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Modulation by estrogen-receptor directed drugs of 5-hydroxytryptamine-2A receptors in rat brain
1Oncology and Molecular Endocrinology Research Center and Faculté de Pharmacie, Université Laval, Sainte-Foy, Québec, Canada.
Abstract:
Hormonal specificity of modulation of brain 5-HT(2A) receptors was investigated by comparing activity of compounds with varying effects on estrogen response in breast, bone, and uterus. A two-week estradiol treatment stimulated the decreased uterine weight of ovariectomized rats to intact rat values whereas an increase of 29% with tamoxifen and 16% with raloxifene was observed compared to vehicle-treated ovariectomized rats. In 18 assayed brain regions, ovariectomy decreased 5-HT(2A) receptor binding and mRNA levels in anterior cingulate and frontal cortices, striatum, and nucleus accumbens; estradiol restored this decrease to intact rat values. Dehydroepiandrosterone (DHEA) increased ovariectomized rats 5-HT(2A) receptor expression only in striatum and cortical amygdala. Tamoxifen increased 5-HT(2A) receptor density only in striatum. Raloxifene, an uterine estrogen receptor (ER) antagonist, increased, like estradiol, 5-HT(2A) receptor density and expression in cingulate and frontal cortices, striatum, and nucleus accumbens. Brain regional specificity of estradiol, DHEA, tamoxifen, and raloxifene on 5-HT(2A) receptors was observed which can be dissociated from peripheral activity.
Insights
Hormones like estradiol and raloxifene specifically alter brain serotonin 5-HT(2A) receptors, distinct from their effects on peripheral tissues like the uterus.
Area of Science:
- Neuroendocrinology
- Pharmacology
Background:
- Estrogen influences brain function, including serotonin receptor activity.
- Selective estrogen receptor modulators (SERMs) like tamoxifen and raloxifene have varying effects on estrogen pathways.
Purpose of the Study:
- To investigate the hormonal specificity of brain 5-HT(2A) receptor modulation.
- To compare the effects of estradiol and SERMs on 5-HT(2A) receptors in different brain regions.
Main Methods:
- Ovariectomized rats were treated with estradiol, dehydroepiandrosterone (DHEA), tamoxifen, or raloxifene.
- 5-HT(2A) receptor binding and mRNA levels were measured in 18 brain regions.
- Peripheral effects on uterine weight were also assessed.
Main Results:
- Estradiol and raloxifene restored ovariectomy-induced decreases in 5-HT(2A) receptors in specific brain areas (cingulate cortex, frontal cortex, striatum, nucleus accumbens).
- DHEA and tamoxifen showed more limited effects, increasing 5-HT(2A) receptors only in the striatum and/or cortical amygdala.
- Peripheral effects on uterine weight differed significantly between compounds, demonstrating dissociation from brain receptor activity.
Conclusions:
- Estradiol and raloxifene exhibit brain-specific modulation of 5-HT(2A) receptors, separable from their peripheral actions.
- Different hormonal agents display distinct regional specificities in their effects on brain 5-HT(2A) receptors.