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Parkinson's disease (PD) is the second most common neurodegenerative disease worldwide. The loss of nigrostriatal dopaminergic neurons produces its characteristic motor symptoms, but PD patients also have non-motor symptoms such as constipation and orthostatic hypotension. The pathological hallmark of PD is the presence of α-synuclein-containing Lewy bodies and neurites in the brain. However, the PD pathology is observed in not only the central nervous system (CNS) but also in parts of the peripheral nervous system such as the enteric nervous system (ENS). Since constipation is a typical prodromal non-motor symptom in PD, often preceding motor symptoms by 10-20 years, it has been hypothesized that PD pathology propagates from the ENS to the CNS via the vagal nerve. Discovery of pharmacological and other methods to halt this progression of neurodegeneration in PD has the potential to improve millions of lives. Astrocytes protect neurons in the CNS by secretion of neurotrophic and antioxidative factors. Similarly, astrocyte-like enteric glial cells (EGCs) are known to secrete neuroprotective factors in the ENS. In this article, we summarize the neuroprotective function of astrocytes and EGCs and discuss therapeutic strategies for the prevention of neurodegeneration in PD targeting neurotrophic and antioxidative molecules in glial cells.

Anxiety-like behavior induced by a combination of doxorubicin and cyclophosphamide may be mediated by serotonin (5-HT)2A receptor hyperactivity. The anxiolytic effects of fluoxetine may be inhibited by this combination. The present study examined the mechanisms underlying anxiety-like behavior induced by the combination doxorubicin and cyclophosphamide in rats. Anxiety-like behavior was induced during a light–dark test by the doxorubicin and cyclophosphamide treatment (once a week for 2 weeks). 5-HT2A receptor and 5-HT2A receptor-mediated extracellular signal-related kinase (ERK)1/2 levels were measured using Western blotting. 5-HT reuptake activity in fluoxetine-treated rats was also examined using microdialysis. ( ±)-1-(2,5-Dimethoxy-4-iodophenyl)-2-aminopropane, a 5-HT2A receptor agonist, induced anxiety-like behavior. The fluoxetine treatment increased extracellular 5-HT concentrations in the hippocampus of vehicle- and doxorubicin and cyclophosphamide-treated rats. 5-HT transporter levels in the hippocampus were not affected by chemotherapy. The doxorubicin and cyclophosphamide treatment did not alter 5-HT2A receptor levels in the frontal cortex. However, chemotherapy increased 5-HT2A receptor-mediated ERK1/2 phosphorylation levels significantly more than the vehicle treatment. The present results suggest that anxiety-like behavior induced by the combination of doxorubicin and cyclophosphamide is mediated by 5-HT2A receptor hyperactivity without an increase in 5-HT2A receptor levels in rats.

Background: Cancer patients can suffer from psychological and cognitive disorders after chemotherapy, which influence quality of life. Objective: Oxidative stress may contribute to the psychological and cognitive disorders induced in rats by chemotherapy. In the present study, we examined the effects of N-acetylcysteine, an anti-oxidant, on anxiety-like behavior and cognitive impairment in rats treated with a combination of doxorubicin and cyclophosphamide. Methods: Rats were intraperitoneally injected with doxorubicin and cyclophosphamide once a week for 2 weeks. The light-dark test and the novel location recognition test were used to assess anxiety-like behavior and spatial cognition, respectively. The rats’ hippocampal levels of glutathione (GSH) and glutathione disulfide (GSSG) were measured using a GSSG/GSH quantification kit. Results: Combined treatment with doxorubicin and cyclophosphamide produced anxiety-like behavior and cognitive impairment in rats. N-acetylcysteine reversed the anxiety-like behavior and inhibition of novel location recognition induced by the combination treatment. Furthermore, the combination of doxorubicin and cyclophosphamide significantly reduced the rats’ hippocampal GSH/GSSG ratios. N-acetylcysteine reversed the reduction in the GSH/GSSG ratio seen in the doxorubicin and cyclophosphamide-treated rats. Conclusion: These results suggest that N-acetylcysteine inhibits doxorubicin and cyclophosphamide-induced anxiety-like behavior and cognitive impairment by reducing oxidative stress in the hippocampus.

Parkinson’s disease (PD) is a complex, multi-system, neurodegenerative disorder; PD patients exhibit motor symptoms (such as akinesia/bradykinesia, tremor, rigidity, and postural instability) due to a loss of nigrostriatal dopaminergic neurons, and non-motor symptoms such as hyposmia, autonomic disturbance, depression, and REM sleep behavior disorder (RBD), which precedes motor symptoms. Pathologically, α-synuclein deposition is observed in the central and peripheral nervous system of sporadic PD patients. To clarify the mechanism of neurodegeneration in PD and to develop treatment to slow or stop PD progression, there is a great need for experimental models which reproduce neurological features of PD. Animal models exposed to rotenone, a commonly used pesticide, have received most attention since Greenamyre and his colleagues reported that chronic exposure to rotenone could reproduce the anatomical, neurochemical, behavioral, and neuropathological features of PD. In addition, recent studies demonstrated that rotenone induced neuropathological change not only in the central nervous system but also in the peripheral nervous system in animals. In this article, we review rotenone models especially focused on reproducibility of central and peripheral multiple features of PD. This review also highlights utility of rotenone models for investigation of PD pathogenesis and development of disease-modifying drugs for PD in future.

