Enriched chitosan nanoparticles loaded with siRNA are effective in lowering Huntington's disease gene expression following intranasal administration.

Therapies to lower gene expression in brain disease currently require chronic administration into the cerebrospinal fluid (CSF) by intrathecal infusions or direct intracerebral injections. Though well-tolerated in the short-term, this approach is not tenable for a life-time of administration. Nose-to-brain delivery of enriched chitosan-based nanoparticles loaded with anti-HTT siRNA was studied in a transgenic YAC128 mouse model of Huntington's Disease (HD). A series of chitosan-based nanoparticle (NP) formulations encapsulating anti-HTT small interfering RNA (siRNA) was designed to protect the payload from degradation "en route" to the target. Factors to improve production of effective nanocarriers of anti-HTT siRNA were identified and tested in a YAC128 mouse model of Huntington's disease. Four formulations of nanocarriers were identified to be effective in lowering HTT mRNA expression by at least 50%. Intranasal administration of nanoparticles carrying siRNA is a promising therapeutic alternative for safe and effective lowering of mutant HTT expression.

Chitosan-Mangafodipir nanoparticles designed for intranasal delivery of siRNA and DNA to brain.

The overall objective of the present research was to develop a nanocarrier system for non-invasive delivery to brain of molecules useful for gene therapy. Manganese-containing nanoparticles (mNPs) carrying anti-eGFP siRNA were tested in cell cultures of eGFP-expressing cell line of mouse fibroblasts (NIH3T3). The optimal mNPs were then tested in vivo in mice. Following intranasal instillation, mNPs were visualized by 7T MRI throughout brain at 24 and 48 hrs. mNPs were effective in significantly reducing GFP mRNA expression in Tg GFP+ mice in olfactory bulb, striatum, hippocampus and cortex. Intranasal instillation of mNPS loaded with dsDNA encoding RFP also resulted in expression of the RFP in multiple brain regions. In conclusion, mNPs carrying siRNA, or dsDNA were capable of delivering the payload from nose to brain. This approach for delivery of gene therapies to humans, if successful, will have a significant impact on disease-modifying therapeutics of neurodegenerative diseases.

Effects of an Inhibitor of Monocyte Recruitment on Recovery from Traumatic Brain Injury in Mice Treated with Granulocyte Colony-Stimulating Factor.

Administration of the hematopoietic growth factor granulocyte-colony stimulating Factor (G-CSF) has been reported to enhance recovery from controlled cortical impact (CCI) in rodent models. G-CSF exerts actions in both the periphery (stimulation of hematopoiesis) and in the brain, where it serves as a neurotrophic factor, promoting neuronal survival and stimulating neural stem/progenitor cell proliferation in the hippocampus. In order to distinguish the direct CNS actions of G-CSF from its peripheral actions, experiments were designed to block the recruitment of peripheral monocytes to the site of the lesion produced by CCI. The selective C-C motif receptor 2 (CCR2) antagonist (RS504303) was co-administered with G-CSF for three days after CCI in a chimeric mouse previously transplanted with GFP-expressing (GFP+) blood stem-progenitor cells. RESULTS: The drug significantly impaired infiltration of GFP+ bone marrow-derived cells to the frontal cortex and striatum without impeding recovery performance and hippocampal neurogenesis in the behavioral test, the Radial Arm Water Maze (RAWM). Administration of the CCR2 antagonist alone, without G-CSF, was effective in promoting recovery in RAWM. These results support the hypothesis that the direct action of G-CSF on neural cells, independent of its hematopoietic effects, is primarily responsible for enhanced recovery from CCI. In addition, this study confirms the importance of CCR2 and its ligand, monocyte chemotactic protein-1 (MCP-1), in mediating the inflammatory response following CCI.

Granulocyte colony-stimulating factor promotes behavioral recovery in a mouse model of traumatic brain injury.

