University of Macau / Institute of Chinese Medical Sciences

Parkinson's disease (PD) is one of the most common motor neurodegenerative diseases, affecting 1-2% of the world's population over the age of 65. It is characterised by a loss of dopamine neurons within the substantia nigra, which is an integral part of the basal ganglia (BG) where dopamine is the most important modulating neurotransmitter. As the BG is primarily involved with the execution of movement, the lack of dopamine input results in dysfunctional motor control. The current PD treatment, L-DOPA, improves these motor symptoms, however only provides patients 5 to 10 years of improved quality of life before debilitating side effects, often worse than the original symptoms, begin. The neuropeptide substance P (SP) is found in high concentration in the substantia nigra, and BG in general, where it is involved in dopamine release. In the late stages of PD, SP content within the substantia nigra and BG is decreased, thus implicating SP in the pathophysiology of PD. However, SP production has not been examined in the early stages of PD when dopaminergic degeneration is first initiated. This thesis therefore sought to characterise the role of SP in dopaminergic degeneration in an experimental model of early PD, the 6-hydroxydopamine model in rats. In contrast to the prevailing dogma that a decline in SP is associated with neurodegeneration in PD, this thesis demonstrates that SP is actually increased within the striatum in early PD, particular in perivascular tissue and within surviving dopaminergic neurons during the degenerative process. Increasing exposure of the dopaminergic neurons to SP, either by inhibition of substance P breakdown with Captopril or by direct injection with SP, exacerbated the disease progression as indicated by more profound neurogenic inflammation, functional deficits and increased dopaminergic cell death. However, when SP was inhibited by treatment with a SP NK₁ receptor antagonist, dopaminergic neurons were conserved, the inflammatory response was reduced and motor function was returned to near normal levels. We conclude that SP is increased in early PD, and that increased SP plays an important role in the degenerative process, specifically, in the genesis of BBB breakdown and initiation of neurogenic inflammation. Treatment with an NK1 antagonist may thus represent a novel therapeutic approach to early stage Parkinson’s disease. / Thesis (Ph.D.) -- University of Adelaide, School of Medical Sciences, 2009

Parkinson's disease (PD) is one of the most common motor neurodegenerative diseases, affecting 1-2% of the world's population over the age of 65. It is characterised by a loss of dopamine neurons within the substantia nigra, which is an integral part of the basal ganglia (BG) where dopamine is the most important modulating neurotransmitter. As the BG is primarily involved with the execution of movement, the lack of dopamine input results in dysfunctional motor control. The current PD treatment, L-DOPA, improves these motor symptoms, however only provides patients 5 to 10 years of improved quality of life before debilitating side effects, often worse than the original symptoms, begin. The neuropeptide substance P (SP) is found in high concentration in the substantia nigra, and BG in general, where it is involved in dopamine release. In the late stages of PD, SP content within the substantia nigra and BG is decreased, thus implicating SP in the pathophysiology of PD. However, SP production has not been examined in the early stages of PD when dopaminergic degeneration is first initiated. This thesis therefore sought to characterise the role of SP in dopaminergic degeneration in an experimental model of early PD, the 6-hydroxydopamine model in rats. In contrast to the prevailing dogma that a decline in SP is associated with neurodegeneration in PD, this thesis demonstrates that SP is actually increased within the striatum in early PD, particular in perivascular tissue and within surviving dopaminergic neurons during the degenerative process. Increasing exposure of the dopaminergic neurons to SP, either by inhibition of substance P breakdown with Captopril or by direct injection with SP, exacerbated the disease progression as indicated by more profound neurogenic inflammation, functional deficits and increased dopaminergic cell death. However, when SP was inhibited by treatment with a SP NK₁ receptor antagonist, dopaminergic neurons were conserved, the inflammatory response was reduced and motor function was returned to near normal levels. We conclude that SP is increased in early PD, and that increased SP plays an important role in the degenerative process, specifically, in the genesis of BBB breakdown and initiation of neurogenic inflammation. Treatment with an NK1 antagonist may thus represent a novel therapeutic approach to early stage Parkinson’s disease. / Thesis (Ph.D.) -- University of Adelaide, School of Medical Sciences, 2009

