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Aim: The role of the serotonin transporter (SERT) is to remove serotonin (5-HT) from the synaptic space. In vitro studies have shown that 5-HT uptake via SERT is influenced by the availability of its substrate, 5-HT. We used RN46A cells, a line that expresses SERT, to investigate 5-HT regulation of 5-HT uptake and the intracellular signaling pathways involved. RN46A cells also express mRNAs for 5-HT receptors (5-HT(1A), 5-HT(1B), 5-HT(2A), and 5-HT(2C)) and as cAMP and intracellular Ca(2+) are modulated by different 5-HT receptors, we studied both pathways., Methods: 5-HT uptake was determined as imipramine-inhibitable uptake of [(3)H]5-HT, intracellular cAMP was measured by RIA and intracellular Ca(2+) changes were determined using the ratiometric method of intracellular Ca(2+) imaging., Results: For uptake experiments, cells were kept for 30 min either with or without 1 microM 5-HT in the medium before measuring uptake. Removal of 5-HT for 30 min significantly decreased [(3)H]5-HT uptake. The absence of 5-HT for 15 min failed to induce any changes in intracellular cAMP levels. Removal of 5-HT from the medium did not change intracellular Ca(2+) levels either; however, adding 1 microM 5-HT after 5 min in 5-HT-free conditions rapidly increased intracellular Ca(2+) levels in 50% of the cells. The remaining cells showed no changes in the intracellular Ca(2+) levels., Conclusions: We have shown that in RN46A cells, that endogenously express SERT and mRNAs for several 5-HT receptors, changes in 5-HT levels influence 5-HT uptake rate as well as induce changes in intracellular Ca(2+) levels. This suggests that 5-HT may utilize intracellular Ca(2+) to regulate 5-HT uptake.

17beta-estradiol (E2) regulates neuronal activity via genomic and rapid, non-genomic mechanisms. The rat serotonergic neuronal cell line (RN46A) was used to investigate the rapid effects of E2 on serotonin (5-HT) reuptake and on potential intracellular signaling pathways. RN46A cells express the serotonin transporter (SERT) and estrogen receptor (ER)beta, but not ERalpha. Fifteen minute E2 treatment (10(-9)M) decreased 5-HT uptake. Intracellular cAMP levels were not increased by 15 min E2 treatment; however, E2 caused an increase in intracellular Ca2+ levels, with a maximum response within the first minute. The response was E2 specific, since other steroids (17alpha-estradiol, testosterone, and progesterone) had no effect. The ER antagonist ICI 182,780 blocked the rapid E2 effects on intracellular Ca2+ levels as did the selective ER modulator tamoxifen. In summary, changes in intracellular Ca2+ levels caused by E2 and mediated through ERbeta may be responsible for observed rapid effects of E2 on SERT activity.

The effects in the brain of selective estrogen receptor modulators (SERMs) such as tamoxifen and raloxifene have not yet been fully elucidated. Based upon the hypothesis that serotonin (5-HT)-steroid hormone interactions are important in mood regulation, we have compared six SERMs (tamoxifen, raloxifene, levormeloxifene, NNC 45-0781, NNC 45-0320, NNC 45-1506) with 17beta-estradiol (E(2)) in terms of their ability to regulate mRNA levels of estrogen receptor (ER)alpha, ER beta, 5-HT(1A) receptor, and 5-HT reuptake transporter (SERT) in the midbrain, amygdala, and hypothalamus of ovariectomized (OVX) rats. Female rats (n = 6/group, 8 groups total) were OVX and allowed to recover for 2 weeks. During the third post-OVX week, rats were injected subcutaneously with E(2) (0.1 mg/kg) or one of the SERMs (5 mg/kg) once per day for 7 days. Twenty-four hours after the last injection, tissue was collected for the determination of mRNA levels by ribonuclease protection assay (RPA). E(2) treatment significantly decreased mRNA levels for ER alpha, ER beta, and SERT in midbrain and ER alpha in hypothalamus. Tamoxifen increased ER beta mRNA levels in hypothalamus, while raloxifene increased ER beta mRNA levels in amygdala. NNC 45-0320 decreased ER alpha mRNA in hypothalamus and decreased ER beta mRNA in amygdala. These results suggest that while SERMs are not full estrogen receptor agonists in the brain, the agonist/antagonist profiles for individual SERMs may differ among brain areas. This raises the possibility of developing new SERMs for selective functions in specific brain areas., (Copyright 2002 S. Karger AG, Basel)

