Many studies of ‘executive control’ have focused on the prefrontal cortex (PFC), which contains the neuronal functional properties, modulatory neurotransmitters, and network connections with sensory and motor regions to make this large brain area a candidate region to provide all the necessary elements to voluntarily control behavior. However, like the motor and premotor cortex, the PFC is integrated with the basal ganglia (BG) in such a similar fashion, that it is impossible not to consider that the PFC might depend on the BG to implement executive control effectively. This thesis draws on knowledge of PFC and BG function, and combines studies that require the instantaneous top-down control over motor behavior with a neurological patient group with primarily BG dysfunction (Parkinson’s disease), to provide for a new understanding of prefrontal-BG networks sub-serving executive control. The tasks performed by subjects consist of antisaccades (generate a voluntary eye-movement away from a visual stimulus) and those dealing with task switching (change behavior after an alternate was previously required). Numerous neural and functional imaging studies have identified key areas of the prefrontal cortex and BG that are critical to antisaccade generation, and studies in task switching have implicated similar neural mechanisms that are involved in overriding one behavior with another. By combining task switching with antisaccades, this thesis specifically examines the neural mechanisms related to suddenly changing behavior, under conditions where one behavior is easier to perform than the other. The methods utilize on-line eye-tracking in healthy young adults and older adults with, and without, Parkinson’s disease, to develop theories of a role of the BG in executive control, and to search for specific neural correlates of executive control signals in the PFC, premotor cortex and BG using functional magnetic resonance imaging (fMRI). Together, the conclusions drawn from this thesis point to an important role of the BG in overriding more automatic behavior with behavior that is more difficult to perform. This thesis also suggests that this overriding mechanism occurs through the boosting of cortical executive control signals via net excitatory feedback from the BG. / Thesis (Ph.D, Neuroscience Studies) -- Queen's University, 2010-09-09 12:17:46.904

Parkinson’s disease (PD) is a movement disorder that is of basal ganglia origin. It is characterized by a severe loss of dopaminergic input to the striatum and symptoms such as bradykinesia, rigidity and tremor. There is growing evidence that PD is associated with pathological synchronous oscillatory activity in the basal ganglia, which primarily occurs in the 11-30 Hz range, the so-called beta band. The aim of this project was to better understand the oscillatory activity recorded from the basal ganglia of PD patients and to elucidate the significance of this activity in PD. To do this, neuronal firing and local field potentials (LFPs) were recorded from the subthalamic nucleus (STN) and globus pallidus internus (GPi) of PD patients undergoing stereotactic neurosurgery for implantation of therapeutic deep brain stimulation electrodes. Beta oscillatory LFP activity in the STN and GPi was found to be coherent with, and reflect to a certain degree, rhythmic activity in a population of local neurons. I have demonstrated for the first time that the degree of beta oscillatory firing in the STN, which is maximal in the motor portion, correlates with the patients’ benefit from dopaminergic medications, but not with baseline motor deficits. My study has also established that beta oscillatory firing in the STN does not positively correlate with the patients’ tremor scores and that during periods of tremor patients tend to have less beta oscillatory firing and increased neuronal oscillatory firing at the tremor frequency. Temporal examination of the LFPs recorded during periods of intermittent resting tremor revealed that stronger tremor is associated with increased LFP power in the low gamma range (35-55 Hz) and there is a decrease in the ratio of beta to gamma coherence. Similarly, a change in balance between oscillatory activities was observed during levodopa-induced dyskinesias. Finally, when the oscillatory activity in the GPi of PD patients was compared to that in dystonia I found that in dystonia, oscillatory LFP activity is less likely to reflect the neuronal firing. These findings indicate that beta oscillatory activity in the basal ganglia might reflect the degree of dopamine deficiency in the striatum and that the relative strength of oscillatory rhythms may play an important role in mediating the pathological features in PD.

