Roles of Rho Guanine Nucleotide Triphosphatases in Hippocampal Mossy Fiber Sprouting in the Pentylenetetrazole Kindling Model

Abstract

One unique feature of chronic human and experimental epilepsy is hippocampal dentate granule cell axon (mossy fiber) sprouting which creates an aberrant positive-feedback circuit that may be epileptogenic. However, the mechanism underlying this process remains unclear. Rho guanine nucleotide triphosphatases (RhoGTP ases) Rac1 and RhoA are important regulators of axon growth and synaptic plasticity and can be blocked by treatment with fasudil. We hypothesized that Rac1 and RhoA are involved in aberrant mossy fiber sprouting (MFS). A temporal lobe epilepsy model was established by intraperitoneal pentylenetetrazole (PTZ) injection for animals in PTZ group, and fasudil was injected 30 minutes prior to PTZ injection for animals in PTZ + Fas group. The expression of Rac1 and RhoA in the rat hippocampus was tested at different time points by immunohistochemistry, Western blot and quantitative real-time PCR. Mossy fiber sprouting in the hippocampus was evaluated by Timm staining. Rac1 and RhoA were significantly up-regulated in the PTZ group, and as predicted, the degree of aberrant MFS was correspondingly increased. However, the expression of Rac1 and RhoA was not inhibited in the PTZ + Fas group, and the epileptiform activity, EEG and aberrant MFS were not suppressed following PTZ + Fas treatment. RhoGTPases play a role in MFS but fasudil is not sufficient to inhibit RhoGTPases and MFS in the PTZ kindling model.