The aim of this study was to evaluate the neurotoxicity of psychoactive abused 2,5-dimethoxy-substituted phenethylamines “2C series” in monoaminergic neurons. After the exposure to “2C series”, 2,5-dimethoxy-4-propylthiophenethylamine (2C-T-7), 2,5-dimethoxy-4-isopropylthiophenethylamine (2C-T-4), 2,5-dimethoxy-4-ethylthiophenthylamine (2C-T-2), 2,5-dimethoxy-4-iodophenethylamine (2C-I) or 2,5-dimethoxy-4-chlorophenethylamine (2C-C), we examined their neurotoxicity, morphological changes, and effects of concomitant exposure to 3,4-methylenedioxymethamphetamine (MDMA) or methamphetamine (METH), using cultured neuronal dopaminergic CATH.a cells and serotonin-containing B65 cells. Single dose exposure to “2C series” for 24 h showed significant cytotoxicity as increase in lactate dehydrogenase (LDH) release from both monoaminergic neurons: 2C-T-7, 2C-C (EC50; 100 µM) > 2C-T-2 (150 µM), 2C-T-4 (200 µM) > 2C-I (250 µM) in CATH.a cells and 2C-T-7, 2C-I (150 µM) > 2C-T-2 (250 µM) > 2C-C, 2C-T-4 (300 µM) in B65 cells. The “2C series”-induced neurotoxicity in both cells was higher than that of MDMA or METH (EC50: ≥ 1–2 mM). In addition, apoptotic morphological changes were observed at relatively lower concentrations of “2C series”. The concomitant exposure to non-toxic dose of MDMA or METH synergistically enhanced 2C series drugs-induced LDH release and apoptotic changes in B65 cells, but to a lesser extent in CATH.a cells. In addition, the lower dose of 2C-T-7, 2C-T-2 or 2C-I promoted reactive oxygen species production in the mitochondria of B65 cells, even at the early stages (3 h) without apparent morphological changes. The 2,5-dimethoxy-substitution of “2C series” induced severe neurotoxicity in both dopaminergic and serotonin-containing neurons. The non-toxic dose of MDMA or METH synergistically enhanced its neurotoxicity in serotonergic neurons.

High mobility group box-1 (HMGB1) is a ubiquitous non-histone nuclear protein that plays a key role as a transcriptional activator, with its extracellular release provoking inflammation. Inflammatory responses are essential in methamphetamine (METH)-induced acute dopaminergic neurotoxicity. In the present study, we examined the effects of neutralizing anti-HMGB1 monoclonal antibody (mAb) on METH-induced dopaminergic neurotoxicity in mice. BALB/c mice received a single intravenous administration of anti-HMGB1 mAb prior to intraperitoneal injections of METH (4 mg/kg × 2, at 2-h intervals). METH injections induced hyperthermia, an increase in plasma HMGB1 concentration, degeneration of dopaminergic nerve terminals, accumulation of microglia, and extracellular release of neuronal HMGB1 in the striatum. These METH-induced changes were significantly inhibited by intravenous administration of anti-HMGB1 mAb. In contrast, blood–brain barrier disruption occurred by METH injections was not suppressed. Our findings demonstrated the neuroprotective effects of anti-HMGB1 mAb against METH-induced dopaminergic neurotoxicity, suggesting that HMGB1 could play an initially important role in METH toxicity.

Anxiety-like behavior induced by a combination of doxorubicin and cyclophosphamide may be mediated by serotonin (5-HT)

Recently, it has been reported that dysfunction of astrocytes is involved vulnerability of neuronal cells in several neurological disorders. Glutathione (GSH) is the most abundant intrinsic antioxidant in the central nervous system, and its substrate cysteine is readily becomes the oxidized dimeric cystine. Since neurons lack a cystine transport system, neuronal GSH synthesis depends on cystine uptake via the cystine/glutamate exchange transporter (xCT), GSH synthesis and release in/from surrounding astrocytes. The expression and release of the zinc-binding protein metallothionein (MT) in astrocytes, which is a strong antioxidant, is induced and exerts neuroprotective in the case of dopaminergic neuronal damage. In addition, the transcription factor Nrf2 induces expression of MT-1 and GSH related molecules. We previously revealed that several antiepileptic drugs, serotonin 5-HT1A receptor agonists, plant-derived chemicals (phytochemicals) increased xCT expression, Nrf2 activation, GSH or MT expression and release in/from astrocytes, and exerted a neuroprotective effect against dopaminergic neurodegeneration in Parkinson's disease model. Our serial studies on neuroprotection via antioxidant defense mechanism of astrocytes have found three target molecular systems of astrocytes for neuroprotection: (1) xCT-GSH synthetic system, (2) Nrf2 system and (3) 5-HT1A receptor-Nrf2-MT system, 5-HT1A-S100β system. In this article, possible neuroprotective strategy for Parkinson's disease has been reviewed targeting antioxidative molecules in astrocytes.

