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Howard Florey Institute of Experimental Physiology and Medicine, University of Melbourne, Parkville 3052, Australia
The
responses of sympathetic premotor neurons in the rostral ventrolateral
medulla (RVLM) to activation or inactivation of neurons in the caudal
pressor area (CPA) were studied in urethan-anesthetized rats.
Extracellular recordings were made from 32 barosensitive single units
in the RVLM, of which 26 were antidromically activated from the
cervical cord. Unilateral microinjections of
L-glutamate (0.5-5 nmol)
into the CPA increased firing in 13 of 14 premotor neurons by 90 ± 30% while raising blood pressure. Both ipsilateral and contralateral
injections were effective. Unilateral or bilateral inhibition of CPA
neuron activity by microinjecting glycine (5-200 nmol/side)
lowered blood pressure, while it reduced firing in 9 of 10 and 16 of 17 premotor neurons, respectively, by 45 ± 9 and 39 ± 6%. A
significant proportion of tonic activity in RVLM sympathetic premotor
neurons is thus driven, directly or indirectly, by neurons in the CPA.
blood pressure; brain stem; vasomotor tone
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