We studied nerve endings in the parafollicular cells of thyroid glands in necropsy examinations of 50 young males with no know thyroid disorder. The Jabonero and Maillet techniques. ultrastructural and morphology study were performed together with a statistical analysis of nerve endings. Optic microscope visualized preterminal and exceptionally terminal nerve endings located near parafollicular cells. Swellings of the axons without Schwann's cell sheath were identified close to the par follicular cells with electronic microscopy, these swellings had an ellipsoidal or spherical shape and laid close to the cellular membrane (30 nm). Three types of synaptic-like vesicles were found in these nerve endings. a) Abundant clear vesicles, generally spherical in shape (average diameter 50.40 +/- 5.91 nm); b) A few large granural vesicles with an electron-dense core (average diameter 105.49 +/- 9.98 nm); and c) Several small granular vesicles with an electron-dens core (average diameter 55.09 +/- 6.56 nm). Emphasis should be given to the finding of nerve endings (cholinergic-like, adrenergic-like and peptidergic-like nerve endings) in the parafollicular cells. We discuss their possible function.
