The posterior pituitary: from Geoffrey Harris to our present understanding

Geoffrey Harris pioneered our understanding of the posterior pituitary, mainly by experiments involving electrical stimulation of the supraoptico-hypophysial tract. Here we explain how his observations included key clues to the pulsatile nature of the oxytocin signal, clues which were followed up by subsequent workers including his students and their students. These studies ultimately led to our present understanding of the milk-ejection reflex and of the role of oxytocin in parturition. Key discoveries of wide significance followed: the recognition of the importance of pulsatile hormone secretion, the recognition of the importance of stimulus-secretion coupling mechanisms in interpreting patterned electrical activity of neurons, the physiological importance of peptide release in the brain, the recognition that peptide release comes substantially from dendrites and can be regulated independently of nerve terminal secretion, and the importance of dynamic morphological changes to neuronal function in the hypothalamus, all followed from the drive to understand the milk-ejection reflex. We also reflect on Harris' observations on vasopressin secretion, on the effects of stress, and on oxytocin secretion during sexual activity.