Parkinson’s disease (PD) is the second most common neurodegenerative disease. PD patients exhibit motor symptoms such as akinesia/bradykinesia, tremor, rigidity, and postural instability due to a loss of nigrostriatal dopaminergic neurons. Although the pathogenesis in sporadic PD remains unknown, there is a consensus on the involvement of non-neuronal cells in the progression of PD pathology. Astrocytes are the most numerous glial cells in the central nervous system. Normally, astrocytes protect neurons by releasing neurotrophic factors, producing antioxidants, and disposing of neuronal waste products. However, in pathological situations, astrocytes are known to produce inflammatory cytokines. In addition, various studies have reported that astrocyte dysfunction also leads to neurodegeneration in PD. In this article, we summarize the interaction of astrocytes and dopaminergic neurons, review the pathogenic role of astrocytes in PD, and discuss therapeutic strategies for the prevention of dopaminergic neurodegeneration. This review highlights neuron-astrocyte interaction as a target for the development of disease-modifying drugs for PD in the future.

Crossed cerebellar diaschisis (CCD) is a state of hypoperfusion and hypometabolism in the contralesional cerebellar hemisphere caused by a supratentorial lesion, but its pathophysiology is not fully understood. We evaluated chronological changes in cerebellar blood flow (CbBF) and gene expressions in the cerebellum using a rat model of transient middle cerebral artery occlusion (MCAO). CbBF was analyzed at two and seven days after MCAO using single photon emission computed tomography (SPECT). DNA microarray analysis and western blotting of the cerebellar cortex were performed and apoptotic cells in the cerebellar cortex were stained. CbBF in the contralesional hemisphere was significantly decreased and this lateral imbalance recovered over one week. Gene set enrichment analysis revealed that a gene set for &ldquo, oxidative phosphorylation&rdquo, was significantly upregulated while fourteen other gene sets including &ldquo, apoptosis&rdquo, &ldquo, hypoxia&rdquo, and &ldquo, reactive oxygen species&rdquo, showed a tendency toward upregulation in the contralesional cerebellum. MCAO upregulated the expressions of nuclear factor erythroid 2-related factor 2 (Nrf2) and heme oxygenase-1 (HO-1) in the contralesional cerebellar cortex. The number of apoptotic cells increased in the molecular layer of the contralesional cerebellum. Focal cerebral ischemia in our rat MCAO model caused CCD along with enhanced expression of genes related to oxidative stress and apoptosis.

Bisphenol A diglycidyl ether (BADGE) is an epoxy resin used for the inner coating of canned food and beverages. BADGE can easily migrate from the containers and become a contaminant. In this study, we examined the effects of BADGE exposure to the dams on the behavioral, structural, and developmental abnormalities in the offspring. Female pregnant mice were fed with a diet containing BADGE (0.15 or 1.5 mg/kg/day) during gestation and lactation periods. In an open field test, the time spent in the corner area significantly increases in male mice of high-dose BADGE group at 5 weeks old. The histological analysis using offspring brain at postnatal day 1 delivered from BADGE (1.5 mg/kg/day)-treated dams demonstrates that positive signals of Forkhead box P2- and COUP-TF interacting protein 2 are restricted in each cortical layer, but not in the control brain. In addition, the maternal BADGE exposure reduces nestin-positive fibers of the radial glia and T-box transcription factor 2-positive intermediate progenitors in the inner subventricular zone. Furthermore, a direct BADGE exposure promotes neurite outgrowth and neuronal connection in the primary cultured cortical neurons. These data suggest that maternal BADGE exposure can accelerate neuronal differentiation in fetuses and induce anxiety-like behavior in juvenile mice.

We examined whether combination treatment with doxorubicin and cyclophosphamide, a traditional chemotherapy for breast cancer, induced anxiety-like behavior in rats. Furthermore, we evaluated the role of the serotonin (5-HT)2A receptor subtype in the anxiety-like behavior induced by such chemotherapy. Rats were intraperitoneally injected with doxorubicin and cyclophosphamide once a week for 2 weeks. This caused the rats to display anxiety-like behavior during the light–dark test. In addition, we examined the rats' 5-HT2A receptor-mediated behavioral responses. Combination treatment with doxorubicin and cyclophosphamide significantly increased (±)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane, (a 5-HT2A receptor agonist)-induced wet-dog shake activity. This anxiety-like behavior was significantly inhibited by mirtazapine, a 5-HT2A receptor antagonist/5-HT1A receptor agonist, and tandospirone, a partial 5-HT1A receptor agonist, but not by fluoxetine, a selective serotonin reuptake inhibitor. The anxiety-like behavior induced by doxorubicin and cyclophosphamide combination treatment is mediated by hyperfunctioning of the 5-HT2A receptor. Thus, 5-HT2A receptor antagonists or 5-HT1A receptor agonists might be useful for treating chemotherapy-induced anxiety disorders. Keywords: Doxorubicin, Cyclophosphamide, 5-HT2A receptor, Anxiety