The aim of this study is to establish a brief screening tool to classify PD patients as PD with normal cognition (PD-N), PD patients with mild cognitive impairment (PD-MCI) and PD patients with dementia (PD-D). There has been emerging evidence that the MoCA (Montreal Cognitive Assessment) shows potential for the brief assessment of cognition to differentiate among PD patients. One possible solution to further improve the discrimination among PD-D, PD-MCI and PD-N groups is to examine Instrumental Activities of Daily Living (IADL) measures in conjunction with the MoCA. A convenience sample of 162 patients suffering from PD and 53 volunteer control subjects were examined in a movement disorders center. Extensive neuropsychological testing was done to classify the PD patients into PD-N, PD-MCI or PD-D. The 24 patients were diagnosed as PD-D based on the Movement Disorders Society Task Force criteria. For PD-MCI, two criteria were used: 1.5SD:2 in one-domain (1.5 SD below the norms on two measures in at least one of four cognitive domains) and 1.5SD:1 in two-domains (1.5 SD below normative data in at least one measure but in two domains) which made a diagnosis of 34 and 39 PD-MCI patients respectively. The remaining patients were classified as PD-N. For both the MCI criteria, the results suggest that 1) for discriminating PD-MCI from PD-N, the MoCA is a sufficiently suitable screening measure that is not improved by adding ADL measures, 2) for distinguishing PD-D from PD-MCI, the MoCA and the full ADL-IS questionnaire can be administered to a patient suffering from PD. When time is limited and depending on the possibility of answering the questions regarding the ADL-IS items, the MoCA along with the Muddled and Complex Medication ADL-IS items should be administered. When no scores are obtained for Muddled, then MoCA along with Complex Medication ADL-IS item is sufficient to discriminate PD-D from PD-MCI. However, if no scores are obtained for Complex Medication item, then an average of four ADL-IS items should be taken along with the MoCA. This attractive brief screening tool helps in detection of cognitive impairment in the elderly.

Mit fortschreitendem Durchschnittsalter der Bevölkerung gewinnen altersbedingte Krankheiten immer mehr an Signifikanz. Demenz und Einschränkungen der Beweglichkeit wirken sich auf Individuen sowie auf Familien aus, da die progressive Abnahme kognitiver und physischer Fähigkeiten ihren Tribut von der Lebensqualität Betroffener sowie den Pflegenden fordert. Morbus Parkinson (PD) ist eine neurodegenerative Erkrankung, welche sich durch Symptome des Bewegungsapparates äußert, bedingt durch degenerative Prozesse im Mittelhirn, und welche mit Veränderungen des Gemütszustandes, Verhaltens sowie Depression und Demenz fortschreiten können. PD betrifft in der Regel ältere Personen, jedoch wurden Gene verschiedener zellulärer Funktionen identifiziert, deren Mutation zu einer frühen oder gar juvenilen Ausprägung der Krankheit führen kann. Ein Hauptakteur in PD ist α-Synuclein (ASYN), ein kleines Protein welches in PD-typischen Proteinablagerungen gefunden wurde. Die zelluläre Funktion von ASYN ist immernoch unbekannt, Mutation oder Überexpression jedoch können zu einem hypermorphen Phänotyp führen und die Verbindung zu PD ist daher unumstritten. Studien haben gezeigt, dass ASYN mit Proteintransportwegen und der Aufstellung der Transportmaschinerie interferiert. Genetische Rasterstudien identifizierten Modulatoren von ASYN-Toxizität in Genclustern des Vesikeltransports. Ebenso konnten Studien in Hefe zeigen, dass Überexpression von ASYN diverse Transportwege stört, besonders zu beachten ist hier der ER-zu-Golgi Transportweg, welcher kritisch für Posttranslationale Modifikationen verschiedener Proteine ist. Des Weiteren greift ASYN-Pathologie störend in die Homöostase von Rab GTPasen ein, eine Proteinfamilie involviert in Vesikeltransport, manche deren Mitglieder ASYN-Toxizität reduzieren können. In dieser Studie zeigen wir in einer Rasteruntersuchung mit Rab GTPasen in einem Säugerzellmodell von ASYN-Proteinanreichungen, dass die ASYN-Pathologe zu einer weitreichenden Störung von Rab GTPase assoziierten Transportwegen führt. Wir identifizieren zwei unterschiedliche endosomale Stoffwechselwege welche beim Auftreten von ASYN-Proteinablagerungen fehlreguliert werden: der endosomale-lysosomale-Proteintransportweg welcher das frühe Endosom beinhaltet, sowie den trans-Golgi Netzwerk (TGN) Transportweg. Die kleinen Rab GTPasen Rab5A, Rab7 und Rab8A haben fundamentale Auswirkungen auf die Formation von ASYN-Proteinansammlungen, Sekretion und Toxizität. Wir zeigen dass Rab8A in der Lage ist ASYN-Proteinansammlungen zu modulieren und agiert protektiv in Bezug auf zelluläre Toxizitätslevel in unserem Modell. Rab5A, ein Protein des frühen Endosoms, fehllokalisiert mit Formation der Ablagerungen, während das lysosomale Rab7 die Anzahl der Ablagerungen erhöht, aber nicht ihnen kolokalisiert. Des Weiteren benutzen wir Größenexklusionschromatographie (SEC) und Enzyme Linked Immunosorbent Assay (ELISA) um zu zeigen, dass Rab5A und Rab7 in Abhängigkeit ihres Aktivitätszustandes die Partikelgröße von ASYN ändert und die Sekretion moduliert. Die abschließende Bewertung eines Tiermodells welches humanes ASYN pan-neuronal überexpremiert zeigte, dass lysosomales Rab7 und die Protease Cathepsin D (CatD) in Hirnregionen verantwortlich für Bewegung, Motivation und Gedächtnis herausreguliert sind. Unsere Arbeit sowohl in Säugerzellkultur sowie in transgenen Tieren deutet darauf hin, dass die ASYN-Pathologie Auswirkungen auf das endosomale Transportsystem hat, aber zeigt auch die Fähigkeit von Proteinen, welche mit diesem Transportsystem assoziiert sind, die Toxizität von ASYN zu modulieren. Daher schließen wir, dass Anomalien in der Transportmaschinerie von Endosomen, welche durch Fehlregulation ASYN verursacht wurden, zur Entstehung der PD Pathologie beitragen.

