Activation of descending noradrenergic system by peripheral nerve stimulation.
Noradrenaline (NA) release in the rat lumbar spinal cord (L3-4) in response to variable intensity, selective stimulation of large (A-beta), small myelinated (A-delta), and unmyelinated (C) afferent fibers was examined by in vivo microdialysis with high performance liquid chromatography and electrochemical detection. Application of 100 mM K+ solution via the dialysis probe increased NA in the dialysate. Thoracic segment transection rostral to the probe depressed the NA level. Transcutaneous stimulation of peripheral nerves had the following effects: 1) High intensity stimulation of afferent A-delta or C fibers increased spinal NA release, which was decreased by thoracic spinal cord transection. 2) Stimulation of afferent A-beta or A-delta fibers at low intensity did not affect the NA level. 3) High intensity stimulation of afferent A-beta fibers depressed NA release in half of the trials. Results indicate that many NA-containing nerve terminals that innervate the lumbar spinal cord originate from supraspinal structures. Somatic neural inputs from afferent C fibers and high-threshold A-delta, but not A-beta nor low-threshold A-delta fibers, activate the descending NA system and release the NA in the spinal cord. The descending NA system may participate in antinociception.
Men
D S
DS
Department of Physiology, Showa University School of Dentistry, Tokyo, Japan.
Matsui
Y
Y
D000818:Animals; D003714:Denervation; D004525:Efferent Pathways / Q000502:physiology; D004558:Electric Stimulation; D005260:Female; D008161:Lumbosacral Region; D009638:Norepinephrine / Q000378:metabolism / Q000502:physiology*; D009994:Osmolar Concentration; D010525:Peripheral Nerves / Q000502:physiology*; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D013116:Spinal Cord / Q000378:metabolism
D011188:Potassium; D009638:Norepinephrine