Supraspinal control of motoneurons innervating the striated muscles of the pelvic floor including urethral and anal sphincters in the cat.

The nucleus of Onuf (ON) in mammals contains motoneurons innervating the pelvic floor muscles including the external urethral and anal sphincters. Recently, direct pathways from the dorsolateral pons to the ON, probably involved in supraspinal micturition control, have been reported (Holstege et al., 1986). Since the pelvic floor muscles are involved not only in micturition but also in various other functions (e.g., coughing, vomiting, defaecation, parturition), an attempt has been made to establish whether, in the cat, there exist other direct brainstem pathways to the ON motoneurons. Our results indicate that specific projections to the ON are derived from 3 different areas: (1) the ipsilateral paraventricular hypothalamic nucleus; (2) the ipsilateral caudal pontine lateral reticular formation; and (3) the contralateral caudal nucleus retroambiguus. More diffuse projections (to all motoneuronal cell groups in the spinal cord including the ON) are derived from (1) neurons in the area of the nucleus subcoeruleus in the dorsolateral pontine reticular formation, (2) the nucleus raphe pallidus, and (3) the ventral part of the medullary medial reticular formation. Possible functional implications of these pathways are discussed.