Recent research has found that perceptual deficits exist in Parkinson???s disease (PD), yet the link between perception and movement impairments is not well understood. Inaccurate estimation of distance has the potential to be an underlying cause of movement impairments. Alternatively, those with PD may not be able to perceive their own movements accurately. The main objective of this thesis was to evaluate (1) whether distance estimation is influenced by static perception compared to perception during movement in PD, (2) how visual motion processing contributes to distance estimation during movement, and (3) how dopaminergic medication contributes to these distance estimation deficits. Thirty-seven participants (19 individuals with PD, 18 age-matched healthy control participants (HC) estimated distance to a remembered target in a total of 48 trials, in 4 randomized blocks. Estimation conditions included: (i) no motion: participants pointed with a laser, (ii) motion: participants walked to the estimated position, (iii) visual motion (wheelchair): participants were pushed in a wheelchair while they gave their estimate, (iv) visual motion (VR): participants completed their distance estimate while seated and viewed themselves (as if they were walking) in VR. PD patients completed this protocol twice; once OFF and once ON dopaminergic medication. Participants were matched for age, distance acuity, Modified Mini Mental State Exam (3MS), spatial working memory and motor planning ability. In Study 1 (no motion vs. motion), individuals with PD and healthy control participants did not differ in judgment accuracy during the no motion condition. However, those with PD did have greater amounts of error compared to healthy control participants while estimating distance during the motion condition. Similarly, those with PD significantly underestimated the target position compared to healthy control participants during the motion condition only. Individuals with PD demonstrated greater variability overall. In Study 2, error did not differ between PD and HC groups during visual motion perception (wheelchair). Interestingly, the HC group tended to perform significantly worse than those with PD in the VR condition. Overall, across both studies there was no significant influence of dopaminergic medication in any of the conditions. Individuals with PD demonstrated distance estimation deficits only when required to move through their environment. In contrast to estimations made with movement, neither static estimation nor estimations made with visual motion revealed significant differences between the two groups. Thus perceptual estimation deficits appear to occur only during movement, which may be suggestive of an underlying sensory processing deficit which leads to a problem integrating vision and self-motion information.

