Another method for detect ing hormone receptors is im munocytochemistry ICC In

Another method for detect ing hormone receptors is im

This preview shows page 11 - 12 out of 24 pages.

Another method for detect- ing hormone receptors is im- munocytochemistry (ICC). In this method (described in more detail in Box 2.1), we use antibodies that rec- ognize the hormone receptor (Figure D). This method allows us to map the distribution of hormone receptors in the brain. We put the antibodies on slices of brain tissue, wait for them to bind to the receptors, wash off the unbound antibodies, and use chemi- cal methods to visualize the antibod- ies by creating a tiny dark spot in the nuclei of target brain cells. We can also use in situ hybridization (see Box 2.1) to look for the neurons that make the mRNA for the steroid recep- tor. Because these cells make the transcript for the receptor, they are likely to possess the receptor protein itself. What Happens at the Target Cells? Once we have used autoradiogra- phy, immunocytochemistry, or in situ hybridization (or, better yet, all three) to identify brain regions that have recep- tors for the hormone, those regions become candidates for the places at which the hormone works to change behavior. Now we can take castrated (B) Autoradiogram (D) Immunocytochemistry (C) Autoradiogram males and implant tiny pellets of testosterone into one of those brain regions. We use RIA to ensure that the pellets are small enough that they have no effect on hormone levels in the blood. Then we ask whether the small implant in that brain region restores the behavior. If not, then in other animals we can implant pellets in a different region or try placing implants in a combination of brain sites. It turns out that such implants can restore male sexual behavior in rats only if they are placed in the medial preoptic area (mPOA) of the hypo- thalamus. Thus, we have found so far that testosterone does something to the mPOA to permit individual males to display sexual behavior. Now we can examine the mPOA in detail to learn which changes in the anatomy, physiology, or protein production of this region are caused by testoster- one. We have more or less caught up to modern-day scientists who work on this very question. Some of the preliminary answers suggested by their research will be discussed in Chapter 12. (Figure C courtesy of Dr. Bruce McEwen; D courtesy of Dr. Cynthia Jordan.) (B) An autoradiogram showing that spinal motor neurons (purple cell profiles) accumulate radioactive tes- tosterone (small dots). (C) An autora- diogram showing the concentration of oxytocin receptors in the ventro- medial hypothalamus (oval outlines). (D) Immunocytochemistry revealing cells with nuclei that contain andro- gen receptors (dark circles), to which testosterone can bind. The somata of these neurons have been labeled with the tracers Fluoro-Gold (white) and Fluoro-Ruby (red). knockout organism An individual in which a particular gene has been disabled by an experimenter.
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