GDNF administration induces recovery of the nigrostriatal dopaminergic system both in young and aged parkinsonian mice

Glial cell line-derived neurotrophic factor (GDNF) is a member of the transforming growth factor beta superfamily and acts as a neurotrophic factor for the nigrostriatal dopaminergic system. GDNF was injected stereotaxically into the striatum of young (2 months old) and aged (12 months old) C57BL/6 mice that were treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) 1 week earlier. Immunocytochemical and neurochemical analyses showed significant recovery of the nigrostriatal dopaminergic system both in young and in aged mice. Since Parkinson's disease is a neurodegenerative disorder mainly affecting elderly people, this result demonstrates the potential usefulness of GDNF in treating Parkinson's disease.     

Effects of testosterone upon MPTP-induced neurotoxicity of the nigrostriatal dopaminergic system of C57/B1 mice

We have recently reported that treatment of gonadectomized female and male C57/B1 mice with the gonadal steroid hormone, estrogen, reduced nigrostriatal dopaminergic neurotoxicity resulting from the Parkinson's-like inducing agent 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). In the present report we examined whether the predominantly male gonadal steroid hormone, testosterone, would similarly modulate MPTP-induced neurotoxicity. Male C57/B1 mice were assigned to one of the following five treatment conditions: (1) Intact, (2) Orchidectomized, (3) Intact + MPTP, (4) Orchidectomized + Testosterone + MPTP and (5) Orchidectomized + MPTP. Corpus striatal and olfactory tubercle dopamine. DOPAC and norepinephrine concentrations were determined from the animals within each of the five treatment conditions. Orchidectomy alone failed to alter striatal dopamine and DOPAC concentrations, with levels obtained being similar to that of Intact animals. MPTP treatment significantly reduced striatal reduced striatal dopamine and DOPAC concentrations, regardless of hormonal condition of the animal. Similar results were obtained for olfactory tubercle determinations, with the exception that DOPAC levels from Orchidectomized mice were significantly greater than Intact males. No significant differences were obtained for norepinephrine within either brain area sampled. These results show that unlike estrogen, testosterone is devoid of any capacity to modulate nigrostriatal dopaminergic neurotoxicity resulting from MPTP. These findings may be related to the gender differences which exist in the prevalence of Parkinson's disease.     

Induction of interleukin-1 associated with compensatory dopaminergic sprouting in the denervated striatum of young mice: model of aging and neurodegenerative disease

Young mice challenged with the neurotoxin 1-methyl-4-phenyl-1,2,3, 6-tetrahydropyridine (MPTP), which selectively destroys the substantia nigra dopaminergic neurons in the midbrain, exhibit spontaneous recovery of dopaminergic nerve terminals. However, such recovery becomes attenuated with age. Here we report that newly sprouted fibers originate from spared dopaminergic neurons in the ventral tegmental area. We found that interleukin-1 (IL-1), an immune response-generated cytokine that can enhance dopaminergic sprouting when exogenously applied, increased dramatically in the denervated striatum of young mice (2 months) compared with middle-aged mice (8 months) after MPTP treatment. Young mice displayed a maximal 500% induction of IL-1alpha synthesis that remained elevated for several weeks in the dorsal and ventral striatum, whereas middle-aged mice exhibited a modest 135% induction exclusively in the dorsal striatum for a week. IL-1alpha immunoreactivity was localized in GFAP-immunoreactive hypertrophied astrocytes and neurons within the denervated striatum of young mice. However, no induction of IL-1alpha mRNA was seen in the midbrain in either age group despite glial activation. Because we have reported that IL-1 can regulate astroglia-derived dopaminergic neurotrophic factors, it was surprising that no changes were observed in acidic and basic fibroblast growth factor or glial cell line-derived neurotrophic factor mRNA levels associated with MPTP-induced plasticity of dopaminergic neurons in the striatum of young mice. Interestingly, we found that dopaminergic neurons express IL-1 receptors, thus suggesting that IL-1alpha could directly act as a target-derived dopaminergic neurotrophic factor to initiate or enhance the sprouting of dopaminergic axonal terminals. These findings strongly suggest that IL-1alpha could play an important role in MPTP-induced plasticity of dopaminergic neurons.     

