ULTRASTRUCTURAL QUANTITATIVE-ANALYSIS OF THE INNERVATION OF AXILLARY LYMPH-NODES IN JUVENILE AND OLD RATS

Background: Earlier studies have shown that the innervation of axillar y lymph nodes is increased in old animals, compared to juvenile rats, The question thus arose, whether changes are also observable at an ult rastructural level for varicosities which form the actual transmission units, Methods: Ensheathed (axons) and unensheathed axonal profiles ( open areas), were quantified with their spatial relationships to cells at the ultrastructural level in the axillary lymph nodes of juvenile (< 6 weeks) and old (> 2 years) Wistar rats. Results: In both groups o f animals the majority of open areas, irrespective of their content of vesicles, lie at distances of more than 1,000 nm from cells in the pl ane of the section, Almost all open areas, located within 1,000 nm of a cell, are related to reticular cells, a small minority to plasma cel ls, and even fewer to lymphocytes. In the old animals there is a highl y significant increase in the total number of sections of open areas w ith and without vesicles per unit area of medulla, The number of open areas related to cells does not change significantly in the old animal s, as also the percentage of profiles containing vesicles. Only the pe rcentages of open areas with and without vesicles related to plasma ce lls increase significantly in the old animals, This change is parallel ed by a highly significant increase in the percentage volume of plasma cells in the old animals, On average, the profiles related to cells a re closer to the cells in the older animals, Conclusions: The observed changes indicate that the innervation of lymph nodes of the rat is ab solutely increased in the old animals, but that the relations between the various categories of profiles and their relations to cells tend t o remain constant. (C) 1995 Wiley-Liss, Inc.