Publisher Summary This chapter addresses problem of how neurones secrete peptides by discussing the hypothalamo-neurohypophyseal system secreting the octapeptide hormones oxytocin and vasopressin (ADH). The secretory elements of this system are the archetypical “peptidergic” nerves, and more is known of their function than that of all other such neurones combined. It has long been suspected that these hypothalamo-neurohypophyseal cells possessing neuronal as well as glandular morphological characteristics generate impulses in response to osmotic or reflex synaptic activation and propagate them to their terminals in the neurohypophysis. The chapter also explores the following questions: (1) whether impulses provide the adequate stimulus for release of the posterior pituitary hormones, (2) if so, how these impulses act, and (3) what kind of secretory process is set in motion. The peptide-secreting nerves of the hypothalamo-neurohypophyseal tract possess the essential electrophysiological attributes of neurones: generation and propagation of impulses by means of the familiar regenerative sodium mechanism sensitive to tetrodotoxin (TTX). In neurohypophyseal terminals, granule membrane retrieved in this way is probably destroyed by lysosomes but a comparable mechanism in conventional neurones could permit recycling of synaptic vesicles.