Ultrastructural immunolocalization of vasopressin and neurophysin in neurosecretory cells of dehydrated rats.

It has been proposed that neurosecretory material may be transported in a non-vesicular compartment in magnocellular neurons in the hypothalamus of osmotically stimulated rats. We have reexamined this issue using postembedding electron microscopic immunoperoxidase labeling of the secreted peptides (vasopressin and neurophysin) found in these neurons. Reaction product was found exclusively over neurosecretory vesicles in cell bodies, and in axons in the median eminence and neurohypophysis. The findings are consistent with an exclusive secretory vesicle location of the neuropeptides in the hypothalamo-neurohypophysial system of both normal and dehydrated rats.