Glutathione (GSH) is the most abundant intrinsic antioxidant in the central nervous system, and its substrate cysteine readily becomes the oxidized dimeric cystine. Since neurons lack a cystine transport system, neuronal GSH synthesis depends on cystine uptake via the cystine/glutamate exchange transporter (xCT), GSH synthesis, and release in/from surrounding astrocytes. Transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2), a detoxifying master transcription factor, is expressed mainly in astrocytes and activates the gene expression of various phase II drug-metabolizing enzymes or antioxidants including GSH-related molecules and metallothionein by binding to the antioxidant response element (ARE) of these genes. Accumulating evidence has shown the involvement of dysfunction of antioxidative molecules including GSH and its related molecules in the pathogenesis of Parkinson’s disease (PD) or parkinsonian models. Furthermore, we found several agents targeting GSH synthesis in the astrocytes that protect nigrostriatal dopaminergic neuronal loss in PD models. In this article, the neuroprotective effects of supplementation and enhancement of GSH and its related molecules in PD pathology are reviewed, along with introducing new experimental findings, especially targeting of the xCT-GSH synthetic system and Nrf2–ARE pathway in astrocytes.

Nitric oxide (NO) is a key signaling molecule that has various effects via S-nitrosylation, a reversible post-translational modification that affects the enzymatic activity, localization, and metabolism of target proteins. As chronic nitrosative stress correlates with neurodegeneration, the targets have received focused attention. Macrophage migration inhibitory factor (MIF) plays a pivotal role in the induction of gene expression to control inflammatory responses. MIF acts as a ligand for CD74 receptor and activates the Src-p38 mitogen-activated protein kinase (MAPK) cascade. MIF also elevates the expression of brain-derived neurotrophic factor (BDNF), which contributes to the viability of neurons. Here, we show that MIF is S-nitrosylated by a physiological NO donor. Interestingly, the induction of S-nitrosylation resulted in a loss of MIF activity following stimulation of the Src and p38 MAPK signaling pathways and the induction of BDNF expression. Our results shed light on the pathogenic mechanisms of neurodegenerative diseases, such as Alzheimer's disease and Parkinson's disease.

In previous studies, we found regional differences in the induction of antioxidative molecules in astrocytes against oxidative stress, postulating that region-specific features of astrocytes lead region-specific vulnerability of neurons. We examined region-specific astrocytic features against dopaminergic neurotoxin 6-hydroxydopamine (6-OHDA) as an oxidative stress using co-culture of mesencephalic neurons and mesencephalic or striatal astrocytes in the present study. The 6-OHDA-induced reduction of mesencephalic dopamine neurons was inhibited by co-culturing with astrocytes. The co-culture of midbrain neurons with striatal astrocytes was more resistant to 6-OHDA than that with mesencephalic astrocytes. Furthermore, glia conditioned medium from 6-OHDA-treated striatal astrocytes showed a greater protective effect on the 6-OHDA-induced neurotoxicity and oxidative stress than that from mesencephalic astrocytes. The cDNA microarray analysis showed that the number of altered genes in both mesencephalic and striatal astrocytes was fewer than that changed in either astrocyte. The 6-OHDA treatment, apparently up-regulated expressions of Nrf2 and some anti-oxidative or Nrf2-regulating phase II, III detoxifying molecules related to glutathione synthesis and export in the striatal astrocytes but not mesencephalic astrocytes. There is a profound regional difference of gene expression in astrocytes induced by 6-OHDA. These results suggest that protective features of astrocytes against oxidative stress are more prominent in striatal astrocytes, possibly by secreting humoral factors in striatal astrocytes.

In previous studies, we detected the photoinitiators 1-hydroxycyclohexyl phenyl ketone (1-HCHPK) and 2-methyl-4'-(methylthio)-2-morpholinopropiophenone (MTMP) in an intravenous injection solution. Importantly, 1-HCHPK and MTMP have been demonstrated to be cytotoxic to normal human peripheral blood (PB) mononuclear cells (MNC). Cell death (apoptosis) pathways can be classified into two modes, caspase-dependent and -independent pathways. However, it is unclear whether methyl 2-benzoylbenzoate (MBB) induces the caspase-dependent and/or -independent pathway in normal human PBMNC. In the present in vitro study, we examined the levels of MBB in a solution from an intravenous fluid bag and the cytotoxicity of MBB towards normal human PBMNC via the caspase-8-, caspase-9-, or apoptosis-inducing factor (AIF)-mediated apoptosis pathways. We found that extracts from the injection solution had been contaminated with approximately 80 μM of the photoinitiator MBB. In addition, MBB induced apoptosis in the high concentration range in normal human PBMNC in vitro. Moreover, we found that MBB-induced apoptosis occurs via the caspase-9 pathway, but not the AIF pathway. In conclusion, we suggest that MBB has cytotoxic effects on normal human PBMNC in vitro, which are mediated via the caspase-dependent pathway.

