Submitted on November 1, 2002
Accepted on December 31, 1969
SOMATOSYMPATHETIC REFLEXES FROM THE LOW BACK IN THE ANESTHETIZED CAT
Yu-Ming Kang1, Michael J. Kenney2, Kevin F. Spratt3, and Joel G. Pickar4*
1 Biomedical Engineering, University of Iowa, Iowa City, IA, USA; Iowa Spine Research Center, University of Iowa, Iowa City, IA, USA
2 Anatomy and Physiology, Kansas State University, Manhattan, KS, USA
3 Iowa Spine Research Center, University of Iowa, Iowa City, IA, USA; Iowa Testing Programs, University of Iowa, Iowa City, IA, USA; UI Back Care, University of Iowa, Iowa City, IA, USA
4 Palmer Center for Chiropractic Research, Palmer College of Chiropractic, Davenport, IA, USA; Biomedical Engineering, University of Iowa, Iowa City, IA, USA; Iowa Spine Research Center, University of Iowa, Iowa City, IA, USA
* To whom correspondence should be addressed. E-mail: pickar_j{at}palmer.edu.
In the appendicular skeleton substantial evidence demonstrates that somatosensory input from deep tissues including limb muscles and joints elicits somatosympathetic reflexes. Much less is known about the presence and organization of these reflexes from the axial skeleton. We determined if mechanical loading of the lumbar spine and lumbar paraspinal muscle irritation reflexively affects post-ganglionic sympathetic nerve discharge (SND) to the spleen and kidney. In 27 
-chloralose-anesthetized cats the L2-4 multifidus muscles were injected with the inflammatory irritant mustard oil (20%, 60µl total) and a vertebral load (100% body weight) was applied dorsal-ventral at the L3 spinous process. Mustard oil injection alone without vertebral loading (n=7) increased mean splenic SND (60%), renal SND (30%), and heart rate (52 bpm). Mustard oil injection accompanied by the vertebral load (n=7) increased mean splenic SND (55%), renal SND (16%) and HR (27 bpm). Blood pressure changes were biphasic and could not account for these changes. When the vertebral load accompanied mustard oil the increases in splenic SND, renal SND, and heart rate remained elevated in a pattern significantly different from when the vertebral load was absent. Vehicle injection combined with the mechanical load (n=3) did not change any of the autonomic responses. Similarly mustard oil injection combined with a mechanical load did not change these responses when either the medial branches of the dorsal rami from T11 to L5 had been cut (n=4) nor when the spinal cord had been transected between the 2nd and 3rd cervical vertebrae (n=6). The results indicate that inflammatory stimulation of multifidus muscle in the low back evokes a somatosympathetic reflex integrated supraspinally in the upper cervical spinal cord or higher. The reflex's afferent arm travels in the medial branch of the dorsal ramus and its efferent arm can affect sympathetic outflow to the spleen and the kidney as well as HR and BP. A static mechanical load applied to the lumbar spine accompanying the inflammatory stimulus appears to sustain the inflammatory-induced reflex activity.
