ABSTRACT
I. Introduction................................................................................. 362 A. General Role of Estrogen Receptors .................................... 362 B. Polyclonal Antibody Specific to Rat ER
α
............................ 362 C. ER in Well-Known Brain Regions ........................................ 363 D. Estrogen Receptor Appears Transiently in Two Places
in the Brain ............................................................................ 363 II. Transient Expression of ER
α
in the Developing Rat Brain ..... 364 A. Facial Nucleus ....................................................................... 364
1. Newborn Rats ................................................................... 364 2. Fetal Rats .......................................................................... 364 3. ER
α
Detected by Different Antibodies that Recognize Different Epitopes .......................................... 364
4. Down-Regulation of ER
α
Signals by the Ligand .......... 364 5. Absence of Sex Differences.............................................. 364
B. Characterization of ER
α
in the Facial Nucleus .................. 365 1. Retrograde Tract Tracing in Newborn Rats ................... 365 2. EM Studies that Indicate Motoneurons
Contain ER
α
..................................................................... 365 3. Colocalization of ChAT and ER
α
..................................... 366 4. Denervation Diminishes the Facial Nucleus................... 366
C. ER
α
Signals in the Primary Auditory Cortex ..................... 366 1. ER
α
Signals in the Cortex ............................................... 366 2. Application of Retrograde Track Tracer to
Potential Target Regions .................................................. 366 3. Colocalization with Calretinin ........................................ 366
III. Discussion.................................................................................... 367 A. What Does ER
α
Do in These Regions?................................ 367 1. Two Types of ER
α
-
Expressing Neurons ......................... 367 2. ER
α
but not ER
β
was Detected....................................... 367 3. Lack of Relationship to Sexual Differentiation
of the Brain ....................................................................... 367 4. ER
α
Signals Disappear at About the Same Age........... 368 IV. Acknowledgments ...................................................................... 368
References ............................................................................................. 368
A. General Role of Estrogen Receptors
Steroid hormones, including estrogen, have various actions in animals. Their influence is not limited to physiological actions. Steroid hormones evoke pathological changes in animals when they exist in the body in excess amounts. It is generally accepted that steroid hormones become functional after binding to their cognate receptor molecules. Since all of these receptor molecules are proteins that have a common structure such as the DNAbinding domain and the steroid-binding domain, they are now classified into a large superfamily. Estrogen receptor(s) (ER) are activated by binding with the ligand, estrogen, and then attach to an estrogen-responsive element located in the 5
′
-upstream region of estrogen target genes. Estrogen receptors alter transcriptional processes in cooperation with several cellular cofactors. Because of this sequence of action, ER is considered essential for estrogen action. Therefore, to identify the target sites for estrogen action in the brain, the distribution pattern of ER must be examined.
