Key result
Activation of the rostral ventrolateral medulla by microinjection of DLH or bicuculline methiodide inhibits baroreflex vagal bradycardia at the brain stem level independently of central inspiratory drive.
Why the study?
Does activation of the rostral ventrolateral medulla inhibit baroreflex vagal bradycardia in rats?
Does activation of the rostral ventrolateral medulla inhibit baroreflex vagal bradycardia in rats?
Activation of the rostral ventrolateral medulla inhibits baroreflex vagal bradycardia at the brain stem level independently of central inspiratory drive.
Brainstem inhibition of baroreflex vagal bradycardia in rats warrants mechanistic follow-up; leaves open human relevance.
In stressful conditions, baroreflex vagal bradycardia (BVB) is often suppressed while blood pressure is increased. To address the role of the rostral ventrolateral medulla (RVL), a principal source of sympathetic tone, in inhibition of BVB, we microinjected DL-homocysteic acid (DLH, 6 nmol) into the RVL of chloralose-urethan-anesthetized, sinoaortic-denervated rats to examine the effect on BVB. The BVB was provoked by electrical stimulation of the aortic depressor nerve ipsilateral to the injection sites. DLH microinjection was found to suppress BVB while increasing blood pressure. The inhibition of BVB was observed even during the early phase in which DLH transiently suppressed central inspiratory activity. The inhibition was not affected either by upper spinal cord transection or suprapontine decerebration. Similar results were obtained by microinjection of bicuculline methiodide (160 pmol), a GABA antagonist, into the RVL of carotid sinus nerve-preserved rats due to withdrawal of a tonic GABA-mediated, inhibitory influence including the input from arterial baroreceptors. In conclusion, activation of the RVL inhibits BVB at brain stem level independently of central inspiratory drive.
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Nosaka et al. (2000) studied Baroreflex vagal bradycardia. Microinjection of DL-homocysteic acid (DLH) or bicuculline methiodide into the RVL was evaluated on Suppression of baroreflex vagal bradycardia (BVB). Activation of the rostral ventrolateral medulla by microinjection of DLH or bicuculline methiodide inhibits baroreflex vagal bradycardia at the brain stem level independently of central inspiratory drive.
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