Bidirectional regulation of dendritic spine dimensions by glutamate receptors

The recent conflicting observations on the effects of excitatory afferent a ctivity on dimensions of dendritic spines central neurons led us to examine the possibility that the same spine can either increase or decrease its le ngth in response to different stimuli. Cultured hippocampal neurons labeled with calcein, were 3D reconstructed in a confocal laser scanning microscop e. Their responses to pulse application of glutamate were examined. Short p urses of glutamate caused elongation of dendritic spines, while long pulses caused fast shrinkage of the same set of spines. Thus, the same spine can undergo two opposite responses to application of glutamate, depending on th e stimulation intensity/duration. These observations have important implica tions for understanding the roles of dendritic spines in information proces sing in central neurons. (C) 1999 Lippincott Williams & Wilkins.