Infusion of anti-Nogo-A antibodies in adult rats increases growth and synapse related proteins in the absence of behavioral alterations

Restricted structural re-growth in the adult CNS is a major limitation to fully functional recovery following extensive CNS trauma. This limitation is partly due to the presence of growth inhibitory proteins, in particular, Nogo-A. Pre-clinical studies have demonstrated that intrathecally infused anti-Nogo-A antibodies are readily distributed via the cerebrospinal fluid penetrating throughout the spinal cord and brain, where they promote sprouting, axonal regeneration and improved functional recovery after CNS injury. Whether anti-Nogo-A treatments of intact animals might induce behavioral alterations has not been systematically tested. This is addressed here in an adult rat model of chronic intrathecal infusion of function-blocking anti-Nogo-A antibodies for 2 to 4. weeks. We observed by proteomic and immunohistochemical techniques that chronic Nogo-A neutralization in the intact CNS increased expression of cytoskeletal, fiber-growth-related, and synaptic proteins in the hippocampus, a brain region which might be particularly sensitive to Nogo-A depletion due to the high expression level of Nogo-A. Despite such molecular and proteomic changes, Nogo-A blockade was not associated with any pronounced cognitive-behavioral changes indicative of hippocampal functional deficiency across several critical tests. Our results suggest that the plastic changes induced by Nogo-A blockade in the adult hippocampus are counter-balanced by homeostatic mechanisms in the intact and the injured CNS. The data indicate that anti-Nogo-A therapy appears safe in the adult CNS over 4. weeks of continuous administration.