Maternal hypothyroidism decreases progesterone receptor expression in the cortical subplate of foetal rat brain

Perinatal phthalate exposure increases developmental apoptosis in the rat medial prefrontal cortex

Phthalates are a class of endocrine disruptors found in a variety of consumer goods, and offspring can be exposed to these compounds during gestation and lactation. Our laboratory has found that perinatal exposure to an environmentally relevant mixture of phthalates resulted in a decrease in cognitive flexibility and in neuron number in the adult rat medial prefrontal cortex (mPFC). Here, we examine effects of phthalate treatment on prenatal cellular proliferation and perinatal apoptosis in the mPFC. To examine the phthalate effects on cellular proliferation, dams consumed 0, 1, or 5 mg/kg of the phthalate mixture daily from embryonic day 2 (E2) through the day of birth (P0), and on E16 and E17, they were injected with BrdU. The mPFC of offspring was analyzed on P5 and showed a decrease in labelled cells in the phthalate exposed groups. To examine whether changes in BrdU density observed on P5 were due to altered cell survival, cell death was measured on E18, P0, and P5 using a TUNEL assay in a separate cohort of prenatally exposed offspring. There was an increase in TUNEL labelled cells at E18 in the phthalate exposed groups. In the final experiment, dams consumed the phthalate mixture from E2 through P10, at which time mPFC tissue was stained with TUNEL. Phthalate treated subjects showed a higher density of apoptotic cells at P10. These results indicate both pre- and postnatal phthalate exposure increases apoptosis in the male and female rat mPFC. While the impact of phthalates on proliferation cannot be ruled out, these data do not allow for definitive conclusions.

Perchlorate in shellfish from South China Sea and implications for human exposure

Shellfish can absorb and accumulate contaminants. The consumption of shellfish could expose humans to pollutants and increase related health risk. Perchlorate (ClO₄^-) is a ubiquitous pollutant and could affect thyroid functions, especially for children and pregnant women. However, knowledge on the contamination of perchlorate in aquatic food such as shellfish remains limited. This study aimed to investigate the abundances of perchlorate in shellfish from South China Sea and to assess human exposure risks. A total of 178 shellfish samples from eight species were collected from offshore aquaculture waters in South China Sea. Perchlorate was detected in 99.4% of them, suggesting widespread pollution in coastal waters. Concentrations of perchlorate ranged from not detected (N.D.) to 71.5 μg kg^-1, with a median value of 4.33 μg kg^-1. Estimated daily intake (EDI) and hazard quotient (HQ) were used to assess human exposure dose and health risks, respectively. The HQ values were determined to be less than 1, indicating no significant health risks to local residents via shellfish consumption. To our knowledge, this is the first study to investigate perchlorate contamination in South China shellfish and assess potential human risks.

Influence of maternal thyroid hormones during gestation on fetal brain development

Thyroid hormones (THs) play an obligatory role in many fundamental processes underlying brain development and maturation. The developing embryo/fetus is dependent on maternal supply of TH. The fetal thyroid gland does not commence TH synthesis until mid gestation, and the adverse consequences of severe maternal TH deficiency on offspring neurodevelopment are well established. Recent evidence suggests that even more moderate forms of maternal thyroid dysfunction, particularly during early gestation, may have a long-lasting influence on child cognitive development and risk of neurodevelopmental disorders. Moreover, these observed alterations appear to be largely irreversible after birth. It is, therefore, important to gain a better understanding of the role of maternal thyroid dysfunction on offspring neurodevelopment in terms of the nature, magnitude, time-specificity, and context-specificity of its effects. With respect to the issue of context specificity, it is possible that maternal stress and stress-related biological processes during pregnancy may modulate maternal thyroid function. The possibility of an interaction between the thyroid and stress systems in the context of fetal brain development has, however, not been addressed to date. We begin this review with a brief overview of TH biology during pregnancy and a summary of the literature on its effect on the developing brain. Next, we consider and discuss whether and how processes related to maternal stress and stress biology may interact with and modify the effects of maternal thyroid function on offspring brain development. We synthesize several research areas and identify important knowledge gaps that may warrant further study. The scientific and public health relevance of this review relates to achieving a better understanding of the timing, mechanisms and contexts of thyroid programing of brain development, with implications for early identification of risk, primary prevention and intervention.

Revisiting the roles of progesterone and allopregnanolone in the nervous system: resurgence of the progesterone receptors

Progesterone is commonly considered as a female reproductive hormone and is well-known for its role in pregnancy. It is less well appreciated that progesterone and its metabolite allopregnanolone are also male hormones, as they are produced in both sexes by the adrenal glands. In addition, they are synthesized within the nervous system. Progesterone and allopregnanolone are associated with adaptation to stress, and increased production of progesterone within the brain may be part of the response of neural cells to injury. Progesterone receptors (PR) are widely distributed throughout the brain, but their study has been mainly limited to the hypothalamus and reproductive functions, and the extra-hypothalamic receptors have been neglected. This lack of information about brain functions of PR is unexpected, as the protective and trophic effects of progesterone are much investigated, and as the therapeutic potential of progesterone as a neuroprotective and promyelinating agent is currently being assessed in clinical trials. The little attention devoted to the brain functions of PR may relate to the widely accepted assumption that non-reproductive actions of progesterone may be mainly mediated by allopregnanolone, which does not bind to PR, but acts as a potent positive modulator of γ-aminobutyric acid type A (GABA(A) receptors. The aim of this review is to critically discuss effects of progesterone on the nervous system via PR, and of allopregnanolone via its modulation of GABA(A) receptors, with main focus on the brain.