DEVELOPMENT OF A TOPOGRAPHICALLY ORGANIZED AUDITORY NETWORK IN SLICE CULTURE IS CALCIUM-DEPENDENT

Inhibitory and excitatory connections of remarkably precise topographi c order are characteristic features of the mammalian auditory system, particularly within the superior olivary complex (SOC), Little is know n about the requirements for the correct development of these specific connections, Previous irt vivo experiments have demonstrated a high e xpression of calcium-binding proteins in this system during developmen t, pointing to the need for precise calcium regulation, Here, we have employed an organotypic slice culture from the above neuronal network and analyzed the requirements for the maintenance and development of t his system in vitro. When slices from neonatal rats were incubated in standard culture medium for up to 7 days, we found no organotypic feat ures, Only if 25 mM KCI was added to the culture medium, the cytoarchi tecture of the nuclei, the neuronal morphology, and the specificity an d topography of internuclear connections were indistinguishable from t hat in vivo. The addition of calcium channel blockers (MgCl2 and nifed ipine) to the high-KCl medium reduced organotypicity drastically, indi cating that a depolarization-induced increase of intracellular calcium is indispensable, Furthermore, the temporal course of the expression of the calcium-binding protein parvalbumin in culture under high KCI m imics that in vivo, demonstrating developmental processes during incub ation, The need for calcium influx into neurons of this auditory netwo rk in vitro (which is not seen in other slice culture systems) strengt hens the hypothesis that an optimal calcium concentration is exception ally important in auditory neurons. The effect of KCI in the slice cul tures may substitute for input activity regulating intracellular calci um in auditory neurons in vivo. (C) 1998 John Wiley & Sons, Inc.