Behavioral characterization of mice lacking the neurite outgrowth inhibitor Nogo-A

The membrane protein Nogo-A inhibits neurite outgrowth and regeneration in the injured central nervous system, primarily because of its expression in oligodendrocytes. Hence, deletion of Nogo-A enhances regeneration following spinal cord injury. Yet, the effects of Nogo-A deletion on general behavior and cognition have not been explored. The possibility of potential novel functions of Nogo-A beyond growth inhibition is strongly suggested by the presence of subpopulations of neurons also expressing Nogo-A - not only during development but also in adulthood. We evaluated here Nogo-A ^-/- mice in a series of general basic behavioral assays as well as functional analyses related to brain regions with notable expression levels of Nogo-A. The SHIRPA protocol did not show any major basic behavioral changes in Nogo-A ^-/- mice. Anxiety-related behavior, pain sensitivity, startle reactivity, spatial learning, and associative learning also appeared indistinguishable between Nogo-A ^-/- and control Nogo-A ^+/+ mice. However, motor co-ordination and balance were enhanced in Nogo-A ^-/- mice. Spontaneous locomotor activity was also elevated in Nogo-A ^-/- mice, but this was specifically observed in the dark (active) phase of the circadian cycle. Enhanced locomotor reaction to systemic amphetamine in Nogo-A ^-/- mice further pointed to an altered dopaminergic tone in these mice. The present study is the first behavioral characterization of mice lacking Nogo-A and provides significant insights into the potential behavioral relevance of Nogo-A in the modulation of dopaminergic and motor functions.