Mj. Coleman et Ral. Dampney, SYMPATHOINHIBITION EVOKED FROM CAUDAL MIDLINE MEDULLA IS MEDIATED BY GABA RECEPTORS IN ROSTRAL VLM, American journal of physiology. Regulatory, integrative and comparative physiology, 43(2), 1998, pp. 318-323
The present study was performed to determine whether the powerful depr
essor and sympathoinhibitory response that can be evolved from neurons
in the caudal midline medulla is mediated by gamma-aminobutyric acide
rgic (GABAergic) inhibition of sympathoexcitatory neurons in the rostr
al part of the ventrolateral medulla (VLM). In anesthetized barointact
and barodenervated rabbits, bilateral microinjections of bicuculline
into sympathoexcitatory sites in the rostral VLM resulted in a sustain
ed increase in renal sympathetic nerve activity and abolished or rever
sed the depressor and sympathoinhibitory response evoked by glutamate
microinjection into the caudal midline medulla. By contrast, the sympa
thoinhibitory response evoked from the caudal midline medulla persiste
d when the background level of renal sympathetic nerve activity was re
flexly raised by baroreceptor unloading. The results indicate that 1)
the depressor and sympathoinhibitory response evoked by stimulation of
neurons in the caudal midline medulla is mediated by a GABAErgic syna
pse in the rostral VLM and 2) there are also sympathoexcitatory neuron
s in the caudal midline medulla whose presence is revealed by blockade
of the more powerful sympathoinhibitory response.