Vol. 279, Issue 1, R210-R221, July 2000
Differential pattern of spinal sympathetic outflow in response
to stimulation of the caudal medullary raphe
Peter D.
Larsen,
Sheng
Zhong,
Gerard L.
Gebber, and
Susan M.
Barman
Department of Pharmacology and Toxicology, Michigan State
University, East Lansing, Michigan 48824
In
urethan-anesthetized cats, frequency domain analysis was used to
explore the mechanisms of differential responses of inferior cardiac
(CN), vertebral (VN), and renal (RN) sympathetic nerves to electrical
stimulation of a discrete region of the medullary raphe (0-2 mm
caudal to the obex). Raphe stimulation in baroreceptor-denervated cats
at frequencies (7-12 Hz) that entrained the 10-Hz rhythm in nerve
activity decreased CN and RN activities but increased VN activity. The
reductions in CN and RN discharges were associated with decreased
low-frequency (
6 Hz) power and either increased (low stimulus
intensity) or decreased (high stimulus intensity) 10-Hz band power. In
contrast, VN 10-Hz band power was increased at all stimulus
intensities, without changes in low-frequency power. High-frequency (25 Hz) stimulation decreased low-frequency activity of CN and RN
discharges in both baroreceptor-denervated and baroreceptor-intact
cats, without decreasing VN low-frequency activity. We propose that the
differential pattern produced by raphe stimulation involves resonance
at the level of the 10-Hz oscillators and differential inhibition of
follower circuits that transmit both 10-Hz and low-frequency activity
to sympathetic nerves.
coupled oscillators; differential inhibition; follower circuits; resonance
