Protective actions of ovarian hormones in the serotonin system of macaques

Overexpression or knockdown of rat tryptophan hyroxylase-2 has opposing effects on anxiety behavior in an estrogen-dependent manner

Previous studies showed that chronic estrogen treatment increases tryptophan hydroxylase-2 (TpH2) mRNA in the caudal dorsal raphe nucleus (DRN), and this increase was associated with decreased anxiety. The present study explored the interaction of estrogen and targeted, bidirectional manipulation of TpH2 expression in the caudal DRN by knockdown or viral overexpression, to decrease or increase tryptophan hydroxylase expression respectively, on anxiety behavior. Rats were ovariectomized and replaced with empty or estradiol capsules (OVX, OVX/E, respectively). Animals received microinfusions of either antisense TpH2 or control morpholino oligonucleotides into caudal DRN and were later tested in the open field test. A separate group of animals were microinfused with TpH2-GFP or GFP-only herpes simplex viral vectors into caudal DRN and tested in the open field. The bidirectional impact of manipulations on TpH2 expression was confirmed using a combination of quantitative protein and mRNA measurements; TpH2 expression changes were limited to discrete subregions of DRN that were targeted by the manipulations. Estradiol decreased anxiety in all behavioral measures. In the OVX/E group, TpH2 knockdown significantly decreased time spent in the center of the open field, but not in the OVX group, suggesting that TpH2 knockdown reduced the anxiolytic effects of estrogen. Conversely, TpH2 overexpression in the OVX group mimicked the effects of estrogen, as measured by increased time spent in the center of the open field. These results suggest that estrogen and TpH2 in the caudal DRN have a critical interaction in regulating anxiety-like behavior.

Antidepressant effects of estrogens: a basic approximation

The use of estrogenic compounds as antidepressants or as coadjuvants to facilitate the effect of antidepressants has reported controversial results, suggesting that many factors could influence their actions. This review analyzes, from a basic research perspective, the possible factors that may underlie the antidepressant action of estrogens alone or in combination. The possible mechanisms of action of estrogens alone and in combination with the selective serotonin reuptake inhibitor, fluoxetine, the selective noradrenaline reuptake inhibitor, desipramine, and the mixed serotonin/noradrenaline reuptake inhibitor, venlafaxine are reviewed, focusing on monoaminergic systems and estrogen receptors as main targets. The antidepressant effect of estrogens depends on the type of estrogen, treatment duration, doses, sex, time after ovariectomy, and age. Estrogens potentiate the antidepressant-like action of fluoxetine, venlafaxine, and desipramine and drastically shorten their latency of action. The antidepressant-like effect of estrogens alone or in combination with antidepressants seems to be mediated by monoaminergic and classic estrogen receptors, as WAY100635, an antagonist to the serotonin 1A receptor, idaxozan, an antagonist to alpha2 adrenergic receptors, and RU 58668, an estrogen receptor antagonist, blocked their antidepressant-like effect. In conclusion, estrogens produce antidepressant-like actions by themselves and importantly facilitate the action of clinically used antidepressants.

Ovarian steroid regulation of the midbrain corticotropin releasing factor and urocortin systems in macaques

A significant number of postmenopausal women report increased anxiety and vulnerability to stress, which has been linked to decreased secretion of ovarian steroids. Communication between the serotonin system and the corticotropin releasing factor (CRF) system determines stress sensitivity or resilience. This study examines the effects of the ovarian steroids, estradiol (E) and progesterone (P) on the CRF system components that impact serotonin neurons in the midbrain of nonhuman primates. Ovariectomized rhesus macaques were treated with placebo, E alone for 1 month, or E supplemented with P for the last 2 weeks. Quantitative (q)RT-PCR and immunocytochemistry were employed. E±P treatment decreased CRF-R1 and increased CRF-R2 gene expression in hemi-midbrain blocks and in laser captured serotonin neurons. Also in hemi-midbrains, E treatment increased urocortin 1 (UCN1) and CRFBP gene expression, but supplemental P treatment reversed these effects. E±P decreased CRF fiber density in the dorsal, interfascicular and median raphe nuclei and decreased CRF-R1 immunostaining in the dorsal raphe. E increased CRF-R2 immunostaining in the dorsal and median raphe. E±P increased UCN1 immunostaining in the cell bodies and increased UCN1 fiber density in the caudal linear nucleus. Estrogen receptor beta (ERβ), but not ERα was detected in the nucleus of UCN1-positive neurons. While the mechanism of ovarian hormone regulation of the midbrain CRF system requires further investigation, these studies clearly demonstrate another pathway by which ovarian hormones may have positive effects on anxiety and mood regulation.