Effects of dental amalgam and heavy metal cations on cytokine production by peripheral blood mononuclear cells in vitro

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is known to produce a differential toxicity in the nigrostriatal and mesolimbic dopaminergic pathways with the nigrostriatal pathway being more vulnerable. We, therefore, investigated whether oxidative stress and the antioxidant system play a role in this phenomenon. Balb/c mice were treated with either saline or MPTP (30 mg/kg/d) for 7 d, and were sacrificed on the next day. Results revealed that MPTP increased lipid peroxidation in the striatum (ST) and decreased glutathione concentration in the substantia nigra (SN) without markedly affecting these measures in the nucleus accumbens (NAc) and ventral tegmental area (VTA). Further, MPTP produced approximately twofold increases in both manganese superoxide dismutase (MnSOD) and copper-zinc superoxide dismutase (CuZnSOD) activities in the VTA while it only increased MnSOD activity in the SN. Both catalase and glutathione peroxidase (GPx) activities were not markedly altered by MPTP in both systems. However, the basal levels of catalase and GPx activities were higher in the VTA and NAc than in the SN and ST. These results together suggest that a lesser degree of oxidative damage and a more inducible CuZnSOD activity observed in the mesolimbic dopaminergic pathway may partially explain the differential toxicity MPTP produced in these two dopaminergic systems.     

Gangliosides and parkinsonism

The protective effect of GM1 ganglioside against nerve cell death induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) was analyzed in monkey mesencephalon. Administration of GM1 before and during MPTP treatment improved motor performances compared with MPTP-treated animals that received saline rather than GM1. Postmortem analysis revealed that GM1 did not protect dopaminergic cell bodies from MPTP intoxication but resulted in an increased immunoreactivity of tyrosine hydroxylase in the perikarya and processes of the surviving neurons. These data suggest that GM1 may be potentially used as a palliative rather than a curative therapy in Parkinson's disease.     

Platelet-derived growth factor promotes survival of rat and human mesencephalic dopaminergic neurons in culture

The effect of two isoforms of platelet-derived growth factor (PDGF), PDGF-AA and PDGF-BB, was tested on dissociated cell cultures of ventral mesencephalon from rat and human embryos. PDGF-BB but not PDGF-AA reduced the progressive loss of tyrosine hydroxylase- (TH)-positive neurons in rat and human cell cultures. The mean number of TH-positive cells in the PDGF-BB-treated rat culture was 64% and 106% higher than in the control cultures after 7 and 10 days in vitro, respectively. Corresponding figures for human TH-positive neurons were 90% and 145%. The influence of PDGF-BB was specific for TH-positive neurons and not a general trophic effect, since no change of either total cell number or metabolic activity was found. In PDGF-BB-treated cultures of human but not rat tissue the TH-positive neurons had longer neurites than observed in control or PDGF-AA-treated cultures. These data indicate that PDGF-BB may act as a trophic factor for mesencephalic dopaminergic neurons and suggest that administration of PDGF-BB could ameliorate degeneration and possibly promote axonal sprouting of these neurons in vivo.     

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) disrupts social memory/recognition processes in the male mouse

Male mice treated with MPTP or vehicle were tested for their ability to demonstrate a memory-recognition response as evaluated in a habituation-dishabituation task. Treatment with MPTP severely disrupted the male's habituation-dishabituation response profile compared to vehicle treated animals. Administration of L-DOPA at 45 min prior to behavioral testing in MPTP animals restored their performance on the habituation-dishabituation test to levels observed in vehicle treated animals. There was also a tendency for L-DOPA to produce enhanced responsiveness in vehicle treated animals. Mice treated with MPTP had significantly reduced concentrations of norepinephrine within the olfactory bulb and hippocampus. Vehicle treated mice administered L-DOPA had significantly increased dopamine concentrations within the corpus striatum. These results suggest that, in addition to its putative effects upon the nigrostriatal dopaminergic system and motor behavior, MPTP is also exerting substantial effects upon other systems. In particular, the noradrenergic system and its potential involvement with memory/recognition processes in the CD-1 mouse appears to be very sensitive to the neurotoxic effects of MPTP.     

