Key result
Chemical activation of the midbrain periaqueductal gray in cats induced defenselike cardiovascular responses and differential patterns of sympathetic outflow depending on baroreceptor innervation.
Chemical activation of the midbrain defense region in cats induces differential sympathetic nerve discharge patterns depending on baroreceptor innervation, despite similar cardiovascular responses.
Highlights baroreceptor-dependent sympathetic patterning in feline defense models; leaves open human translation.
The changes in mean arterial pressure (MAP), renal (RBF) and femoral (FBF) blood flows, and inferior cardiac (CN) and vertebral nerve (VN) sympathetic nerve discharges (SND) produced by chemical activation (D,L-homocysteic acid) of the midbrain periaqueductal gray (PAG) were compared in baroreceptor-denervated and -innervated cats anesthetized with urethan. Defenselike cardiovascular responses in both states were similar in magnitude and consisted of increased MAP and FBF and decreased RBF; however, the nerve responses differed. In baroreceptor-denervated cats, PAG activation increased CN 10-Hz activity, decreased VN 10-Hz activity, and lengthened the CN-VN phase angle. In baroreceptor-innervated cats in which the rhythm in SND was cardiac related, PAG activation increased CN activity, but VN activity and the CN-VN phase angle were unchanged. These results demonstrate that chemical activation of PAG neurons induces differential patterns of sympathetic outflow generally consistent with accompanying defenselike cardiovascular responses. However, the mechanisms responsible for the changes in 10-Hz and cardiac-related SND appear to be different.
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Larsen et al. (2001) studied this question. Chemical activation (D,L-homocysteic acid) of the midbrain periaqueductal gray (PAG) vs. Baroreceptor-denervated vs. -innervated states was evaluated on Changes in mean arterial pressure, renal and femoral blood flows, and sympathetic nerve discharges. Chemical activation of the midbrain periaqueductal gray in cats induced defenselike cardiovascular responses and differential patterns of sympathetic outflow depending on baroreceptor innervation.
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