Behaviorally conditioned changes in atrio-ventricular transmission in awake dog.

Area of Science:

• Cardiovascular Physiology
• Autonomic Nervous System
• Behavioral Conditioning

Background:

• Autonomic nervous system activity significantly influences cardiac electrophysiology, including atrio-ventricular (AV) nodal function.
• Behavioral conditioning offers a method to study the impact of neural changes on cardiovascular control.
• Understanding how conditioned autonomic responses affect AV transmission is crucial for comprehending cardiac regulation.

Purpose of the Study:

• To investigate the effects of behaviorally conditioned autonomic activity on AV transmission fidelity in conscious dogs.
• To determine if classical conditioning can alter cardiac nerve activation and subsequently influence AV nodal conduction.

Main Methods:

• A classical appetitive conditioning paradigm was employed using auditory stimuli (CS+, CS-) and food reward (UCS) in seven awake dogs.
• Hemodynamic parameters, including heart rate and left ventricular pressure, were monitored during conditioning.
• AV nodal function was assessed by measuring the difference between atrial pacing rate and ventricular response rate (mean difference score) during control, conditioned stimulus (CS+), and unconditioned stimulus (UCS) periods.

Main Results:

• Conditioning (CS+) induced moderate tachycardia and increased ventricular contractility, significantly reducing the AV nodal mean difference score.
• The unconditioned response (food reward) resulted in a greater increase in heart rate and ventricular contractility, further improving AV transmission.
• Beta-adrenergic blockade (propranolol) abolished the conditioned improvement in AV transmission during CS+ but not during food delivery.

Conclusions:

• Behavioral conditioning can modulate autonomic activity to enhance atrio-ventricular transmission fidelity.
• The conditioned effects on AV transmission are mediated, at least in part, by beta-adrenergic pathways.
• These findings highlight the brain's capacity to influence cardiac conduction through learned autonomic responses.