A conformational epitope in the N-terminus of the Escherichia coli heat-stable enterotoxins is involved in receptor-ligand interactions

The relationship between the central dopaminergic and the immune system is poorly understood. Experimental work suggest that damage of the nigrostriatal system may influence immunity. Immunological abnormalities have been described in Parkinson's disease and in a mouse model of this disorder induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). In this report, we present evidence that reduced numbers of L3T4 T cells in blood, and diminished primary antibody response to sheep erythrocytes in MPTP treated mice can be restored by pargyline pretreatment. Since pargyline prevents dopamine depletion in the striatum in MPTP treated animals, our data extend previous experimental observations and support a possible role for dopamine in immune regulation.     

Biochemistry and genetics of thiodicarb resistance in the house fly (Diptera: Muscidae)

We have recently reported that environmental toxicants, such as DDT, PCBs, pyrethroids, and nicotine can induce permanent functional and neurochemical changes in adult mice when given to neonatal mice during the peak of rapid brain growth. In the present investigation the neurotoxic effects following neonatal exposure to paraquat (N,N'-dimethyl-4,4'-bipyridylium), a broad-spectrum herbicide with structural similarity to the 1-methyl-4-phenylpyridium ion (MPP+), the active metabolite of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) which can induce Parkinson's syndrome, and MPTP were studied. Five groups of mice were given paraquat or MPTP orally: group 1, vehicle; groups 2 and 3, MPTP 0.3 and 20 mg/kg; groups 4 and 5, paraquat 0.07 and 0.36 mg/kg when 10 and 11 days old. Neonatal spontaneous motor activity was tested on Day 18 in mice given paraquat 0.36 mg/kg body wt. Adult spontaneous motor activity testing was performed at ages 60 and 120 days. On Day 125 the mice were decapitated and the contents of dopamine (DA), serotonin (5-HT), and metabolites in striatum were analyzed. The results may be summarized as follows: (1) No signs of acute toxicity or differences in weight gain were observed in any of the groups. Nor was any respiratory distress or motor performance dysfunction evident on Day 18 in mice given paraquat 0.36 mg/kg body wt. (2) The behavioral tests at 60 days of age showed a marked hypoactive condition in the mice given paraquat (at both doses) and MPTP (at both doses). (3) At the age of 120 days the hypoactive behavior persisted and appeared even more pronounced. (4) The high doses of MPTP and paraquat--and to a less extent the low doses--reduced the striatal content of DA and metabolites without affecting 5-HT. The altered behavior, together with the dose-dependent reduction of DA and metabolites in neostriata in this study, further demonstrates the susceptibility to low-dose exposure to environmental pollutants during the neonatal period.     

Swimming lessons--check the water before jumping in

To mimic chronic exposure to neurotoxins in inducing dopaminergic cell damage, multiple doses of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) were injected in C57BL/6 mice. Effects of pre- and post-treatment with the glial cell line-derived neurotrophic factor (GDNF) by injections into the striatum were investigated. GDNF exerts protective and reverse effects on the dopaminergic damage, supporting the potential application of GDNF in prevention and treatment of Parkinson's disease.     

Kidney cografts enhance fiber outgrowth from ventral mesencephalic grafts to the 6-OHDA-lesioned striatum, and improve behavioral recovery

Recent studies have demonstrated the presence of many different neurotrophic factors in the developing and adult kidney. Due to its production of this mixture of neurotrophic factors, we wanted to investigate whether fetal kidney tissue could be beneficial for neuritic fiber growth and/or cell survival in intracranial transplants of fetal ventral mesencephalic tissue (VM). A retrograde lesion of nigral dopaminergic neurons was performed in adult Fischer 344 male rats by injecting 6-hydroxydopamine into the medial forebrain. The animals were monitored for spontaneous locomotor activity in addition to apomorphine-induced rotations once a week. Four weeks following the lesion, animals were anesthetized and embryonic day 14 VM tissue from rat fetuses was implanted stereotaxically into the dorsal striatum. One group of animals received a cograft of kidney tissue from the same embryos in the same needle track. The animals were then monitored behaviorally for an additional 4 months. There was a significant improvement in both spontaneous locomotor activity (distance traveled) and apomorphine-induced rotations with both single VM grafts and VM-kidney cografts, with the VM-kidney double grafts enhancing the motor behaviors to a significantly greater degree. Tyrosine hydroxylase (TH) immunohistochemistry and image analysis revealed a significantly denser innervation of the host striatum from the VM-kidney cografts than from the single VM grafts. TH-positive neurons were also significantly larger in the cografts compared to the single VM grafts. In addition to the dense TH-immunoreactive innervation, the kidney portion of cografts contained a rich cholinergic innervation, as evidenced from antibodies against choline acetyltransferase (ChAT). The striatal cholinergic cell bodies surrounding the VM-kidney cografts were enlarged and had a slightly higher staining density for ChAT. Taken together, these data support the hypothesis that neurotrophic factors secreted from fetal kidney grafts stimulated both TH-positive neurons in the VM cografts and cholinergic neurons in the host striatum. Thus, these factors may be combined for treatment of degenerative diseases involving both dopaminergic and cholinergic neurons.     

