Noradrenergic neurons are implicated in the estrogen-dependent neural regulation of luteinizing hormone secretion in a variety of mammalian species. The current study has used immunocytochemical methods to determine whether estrogen receptors (ER) are expressed within the brainstem of the ewe and to establish their relationship to noradrenergic neurons. Using a monoclonal mouse antiserum directed against the N-terminal of ERα, four distinct populations of ERα-immunoreactive cells were identified in ovine medulla and pons. The largest population was found in the superficial laminae of the spinal nucleus of the trigeminal nerve, followed by the nucleus tractus solitarius, lateral area postrema, and ventrolateral medulla. Double-labelling immunocytochemistry using antisera directed against the ERα and dopamine-β-hydroxylase revealed that noradrenergic neurons expressing ER immunoreactivity were only found in ventrolateral medulla (A1 cell group) and nucleus tractus solitarius (A2 cell group). No double-labelled cells were identified in the A5, A6, or A7 noradrenergic cell groups. ERs were expressed with a clear rostrocaudal topography within the A1 and A2 populations, with 80–90% of noradrenergic neurons expressing ERα in the caudalmost medulla as compared with less than 5% rostral to the obex. Our findings demonstrate that, as in the rat, the ovine A1 and A2 neurons express ERs in a defined topographical manner, while, dissimilar to the rat, ERα is not synthesized by noradrenergic neurons in the other cell groups. These observations indicate that A1 and A2 noradrenergic neurons in the ovine brainstem are likely to be influenced by circulating estrogens and lay the neuroanatomical foundations for investigating the functional role of these cell populations within the gonadotropin-releasing hormone neuron network of the sheep.

Keywords:
Gonadal steroid receptors, Catecholamines, Nucleus of the solitary tract, Gonadotropin releasing hormone, Brainstem
1.
Herbison AE: Noradrenergic regulation of cyclic GnRH secretion. Rev Reprod 1997;2:1–6.
2.
Spies HG, Pau KYF, Yang S: Coital and estrogen signals: A contrast in the preovulatory neuroendocrine networks of rabbits and rhesus monkeys. Biol Reprod 1997;56:310–319.
3.
Clarke IJ: The preovulatory LH surge: A case of a neuroendocrine switch. Trends Endocrinol Metab 1995;6:241–247.
4.
Lehman MN, Karsch FJ, Silverman AJ: Potential sites of interaction between catecholamines and LHRH in the sheep brain. Brain Res Bull 1988;29:49–58.
5.
Tillet Y, Caldani M, Batailler M: Anatomical relationships on monoaminergic and neuropeptide Y-containing fibres with luteinizing hormone-releasing hormone systems in the preoptic area of the sheep brain: Immunohistochemical studies. J Chem Neuroanat 1989;2:319–326.
6.
Jackson GL: Effect of adrenergic blocking drugs on secretion of luteinizing hormone in the ovariectomized ewe. Biol Reprod 1977;16:543–548.
7.
Havern RL, Whisnant CS, Goodman RL: Hypothalamic sites of catecholamine inhibition of luteinizing hormone in the anestrous ewe. Biol Reprod 1991;44:476–482.
8.
Scott CJ, Cummins JT, Clarke IJ: Effects on plasma luteinizing hormone levels of microinjection of noradrenaline and adrenaline into the septo-preoptic area of the brain of the ovariectomized ewe: Changes with season and chronic oestrogen treatment. J Neuroendocrinol 1992;4:131–141.
9.
Goodman RL, Havern RL, Whisnant CS: Alpha adrenergic neurons inhibit luteinizing hormone pulse amplitude in breeding season ewes. Biol Reprod 1996;54:380–386.
10.
Demling J, Fuchs E, Baumert M, Wuttke W: Preoptic catecholamine, GABA, and glutamate release in ovariectomised and ovariectomised estrogen-primed rats utilising a push-pull cannula technique. Neuroendocrinology 1985;41:212–218.
11.
Mohankumar PS, Thyagarajan S, Quadri SK: Correlations of catecholamine release in the medial preoptic area with proestrous surges of luteinizing hormone and prolactin: Effects of aging. Endocrinology 1994;135:119–126.
12.
Robinson JE, Kendrick KM, Lambart CE: Changes in the release of gamma-aminobutyric acid and catecholamines in the preoptic/septal area prior to and during the preovulatory surge of luteinizing hormone in the ewe. J Neuroendocrinol 1991;3:393–399.
13.
Wright DE, Jennes L: Origin of noradrenergic projections to GnRH perikarya-containing areas in the medial septum-diagonal band and preoptic area. Brain Res 1993;621:272–278.
14.
Simonian SX, Herbison AE: Differential expression of estrogen receptor and neuropeptide Y by brainstem A1 and A2 noradrenaline neurons. Neuroscience 1997;76:517–529.
