Location of bladder and urethral sphincter motoneurons in the male guinea pig (Cavia porcellus).

Although the guinea pig is used widely in experimental medical research, including in studies on micturition control, the spinal origin of preganglionic parasympathetic bladder and somatic external urethral sphincter motoneurons is not known. In the male guinea pig using wheat germ agglutinin-conjugated horseradish peroxidase and dextran Alexa Fluor 488/568 tracers, preganglionic parasympathetic bladder motoneurons were observed in the ventrolateral part of the intermediolateral cell group of the first sacral segment. The external urethral sphincter motoneurons were found to be located in the ventral horn of the first sacral segment, in a cell group corresponding with the nucleus of Onuf in cat and human.