Dendrites and spines undergo dynamic changesin physiological conditions, such as learning and memory, and in pathological conditions, such as Alzheimer's diseaseand epilepsy. Long-term dendritic plasticity has also beenreported after ischemia/hypoxia, which might be compensatoryeffects of surviving neurons for the functional recoveryafter the insults. However, the dendritic changes shortly afterischemia, which might be associated with the pathogenesisof ischemic cell death, remain largely unknown. To reveal themorphological changes of ischemia-vulnerable neurons after ischemia, the present study investigated the alteration ofdendritic arborization of CA1 pyramidal neurons in rats aftertransient cerebral ischemia using intracellular staining techniquein vivo. The general appearance of dendritic arborizationof CA1 neurons within 48 h after ischemia was similar tothat of control neurons. However, a dramatic increase ofdendritic disorientation was observed after ischemia withmany basal dendrites coursed into the territory of apicaldendrites and apical dendrites branched into the region ofbasal dendrites. In addition, a significant increase of apicaldendritic length was found 24 h after ischemia. The increaseof dendritic length after ischemia was mainly due to thedendritic sprouting rather than the extension of individualdendrites, which mainly occurred in the middle segment ofthe apical dendrites. These results reveal a plasticity changein dendritic arborization of CA1 neurons shortly after cerebralischemia.