Microinjection of a 5-HT3 receptor agonist into the NTS of awake rats inhibits the bradycardic response to activation of the von Bezold-Jarisch reflex.
In the present study we investigated the effects of bilateral microinjection into the lateral commissural nucleus tractus solitarius (NTS) of 2-methyl-5-HT, a 5-HT3 receptor agonist, on the bradycardic response of the von Bezold-Jarisch reflex of awake rats. We evaluated mainly the bradycardic response because in previous studies we documented that the hypotensive response of the von-Bezold-Jarisch reflex in awake rats is secondary to the intense bradycardic response. The Bezold-Jarisch reflex was activated by intravenous injection of serotonin (8 microg/kg) in awake rats before and 1, 3, 10, 20 and 60 min after bilateral microinjection of 2-methyl-5-HT (5 nmol/50 nl, n = 8) into the NTS. Microinjections of 2-methyl-5-HT into the NTS produced a significant increase in basal mean arterial pressure [(MAP), 97 +/- 4 vs. 114 +/- 4 mmHg), no changes in basal heart rate and a significant reduction in bradycardic (-78 +/- 19; -94 +/- 24 and -107 +/- 21 bpm) and hypotensive (-16 +/- 4; -10 +/- 5 and -17 +/- 4 mmHg) responses to activation of the von Bezold-Jarisch reflex at 3, 10 and 20 min, respectively, when compared with the control value (-231 +/- 13 bpm and -43 +/- 4 mmHg). The data of the present study suggest that serotonin acting on 5-HT3 receptors in the NTS may play an important inhibitory neuromodulatory role in the bradycardic response to activation of the von Bezold-Jarisch reflex.
Department of Physiology, School of Medicine of Ribeirão Preto, University of São Paulo, São Paulo, Ribeirão Preto, Brazil.
D M
DM
Leal
J C
JC
Callera
L G
LG
Bonagamba
A
A
Nosjean
R
R
Laguzzi
B H
BH
Machado
D000704:Analysis of Variance; D000818:Animals; D001143:Arousal; D001794:Blood Pressure / Q000187:drug effects; D001919:Bradycardia / Q000139:chemically induced / Q000503:physiopathology*; D006339:Heart Rate / Q000187:drug effects; D008297:Male; D008845:Microinjections; D009412:Nerve Fibers / Q000187:drug effects / Q000502:physiology; D009433:Neural Inhibition / Q000187:drug effects; D010275:Parasympathetic Nervous System / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D011985:Receptors, Serotonin / Q000502:physiology*; D044406:Receptors, Serotonin, 5-HT3; D012021:Reflex, Abnormal / Q000187:drug effects*; D012701:Serotonin / Q000031:analogs & derivatives / Q000494:pharmacology*; D017366:Serotonin Receptor Agonists / Q000494:pharmacology*; D017552:Solitary Nucleus / Q000166:cytology / Q000187:drug effects* / Q000502:physiology; D013564:Sympathetic Nervous System / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D009435:Synaptic Transmission / Q000187:drug effects
D011985:Receptors, Serotonin; D044406:Receptors, Serotonin, 5-HT3; D017366:Serotonin Receptor Agonists; D012701:Serotonin; C045918:2-methyl-5-HT