Prolactin feedback loop help

[colts]

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Can someone please explain the estrogen and prolactin feedback pathway?

What I understand is: TRH stimulates TSH and prolactin, prolactin inhibits GnRH, and dopamin inhibits prolactin. So when prolactin inhibits GnRH, estrogen is inhibited, so how does estrogen stimulate prolactin?

Also, during pregnancy, lactation is not suppose to happen, but prolactin is still high, why is that?

 

[ijn]

High estrogen/progesterone levels produced by the placenta inhibit the action of prolactin on the breast. After delivery of the placenta, estrogen/progesterone levels drop precipitously, so prolactin becomes disinhibited.

 

[lemonade90]

Estrogen stimulates prolactin secretion and blocks its actions. So while prolactin may be up, if estrogen is around, it won't be working on its targets (this likely means the HPG axis too and lactation). In a sense its like estrogen got to the party first and it isn't letting prolactin in the door even though its invited.

Also you need a decrease in progesterone for lactation to happen. That happens after pregnancy is over as the placenta is a hormone factory for estrogen and progesterone.

 

[colts]

Thanks! makes sense.

Just another unrelated questions about neuroanatomy...how do you tell where the central sulcus is? I get that its in the middle, but there have been questions where it seems slightly off center, and I can't seem to pinpoint where the exact location is...

 

[withrye]

Look at many brains with the sulcus labeled; you'll start to get a feel for it. It usually runs slightly posterior to anterior. From the side, it's usually the only sulcus that runs all the way from the midline to almost the Sylvian fissure. Ideally you would see two fat gyri next to one big sulcus.