Central autonomic innervation of the kidney. What can we learn from a transneuronal tracing study in an animal model?

Renal sympathetic innervation is involved in the maintenance of fluid homeostasis, modulation of renal secretion from juxtaglomerular cells, sodium resorption from renal tubular cells and renal hemodynamics. The understanding of central innervation and neuronal connections is important for studying the consequences of renal disease and surgical interventions compromising renal nerves.

A total of 38 individual adult male Sprague-Dawley rats were used for retrograde transneuronal mapping of the spinal cord and brain stem after pseudorabies virus (PRV) injection into the left kidney in 30 and control experiments in 8. After a survival time of 72, 96 or 120 hours the animals were sacrificed. Exploration of the abdominal and pelvic visceral organs was done, and the brain and spinal cord were harvested via dorsal laminectomy. After cutting on a freezing microtome the tissue was immunostained for PRV.

After kidney injection inspection of the abdominal and pelvic cavity revealed an enlarged bladder with hemic urine. The urine was sterile and the bladder wall showed signs of neurogenic inflammation. Other organs were not affected. PRV positive cells were primarily found within the ipsilateral nucleus intermediolateralis of thoracic spinal cord segments T6 to T13. At the supraspinal level PRV positive cells were found within certain regions, namely the nuclei raphes, rostral ventromedial and ventrolateral medulla, A5 noradrenergic cell region, locus coeruleus and nucleus paraventricularis of the hypothalamus.

This investigation demonstrates the anatomical basis for broad central sympathetic innervation of the kidney. The neurogenic inflammation within the spinal cord inherent to the PRV tracing method causes an inflammatory reaction within the bladder. This can be due to increased sympathetic nerve activity, followed by peripheral, neurogenically mediated inflammation.