MPTP-induced deficits in motor activity: neuroprotective effects of the spintrapping agent, alpha-phenyl-tert-butyl-nitrone (PBN)

In Experiment 1, groups of mice were administered either saline or MPTP (2 x 30 mg/kg, s.c., separated by a 24-hr interval) 30 min after being injected either PBN (15, 50 or 150 mg/kg, s.c., low, medium and high doses, respectively) or L-Deprenyl (0.25 or 10.0 mg/kg, s.c., low and high doses, respectively), the reference compound used, or saline. Tests of spontaneous motor activity 14 days later indicated that the MPTP-induced hypokinesia for locomotion and rearing was alleviated by prior administration with PBN (50 or 150 mg/kg) or L-Deprenyl (10.0 mg/kg); lower doses of PBN (15 mg/kg) and L-Deprenyl (0.25 mg/kg) did not affect the MPTP-induced deficits. Dopamine (DA) concentrations in the striatum confirmed a more severe loss of DA in the MPTP, PBN (15) + MPTP and Deprenyl(0.25) + MPTP groups than in the control group. Significant protection of DA was observed in the PBN(50) + MPTP, PBN(150) + MPTP and Deprenyl(10) + MPTP groups that did not exhibit an hypokinetic behaviour. In Experiment 2, the effects of repeated treatment with PBN (50 mg/kg, s.c. over 12 days), post-MPTP, were studied in aged (15-month-old) and young (3-month-old) mice. Subchronic administration of PBN increased substantially the motor activity of old and young mice that had received MPTP. Aged control (saline) mice showed an activity deficit compared to young control mice; this deficit was abolished by repeated PBN treatment. The results suggest that moderate-to-high doses of PBN whether injected in a single dose prior to MPTP or subchronically following MPTP injections may afford protective effects against both the functional changes and DA-loss caused by MPTP treatment, possibly through an antioxidant mechanism.     

Melatonin protects 6-OHDA-induced neuronal death of nigrostriatal dopaminergic system

In vivo neuroprotective effects of melatonin on the nigrostriatal dopaminergic system in rats unilateral 6-hydroxydopamine (6-OHDA) lesions were tested. Two weeks after lesioning the dopamine receptor agonist, apomorphine produced rotational asymmetry. In contrast, melatonin treatment significantly reduced the motor deficit following apomorphine challenge. Analysis by tyrosine hydroxylase (TH) immunocytochemistry revealed the loss of cell bodies in the substantia nigra (SN) and absence of terminals in the dorsolateral striatum ipsilaterally. Melatonin treatment also resulted in the survival of dopaminergic neurons in SN and TH-immuoreactive terminals in the dorsolateral striatum. These behavioral and histochemical results may indicate a neuroprotective action of melatonin and suggest a potential pharmacological role in the treatment of Parkinson's disease.     

Dopaminergic neurons intrinsic to the primate striatum

Intrinsic, striatal tyrosine hydroxylase-immunoreactive (TH-i) cells have received little consideration. In this study we have characterized these neurons and their regulatory response to nigrostriatal dopaminergic deafferentation. TH-i cells were observed in the striatum of both control and 1-methyl-4-phenyl-1,2,3, 6-tetrahydropyridine (MPTP)-treated monkeys; TH-i cell counts, however, were 3.5-fold higher in the striatum of MPTP-lesioned monkeys. To establish the dopaminergic nature of the TH-i cells, sections were double-labeled with antibodies to dopamine transporter (DAT). Immunofluorescence studies demonstrated that nearly all TH-i cells were double-labeled with DAT, suggesting that they contain the machinery to be functional dopaminergic neurons. Two types of TH-i cells were identified in the striatum: small, aspiny, bipolar cells with varicose dendrites and larger spiny, multipolar cells. The aspiny cells, which were more prevalent, corresponded morphologically to the GABAergic interneurons of the striatum. Double-label immunofluorescence studies using antibodies to TH and glutamate decarboxylase (GAD67), the synthetic enzyme for GABA, showed that 99% of the TH-i cells were GAD67-positive. Very few (<1%) of the TH-i cells, however, were immunoreactive for the calcium-binding proteins calbindin and parvalbumin. In summary, these results demonstrate that the dopaminergic cell population of the striatum responds to dopamine denervation by increasing in number, apparently to compensate for loss of extrinsic dopaminergic innervation. Moreover, this population of cells corresponds largely with the intrinsic GABAergic cells of the striatum. This study also suggests that the adult primate striatum does retain some intrinsic capacity to compensate for dopaminergic cell loss.     

