Ž .
the preoptic area Robinson and Kendrick, 1992 , dopamine levels in the mediobasal Ž
. Ž
hypothalamus Fabre-Nys et al., 1994 , and b-endorphin in the arcuate nucleus Yang et .
al., 1988; Whisnant et al., 1991 . Progesterone treatment altered levels of pre-proen- Ž
kephalin mRNA in the ventromedial nucleus of ovariectomised ewes Broad et al., .
Ž 1993 , although we did not detect any changes across the estrous cycle Walsh, J.P.,
. Clarke, I.J., unpublished . There is also evidence that endogenous opioids mediate
Ž .
Ž .
progesterone feedback in cattle Stumpf et al., 1993 and pigs Okrasa et al., 1992 . Thus, in these species, the cells producing these neurotransmitters are good candidates to
also co-express PR.
5. AR
5.1. Location of cells containing AR The distribution of AR-containing cells in the ram hypothalamus has been described
using immunocytochemistry and large populations were found in the preoptic area, Ž
. ventromedial, arcuate and premamillary nuclei Herbison et al., 1996 . Numerous cells
containing AR were also detected in the bed nucleus of the stria terminalis and anterior Ž
hypothalamic area. We have used in situ hybridisation for AR in the ram Scott, C.J., .
Tilbrook, A.J., Rao, A., Chu, S., Fuller, P.J., Clarke, I.J., unpublished and found a similar distribution. We also found moderate labelling of cells in the median preoptic
nucleus and the stria terminalis. This distribution of ARs is similar to that in the rat Ž
. Simerly et al., 1990 . It is notable, however, that the bed nucleus of the stria terminalis
contains very high levels of AR expression in the rat brain, but only moderate numbers of AR-containing cells are found at this site in the ram brain.
5.2. Neurochemical identity of neurones containing AR Ž
. Herbison et al. 1996 have shown that GnRH neurones do not contain AR, nor do
the majority of dopaminergic neurones. Only a small number of tyrosine hydroxylase Ž
. TH positive cells in the lateral hypothalamus contained AR, while none of the TH
positive cells in the major hypothalamic dopamine cell groups contained AR. It therefore appears unlikely that testosterone feedback is mediated via dopaminergic cells in the
ram. Around 40 of somatostatin cells in the ventromedial nucleus contain AR, which accounted for nearly half of the AR-ir cells in that nucleus. It is possible that these
somatostatin cells may be involved in the feedback regulation of GnRH secretion in the ram, but the role of somatostatin in the control of GnRH secretion has not been
examined. On the other hand, dihydrotestosterone implants into the ventromedial
Ž .
nucleus did not affect the pattern of LH secretion in castrated rams, Scott et al., 1997 and AR-containing cells in this region may subserve some other function, e.g. reproduc-
tive behaviour.
6. Conclusions
