The Cholinergic and Adrenergic Innervation of the Rat Thymus

Abstract

The first major studies on the innervation of the thymus were made by Hammar in 1935 (1) using silver stained preparations. He describes the innervation in man as reaching the gland from the vagus before the gland descends to the thorax (middle of the second month). Nerves enter medially, laterally and dorsally accompanying the blood vessels and ramify in the medulla to form a network of fibres which appears complete 16-18 weeks in utero. He and other authors (2) describe the presence of sympathetic fibres, acquired after the gland has descended into the superior and anterior mediastinum, that meet the vagal supply at the cortico-medullary junction. These are probably derived from the cervicothoracic (stellate) ganglion or ansa cervicalis and ansa subclavia with contributions from the phrenic nerves. Sergeeva (3) and Feiten et al. (4) have described adrenergic fibres in the cortex, accompanying blood vessels, and running to Hassall’s corpuscles (3).