Outgrowth-regulating actions of glutamate in isolated hippocampal pyramidal neurons.
The present study examined the effects of glutamate on the outgrowth of dendrites and axons in isolated hippocampal pyramidal-like neurons in cell culture. During the first day of culture the survival and outgrowth of these neurons was unaffected by high concentrations (up to 1 nM) of glutamate, quisqualic acid (QA), kainic acid (KA), and N-methyl-D-aspartic acid. Beginning on day 2 of culture high levels of glutamate, KA and QA were toxic to the majority of pyramidal neurons, while subtoxic levels of these agents caused a well-defined, dose-dependent, sequence of effects on dendritic outgrowth. At increasing concentrations of glutamate, QA, and KA, the following events were observed: (1) dendritic outgrowth rates were reduced, while axonal elongation rates were unaffected; (2) dendritic length was reduced, while axons continued to grow; (3) dendrites regressed dramatically, and axonal outgrowth rate was reduced. These dendrite-specific effects of glutamate were apparently mediated at the growth cones since focal application of glutamate to individual dendritic growth cones resulted in suppression of growth cone activity and a regression of the dendrite; axons were unaffected by focal glutamate application. Pharmacological tests using glutamate receptor agonists and antagonists demonstrated that receptors of the KA/QA type mediated the glutamate effects on outgrowth and survival. The calcium channel blocker Co2+ prevented both glutamate neurotoxicity and glutamate-induced dendritic regression. Ionophore A23187 and elevations in extracellular K+ levels each caused a dose-dependent series of outgrowth and survival responses similar to those caused by glutamate. Taken together, these results indicate that activation of glutamate receptors leads to the opening of voltage-dependent calcium channels; the resulting increases in calcium influx lead to the observed alterations in dendritic outgrowth and neuronal survival.
D000818:Animals; D001369:Axons / Q000502:physiology / Q000648:ultrastructure; D002118:Calcium / Q000378:metabolism / Q000502:physiology; D002469:Cell Separation; D002470:Cell Survival / Q000187:drug effects; D003712:Dendrites / Q000502:physiology / Q000648:ultrastructure; D005971:Glutamates / Q000494:pharmacology*; D018698:Glutamic Acid; D006624:Hippocampus / Q000166:cytology* / Q000502:physiology / Q000648:ultrastructure; D009474:Neurons / Q000187:drug effects* / Q000502:physiology / Q000648:ultrastructure; D017470:Receptors, Glutamate; D017981:Receptors, Neurotransmitter / Q000378:metabolism
D005971:Glutamates; D017470:Receptors, Glutamate; D017981:Receptors, Neurotransmitter; D018698:Glutamic Acid; D002118:Calcium