Table 1 Neuronal cells that contain ERa-ir in the sheep brain
Neurotransmitter Nucleus
Percentage of Reference
or marker labelled cells that
contain ERa-ir Ž
. Ž
Tyrosine hydroxylase Arcuate A12
-10 of Batailler et al.
Ž .
. Ž
. Dopamine
ER-ir cells 1992
3–5 Lehman and
Ž .
Karsch 1993b 15
Skinner and Ž
. Herbison 1997
Ž .
Preoptic area A14 Lehman and
Ž .
Karsch 1993b 13–18
Skinner and Ž
. Herbison 1997
Anterior hypothalamus 3–5
Lehman and Ž
. Ž
. A14
Karsch 1993b 25
Skinner and Ž
. Herbison 1997
Glutamic acid decarboxylase Preoptic area
44 Herbison et al.
Ž .
Ž .
GABA 1993
b -Endorphin
Arcuate 15–20
Lehman and Ž
. Karsch 1993b
Neuropeptide Y Arcuate
3 Skinner and
Ž .
Herbison 1997 Ž
Ž .
Somatostatin Ventromedial Nucleus
; 35 ; 70 Herbison 1995
. of ER-ir cells
Ž .
Dopamine b hydroxylase Ventrolateral medulla A1
20–70 Simonian et al.
Ž .
Ž .
noradrenaline 1998
Ž .
4–20 Scott et al. 1999
Nucleus of the solitary 16–60
Simonian et al. Ž
. Ž
. tract A2
1998 Ž
. 8–25
Scott et al. 1999 GnRH
Preoptic area Herbison et al.
Ž .
1993 Lehman and Karsch
Ž .
1993b
produce neurotransmitters not yet identified. The neurochemical identity of ERa-con- taining cells in the brain of male sheep has not been described.
3. ERb
3.1. Location of cells containing ER b Currently, there are no antibodies available that reliably detect ERb in the brains of
domestic species. The distribution of ERb mRNA in the hypothalamus of the ram was mapped using in situ hybridization and found to be broadly similar to the distribution of
Ž .
ERa mRNA-containing cells Hileman et al., 1999 . The highest levels of ERb
expression were found in the preoptic area, bed nucleus of the stria terminalis, paraventricular nucleus and supraoptic nucleus. In contrast to ERa mRNA, ERb
mRNA was observed in the retrochiasmatic area, but very few ERb mRNA-containing cells were observed in the ventromedial nucleus and arcuate nucleus.
Ž .
We have cloned a portion of ovine ERb Genebank accession number applied for and compared the distribution and abundance of ERb mRNA in the hypothalamus of
ewes in the luteal phase of the oestrous cycle and intact rams using in situ hybridisation ŽScott, C.J., Tilbrook, A.J., Simmons, D.M. Rawson, J.A., Chu, S., Fuller, P.J., Ing,
. N.H., Clarke, I.J., unpublished data . Preliminary results indicate that the distribution
and level of expression of ERb mRNA is similar in rams and ewes with the exception of the ventromedial and arcuate nuclei where moderate levels were detected in the ewe;
Ž .
there was almost no ERb mRNA in this region of the ram brain Fig. 1 . We compared Ž
the distribution of ERb mRNA with ERa mRNA in ewes and rams as outlined in .
Ž Section 2.1 and a number of differences were observed Scott, C.J., Tilbrook, A.J.,
Simmons, D.M., Rawson, J.A., Chu, S., Fuller, P.J., Ing, N.H., Clarke, I.J., unpublished .
data . In both sexes, ERa-mRNA was widely distributed in the preoptic area, whereas in the rostral preoptic area, ERb mRNA was localised to a thin strip down the midline of
the brain. In addition, the preoptic area, lateral septum, ventromedial and arcuate nuclei all contained higher numbers of ERa than ERb mRNA-containing cells. By contrast,
the median preoptic nucleus, and the zona incerta contained higher numbers of ERb than ERa mRNA-containing cells, with the retrochiasmatic nucleus containing only
ERb mRNA.
3.2. A role for ER b — the control of LH secretion? Ž
. Male mice lacking a functional ERb appear to be fully fertile Krege et al., 1998 .
This, combined with a paucity of ERb-containing cells in hypothalamic nuclei known to Ž
. be important in the regulation of GnRH secretion vide supra , suggests that ERb may
not be involved in the feedback regulation of GnRH secretion. Nevertheless, the Ž
presence of ERb mRNA-containing cells in the retrochiasmatic nucleus A15 dopamin- .
ergic cell group of the sheep, raises an intriguing possibility of involvement in
Ž .
oestrogen negative feedback during anoestrus Thiery et al., 1995 . Implantation of oestrogen directly into the retrochiasmatic nucleus suppressed plasma LH levels in
Ž .
ovariectomised ewes during an inhibitory photoperiod Gallegos-Sanchez et al., 1997 , Ž
. Ž .
yet ERa has not been detected in this nucleus Lehman et al., 1993a vide supra . It
remains possible, therefore, that oestrogen acts via ERb within the retrochiasmatic nucleus to inhibit LH secretion during the non-breeding season in the sheep.
4. Progesterone receptor
