MORPHOLOGICAL AND MORPHOMETRIC CHARACTERIZATION OF ONUFS NUCLEUS IN THE SPINAL-CORD IN MAN

In the absence of a systematic morphometric study of Onuf's nucleus in man, this investigation defines the limits of variation of segmental position and the range of length and volume of Onuf's nucleus in 6 nor mal humans displaying no neurological disease (2 males, 4 females). Se rial section reconstruction methods in conjunction with the bisector m ethod provided information on the numbers, Sizes and shapes of the con stituent motor neurons of Onuf's nucleus. In contrast to previous desc riptions, the cranial origin of Onuf's nucleus occurred in rostral S1 in 50 % of subjects, and midcaudal S1 in the remaining subjects. Onuf' s nucleus varied in length between 4 and 1 mm) and was 0.2-0.37 mm(3) in volume. Differences in length or volume between males or females, o r between the left and right side of the cord were not statistically s ignificant. Neurons in Onuf's nucleus varied in diameter between 10 mu m and 60 mu m (mean 26 mu m) and their mean number was 625 +/- 137. A higher density of neurons occurred at the cranial and caudal ends of the nucleus relative to the middle. While 37 % of neurons mere approxi mately spherical (shape index similar to 1), 44 % were ellipsoid and 1 9% fusiform (shape indices varying between 0.26 and 0.8). These findin gs are compared with previous studies of Onuf's nucleus in man and ani mals. The results form a basis for further studies on Onuf's nucleus i n normality and neurodegenerative diseases.