EXPERIENCE-DEPENDENT MODIFICATIONS IN MAP2 PHOSPHORYLATION IN RAT OLFACTORY-BULB

Microtubule-associated protein 2 (MAP2) is a neuron-specific cytoskele tal protein, enriched in dendrites and cell bodies, that helps determi ne dendritic shape. MAP2 regulates microtubule stability in a phosphor ylation-dependent manner. The present study used immunocytochemistry w ith phosphoepitope-specific and phosphorylation state-independent anti bodies to examine experience-dependent changes in MAP2 expression duri ng postnatal development of the olfactory bulb. Our results demonstrat e that immunoreactivity reflecting total MAP2 expression reaches a max imal level by postnatal day 20 (P20). The degree of staining for phosp hoindependent forms of MAP2 is relatively unaffected by blocking odora nt passage to one half the nasal epithelium via unilateral naris closu re, a manipulation that attenuates physiological activity in the bulb. However, olfactory restriction from P1 dramatically reduces immunorea ctivity for antibody AP18, which recognizes MAP2 only when phosphoryla ted on Ser(136). Quantification of staining in the granule cell layer indicates that the greatest difference (64%) between control and exper imental bulbs occurs after occlusion from P1 to P30 compared with anim als deprived from P1 to P10 or P1 to P20. The shift in MAP2 phosphoryl ation occurs even when deprivation is delayed until P30, after the sen sitive period for experience-dependent changes in bulb volume. Thus, t he degree of the phosphorylation shift depends on the duration but not the time of onset of naris closure. Because staining for phosphorylat ion-independent forms of MAP2 is unchanged by naris closure, the total amount of the protein per unit area is probably not significantly alt ered. However, the large reductions of AP18-immunoreactivity in the bu lb after olfactory restriction suggest that there is an activity-depen dent stimulation of MAP2 phosphorylation.