Parkinson's disease (PD) is the most common neurodegenerative motor disorder, whose clinical features are rest tremor, bradykinesia, muscular rigidity and postural instability. Although most reported cases are sporadic, a handful of familial cases and their causative genes have been identified. Loss-of-function mutations in DJ-1, one of these genes, are responsible for 1% of familial PD cases. Our laboratory has previously reported that DJ-1- lacking neurons are sensitive to oxidative stress, induced by hydrogen peroxide or the neurotoxin MPTP. To investigate the possible mechanisms through which DJ-1 protects against oxidative stress, we performed a proteomic screen and identified Von Hippel Lindau (VHL) and Paraoxonase2 (PON2) as potential DJ-1 interacting partners. VHL is an E3 ubiquitin ligase which, in normal conditions, poly-ubiquitinates HIF-1 , a subunit of a master hypoxic/oxidative stress transcription factor, whose function is protective in oxidative and hypoxic stresses. In the present study, we provided further evidence of interaction of DJ-1 with VHL. We also demonstrated that HIF-1 protein level, as an indicator of VHL activity, is lower in cells lacking DJ-1, suggesting the inhibitory role of DJ-1 on VHL. Our in vitro studies also showed that DJ-1 inhibits ubiquitin ligase activity of VHL on HIF-1 by reducing the VHL-HIF-1 interaction. Importantly, accumulation of HIF-1 protects embryonic cortical neurons against MPP+ induced neuronal death. Finally, we confirmed the impairment of HIF-1 response to oxidative stress in human lymphoblastoids of DJ-1-linked PD cases. In the second part of this study, we demonstrated the interaction of DJ-1 and PON2. Interestingly, PON2 lactonase activity is reduced in DJ-1 deficient cells which could be rescued by re-introduction of DJ-1, suggesting a modulating role of DJ-1 on PON2 activity. In addition, PON2 deficiency, like DJ-1 deficiency, hypersensitizes neurons to MPP+, which could be rescued by over-expression of PON2 in both cases. Taken together, our data provide evidence that DJ-1 exerts its protective role by inhibiting VHL activity, enhancing HIF-1 stability, and increasing PON2 pro-survival function in PD models.

Mitochondrial dysfunction has been implicated as one of the primary causes of Parkinson's disease (PD). The proteins PINK1, a serine-threonine kinase, and Parkin, an E3 ubiquitin ligase, are mutated in many genetic cases of PD. In healthy individuals, Parkin is recruited to damaged mitochondria and leads to autophagic degradation of mitochondria in a process termed mitophagy. Following depolarization of the mitochondrial membrane, PINK1 is stabilized on the outer mitochondrial membrane, and triggers Parkin translocation from the cytosol to mitochondria. Precisely how this phenomenon is regulated is still unclear. We employed RNA interference (RNAi) technology in a 384-well format to identify novel genes that are required for Parkin recruitment to mitochondria. We identified ATPase inhibitory factor 1 (IF1) as the strongest hit required for Parkin recruitment following treatment with the protonophore CCCP. We show that IF1 is upstream of PINK1 and Parkin, and required to sense mitochondrial damage by allowing the loss of membrane potential. In cells treated with CCCP, the absence of IF1 permits the ATP synthase to run freely in reverse, consuming ATP to maintain potential across the inner mitochondrial membrane, thus blocking PINK1 and Parkin activation. Interestingly, Rho0 cells, that lack mitochondrial DNA, have downregulated endogenous expression of IF1 in order to maintain mitochondrial function. Overexpression of IF1 in Rho0 cells results in the depletion of mitochondrial membrane potential and the initiation of mitophagy. These data demonstrate a unique role for IF1 in the regulation of mitochondrial quality control that has not been explored in the etiology of PD.

