The long term goal of this research program is to define the mechanism(s) by which progesterone (P) increases prolactin secretion in estrogen (E)- primed nonhuman primates. Lactotropes do not contain progestin receptors (PR) and hence the action of P on prolactin is probably mediated by the CNS. In the monkey hypothalamus, E induced progestin receptors (PR), and PR is maintained with supplemental P treatment. This pattern differs from other reproductive tissues and may be due to a tissue specific expression of the A and B isoforms of PR. Dopamine neurons in the arcuate nucleus, which tonically inhibit prolactin, do not contain PR in monkeys, but do show a decrease in mRNA for tyrosine hydroxylase with E+P treatment. Likewise, oxytocin neurons which may stimulate prolactin, do not contain PR, but show an increase in oxytocin content with ovarian steroids. Thus, the action of P on prolactin regulatory neurons is transduced by afferent neurons. Serotonin (5HT), beta-endorphin (BE) and GABAergic neurons exhibit an induction of PR with E treatment and maintain expression of PR upon addition of P to the E regimen, but only 5HT increases with E+P treatment in guinea pigs. We hypothesize that 5HT stimulates BE and GABA neurons which in turn, inhibit the arcuate dopamine neurons.
Aims 1 and 2 will determine whether P increases the expression of the mRNAs for tryptophan hydroxylase and the serotonin reuptake transporter.
Aim 3 will determine whether BE and GABA neurons express mRNA for the stimulatory 5HT2A or 2C receptors and whether the dopamine neurons express mRNA for the inhibitory 5HT1A or 1Dbeta receptors. Since the 5HT1A receptor is predominately an autoreceptor, the regulation of its expression by E and P will also be examined within the 5HT neurons of the raphe nucleus.
Aim 4 will attempt to block p induced prolactin secretion with intrahypothalamic injection of antisense oligonucleotides to the 5HT receptor subtypes which were characterized in Aim 3.
Aim 5 proposes to examine the ratio of the isoforms of PR in brain, pituitary and reproductive tract of steroid- treated monkeys. In summary, experiments in this proposal will further the hypothesis that the 5HT neural system transduces the action of P on prolactin secretion in nonhuman primates and in addition, the hypothesis that the A and B isoforms of PR are expressed in a tissue specific manner will be pursued.