Journal of Neuroscience, Vol 14, 3263-3270, Copyright © 1994 by Society for Neuroscience
Induction of a cellular defense reaction is accompanied by an increase in sensory neuron excitability in Aplysia
AL Clatworthy, GA Castro, BU Budelmann and ET Walters
Department of Physiology and Cell Biology, University of Texas Medical School at Houston 77225.
The complexity of vertebrate immune and nervous systems makes detailed
cellular analysis of neuroimmune interactions a challenging prospect. The
immune systems of invertebrates, although much less complex than their
vertebrate counterparts, share basic cellular defense responses to wounded
self or nonself. We have developed a simple model system to study
neuroimmune interactions using an invertebrate preparation well suited to
detailed cellular analysis. Loose ligation of peripheral nerves in Aplysia
induced a cellular defense reaction evidenced by the accumulation of large
numbers of amebocytes at the ligation site. From 5 to 30 d after ligation,
the excitability of the soma of sensory neurons having axons in ligated
nerves was increased compared to contralateral sensory neurons with axons
in nonligated nerves. Spike threshold and afterhyperpolarization were
reduced, and spike amplitude and duration were increased. Spike
accommodation was also decreased such that sensory neurons on the ligated
side fired more spikes to a 1 sec intracellular depolarizing pulse than
control sensory neurons. These effects are unlikely to be accounted for by
ligation-induced injury of sensory axons since both morphological and
electrophysiological evidence indicated that the axons in ligated nerves
were healthy and able to conduct action potentials. Amebocytes activated by
the presence of nonself may release factors that lead to a central
sensitization of sensory neurons with axons in close proximity to the
amebocytes.
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