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1 Howard Florey Institute of Experimental Physiology and Medicine, University of Melbourne, Parkville, Victoria 3052, Australia; and Departments of 2 Neuroscience and 3 Otolaryngology, University of Pittsburgh, Pittsburgh, Pennsylvania 15213
To investigate the possibility that expression of
vestibulosympathetic reflexes (VSR) is related to a nerve's anatomic
location rather than its target organ, we compared VSR recorded from
the same type of postganglionic fiber [muscle vasoconstrictor (MVC)] located at three different rostrocaudal levels: hindlimb, forelimb, and
face. Experiments were performed on chloralose-anesthetized cats, and
vestibular afferents were stimulated electrically. Single MVC unit
activity was extracted by spike shape analysis of few-fiber recordings,
and unit discrimination was confirmed by autocorrelation. Poststimulus
time histogram analysis revealed that about half of the neurons were
initially inhibited by vestibular stimulation (type 1 response),
whereas the other MVC fibers were initially strongly excited (type 2 response). MVC units with types 1 and 2 responses were present in the
same nerve fascicle. Barosensitivity was equivalent in the two groups,
but fibers showing type 1 responses fired significantly faster than
those giving type 2 responses (0.29 ± 0.04 vs. 0.20 ± 0.02 Hz). Nerve fibers with type 1 responses were most common in the
hindlimb (21 of 29 units) and least common in the face (2 of 11 units),
the difference in relative proportion being significant
(P < 0.05,
2 test). These results
support the hypothesis that VSR are anatomically patterned.
muscle vasoconstrictor fibers; vasomotor pathways; sympathetic nerves
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