Treatment of brain diseases remains extremely challenging partly due to the fact that critical drug delivery is hindered by the blood-brain barrier (BBB), a specialized and highly selective barrier lining the brain vasculature. Focused ultrasound (FUS), combined with systematically administered microbubbles (MBs), has been established as a technique to noninvasively, locally, and transiently open the BBB. The primary mechanism for temporarily opening the BBB using FUS is microbubble cavitation, a phenomenon that occurs when the circulating microbubbles interact with the FUS beam in the brain vasculature. Over the past two decades, many preclinical and clinical applications of FUS-induced BBB opening have been developed, but certain challenges, such as drug delivery route, cavitation control, inflammation onset, and overall accessibility of the technology, have affected its efficient translation to the clinic. This dissertation focuses on optimizing three aspects of FUS-induced BBB opening for therapeutic applications. The first specific aim investigated FUS-induced BBB opening for drug delivery through the intranasal route. Optimal sonication parameters were determined and applied to FUS-enhanced intranasal delivery of neurotrophic factors in a Parkinson’s Disease mouse model. In the second specific aim, cavitation levels affecting the inflammatory response due to BBB opening with FUS were optimized. The relationship between cavitation during FUS-induced BBB opening and the local inflammation was examined, and a cavitation-based controller system was developed to modulate the inflammatory response. In the third specific aim, the devices used for FUS-induced BBB opening were streamlined. A conventional system for FUS-induced BBB opening includes two transducers: one for therapy and another for cavitation monitoring (single element) or imaging (multi-element). In this aim, a single linear array transducer capable of synchronous BBB opening and cavitation imaging was developed, creating a cost-effective and highly accessible “theranostic ultrasound” device. The feasibility of theranostic ultrasound (TUS) was demonstrated in vivo in both mice and non-human primates. In summary, the findings and methodologies in this dissertation optimized FUS-enhanced intranasal delivery across the BBB, developed a cavitation-controlled system to modulate inflammation in the brain, which has been advantageous in reducing pathology and designed a new system for theranostic ultrasound for drug delivery to the brain. Taken altogether, this thesis contributes to the efficient advancement and optimization of FUS-induced BBB opening technology, thus enhancing its clinical adoption in the fight to treat many challenging brain diseases.

Based on the belief that it is a locomotor control structure, the pedunculopontine tegmental nucleus (PPTg) has been considered a potential target for deep brain stimulation (DBS) for Parkinson's disease (PD) patients with symptoms refractory to medication and/or stimulation of established target sites. To date, a number of patients have been implanted with PPTg electrodes with mostly disappointing results. Exact target site in PPTg, possible mechanisms of PPTg-DBS and likely potential benefits need to be systematically explored before consideration of further clinical application. The research described here approaches these questions by (i) investigating the role of the PPTg in gait per se; (ii) developing a refined model of PD that mimics the underlying pathophysiology by including partial loss of the PPTg itself; (iii) adapting a wireless device to let rats move freely while receiving DBS; and (iv) investigating the effect of DBS at different sites in the PPTg on gait and posture in the traditional and refined model of PD. Underlining the concern that understanding the PPTg as a locomotor control structure is inadequate, the experiments showed that neither partial nor complete lesions of PPTg caused gait deficits. The refined model showed hardly any differences compared to the standard one, but the effect of DBS in each was very different, highlighting the need to take degeneration in the PPTg into consideration when investigating it as a DBS target. The differential results of anterior and posterior PPTg-DBS show the critical importance of intra-PPTg DBS location: Anterior PPTg electrodes caused severe freezing and worsened gait while some gait parameters improved with stimulation of posterior PPTg. The results suggest mechanisms of PPTg-DBS beyond the proposed activation of over-inhibited PPTg neurons, including aggravation of already dysfunctional inhibitory input by anterior PPTg-DBS and activation of ascending projections from posterior PPTg to the forebrain.