Glutamate-induced changes in the pattern of hippocampal dendrite outgrowth: A role for calcium-dependent pathways and the microtubule cytoskeleton

Glutamate regulation of a variety of aspects of dendrite development may be involved in neuronal plasticity and neuropathology, In this study, we exam ine the calcium-dependent pathways and alterations in the microtubule (MT) cytoskeleton that may mediate glutamate-induced changes in the pattern of d endrite outgrowth. We used Fura-2 AM and inhibitors of the calcium-dependen t proteins, calmodulin and calpain, to identify the role of specific calciu m-dependent pathways in glutamate-regulated dendrite outgrowth. Additionall y, we used a quantitative fluorescence technique to correlate changes in MT levels with glutamate-induced changes in dendrite outgrowth. We show that the intracellular calcium concentration ([Ca2+](i)) changes in a biphasic m anner over a 12-h period in the presence of glutamate. A transient increase in [Ca2+](i) over the first hour of glutamate exposure correlated with a c almodulin-associated increase in the rate of dendrite outgrowth, whereas a sustained increase in [Ca2+](i) was correlated with calpain-associated dend rite retraction. Quantitative fluorescence measurements showed no net chang e in the level of MTs during calmodulin-associated increases in dendrite ou tgrowth, but showed a significant decline in the level of MTs during calpai n-associated dendrite retraction. These findings provide insights into the intracellular mechanisms involved in activity-dependent regulation of dendr ite morphology during development and after pathology. (C) 2000 John Wiley & Sons, Inc. J Neurobiol 43: 159-172, 2000.