Does the brain make prolactin?

Area of Science:

• Neuroendocrinology
• Molecular Psychiatry
• Hormone Signaling

Background:

• Prolactin receptor (Prlr) is widely distributed in the brain, particularly the hypothalamus.
• Prolactin exerts known effects on central nervous system function, prompting investigation into its brain synthesis.
• The potential for prolactin to act as a brain neuropeptide has been a long-standing research question.

Purpose of the Study:

• To critically evaluate the existing evidence for the endogenous production of prolactin within the brain.
• To assess whether prolactin synthesized in the brain has significant physiological relevance.

Main Methods:

• Review of studies using various antibodies to detect prolactin-like immunoreactivity in the brain.
• Analysis of data on prolactin mRNA detection in brain tissue, often using sensitive amplification techniques.
• Consideration of findings from modern molecular techniques like in situ hybridization and single-cell RNA sequencing.

Main Results:

• Evidence for brain prolactin production is inconsistent and variable, unlike the well-established Prlr distribution.
• Prolactin mRNA is detected at very low levels in the brain compared to the pituitary gland.
• Highly sensitive detection methods carry a risk of false-positive results; advanced techniques have not confirmed brain prolactin synthesis.

Conclusions:

• Based on current evidence, endogenous production of prolactin in the brain is considered unlikely.
• Even if prolactin is produced in the brain under specific conditions (e.g., neuroprotection), its physiological impact is likely minimal.
• The observed effects of prolactin in the brain are best explained by prolactin from the pituitary gland accessing brain tissue.