| Parkinson's disease (PD) is a neurodegenerative disorder characterized by the progressive loss of the nigrostriatal dopamine (NSDA) neurons. The loss of these neurons leads to several debilitating symptoms including slowness of movement, rigidity, postural instability, and resting tremor. Current therapies for PD are aimed at replacing DA deficits for symptomatic relief, but treatments to slow or halt the progressive loss of NSDA neurons are not yet available. Therefore, the primary goal of this dissertation was to examine potential neuroprotective therapies using rodent models of PD.;Several potential etiologies of PD have been proposed including environmental exposure to neurotoxins, oxidative stress, inflammation, mitochondrial dysfunction, and protein aggregation. The neuroprotective strategies explored in this dissertation were targeted to reduce one or more of these causes of PD, induce the development of new NSDA neurons, or explore the effects of a lack of specific functional proteins in either a neurotoxin or inflammatory model of PD. The potential neuroprotective effect of the drug sildenafil in the neurotoxin MPTP (1-methyl-2-phenyl-1,2,3,6-tetrahydropyridine) model of PD was examined. However, sildenafil failed to demonstrate neurogenesis or a neuroprotective effect as indicated by a lack of attenuation of the loss of NSDA cell bodies and axon terminals following MPTP treatment.;Increased inflammation and oxidative stress observed in models of PD are primarily mediated by microglial cells within the brain. These two processes contribute to the progression of PD and partially result from activation of the microglial enzyme nicotinamide adenine dinucleotide phosphate (NADPH) oxidase. Inhibition of NADPH oxidase using the inhibitor apocynin was tested as a potential neuroprotective drug in the MPTP model of PD but was found to be ineffective in attenuating MPTP induced activation of NADPH oxidase and loss of NSDA axon terminals.;Endogenous cannabinoids (ECB) are involved in the regulation of NSDA neurons and microglial inflammation. NSDA neuronal integrity, activity, and regulation were initially characterized in mice lacking functional cannabinoid (CB) 1 and CB2 receptors, to determine if these mice were comparable to wildtype (WT) control mice. Mice lacking CB1 and CB2 receptors were determined to have typical integrity, activity and regulation of NSDA neurons. Next, CB1/CB2 knockout (KO) mice were used to determine if absence of CB1 and CB2 receptors alters NSDA neuronal susceptibility to MPTP neurotoxicity or lipopolysaccharide (LPS) induced acute inflammation. The loss of axon terminal DA concentrations was found to be attenuated in a MPTP model of PD suggesting inhibition of one or more of these receptors could be neuroprotective in PD. However, pharmacologic inhibition of these receptors (either individually or together) failed to replicate the neuroprotective results seen in CB1/CB2 KO mice. In addition, acute inflammation induced by LPS did not alter the integrity or activity of NSDA neurons. These findings suggest that neither sildenafil or apocynin are viable neuroprotective agents in the treatment of PD, and that CB1 and CB2 receptors may play a role in MPTP induced loss of NSDA neurons. |
