Kainic acid stimulates uptake of divalent cations in postnatal cochlear neurons

Excitatory amino acids were tested for their ability to induce cobalt uptake in cochlear explants of spiral ganglion neurons. Explants were taken from postnatal day 5 hamsters. Compared with NMDA and quisqualate, kainic acid (KA) stimulated the greatest amount of Co2+ uptake within spiral ganglion neurons as indicated by precipitation of the Co2+ accumulation and relative optical density measurements. Both L-glutamate and KA stimulation were blocked by non-NMDA receptor antagonists kynurenate and DNQX. Nifedipine, a dihydropyridine-sensitive calcium channel blocker, also partially inhibited Co2+ uptake. These data suggest that a mixed population of NMDA and non-NMDA receptors are present. Additionally non-NMDA receptors may have a role in cochlear synaptic maturation.