Hematopoietic growth factors such as granulocyte colony-stimulating factor (G-CSF) represent a novel approach for treatment of traumatic brain injury (TBI). After mild controlled cortical impact (CCI), mice were treated with G-CSF (100 µg/kg) for 3 consecutive days. The primary behavioral endpoint was performance on the radial arm water maze (RAWM), assessed 7 and 14 days after CCI. Secondary endpoints included 1) motor performance on a rotating cylinder (rotarod), 2) measurement of microglial and astroglial response, 3) hippocampal neurogenesis, and 4) measures of neurotrophic factors (brain-derived neurotrophic factor [BDNF] and glial cell line-derived neurotrophic factor [GDNF]) and cytokines in brain homogenates. G-CSF-treated animals performed significantly better than vehicle-treated mice in the RAWM at 1 and 2 weeks but not on the rotarod. Cellular changes found in the G-CSF group included increased hippocampal neurogenesis as well as astrocytosis and microgliosis in both the striatum and the hippocampus. Neurotrophic factors GDNF and BDNF, elaborated by activated microglia and astrocytes, were increased in G-CSF-treated mice. These factors along with G-CSF itself are known to promote hippocampal neurogenesis and inhibit apoptosis and likely contributed to improvement in the hippocampal-dependent learning task. Six cytokines that were modulated by G-CSF treatment following CCI were elevated on day 3, but only one of them remained altered by day 7, and all of them were no different from vehicle controls by day 14. The pro- and anti-inflammatory cytokines modulated by G-CSF administration interact in a complex and incompletely understood network involving both damage and recovery processes, underscoring the dual role of inflammation after TBI.

In vivo administration of granulocyte colony-stimulating factor restores long-term depression in hippocampal slices prepared from transgenic APP/PS1 mice.

Granulocyte colony-stimulating factor (G-CSF) is a hematopoietic cytokine that also possesses neurotrophic and antiapoptotic properties. G-CSF has been reported to decrease amyloid burden significantly, promote hippocampal neurogenesis, and improve spatial learning in a mouse model of Alzheimer's disease. To understand better the effects of G-CSF on hippocampal-dependent learning, the present study focused on electrophysiological correlates of neuroplasticity, long-term potentiation (LTP), and long-term depression (LTD). Two cohorts of transgenic APP/PS1 mice, with or without prior bone marrow transplantation from Tg GFP mice, were treated in vivo for 2 weeks with G-CSF or vehicle. After completion of the treatments, hippocampal slices were prepared for electrophysiological studies of LTP and LTD. LTP was induced and maintained in both G-CSF-treated and vehicle-treated groups of Tg APP/PS1. In contrast, LTD could not be induced in vehicle-treated Tg APP/PS1 mice, but G-CSF treatment restored LTD. The LTP and LTD results obtained from the cohort of bone marrow-grafted Tg APP/PS1 mice did not differ from those from nongrafted Tg APP/PS1 mice. The mechanism by which G-CSF restores LTD is not known, but it is possible that its capacity to reduce amyloid plaques results in increased soluble oligomers of amyloid-ß (A-ß), which in turn may facilitate LTD. This mechanism would be consistent with the recent report that soluble A-ß oligomers promote LTD in hippocampal slices.

Key Features in the Design and Function of Nanocarriers for Intranasal Administration of Gene Therapy in Huntington Disease.

A major obstacle to fulfilling the therapeutic promise of gene therapies for hereditary brain diseases, such as Huntington' Disease (HD), is the requirement for viral vectors and/or an invasive delivery system (stereotaxic injection into brain or infusion into the intrathecal space). HD is an autosomal dominant neurodegenerative disease for which several clinical trials have demonstrated gene-lowering effects following intrathecal administration. These technical limitations have given impetus to the development of alternative non-invasive delivery systems for gene therapy of brain diseases. The overall objective of this review is to discuss the key features in the design of nanocarriers for intranasal administration of gene-therapy for HD, focusing primarily on our series of published work on the use of nanocarriers for gene therapy. Design and development of nanocarriers packaged with gene-lowering agents represents a significant advance towards non-invasive nose-to-brain delivery of gene therapy for HD and other hereditary brain disorders.

Improving solubility and pharmacokinetics of meloxicam via multiple-component crystal formation.

Meloxicam is a nonsteroidal anti-inflammatory drug prescribed for rheumatoid arthritis, osteoarthritis, postoperative pain and fever. Meloxicam exhibits low solubility in acidic aqueous media and a slow onset of action in biological subjects. An oral dosage form of meloxicam with enhanced aqueous solubility is desired to enable a faster onset of action and its use for mild-to-medium-level acute pain relief. With this in mind, we examine the solubility and pharmacokinetics of 12 meloxicam cocrystals with carboxylic acids. Dissolution studies of meloxicam and its cocrystals were performed in pH 6.5 phosphate buffer solutions at 37 °C. In addition, pharmacokinetic profiles over four hours were acquired after oral administration of a 10 mg/kg (meloxicam equivalent) solid suspension in rats. The majority of meloxicam cocrystals were found to achieve higher meloxicam concentrations in dissolution media and enhanced oral absorption compared to that of pure meloxicam. All meloxicam cocrystals were converted to meloxicam form I when the slurry reached equilibrium. To better understand how cocrystallization impacts the absorption of meloxicam after oral administration, correlations between the in vitro and in vivo data were explored. The results suggest that the meloxicam cocrystals with a faster dissolution rate would exhibit increased oral absorption and an earlier onset of action.