Parkinson’s disease is a common neurological disorder with a complex etiology. The disease is characterized by a progressive loss of dopaminergic cells in the substantia nigra, which leads to motor function and sometimes cognitive function disabilities. One of the pathological hallmarks in Parkinson’s disease is the cytoplasmic inclusions called Lewy bodies found in the dopamine neurons. The aggregated protein α-synuclein is a main component of Lewy bodies. In view of severe symptoms and the upcoming of problematic side effects that are developed by the current most commonly used treatment in Parkinson’s disease, new treatment strategies need to be elucidated. One such strategy is replacing the lost dopamine neurons with new dopamine-rich tissue. To improve survival of the implanted neurons, neurotrophic factors have been used. Glial cell line-derived neurotrophic factor (GDNF), which was discovered in 1993, improves survival of ventral mesencephalic dopamine neurons and enhances dopamine nerve fiber formation according to several studies. Thus, GDNF can be used to improve dopamine-rich graft outgrowth into the host brain as well as inducing sprouting from endogenous remaining nerve fibers. This study was performed on Gdnf gene-deleted mice to investigate the role of GDNF on the nigrostriatal dopamine system. The transplantation technique was used to create a nigrostriatal microcircuit from ventral mesencephalon (VM) and the lateral ganglionic eminence (LGE) from different Gdnf gene-deleted mice. The tissue was grafted into the lateral ventricle of wildtype mice. The results revealed that reduced concentrations of GDNF, as a consequence from the Gdnf gene deletion, had effects on survival of dopamine neurons and the dopamine innervation of the nigrostriatal microcircuit. All transplants had survived at 3 months independently of Gdnf genotype, however, the grafts derived from Gdnf gene-deleted tissue had died at 6 months. Transplants with partial Gdnf gene deletion survived up to 12 months after transplantation. Moreover, the dopaminergic innervation of striatal co-grafts was impaired in Gdnf gene-deleted tissue. These results highlight the role of GDNF for long-term maintenance of the nigrostriatal dopamine system. To further investigate the role of GDNF expression on survival and organization of the nigrostriatal dopamine system, VM and LGE as single or combined to double co-grafts created from mismatches in Gdnf genotypes were transplanted into the lateral ventricle of wildtype mice. Survival of the single grafts was monitored over one year using a 9.4T MR scanner. The size of single LGE transplants was significantly reduced by the lack of GDNF already at 2 weeks postgrafting while the size of single VM was maintained over time, independently of GDNF expression. The double grafts were evaluated at 2 months, and the results revealed that lack of GDNF in LGE reduced the dopamine cell survival, while no loss of dopamine neurons was found in VM single grafts. The dopaminergic innervation of LGE was affected by absence of GDNF, which also caused a disorganization of the striatal portion of the co-grafts. Small, cytoplasmic inclusions were frequently found in the dopamine neurons in grafts lacking GDNF expression. These inclusions were not possible to classify as Lewy bodies by immunohistochemistry and the presence of phospho-α-synuclein and ubiquitin; however, mitochondrial dysfunction could not be excluded. To further study the death of the dopamine neurons by the deprivation of GDNF, the attention was turned to how Lewy bodies are developed. With respect to the high levels of α-synuclein that was found in the striatum, this area was selected as a target to inject the small molecule – FN075, which stimulates α-synuclein aggregation, to further investigate the role of α-synuclein in the formation of cytoplasmic inclusions. The results revealed that cytoplasmic inclusions, similar to those found in the grafts, was present at 1 month after the injection, while impairment in sensorimotor function was exhibited, the number of dopamine neurons was not changed at 6 months after the injection. Injecting the templator to the substantia nigra, however, significantly reduced the number of TH-positive neurons at 3 months after injection. In conclusion, these studies elucidate the role of GDNF for maintenance and survival of the nigrostriatal dopamine system and mechanisms of dopamine cell death using small molecules that template the α-synuclein aggregation.

Parkinson’s disease (PD) is characterized by the loss of dopamine in the basal ganglia and leads to paucity of movements, rigidity of the limbs, and rest tremor. Synaptic plasticity was characterized in the substantia nigra pars reticulata (SNr), a basal ganglia output structure, in 18 PD patients undergoing implantation of deep brain stimulating electrodes. Field evoked potentials (fEPs) in SNr were measured with one microelectrode using single pulses from a second microelectrode ~ 1 mm away. High frequency stimulation (HFS – 4 trains of 2s at 100Hz) in the SNr failed to induce a lasting change in test fEPs amplitudes in patients OFF medication. Following L-Dopa, HFS induced a potentiation of the fEPs that lasted more than 150s. Our findings suggest that extrastriatal dopamine modulates activity dependent synaptic plasticity at basal ganglia output neurons. Dopamine medication state clearly impacts fEP amplitude, and the lasting nature of the increase is reminiscent of LTP-like changes, indicating that aberrant synaptic plasticity may play a role in the pathophysiology of PD.

Parkinson’s disease (PD) is accompanied by a significant amount of beta β-band (11Hz-30Hz) neuronal and local field potential (LFP) oscillatory activity in the subthalamic nucleus (STN). The aim of this study was to measure the spatial extent of β coherent activity in the STN and coherence between STN-SNr in PD patients OFF levodopa by systematically varying the vertical distance between two microelectrodes. We found significant β-LFP coherence across the dorsoventral extent of STN. Spatially extended beta LFP was positively correlated with the mUPDRS scores of the PD patients in the OFF state. Additionally, a significant coherence was found between β-LFPs in dorsal STN and dorsal SNr. These data suggest that the whole STN may be entrained within the β band in PD patients OFF meds. The finding of coherence between STN and SNr suggests that β oscillations synchronize both the input and output nuclei of the basal ganglia.