Diabetes mellitus: channeling care through cellular discovery

Diabetes mellitus (DM) impacts a significant portion of the world's population and care for this disorder places an economic burden on the gross domestic product for any particular country. Furthermore, both Type 1 and Type 2 DM are becoming increasingly prevalent and there is increased incidence of impaired glucose tolerance in the young. The complications of DM are protean and can involve multiple systems throughout the body that are susceptible to the detrimental effects of oxidative stress and apoptotic cell injury. For these reasons, innovative strategies are necessary for the implementation of new treatments for DM that are generated through the further understanding of cellular pathways that govern the pathological consequences of DM. In particular, both the precursor for the coenzyme beta-nicotinamide adenine dinucleotide (NAD(+)), nicotinamide, and the growth factor erythropoietin offer novel platforms for drug discovery that involve cellular metabolic homeostasis and inflammatory cell control. Interestingly, these agents and their tightly associated pathways that consist of cell cycle regulation, protein kinase B, forkhead transcription factors, and Wnt signaling also function in a broader sense as biomarkers for disease onset and progression.

Conceptualizing the role of estrogens and serotonin in the development and maintenance of bulimia nervosa

Serotonergic dysregulation is thought to underlie much of the pathology in bulimia nervosa (BN). The purpose of this review is to expand the serotonergic model by incorporating specific and nonspecific contributions of estrogens to the development and maintenance of bulimic pathology in order to guide research from molecular genetics to novel therapeutics for BN. Special emphasis is given to the organizing theory of general brain arousal which allows for integration of specific and nonspecific effects of these systems on behavioral endpoints such as binge eating or purging as well as arousal states such as fear, novelty seeking, or sex. Regulation of the serotonergic system by estrogens is explored, and genetic, epigenetic, and environmental estrogen effects on bulimic pathology and risk factors are discussed. Genetic and neuroscientific research support this two-system conceptualization of BN with both contributions to the developmental and maintenance of the disorder. Implications of an estrogenic-serotonergic model of BN are discussed as well as guidelines and suggestions for future research and novel therapeutic targets.

Functional characterization of rhesus embryonic stem cell-derived serotonin neurons

Optimal function of the serotonin system is essential for mental health and its role in psychopathologies is undisputed. Enhancing the ability to study primate serotonin neurons in culture would facilitate understanding of intracellular signaling pathways that mediate the action of drugs and other epigenetic or developmental factors impacting human mental health. We were the first group to report differentiation of the non-human primate rhesus monkey embryonic stem cell (ESC) line 366.4 into cultures of serotonin neurons. In this study, we optimized yield and obtained functional characteristics of the derived serotonin neurons. Sequential treatments of ESC 366.4 during expansion stage with fibroblast growth factor 4 and sonic hedgehog markedly increased the yield of serotonin neurons. These serotonin neurons propagated action potentials and expressed GABA receptors. Also, for the first time we demonstrate that these ESC-derived serotonin neurons exhibit functional high-affinity transporter sites, as well as high-affinity 5HT(1A) binding sites, which are essential targets of common psychoactive drugs. Finally, to test the generality of this method, we utilized another rhesus ESC line, ORMES-22, which efficiently differentiated into serotonin neurons. Together, these findings demonstrate the feasibility of our protocol to direct different primate ESC lines to serotonin neurons with physiological characteristics, which makes them a useful in vitro model system.

