W e previously demonstrated that inhibitory synaptic transmission influences dendrite development in vivo. We now report an analogous finding in an organotypic culture of a glycinergic projection nucleus, the medial 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 without the glycine receptor antagonist, strychnine (SN), a t 2 PM. LSO neurons were then labeled with biocytin, and the dendritic arbors were analyzed morphometrically. Compared to neurons from age-matched in vivo tissue, the neurons cultured in control media were somewhat atrophic, including decreases in dendritic branching and length. Incubation in strychnine led to a dramatic increase in dendritic branching and total dendritic length.
Control neurons averaged 6.3 branches, compared to 18 branches /neuron in SN-treated cultures. There was a similar increase in primary dendrites and total dendritic length. The physical elimination of M N T B cells did not mimic S N treatment, presumably because glycinergic LSO neurons generated intrinsic connections. In fact, the LSO soma area was significantly greater following MNTB removal, suggesting that these afferents provide a second signal to postsynaptic neurons. These results suggest that spontaneous glycinergic transmission regulates the growth of postsynaptic processes. 0 1996 John