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Dorsal medullary 5‐HT 3 receptors and sympathetic premotor neurones in the rat
Author(s) -
SévozCouche Caroline,
Nosjean Anne,
Franc Bernard,
Hamon Michel,
Laguzzi Raul
Publication year - 1998
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.1998.747bp.x
Subject(s) - rostral ventrolateral medulla , medulla oblongata , microinjections , damgo , solitary nucleus , stimulation , chemistry , endocrinology , rostral ventromedial medulla , medicine , receptor , agonist , central nervous system , nociception , opioid receptor , hyperalgesia
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‐HT 3 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 μg 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‐HT 3 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‐HT 3 receptor stimulation in the NTS. 6 Prior intra‐NTS microinjections of ondansetron (300 pmol, a selective 5‐HT 3 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 CO 2 (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‐HT 3 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.