Final answer:
Oxytocin release during breastfeeding is stimulated by the suckling of an infant and terminated when the let-down reflex is complete.
Step-by-step explanation:
Oxytocin release is stimulated by the suckling of an infant, which triggers the synthesis of oxytocin in the hypothalamus and its release into circulation at the posterior pituitary. The stimulus for oxytocin release is a sensory input, specifically the sensation of suckling on the breast.