[Neuropathology of Onuf's nucleus]

Onuf's nucleus is a small motoneuron group in S2 anterior horn, which was described by Onufrowicz in 1900. He suggested that the motoneurons in the nucleus innervated striated muscles involved in election and ejaculation. The nucleus is readily shown by the K-B stain on account of its pale staining background which is sharply demarcated from the surrounding network of fine myelinated fibers. However, neuropathological descriptions of the nucleus are very rare. Pons-Tortella et al reported the sparing of this nucleus in acute anterior poliomyelitis. In 1977. We reported that Onuf's nucleus were well preserved in cases with ALS, in which the function of bladder and rectal sphincters is often intact until the latest stage of the illness. On the control , Shy-Drager syndrome showed severe degeneration of Onuf's nucleus. The patients with Shy-Drager syndrome showed clinically evident urinary and/or fecal incontinence. Combination of these clinical and pathological findings led to conclusion that Onuf's nucleus innervates the striated muscles of the sphincters. In 1990, Iwatsubo et al studied corticofugal projections to the motoneurons with Nauta-Gygax's technique in a patient with cerebral infarction. They verified that the oculomotor and abducens nuclei and Onuf's nucleus do not receive direct cortical projections. These motoneurons are characteristically spared in ALS. For the studies on ALS, it is important to know what differences between Onuf's nucleus and other motoneuron groups in anterior horn are biochemically and physiologically.