IDENTIFICATION AND CHARACTERIZATION OF CEREBRAL-GANGLION NEURONS THAT
INDUCE SWIMMING AND MODULATE SWIM-RELATED PEDAL- GANGLION NEURONS IN APLYSIA
BRASILIANA.
Gamkrelidze, G.N., P.J. Laurienti and J.E. Blankenship.
The Marine Biomedical Institute, University of Texas Medical Branch,
Galveston, Texas 77555-1069.
APStracts 2:0167N, 1995.
SUMMARY AND CONCLUSIONS
1. We have identified and characterized a family of several pairs of neurons
in the cerebral ganglion of Aplysia brasiliana which are capable of inducing,
maintaining or modulating a motor program that underlies swim locomotion in
this marine mollusc. We have operationally defined these cells as command
neurons (CN's) for swimming. 2. The command cells occur in bilateral pairs in
the cerebral ganglion and make direct and indirect outputs to neurons in the
pedal ganglia, including motoneurons, a central pattern generator circuit, and
modulatory neurons that enhance muscle contractions during swimming. Several
of the CN's are sufficient individually to induce the swim motor program
(SMP), all receive sensory feedback from the periphery, and several
interconnect with other swim-related CN's. 3. Tonic discharges of about 10 Hz
in CN types 1-3 are capable of eliciting the oscillatory, phasic SMP as
recorded in peripheral nerves that innervate the swim appendages, the
parapodia. CN1, CN2, and CN3 make monosynaptic excitatory connections onto
ipsilateral, contralateral and bilateral pedal swim-modulatory neurons
(parapodial opener- phase (POP) cells), respectively; and each command cell
type activates the pedal CPG, leading to sustained phasic output of
motoneurons and POP cells. 4. Tonic firing of CN4 causes weak activation of
the SMP contralaterally. These neurons occur as two pairs of neurons in each
cerebral hemiganglion, with mutual electrical and chemical synaptic
interconnections. CN4 cells also excite CN1 and CN2 cells. Thus, CN4 is
classified as a higher-order swim command cell type. 5. Command cells
classified as types 5-8 (CN5-CN8), while not capable of inducing the SMP
individually, nonetheless have strong synaptic connections with pedal POP
cells and/or with other command neurons. These command cells may excite or
inhibit follower cells on the same or opposite sides of the preparation and
modulate the swim output. 6. All the command cells tested received strong
input from mechanical stimulation, either stretch or pinching, of either
parapodium. Mechanosensory input from the parapodia was shown to depend on the
presence of the pedal ganglion, but not the pleural. Sensory stimulation
activated command cells and motoneurons, but POP cells received input from
sensory stimuli only through the cerebral ganglion, probably via command
cells. The effects of applied mechanosensory stimuli could be entirely
mimicked by motoneuron-induced contractions of the parapodia.
Received 10 February 1994; accepted in final form 22 May 1995.
APS Manuscript Number J94-5.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 8 June 1995.