Journal of Neurophysiology, Vol 52, Issue 6 1094-1105, Copyright © 1984 by APS
Stability of new electrical connections between adult Helisoma neurons is influenced by preexisting neuronal interactions
A. G. Bulloch, S. B. Kater and H. R. Miller
The factors responsible for the selective stability of new electrical
connections between regenerating, adult Helisoma neurons (5, 6) were
examined. In particular the alternative hypotheses that the normal
reduction in strength of a specific connection is dependent on the
formation of a new stable connection or the maintenance of a preexisting
connection were tested. To this end, single neurons were eliminated either
by microdissection or photoinactivation. Formation of stable 5-5 [i.e.,
left neuron 5 (L5) to right neuron 5 (R5)] coupling was prevented by
removal of a single neuron 5 soma. The time course of the normally
transient neuron 5-4 connection in these ganglia, however, was the same as
that of control preparations. Thus the 5-4 connection is transient even
when stable 5-5 coupling is unable to develop. After removal of a single
neuron 4 soma, however, the 5-4 connection was stabilized. This was despite
the concurrent development of stable 5-5 coupling in these preparations.
Similar results were obtained when neurons were eliminated by
photoinactivation, a procedure that kills axonal processes in addition to
the neuronal cell body. Morphological examination of untreated neurons by
Lucifer Yellow CH stain showed that neurite outgrowth was not prevented by
either of the techniques employed to eliminate single neurons. It is
concluded that the development of the new, stable 5-5 electrical connection
does not influence the transient nature of the 5-4 connection. The presence
of both neurons 4, however, which have a preexisting connection, is
required for reduction of 5-4 coupling. Thus preexisting neurons and/or
their connections appear to play a role in the stability of new connections
in this adult nervous system.
