Vol. 273, Issue 6, H2899-H2909, December 1997
SPECIAL COMMUNICATION
Extracellular serotonin changes in VLM during muscle
contraction: effects of
5-HT1A-receptor
activation
Gudbjorn
Asmundsson,
Daryl
Caringi,
David J.
Mokler,
Toshio
Kobayashi,
Takeshi
Ishide, and
Ahmmed
Ally
Departments of Pharmacology and Biochemistry, College of Osteopathic
Medicine, University of New England, Biddeford, Maine 04005; and
The Health Science Center, Tokyo University of Mercantile Marine,
Tokyo 135, Japan
This study determined whether muscle
contraction causes an increase in extracellular levels of serotonin
(5-HT) in the rostral (rVLM) or caudal ventrolateral medulla (cVLM) in
anesthetized rats. Muscle contraction, evoked by tibial nerve
stimulation, increased mean arterial blood pressure (MAP) by 27 ± 4 mmHg (n = 8). In addition, 5-HT levels
in the rVLM were elevated by 65 ± 9% during the contraction
(n = 8). Results were similar over two
repeated contractions. In contrast, muscle contraction increased MAP,
but not 5-HT, levels in the cVLM (n = 6). Tibial nerve stimulation after muscle paralysis had no effect on
either MAP or 5-HT levels in both rVLM and cVLM. Microdialysis of a
5-HT1A agonist, 8-OH-DPAT (10 mM),
into the rVLM for 30 min (n = 6)
blunted the MAP change and reduced 5-HT release during contraction.
Administration of NAN-190, a
5-HT1A antagonist, into the rVLM
had no effect on 5-HT release and cardiovascular responses during
muscle contraction and blocked the changes in 5-HT, MAP, and heart rate
to static contraction after subsequent microdialysis of 8-OH-DPAT.
Results demonstrate that 5-HT levels in the rVLM increase during muscle contraction and that
5-HT1A-receptor activation in the
rVLM blunts MAP response to muscle contraction via a decrease in the
extracellular concentration of 5-HT.
arterial blood pressure; heart rate; exercise pressor reflex; rostral ventrolateral medulla; caudal ventrolateral medulla; rat
