Journal of Neuroscience, Vol 5, 16-22, Copyright © 1985 by Society for Neuroscience
Excitatory and inhibitory activity in the dorsal musculature of the nematode Ascaris evoked by single dorsal excitatory motonerons
JP Walrond and AO Stretton
A physiological preparation, in which identified motoneurons of the
nematode Ascaris lumbricoides can be individually stimulated, was used to
map the response evoked by single dorsal excitatory (DE) motoneurons in
muscle cells innervated along the length of the dorsal nerve cord. As
previously reported (Walrond, J. P., I. S. Kaas, A. O. W. Stretton, and J.
E. Donmoyer (1985) J. Neurosci. 5: 1-8), stimulation of a DE cell produces
excitatory responses in muscle cells which it directly innervates.
Excitatory activity propagates along the most strongly activated region of
muscle at a velocity of approximately 28 cm/sec, then relaxes into a slower
velocity of approximately 12 cm/sec. When either the DE1 or DE3 neurons
were stimulated, excitatory responses were also observed in muscle cells
not directly innervated by the neuron. These signals propagate in the
opposite direction from the fast- propagating activity at a velocity of
approximately 13 cm/sec. Injection of hyperpolarizing current into muscle
cells blocks this slower propagation but fails to block the faster
conduction. We conclude that the fast-conducting responses result from
signals propagating in the motor axon, whereas the slow responses are
conducted through gap junctions which connect Ascaris muscle cells.
Stimulating a single DE motoneuron also evokes hyperpolarizing muscle
responses in regions adjacent to the zones of fast and slow
excitation.(ABSTRACT TRUNCATED AT 250 WORDS)