Vol. 90, Issue 1, 248-260, January 2001
Dorsomedial medulla is more susceptible than
rostral ventrolateral medulla to hypoxic insult in cats
Ling-Zong
Hong1,2,
Jon-Son
Kuo2,
Mao-Hsiung
Yen1, and
Chok-Yung
Chai1,3
1 Graduate Institute of Life Sciences, National Defense
Medical Center, Taipei 100; 3 Institute of Biomedical Sciences,
Academia Sinica, Taipei 115; and 2 Department of Education and
Medical Research, Taichung Veterans General Hospital, Taichung 40705,
Taiwan, Republic of China
We investigated the responses
of systemic arterial pressure and vertebral sympathetic nerve activity
to glutamate microinjections (0.1 M, 70 nl) in the dorsomedial (DM) and
the rostral ventrolateral medulla (RVLM) before hypoxia and after
reoxygenation (posthypoxia) after various degrees of hypoxia in
anesthetized cats. Hypoxia was produced by ventilating 5%
O2 and 95% N2 for different durations (hypoxia
I-III). In intact cats, the glutamate-induced systemic arterial
pressure and vertebral nerve activity responses of the DM were
depressed after all degrees of hypoxia. Posthypoxic depression in the
RVLM, however, was not observed until hypoxia II and III. Precollicular
decerebration prevented depression in the RVLM, but, for the DM, it was
effective only for hypoxia I. Baro- and chemoreceptor denervation
abolished all posthypoxic depression in both the DM and the RVLM.
Pressor responses to tyramine (100-400 µg/kg iv) remained
unchanged after all degrees of hypoxia. These results suggest that the
DM is more susceptible to hypoxia than the RVLM. The peripheral baro-
and chemoreceptors and the suprapontine structures apparently play an
important role in posthypoxic depression. Moreover, the depression is
not due to the postganglionic norepinephrine depletion.
vertebral sympathetic nerve; reoxygenation; decerebration; baroreceptor; chemoreceptor
