The distribution of immunoreactive (IR) estrogen receptor (ER)-contain
ing cells was studied in the brains of adult Suffolk ewes using a rat
monoclonal antibody (H222) which recognizes the human estrogen recepto
r. IR cells were characterized by dense nuclear reaction product, and
in some instances, cytoplasmic immunostaining which filled dendrite-li
ke processes. The greatest densities of ER-IR cells were found in the
medial preoptic area, the mediobasal hypothalamus, and in a number of
limbic system structures (amygdala, bed nucleus of the stria terminali
s, lateral septum). ER-IR cells were found at lower densities in sever
al other subregions of the hypothalamus and limbic system, and in the
periaqueductal gray of the caudal midbrain. Cytoplasmic ER immunoreact
ivity was most prominent among ER-IR cells in the ventrolateral-ventro
medial nucleus, the bed nucleus of the stria terminalis, the midbrain
periaqueductal gray, and some ER-IR cells in the substantia innominata
. The distribution of ER-containing cells in the sheep brain closely p
arallels that seen in other mammals. ER-IR cells are found in sites su
ch as the medial preoptic area and ventrolateral-ventromedial hypothal
amus which have been implicated as targets in this species and others
for the influence of estradiol on sexual behavior and reproductive neu
roendocrine function.