Dual-function hybrid nanoparticles with gene silencing and anti-inflammatory effects.

Background: Nanocarriers loaded with siRNA can be administered intranasally to provide a noninvasive, safe alternative to direct intracerebral or intrathecal infusions. Dual-function nanocarriers can also be designed to deliver several payloads that address different components of the pathological process. Aim: To design and test a hybrid nanocarrier with the capacity to lower Huntington's Disease gene (HTT) expression and prevent or diminish inflammation. Methods: Novel hybrid nanoparticles were fabricated using a chitosan-based matrix core loaded with siRNA and an outer shell consisting of a lipid composition containing cannabidiol. Results: Incubation of hybrid nanoparticles in mesenchymal stem cell cultures obtained from a YAC128 transgenic mouse modeling Huntington's disease resulted in effective lowering of mutant HTT gene expression and reduced levels of expression of the proinflammatory cytokine IL-6. Conclusion: A novel hybrid nanocarrier system with dual actions is effective in lowering HTT gene expression and attenuating inflammatory processes.

Granulocyte Colony-Stimulating Factor Enhances Brain Repair Following Traumatic Brain Injury Without Requiring Activation of Cannabinoid Receptors.

Introduction: Treatment of traumatic brain injury (TBI) with granulocyte colony-stimulating factor (G-CSF) has been shown to enhance brain repair by direct neurotrophic actions on neural cells and by modulating the inflammatory response. Administration of cannabinoids after TBI has also been reported to enhance brain repair by similar mechanisms. Objectives: The primary objective of this study was to test the hypothesis that G-CSF mediates brain repair by interacting with the endocannabinoid system. Methods and Results: (i) Mice that underwent controlled cortical impact (CCI) were treated with G-CSF for 3 days either alone or in the presence of selective cannabinoid receptor 1 (CB1-R) or cannabinoid receptor 2 (CB2-R) agonists and antagonists. The trauma resulted in decreased expression of CB1-R and increased expression of CB2-R in the cortex, striatum, and hippocampus. Cortical and striatal levels of the major endocannabinoid ligand, 2-arachidonoyl-glycerol, were also increased by the CCI. Administration of the hematopoietic cytokine, G-CSF, following TBI, resulted in mitigation or reversal of trauma-induced CB1-R downregulation and CB2-R upregulation in the three brain regions. Treatment with CB1-R agonist (WIN55) or CB2-R agonist (HU308) mimicked the effects of G-CSF. (ii) Pharmacological blockade of CB1-R or CB2-R was not effective in preventing G-CSF's mitigation or reversal of trauma-induced alterations in these receptors. Conclusions: These results suggest that cellular and molecular mechanisms that mediate subacute effects of G-CSF do not depend on activation of CB1 or CB2 receptors. Failure of selective CB receptor antagonists to prevent the effects of G-CSF in this model has to be accepted with caution. CB receptor antagonists can interact with other CB and non-CB receptors. Investigation of the role of CB receptors in this TBI model will require studies with CB1-R and in CB2-R knockout mice to avoid nonspecific interaction of CB receptor agents with other receptors.

Data on enrichment of chitosan nanoparticles for intranasal delivery of oligonucleotides to the brain.

Data on preparation and characterization of chitosan-based nanoparticles (NP) carrying small interfering RNA (siRNA) for non-invasive gene therapy is presented. Polyelectrolyte complexation method was carried out in diluted concentrations to obtain relatively small (less than 200 nm) NP. To provide substantial dose of siRNA within tolerable volume of intranasal administration the NP were subjected to enrichment process. Offered here NP fabrication does two steps process comprise provisional and enriched preparations? The differences between these preparations were analyzed with hydrodynamic size distribution and zeta potential measurements. The effect of siRNA lipophilicity on NP physical instability was also tested. Biological evaluation of nanoparticles is described in our published article [1].

