Effects of estrogen on the serotonergic system and calcitonin gene-related peptide in trigeminal ganglia of rats

Abstract

Background: The prevalence of migraine is 3-folds higher in females than in males, and it is intricately related to the levels of estrogen. Estrogen may regulate the expression of metabolic enzymes and receptors of serotonin and also calcitonin gene-related peptide (CGRP), which are implicated in migraine pathogenesis.

Purpose: To study the effects of estrogen on the components of serotonin system and CGRP in trigeminal ganglia of ovariectomized (OVX) rats.

Methods: OVX rats were administered estrogen in silastic tubes and after 48 h, serum estrogen levels were determined. Trigeminal ganglia tissues were used for RT-PCRs of tryptophan hydroxylase (TPH), monoamine oxidase (MAO), serotonin receptors (5-HT1A, 5-HT1B, 5-HT2A), estrogen receptor (ER) and CGRP. Western blots of TPH and MAO were performed.

Results: Estradiol administration to OVX rats increased TPH mRNA levels, while decreased MAO mRNA levels in trigeminal ganglia tissue. Western blot data correlate with the gene expression results. The decreased mRNA levels of serotonin receptors following ovariectomy were restored in estrogen-replenished rats. The induced gene expression of ER in OVX rats was restored following estrogen replenishment.

Conclusion: Estrogen levels affect the levels of serotonin metabolizing enzymes and its receptors besides CGRP levels. Since TPH and MAO levels regulate circulating and physiologically available serotonin content, the regulation of serotonin metabolizing enzymes suggest a plausible mechanism by which estrogen alleviates migraine in women.

Keywords: 17β-estradiol; Migraine; Ovariectomy; Serotonin.

Fig. 1:

Expression of genes of the components of serotonin system, estrogen receptor and CGRP in trigeminal ganglia. (a) Ethidium bromide-stained agarose gels of RT-PCRs of tryptophan hydroxylase, monoamine oxidase, 5-HT1A, 5-HT1B, 5-HT2A, estrogen receptor and Rig/S15. Each gel depicts representative data from cycling (control), sham-operated, ovariectomized and estrogen-replenished ovariectomized rats. (b) Quantitation of RT-PCR data demonstrates significant changes in various genes expression. The ordinate represents the ratio of the intensity of the gene of interest to the housekeeping gene (Rig/S15), mean + standard error (n=5). *Means differ from control, P<0.05. $Means differ from OVX, P<0.05.

Fig. 2:

Western blot analysis of proteins in trigeminal ganglia of cycling (control), sham-operated, ovariectomized and estrogen-replenished ovariectomized rats. (a) Western blot of TPH, MAO and GAPDH proteins. (b) Quantitaion of proteins using chemiluminescence, mean ± standard error (n=5). *Means differ from control, P&0.05. $Means differ from OVX, P<0.05.

Fig. 3:

Expression of CGRP gene in trigeminal ganglia. (a) Ethidium bromide-stained agarose gels of RT-PCRs of CGRP and Rig/S15. Each gel depicts representative data from cycling (control), sham-operated, ovariectomized and estrogen-replenished ovariectomized rats. (b) Quantitation of RT-PCR data demonstrates significant changes in gene expression. The ordinate represents the ratio of the intensity of CGRP gene to the housekeeping gene (Rig/S15), mean + standard error (n=5). *Means differ from control, P<0.05. $Means differ from OVX, P<0.05.