Volume 16, Number 14,
Issue of July 15, 1996
pp. 4518-4528
Copyright ©1996 Society for Neuroscience
A Pair of Identified Interneurons in Aplysia that Are
Involved in Multiple Behaviors Are Necessary and Sufficient for the
Arterial-Shortening Component of a Local Withdrawal Reflex
Received Feb. 16, 1996; revised April 24, 1996; accepted April 26, 1996.
Yuanpei Xin1,
Klaudiusz
R. Weiss2, and
Irving Kupfermann1
1 Center for Neurobiology and Behavior, College of
Physicians and Surgeons, Columbia University, New York, New York 10032, and 2 Department of Physiology and Biophysics, Mt. Sinai
Medical Center, New York, New York 10029
A bilateral pair of cerebral interneurons, called CC5, contribute
to the generation of a number of different behaviors involving head
movements. Each cell sends its axon to the ipsilateral and
contralateral pedal and pleural ganglia. A weak tactile stimulus to the
head excites the ipsilateral CC5; a strong stimulus excites both the
ipsilateral and contralateral cells. Firing of CC5 produces powerful
shortening of the ipsilateral pedal artery (PA) by means of
monosynaptic excitation of the pedal artery shortener (PAS) neuron, the
single motor neuron for the artery. A weak touch to a tentacle excites
the ipsilateral PAS and evokes a local withdrawal response accompanied
by shortening of the ipsilateral PA. In vivo recording of
the pedal artery nerve (PAn) showed that PAS was activated bilaterally
during defensive head withdrawal elicited by a strong stimulus and was
activated unilaterally by a weak stimulus. The responses were
eliminated by cutting the ipsilateral cerebral-pleural connective
(C-PLC). Electrical stimulation of the cerebral-pleural connective
provided evidence that all of the excitatory input to PAS via this
connective is provided by CC5. A variety of experimental results
indicates that during a local withdrawal reflex of the tentacle, CC5 is
necessary and sufficient for the unilateral PA-shortening component of
the response and therefore functions as a command neuron for a
component of the behavior. The data suggest that during defensive head
withdrawal, the two CC5 neurons may act conjointly as a two-neuron
command system that is necessary and sufficient for the bilateral
arterial-shortening component of the behavior.
Key words:
command;
withdrawal reflex;
Aplysia;
mechanosensory;
feeding;
head turning