Optimizing Nanoparticle Design for Gene Therapy: Protection of Oligonucleotides from Degradation Without Impeding Release of Cargo.

Gene therapy delivery systems that rely on synthetic nanocarriers can be optimized by assays of nucleic acid protection and kinetic studies of nucleic acid release. These empirical measurements ensure nanoparticle stability and predict potential in vivo efficacy. Quantitative methods for assessment of the capacity of nanoparticles to protect oligonucleotide cargo and to measure the rate of release of the cargo were developed and tested based on six commercial cationic matrices. in vitro study of drug release kinetics provides predictable release rates under a variety of conditions which can be adapted to appropriate physiological factors that affect release in vivo. In brief, in vitro DNA release and DNase I degradation assays described here will be useful for optimization of nanocarrier-mediated gene therapy administration by various routes.

Adult hippocampal neural stem/progenitor cells in vitro are vulnerable to the mycotoxin ochratoxin-A.

The common mycotoxin ochratoxin-A (OTA) accumulates in brain, causes oxidative stress, and elicits a DNA repair response that varies across brain regions and neuronal populations. Neural stem/progenitor cells (NSCs) prepared from hippocampus of adult mouse brain were tested for their vulnerability to the toxin in vitro. The following measurements were made in NSC cell cultures in both proliferation and differentiation media: (1) viability (trypan blue exclusion), (2) proliferative activity ([(3)H]-thymidine uptake), (3) the DNA repair response (oxyguanosine glycosylase activity), and (4) antioxidative response (superoxide dismutase). Cells that had proliferated to 90-100% confluency in the presence of epidermal growth factor and basic fibroblast growth factor were induced to differentiate by removal of the growth factors. OTA, added to the cultures in concentrations of 0.01-100 microg/ml, caused a dose- and time-dependent (6-72 h) decrease in viability of both proliferating and differentiating NSC. Proliferating NSC exhibited a greater vulnerability to the toxin than differentiated neurons despite robust DNA repair and antioxidative responses. Preconditioning of NSC with a 12-h incubation with the pro-oxidant diethyl maleate increased DNA repair activity and, subsequently, provided a moderate degree of neuroprotection. Overall, these results lead to speculation that OTA exposure may contribute to impaired hippocampal neurogenesis in vivo, resulting in depression and memory deficits, conditions reported to be linked to mycotoxin exposure in humans.

Granulocyte-colony stimulating factor promotes brain repair following traumatic brain injury by recruitment of microglia and increasing neurotrophic factor expression.

PURPOSE: The overall objective was to elucidate cellular mechanisms by which G-CSF enhances recovery from traumatic brain injury in a hippocampal-dependent learning task. METHODS: Chimeric mice were prepared by transplanting bone marrow cells that express green fluorescent protein (GFP+) from a transgenic "green" mice into C57BL/6 mice. Two months later, the animals sustained mild controlled cortical impact (CCI) to the right frontal-parietal cortex, followed by G-CSF (100 µg/kg) treatment for 3 consecutive days. The primary behavioral end-point was performance on the radial arm water maze (RAWM) assessed before and after CCI (days 7 and 14). Secondary endpoints included a), motor performance on a rotating cylinder (rotarod), b) measurement of microglial and astroglial response, c) hippocampal neurogenesis, and d) measures of neurotrophic factors (BDNF, GDNF) in brain homogenates. RESULTS: G-CSF treatment resulted in significantly better performance on the rotorod at one week, and in the RAWM after one and two weeks. The cellular changes found 2 wks after CCI in the G-CSF group included increased numbers of hippocampal newborn neurons as well as astrocytosis and microgliosis in striatum and frontal cortex on both sides of brain. GFP+ cells that co-labeled with Iba1 (microglial marker) comprised a significant proportion of striatal microglia in G-CSF treated animals, indicating the capacity of G-CSF to increase microglial recruitment to the site of injury. Neurotrophic factors GDNF and BDNF, elaborated by activated microglia and astrocytes, were increased in G-CSF treated mice. CONCLUSIONS: G-CSF serves as a neurotrophic factor that increases hippocampal neurogenesis (or enhances survival of new-born neurons), and activates astrocytes and microglia. In turn, these activated glia release a plethora of cytokines and neurotrophic factors that contribute, in a poorly understood cascade, to the brain's repair response. G-CSF also acts directly on bone marrow-derived cells to enhance recruitment of microglia to the site of CCI from circulating monocytes to the site of CCI.

