The Journal of Neurophysiology Vol. 83 No. 3 March 2000, pp. 1605-1620
Copyright ©2000 by the American Physiological Society
Diverse Synaptic Connections Between Peptidergic Radula
Mechanoafferent Neurons and Neurons in the Feeding System of
Aplysia
Steven C.
Rosen,1
Mark W.
Miller,2
Colin G.
Evans,3
Elizabeth C.
Cropper,3 and
Irving
Kupfermann1
1Center for Neurobiology and Behavior, New
York State Psychiatric Institute and College of Physicians and Surgeons
of Columbia University, New York, New York 10032;
2Institute of Neurobiology and Department of
Anatomy, University of Puerto Rico Medical Science Campus, San Juan,
Puerto Rico 00901; and 3Department of Physiology
and Biophysics and Fishberg Research Center for Neurobiology, Mount
Sinai School of Medicine, New York, New York 10029
Rosen, Steven C.,
Mark W. Miller,
Colin G. Evans,
Elizabeth C. Cropper, and
Irving Kupfermann.
Diverse Synaptic Connections Between Peptidergic Radula
Mechanoafferent Neurons and Neurons in the Feeding System of
Aplysia. J. Neurophysiol. 83: 1605-1620, 2000. The buccal ganglion of
Aplysia contains a heterogeneous population of
peptidergic, radula mechanoafferent (RM) neurons. To investigate their
function, two of the larger RM cells (B21, B22) were identified by
morphological and electrophysiological criteria. Both are
low-threshold, rapidly adapting, mechanoafferent neurons that responded
to touch of the radula, the structure that grasps food during ingestive
and egestive feeding movements. Sensory responses of the cells
consisted of spike bursts at frequencies of 8-35 Hz. Each cell was
found to make chemical, electrical, or combined synapses with other
sensory neurons, motor neurons and interneurons involved in radula
closure and/or protraction-retraction movements of the odontophore.
Motor neurons receiving input included the following: B8a/b, B15, and
B16, which innervate muscles contributing to radula closing; and B82, a
newly identified neuron that innervates the anterodorsal region of the
I1/I3 muscles of the buccal mass. B21 and B22 can affect buccal motor
programs by way of their connections to interneurons such as B19 and
B64. Fast, chemical, excitatory postsynaptic potentials (EPSPs)
produced by RM neurons, such as B21, exhibited strong,
frequency-dependent facilitation, a form of homosynaptic plasticity.
Firing B21 also produced a slow EPSP in B15 that increased the
excitability of the cell. Thus a sensory neuron mediating a behavioral
response may have modulatory effects. The data suggest multiple
functions for RM neurons including 1) triggering of
phase transitions in rhythmic motor programs, 2) adjusting the force of radula closure, 3) switching from
biting to swallowing or swallowing to rejection, and 4)
enhancing food-induced arousal.