Androgenic and oestrogenic influences on tyrosine hydroxylase-immunoreactive cells of the prairie vole medial amygdala and bed nucleus of the stria terminalis

The posterodorsal medial amygdala (MeApd) and principal nucleus of the bed nucleus of the stria terminalis (pBST) are densely interconnected sites integrating steroid hormone and olfactory information necessary for sociosexual behaviours in many rodents. Our laboratory recently reported sexually dimorphic populations of cells containing tyrosine hydroxylase (TH) located in the MeApd and pBST of prairie voles (Microtus ochrogaster), with males having many more TH-immunoreactive (-ir) cells in these sites than do females. Gonadal hormones circulating during adulthood were showm to regulate this sex difference because it was eliminated by castrating adult males or implanting females with testosterone-filled capsules. In the present study, we demonstrate that many (25-65%) TH-ir cells in the MeApd and pBST of adult virgin male and female prairie voles also contain immunoreactivity for either the androgen receptor or oestrogen receptor alpha. Subcutaneous implants of oestradiol benzoate mimicked the effects of testosterone and maintained high numbers of TH-ir cells in these sites in castrated males. However, implants of dihydrotestosterone (DHT) did not, and these males had low numbers of TH-ir cells similar to castrated males given empty capsules. A similar effect was found in females, where testosterone or oestradiol benzoate greatly increased the number of TH-ir cells in these sites compared to intact or ovariectomised controls, but DHT did not. DHT implants did, however, maintain high seminal vesicle weights in males. Thus, many of the TH-ir cells in the prairie vole MeApd and pBST are potentially sensitive to androgens and oestrogens, although maintaining immunocytochemically detectable levels of TH in these cells may depend more on an oestrogen-mediated mechanism in both sexes. These data have implications for understanding how gonadal hormone release across the reproductive cycle modulates these species-specific groups of catecholaminergic cells and socially monogamous behaviours in prairie voles.

Different expression of alpha and beta mitochondrial estrogen receptors in the aging rat brain: interaction with respiratory complex V

Recent evidence suggests that hormonal effects on mitochondria could be mediated by mitochondrial estrogen receptors (mtERs). These receptors are new candidates for the beneficial estrogenic effects on mitochondria in different physiological conditions. The aim of this investigation was to study mtER expression during brain aging. We analyzed mtERalpha and mtERbeta expression in cortical, hippocampal and hypothalamic mitochondria of young adult (3months) and aged (18 months) female Wistar rats by Western blot. In addition, we explored the interaction of mtERbeta with respiratory complex V by using coimmunoprecipitation assays. The results show that mtERalpha and mtERbeta are present in young and aged brain mitochondria. We also demonstrate that mtERs are expressed as variants and have a brain region specific distribution. The predominant mtER variants detected were of 61 and 55KDa for mtERalpha and of 63 and 52KDa for mtERbeta. However, we did not observe differences in the mtERalpha or beta content between the two age groups studied. Additionally, we show that mtERbeta interacts with complex V. The overall results demonstrate that there is a differential expression of mtERalpha and mtERbeta variants in different brain areas, indicating that they may participate in different functions in the brain during aging.

Steroids and neuroprotection: New advances

Gonadal hormones exert neuroprotective actions. In addition, it has become evident that the local synthesis of these molecules in the central nervous system may prevent or reduce neurodegeneration.The neuroprotective actions of steroids involve neurons, glial cells and blood vessels, are exerted via steroid receptor signaling initiated at the nuclear or membrane level and steroid receptor independent mechanisms. They include the regulation of phosphatases and kinases and the regulation of the expression of molecules controlling inflammation and apoptosis. In addition, mitochondria have emerged as new central targets for neuroprotective actions of steroids. These neuroprotective actions have been documented in different experimental models of neurological alterations, including motoneuron injury, Parkinson's disease, traumatic brain injury, multiple sclerosis, stroke and Alzheimer's disease. In addition, steroids promote serotonergic neuronal function and protect against affective disorders. This special issue of Frontiers in Neuroendocrinology contains a collection of reviews of the most recent ideas and findings on these various aspects of sex steroid-dependent neuroprotection