Role of serotonergic neurons in the maintenance of the 10-Hz rhythm in sympathetic nerve discharge.
We studied the effects of serotonin (5-HT)-receptor agonists and antagonists on the naturally occurring 10-Hz rhythm in sympathetic nerve discharge (SND) of urethan-anesthetized, baroreceptor-denervated cats. Intravenous doses of the 5-HT1A-receptor agonists 8-hydroxy-2(di-n-propylamino)-tetralin (8-OH-DPAT) and U-93385E, which inhibit the firing of serotonergic medullary raphe neurons, decreased the power in the 10-Hz band of SND without affecting the power at frequencies < or = 6 Hz. The inhibitory effects of 8-OH-DPAT and U-93385E were reversed by the 5-HT1A-receptor antagonists spiperone and WAY-100135. Microinjection of 8-OH-DPAT into medullary raphe nuclei also selectively eliminated the 10-Hz rhythm in SND. Intravenous administration of the 5-HT2-receptor antagonist methysergide blocked the 10-Hz rhythm in SND, whereas the 5-HT2-receptor agonist 1-(2,5-dimethoxy-4-iodophenyl)-2-amino-propane increased peak frequency and power in the 10-Hz band of SND. Microinjection of N-methyl-D-aspartic acid into the medullary raphe also enhanced the 10-Hz rhythm in SND. These data support the view that the naturally occurring discharges of serotonergic medullary raphe neurons preferentially enhance the 10-Hz rhythm in SND.
Orer
H S
HS
Department of Pharmacology and Toxicology, Michigan State University, East Lansing 48824, USA.
Clement
M E
ME
Barman
S M
SM
Zhong
S
S
Gebber
G L
GL
McCall
R B
RB
D000818:Animals; D002415:Cats; D003714:Denervation; D004594:Electrophysiology; D008526:Medulla Oblongata; D009474:Neurons / Q000502:physiology*; D010507:Periodicity; D011311:Pressoreceptors / Q000502:physiology; D011903:Raphe Nuclei / Q000166:cytology / Q000502:physiology; D011985:Receptors, Serotonin / Q000187:drug effects; D012701:Serotonin / Q000502:physiology*; D012702:Serotonin Antagonists / Q000494:pharmacology; D017366:Serotonin Receptor Agonists / Q000494:pharmacology; D013564:Sympathetic Nervous System / Q000187:drug effects / Q000502:physiology*
D011985:Receptors, Serotonin; D012702:Serotonin Antagonists; D017366:Serotonin Receptor Agonists; D012701:Serotonin