Transient Microneedle Insertion into Hippocampus Triggers Neurogenesis and Decreases Amyloid Burden in a Mouse Model of Alzheimer's Disease.

Targeted microlesions of the hippocampus have been reported to enhance neurogenesis in the subgranular zone (SGZ). The potential therapeutic impact of transient insertion of a microneedle was investigated in a mouse model of Alzheimer's disease (AD). We tested the hypothesis that transient microinjury to the brain elicits cellular responses that mediate beneficial regenerative processes. Brief stereotaxic insertion and removal of a microneedle into the right hippocampus of 14-month-old APP/PS1 mouse brains resulted in (a) stimulation of hippocampal neurogenesis and (b) reduction of amyloid-ß plaque number in the CA-1 region. This treatment also resulted in a trend toward improved performance in the radial arm water maze (RAWM). Further studies of fundamental cellular mechanisms of the brain's response to microinjury will be useful for investigation of potential neuroprotective and deleterious effects of targeted microlesions and deep brain stimulation in AD.

Effects of melanin and manganese on DNA damage and repair in PC12-derived neurons.

The mechanism of neurotoxicity produced by the interaction of melanin with manganese was investigated in PC12-derived neuronal cell cultures. The cells were incubated with melanin (25-500 microg/ml), MnCl2 (10 ng/ml-100 microg/ml) and a combination of both substances for 24 and 72 h. Incubation with either toxicant alone resulted in a minimal decrease in cell viability. The combination of melanin and manganese caused significant (up to 60%) decreases in viability of PC12 cells in a dose-dependent manner. Increases in oxidative DNA damage, indicated by levels of 8-hydroxy-2'deoxyguanosine (8-oxodG), was associated with decreased cell viability. Melanin alone, but not manganese alone, resulted in increased oxidative DNA damage. The maximal increase in 8-oxodG caused by melanin was about seven times higher than control after 24 h of exposure. The activity of the DNA repair enzyme, 8-oxoguanine DNA glycosylase (OGG1), was increased in cells incubated with single toxicants and their combinations for 24 h. On the third day of incubation with the toxicants, activity of OGG1 declined below control levels and cell viability significantly decreased. Melanin was observed to have an inhibitory effect on OGG1 activity. Study of the regulation of OGG1 activity in response to melanin and manganese may provide insights into the vulnerability of nigral neurons to oxidative stress in Parkinson's disease.

Inhibitory effects on phospholipase A2 and antivenin activity of melanin extracted from Thea sinensis Linn.

Antivenin activity of melanin extracted from black tea (MEBT) was reported for the first time. The antagonistic effect of MEBT was evaluated for Agkistrodon contortrix laticinctus (broadbanded copperhead), Agkistrodon halys blomhoffii (Japanese mamushi), and Crotalus atrox (western diamondback rattlesnake) snake venoms administered i.p. to ICR mice. MEBT was injected i.p. immediately after the venom administration in dose of 3 mg per mouse in the same place of venom injection. MEBT demonstrated neutralization effect against all venoms tested. The greatest antivenin effect of MEBT was found against Japanese mamushi snake venom. In this case, half the mice died within 2.5 +/- 0.7 h after injection of 0.9 mg/kg of venom. An immediate injection of MEBT substantially reduced the toxic effect of venom and extended time at the 50% level of survival up to 52.3 +/- 2.3 h. The antivenin activity of MEBT is due to chelating of Ca++ and non-specific binding of phospholipase A2. The inhibitory effect of MEBT on phospholipase A2 assessed for different venoms was similar to that obtained with pure enzyme. Low toxicity of MEBT in combination with its antagonistic activity against different venoms may allow effective life-saving treatment against snakebites. Such application of MEBT is important when identification of the snake is impossible or if specific treatment is unavailable.

Preventive effect of Thea sinensis melanin against acetaminophen-induced hepatic injury in mice.

