Development of glutamate receptors in auditory neurons from long-term organotypic cultures of the embryonic chick hindbrain.

We used long-range organotypic cultures of auditory nuclei in the chick hindbrain to test the development of glutamate receptor activity in auditory neurons growing in a tissue environment that includes early deprivation of peripheral glutamatergic input, subsequent to removal of the otocyst. Cultures started at embryonic day (E)5, and lasted from 6 h to 15 days. Neuronal migration, clustering and axonal extension from the nucleus magnocellularis (NM) to the nucleus laminaris (NL) partially resembled events in vivo. However, the distinctive laminar organization of the NL was not observed. Glutamate receptor (GluR) activity was tested with optical recordings of intracellular Ca2+ in the NM. alpha-Amino-3-hydroxy-5-methyl-4-isoxazoleproprionic acid (AMPA)/kainate receptors had Ca2+ responses with a time course similar to that in control slices. Peak amplitude, however, was significantly lower. N-methyl-D-aspartate (NMDA)-mediated Ca2+ responses were higher in 2-day cultures (E5 + 2d) than in E7 explant controls, returning later to control values. Metabotropic GluRs did not elicit Ca2+ responses at standard agonist doses. Blocking NMDA or AMPA/kainate receptors with specific antagonists for 10 days in culture did not limit neuronal survival. Blocking metabotropic GluRs resulted in complete neuronal loss. Thus, ionotropic GluRs are not required for NM neuronal survival. However, their activity during development is affected when neurons grow in an in vitro environment that includes prevention of arrival of peripheral glutamatergic input.