Crossing dendrites may be a substrate for synchronized activation of penile motoneurons.

The morphology of perineal and extensor hindlimb motoneurons in adult male rats was examined using retrograde labelling with wheat germ agglutinin and horseradish peroxidase. Bulbocavernosus and levator ani motoneurons, located in the spinal nucleus of the bulbocavernosus, were organized as distinct clusters of motoneurons in the medial ventral area of the lumbar (L6-L5) spinal cord and possessed prominent contralaterally projecting dendritic arborizations. In similar experiments, laterally located soleus and extensor digitorum longus motoneurons did not exhibit a similar organization. These findings are discussed with respect to their possible role in the synchronized bilateral activation of penile muscles.