DEVELOPING RAT BRAIN-STEM MOTONEURONS IN ORGANOTYPIC CULTURE EXPRESS CALCIUM-PERMEABLE AMPA-GATED RECEPTORS

Recent studies suggest that calcium permeable excitatory amino acid re ceptors may play an important role in many developmental processes inc luding dendritic differentiation, synaptogenesis and activity dependen t plasticity or excitotoxicity related disorders. In this work, we inv estigate the existence of calcium permeable AMPA receptors in embryoni c rat motoneurones in organotypic slice culture, which display an earl y sensitivity to AMPA and Kainate. We used excitatory amino acids indu ced cobalt uptake and show that developing motoneurones express Ca2+ p ermeable AMPA receptors. We demonstrate, as already described for othe r neuronal types in acute slices of adult animals, that the cobalt loa ding of motoneurones is not suppressed by blockade of synaptic activit y by TTX. It is not induced by NMDA stimulation and does not result fr om the activation of voltage dependent calcium channels. It is specifi cally suppressed by the non-competitive AMPA antagonist GYKI 53784 (LY 303070) and enhanced by the AMPA-receptor desensitization blocker Anir acetam. We conclude that cobalt loading results from the specific acti vation of AMPA receptors. We further show that, when cobalt loading is induced by threshold doses of Glutamate agonists, cobalt-sulfide depo sits are found specifically in primary dendrites, dendritic spines and localized spots on the somatic and peripheral dendritic membrane. We suggest that this particular pattern of staining, different from the G olgi-Like staining obtained with excitotoxic doses, may offer new info rmation regarding the membrane density and distribution of calcium per meable AMPA receptors. (C) 1998 Elsevier Science B.V.