Involvement of Onuf's nucleus in amyotrophic lateral sclerosis

The Onufrowicz (Onuf's) nuclei from eight amyotrophic lateral sclerosis (ALS) cases and nine neurological control cases were studied histologically and morphometrically. To clarify the factors relating to the involvement of the Onuf's nucleus in ALS, we correlated the relationships among the age at death, clinical duration, morphometric findings for Onuf's neurons, and neuronal numbers in the posteroposterolateral (PPL) nuclei in the ALS cases with those in neurological controls. Intracytoplasmic inclusions such as Bunina bodies, ubiquitin-reactive inclusions, and conglomerate inclusion were found in the Onuf's neurons in ALS, but not in the controls. The total number of Onuf's neurons in the ALS cases was not decreased, but that of normal-appearing neurons was decreased while that of atrophic neurons was increased. Significantly decreased perikaryal, nuclear and nucleolar areas and decreased perikaryal (P)/nuclear and P/nucleolar area ratios of Onuf's neurons were found in ALS, not only in the atrophic neurons but also in the normal-appearing neurons, compared with the controls. The shrinkage in Onuf's neurons of ALS was different from that seen in the ageing process or in the axonal reactions of controls with atonic bladder. In ALS, the morphometric findings for the Onuf's neurons showed no correlation with age at death, clinical duration, or number of PPL neurons. Our results indicate that in ALS Onuf's nucleus is principally vulnerable to the ALS process, although the degree of degeneration differs from that seen in other motor neurons. The involvement of Onuf's nucleus might be slowed due to factors specific to this nucleus, including the biochemical and autonomic properties of the nucleus; nevertheless, it is histologically classified as part of the somatic cell column.