The preventive effect of Thea sinensis melanin (TSM) against overdoses of N-acetyl-p-aminophenol (NAPAP) was studied on ICR mice. Animals were given 400 mg/kg intraperitoneally (i.p.) of NAPAP, and TSM was injected i.p. in doses 10-40 mg/kg 2 h before intoxication. The protective effects were evidenced by a complete blockage of the NAPAP-induced elevation of plasma alanine aminotransferase (ALT) activity, decreased concentration of thiobarbituric acid reactive substances (TBARS) to the control level, and a partial prevention of reduced glutathione (GSH) depletion in the liver tissue. Preadministration of TSM also caused restoration of superoxide dismutase (SOD) activity and resumed content of coenzymes Q9 and Q10. TSM by itself, however, did not affect the hepatic functional parameters, including serum ALT, TBARS, GSH, SOD, or coenzymes Q in the liver. Administration of TSM caused a dose-dependent inhibition of N-nitrosodimethylamine demethylase activity with ED50 of 15.8 mg/kg. Activities of ethoxyresorufin O-dealkylase and pentoxyresorufin O-alkylase isozymes were changed insignificantly. The immune suppressive effect of NAPAP on the in vivo antibody-forming cell responses was demonstrated using ICR-sensitized mice with sheep red blood cells. The joint effect of TSM and NAPAP indicated the capability of TSM to recover immunity of the animals to the level of intact mice. Results obtained demonstrate that TSM preadministration can prevent the multiple toxic effects of NAPAP.

Gastrointestinal enhancement of MRI with melanin derived from tea leaves (Thea sinensis Linn.).

Melanin was extracted from tea leaves (Thea sinensis Linn.) for the first time. Characterization of melanin proved similarity of the original compound to standard melanin. The Langmuir adsorption isotherms for gadolinium (Gd) binding were obtained using melanin. Melanin-Gd preparation demonstrated low acute toxicity. LD(50) for this preparation was in a range of 1250-1500 mg/kg in mice. Magnetic Resonance Imaging (MRI) properties of melanin itself and melanin-Gd complexes have been estimated. Gd free melanin fractions possess slighter relaxivity compared with its complexes. The relaxivity of lower molecular weight fraction was two times higher than relaxivity of Gd(DTPA) standard. Postcontrast images demonstrate that oral administration of melanin complexes in concentration 0.1 mM provides essential enhancement to longitudinal relaxation times (T(1))-weighted spin echo image. The required contrast and delineation of the stomach wall demonstrated uniform enhancement of MRI with proposed melanin complex.

Hippocampal neurogenesis and the brain repair response to brief stereotaxic insertion of a microneedle.

We tested the hypothesis that transient microinjury to the brain elicits cellular and humoral responses that stimulate hippocampal neurogenesis. Brief stereotaxic insertion and removal of a microneedle into the right hippocampus resulted in (a) significantly increased expression of granulocyte-colony stimulating factor (G-CSF), the chemokine MIP-1a, and the proinflammatory cytokine IL12p40; (b) pronounced activation of microglia and astrocytes; and (c) increase in hippocampal neurogenesis. This study describes immediate and early humoral and cellular mechanisms of the brain's response to microinjury that will be useful for the investigation of potential neuroprotective and deleterious effects of deep brain stimulation in various neuropsychiatric disorders.

Granulocyte-colony stimulating factor (G-CSF) enhances recovery in mouse model of Parkinson's disease.

INTRODUCTION: Granulocyte-colony stimulating factor (G-CSF) is used routinely in clinical practice for the treatment of neutropenia and to increase generation of hematopoietic stem cells in bone marrow donors. A growing body of literature on the neurotrophic effects of G-CSF has led to clinical trials in stroke, Alzheimer's disease (AD) and Parkinson's disease (PD). OBJECTIVES: The primary objective of this study was to determine if G-CSF administration would rescue the nigro-striatal system and restore locomotor function after completion of a sub-acute course of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) administration (30mg/kg i.p. for 5 days) in 12 month-old mice. A secondary aim was to determine if G-CSF affects the neuro-inflammatory response by modulating microglial activation in striatum and midbrain. RESULTS: MPTP-treated mice were impaired on the rotometer test after the last dose of the toxicant and remained impaired until euthanasia. MPTP-treated mice that were given an 8-day regimen of G-CSF starting 2 days after the last dose of toxicant enhanced motor performance compared to the MPTP alone group. MPTP treatment depleted striatal DA (DA) levels; G-CSF given after MPTP resulted in a partial, significant repletion of DA levels. Total microglial burden in the striatum was increased significantly in MPTP-treated mice and was reduced after G-CSF rescue. CONCLUSION: G-CSF enhances recovery of DA nigro-striatal function from MPTP toxicity in part by modulating the microglial response to injury. The G-CSF receptor may provide a novel target for modifying the disease process in Parkinson's disease.