Parkinson's disease results from the progressive degeneration of dopamine neurons that innervate the striatum. In rodents, glial-cell-line-derived neurotrophic factor (GDNF) stimulates an increase in midbrain dopamine levels, protects dopamine neurons from some neurotoxins, and maintains injured dopamine neurons. Here we extend the rodent studies to an animal closer to the human in brain organization and function, by evaluating the effects of GDNF injected intracerebrally in rhesus monkeys that have had the symptomatology and pathophysiological features of Parkinson's disease induced by the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). The recipients of GDNF displayed significant improvements in three of the cardinal symptoms of parkinsonism: bradykinesia, rigidity and postural instability. GDNF administered every four weeks maintained functional recovery. On the lesioned side of GDNF-treated animals, dopamine levels in the midbrain and globus pallidus were twice as high, and nigral dopamine neurons were, on average, 20% larger, with an increased fibre density. The results indicate that GDNF may be of benefit in the treatment of Parkinson's disease.

The powerful trophic effects that glial cell line-derived neurotrophic factor (GDNF) exerts on midbrain dopamine neurones suggest its use in treating Parkinson's disease. However, some important questions remain about the possible therapeutic applications of GDNF. Here we demonstrate that the chronic infusion of 5 or 15 micro g/day GDNF into the lateral ventricle or the striatum, using programmable pumps, promotes restoration of the nigrostriatal dopaminergic system and significantly improves motor functions in rhesus monkeys with neural deficits modelling the terminal stages of Parkinson's disease. The functional improvements were associated with pronounced upregulation and regeneration of nigral dopamine neurones and their processes innervating the striatum. When compared with vehicle recipients, these functional improvements were associated with (i) >30% bilateral increase in nigral dopamine neurone cell size; (ii) >20% bilateral increase in the number of nigral cells expressing the dopamine marker tyrosine hydroxylase; (iii) >70 and >50% bilateral increase in dopamine metabolite levels in the striatum and the pallidum, respectively; (iv) 233 and 155% increase in dopamine levels in the periventricular striatal region and the globus pallidus, respectively, on the lesioned side; and (v) a five-fold increase in tyrosine hydroxylase-positive fibre density in the periventricular striatal region on the lesioned side. In addition, chronic GDNF treatment did not induce the side-effects generally associated with chronic administration of levodopa, the most widely used treatment for Parkinson's disease. Thus, the results suggest that the prolonged and controlled delivery of GDNF into the brain could be used to intervene in long-term neurodegenerative disease processes like Parkinson's disease. Additional studies are required to determine the potential differences between chronic, intraventricular and intraputamenal (or intranigral) delivery of GDNF to maximize the efficacy of infusion treatments.

No abstract

Huntington's disease is caused by expression of a mutant form of Huntingtin protein containing an expanded polyglutamine repeat. One possible treatment for Huntington's disease may be to reduce expression of mutant Huntingtin in the brain via RNA interference. Unless the therapeutic molecule is designed to be allele-specific, both wild-type and mutant protein will be suppressed by an RNA interference treatment. A key question is whether suppression of wild-type as well as mutant Huntingtin in targeted brain regions can be tolerated and result in a net benefit to patients with Huntington's disease. Whether Huntingtin performs essential functions in the adult brain is unclear. Here, we tested the hypothesis that the adult primate brain can tolerate moderately reduced levels of wild-type Huntingtin protein for an extended period of time. A serotype 2 adeno-associated viral vector encoding for a short hairpin RNA targeting rhesus huntingtin messenger RNA (active vector) was bilaterally injected into the striatum of four adult rhesus monkeys. Four additional animals received a comparable vector encoding a scrambled control short hairpin RNA (control vector). General health and motor behaviour were monitored for 6 months. Upon termination, brain tissues were sampled and assessed blindly for (i) huntingtin messenger RNA knockdown; (ii) Huntingtin protein expression; and (iii) neuropathological changes. Reduction in wild-type huntingtin messenger RNA levels averaging ∼30% was measured in the striatum of active vector recipients 6 months post-injection. A widespread reduction in Huntingtin protein levels was also observed by immunohistochemistry in these animals, with an average protein reduction of ∼45% relative to controls measured by western blot analysis in the putamen of active vector recipients. As with control vector recipients, no adverse effects were observed behaviourally, and no neurodegeneration was found on histological examination of active vector recipients. Our results suggest that long-term partial suppression of wild-type Huntingtin may be safe, and thus if a comparable level of suppression of mutant Huntingtin is beneficial, then partial suppression of both wild-type and mutant Huntingtin may result in a net benefit in patients with heterozygous Huntington's disease.