l-Theanine (γ-glutamylethylamide), a component of green tea, is considered to have regulatory and neuroprotective roles in the brain. The present study was designed to determine the effect of l-theanine on excess dopamine-induced neurotoxicity in both cell culture and animal experiments. The primary cultured mesencephalic neurons or co-cultures of mesencephalic neurons and striatal astrocytes were pretreated with l-theanine for 72 h, and then treated with excess dopamine for further 24 h. The cell viability of dopamine neurons and levels of glutathione were evaluated. Excess dopamine-induced neurotoxicity was significantly attenuated by 72 h preincubation with l-theanine in neuron-astrocyte co-cultures but not in neuron-rich cultures. Exposure to l-theanine increased the levels of glutathione in both astrocytes and glial conditioned medium. The glial conditioned medium from l-theanine-pretreated striatal astrocytes attenuated dopamine-induced neurotoxicity and quinoprotein formation in mesencephalic neurons. In addition, replacement of l-glutamate with l-theanine in an in vitro cell-free glutathione-synthesis system produced glutathione-like thiol compounds. Furthermore, l-theanine administration (4 mg/kg, p.o.) for 14 days significantly increased glutathione levels in the striatum of mice. The results suggest that l-theanine provides neuroprotection against oxidative stress-induced neuronal damage by humoral molecules released from astrocytes, probably including glutathione.

Mirtazapine, a noradrenergic and specific serotonergic antidepressant (NaSSA), is known to activate serotonin (5-HT) 1A receptor. Our recent study demonstrated that stimulation of astrocytic 5-HT1A receptors promoted astrocyte proliferation and upregulated antioxidative property in astrocytes to protect dopaminergic neurons against oxidative stress. Here, we evaluated the neuroprotective effects of mirtazapine against dopaminergic neurodegeneration in models of Parkinson’s disease (PD). Mirtazapine administration attenuated the loss of dopaminergic neurons in the substantia nigra and increased the expression of the antioxidative molecule metallothionein (MT) in the striatal astrocytes of 6-hydroxydopamine (6-OHDA)-injected parkinsonian mice via 5-HT1A receptors. Mirtazapine protected dopaminergic neurons against 6-OHDA-induced neurotoxicity in mesencephalic neuron and striatal astrocyte cocultures, but not in enriched neuronal cultures. Mirtazapine-treated neuron-conditioned medium (Mir-NCM) induced astrocyte proliferation and upregulated MT expression via 5-HT1A receptors on astrocytes. Furthermore, treatment with medium from Mir-NCM-treated astrocytes protected dopaminergic neurons against 6-OHDA neurotoxicity, and these effects were attenuated by treatment with a MT-1/2-specific antibody or 5-HT1A antagonist. Our study suggests that mirtazapine could be an effective disease-modifying drug for PD and highlights that astrocytic 5-HT1A receptors may be a novel target for the treatment of PD.

Epidemiological studies demonstrated that pesticide exposure, such as rotenone and paraquat, increases the risk of Parkinson&rsquo, s disease (PD). Chronic systemic exposure to rotenone, a mitochondrial complex I inhibitor, could reproduce many features of PD. However, the adoption of the models is limiting because of variability in animal sensitivity and the inability of other investigators to consistently reproduce the PD neuropathology. In addition, most of rotenone models were produced in rats. Here, we tried to establish a high-reproducible rotenone model using C57BL/6J mice. The rotenone mouse model was produced by chronic systemic exposure to a low dose of rotenone (2.5 mg/kg/day) for 4 weeks by subcutaneous implantation of rotenone-filled osmotic mini pump. The rotenone-treated mice exhibited motor deficits assessed by open field, rotarod and cylinder test and gastrointestinal dysfunction. Rotenone treatment decreased the number of dopaminergic neuronal cells in the substantia nigra pars compacta (SNpc) and lesioned nerve terminal in the striatum. In addition, we observed significant reduction of cholinergic neurons in the dorsal motor nucleus of the vagus (DMV) and the intestinal myenteric plexus. Moreover, &alpha, synuclein was accumulated in neuronal soma in the SNpc, DMV and intestinal myenteric plexus in rotenone-treated mice. These data suggest that the low-dose rotenone mouse model could reproduce behavioral and central and peripheral neurodegenerative features of PD and be a useful model for investigation of PD pathogenesis.

