Astrocytes in the hypoglossal nuclei of sudden infant death syndrome (SIDS) infants: a quantitative study.

It has been suggested that brain stem hypoxia or ischaemia underlies the sudden infant death syndrome (SIDS), but previous reports of astrocytosis in the brain stems of SIDS infants have been contradictory. A volumetric quantitative technique was, therefore, developed to compare astrocyte numbers and sizes in the hypoglossal nuclei of SIDS and control infants. In 12 SIDS and eight control infants, serial sagittal sections were taken through the hypoglossal nucleus and every tenth section was stained for glial fibrillary acidic protein. Astrocytes were counted in the central 4% of a grid stepped throughout the hypoglossal nucleus, and the heights of 100 astrocyte nuclei were measured with a microcator. Astrocyte number, corrected for section thickness and nuclear height, was divided by the volume of the hypoglossal nucleus to calculate astrocyte density. Numbers of astrocytes did not differ significantly between SIDS (mean number 44729, SD 12096) and control (mean number 46562, SD 11060) infants. Astrocyte nuclear height did not differ significantly between groups (SIDS: mean height 3.98 microns, SD 0.22; control: mean height 3.84 microns, SD 0.31). Astrocyte density was similar in SIDS (mean density 24378 astrocytes/mm3, SD 6155) and control (mean density 23978 astrocytes/mm3, SD 4031) infants. No quantitative evidence of astrocytosis was found in the hypoglossal nuclei of SIDS infants. This implies that SIDS infants die without previous episodes of hypoxia/ischaemia severe enough to damage the brain stem.