Immunohistochemical characterization of pelvic neurons which project to the bladder, colon, or penis in rats

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Abstract
Retrograde‐tracing and immunohistochemical techniques were used in combination to investigate the types of putative transmitters in pelvic neurons that project to the bladder, colon or penis of rats. In addition, populations of axon varicosities associated with these neurons were characterized. Subpopulations of neurons in colchicine‐treated major pelvic ganglia and accessory ganglia of male rats contained immunoreactivity (IR) for tyrosine hydroxylase (TH), vasoactive intestinal peptide (VIP), neuropeptide Y (NPY), or enkephalin (ENK), while types of immunoreactivity found in major groups of varicose axons were ENK, cholecystokinin (CCK), and somatostatin (SOM). Substance P (SP)‐IR varicose axons were much less common. Bladder and colon neurons were similar in a number of ways. Many neurons contained NPY‐IR (≥50%), fewer contained TH‐IR (25–30%), and even fewer contained ENK‐IR (5–15%) or VIP‐IR (5–10%); many neurons were associated with baskets of ENK‐IR varicosities (50–65%) and fewer neurons were surrounded by CCK‐ or SOM‐IR varicosities (30–35%). Colon neurons differed from penis neurons in having a slightly larger proportion that contained ENK‐IR (10–15%, compared with 1–3%). Penis neurons were markedly different from the other two groups in additional ways. More than 90% of them contained VIP‐IR, whereas only 5–7% contained NPY‐IR and none were immunoreactive for TH. Furthermore, although the proportion of penile neurons associated with many ENK‐IR varicosities was similar to the bladder and colon neurons (45–50%), they were rarely seen close to CCK‐ or SOM‐IR varicose axons. These studies describe similarities and differences in the histochemical properties of neurons which project to the bladder, colon, or penis and of the varicose axons associated with those neurons. This gives further insights into the possible transmitter mechanisms involved in the regulation of different pelvic functions.