The pars tuberalis subdivision of the pituitary gland is an enigma. It has the highest expression of melatonin binding sites in the mammal and current hypotheses suggest that this area plays a central role in transducing the photoperiodic melatonin signal to seasonal hormone release. We have recently discovered that the pars tuberalis contains a significant population of tachykinin-immunoreactive cells. We and others have found that tachykinins can affect prolactin secretion. Using the hypophyseal portal approach, we are investining in vivo tachykinin release and how these peptides may regulate prolactin secretion.
Although GnRH is a critical component of the hypothalamo-pituitary-reproductive axis, we and others have determined that GnRH receptors are expressed in multiple loci in the brain that are outside this axis as well as in sites outside the brain. Recent evidence from our laboratory indicates that the heart is a novel self-contained GnRH producing and responsive target.