Electron microscopy and morphometry of nucleoli in rat neurosecretory cells with stimulated and suppressed secretion

The nucleoli in the neurons of the supraoptic nucleus in the rat were analyzed by electron microscopy and morphometry after the secretion of vasopressin had been fully suppressed by water load, after the secretion had been stimulated by water deprivation and in normal rats which had water ad libitum. Suppression of the secretion increased the proportion of fibrillar centres in the nucleoli 2-fold. Stimulation of the secretion increased the proportion of the granular component by 22%. The overall nucleolar organization did not change very much with the secretory activity. The results show that an increased proportion of fibrillar centres in nucleoli is an indicator of decreased secretory activity and, moreover, that an increased volume of the nucleolar fibrillar and granular components per cell indicates an increased secretory activity.