Journal of Neuroscience, Vol 6, 318-324, Copyright © 1986 by Society for Neuroscience
Regeneration of a distinctive set of axosomatic contacts in the leech central nervous system
KA French and KJ Muller
The nociceptive sensory neurons (N cells) in the leech Hirudo medicinalis
contact other neurons through conventional synapses in the neuropile and
through baskets of processes that wrap the somata of particular cells.
These axosomatic contacts are made with the pressure (P) and N sensory
neurons in the adjacent segmental ganglia, but not with cells within the
same ganglion as the wrapping cell. Physiological evidence indicates that
these contacts may be synaptic, although conventional synapses have not
been observed with electron microscopy. After they have been injured,
lateral N cell processes can grow into the anterior adjacent ganglion and
regenerate somatic contacts. In general, regenerated N cell processes wrap
the same somata as do intact N cells, but they often wrap fewer somata.
However, six of 14 regenerated N cells also wrapped the soma of a small
posterior cell that was contacted in only one of 120 normal ganglia
examined. It thus appears that the growing processes of an injured N cell
select certain cell somata to wrap, but that the selection is somewhat
broader than that in the embryonic leech.