Motor and learning dysfunction during postnatal development in mice defective in dopamine neuronal transmission

Mice lacking expression of tyrosine hydroxylase (TH), the first and rate-limiting enzyme of the catecholamine biosynthetic pathway, in dopaminergic neuronal cell types were generated by a transgenic rescue approach to clarify the role of dopamine signaling during postnatal development. Introduction of the TH transgene directed by the dopamine beta-hydroxylase gene promoter into TH knockout mice restored noradrenaline and adrenaline synthesis, preventing perinatal lethality and cardiac dysfunction in the knockout mice. Lack of TH expression in the cells that normally express the dopaminergic phenotype resulted in a marked reduction of dopamine accumulation in the tissues, which led to multiple behavioral abnormalities at the juvenile stage. These abnormalities were characterized by a reduction in spontaneous locomotor activity, blockade of methamphetamine-induced hyperactivity, cataleptic behavior, and defects in active avoidance learning. In contrast, development of the pituitary gland as well as production and secretion of the pituitary peptide hormones dependent on hypothalamic dopaminergic control were normally maintained, despite defective dopamine synthesis. These results demonstrate that dopamine neurotransmission is essential for controlling spontaneous and voluntary movement and associative learning during postnatal development through the nigrostriatal and mesocorticolimbic pathways.     

Effect of buthionine sulfoximine, a synthesis inhibitor of the antioxidant glutathione, on the murine nigrostriatal neurons

This study analyzed the effects of acute systemic treatment with buthionine sulfoximine (BSO), a synthesis inhibitor of the antioxidant reduced glutathione (GSH), on dopaminergic neurons of the murine nigrostriatal pathway. Part 1 of the study established a dose-response curve and the temporal pattern of GSH loss and recovery in the substantia nigra and striatum following acute BSO treatment. Part 2 of the study determined the effect of acute BSO treatment on the morphology and biochemistry of nigrostriatal neurons. We found that decreases in GSH levels had profound morphological effects, including decreased catecholamine fluorescence per cell, increased levels of lipid peroxidation and lipofuscin accumulation, and increased numbers of dystrophic axons in dopaminergic neurons of the nigrostriatal pathway. However, no measurable effects were observed in biochemical levels of either dopamine or its metabolites. These changes mimic those that have been reported to occur in the nigrostriatal system of rodents with advancing age. Our data suggest that reduction of GSH via BSO treatment results in the same types of nigrostriatal degenerative effects that occur during the aging process and consequently is a good model system for examining the role of GSH in protecting this area of the brain against the harmful effects of age-related oxidative stress.     

Expression of matrix proteins in uterine cervical neoplasia using immunohistochemistry

We investigated whether oral administration of coenzyme Q10 (CoQ10) could attenuate 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) neurotoxicity in one-year-old mice. Four groups of one-year-old, male C57BL/6 mice received a either standard diet or a diet supplemented with CoQ10 (200 mg/kg/day) for five weeks. After four weeks, one group that had received the standard diet and one group that had received the CoQ10 supplemented diet were treated with MPTP. The four groups continued on their assigned diets for an additional week prior to sacrifice. Striatal dopamine concentrations were reduced in both groups treated with MPTP, but they were significantly higher (37%) in the group treated with CoQ10 and MPTP than in the group treated with MPTP alone. The density of tyrosine hydroxylase immunoreactive (TH-IR) fibers in the caudal striatum was reduced in both MPTP-treated groups, but the density of TH-IR fibers was significantly (62%) greater in the group treated with CoQ10 and MPTP than in the group treated with MPTP alone. Our results indicate that CoQ10 can attenuate the MPTP-induced loss of striatal dopamine and dopaminergic axons in aged mice and suggest that CoQ10 may be useful in the treatment of Parkinson's disease.     

