Further studies on the afferent path of the milk-ejection reflex in the brain stem of the rabbit.

When the afferent pathway of the milk-ejection reflex, which we had previously reported, was surgically severed bilaterally in the mid-brain of the lactating rabbit, the reflex release of oxytocin in response to suckling was blocked for up to 11 days; unilateral severance did not block the reflex. The position and discrete nature of the pathway were also further substained by electrical stimulation experiments in acute studies in the anaesthetized rabbit. Some animals, however, did not release oxytocin in response to stimulation of the pathway. Furthermore, whereas stimulation of this reflex pathway in the guinea-pig brain at intervals of a few minutes evokes release of oxytocin after each stimulation, in the present study the release of oxytocin in the rabbit in response to repeated electrical stimulation was either progressively attenuated or did not occur at all after the initial release. There appears, therefore, to be a powerful overriding central inhibitory mechanism in the rabbit which can prevent release of oxytocin, even when the appropriate stimulus for release is applied.