Astrocytes exert neuroprotective effects through production of antioxidant molecules and neurotrophic factors. A recent study showed that stimulation of astrocyte serotonin 1A (5-HT1A) receptors promotes astrocyte proliferation and upregulation of the antioxidant molecules metallothionein (MT)-1,2, which protect dopaminergic neurons against oxidative stress. Rotigotine, an anti-parkinsonian drug, can bind to dopamine and 5-HT1A receptors. In this study, we examined neuroprotective effects of rotigotine in models of Parkinson's disease and involvement of astrocyte 5-HT1A receptors in neuroprotective effects of rotigotine against dopaminergic neurodegeneration. Rotigotine increased the number of astrocytes and MT-1,2 expression in cultured astrocytes. Pretreatment with conditioned media from rotigotine-treated astrocytes significantly inhibited 6-hydroxydopamine (6-OHDA)-induced dopaminergic neurotoxicity. These effects were completely blocked by a 5-HT1A antagonist or MT-1,2 specific antibody. Subcutaneous administration of rotigotine increased MT-1,2 expression in striatal astrocytes and prevented reduction of dopaminergic neurons in the substantia nigra of a 6-OHDA-lesioned mouse model of Parkinson's disease. These effects were blocked by co-administration with a 5-HT1A antagonist. These results suggest that rotigotine exerts neuroprotective effects through upregulation of MT expression in astrocytes by targeting 5-HT1A receptors. Our findings provide a possible therapeutic application of rotigotine to prevent dopaminergic neurodegeneration in Parkinson's disease.

Parkinson's disease (PD) is a progressive neurodegenerative disease with motor symptoms, such as tremor, akinesia/bradykinesia, rigidity and postural instability due to a loss of nigrostriatal dopaminergic neurons; PD patients also exhibit non-motor symptoms, such as hyposmia, orthostatic hypotension and constipation, which precede motor symptoms. Pathologically, Lewy bodies and neurites, which contains α-synuclein, are observed in the central and peripheral nervous system. To date, it is hypothesized that PD pathology appears first in the olfactory bulb and the enteric nervous system, and propagates progressively through the substantia nigra to finally reach the cerebral cortex. Major medications at present are nosotropic treatments to improve motor dysfunction in PD. Therefore, development of disease-modifying drug is required to slow or prevent PD progression. Astrocytes are known to play an important role in the maintenance of the neuronal environment and exert neuroprotective effects by production of antioxidants and neurotrophic factors and clearing toxic molecules. In the previous study, we demonstrated that astrocytes produced antioxidative molecules metallothionein (MT)-1/2 in response to oxidative stress and protected dopaminergic neurons against oxidative stress. MTs are cysteine-rich proteins possessing antioxidative properties. MTs bind to metals such as zinc (Zn) and copper (Cu) and function in metal homeostasis and detoxification; MTs regulate Zn-mediated transcriptional activation of various genes. Recently, it is reported that MTs prevent Cu-induced aggregation of α-synuclein. In this article, we review a new therapeutic strategy of neuroprotection in PD by targeting MTs in astrocytes.

Many patients who have received chemotherapy to treat cancer experience depressive- and anxiety-like symptoms or cognitive impairment. However, despite the evidence for this, the underlying mechanisms are still not understood. This study investigated behavioral and biochemical changes upon treatment with doxorubicin and cyclophosphamide, focusing on mental and cognitive systems, as well as neurogenesis in male rats. Doxorubicin (2 mg/kg), cyclophosphamide (50 mg/kg), and the combination of doxorubicin and cyclophosphamide were injected intraperitoneally once per week for 4 weeks. In particular, the co-administration of doxorubicin and cyclophosphamide produced anhedonia-like, anxiety-like, and spatial cognitive impairments in rats. It also reduced both the number of proliferating cells in the subgranular zone of the hippocampal dentate gyrus and their survival. Serum brain-derived neurotrophic factor (BDNF) levels were decreased along with chemotherapy-induced decreases in platelet levels. However, hippocampal BDNF levels and Bdnf mRNA levels were not decreased by this treatment. On the other hand, hippocampal cyclin D1 levels were significantly decreased by chemotherapy. These results suggest that the co-administration of doxorubicin and cyclophosphamide induces psychological and cognitive impairment, in addition to negatively affecting hippocampal neurogenesis, which may be related to hippocampal cyclin D1 levels, but not hippocampal BDNF levels.

Parkinson's disease (PD) is one of common neurodegenerative diseases, which shows motor symptoms including tremor, bradykinesia, rigidity and postural instability. It also involves non-motor symptoms such as cognitive impairment, mental manifestation, autonomic disorder and sensory disturbance. Although treatments to improve the motor disability in PD are being assessed at present, the main challenge remains that is the development of neuroprotective or disease-modifying treatments. Therefore, it is desirable to find approaches that can inhibit the progression of dopaminergic neurodegeneration. Astrocytes are known to play an important role in the maintenance of the neuronal environment and exert neuroprotective effects. Additionally, astrocyte dysfunction increases the susceptibility of neurons to cytotoxicity. We have demonstrated neuroprotective approaches in parkinsonian models in various studies targeting astrocytes. In this article, we summarize the neuroprotective function of astrocytes in the brain, involvement of astrocyte dysfunction in neurodegeneration, and experimental approaches to dopaminergic neuroprotection. We review findings reported in several papers including our own studies. We also address target molecules and pivotal pathways in astrocytes for dopaminergic neuroprotection. The review discusses new promising therapeutic strategies to prevent dopaminergic neurodegeneration in PD.

