Abstract â–¡ 87

In the present study we postulate that age-related quantitative modifications of medullary cardio-respiratory centers may be associated to the abnormalities in central respiratory control during sleep and cardiac activity in infants dying from SIDS. Morphometric analysis focussed mainly on the evaluation of numerical and dimensional variations in the neuronal population of the dorsal vagal nucleus (An), solitary tract nucleus (STn) and ambiguus nucleus (An), which make up the centers of cardiac regulation, and also the hypoglossal nucleus (XIIn), which the reference point of the parahypoglossal area responsible for central vagal control of the heart and beat.

To test this hypothesis, we analyzed the brainstem tissues from 57 infants including 45 SIDS cases and 12 age-matched infants who died of known causes. The brains were fixed for two-three weeks in 10% phosphate-buffered formalin. Subsequently the brainstem was removed, sectioning perpendicular to the main axis of the medulla, about 10 mm above the obex and the same below, through the portion of the brainstem between the caudal pole of the inferior olive and the caudal border of the pons. After embedding in paraffin, the entire block was sectioned proceeding in a rostro-caudal direction. The serial section of 5 µm were stained with haematoxylin-eosin, Bielschowsky and Klüver-Barrera methods. We observed all serial section of the brainstem and analyzed both side.

A quantitative technique with image analyzed was developed to compared dorsal vagal, solitary tract and ambiguus nuclei studied in these two-matched groups. The following parameters were evaluated: total Neuronal Area, number of neurons (Neuronal Density), Circularity Shape Factor.

The morphometric results revealed an increase in the Neuronal Area and, conversely, a decrease in matched-control group. Linear regression analysis showed a decreased in the Circularity Shape Factor, this gives proof of the neuronal maturation. This last parameter is an index of cell maturity in that shape factors closest to unity correspond to round-shaped cells, which are considered immature, whereas values below unity represent oval, fusiform or multipolar shapes, typical of mature neurons.

The process of neuronal maturation in cases of SIDS and controls has been quantitatively studied by other authors using different techniques from ours, namely Golgi silver staining. We have made morphometrical analyze because few morphometric studies exist on natural aging of certain bulbar nuclei. Our results support the hypothesis that brainstem of SIDS infants presents neuropathological alteration in the medullary cardio-respiratory centers.