Final answer:
The true statement about sympathetic preganglionic neuron axons innervating the abdominopelvic viscera is that they release acetylcholine. These myelinated preganglionic fibers are short and synapse on ganglionic neurons within sympathetic ganglia.
Step-by-step explanation:
The question asks which statement is TRUE regarding the sympathetic preganglionic neuron axons that innervate the abdominopelvic viscera. The correct statement is that these axons release acetylcholine (ACh). Sympathetic preganglionic neurons originate from the thoracolumbar spinal cord and project to sympathetic ganglia, where they synapse on ganglionic neurons. The neurotransmitter released by these preganglionic fibers is ACh, and it excites the ganglionic neuron through the nicotinic receptor.
The sympathetic preganglionic fibers are relatively short since the ganglia are close to the spinal cord, and unlike postganglionic sympathetic fibers, they are myelinated. Additionally, postganglionic fibers are generally long as they must reach distant effector organs, and these fibers are typically unmyelinated. In summary, the sympathetic preganglionic neurons do release ACh, are myelinated, and the correct answer to the question is C) They release acetylcholine.