REJUVENATION RESEARCH Volume 9, Number 1, 2006 © Mary Ann Liebert, Inc. Level and Distribution of Microtubule- Associated Protein-2 (MAP2) as an Index of Dendritic Structural Dynamics GIUSEPPINA DI STEFANO, TIZIANA CASOLI, PATRIZIA FATTORETTI, MARTA BALIETTI, YESSICA GROSSI, BELINDA GIORGETTI, and CARLO BERTONI-FREDDARI ABSTRACT Optical density of MAP2 immunoreactivity (OD), the ratio between the MAP2 stained area/to- tal test area (area fraction: AF), the total length of MAP2 labeled profiles (TL) and the ratio perimeter/area of the immunostained profiles (pleomorphism index [PI]) were measured by quantitative immunohistochemistry in the brain of rats of different ages. In old rats versus young and adult animals, OD and AF were significantly lower, whereas PI was significantly higher, in dentate gyrus molecular layer, CA1 stratum radiatum and olfactory bulb. These findings lend support to the many converging results on the higher vulnerability to aging of the CNS areas featuring higher plasticity. 94 INTRODUCTION T HE MORPHOLOGIC STABILITY AND PLASTICITY of neuronal processes depend on the integrity of the neuronal cytoskeleton and its components (i.e., actin filaments, neurofilaments, and micro- tubules [MTs]) with their associated proteins. 1 Microtubule associated protein-2 (MAP2) is one of the most important cytoskeletal proteins selectively located in the somatodendritic com- partment of neurons where it stabilizes poly- merized tubulin and may regulate both micro- tubule spacing and the crosslinking of actin filaments. 2 MAP2 is currently considered as a reliable marker of structural integrity as it is in- volved in the morphologic stabilization of den- dritic processes. MAP2 modulates growth, dif- ferentiation and plasticity of neurons playing a pivotal role in neuronal response to growth fac- tors, neurotransmitters, synaptic activity, and neurotoxins. 3 Although alterations of MAP2 ex- pression have been reported in age-associated neuronal disorders, such as ischemia and Alz- heimer disease (AD), 4 MAP2 metabolism is still poorly understood in aging. To investigate the role of MAP2 on neuronal dendritic stability and plasticity in aging, quantitative immunohisto- chemical analysis of MAP2 levels in the hip- pocampus and olfactory bulb of rats of different ages was performed. MATERIALS AND METHODS Immunohistochemical staining procedure Three groups of female Wistar rats (3, 12, and 28 months of age) each of four animals, were INRCA Research Department, Neurobiology of Aging Laboratory, Ancona, Italy.