Volume 17, Number 12,
Issue of June 15, 1997
pp. 4873-4885
Copyright ©1997 Society for Neuroscience
Parallel Medullary Gustatospinal Pathways In a Catfish: Possible
Neural Substrates for Taste-Mediated Food Search
Received May 30, 1996; revised March 21, 1997; accepted April 7, 1997.
Jagmeet S. Kanwal and
Thomas E. Finger
Department of Cellular and Structural Biology, University of
Colorado School of Medicine, 4200 East Ninth Avenue, Denver, Colorado
80262
Taste and tactile fibers in the facial nerve of catfish innervate
extraoral taste buds and terminate somatotopically in the facial lobe
(FL)
a medullary structure crucial for gustatory-mediated food search.
The present study was performed to determine the neural linkages
between the gustatory input and the spinal motor output. Spinal
injections of horseradish peroxidase (HRP) label spinopetal cells in
the octaval nuclei, the nucleus of the medial longitudinal fasciculus,
and reticulospinal neurons (Rsps) in the brainstem medial reticular
formation (RF), including the Mauthner cell. A somatotopically
organized, direct faciospinal system originating from superficial cells
scattered in the lateral lobule of the facial lobe (ll) is also
labeled. The brainstem reticulospinal cells are segmentally organized
into 14 clusters within eight segments of the reticular formation and
includes one cluster (RS5) directly ventral to the FL. Injections of
HRP or fluorescent tracers into the medial lobule of the FL label a
facioreticular projection terminating around the Rsps of RS5. DiI
injections into this area of the RF retrogradely label deeply situated
bipolar neurons, especially in the medial and intermediate lobules of
the FL. Electrophysiological recordings in and around RS5 show units
with large receptive fields and with responses to chemical and tactile
stimulation. The FL projects to the spinal cord via two pathways: (1) a
topographically organized direct faciospinal pathway, and (2) an
indirect facioreticulospinal pathway in which reticular neurons process
and integrate gustatory information before influencing spinal circuitry
for motor control during food search.
Key words:
facial lobe;
nucleus of the solitary tract;
reticular
formation;
taste;
reticulospinal;
feeding
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