Journal of Neuroscience, Vol 10, 194-204, Copyright © 1990 by Society for Neuroscience
Locomotion evoked by stimulation of the brain stem in the Atlantic stingray, Dasyatis sabina
CA Livingston and RB Leonard
University of Texas Medical Branch, Marine Biomedical Institute, Galveston 77550.
The primary pathway descending to the spinal cord to initiate locomotion in
the stingray is located in the intermediate to ventral portion of the
lateral funiculus; a second pathway is located in the dorsolateral
funiculus. The goal of this study was to identify the origins of these
pathways in the rhombencephalic reticular formation (RF). To do this we
used microstimulation of the RF in conjunction with selective lesions of
the brain stem and spinal cord. In some animals microinjections of
excitatory amino acids were used to avoid stimulating axons of passage.
Locomotion in the contralateral pectoral fin was evoked by microstimulation
of the dorsal and ventral reticular nuclei, the middle and superior RF, and
the ventral portion of the lateral RF. The regions from which locomotion
was evoked by chemical stimulation were more restricted and included the
rostral dorsal reticular nucleus, the middle RF, and the adjacent ventral
lateral RF. This area encompasses the magnocellular RF and coincides with
the distribution of numerous reticulospinal cells that project
ipsilaterally into the ventral half of the lateral funiculus. Our results
indicate, then, that locomotion in the stingray is mediated primarily by a
pathway originating in the magnocellular RF that descends ipsilaterally in
the ventral half of the lateral funiculus to elicit swimming in the
contralateral pectoral fin. We suggest that this primary pathway is
specifically associated with the control of locomotion. We also
demonstrated that locomotion can be evoked independently from the lateral
RF, but is probably mediated by an indirect pathway relaying near the
spinomedullary junction or in the rostral spinal cord.
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