CDK5 and Parkinson disease: While the exact effects of superfluous NO or its derivatives on synaptic function in PD have not been fully elucidated, there is evidence that excess NO alters axo-dendritic function, specifically impairing neurite length through the S-nitrosylation of protein disulfide isomerase or microtubule associated protein 1b, and causing synaptic spine loss through the hyperactivity of Cyclic-dependent kinase 5 (CDK5) following CDK5 S-nitrosylation53,54.