Effects of perinatal lipopolysaccharide (LPS) exposure on the developing rat brain; modeling the effect of maternal infection on the developing human CNS.

In the present study, we examined the effect of perinatal Escherichia coli lipopolysaccharide (LPS) exposure on the developing rat cerebellum and tested the hypothesis that maternal infections impact brain structure and function by mechanisms involving increase in oxidative stress and changes in brain type 2 iodothyronine deiodinase (D2)- and thyroid hormone (TH)-responsive genes. Spontaneously hypertensive rat (SHR) and Sprague-Dawley (SD) rat dams were challenged with LPS (200 µg/kg body weight) exposure during pregnancy (G10-G15) and lactation (P5-P10), the time periods corresponding, respectively, to the first/second and the third trimesters of human pregnancy. LPS exposure resulted in a significantly decreased motor learning in SD male (29.8 %) and in female (55.0 %) pups (p < 0.05); changes in rollover and startle response showed only a trend. The LPS challenge also resulted in a trend (p = 0.09) toward increased cerebellar levels of the oxidative stress marker 3-nitrotyrosine (3-NT) in SD male (16.2 %) and female (21.2 %) neonates, while 3-NT levels were significantly decreased (p < 0.05) in SHR female pups. D2 activity, responsible for local intra-brain conversion of thyroxine (T4) to the active hormone, 3',3,5-triiodothyronine (T3), was significantly (p < 0.05) decreased in LPS-challenged SHR male (40.3 %) and SD female (47.4 %) pups. Several genes were affected by LPS. Notably, D2 (DIO2) and brain-derived neurotrophic factor (BDNF) were significantly elevated in SHR females, while transthyretin (TTR) expression was decreased in both SD males and females (P < 0.05). In vitro chronic exposure of cerebellar cultures to LPS resulted in decreased arborization of Purkinje cells while D2 was only increased transiently. Our data demonstrate that perinatal LPS exposure impacts the developing cerebellum in strain- and sex-dependent manner via complex mechanisms that involve changes in oxidative stress, enzymes involved in maintaining local TH homeostasis, and downstream gene expression.

Sex-dependent changes in cerebellar thyroid hormone-dependent gene expression following perinatal exposure to thimerosal in rats.

Mammalian brain development is regulated by the action of thyroid hormone (TH) on target genes. We have previously shown that the perinatal exposure to thimerosal (TM, metabolized to ethylmercury) exerts neurotoxic effects on the developing cerebellum and is associated with a decrease in cerebellar D2 activity, which could result in local brain T3 deficiency. We have also begun to examine TM effect on gene expression. The objective of this study was to expand on our initial observation of altered cerebellar gene expression following perinatal TM exposure and to examine additional genes that include both TH-dependent as well as other genes critical for cerebellar development in male and female neonates exposed perinatally (G10-G15 and P5 to P10) to TM. We report here for the first time that expression of suppressor-of-white-apricot-1 (SWAP-1), a gene negatively regulated by T3, was increased in TM-exposed males (61.1% increase), but not in females; (p<0.05). Positively regulated T3-target genes, Purkinje cell protein 2 (Pcp2; p=0.07) and Forkhead box protein P4 (FoxP4; p=0.08), showed a trend towards decreased expression in TM-exposed males. The expression of deiodinase 2 (DIO2) showed a trend towards an increase in TM-exposed females, while deiodinase 3 (DIO3), transthyretin (TTR), brain derived neurotrophic factor (BDNF) and reelin (RELN) was not significantly altered in either sex. Since regulation of gene splicing is vital to neuronal proliferation and differentiation, altered expression of SWAP-1 may exert wide ranging effects on multiple genes involved in the regulation of cerebellar development. We have previously identified activation of another TH-dependent gene, outer dense fiber of sperm tails 4, in the TM exposed male pups. Together, these results also show sex-dependent differences between the toxic impacts of TM in males and females. Interestingly, the genes that were activated by TM are negatively regulated by TH, supporting our hypothesis of local brain hypothyroidism being induced by TM and suggesting a novel mechanism of action TM in the developing brain.

Maternal thimerosal exposure results in aberrant cerebellar oxidative stress, thyroid hormone metabolism, and motor behavior in rat pups; sex- and strain-dependent effects.

Methylmercury (Met-Hg) and ethylmercury (Et-Hg) are powerful toxicants with a range of harmful neurological effects in humans and animals. While Met-Hg is a recognized trigger of oxidative stress and an endocrine disruptor impacting neurodevelopment, the developmental neurotoxicity of Et-Hg, a metabolite of thimerosal (TM), has not been explored. We hypothesized that TM exposure during the perinatal period impairs central nervous system development, and specifically the cerebellum, by the mechanism involving oxidative stress. To test this, spontaneously hypertensive rats (SHR) or Sprague-Dawley (SD) rat dams were exposed to TM (200 µg/kg body weight) during pregnancy (G10-G15) and lactation (P5-P10). Male and female neonates were evaluated for auditory and motor function; cerebella were analyzed for oxidative stress and thyroid metabolism. TM exposure resulted in a delayed startle response in SD neonates and decreased motor learning in SHR male (22.6%), in SD male (29.8%), and in SD female (55.0%) neonates. TM exposure also resulted in a significant increase in cerebellar levels of the oxidative stress marker 3-nitrotyrosine in SHR female (35.1%) and SD male (14.0%) neonates. The activity of cerebellar type 2 deiodinase, responsible for local intra-brain conversion of thyroxine to the active hormone, 3',3,5-triiodothyronine (T3), was significantly decreased in TM-exposed SHR male (60.9%) pups. This coincided with an increased (47.0%) expression of a gene negatively regulated by T3, Odf4 suggesting local intracerebellar T3 deficiency. Our data thus demonstrate a negative neurodevelopmental impact of perinatal TM exposure which appears to be both strain- and sex-dependent.