Don M. Gash

GDNF protects nigral dopamine neurons against 6-hydroxydopamine in vivo

Glial cell line-derived neurotrophic factor (GDNF), a novel member of the TGF-beta superfamily, has been shown to promote the survival and morphological differentiation of fetal dopamine neurons in culture and increase dopamine levels and metabolism in adult rats. Since several other trophic factors are able to rescue specific populations of mature CNS neurons following injury, the present study was designed to investigate a possible neuroprotective role by GDNF for midbrain dopamine neurons in rats exposed to the neurotoxin 6-hydroxydopamine (6-OHDA). Prior to surgery, young adult male Fisher 344 rats were divided into the following groups (n = 7-8/group): (1) intranigral saline + intranigral 6-OHDA; (2) intranigral GDNF + intranigral 6-OHDA; (3) intranigral saline + intrastriatal 6-OHDA; and (4) intranigral GDNF + intrastriatal 6-OHDA. The saline treated groups received a single 2 microliters intranigral injection of phosphate buffered saline (PBS) while the GDNF treated rats received 10 micrograms/2 microliters GDNF in PBS. Twenty-four hours later, the animals received a unilateral 4 micrograms/microliters 6-OHDA infusion either into the substantia nigra or striatum. The rats were sacrificed two weeks postsurgery and the brains processed for tyrosine hydroxylase (TH) immunocytochemistry. Representative TH immunoreactive (TH-IR) sections were also counterstained with hematoxylin and eosin to determine the total number of neurons remaining in the substantia nigra pars compacta and ventral tegmental area. In the nigral lesion groups, there was significantly less loss of TH-IR neurons in the substantia nigra pars compacta of GDNF (47% survival) vs. PBS (9% survival) treated animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Caloric restriction increases neurotrophic factor levels and attenuates neurochemical and behavioral deficits in a primate model of Parkinson's disease

We report that a low-calorie diet can lessen the severity of neurochemical deficits and motor dysfunction in a primate model of Parkinsons disease. Adult male rhesus monkeys were maintained for 6 months on a reduced-calorie diet [30% caloric restriction (CR)] or an ad libitum control diet after which they were subjected to treatment with a neurotoxin to produce a hemiparkinson condition. After neurotoxin treatment, CR monkeys exhibited significantly higher levels of locomotor activity compared with control monkeys as well as higher levels of dopamine (DA) and DA metabolites in the striatal region. Increased survival of DA neurons in the substantia nigra and improved manual dexterity were noted but did not reach statistical significance. Levels of glial cell line-derived neurotrophic factor, which is known to promote the survival of DA neurons, were increased significantly in the caudate nucleus of CR monkeys, suggesting a role for glial cell line-derived neurotrophic factor in the anti-Parkinsons disease effect of the low-calorie diet.

Critical decline in fine motor hand movements in human aging

BACKGROUND Slowing of motor movements in human aging is a well-known occurrence, but its biologic basis is poorly understood. Reliable quantitation may refine observations of this phenomenon to better aid research on this entity. METHODS A panel equipped with timing sensors under computer control was used to measure upper extremity movement times in two groups of healthy individuals: adults younger than 60 years of age (n = 56; range, 18-58 years) and adults older than 60 years of age (n = 38; range, 61-94 years). RESULTS Fine motor performance was better in the dominant hand (p = 0.0007) regardless of age. Adult and aged groups differed on two basic timing measures, which reflect coarse motor and fine motor performance (p < 0.0001). There were no gender differences on either measure. There was a strong effect of task difficulty with age on coarse motor (p < 0.01) and fine motor (p < 0.0001) measures. The fine motor measure of hand performance in healthy individuals correlated in a nonlinear fashion with age for more difficult tasks (r2 = 0.63) but showed a simple linear relation for less-demanding tasks (r2 = 0.5). CONCLUSION This technique sensitively detects age-related motor performance decline in humans. There may be a critical period in late midlife when fine motor performance decline either begins or abruptly worsens.

Point source concentration of GDNF may explain failure of phase II clinical trial.

Significant differences have been reported in results from three clinical trials evaluating intraputamenal infusion of glial cell line-derived neurotrophic factor (GDNF) for the treatment of Parkinsons disease. To determine if problems in drug bioavailability could have contributed to the discrepancies between studies, we have analyzed the distribution of intraputamenally infused GDNF in the rhesus monkey brain using the delivery system and infusion protocol followed in a phase 2 clinical trial that failed to achieve its primary endpoint. I125-GDNF was unilaterally infused into the putamen of three adult rhesus monkeys for 7 days. Three age- and sex-matched animals received vehicle infusions following identical procedures. GDNF levels in the brain, peripheral organs, blood and CSF were quantified and mapped by GDNF immunocytochemistry, GDNF ELISAs and I125 measurements. Infused GDNF was found to be unevenly concentrated around the catheter, with tissue levels dropping exponentially with increasing distance from the point source of the single opening in the catheter tip. The volume of distribution of GDNF around the catheter, as determined by immunocytochemistry, varied over four-fold between animals ranging from 87 to 369 mm3. The concentration of GDNF around the catheter tip and limited diffusion into surrounding brain parenchyma support the hypothesis that drug bioavailability was limited to a small portion (2-9%) of the human putamen in the clinical trial using this catheter and infusion protocol.

Principal component analysis of the dynamic response measured by fMRI: a generalized linear systems framework.

