Morphotopographic characteristics of the extrinsic innervation of the heart in guinea pigs (Cavia porcellus).

BACKGROUND

No reports have been made on the entire extrinsic innervation of the heart in small laboratory animals. Therefore, this study examined the detailed morphotopographic features of the extrinsic cardiac autonomic nervous system (ECANS) with its adjacent structures (1) to record the general morpho-topography and variations of the ECANS in guinea pigs, (2) to compare it with previous reports on common laboratory rodents (rats, mice, and Syrian hamsters), rabbits, domesticated animals (cats, dogs, sheep, goats, oxen, pigs, and horses), primates, and humans, and (3) to infer the macroscopic evolutionary changes they presented.

METHODS

The sympathetic ganglia, vagi, and emitting cardiac nerves/branches in the cervical and thoracic regions were dissected in 24 sides of 12 formalin-fixed, arterially injected adult male and female guinea pigs under a stereomicroscope.

RESULTS

The ECANS in guinea pigs presented following general morphologic characteristics: (1) constant existence of the cranial cervical ganglion (CG) and placing caudal to the cranial base over the ventrolateral aspect of the longus capitis muscle, dorsomedial to the common carotid artery and communicating to the first two cervical spinal nerves, (2) the lack of the vago-sympathetic trunk, (3) the existence of the middle cervical ganglion (MG) and lying on the lateral aspect of the longus colli muscle (LC) at the level of the seventh cervical vertebra, (4) constant existence of the cervicothoracic ganglion (CT) composing generally from the caudal cervical ganglion and 1-3 thoracic ganglia and placing ventral to the first and second intercostal spaces over the lateral aspect of the LC and communicating to the eight cervical and first three thoracic spinal nerves in addition to the vertebral nerve, (5) constant existence of the limbs of the ansa subclavia (AS) joining the CT to MG, (6) the existence of individual thoracic ganglia from the 4th to the 12th and joining by single interganglionic branches (IGBs), and communicating to corresponding thoracic nerve, (7) the intimate relation between the caudal part of the thoracic sympathetic chain and the quadratus lumborum muscle, (8) the main cardiac nerves (CNs) emerging from the CT, (9) the lack of CNs springing generally from the CG, ST, AS, MG, or individual thoracic ganglia or their IGBs, and (10) the existence of the cardiac branches (CBs) emerging from the vagi and recurrent laryngeal nerves. The ECANS morphology in guinea pigs also shows sex and laterality differences.

CONCLUSIONS

The general anatomical arrangement of the sympathetic components of the ECANS in guinea pigs extremely displaced features common to rats and Syrian hamsters regardless of the existence of MG and the close relation between the thoracic sympathetic chain and the quadratus lumborum muscle. However, the position and organization of the CT, along with its rami communicantes to spinal nerves in guinea pigs quite resembled those seen in rats. The general macroscopic arrangement of the sympathetic components of the ECANS in guinea pigs resembled that seen in rabbits regardless of the organization and location of the CT. The general morphology of the sympathetic components of the ECANS demonstrated markedly morphological variations and similarities among common laboratory rodents, rabbits, domesticated animals (DNs), primates, and humans. The main variations consisted of the position of the CG and its rami communicantes with the spinal nerves, the relation between the vagi and sympathetic trunks in the neck, the existence of the MG, the location and arrangement of the CT, the origins and incidences of the cardiac nerves, and the main sympathetic contributors. The general macroscopic architecture of the parasympathetic components of the ECANS in guinea pigs quite resembled that seen in domesticated animals, primates, and humans. Evolutionary comparative morphologic characteristics of the ECANS are discussed in detail and evolutionary differences and similarities of the ECANS have been found from common laboratory rodents, rabbits, domesticated animals, and primates to humans.

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Déclaration de conflit d'intérêts

Conflicts of interest The authors declare no conflicts of interest.