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A single subcutaneous injection of monosodium-L-glutamate induces severe ultrastructural alterations in certain AChE positive parenchymal cells of the Area postrema of the adult rat. Signs of cellular degeneration include massive intracellular edema, swelling of mitochondria, vacuolization of the cisternae of the rough endoplasmic reticulum and marked alterations in the chromatin pattern of the nucleus. Identification of these cells as neurons is based on the presence of axosomatic synapses.

The calcium accumulating capacity of neurohypophysial axon terminals stimulated by the intravenous injection of hypertonic saline has been studied by using light and electron microscopic histochemical methods and X-ray microanalysis. In the stimulated neurosecretory terminals Ca++ containing granules appeared in the mitochondria. Smaller granules of similar morphological appearance occurred in the smooth endoplasmic reticulum as well. It is suggested that the mitochondria and the smooth endoplasmic reticulum are intimately involved in the regulation of the intraaxonal free calcium level during the process of vasopressin secretion.