Neuronal and cardiovascular responses to ANF microinjected into nucleus ambiguous

Area of Science:

• Neuroscience
• Cardiovascular Physiology
• Pharmacology

Background:

• The nucleus ambiguous (NA) plays a critical role in regulating heart rate through vagal cardioinhibitory neurons (VCN).
• Atrial natriuretic factor (ANF) is a hormone with known cardiovascular effects, but its specific role in neuronal regulation of heart rate is less understood.

Purpose of the Study:

• To investigate the effects of atrial natriuretic factor (ANF) on cardioinhibitory sites within the nucleus ambiguous (NA) and on single vagal cardioinhibitory neurons (VCN).
• To determine if ANF acts as a neuromediator in the excitation of these neurons.

Main Methods:

• Microinjection and microiontophoresis of L-glutamate to identify cardioinhibitory sites in anesthetized rats.
• Microinjection of ANF into identified sites and onto single VCN.
• Measurement of heart rate (HR) and neuronal activity.
• Pharmacological interventions including vagotomy, atropine, and propranolol.

Main Results:

• ANF microinjections into 87.5% of identified cardioinhibitory sites in the NA decreased heart rate.
• ANF microinjections excited 90% of single VCN, followed by a decrease in HR.
• Cardiac slowing was abolished by vagotomy or atropine, but neuronal activation by ANF was unaffected.
• Propranolol did not alter ANF's effects on neurons or heart rate.

Conclusions:

• Atrial natriuretic factor (ANF) is a neuromediator that excites cardioinhibitory neurons in the nucleus ambiguous (NA).
• This neuronal excitation by ANF leads to a reduction in heart rate via the vagal pathway.
• ANF's action on VCN is independent of beta-adrenergic pathways.