Pelvic ganglia contain autonomic neurons essential for urogenital and lower bowel function. They are atypical autonomic ganglia in their sexual dimorphism, steroid hormone sensitivity and anatomy, being a mixture of neurons with inputs from thoracolumbar (sympathetic) or sacral (parasympathetic) spinal cord. In humans, these neurons are located bilaterally within a large plexus, the inferior hypogastric plexus (IHP). The development of the human IHP is poorly understood.  

We aimed to elucidate the development of the IHP in both male and female human embryos, specifically to construct the first 3D atlas of connections between the IHP and pelvic organs from the seventh to twentieth post-conceptional weeks (PCW7-PCW20). This work comprises part of the Human Cell Atlas (HCA) and Human Developmental Cell Atlas (HuDeCa) consortia.  

In 29 samples, we have applied tissue clearing, immunofluorescence and light sheet microscopy to visualise combinations of markers for all neurons (beta-tubulin), transmitter class (tyrosine hydroxylase), transcription factors (e.g., Phox2b) and/or organ morphology (smooth muscle actin). Using a 3D virtual reality tool (syGlass), in 12 samples the entire IHP and its primary neural connections have been segmented. This has revealed distinct patterning of neural aggregates in the IHP, the hypogastric nerves, specific spinal nerves contributing to the pelvic and sacral splanchnic.