The heart's 'little brain' controlling cardiac function in the rabbit

Area of Science:

• Cardiovascular Physiology
• Neuroscience
• Cardiac Anatomy

Background:

• Neural mechanisms are vital in cardiac pathologies, with a focus on extrinsic autonomic nerves.
• The intrinsic cardiac nervous system, comprising numerous cardiac ganglia, also significantly influences heart function.
• A comprehensive understanding of the rabbit intrinsic cardiac nervous system is lacking.

Purpose of the Study:

• To delineate the anatomy and histochemistry of intrinsic cardiac ganglia in rabbits.
• To investigate the functional impact of activating these intrinsic cardiac ganglia on heart rate and atrioventricular conduction.

Main Methods:

• Utilized an isolated, perfused, innervated rabbit Langendorff heart preparation.
• Employed acetylcholinesterase histology to locate intrinsic cardiac ganglia.
• Applied immunohistochemistry to identify neuronal subtypes (cholinergic, adrenergic, nitric oxide synthase-positive).
• Administered nicotine and electrical stimulation to ganglionic sites to assess functional responses.

Main Results:

• Identified six main regions of intrinsic cardiac ganglia in the rabbit heart.
• Confirmed the presence of cholinergic, adrenergic, and neuronal nitric oxide synthase-positive neurons.
• Activation of atrial ganglia by nicotine induced bradycardia or tachycardia, with the right atrial plexus showing the largest chronotropic effects.
• Electrical stimulation of ganglionic sites primarily resulted in bradycardia and significant atrioventricular conduction prolongation.

Conclusions:

• The intrinsic cardiac nervous system in rabbits possesses distinct anatomical and functional characteristics.
• These intrinsic cardiac plexuses play a significant role in modulating cardiac function, independent of extrinsic nerves.
• The findings provide a foundation for further research into cardiac neural mechanisms and associated diseases.