Anatomic patterning in the expression of vestibulosympathetic reflexes.
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, chi(2) test). These results support the hypothesis that VSR are anatomically patterned.
Kerman
I A
IA
Howard Florey Institute of Experimental Physiology and Medicine, University of Melbourne, Parkville, Victoria 3052, Australia.
Yates
B J
BJ
McAllen
R M
RM
D000200:Action Potentials / Q000502:physiology; D000818:Animals; D017704:Baroreflex / Q000502:physiology*; D001794:Blood Pressure / Q000502:physiology; D019521:Body Patterning / Q000502:physiology*; D002339:Carotid Arteries / Q000294:innervation / Q000502:physiology; D002415:Cats; D007758:Ear, Inner / Q000294:innervation / Q000502:physiology; D004525:Efferent Pathways / Q000502:physiology; D004558:Electric Stimulation; D005145:Face / Q000294:innervation / Q000502:physiology; D005552:Forelimb / Q000294:innervation / Q000502:physiology; D006614:Hindlimb / Q000294:innervation / Q000502:physiology; D012027:Reflex, Vestibulo-Ocular / Q000502:physiology*; D017779:Sympathetic Fibers, Postganglionic / Q000502:physiology*; D014661:Vasoconstriction / Q000502:physiology; D014725:Vestibular Nerve / Q000502:physiology*