Master of Science
Physiology and Pharmacology
The cerebellum is a brain structure that is responsible for coordinating voluntary movement such as balance, coordination, and posture. Purkinje neurons (PNs) are the sole GABAergic output from the cerebellar cortex and receive major excitatory inputs via parallel fibers (PFs) that produce high levels of nitric oxide (NO) via neuronal nitric oxide synthase (nNOS). Previous studies demonstrate that nNOS/NO signaling is crucial for PF-PN synaptic transmission. This study sought to examine nNOS/NO signaling regulation of excitatory amino acid transporter 4 (EAAT4) on PN dendrites and glutamic acid decarboxylase (GAD) expression/function between sexes by using wildtype (WT) and nNOS-/- mice at different postnatal developmental time points. This study revealed that there are gene- and sex-dependent differences in GABA concentration in the cerebellum during early postnatal development. Additionally, there is decreased EAAT4 expression in male nNOS-/- mice. Lastly, there is decreased GAD65/67 expression in both male and female nNOS-/- nice compared to age-matched WT mice. Our results provide new knowledge of NO regulation of cerebellar synaptic transmission, which may advance the development of cerebellar ataxia therapeutics.
Summary for Lay Audience
The cerebellum is a brain structure in the central nervous system that is responsible for coordinating voluntary movement such as balance, coordination, blinking, and posture. Cerebellar ataxia is a neurodegenerative disorder characterized by uncoordinated voluntary muscle movement that can arise from a traumatic brain injury or can be inherited. Physical therapy has been used as a treatment method however, there are currently no definitive clinical treatments or cure. Genetically modified mice have been used in many studies to study the molecular mechanism in neurodegenerative diseases and ataxia. However, many ataxic mouse models have not been characterized at the molecular level. Current understanding of Purkinje neurons (PNs), the main cells of the cerebellum, demonstrate the importance of glutamate uptake to prevent excessive neuron damage. Nitric oxide, a signaling molecule in the cerebellum produced by the enzyme neuronal nitric oxide synthase (nNOS), regulates cerebellar neuron activity and has possible implications in the development of cerebellar ataxia. Specifically, previous research in mice lacking nNOS demonstrate morphological deficits in the PN dendrites and increased calcium entry in PNs due to an overactivation of metabotropic glutamate receptor 1 compared to wildtype mice. This study aims to determine the role of nitric oxide in regulating the expression of glutamate transporters and Purkinje neuron output in the cerebellum. Specifically, this thesis aims to uncover how nitric oxide can influence other signaling molecules that affect Purkinje neurons, including glutamate and GABA - a molecule that regulates movement in the cerebellum and other parts of the brain. This thesis answers this research question by using nNOS-/- mice and comparing it to a normal, wildtype mouse at 4 postnatal developmental time points. Results from this study demonstrate that nitric oxide influences cerebellar GABA production and glutamate uptake in Purkinje neurons, with notable differences between sexes. This study provides new knowledge of the mechanisms in cerebellar ataxia and possible drug interventions that can prevent neuronal damage caused by glutamate.
Jassal, Gurneet, "Neuronal Nitric Oxide synthase regulates the expression of EAAT4 and GAD65/67 in the murine cerebellum" (2022). Electronic Thesis and Dissertation Repository. 9091.
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