Dorsal medullary 5-HT3 receptors and sympathetic premotor neurones in the rat.
1. Our aim was to determine whether the cardiovascular neurones in the rostro-ventrolateral medulla (CV-RVLM neurones) were involved in the sympathoexcitation induced by stimulation of 5-HT3 receptors in the region of the nucleus tractus solitarii (NTS). Experiments were performed in pentobarbitone-anaesthetized rats, artificially ventilated and paralysed with pancuronium bromide. 2. Using extracellular recordings, different types of RVLM neurones were characterized: cardiovascular (CV), ventilation-related and baroreflex-insensitive (unidentified) neurones. The CV-RVLM cells were further subdivided into three populations according to their axonal conduction velocities: A (1.2 +/- 0.1 m s-1), B (2.5 +/- 0.2 m s-1) and C (6.8 +/- 1.1 m s-1). 3. Only the CV-RVLM neurones of the A and B categories were partially inhibited (-30 %) by a hypotensive dose (2.5 microg kg-1 i.v.) of clonidine. 4. Microinjections into the region of the commissural NTS of 1-(m-chlorophenyl)-biguanide (CPBG, 2 nmol), a selective 5-HT3 receptor agonist, elicited an increase in both lumbar sympathetic nerve discharge (SND) and arterial pressure. In addition, this treatment produced a marked excitation of CV-RVLM neurones of the A and B categories, without affecting those of the C type, as well as ventilation-related and unidentified RVLM cells. 5. The activity of the CV neurones in the caudo-ventrolateral part of the medulla oblongata (CV-CVLM) was not modified by 5-HT3 receptor stimulation in the NTS. 6. Prior intra-NTS microinjections of ondansetron (300 pmol, a selective 5-HT3 receptor antagonist) into the region of the commissural NTS prevented the excitation of A and B CV-RVLM neurones induced by CPBG. 7. Intracarotid administration of saline saturated with CO2 (chemoreceptor activation) elicited both an increase in the SND and an excitation of the clonidine-insensitive CV-RVLM neurones of the C type, without affecting A and B neurones. 8. In conclusion, the sympathoexcitation elicited following 5-HT3 receptor stimulation in the region of the commissural NTS of pentobarbitone-anaesthetized rats seems to result from the excitation of two different pools of clonidine-sensitive CV-RVLM neurones. These neurones are apparently not involved in the sympathetic component of the chemoreceptor reflex.
Sévoz-Couche
C
C
INSERM U. 288, C. H. U. Pitie-Salpetriere, 75634 Paris cedex 13, France.
Nosjean
A
A
Franc
B
B
Hamon
M
M
Laguzzi
R
R
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000818:Animals; D001012:Aorta, Abdominal; D017704:Baroreflex / Q000502:physiology; D001645:Biguanides / Q000494:pharmacology; D001794:Blood Pressure; D002245:Carbon Dioxide / Q000494:pharmacology; D002316:Cardiotonic Agents / Q000494:pharmacology; D002319:Cardiovascular System / Q000294:innervation; D002344:Carotid Body / Q000502:physiology; D004594:Electrophysiology; D008026:Ligation; D008168:Lung / Q000294:innervation; D008297:Male; D008845:Microinjections; D009046:Motor Neurons / Q000737:chemistry / Q000187:drug effects / Q000502:physiology*; D010656:Phenylephrine / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D011985:Receptors, Serotonin / Q000502:physiology*; D044406:Receptors, Serotonin, 5-HT3; D012119:Respiration / Q000502:physiology; D017366:Serotonin Receptor Agonists / Q000494:pharmacology; D017552:Solitary Nucleus / Q000737:chemistry* / Q000166:cytology; D013564:Sympathetic Nervous System / Q000737:chemistry* / Q000166:cytology
D001645:Biguanides; D002316:Cardiotonic Agents; D011985:Receptors, Serotonin; D044406:Receptors, Serotonin, 5-HT3; D017366:Serotonin Receptor Agonists; D002245:Carbon Dioxide; D010656:Phenylephrine; C065734:1-(3-chlorophenyl)biguanide