Quantification of adrenergic nerve fibers in human thymus at various ages

Adrenergic nerve fibers were studied in human thymus at various ages by biochemical and morphological methods and by quantitative analysis of images. The whole thymus was harvested during autopsies in prenatal of six months (n=6), newborn (n=6), infant (n=3), young (n=3), adult (n=3) and elderly (n=3) men. The thymuses were weighed, dissected and studied. Thymic slices were subjected to specific staining for the detection of microanatomical details regarding thymic microenvironment and nerve fibers. Histofluorescence microscopy was used for staining of adrenergic nerve fibers, while immunofluorescence microscopy was employed for staining of neuropeptide Y-like immunoreactivity. Biochemical dosage of proteins and of noradrenaline amount was performed. All morphological results were subjected to the quantitative analysis of images. Our results confirmed that many changes occur with age in the whole weight of the thymus and in thymic protein content and, as a new finding, demonstrated the specific pattern of three independent markers able to characterize sympathetic nerve fibers of the human thymus and its modifications with age: neuropeptide Y-related staining decreases with age, whereas the density of adrenergic nerve fibers remains unchanged. The apparent discrepancy among these three independent markers for sympathetic nerves was discussed. (author abst.)