Innervation of the carotid body. An experimental quantitative study

Area of Science:

• Neuroscience
• Anatomy
• Histology

Background:

• The carotid body is a vital sensory organ involved in regulating respiration and cardiovascular function.
• Understanding its innervation is crucial for comprehending its physiological roles.

Purpose of the Study:

• To investigate the source and mechanisms of carotid body reinnervation after nerve injury.
• To elucidate the role of sympathetic fibers in carotid body innervation.

Main Methods:

• Light and electron microscopy were employed to study carotid body innervation in cats.
• Surgical procedures included sinus nerve resection, glossopharyngeal resection, and bilateral cervical sympathectomy.
• 6-hydroxydopamine (6-OH-DA) was used to assess the role of sympathetic fibers.

Main Results:

• Sinus nerve resection led to rapid degeneration and subsequent reinnervation of intralobular fibers and synaptic boutons.
• Reinnervation was delayed by sympathectomy and prevented by 6-OH-DA, indicating sympathetic origin.
• Efferent synaptic contacts between the sinus nerve and principal cells were suggested by increased argentaffin cells and dense-cored vesicles.
• Sympathetic axons were confirmed to form synaptic connections with principal cells.

Conclusions:

• Reinnervation of the carotid body after sinus nerve injury is mediated by collateral regeneration of sympathetic fibers.
• Sympathetic fibers contribute significantly to carotid body innervation, originating from various sources including cervical plexuses and the common carotid artery.
• The vagus nerve plays a minor role in innervating the carotid body parenchymal lobules.