Expression of estrogen receptor-alpha and c-Fos in adrenergic neurons of the female rat during the steroid-induced LH surge

Epinephrine is an important neurotransmitter that is synthesized in relativ ely few neurons of the medullary regions C1-C3. Epinephrine is involved, am ong others in the control of most neuroendocrine systems, such as corticotr opin releasing hormone-, gonadotropin releasing hormone- and oxytocin/vasop ressin-containing neurons as part of complex feedback loop systems that oft en include interactions with the gonadal or adrenal steroid hormones. In or der to determine if the interactions between gonadal steroid hormones with the adrenergic neurons are direct or involve steroid-receptive interneurons that in turn innervate the adrenergic neurons, dual immunohistochemistry w as applied to identify if estrogen receptor-alpha (ER alpha) protein was ex pressed by adrenergic, phenylethanolamine-N-methyl transferase (PNMT)-posit ive neurons and if estradiol can activate these neurons as determined by th e transient expression of the transcription factor c-Fos. The results show that an average of 22% Of all PNMT neurons in the: C1 region, 38% in C2 and 42% in the C3 region express estrogen receptor-alpha protein with the high est numbers of dual labeled neurons in the central levels of the C1-C3 regi ons. Overall, the percentages of dual labeled PNMT/ER alpha neurons did not change during the steroid-induced LW surge. In contrast, the percentage of c-Fos expressing PNMT neurons changed significantly during the LPI surge. Thus, c-Fos immunoreactivity was highest in all three regions at 1200 h wit h 69% of the PNMT neurons in C1, 60% in C2 and 79% in C3 co-expressing c-Fo s. C-Fos expression was lowest before and after the surge with 39% of the P NMT neurons in the C2 region containing c-Fos at 0800 h, 52% c-Fos-positive PNMT neurons in C1 and 54% in area C3. The results show that many adrenerg ic neurons are direct targets for estradiol and that most PNMT neurons in t he brainstem are activated during the initiation of the steroid-induced LII surge which suggests that epinephrine is one of the triggers that stimulat es GnRH release during the surge. (C) 2000 Elsevier Science B.V. All rights reserved.