Identifying crash involvement among older drivers: agreement between self-report and state records

Methamphetamine (METH)- and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced dopaminergic neurotoxicity is thought to be associated with the formation of free radicals. Since evidence suggests that melatonin may act as a free radical scavenger and antioxidant, the present study was undertaken to investigate the effect of melatonin on METH- and MPTP-induced neurotoxicity. In addition, the effect of melatonin on METH-induced locomotor sensitization was investigated. The administration of METH (5 mg kg(-1) x 3) or MPTP (20 mg kg(-1) x 3) to Swiss Webster mice resulted in 45-57% depletion in the content of striatal dopamine and its metabolites, 3,4-dihydroxyphenylacetic acid and homovanillic acid, and 57-59% depletion in dopamine transporter binding sites. The administration of melatonin (10 mg kg(-1)) before each of the three injections of the neurotoxic agents (on day 1), and thereafter for two additional days, afforded a full protection against METH-induced depletion of dopamine and its metabolites and dopamine transporter binding sites. In addition, melatonin significantly diminished METH-induced hyperthermia. However, the treatment with melatonin had no significant effect on MPTP-induced depletion of the dopaminergic markers tested. In the set of behavioral experiments, we found that the administration of 1 mg kg(-1) METH to Swiss Webster mice for 5 days resulted in marked locomotor sensitization to a subsequent challenge injection of METH, as well as context-dependent sensitization (conditioning). The pretreatment with melatonin (10 mg kg(-1)) prevented neither the sensitized response to METH nor the development of conditioned locomotion. Results of the present study indicate that melatonin has a differential effect on the dopaminergic neurotoxicity produced by METH and MPTP. Since it is postulated that METH-induced hyperthermia is related to its neurotoxic effect, while regulation of body temperature is unrelated to MPTP-induced neurotoxicity or METH-induced locomotor sensitization, the protective effect of melatonin observed in the present study may be due primarily to diminishing METH-induced hyperthermia.     

Cardiovirulent coxsackieviruses and the decay-accelerating factor (CD55) receptor

To determine the differences in behavioral effects between intrastriatal and intracerebroventricular glial cell-derived neurotrophic factor (GDNF) administration, spontaneous locomotor activity was measured after intrastriatal or intracerebroventricular injection of GDNF (10 microg) in normal adult rats with implanted guide cannulae. In addition, the distribution of GDNF after intracerebral injection was studied immunohistochemically. Intrastriatal administration of GDNF significantly increased rearing behavior 3-4 h after injection. Increases in all three aspects of locomotor activity (motility, locomotion, and rearing) were most pronounced 3 days after intrastriatal injection, and they lasted for several days. This hyperactivity was blocked by the selective dopamine D1 receptor antagonist SCH22390 and by the selective D2 receptor antagonist raclopride at doses of the dopamine receptor antagonists, which by themselves did not affect spontaneous locomotor activity. These results suggest that GDNF has both acute and long-lasting pharmacological effects on dopamine neurons in adult animals and stimulates locomotor activity by activating both dopamine D1 and D2 receptors. On the other hand, intracerebroventricular administration of the same dose of GDNF failed to increase locomotor activity at any time during the test period (12 days). The immunohistochemical study demonstrated widespread distribution of GDNF in the entire body of the striatum within 24 h after intrastriatal injection. It also revealed deep penetration of GDNF from the ventricular space into the brain parenchyma after intracerebroventricular injection. GDNF-immunoreactive neuronal cell bodies were seen in the ipsilateral substantia nigra pars compacta most frequently 6 h after intrastriatal injection. The number of such cell bodies after intracerebroventricular administration, on the other hand, was much lower than that seen after intrastriatal administration. Taken together, these data suggest that intrastriatal administration of GDNF is an effective approach for affecting DA transmission. Long-lasting behavior effects are mediated via dopamine D1 and D2 receptors. Higher doses of GDNF would probably be needed using the intracerebroventricular route as compared to intraparenchymal delivery to exert effects on the nigrostriatal system in Parkinson's disease patients.