Principal component analysis (PCA) is one of several structure-seeking multivariate statistical techniques, exploratory as well as inferential, that have been proposed recently for the characterization and detection of activation in both PET and fMRI time series data. In particular, PCA is data driven and does not assume that the neural or hemodynamic response reaches some steady state, nor does it involve correlation with any pre-defined or exogenous experimental design template. In this paper, we present a generalized linear systems framework for PCA based on the singular value decomposition (SVD) model for representation of spatio-temporal fMRI data sets. Statistical inference procedures for PCA, including point and interval estimation will be introduced without the constraint of explicit hypotheses about specific task-dependent effects. The principal eigenvectors capture both the spatial and temporal aspects of fMRI data in a progressive fashion; they are inherently matched to unique and uncorrelated features and are ranked in order of the amount of variance explained. PCA also acts as a variation reduction technique, relegating most of the random noise to the trailing components while collecting systematic structure into the leading ones. Features summarizing variability may not directly be those that are the most useful. Further analysis is facilitated through linear subspace methods involving PC rotation and strategies of projection pursuit utilizing a reduced, lower-dimensional natural basis representation that retains most of the information. These properties will be illustrated in the setting of dynamic time-series response data from fMRI experiments involving pharmacological stimulation of the dopaminergic nigro-striatal system in primates.

Intraputamenal infusion of GDNF in aged rhesus monkeys: Distribution and dopaminergic effects

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 μg/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. J. Comp. Neurol. 461:250–261, 2003.

Trichloroethylene: Parkinsonism and complex 1 mitochondrial neurotoxicity

To analyze a cluster of 30 industrial coworkers with Parkinsons disease and parkinsonism subjected to long‐term (8–33 years) chronic exposure to trichloroethylene.

GDNF Protection against 6-OHDA: Time Dependence and Requirement for Protein Synthesis

Glial cell line-derived neurotrophic factor (GDNF) injected intranigrally protects midbrain dopamine neurons against 6-hydroxydopamine (6-OHDA) toxicity. The timing between GDNF administration and exposure to 6-OHDA is critical in achieving optimal protection. When injected 6 hr before an intranigral injection of 6-OHDA, GDNF provides complete protection as measured by the number of surviving neurons in the substantia nigra of adult rats. The surviving neuronal population decreases by ∼50% with 12 and 24 hr separating GDNF and 6-OHDA administrations. In controls with 6-OHDA lesions, there is <10% survival of nigral dopamine neurons. No significant increase in survival is seen with either concurrent injections of GDNF and 6-OHDA or 1 hr GDNF pretreatment. Based on HPLC measurements, striatal and midbrain dopamine levels are at least twofold higher on the lesioned side in animals receiving GDNF 6 hr before a 6-OHDA lesion compared with vehicle recipients. Protein synthesis is necessary for GDNF-induced neuroprotective effects because cycloheximide pretreatment that inhibits protein synthesis also blocks neuroprotection.

Glial cell line-derived neurotrophic factor (GDNF): a drug candidate for the treatment of Parkinson’s disease

Abstract Considerable effort has been devoted to the search for molecules that might exert trophic influences on midbrain dopamine neurons, and potentially be of therapeutic value in the treatment of Parkinson’s disease. One such candidate is glial cell line-derived neurotrophic factor (GDNF). GNDF is distantly related to the transforming growth factor-β superfamily and is widely expressed in many neuronal and non-neuronal tissues. GDNF uses a multisubunit receptor system in which GFRα-1 and Ret function as the ligand-binding and signalling components, respectively. In addition to its effects on cultured fetal midbrain dopamine neurons, GDNF promotes recovery of the injured nigrostriatal dopamine system and improves motor functions in rodent and nonhuman primate models of Parkinson’s disease. Intraventricular, intrastriatal and intranigral routes of administration are efficacious in both models. In parkinsonian nonhuman primates, GDNF treatment improves bradykinesia, rigidity and postural instability. In this model, adult midbrain dopamine neurons stimulated by GDNF show increased cell size, neuritic extent, and expression of phenotypic markers. The neurorestorative effects of a single administration of GDNF last for at least a month and can be maintained in rhesus monkeys by monthly injections. GDNF also induces neuroprotective changes in dopamine neurons, which are active within hours following trophic factor administration in rodents. The powerful neuroprotective and neurorestorative properties of GDNF seen in preclinical studies suggest that trophic factors may play an important role in treating Parkinson’s disease.

Glial Cell Line-Derived Neurotrophic Factor Increases Stimulus-Evoked Dopamine Release and Motor Speed in Aged Rhesus Monkeys

Changes in the functional dynamics of dopamine release and regulation in the basal ganglia have been posited to contribute to age-related slowing of motor functions. Here, we report the effects of glial cell line-derived neurotrophic factor (GDNF) on the stimulus-evoked release of dopamine and motor speed in aged monkeys (21–27 years of age; n = 10). Although no changes were observed in the vehicle controls (n = 5), chronic infusions of 7.5 μg of GDNF per day for 2 months into the right lateral ventricle initially increased hand movement speed up to 40% on an automated hand-reach task. These effects were maintained for at least 2 months after replacing GDNF with vehicle, and increased up to another 10% after the reinstatement of GDNF treatment for 1 month. In addition, upper-limb motor performance times of the aged GDNF-treated animals (n = 5) recorded at the end of the study were similar to those of five young adult monkeys (8–12 years of age). The stimulus-evoked release of dopamine was significantly increased, up to 130% in the right caudate nucleus and putamen and up to 116% in both the right and left substantia nigra of the aged GDNF recipients compared with vehicle controls. Also, basal extracellular levels of dopamine were bilaterally increased, up to 163% in the substantia nigra of the aged GDNF-treated animals. The data suggest that the effects of GDNF on the release of dopamine in the basal ganglia may be responsible for the improvements in motor functions and support the hypothesis that functional changes in dopamine release may contribute to motor dysfunctions characterizing senescence.