Journal of Neuroscience, Vol 7, 2618-2629, Copyright © 1987 by Society for Neuroscience
Morphological changes in leech Retzius neurons after target contact during embryogenesis
J Jellies, CM Loer and WB Kristan Jr
Segmental variation in identified neurons may provide an opportunity to
examine extrinsic influences on neuronal phenotype, since segmentally
homologous neurons must contain much the same intrinsic information, having
arisen from very similar or identical precursors. Two large serotonergic
Retzius (Rz) cells are found in each segmental ganglion of the leech Hirudo
medicinalis. While most Rz cells innervate the body wall in their own
segment and, by way of axons in the interganglionic connectives, the body
wall of adjacent segments, the Rz cells in ganglia 5 and 6 [Rz(5,6)] lack
interganglionic axons and innervate only the reproductive tissue (Glover
and Mason, 1986). Here we describe and quantify the development of
differences between Rz(5,6) and other Rz cells in peripheral innervation,
neuropilar arborization, and soma size. We filled individual Rz cells with
Lucifer yellow or HRP in adults and in staged embryos. During the first 72
hr of outgrowth of Rz cell processes, the morphology of Rz(5,6) was
indistinguishable from that of other Rz cells. Only after the processes of
Rz(5,6) reached the reproductive tissue did they begin to differ from their
segmental homologs. This temporal correlation suggests that these
morphological differences arise because of some interaction between Rz(5,6)
and their target tissue.