Postnatal changes in glutamate stimulated phosphoinositide turnover in rat neocortical synaptoneurosomes

Glutamate was found to stimulate the accumulation of [3H]inositol phosphate in synaptoneurosomes prepared from rat neocortex during a narrowly defined period of postnatal development. No glutamate stimulation was observed on the day of birth, even though high levels of phosphoinositide (PIns) turnover were observed with the muscarinic agonist carbachol. Glutamate-stimulated PIns turnover reached a maximum at one week of age, and decreased to adult levels by five weeks of age. Of the glutamate analogs tested, only ibotenate produced significant stimulation. N-Methyl-D-aspartate (NMDA) showed negligible stimulation and kainate showed only minor stimulation at the highest concentration tested (1 mM). Glutamate stimulation was not blocked by either the NMDA receptor antagonist 2-amino-5-phosphonovaleric acid (APV) or the broad spectrum glutamate antagonist kynurenic acid. These results suggest that a specific subclass of excitatory amino acid receptor linked to PIns metabolism, or a phospholipase associated with the receptor, is transiently expressed in the neocortex during early postnatal development.