Identification of the origin of adrenergic and cholinergic nerve fibers within the superior hypogastric plexus of the human fetus.

Nerve fibers contributing to the superior hypogastric plexus (SHP) and the hypogastric nerves (HN) are currently considered to comprise an adrenergic part of the autonomic nervous system located between vertebrae (T1 and L2), with cholinergic aspects originating from the second to fourth sacral spinal segments (S2, S3 and S4). The aim of this study was to identify the origin and the nature of the nerve fibers within the SHP and the HN, especially the cholinergic fibers, using computer-assisted anatomic dissection (CAAD). Serial histological sections were performed at the level of the lumbar spine and pelvis in five human fetuses between 14 and 30 weeks of gestation. Sections were treated with histological staining [hematoxylin-eosin (HE) and Masson's trichrome (TriM)] and with immunohistochemical methods to detect nerve fibers (anti-S100), adrenergic fibers (anti-TH), cholinergic fibers (anti-VAChT) and nitrergic fibers (anti-nNOS). The sections were then digitalized using a high-resolution scanner and the 3D images were reconstructed using winsurf software. These experiments revealed the coexistence of adrenergic and cholinergic fibers within the SHP and the HNs. One-third of these cholinergic fibers were nitrergic fibers [anti-VACHT (+)/anti-NOS (+)] and potentially pro-erectile, while the others were non-nitrergic [anti-VACHT (+)/anti-NOS (-)]. We found these cholinergic fibers arose from the lumbar nerve roots. This study described the nature of the SHP nerve fibers which gives a better understanding of the urinary and sexual dysfunctions after surgical injuries.