15.
Jennes L, Jennes ME, Purvis C, Nees M: C-fos expression in noradrenergic A2 neurons of the rat during the estrous cycle and after steroid hormone treatments. Brain Res 1992;586:171–175.
16.
Conde GL, Bicknell RJ, Herbison AE: Changing patterns of Fos expression in brainstem catecholaminergic neurons during the rat oestrous cycle. Brain Res 1995;672:68–76.
17.
Herbison AE: Multi-modal influence of estrogen on GnRH neurons. Endocr Rev, in press.
18.
Tillet Y, Batailler M, Thibault J: Neuronal projections to the medial preoptic area of the sheep, with special reference to monoaminergic afferents: Immunohistochemical and retrograde tract tracing studies. J Comp Neurol 1993;330:195–220.
19.
Herbison AE, Robinson JE, Skinner DC: Distribution of estrogen receptor-immunoreactive cells in the preoptic area of the ewe: Co-localization with glutamic acid decarboxylase but not luteinizing hormone-releasing hormone. Neuroendocrinology 1993;57:751–759.
20.
Lehman MN, Ebling FJP, Moenter SM, Karsch FJ: Distribution of estrogen receptor-immunoreactive cells in the sheep brain. Endocrinology 1993;133:876–886.
21.
Goding JR, Catt KJ, Brown JM, Kaltenbach CC, Cumming TA, Mole BJ: Radioimmunoassay for ovine luteinizing hormone: Secretion of luteinizing hormone following estrogen administration in the sheep. Endocrinology 1969;86:133–142.
22.
Simerly RB, Young BJ: Regulation of estrogen receptor messenger ribonucleic acid in rat hypothalamus by sex steroids. Mol Endocrinol 1991;5:424–432.
23.
Al Saati T, Clamens S, Cohen-Knafo E, Faye JC, Prats H, Coindre JM, Wafflart J, Caveriviere P, Bayard F, Delsol G: Production of monoclonal antibodies to human estrogen-receptor protein (ER) using recombinant ER (RER). Int J Cancer 1993;55:651–656.
24.
Skinner DC, Herbison AE: Effects of photoperiod on estrogen receptor, tyrosine hydroxylase, neuropeptide Y, and β-endorphin immunoreactivity in the ewe hypothalamus. Endocrinology 1997;138:2585–2595.
25.
Tillet Y, Thibault J: Catecholamine-containing neurons in the sheep brainstem and diencephalon: Immunohistochemical study with tyrosine hydroxylase (TH) and dopamine-β-hydroxylase (DBH) antibodies. J Comp Neurol 1989;290:69–104.
26.
Greene GL, Sobel NB, King WJ, Jensen EV: Immunochemical studies of estrogen receptors. J Steroid Biochem 1984;20:51–56.
27.
Blaustein JD: Estrogen receptor immunoreactivity in rat brain: Rapid effects of estradiol injection. Endocrinology 1993;132:1218–1224.
28.
Shugrue PJ, Lane MV, Merchenthaler I: The comparative distribution of estrogen receptor α and β mRNA in the rat central nervous system. J Comp Neurol 1997;388:507–525.
29.
Kuiper GGJM, Enmark E, Pelto-Huikko M, Nilsson S, Gustafsson J-A: Cloning of a novel estrogen receptor expressed in rat prostate and ovary. Proc Natl Acad Sci USA 1996;93:5925–5930.
30.
Heritage AS, Grant ID, Stumpf WE: 3H-estradiol in catecholamine neurons of rat brain stem: Combined localisation by autoradiographic and formaldehyde-induced fluorescence. J Comp Neurol 1977;176:607–630.
31.
Simerly RB, Chang C, Muramatsu M, Swanson LW: Distribution of androgen and estrogen receptor mRNA-containing cells in the rat brain: An in situ hybridization study. J Comp Neurol 1990;294:76–95.
32.
Amandusson A, Hermanson O, Blomqvist A: Estrogen receptor-like immunoreactivity in the medullary and spinal dorsal horn of the female rat. Neurosci Lett 1995;196:25–28.
33.
Schutzer WE, Bethea CL: Lack of ovarian steroid hormone regulation of norepinephrine transporter mRNA expression in the non-human primate locus coeruleus. Psychoneuroendocrinology 1997;22:325–336.
34.
Voisin DL, Simonian SX, Herbison AE: Identification of estrogen receptor-containing neurons projecting to the rat supraoptic nucleus. Neuroscience 1997;78:215–228.
35.
Caraty A, Fabre-Nys C, Delaleu B, Locatelli A, Bruneau G, Karsch F, Herbison A: Evidence that the mediobasal hypothalamus is the primary site of action of estradiol in inducing the preovulatory GnRH surge in the ewe. Endocrinology 1998;139:1752–1760.
1998
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