Morphometric analysis of nerve endings isolated from bovine and rat neurohypophysis

A simple two-step centrifugation procedure has been used to obtain a preparation of isolated nerve endings (neurosecretosomes) from homogenates of bovine and rat neural lobe. It is likely that during homogenisation and centrifugation the large axonal swellings observed in fixed neural lobes are preferentially disrupted, which explains the smaller mean diameter of these structures in the neurosecretosomal fraction. Although the rat neurosecretosomal fraction provided a better yield of axon-related structures (nerve endings and swellings), the morphological appearance of both swellings and nerve endings, respectively, was very similar in rat and bovine neurosecretosomal fractions. An important increase of the relative volume occupied by the axon-related structures, associated with decrease of contamination, can be achieved by density-gradient centrifugation; this procedure also separates two populations of endings which differ significantly in terms of their sizes. Extended incubation of neurosecretosomal fraction induces morphological damage, which affects mainly the population of nerve endings.