C. Orikasa et al., Estrogen receptor alpha, but not beta, is expressed in the interneurons ofthe hippocampus in prepubertal rats: an in situ hybridization study, DEV BRAIN R, 120(2), 2000, pp. 245-254
Estradiol is involved in the differentiation and plasticity of hippocampal
neurons. In the CA1 region, estrogen treatment increases dendritic spines a
nd synapse density on pyramidal cells. In the adult hippocampus, immunoreac
tivity for estrogen receptor alpha (ER alpha) has been reported in inhibito
ry interneurons, but neither in the pyramidal neurons nor in granule cells.
Estrogens also mediate aspects of sexual differentiation of the hippocampu
s. To examine the possibility that an alteration in expression of the two t
ypes of estrogen receptors (ER alpha and ER beta) in the hippocampus underl
ies different roles of estrogen and/or ERs during development and in adult
life, we applied non-isotopic, digoxigenin (dig)-labeled, in situ hybridiza
tion histochemistry (ISHH) for the both ER forms and examined the distribut
ion pattern of their messages in serial, frontal sections over the postnata
l period and in the adult. ER alpha mRNA expression was found scattered thr
oughout the hippocampus especially in the hilar region of the dentate gyrus
, and in the strata radiatum and pyramidale in the cornus ammonis at postna
tal days (PND) 14, 21 and 35. In the hilus of the dorsal hippocampus, the d
ensity of ER alpha-labelled cells was greater in the rostro-medial aspect,
while less in the lateral and the caudal region. In the ventral hippocampus
the signals for ER alpha mRNA were also found in relatively high density i
n the hilus. No significant sex difference in distribution and intensity of
the ER alpha mRNA positive cells were detected. The hippocampal distributi
on of ER alpha mRNA expression at PND 14 remained the same on PND 21 and 35
and in adulthood. As reported for adults, ER alpha mRNA signals appear to
be in interneurons of the hippocampus but neither in the pyramidal cells no
r in the dentate granular cells based on their size and location. In contra
st to the result of ER alpha, no clear signals for ER beta mRNA were detect
ed in the hippocampus across all ages examined, whereas they were clearly d
etected in the hypothalamus. (C) 2000 Elsevier Science B.V. All rights rese
rved.