The effects in the brain of selective estrogen receptor modulators (SERMs) such as tamoxifen and raloxifene have not yet been fully elucidated. Based upon the hypothesis that serotonin (5-HT)-steroid hormone interactions are important in mood regulation, we have compared six SERMs (tamoxifen, raloxifene, levormeloxifene, NNC 45-0781, NNC 45-0320, NNC 45-1506) with 17β-estradiol (E[sub 2] ) in terms of their ability to regulate mRNA levels of estrogen receptor (ER)α, ERβ, 5-HT[sub 1A] receptor, and 5-HT reuptake transporter (SERT) in the midbrain, amygdala, and hypothalamus of ovariectomized (OVX) rats. Female rats (n = 6/group, 8 groups total) were OVX and allowed to recover for 2 weeks. During the third post-OVX week, rats were injected subcutaneously with E[sub 2] (0.1 mg/kg) or one of the SERMs (5 mg/kg) once per day for 7 days. Twenty-four hours after the last injection, tissue was collected for the determination of mRNA levels by ribonuclease protection assay (RPA). E[sub 2] treatment significantly decreased mRNA levels for ERα, ERβ, and SERT in midbrain and ERα in hypothalamus. Tamoxifen increased ERβ mRNA levels in hypothalamus, while raloxifene increased ERβ mRNA levels in amygdala. NNC 45-0320 decreased ERα mRNA in hypothalamus and decreased ERβ mRNA in amygdala. These results suggest that while SERMs are not full estrogen receptor agonists in the brain, the agonist/antagonist profiles for individual SERMs may differ among brain areas. This raises the possibility of developing new SERMs for selective functions in specific brain areas.Copyright © 2002 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Abstract: Although radioligand binding studies have shown that the serotonin 5-HT2C receptor (5-HT2CR) is widely expressed throughout the brain, more detailed knowledge of 5-HT2CR distribution within different neuronal populations will aid in understanding the mechanisms through which this receptor acts. Double-label immunohistochemical procedures can be utilized to examine the localization of receptors within specific neuronal populations. In order to conduct such studies, however, it was first necessary to examine the utility and specificity of two commercially available anti-5-HT2CR antibodies [from Santa Cruz (SC) and BD PharMingen (PH)]. In male Sprague–Dawley rats, both antibodies produced widespread immunoreactivity (IR) throughout the brain area chosen for study, the ventral tegmental area, which is the origin of the dopamine mesocorticoaccumbens “reward” pathway. Co-labeling with the SC and PH 5-HT2CR antibodies demonstrated that IR for the two antibodies largely overlapped. However, SC 5-HT2CR IR was more concentrated within IR cell bodies and was more consistent among assays than the PH 5-HT2CR IR. Thus, the SC 5-HT2CR antibody was chosen for subsequent studies. When examined in 5-HT2CR knockout vs. wild-type mice, the SC 5-HT2CR antibody produced widespread IR in wild-type, but not 5-HT2CR knockout, mice. In addition, 5-HT2CR-IR was not present in either native CHO cells, known to be devoid of 5-HT2AR or 5-HT2CR, or in CHO cells transfected with the 5-HT2AR. Thus, these studies suggest that the SC 5-HT2CR antibody produces reliable staining selective for 5-HT2CR vs. 5-HT2AR in rodent brains and is therefore suitable for use in future immunofluorescence 5-HT2CR localization studies. [Copyright &y& Elsevier]

Acute behavioral responses to cocaine are more pronounced in female than in male rats. We have shown that 3 weeks of treatment with 17β-estradiol (E2) implants significantly enhanced the hyperactivity induced by cocaine in ovariectomized (OVX) rats. The ligand-bound estrogen receptor (ER) functions as a transcription factor to regulate the expression of E-responsive genes. Thus, we hypothesized that estrogen (E) modulates the behavioral response to cocaine via regulation of expression of components of dopamine (DA) and serotonin (5-HT) systems in mesolimbic nuclei important in the response to cocaine as well as the hypothalamus, a brain area known to be E-responsive. Adult female Sprague–Dawley rats were OVX; half of them then received E2 implant (OVX+E) (n=8/group, two groups). Twenty-seven days later, brain tissue was collected to study E2 effects on mRNA expression for DA D1-like (D1) and D2-like (D2S, D2L, D3) receptors, DA transporter (DAT), 5-HT1A, 5-HT1B, 5-HT2A, 5-HT2C receptors, and 5-HT transporter (SERT) as well as ERα and ERβ in amygdala, hypothalamus, nucleus accumbens, midbrain, and ventral tegmental area (VTA). We found that E2 implants in OVX rats increased mRNA levels for D1 receptor in hypothalamus, D2L receptor in midbrain, and D3 receptor in VTA, and decreased D3 receptor mRNA levels in midbrain relative to OVX controls. E2 also increased 5-HT2C receptor mRNA levels in midbrain and hypothalamus. In addition, E2 decreased mRNA levels for ERα in amygdala and hypothalamus and ERβ in amygdala. The present study demonstrates that E can regulate mRNA expression for specific DA and 5-HT receptors in a region-specific manner and suggests that such modifications may contribute to the behavioral response to cocaine. [Copyright &y& Elsevier]

Summary: This study investigated estradiol (E2) modulation of the antidepressant effects of a selective serotonin (5-HT) reuptake inhibitor (SSRI; sertraline) and a tricyclic antidepressant (imipramine) as measured by the forced swim test (FST) followed by assessment of gene and protein expression for the 5-HT transporter (SERT) and multiple 5-HT receptors. Female Sprague–Dawley rats were ovariectomized (OVX) and two-thirds of the rats received E2 implants (OVE). 4 weeks later, implants were withdrawn in half of the OVE rats (OVW) to capture a time point when E2 levels were rapidly declining. Rats in each hormone group were treated with vehicle, sertraline (10mg/kg) or imipramine (10mg/kg), 24, 5 and 1h before the FST. Immediately after the FST, midbrain, hippocampus and prefrontal cortex tissue was removed and frozen for analysis of gene expression via quantitative real-time PCR (midbrain tissue) and protein expression via Western blot (prefrontal cortex and hippocampal tissue). In the FST, sertraline decreased immobility and increased swimming in OVE rats, as well as increased swimming in OVW rats. In contrast, no sertraline effect was observed in OVX rats. Rats treated with imipramine showed increased climbing but no changes in immobility or swimming. No changes in protein expression were detected in any treatment group. However, in vehicle-treated rats, E2 increased midbrain SERT mRNA expression, with no effect on midbrain mRNA for the 5-HT receptors. In sertraline-treated rats, E2 decreased 5-HT2A receptor mRNA, and E2-withdrawal increased 5-HT1A, 5-HT2A and 5-HT2C receptor mRNA. In imipramine-treated rats, E2 (and E2-withdrawal) did not affect mRNA expression for any of the target genes. Thus, E2 synergized behaviorally and neurochemically with an SSRI but not a tricyclic antidepressant. [Copyright &y& Elsevier]