Neuronal cell death in the Sudden Infant Death Syndrome brainstem and associations with risk factors
1Department of Medicine, Room 206, Blackburn Building, D06, The University of Sydney, NSW 2006 and 2The Children's Hospital, Westmead, Sydney, NSW 2145, Australia
Correspondence to: Dr. Karen A. Waters, Department of Medicine, Room 206, Blackburn Building, DO6, University of Sydney, NSW 2006, Australia E-mail: kaw{at}med.usyd.edu.au
Immunoreactive expression of three cell death markers was quantitatively analysed in the human infant brainstem medulla. We assessed active caspase-3, TUNEL and single-stranded DNA (ssDNA) in a cohort of 92 infants, and analysed for: (i) variations in the immunoreactive expression with development; (ii) comparison of infants diagnosed with the Sudden Infant Death Syndrome (SIDS, n = 67) to infants who died suddenly with another diagnosis (non-SIDS, n = 25); and (iii) correlations with known clinical risk factors for SIDS. Five nuclei from the brainstem medulla (caudal and rostral levels) were studied, including the hypoglossal (XII), dorsal motor nucleus of the vagus (DMNV), the dorsal column nuclei (gracile and cuneate) and the arcuate nucleus. Our main hypothesis was that neuronal cell death would be increased in SIDS compared to non-SIDS infants, and the increase would correlate with risk factors such as prone sleeping and cigarette smoke exposure. Comparing SIDS to non-SIDS, there was an increase in caspase-3 in the rostral DMNV (P = 0.01), and a trend to increased TUNEL in the arcuate nucleus (P = 0.1), which was statistically significant when comparing the male SIDS to male non-SIDS cohort (P = 0.04). No major changes for ssDNA immunoreactivity were found. Moreover, TUNEL expression was affected by post-conceptional age, by sleep-related risk factors (predominantly affecting the dorsal column nuclei), and by cigarette smoke exposure in the rostral DMNV and arcuate nucleus. Active caspase-3 was affected by post-conceptional age but only in the XII, while gender-related differences were seen in the arcuate nucleus. This study provides further evidence of increased apoptosis in the brainstem of SIDS infants, but shows for the first time that these changes are also affected by age and gender, and by clinical risk factors such as the sleep position and cigarette smoke exposure.
Key Words: active caspase-3; apoptosis; cigarette smoking; developmental neuropathology; infant medulla
Abbreviations: AN, arcuate nucleus; DCN, dorsal column nuclei; DMNV, dorsal motor nucleus of the vagus; PCA, post-conceptional age; SIDS, Sudden Infant Death Syndrome; ssDNA, single-stranded DNA; TUNEL, terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling; URTI, upper respiratory tract infection; XII, hypoglossal nucleus.
Received June 26, 2007. Revised October 29, 2007. Accepted October 29, 2007.