Decamethylcyclopentasiloxane affects estradiol production in female rats but not H295R cells.

Sex hormones, such as androgens and estrogens, are predominantly produced in the gonads (ovaries and testes) and adrenal cortex. Endocrine-disrupting chemicals (EDCs) are substances that mimic, block, or interfere with hormones in the endocrine systems of humans and organisms. EDCs mainly act via nuclear receptors and steroidogenesis-related enzymes. In the OECD conceptual framework for testing and assessment of EDCs, several well-known assays are used to identify the potential disruption of nuclear receptors both in vivo and in vitro, whereas the H295R steroidogenesis assay is the only assay that detects the disruption of steroidogenesis. Forskolin and prochloraz are often used as positive controls in the H295R steroidogenesis assay. Decamethylcyclopentasiloxane (D5) was suspected one of EDCs, but the effects of D5 on steroidogenesis remain unclear. To establish a short-term in vivo screening method that detects the disruption of steroidogenesis, rats in the present study were fed a diet containing forskolin, prochloraz, or D5 for 14 days. Forskolin increased plasma levels of 17ß-estradiol (E2) and testosterone as well as the mRNA level of Cyp19 in both the adrenal glands and ovaries. Prochloraz induced the loss of cyclicity in the sexual cycle and decreased plasma levels of E2 and testosterone. D5 increased E2 levels and shortened the estrous cycle in a dose-dependent manner; however, potential endocrine disruption was not detected in the H295R steroidogenesis assay. These results demonstrate the importance of comprehensively assessing the endocrine-disrupting effects of chemicals on steroidogenesis in vivo.

Noradrenaline activation of hippocampal dopamine D1 receptors promotes antidepressant effects.

Dopamine D1 receptors (D1Rs) in the hippocampal dentate gyrus (DG) are essential for antidepressant effects. However, the midbrain dopaminergic neurons, the major source of dopamine in the brain, only sparsely project to DG, suggesting possible activation of DG D1Rs by endogenous substances other than dopamine. We have examined this possibility using electrophysiological and biochemical techniques and found robust activation of D1Rs in mouse DG neurons by noradrenaline. Noradrenaline at the micromolar range potentiated synaptic transmission at the DG output and increased the phosphorylation of protein kinase A substrates in DG via activation of D1Rs and ß adrenergic receptors. Neuronal excitation preferentially enhanced noradrenaline-induced synaptic potentiation mediated by D1Rs with minor effects on ß-receptor-dependent potentiation. Increased voluntary exercise by wheel running also enhanced noradrenaline-induced, D1R-mediated synaptic potentiation, suggesting a distinct functional role of the noradrenaline-D1R signaling. We then examined the role of this signaling in antidepressant effects using mice exposed to chronic restraint stress. In the stressed mice, an antidepressant acting on the noradrenergic system induced a mature-to-immature change in the DG neuron phenotype, a previously proposed cellular substrate for antidepressant action. This effect was evident only in mice subjected to wheel running and blocked by a D1R antagonist. These results suggest a critical role of noradrenaline-induced activation of D1Rs in antidepressant effects in DG. Experience-dependent regulation of noradrenaline-D1R signaling may determine responsiveness to antidepressant drugs in depressive disorders.

The effect of electroconvulsive seizure on survival, neuronal differentiation, and expression of the maturation marker in the adult mouse hippocampus.

Electroconvulsive seizure (ECS), a model of electroconvulsive therapy in rodents, strongly increases neurogenesis in the adult hippocampus. Neurogenesis is a multi-step process that spans proliferation, survival, neuronal differentiation, and functional maturation. Our previous study demonstrated that ECS stimulates the proliferation of neural stem-like cells. However, the contribution of ECS to survival, neuronal differentiation, and maturation in newborn cells remains unknown. To evaluate the effect of ECS on these processes, we labeled newborn cells with bromodeoxyuridine (BrdU) before ECS treatment to determine the cell age and examined the survival rate and expression of cellular markers in the BrdU-labeled cells. Our results revealed that exposure to ECS (11 repetitions) during the differentiation phase significantly increased survival and promoted neuronal differentiation of newborn cells in the dentate gyrus. Four of ECS repetitions during the early differentiation phase were sufficient to promote dendritic outgrowth in immature neurons and enhance the expression of the immature neuronal marker, calretinin, in newborn cells. In contrast, exposure to ECS (11 repetitions) during the late maturation phase significantly suppressed the expression of the mature neuronal marker, calbindin, in newborn neurons. These results demonstrate that ECS during the differentiation phase promoted survival and neuronal differentiation and, in contrast, suppressed mature marker expression during the late maturation phase, suggesting that ECS has multiple effects on the different stages of adult neurogenesis.