Site-specific delivery of trophic factors in the brain may be important for achieving therapeutic efficacy without unwanted side effects. This study evaluated the site-specific infusion of glial cell line-derived neurotrophic factor (GDNF) into the right putamen of aged rhesus monkeys. After 4 weeks of continuous infusion at a rate of 22.5 microg/day, GDNF had diffused up to 11 mm from the catheter openings in the putamen into the rostral putamen, internal capsule, external capsule, caudate nucleus, and globus pallidus. Anisotropic flow along the external capsule tracts carried GDNF into the anterior amygdaloid area. Backflow of GDNF along the catheter track from the frontal cortex infiltrated juxtaposed corpus callosal and cortical tissue. GDNF was carried by retrograde transport to dopamine neurons in the ipsilateral substantia nigra, stimulating an 18% increase in the number of tyrosine hydroxylase (TH)-positive dopamine neurons and a 28% increase in dopamine neuron perikaryal size. Also, TH-positive fiber density was increased in the ipsilateral globus pallidus, caudate nucleus, and putamen. Anatomic effects from GDNF stimulation of the dopaminergic system were restricted to the ipsilateral hemisphere. Retrograde GDNF labeling was also present in a few TH-positive neurons in the locus coeruleus and a large cluster of TH-negative neurons in the ventral anterior thalamus. Anterograde transport of GDNF was evident in axons in the pyramidal tract from the cerebral peduncle to the caudal spinal cord. Tissue injury from the intraparenchymal catheter and continuous infusion was confined primarily to a narrow zone surrounding the track and was mild to moderate in severity.

Purpose: To estimate the relationship between R 2 ϭ 1/T 2 as measured with a double echo spin echo sequence and total iron concentration in gray matter structures in the brains of aging rhesus monkeys. Materials and Methods:Using a 1.5-T magnetic resonance (MR) imager, we collected double echo spin echo images of the brains of 12 female rhesus monkeys aged between 9 and 23 years. From the double echo images, the transverse relaxation rate R 2 ϭ 1/T 2 was calculated in selected gray matter regions. After the animals were euthanized, their brains were excised and tissue punches were taken of the substantia nigra, globus pallidus, and gray matter regions of the cerebellum. Some of the tissue punches were assayed for total iron using atomic absorption spectroscopy. Results:The range of tissue iron concentration spanned from 15 to 450 g/g wet weight, with the highest levels in the globus pallidus and the lowest levels in the cerebellum. The results show that R 2 was highly correlated with the total iron concentration and that the relationship between R 2 and tissue iron concentration appeared to depend upon the iron concentration. For concentrations above approximately 150 g/g wet weight, R 2 increased with a sensitivity of 0.0484 Ϯ 0.0023 second -1 ( g/g) -1 . In contrast, where the iron concentration was below 150 g/g, R 2 increased at 0.0013 Ϯ 0.0073 second -1 ( g/g) -1 . The bilinear behavior may reflect changes with age in the relative amounts of iron distributed diffusely and in granular form in the globus pallidus and substantia nigra. Histological sections of the tissues stained for iron and ferritin support this hypothesis and indicate that the distribution of ferritin is similar to the distribution of iron. Conclusion:This study reaffirms the value of measuring the MR relaxation rate R 2 for a noninvasive estimate of iron content in the brain and identified limitations in the relationship at low tissue iron concentrations.

Microbial communities of human gut directly influence health and bear adaptive potential to different geography environment and lifestyles. However, knowledge about the influences of altitude and geography on the gut microbiota of Tibetans is currently limited. In this study, fecal microbiota from 208 Tibetans across six different locations were analyzed by MiSeq sequencing; these locations included Gannan, Gangcha, Tianzhu, Hongyuan, Lhasa and Nagqu, with altitudes above sea level ranging from 2800 m to 4500 m across the Tibetan plateau. Significant differences were observed in microbial diversity and richness in different locations. At the phylum level, gut populations of Tibetans comprised Bacteroidetes (60.00%), Firmicutes (29.04%), Proteobacteria (5.40%), and Actinobacteria (3.85%) and were marked by a low ratio (0.48) of Firmicutes to Bacteroidetes. Analysis based on operational taxonomic unit level revealed that core microbiotas included Prevotella, Faecalibacterium, and Blautia, whereas Prevotella predominated all locations, except Gangcha. Four community state types were detected in all samples, and they mainly belong to Prevotella, Bacteroides, and Ruminococcaceae. Principal component analysis and related correspondence analysis results revealed that bacterial profiles in Tibetan guts varied significantly with increasing altitude, BMI, and age, and facultative anaerobes were rich in Tibetan guts. Gut microbiota may play important roles in regulating high-altitude and geographical adaptations.

For these studies, young (8±9 years), middle-aged (14± 17 years) and aged (23±28 years) rhesus monkeys were used as a model of normal aging in humans to investigate changes in dopamine (DA)-containing neurons in senescence. Aged monkeys exhibited signi®cant age-related motoric declines as compared to the young animals. In vivo microdialysis studies showed that basal levels of the DA metabolites, homovanillic acid (HVA) and 3,4-dihydroxyphenylacetic acid (DOPAC) were diminished by 44% and 79%, respectively, in the substantia nigra (SN) of aged monkeys. In addition, D-amphetamine-evoked over¯ow of DA in the SN was diminished by 30% in the middle-aged animals and 67% in the aged monkeys. Post-mortem measures of DA and DA metabolites showed signi®cant decreases in DA (20%), DOPAC (47%) and HVA (22%) levels in the putamen and a 25% decline in HVA tissue levels in the SN of the aged monkeys as compared to the young animals. Unbiased stereological cell counting of tyrosine hydroxylase (TH)-immunoreactive neurons in the SN showed a small (15±20%) but signi®cant agerelated decline in TH-positive neurons. In addition, there was a small (15±20%) but signi®cant decline in TH-positive ®ber density and TH-positive cell size. In comparison to the massive loss of DA neurons responsible for the movement dysfunctions seen in Parkinson's disease, pronounced functional changes in DA release in the SN and putamen may signi®-cantly contribute to the motoric dysfunctions characterizing normal aging in rhesus monkeys.