• The Cycad Hypothesis: Sleep alterations in a progressive, environmental neurotoxin-induced model of parkinsonism

      McDowell, Kimberly Anne; Yarowsky, Paul J. (2011)
      Parkinson's disease (PD) is classically defined as a motor disorder resulting from decreased dopamine production in the basal ganglia circuit. In an attempt to better diagnose and treat PD before the onset of severe motor dysfunction, current attention has focused on the early, non-motor symptoms. Sleep disorders, such as excessive daytime sleepiness (EDS), are one of the most prominent initial symptoms in PD. Recently there have been studies revealing that the orexin-containing neurons of the hypothalamus, a cell type vital to sleep regulation, also degenerate in PD and may contribute to these associated sleep disorders. However, the role of orexin neurons in the development of PD remains controversial and relatively unstudied since few animal models can replicate both the motor and non-motor symptoms of the disease. We have developed a novel, progressive, neurotoxin-induced rat model of parkinsonism that accesses this subject. Epidemiological studies elucidated a fundamental connection between the Guamanian variant of Amyotrophic Lateral Sclerosis/Parkinsonism Dementia Complex (ALS/PDC) and the consumption of flour made from the washed seeds of the plant, Cycas micronesica (cycad). We have examined the effects of prolonged cycad consumption on male, Sprague-Dawley rats. Cycad-fed rats displayed a behavioral phenotype resembling that of parkinsonism. Briefly, we found that cycad consumption induced multiple, classical symptoms of PD including locomotor deficits, neurodegeneration of dopamine (DA) cell bodies and aggregation of alpha-synuclein in the remaining neurons of the substantia nigra pars compacta (SNc). Uniquely, preceding these alterations we found that cycad-fed rats displayed a hypersomnolent behavior. Analysis of sleep architecture revealed an increase in the length and/or the number of bouts of rapid eye movement (REM) sleep and Non-REM (NREM) sleep during the active period of cycad-fed rats when compared to control rats. In addition, we found a significant reduction in orexin-A (ORX-A) neurons of cycad-fed rats. Lastly, dose response curves of NMDA-induced DA release in the striatum and SN provide a method to elucidate some of the neurochemical changes behind the early, non-motor symptoms of cycad-fed rats.
    • The HSV-2 protein ICP10PK protects CNS neurons from NMDA-induced excitotoxicity in vitro and in vivo

      Golembewski, Erin; Yarowsky, Paul J. (2006)
      Glutamate excitotocicity occurs in several neurodegenerative diseases such as stroke, Alzheimer's, Parkinson's and Huntington's diseases. Currently, no effective treatments exist for these pathological conditions. Therapeutic approaches for blocking glutamate-induced apoptosis may include introduction of genes that activate survival pathways. Previously, we have shown that the HSV-2 gene ICP10PK inhibits apoptosis in cultured neurons by activating the Ras/MEK/ERK signaling pathway. The current studies examine the neuroprotective activity of ICP10PK in a model of NMDA-induced excitotoxic injury, in vivo and in vitro.;For in vivo experiments, mice were given intrastriatal NMDA injections bilaterally. In the left striatum, NMDA was diluted in PBS; in the right striatum it was combined with an HSV-2 vector delivering ICP10PK (DeltaRR). The data indicate that DeltaRR is not toxic and does not induce an inflammatory response, which is likely related to its failure to replicate in the brain. DeltaRR decreases NMDA-induced lesion volume and increases cell survival by inhibiting caspase-3 cleavage, thus protecting neurons from apoptosis even when given up to four hours after NMDA. Neuroprotection is conferred by the phosphorylation/activation of ERK by MEK. Additionally, behavioral testing showed that protected neurons retained function. An ICP10PK-negative vector (DeltaPK) did not activate ERK or protect neurons from apoptosis or behavioral abnormalities.;For in vitro experiments, organotypic striatal cultures were used to determine the specific neuroprotective mechanism induced by DeltaRR. Employing specific protein kinase inhibitors demonstrates that protection from apoptosis is dependent on the activation of the Ras/MEK/ERK and PI3-K/AKT pathways as well as the inhibiton of the pro-apoptosic JNK pathway and cleavages of caspase-3 and PARP. Neuroprotection also involves the induction of anti-apoptosic Bag-1 and the inhibition pro-apoptosic Bad.;These studies show that ICP10PK delivered by DeltaRR reduces apoptosis induced by an excitotoxin in vivo and in vitro. Neuroprotection is accomplished by activating the Ras/MEK/ERK and P13-K pathways. The data suggest that ICP10PK has anti-apoptosic activity in vivo and is a potential gene therapy for neurodegenerative diseases of the CNS.
    • Putting the Brakes on Proliferation: Gene Dosage Effects on Hippocampal Neurogenesis in the Ts65Dn Mouse Model of Down Syndrome

      Clark, Sarah Michelle; Yarowsky, Paul J. (2011)
      As the most prevalent genetic cause of intellectual disability in the western world, Down syndrome (DS) presents a variety of challenges. This is especially true for the aging DS population, which is facing the reality that virtually all individuals who survive to their fifth decade will develop Alzheimer's disease. Thus, it has become imperative to identify and understand underlying mechanisms that can potentially contribute to cognitive impairments in DS. Given that most of the cognitive deficits in DS have been associated with hippocampal dysfunction and that neurogenesis in the adult hippocampus contributes to cognitive processing, the goal of our research was to determine whether adult hippocampal neurogenesis is impaired in the hippocampi of a mouse model of DS, Ts65Dn. Results presented herein demonstrate that neurogenesis is significantly (~50%) reduced in the subgranular zone (SGZ) of the dentate gyrus of adult male Ts65Dn mice. The use of the thymidine analog 5'-Bromo-2-deoxyuridine (BrdU) and cell-type specific markers led us to conclude that a significantly large proportion of the neuroprogenitor population resident within the SGZ fails to proliferate. The consequence of reduced cell proliferation is a significant deficit in the production of new neurons in the dentate gyrus, which may ultimately impinge upon hippocampal function. Gene overexpression in DS may contribute to cell cycle alterations within the neuroprogenitor population via dysregulation of signaling pathways required for neurogenesis and through the overproduction of reactive oxygen species (ROS), which negatively impact cell viability. Our research has established that chronic treatment with the antidepressant fluoxetine rescues impaired neurogenesis, increasing cell proliferation to control levels. Additionally, we have shown that treatment with the antioxidant curcumin can be neuroprotective through the reduction of oxidative damage, which in turn facilitates the generation of new neurons. Ultimately, we have identified a mechanism that can contribute to hippocampal dysfunction in DS and have established that dysregulation of neurogenesis can be remedied using pharmacological therapies already available, thus, providing hope for future treatments.