PMC

Approach of mobilizing endogenous oxytocin. Oxytocin secretion from the posterior pituitary gland (P.Pit) can be evoked by a variety of stimuli that activate oxytocin neurons in the hypothalamus and involve several pathways such as the sex-/labor-associated Ferguson reflex, the breastfeeding-associated let-down reflex (also called the milk-ejection reflex), the vago-pituitary reflex, as well as a conditioned reflex (acquired as the result of experience) and many other stimuli. The mechanisms underlying pathways from the stimulus to oxytocin secretion largely remain to be identified (the figure is an original drawing).

OT functions at different reproductive stages of women. (A–D) Panels show levels and functions of OT and associated reproductive hormones during Menstruation (A), Pregnancy and parturition (B), Lactation (C) and Peri-menopausal stage (D), respectively. E2, estradiol; FSH, follicle-stimulating hormone; GnRH, gonadotropin-releasing hormone; HCG, Human Chorionic Gonadotropin; LH, Luteinizing hormone; MER, the milk-ejection reflex; P4, progesterone.

Lack of effect of AVP on OT neurons.A, AVP did not affect the basal activity or the bursting pattern of an OT neuron recorded during the milk ejection reflex, whether the reflex was facilitated by an intracerebroventricular injection of 1 ng of OT. The number beside each burst indicates the total number of spikes in that burst. B, AVP applied on a putative OT neuron did not modify the tonic activation induced by a systemic hyperosmotic stimulus (2 ml of 9% NaCl, i.p.).

Hormone levels during and after human pregnancy. Estrogen, progesterone and prolactin steadily increase throughout pregnancy. Childbirth is characterized by a rapid drop in estrogen and progesterone and a surge in oxytocin levels that initiates uterine contractions. During breastfeeding in the postpartum period, pulses of prolactin levels stimulate milk production between feedings, alternating with oxytocin pulses, which lead to milk ejection during breastfeeding in response to the infant’s suckling (let-down reflex).