The three-dimensional structure of neurons in the guinea pig inferior mesenteric and pelvic hypogastric ganglia

The three-dimensional (3-D) morphology of sympathetic inferior mesenteric ganglion (IMG) neurons and sympathetic–parasympathetic pelvic hypogastric ganglion (PHG) neurons was studied using confocal laser scanning microscopy. Cell bodies of IMG neurons were disc-shaped and were arranged orderly in layers. The dendritic arbor of individual neurons was confined to a plane with a thickness that did not exceed the thickness of the parent cell body. The actual dendritic surface area (71,400 μm2) and volume (81,500 μm3) of the IMG neurons were up to 100-fold larger than previously reported for similar sympathetic neurons using data of 2-D measurements and estimations of the third dimension. PHG neurons had a much smaller dendritic surface area (4100 μm2) and volume (2400 μm3) compared to IMG neurons. The ratio dendritic/somal surface area for individual IMG and PHG neurons ranged from 5:1 to 14:1 and from 0.1:1 to 6:1, respectively. The total dendritic path-length was 8–42 times greater for IMG than for PHG neurons. Neurons in the IMG were either stellate with radiating dendrites or bipolar-shaped with dendrites emerging from the two poles of the cell body. Neurons in the PHG were of two morphological types. One type (nearly 2/3 of all the imaged PHG neurons) had two to seven relatively long dendrites and an axon; the other type had only one to three short unbranched dendrites and an axon. The spatial organization of neurons within the ganglia and the structural features of individual neurons are likely to have important implications regarding connectivity patterns between neurons within the ganglion as well as on how information is processed by the ganglion.