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1 Departamento de Fisiologia, Universidade Federal de São Paulo, Brazil CEP: 04023; and Departments of 2 Medicine, 3 Pediatrics, and 4 Neuroscience, Case Western Reserve University, Cleveland, Ohio 44106
We studied the respiratory and
blood pressure responses to chemical stimulation of two regions of the
ventral brainstem in mice: the rostral and caudal ventrolateral medulla
(RVLM and CVLM, respectively). Stimulation of the RVLM by
microinjections of the excitatory amino acid L-glutamate
induced increases in diaphragm activity and breathing frequency,
elevation of blood pressure (BP), and a slight increase in heart rate
(HR). However, activation of the CVLM induced a decrease in breathing
frequency, mainly due to prolongation of expiratory time
(TE), and hypotension associated with a slight slowing of
HR. Because adrenergic mechanisms are known to participate in the
control of respiratory timing, we examined the role of
2-adrenergic receptors in the RVLM region in mediating
these inhibitory effects. The findings demonstrated that blockade of
the
2-adrenergic receptors within the RVLM by prior
microinjection of SKF-86466 (an
2-adrenergic receptor
blocker) significantly reduced changes in TE induced by
CVLM stimulation but had little effect on BP responses. These results
indicate that, in mice, activation of the RVLM increases respiratory
drive associated with an elevation of BP, but stimulation of CVLM
induces prolongation of TE via an
2-adrenergic signal transduction pathway.
respiratory timing; rostral ventrolateral medulla; caudal
ventrolateral medulla; L-glutamate;
2-adrenergic receptors
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