In the present study, we examined the effect of ACTH on the immobilization of rats in the forced swim test and hippocampal cell proliferation after administration of the 5-HT1A receptor agonist, R-(+)-8-hydroxy-2-di-n-propylamino tetralin ((+)-8-OH-DPAT). Chronic treatment with (+)-8-OH-DPAT (0.01-0.1 mg/kg, s.c.) significantly decreased the duration of immobility in saline- and ACTH-treated rats. Chronic administration of ACTH caused a significant decrease in hippocampal cell proliferation. However, (+)-8-OH-DPAT significantly normalized cell proliferation in ACTH-treated rats. We then investigated the effects of (+)-8-OH-DPAT on the expression of brain-derived neurotrophic factor (BDNF) and cyclin D1 (elements of cyclic adenosine monophosphate response element-binding protein (CREB)-BDNF and Wnt signaling pathways, respectively) in the hippocampus of saline- and ACTH-treated rats. ACTH treatment significantly decreased the expression of cyclin D1, while treatment with (+)-8-OH-DPAT normalized the expression of cyclin D1 in ACTH-treated rats. However, the expression of BDNF did not change in either saline- or ACTH-treated rats. These findings suggest that the antidepressant effects of (+)-8-OH-DPAT in treatment-resistant animals may be attributed to an enhancement of hippocampal cell proliferation, at least in part due to an enhancement of cyclin D1 expression.

The specific toxicity to dopaminergic neurons of psychostimulants and neurotoxins has been extensively studied in vivo and in vitro, and findings have been used to establish animal models of amphetamine psychosis or Parkinson’s disease. The multiple mechanisms of neurotoxicity operating in these disorders are known to involve oxidative stress or neuroinflammation, producing the characteristic behavioral and neuropathlogical changes arising from injured dopaminergic neurons and glial cells. A number of studies have shown that glia-targeting antioxidants play important roles in protecting against the neurotoxicity caused by psychostimulants or neurotoxins. Phytochemicals, which are non-nutritive plant chemicals, protect dopaminergic neurons and glial cells from damage caused by psychostimulants or neurotoxins. The objective of this review was to evaluate the involvement of glial cells in dopaminergic neuron–specific toxicity and to explore the neuroprotective activity of phytochemicals in terms of anti-inflammatory and antioxidant action. Keywords:: dopaminergic neurotoxicity, psychostimulant, neurotoxin, phytochemical

Oxidative stress and inflammation play important roles in diabetic complications, including diabetic nephropathy. Metallothionein (MT) is induced in proximal tubular epithelial cells as an antioxidant in the diabetic kidney; however, the role of MT in renal function remains unclear. We therefore investigated whether MT deficiency accelerates diabetic nephropathy through oxidative stress and inflammation. Diabetes was induced by streptozotocin injection in MT-deficient (MT−/−) and MT+/+ mice. Urinary albumin excretion, histological changes, markers for reactive oxygen species (ROS), and kidney inflammation were measured. Murine proximal tubular epithelial (mProx24) cells were used to further elucidate the role of MT under high-glucose conditions. Parameters of diabetic nephropathy and markers of ROS and inflammation were accelerated in diabetic MT−/− mice compared with diabetic MT+/+ mice, despite equivalent levels of hyperglycemia. MT deficiency accelerated interstitial fibrosis and macrophage infiltration into the interstitium in the diabetic kidney. Electron microscopy revealed abnormal mitochondrial morphology in proximal tubular epithelial cells in diabetic MT−/− mice. In vitro studies demonstrated that knockdown of MT by small interfering RNA enhanced mitochondrial ROS generation and inflammation-related gene expression in mProx24 cells cultured under high-glucose conditions. The results of this study suggest that MT may play a key role in protecting the kidney against high glucose-induced ROS and subsequent inflammation in diabetic nephropathy.

We have shown previously that chronic administration of adrenocorticotropic hormone (ACTH) causes a significant decrease in hippocampal cell proliferation and neurogenesis. This effect in rats treated chronically with ACTH was not influenced by the chronic administration of imipramine, but was reversed by coadministration of imipramine and lithium. The present study was undertaken to further characterize the mechanism underlying the effect of imipramine and lithium on hippocampal cell proliferation and neurogenesis, by investigating the effects of treatment on the expression of brain-derived neurotrophic factor (BDNF), total cyclic adenosine monophosphate response element-binding protein (CREB), and phosphorylated CREB (pCREB) of the CREB signaling system, as well as Wnt 3a and cyclin D1 of the Wnt signaling pathway in the hippocampus of saline- and ACTH-treated rats. ACTH treatment significantly decreased the expression of cyclin D1. Treatment with imipramine and lithium increased the expression of cyclin D1 in ACTH-treated rats. However, the expression of BDNF, CREB, pCREB, and Wnt 3a did not change in either saline-treated or ACTH-treated rats. These findings suggest that the antidepressant effect of imipramine and lithium in ACTH-treatment-resistant rats may be attributed, at least in part, to an enhancement of cyclin D1 expression.

