GLYCINERGIC TRANSMISSION REGULATES DENDRITE SIZE IN ORGANOTYPIC CULTURE

We previously demonstrated that inhibitory synaptic transmission influ ences dendrite development in vivo. We now report an analogous finding in an organotypic culture of a glycinergic projection nucleus, the me dial nucleus of the trapezoid body (MNTB), and its postsynaptic target , the lateral superior olive (LSO) of gerbils. Cultures were generated at 6-7 days postnatal and grown in serum containing medium with or wi thout the glycine receptor antagonist, strychnine (SN), at 2 mu M. LSO neurons were then labeled with biocytin, and the dendritic arbors wer e analyzed morphometrically. Compared to neurons from age-matched in v ivo tissue, the neurons cultured in control media were somewhat atroph ic, including decreases in dendritic branching and length. Incubation in strychnine led to a dramatic increase in dendritic branching and to tal dendritic length. Control neurons averaged 6.3 branches, compared to 18 branches/neuron in SN-treated cultures. There was a similar incr ease in primary dendrites and total dendritic length. The physical eli mination of MNTB cells did not mimic SN treatment, presumably because glycinergic LSO neurons generated intrinsic connections. In fact, the LSO soma area was significantly greater following MNTB removal, sugges ting that these afferents provide a second signal to postsynaptic neur ons. These results suggest that spontaneous glycinergic transmission r egulates the growth of postsynaptic processes. (C) 1996 John Wiley & S ons, Inc.