Alpha2Receptor Binding in the Medulla Oblongata in the Sudden Infant Death Syndrome

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Abstract
The sudden infant death syndrome (SIDS) is the leading cause of postnatal infant mortality in the United States. Its etiology remains unknown. We propose that SIDS, or a subset of SIDS, is due to a failure of autoresuscitation, a protective brainstem response to asphyxia or hypoxia, in a vulnerable infant during a critical developmental period. Gasping is an important component of autoresuscitation that is thought to be mediated by the “gasping center” in the lateral tegmentum of the medulla, a region homologous in its cytoarchitecture and chemical anatomy to the intermediate reticular zone (IRZ) in the human. Since we found that [3H]para-aminoclonidine ([3H]PAC) binding to alpha2-adrenergic receptors localizes to this region in human infants and, thereby provides a neurochemical marker for it, we tested the hypothesis that [3H]PAC binding to alpha2-adrenergic receptors is decreased in the IRZ in SIDS victims. Using quantitative tissue autoradiography with [3H]PAC as the radioligand and phentolamine as the displacer, we analyzed alpha2-receptor binding density in the IRZ, as well as in 7 additional sites for comparison, in 10 SIDS and 10 control medullae. There were no significant differences in alpha2 receptor binding in the IRZ, vagal nuclei, or other medullary sites examined between SIDS and control cases. These results suggest that the putative gasping defect in the IRZ in SIDS victims is not related to [3H]PAC binding to alpha2-adrenergic receptors.