of NF proteins have been detected. A reduction of myelinated fiber size is correlated with axonal NFs loss in peripheral nerves of STZ-induced diabetic rats (25, 26), and mRNAs levels encoding for NF-L and NF-H are reduced in the same animal model of diabetes (7). Moreover, changes on the expression of several NF-associated protein kinases isoforms may also contribute to diabetes-induced changes (4). Several protein kinases regulate NF phosphorylation status, being NFs hyperphosphorylation a hallmark of several neurodegenerative diseases. Abnormal NF phosphorylation has been described in sensory neurons of animal models of type 1 diabetes (27). Moreover, in the spinal cord of diabetic rats there is increased phosphorylation of NF-H, (28). Additionally, changes on the activity of Cdk5 and GSK-3β kinases have been described to alter the phosphorylation status of NFs in an animal model of type 1 diabetes. Specifically, in dorsal root ganglion neuronsincreased phosphorylation of GSK-3β correlated linearly with increased phosphorylation of NF-H, while decreasing activity of Cdk5 is associated with reduced phosphorylation of NF-M, which may result in progressive deficits of axonal function (29).

Microfilaments

Microfilaments (or actin filaments) are the thinnest filaments of the cytoskeleton, having 6 nm in diameter, providing both stability and dynamics to neurons. In neurons, actin filaments are packed into networks and stabilized by interacting proteins (22). Microfilaments play a role in spine formation and spine volume stabilization (30), with the dynamics of actin leading to the formation of new synapses as well as increased cell communication. The actin cytoskeleton controls several cellular processes.