T. Ishide et al., Glutamate neurotransmission and nitric oxide interaction within the ventrolateral medulla during cardiovascular responses to muscle contraction, BRAIN RES, 874(2), 2000, pp. 107-115
We previously reported that nitric oxide, within the RVLM and CVLM, plays a
n opposing role in modulating cardiovascular responses during static muscle
contraction [B,J. Freda, R.S. Gaitonde, R, Lillaney, A. Ally, Cardiovascul
ar responses to muscle contraction following microdialysis of nitric oxide
precursor into ventrolateral medulla, Brain Res. 828 (1999) 60-67]. In this
study, we determined whether the effects of administering L-arginine, a pr
ecursor for the synthesis of nitric oxide, and N-G-monomethyl-L-arginine (L
-NMMA), a nitric oxide synthase inhibitor, into the rostral (RVLM) and caud
al (CVLM) ventrolateral medulla on cardiovascular responses elicited during
static muscle contraction were mediated via an alteration of localized glu
tamate concentrations using microdialysis techniques. In experiments within
the RVLM (n=8), muscle contraction increased MAP and HR by 21+/-2 mm Hg an
d 22+/-3 bpm, respectively. Glutamate increased from 1.1+/-0.4 to 4.4+/-0.6
ng/5 mu l measured from bilateral RVLM areas. Microdialysis of L-arginine
(1.0 mu M) for 30 min attenuated the contraction-evoked increases in MAP, H
R, and glutamate levels. After subsequent microdialysis of L-NMMA (1.0 mu M
) into the RVLM, contraction augmented the presser and tachycardic response
s and glutamate release. In experiments within CVLM (n=8), muscle contracti
on increased MAP and HR by 22+/-3 mm Hg and 20+/-2 bpm. respectively. Gluta
mate increased from 0.8+/-0.4 to 3.6+/-0.6 ng/5 mu l measured from the CVLM
. L-Arginine augmented the cardiovascular responses and glutamate release a
nd L-NMMA attenuated all the effects. Results suggest that nitric oxide wit
hin the RVLM and CVLM plays opposing roles in modulating cardiovascular res
ponses during static exercise via decreasing and increasing, respectively,
extracellular glutamate levels. (C) 2000 Elsevier Science B.V. All rights r
eserved.