Epidemiological studies have shown that coffee consumption decreases the risk of Parkinson&rsquo, s disease (PD). Caffeic acid (CA) and chlorogenic acid (CGA) are coffee components that have antioxidative properties. Rotenone, a mitochondrial complex I inhibitor, has been used to develop parkinsonian models, because the toxin induces PD-like pathology. Here, we examined the neuroprotective effects of CA and CGA against the rotenone-induced degeneration of central dopaminergic and peripheral enteric neurons. Male C57BL/6J mice were chronically administered rotenone (2.5 mg/kg/day), subcutaneously for four weeks. The animals were orally administered CA or CGA daily for 1 week before rotenone exposure and during the four weeks of rotenone treatment. Administrations of CA or CGA prevented rotenone-induced neurodegeneration of both nigral dopaminergic and intestinal enteric neurons. CA and CGA upregulated the antioxidative molecules, metallothionein (MT)-1,2, in striatal astrocytes of rotenone-injected mice. Primary cultured mesencephalic or enteric cells were pretreated with CA or CGA for 24 h, and then further co-treated with a low dose of rotenone (1&ndash, 5 nM) for 48 h. The neuroprotective effects and MT upregulation induced by CA and CGA in vivo were reproduced in cultured cells. Our data indicated that intake of coffee components, CA and CGA, enhanced the antioxidative properties of glial cells and prevents rotenone-induced neurodegeneration in both the brain and myenteric plexus.

Nuclear factor erythroid 2-related factor (Nrf2) in astrocyte plays important roles in brain homeostasis. Fermented papaya preparation (FPP) has anti-oxidative, anti-inflammatory, immunoregulatory properties. The present study investigated the effects of FPP on activation of Nrf2 and release of Nrf2-regulated neuroprotective antioxidants and detoxifying molecules.Primary cultured astrocytes from rat embryos were treated with FPP for 6 or 24 hours. The expression levels of nuclear Nrf2 and cytoplasmic Nrf2-regulated molecules were determined by western blot analysis and immunohistochemistry. Glutathione levels were measured in cells and medium. Dopaminergic neurons were exposed 6-hydroxydopamine (6-OHDA) with/without pre-treatment with FPP astrocytes. Mice were treated orally with FPP for 2 weeks.FPP increased nuclear translocation of Nrf2 in striatal astrocytes, induced up-regulation of NAD(P)H quinine oxidoreductase-1, glutathione-S transferase and hemeoxygenase-1, and increased glutathione level and the percentage of metallothionein-expressing astrocytes. Moreover, FPP suppressed 6-OHDA-induced dopaminergic neuronal loss in not only neuron-astrocyte mixed culture, but also neuron-rich cultures pre-treated with glial conditioned medium. Two-week oral treatment of mice with FPP resulted in Nrf2 activation and increase in glutathione level in striatum.The results indicated that FPP enhances the anti-oxidative capacity through activation of Nrf2 in astrocytes, suggesting it may provide neuroprotection in oxidative stress-related neurodegenerative diseases.

Background We evaluated the effects of 3-O-methyldopa (3-OMD), a metabolite of l-DOPA which is formed by catechol-O-methyltransferase (COMT), on the uptake, metabolism, and neuroprotective effects of l-DOPA in striatal astrocytes. We examined changes in the numbers of dopaminergic neurons after treatment with l-DOPA and 3-OMD or entacapone, a peripheral COMT inhibitor, using primary cultured mesencephalic neurons and striatal astrocytes. Results The number of tyrosine hydroxylase-positive dopaminergic neurons was not affected by l-DOPA treatment in mesencephalic neurons alone. However, the increase in viability of dopaminergic neurons in the presence of astrocytes was further enhanced after methyl-l-DOPA treatment (25 µM) in mixed cultured mesencephalic neurons and striatal astrocytes. The neuroprotective effect of 25 µM l-DOPA was almost completely inhibited by simultaneous treatment with 3-OMD (10 or 100 µM), and was enhanced by concomitant treatment with entacapone (0.3 µM). The uptake of l-DOPA into and the release of glutathione from striatal astrocytes after l-DOPA treatment (100 µM) were inhibited by simultaneous exposure to 3-OMD (100 µM). Conclusions These data suggest that l-DOPA exerts its neuroprotective effect on dopaminergic neurons via astrocytes and that 3-OMD competes with l-DOPA by acting on target molecule(s) (possibly including glutathione) released from astrocytes. Since some amount of entacapone can cross the blood–brain barrier, this reagent may enhance l-DOPA transportation by inhibiting COMT and increase the astrocyte-mediated neuroprotective effects of l-DOPA on dopaminergic neurons. Electronic supplementary material The online version of this article (doi:10.1186/s12868-016-0289-0) contains supplementary material, which is available to authorized users.