BACKGROUND: Studies have demonstrated that NG2-positive glial cells in the adult rats are predominantly located in the gray and white matter of the cerebral cortex and hippocampus.Platelet-derived growth factor-a receptor (PDGF-aR) cells are a subset of oligodendrocytes, which are not as mature as NG2-positive cells. Distribution and migration of PDGF-aR-positive cells in the rat brain remain poorly understood.OBJECTIVE: Using immunohistochemical methods, the distribution of oligodendrocyte precursor cells (PDGF-aR-positive) was analyzed in the adult rat brain.DESIGN, TIME AND SETTING: Immunohistochemical study was performed at the Department of Histology and Embryology of the Third Military Medical University from September 2007 to September 2008.MATERIALS: Rabbit anti-PDGF-aR polyclonal antibody was purchased from Santa Cruz Biotechnology, USA. Streptomycin-avidin-biotin complex immunohistochemistry kit was purchased from Zhongshan Goldenbridge Biotechnology, China.METHODS: Whole brains from 5 healthy, adult, Wistar rats were collected for immunohistochemistry,and the mean value of PDGF-aR-expressing cells was quantified. The absolute values were translated to ranked data of high, moderate, and low grades (high grade: 10 positive cells; moderate grade: 5-9 cells; low grade: <5 cells in a 400×visual field). Based on the number of cell processes and branches, as well as the number of PDGF-aR-positive cells, in different regions, the cells were classified into three categories, i.e., type I-III. From type I to type III, the number of processes gradually increased.MAIN OUTCOME MEARSURES: The number and distribution of PDGF-aR-positive cells in different brain regions of adult rats.RESULTS: PDGF-aR-positive cells were located in the forebrain and midbrain, but not in the cerebellum or brainstem. In the olfactory bulb and hippocampus, a total of 60% PDGF-aR-positive cells were type I and these cells were not mature as others. In the cerebral cortex, olfactory system,hippocampus, and optic chiasma, where neuronal bodies aggregated, approximately 40% of the PDGF-aR-positive cells were type II, with few type III cells. In the white matter, corpus callosum,basal nucleus, and thalamus, PDGF-aR-positive cell density was moderate. In the olfactory bulb and hippocampus, PDGF-aR-positive cell density was high. PDGF-aR-positive cells were not observed in the cerebellum or brainstemCONCLUSION: PDGF-aR-positive cells were aggregated in the olfactory bulb and hippocampus in the adult, rat brain, but few cells were detected in the cerebellum and brainstem.