Relationships between monoaminergic and cholinergic innervation of the rat thymus during aging.

The present study has been undertaken in order to investigate whether aging is accompanied by alterations in the thymic autonomic innervation. The results showed that in aged rats compared to young adult rats the density of monoaminergic histofluorescent nerve profiles decreased remarkably, while their pattern of intrathymic distribution remained unchanged. The thymic concentrations of noradrenaline (NA) and dopamine (DA) also significantly decreased between the age of 12 and 18 months. However, the density of thymic autofluorescent cells (afc) markedly increased over the same period, as well as the concentration of 5-hydroxytryptamine (5-HT). The aged rat thymus seemed to be able to maintain its cholinergic innervation in terms of density and pattern of distribution, while the density of cells with intracytoplasmic acetylcholinesterase (AChE) staining even increased. The neurochemical measurement showed an increase in the activity of AChE between the age of 9 to 18 months. The results indicate an altered relation between the components of thymic autonomic innervation of aged rats that might be related to the reduced immunocompetence of their T cells.