Neural control of prolactin secretion in cervically stimulated ovariectomized rats

Prolactin is a protein hormone predominately secreted by lactotrophs in the anterior pituitary gland.  In rodents, the mating stimulus or stimulation of the uterine cervix induces a unique pattern of prolactin secretion characterized by two daily increases which recur for 10-12 days: a nocturnal surge peaking at 0300 h and a diurnal surge peaking at 1700 h. The prolactin rhythm, however, can be initiated by cervical stimulation of ovariectomized rats, indicating that ovarian steroids are not required for its occurrence.  There is evidence that the stimulus is stored as a “memory” in the brain, which allows the prolactin surges to occur for several days without reinforcement of the stimulus, but the exact location and neural pathways involved are currently unknown.

The major control of prolactin secretion is inhibitory by hypothalamic dopamine.  Mathematical modeling and experimental results suggest that the bidirectional feedback between lactotrophs and hypothalamic dopaminergic neurons is responsible for the maintenance of the prolactin rhythmic secretion, but there might be a trigger responsible for the initiation of the hormonal oscillations.  There is abundant evidence that, in addition to inhibition, the hypothalamus also provides stimulatory input to the lactotrophs.  Among several identified factors which have the capability to stimulate prolactin secretion, oxytocin seems to play a pivotal role. Our current research focus on finding a physiological interaction between dopamine, oxytocin and prolactin secretion, and their roles on triggering the prolactin surges in response to cervical stimulation in ovariectomized rats.