Sudden infant death syndrome: postnatal changes in the numerical density and total number of neurons in the hypoglossal nucleus.

Tissue specimens from the medulla were sampled from 28 sudden infant death syndrome (SIDS) victims and from 15 control cases without neurological disease (36-95 postconceptional weeks). Morphometric analyses were performed on serial Nissl sections through the hypoglossal nucleus. The total volume of the hypoglossal nucleus, the numerical density (Nv, cells per mm3) and the total number of motor neurons, interneurons and glia were determined. Normal development was characterized by a linear increase in the volume of the hypoglossal nucleus during the first postnatal year. While the Nv of neurons decreased, the total number of neurons remained relatively constant at approximately 7,600 motor neurons and 3,100 interneurons. In SIDS cases the rate of increase in the volume of the hypoglossal nucleus was significantly greater than in controls (79%). The Nv of neurons was less than in controls (25-30%), although the total number of motor neurons and interneurons did not differ significantly. In SIDS cases the mean profile area of motor neuron cell bodies was significantly greater than in controls (29%), while the mean profile areas of interneurons and glia did not differ. These abnormalities in growth indicate a greater volume of neuropil in a hypoglossal nucleus containing a normal complement of neurons. The disproportionately rapid increase in volume of neuropil in the hypoglossal nucleus of SIDS cases may result from an increased arborization of dendrites on the motor neurons.