On the innervation of mammalian endocrine glands (anterior pituitary and parathyroids)

Summary Electron microscopic studies have been carried out on the innervation of the mammalian anterior pituitary and parathyroids. The total area of grid squares (2.25·10^–2mm²) examined was 2000 per gland and species. In the pituitary pars distalis and in the parenchyma of the parathyroid gland we did not observe a single axon profile. According to the equation proposed by Hennig (1963) we have calculated that there might be—if any—0.133 mm of nerves per 1 mm³ tissue in those two endocrine glands (level of significance 0.95). Comparing these results to the degree of innervation in brown adipose tissue containing more than 160 mm nerve per 1 mm³ tissue we can not imagine that such a small degree of innervation is of any biological importance.In the pituitary pars tuberalis two types of axon terminals have been found both inside and outside the basement membrane surrounding the epithelial complexes. One type contains synaptic and two populations of smaller dense-cored vesicles, the other one contains a population of larger granules which have some properties of the classical elementary granules. Further investigations have to clarify the functional significance of those nerve endings.This investigation was supported by the Deutsche Forschungsgemeinschaft.