Final answer:
Blockade of dopamine in the tuberoinfundibular pathway can lead to increased prolactin levels, causing symptoms like amenorrhea and galactorrhea. Dopamine normally acts to inhibit prolactin secretion, and without this inhibition, there's an overproduction of prolactin.
Step-by-step explanation:
The question pertains to the tuberoinfundibular pathway of the dopaminergic system in the brain that regulates the secretion of prolactin (PRL), which is produced by the anterior pituitary. Prolactin stimulates the mammary glands to produce milk after childbirth. Prolactin levels are typically kept in check by prolactin-inhibiting hormone (PIH), which is actually the neurotransmitter dopamine. By blocking dopamine receptors, such as with certain antipsychotic medications, there can be a reduction in PIH activity, leading to increased prolactin levels in the blood.
This elevation in prolactin can lead to symptoms such as amenorrhea, galactorrhea, and enlargement of the breasts due to excess prolactin production. During pregnancy, the situation is different, with prolactin levels rising and, along with other hormones, preparing the breasts for milk secretion. However, during pregnancy, milk synthesis is inhibited by other hormones until after the placenta is expelled. Post-childbirth, prolactin levels spike with each feeding to promote milk production for subsequent feedings.