The effect of immunostimulation on thymic innervation in the rat.

In order to test whether the thymic innervation shows morphological plasticity in response to thymic functional changes, the density of thymic innervation was determined in sterile control animals and three groups of antigenically stimulated sterile rats. Thymic function was defined from the numbers of mitotic cells present in the thymic cortex, and these were reduced by antigenic stimulation. The innervation was determined separately for the various compartments of the thymus. Nerves were present in the capsule and the septa, but could not be found in either cortex or medulla of the thymic parenchyma. A statistically significant increase in the density of innervation after antigenic stimulation was found for the vessel and the non-vessel innervation of the septa. No significant changes were found in the innervation of the capsule.