Unilateral Lesion Increases Oestrogen Receptor α Expression in the Intact Side of the Ventromedial Hypothalamic Nucleus in Ovariectomised Rats

Abstract

To determine the relationship between the right and left sides of the ventrolateral ventromedial hypothalamic nucleus (vlVMN) in regulating the expression of oestrogen receptor (ER)α, the unilateral vlVMN was lesioned and the number of ERα-immunoreactive cells and the ERα mRNA level in the intact side of the vlVMN and arcuate nucleus (ARC) were measured in ovariectomised rats. Twenty-four hours after lesioning, brain samples were collected for analysis of ERα expression by immunohistochemistry and the real-time reverse transcriptase-polymerase chain reaction. The number of ERα-immunoreactive cells in the intact side of the vlVMN but not the ARC in the unilateral lesioned group was significantly higher than that in the control or sham-lesioned group. Expression levels of ERα mRNA in the intact side of the vlVMN but not the ARC in unilateral lesioned rats were significantly higher than those in the sham-lesioned group. Of transcript variants with alternative 5'-untranslated regions (0S, 0N, 0, 0T and E1), the ERα 0 transcript level was significantly increased. These results indicate that unilateral damage of vlVMN induces an increase in ERα in the intact side by increasing ERα transcription in a promoter-specific manner. The findings also suggest the existence of new neuroendocrine control system between the right and left sides for the expression of ERα in the vlVMN.

Inhibitory role of the serotonergic system on estrogen receptor α expression in the female rat hypothalamus

“…A behavioral experiment using a toxin specific to serotonergic neurons has shown that the target of lordosis-inhibiting 5-HT-positive axons is the VMN [14]. However, serotonergic neurons in the VMN may not be involved in the regulation of ER␣ expression, although neural inputs to the VMN have been reported to control ER␣ expression [23].…”

“…Photomicrographic digital images were taken from two sections for the AVPV or three sections for the vlVMN and ARCN for each rat (corresponding to rat brain atlas of [19]) using a Digital Microscope Camera (DP72, Olympus, Tokyo). Counting areas for the vlVMN and ARCN were chosen from three sections located 2.28-2.76 mm posterior from the bregma that contain the rostral part of vlVMN, according to the previous report [23].…”

“…On the other hand, neuronal inputs are also involved in the regulation of ER␣ expression. Unilateral lesioning of the VMN enhanced the number of ER␣-immunoreactive (ir) cells and ER␣ mRNA in the contralateral VMN [23].…”