Gicerin is a cell adhesion molecule of an immunoglobulin (Ig) superfamily isolated from a chicken. It shows homophilic and heterophilic binding activities and has two isoforms. s-Gicerin which has small cytoplasmic domain and the same extracellular domain as l-gicerin shows stronger cell adhesion activity. In the chick nervous system, gicerin expression is only observed in the developmental stage when neurons extend neurites and migrate. In other tissues, gicerin participates in the tissue regeneration or oncogenesis. In this report, we identified two isoforms of rat gicerin corresponding to chicken and we concluded that gicerin is a homologue of human CD146/MUC18/MCAM. Next we generated antibody to characterize a rat gicerin in the nervous system. Gicerin is expressed in the hippocampal cells, Purkinje cells, and sensory neurons of a spinal chord of an adult rat, while expressed most abundantly in the lung. In addition to this, its expression in the hippocampus was increased by electroconvulsive shock, suggesting some role in the mature nervous system. And we also showed neurite promotion activity of gicerin from hippocampal neurons. Copyright 2003 Wiley-Liss, Inc.