB). Evoked DA overflow was assessed in the striatum as the MFB was electrically stimulated at 60 Hz for 10 s. In 23% of injured animals, but no naïve animals, rotation was observed with amphetamine administration. Compared with naïves, striatal evoked DA overflow was lower for injured animals in the striatum ipsilateral to injury (p < 0.05). Injured animals exhibited a decrease in V(max) (52% of naïve, p < 0.05) for DA clearance in the hemisphere ipsilateral to injury compared with naïves. Dopamine transporter (DAT) expression was proportionally decreased in the striatum ipsilateral to injury compared with naïve animals (60% of naïve, p < 0.05), despite no injury-related changes in vesicular monoamine transporter or D2 receptor expression (DRD2) in this region. Collectively, these data appear to confirm that the clinical efficacy of dopamine agonists in the treatment of TBI may be related to disruptions in the activity of subcortical dopamine systems.

Isatin: role in stress and anxiety

(Indoledione 2,3) isatin is an endogenous indole found both in mammalian brain and peripheral tissues. Isatin concentration in blood can exceed 1 microM and tissue concentrations vary from < 0.1 to 10 microM. Its level in the brain and periphery is increased by stress. Isatin has a wide spectrum of behavioural and metabolic effects. It is anxiogenic at lower doses and sedative at higher doses. Its most potent known in vitro actions are as an antagonist of atrial natriuretic peptide (ANP) function and NO signaling. In this review, we discuss isatin and stress in animal models, the few human studies, and also what it is known to date about the molecular mechanisms of its action. We suggest the possibility that isatin and its analogues may be interesting new pharmacological agents; Isatin antagonists may be anxiolytic, and isatin agonists may activate the HPA axis.

Time dependent effects of 6-OHDA lesions on iron level and neuronal loss in rat nigrostriatal system

The early changes in iron level and neuronal loss in rat nigrostriatal system were investigated using 6-hydroxydopamine (6-OHDA) unilaterally lesioned rats. The results showed that: 1, 3, 5, 7, and 14 days of postlesion, there was a progressive reduction in the density of the tyrosine hydroxylase immunoreactive (TH-ir) cells in the lesioned substantia nigra (SN). Iron level increased in the lesioned SN from 1-14 days following 6-OHDA lesions, but there were no differences in iron level among them. Only on 14 days of postlesion, did the DA release decrease in striatum (Str) of the lesioned side, while there were no changes in other groups. These results implied that the increased iron level in SN occured when there was a moderate reduction of DA neurons. However, the DA release in Str was unchanged until TH-ir cells were highly reduced due to the immense compensatory mechanism of the DA system.

Dopamine release rather than content in the caudate putamen is associated with behavioral changes in the iron rat model of Parkinson's disease

The effects of intranigral iron injection on dopamine (DA) release and content in the caudate putamen (CPu) and their relationship to DA-related behavioral response were investigated in rats. Different concentrations of FeCl(3) (10, 20, and 40 microg) and saline were injected separately into the left substantia nigra. In some experiments, rats were pretreated with desferrioxamine or saline before iron injection. After 3 weeks, changes in behavioral response, DA release, and DA content in the CPu were determined. In all iron injection groups (10, 20, and 40 microg), DA content in the lesioned side of the brain was significantly decreased, showing a significant linear correlation (R(2) = 0.981, P = 0.01), and DA turnover ratio significantly increased (both P = 0.01, 0.01 and 0.001 vs unlesioned sides, respectively). However, injection dosages of 10 or 20 microg of iron did not lead to significant changes in DA release in the CPu or in behavioral response. At the 40-microg dosage, it was found that DA release in the lesioned side and rearing activity both were significantly reduced (all P = 0.01 vs unlesioned side or control) and apomorphine-induced rotation was observed. Pretreatment with desferrioxamine significantly inhibited the effect of iron on DA release and content. These results demonstrate that iron injection can damage dopaminergic neurons and suggest that DA release, rather than DA content, in the CPu is associated with DA-related behavioral changes in this PD model.