Innervation of the heart: Anatomical study with application to better understanding pathologies of the cardiac autonomics

The Lumbar Sympathetic Trunk and Its Branching Variability: Relevance for Clinical and Interventional Strategies

Precision medicine relies on a thorough understanding of lumbar sympathetic anatomy and its branches to elucidate related pathophysiology and improve treatment of conditions such as low back pain, lumbopelvic pain, and vascular autonomic disorders affecting the lower limbs. This study aims to expand knowledge of fetal lumbar sympathetic anatomy by providing a detailed description and systematic classification of the communicating branches, their specific distribution to each lumbar spinal nerve, and the origin of lumbar splanchnic nerves. The lumbar and retroperitoneal regions of 25 human fetuses (50 sides) were subjected to detailed sub-macroscopic dissections. The lumbar sympathetic trunk generally comprises three ganglia. The L2 and L3 ganglia are consistently present, but accessory ganglia along certain communicating branches are rare. The 466 communicating branches examined (229 on the right, 237 on the left) comprised 144 superficial, 251 deep transverse, and 71 deep discal branches. Deep transverse branches appeared consistently across all levels, whereas superficial branches originated only from the L1, L2, and occasionally L3 ganglia. Discal branches were inconsistent across ganglionic levels. All lumbar spinal nerves received at least one communicating branch, though the distribution varied by branch type. Most lumbar splanchnic nerves originated from a single root, those having two roots or accessory splanchnic nerves being less common. The origins of splanchnic nerves were frequent at L1 and L2, less common at L3, and inconsistent at L4 and L5. There were no differences between the left and right sides regarding ganglia, origin, or distribution of sympathetic branches. In conclusion, the fetal autonomic branching patterns and connections of the lumbar sympathetic trunk are significantly variable, though they are more consistent than those in the cervical region. Detailed anatomical knowledge of this area is essential for improving the precision and effectiveness of lumbar sympathetic trunk interventions and minimizing complications in lumbar and retroperitoneal surgeries.

Cardiac neurons expressing a glucagon-like receptor mediate cardiac arrhythmia induced by high-fat diet in Drosophila

Cardiac arrhythmia leads to increased risks for stroke, heart failure, and cardiac arrest. Arrhythmic pathology is often rooted in the cardiac conduction system, but the mechanism is complex and not fully understood. For example, how metabolic diseases, like obesity and diabetes, increase the risk for cardiac arrhythmia. Glucagon regulates glucose production, mobilizes lipids from the fat body, and affects cardiac rate and rhythm, attributes of a likely key player. Drosophila is an established model to study metabolic diseases and cardiac arrhythmias. Since glucagon signaling is highly conserved, we used high-fat diet (HFD)-fed flies to study its effect on heart function. HFD led to increased heartbeat and an irregular rhythm. The HFD-fed flies showed increased levels of adipokinetic hormone (Akh), the functional equivalent to human glucagon. Both genetic reduction of Akh and eliminating the Akh producing cells (APC) rescued HFD-induced arrhythmia, whereas heart rhythm was normal in Akh receptor mutants (AkhRnull ). Furthermore, we discovered a pair of cardiac neurons that express high levels of Akh receptor. These are located near the posterior heart, make synaptic connections at the heart muscle, and regulate heart rhythm. Altogether, this Akh signaling pathway provides new understanding of the regulatory mechanisms between metabolic disease and cardiac arrhythmia.

Anatomical study with clinical significance of communicating and visceral branching of the cervical and upper thoracic sympathetic trunk

Current advances in the management of the autonomic nervous system in various cardiovascular diseases, and in treatments for pain or sympathetic disturbances in the head, neck, or upper limbs, necessitate a thorough understanding of the anatomy of the cervicothoracic sympathetic trunk. Our objective was to enhance our understanding of the origin and distribution of communicating branches and visceral cervicothoracic sympathetic nerves in human fetuses. This was achieved through a comprehensive topographic systematization of the branching patterns observed in the cervical and upper thoracic ganglia, along with the distribution of communicating branches to each cervical spinal nerve. We conducted detailed sub-macroscopic dissections of the cervical and thoracic regions in 20 human fetuses (40 sides). The superior and cervicothoracic ganglia were identified as the cervical sympathetic ganglia that provided the most communicating branches on both sides. The middle and accessory cervical ganglia contributed the fewest branches, with no significant differences between the right and left sides. The cervicothoracic ganglion supplied sympathetic branches to the greatest number of spinal nerves, spanning from C5 to T2. The distribution of communicating branches to spinal nerves was non-uniform. Notably, C3, C4, and C5 received the fewest branches, and more than half of the specimens showed no sympathetic connections. C1 and C2 received sympathetic connections exclusively from the superior ganglion. Spinal nerves that received more branches often did so from multiple ganglia. The vertebral nerve provided deep communicating branches primarily to C6, with lesser contributions to C7, C5, and C8. The vagus nerve stood out as the cranial nerve with the most direct sympathetic connections. The autonomic branching pattern and connections of the cervicothoracic sympathetic trunk are significantly variable in the fetus. A comprehensive understanding of the anatomy of the cervical and upper thoracic sympathetic trunk and its branches is valuable during autonomic interventions and neuromodulation. This knowledge is particularly relevant for addressing various autonomic cardiac diseases and for treating pain and vascular dysfunction in the head, neck, and upper limbs.

Characterization, number, and spatial organization of nerve fibers in the human cervical vagus nerve and its superior cardiac branch

BACKGROUND

Electrical stimulation of the vagus nerve (VN) is a therapy for epilepsy, obesity, depression, and heart diseases. However, whole nerve stimulation leads to side effects. We examined the neuroanatomy of the mid-cervical segment of the human VN and its superior cardiac branch to gain insight into the side effects of VN stimulation and aid in developing targeted stimulation strategies.

METHODS

Nerve specimens were harvested from eight human body donors, then subjected to immunofluorescence and semiautomated quantification to determine the signature, quantity, and spatial distribution of different axonal categories.

RESULTS

The right and left cervical VN (cVN) contained a total of 25,489 ± 2781 and 23,286 ± 3164 fibers, respectively. Two-thirds of the fibers were unmyelinated and one-third were myelinated. About three-quarters of the fibers in the right and left cVN were sensory (73.9 ± 7.5 % versus 72.4 ± 5.6 %), while 13.2 ± 1.8 % versus 13.3 ± 3.0 % were special visceromotor and parasympathetic, and 13 ± 5.9 % versus 14.3 ± 4.0 % were sympathetic. Special visceromotor and parasympathetic fibers formed clusters. The superior cardiac branches comprised parasympathetic, vagal sensory, and sympathetic fibers with the left cardiac branch containing more sympathetic fibers than the right (62.7 ± 5.4 % versus 19.8 ± 13.3 %), and 50 % of the left branch contained sensory and sympathetic fibers only.

CONCLUSION

The study indicates that selective stimulation of vagal sensory and motor fibers is possible. However, it also highlights the potential risk of activating sympathetic fibers in the superior cardiac branch, especially on the left side.