Ultrasonic-induced tonic convulsion in rats after subchronic exposure to perfluorooctane sulfonate (PFOS).

Perfluorooctane sulfonate (PFOS) is one of the persistent organic pollutants distributed widely in the global environment. We have found that a single oral administration of PFOS induced tonic convulsion in mice and rats when a brief ultrasonic stimulus was applied to the animals. The aim of this study is to examine whether the neurotoxicity is caused by subchronic dietary exposure to PFOS. Rats were treated with dietary PFOS at 0, 2, 8, 32 and 128 ppm for 13 weeks. Animals were carefully observed for pharmacotoxic signs and responses to the ultrasonic stimulus applied biweekly. PFOS increased liver weight and decreased food consumption and body weight. PFOS concentrations in the serum, brain, liver and kidney were increased almost proportional to its total dose, although the ratios of PFOS concentrations in tissues to total doses in the group treated with the highest concentration were a little lower. The ranges of relative concentrations in the brain, liver and kidney to serum concentration were 0.13 to 0.24, 2.7 to 6.3 and 0.82 to 1.6, respectively. PFOS alone did not cause any neurotoxic symptoms; however, 5 rats out of 6 showed tonic convulsion in the 6th week when ultrasonic stimulus was applied to the 128 ppm rats with the total PFOS dose of 338 mg/kg. The ultrasonic stimulus did not cause convulsion in the other groups. Histopathological examination including electron microscopic examination could not detect any abnormality in the brain. Because the acute oral dose of PFOS causing the convulsion was 250 mg/kg (Sato et al., 2009), the convulsion induced by PFOS seemed to depend on its total dose regardless of treatment schedule.

Neurotoxicity of perfluorooctane sulfonate (PFOS) in rats and mice after single oral exposure.

Perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA) are widely used in industrial fields and consumer products, and are ubiquitously found in the environment and animal tissues. In the present study, their neurotoxicity was examined using rats and mice by means of neurobehavioral observation, histopathological inspection and chemical assays. PFOS and PFOA alone did not cause any neurotoxic symptoms up to their sublethal doses (PFOS: 500 mg/kg, PFOA: 1,000 mg/kg). However, tonic convulsions were caused in the PFOS-treated rats (> or = 250 mg/kg) and mice (> or = 125 mg/kg) when ultrasonic stimulus was applied to the animals. The same ultrasonic stimulus never induced convulsions in the control animals and in the animals treated with PFOA. Concentration of PFOS in the brain was considerably lower than in other tissue, but it seemed to increase gradually with time after exposure. No morphological changes were detected by histopathological examination of the brain. There were also no changes in concentrations of norepinephrine, dopamine, serotonin, glycine, 4-aminobutylic acid and glutamic acid in the brain. The present study revealed neurotoxic effects of PFOS in animals. Convulsive effect of PFOS may not be attributed to the quantitative alterations of neurotransmitters or lesions of nerve cells in the brain, although the mechanism of its neurotoxicity has not been cleared.

The tyrosinase-encoding gene of Lentinula edodes, Letyr, is abundantly expressed in the gills of the fruit-body during post-harvest preservation.

The gill browning of Lentinula edodes fruit-bodies during preservation is thought to be due to melanin biosynthesis catalyzed by tyrosinase. We isolated a genomic DNA sequence and cDNA encoding a putative tyrosinase from the white rot basidiomycete Lentinula edodes (shiitake mushroom). The gene, named Letyr, consists of a 1,854-bp open reading frame interrupted by eight introns, and encodes a putative protein of 618 amino acid residues with an estimated molecular mass of 68 kDa. Amino acid residues known to be involved in copper-binding domains were conserved in the deduced amino acid residues of LeTyr. Transcriptional and translational expression of Letyr in the gills of the fruit-body increased during preservation after harvest. This correlation between Letyr expression and fruit-body preservation suggests that tyrosinase gene expression contributes to gill browning.

Nonlinear rheology of surfactant wormlike micelles bridged by telechelic polymers.

We have investigated the nonlinear rheology of a soft composite transient network made of a solution of surfactant wormlike micelles (WM) in the semidilute regime that are reversibly bridged by telechelic polymers. The samples are well described, in the linear regime, as two Maxwell fluids components blends, characterized by two markedly different characteristic times. The slow mode is mainly related to the transient network of entangled WM, and the fast mode to the network of telechelic chains. In this paper we investigate the nonlinear viscoelasticity and show that the nonlinear behavior reflects as well the behavior of two coupled networks. On one hand, stress relaxation experiments and time-resolved stress response following the application of a constant shear rate show that, in the weakly nonlinear regime, these novel composite networks stiffen. A fourfold increase of the elastic modulus with respect to the linear value is reached for strain amplitude of about 200%. This strain hardening is due to the nonlinear stretching of the telechelic polymer chains. On the other hand, the samples exhibit shear banding in the highly nonlinear regime, similarly to pure semidilute solutions of WM.

Lamellar to micelle transition of nonionic surfactant assemblies induced by addition of colloidal particles.

We have investigated the entropic interactions between lamellar membranes and spherical colloidal particles using a small-angle neutron scattering (SANS) technique. By adding colloidal particles between lamellar sheets, the first lamellar peaks in SANS profiles become intense and the second and higher order Bragg peaks begin to appear, indicating that the membrane fluctuations are suppressed by the colloidal particles. We estimate the interlamellar interaction potential in the presence of the colloidal particles from the layer compressibility obtained by the SANS profile analysis and propose a phenomenological free energy model based on the restriction of membrane fluctuations. By further addition of the colloidal particles, the lamellar membranes transform to prolate micelles. In order to release the strong frustration due to the restriction of membrane fluctuations, the surfactant assemblies change the morphology from the two dimensional sheets to the one dimensional prolate micelles.