Developmental Morphology and Topography of the Components of the Cervical Sympathetic Trunk in Sheep (Ovis aries) During the Fetal Period

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.

Detailed gross anatomy and topography of the sympathetic cardiac nerves and related ganglia in Syrian hamsters (Mesocricetus auratus)

BACKGROUND

The detailed morphology and topography of the sympathetic cardiac nerves (SCNs) and ganglia with their surrounding structures in Syrian hamsters were examined to document the general topography and morphology and variations and to discuss the comparative anatomy between the SCNs and ganglia in Syrian hamsters and other rodents, as well as their comparative morphology and macroscopic evolutionary changes among rodents, rabbits, domestic animals (cats, dogs, sheep, goats, oxen, pigs and horses), primates, and humans.

METHODS

The composition of the cervical and thoracic parts of the sympathetic trunks and ganglia was bilaterally microdissected in twenty-eight sides of 14 adult male and female Syrian hamsters under a stereomicroscope.

RESULTS

The general morphology of the SCNs and related ganglia in Syrian hamsters was obtained and noted as follows: (1) the absence of the vago-sympathetic trunk, (2) the absence of the middle cervical ganglion (MG), (3) constant presence of the cervicothoracic ganglion (CT) comprising generally from the caudal cervical ganglion and 1-2 thoracic ganglia and locating over the lateral surface of the longus colli muscle ventral to the heads of the first two ribs and communicating to the eight cervical and first two thoracic spinal nerves (C8-T2) in addition to the vertebral nerve, (4) extensive coverage of the lateral surface of the CT by branches of the subclavian artery, (5) the cranial and caudal limbs of the ansa subclavia (AS) joining the CT to the caudal end of the cervical sympathetic trunk, (6) the presence of an independent thoracic ganglion from the 2nd or 3rd to the 13th and connecting by single interganglionic branches, and communicating to each thoracic spinal nerve, (7) close relationship between the caudal portion of the thoracic sympathetic trunk and the psoas minor muscle, (8) the primary cardiac nerves (CNs) arising from the CT, and (9) the absence of CNs originating generally from the cervical sympathetic trunk, AS, MG, or independent thoracic ganglia or their interganglionic branches. Individual variations of the SCNs and ganglia in Syrian hamsters were noted, including the absence of the ansa subclavia on 5/28 sides (17.86%), the presence of the intermediate ganglia (IG) placed on the C7 on 3/28 sides (10.71%) or the C8 on 3/28 sides (10.71%), and no CNs arising from the IG as well as the presence of the double thoracic sympathetic trunk on 5/28 sides (17.86%). The anatomical characteristics of the SCNs and related ganglia were also exhibited sex and laterality differences.

CONCLUSIONS

From a comparative anatomy viewpoint, the general morphology of the SCNs and related ganglia in Syrian hamsters was very similar to that in rats but was considerably different from that in guinea pigs, especially concerning the MG, cranial position and composition of the CT. The general morphology of the SCNs and related ganglia in Syrian hamsters and other laboratory rodents resembled that of rabbits but was essentially different from that in rabbits with respect to the cranial position and composition of the CT. The general morphology of the SCNs and ganglia exhibited significant morphological differences and similarities among laboratory rodents, rabbits, domestic animals, primates, and humans. The main differences include the relationship between the cervical parts of the vagus nerve and sympathetic trunk, the presence of the MG, the position and composition of the CT, the origins and frequencies of the cardiac nerves, and the primary sympathetic contributor. From macroscopic evolutionary change, the expansion of the range of the SCNs origin has occurred from laboratory rodents, rabbits, domestic animals, and primates to humans.