Am J Physiol Regul Integr Comp Physiol. 2005
Dec;289(6):R1693-702. Epub 2005 Aug 11.
Barman SM, Phillips SW, Gebber GL.
In this study, they tried to find out if the medullary
lateral tegmental field (LTF) had a role in mediating the Bezold-Jarisch reflex
in cats. They did this in two ways – they inactivated LTF neurons using
microinjections of either the GABAA agonist, muscimol, or with the excitatory
amino acid receptor antagonist, AP5, and got similar results with both methods.
These results were that the phenylbiguanide-induced Bezold-Jarisch reflex,
which normally decreases SNA, heart rate, and MAP, was either sharply
attenuated or reversed. However, two aspects of the Bezold-Jarisch reflex, an
increase in apnea and a decrease in phrenic nerve activity, were not affected. When
they switched from AP5 to NBQX, a non-NMDA receptor antagonist, they did not
see these effects.
They came away with three main conclusions from this paper.
1) that the LTF plays an important role in activating the Bezold-Jarisch reflex,
2) that there is a separation in the respiratory and cardiovascular effects of
the Bezold-Jarisch reflex in the LTF, and 3) the Bezold-Jarisch reflex is
mediated by NMDA receptors. They closed this paper by mentioning that people
normally think of the CVLM as the major inhibitory control over the RVLM, and
note that their experiments in this paper don’t contradict this since they use
cats when most people use rats and rabbits, so they don’t know if species
differences come into play here or not. -DH
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