Bidirectional regulation of dendritic spine dimensions by glutamate receptors.

The recent conflicting observations on the effects of excitatory afferent activity on dimensions of dendritic spines of central neurons led us to examine the possibility that the same spine can either increase or decrease its length in response to different stimuli. Cultured hippocampal neurons labeled with calcein, were 3D reconstructed in a confocal laser scanning microscope. Their responses to pulse application of glutamate were examined. Short pulses 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 the stimulation intensity/duration. These observations have important implications for understanding the roles of dendritic spines in information processing in central neurons.