Outgrowth-regulating actions of glutamate in isolated hippocampal pyramidal neurons

Abstract

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.

The Actin-Severing Protein Gelsolin Modulates Calcium Channel and NMDA Receptor Activities and Vulnerability to Excitotoxicity in Hippocampal Neurons

“…Hippocampal cell cultures were established from 16-d-old embryos using methods essentially identical to those used in our previous studies (Mattson et al, 1988a;Bruce et al, 1996). Hippocampi from each embryo were dissociated by trypsinization and trituration and plated into culture dishes; DNA from the body of each embryo was isolated and used for PCRbased genotyping.…”

Molecular mechanisms separating two axonal pathways during embryonic development of the avian optic tectum

“…We could not detect a co"apse prior to contact of the growth cone with the neurite; growth cones passing very near an axon showed no morphological changes. Thus, it seems likely that the active agent is membrane associated and not a diffusible substance like, for example, a neurotransmitter, as has been shown in several other studies (Haydon et al, 1984;McCobb et al, 1988;Mattson et al, 1988).…”

Impairment of the Ca2+‐Permeable AMPA/Kainate Receptors by Lead Exposure in Organotypic Rat Hippocampal Slice Cultures

“…In the developing brain, glutamate receptors have been shown to be involved in the dendritic differentiation, synaptagenesis and activity-dependent plasticity (Kater et al 1988;Mattson et al 1988;McDonald & Johnston 1990). These effects are mostly due to modifications of intracellular calcium concentrations.…”