Tissue samples from the brainstem were obtained from autopsies and provided by research partners at the San Diego County Medical Examiner's Office in California.
Compared with controls, the serotonin levels in the lower brainstem were 26 percent lower in the SIDS cases compared to controls, while the tryptophan hydroxylase levels were 22 percent lower.
There's something about sleep that unmasks the defect, which we believe is in serotonin circuits: the baby experiences some kind of stress during sleep, such as rebreathing carbon dioxide in the face-down position or increased temperature from over-bundling, that cannot be compensated for by the defective brainstem circuits, and the baby then goes on to die.
In a normal baby rebreathing carbon dioxide, serotonin pathways in the brainstem would stir the baby awake long enough to turn its head, allowing it to breathe fresh air, Kinney adds.
The infants whose brainstems are intact enough to maintain respiratory drive and regulate blood pressure may succumb over the next few days to endocrine abnormalities.
Animal models and early human fetuses demonstrate that the exposed anterior position of the neural tube initially proliferates, as though attempting to form a forebrain, resulting in disorganized mass of primitive glial, neural, and vascular tissue arising from the upper end of the brainstem.
The brainstem in anencephaly can display a spectrum of involvement anywhere from relatively normal to totally absent, with the congenital defect extending all the way into the spinal canal (craniorachischisis).
Given that the structural anomalies of the brainstem can range from severe to relatively mild, it goes without saying that a corresponding spectrum of neurologic dysfunction can occur.
In the 1840s, Flourens narrowed the field's focus to a specific brainstem region within an area called the medulla.
This tissue contains brainstem nerves that control muscles involved in breathing, such as the tongue and diaphragm muscles.
He painstakingly carved out pieces of the newborn rat brainstem and documented whether the respiratory rhythm persisted.
We look at sites in the brainstem that are critical for the control of things like respiratory function, heart rate, and temperature control," explains David Paterson of Children's Hospital in Boston.