Assessment of sublethal ecotoxicity of solvents on larvae of a model native amphibian (Lithobates pipiens).

Carrier solvents are used frequently in toxicity testing to assist hydrophobic chemicals into solution, but such solvents may have toxic effects on test subjects. Amphibians are model organisms in toxicity studies; however, little is known about the direct effects of solvents on native amphibians. Following modifications to standardized guidelines for native species, we used acute 96-hour exposures to assess the direct effects of three common solvents on survival, differences in morphology and occurrence of abnormalities of northern leopard frog larvae (Lithobates pipiens). The solvents, dimethyl sulfoxide (DMSO), ethanol (ETOH) and acetone (ACE) were used at nominal concentrations ranging from 1 to 100 µL/L. We also conducted a 30-day exposure to assess the direct chronic effects of DMSO at 1 and 5 µL/L, on larval growth, development and sex differentiation, but found no effects. Acute exposure to solvents also had no effect on the survival of larvae, but we found significant abnormalities in tadpoles acutely exposed to 100 µL/L ACE. Acute exposure to DMSO and ETOH had further concentration-dependent effects on larval morphological traits. Our study suggests that DMSO and ETOH at ≤20 µL/L may be used as solvents in amphibian ecotoxicological studies, but ACE should be limited to ≤50 µL/L in ecotoxicity studies and perhaps much less (≤10 µL/L) in studies with other amphibians, based on a review of existing literature. We emphasize pilot studies when using solvents on acute and chronic ecotoxicity tests, using native amphibians.

Naphthenic Acid Mixtures and Acid-Extractable Organics from Oil Sands Process-Affected Water Impair Embryonic Development of Silurana (Xenopus) tropicalis.

Naphthenic acids (NAs) are carboxylic acids naturally occurring in crude oils and bitumen and are suspected to be the primary toxic substances in wastewaters associated with oil refineries and mining of oil sands. Oil sands process-affected water (OSPW) generated by the extraction of bitumen from oil sands are a major source of NAs and are currently stored in tailings ponds. We report on the acute lethality and teratogenic effects of aquatic exposure of Silurana (Xenopus) tropicalis embryos to commercial NA extracts and from the acid extractable organics (AEOs) fraction of a Canadian OSPW. Using electrospray ionization-high resolution mass spectrometry, we determined that the O2 species proportion were 98.8, 98.9 and 58.6% for commercial mixtures Sigma 1 (S1M) and Sigma 2 (S2M), and AEOs, respectively. The 96h LC50 estimates were 10.4, 11.7, and 52.3 mg/L for S1M, S2M, and the AEOs, respectively. The 96h EC50 estimates based on frequencies of developmental abnormalities were 2.1, 2.6, and 14.2 mg/L for S1M, S2M, and the AEOs, respectively. The main effects observed were reduced body size, edema, and cranial, heart, gut and ocular abnormalities. Increasing concentrations of the mixtures resulted in increased severity and frequency of abnormalities ( p < 0.05). The rank-order potency was S1M > S2M > AEO based on LC50 and EC50 estimates. These data provide insight into the effects NAs in amphibian embryos and can contribute to the development of environmental guidelines for the management of OSPW.

Dopamine D1 receptor activation regulates the expression of the estrogen synthesis gene aromatase B in radial glial cells.

Radial glial cells (RGCs) are abundant stem-like non-neuronal progenitors that are important for adult neurogenesis and brain repair, yet little is known about their regulation by neurotransmitters. Here we provide evidence for neuronal-glial interactions via a novel role for dopamine to stimulate RGC function. Goldfish were chosen as the model organism due to the abundance of RGCs and regenerative abilities of the adult central nervous system. A close anatomical relationship was observed between tyrosine hydroxylase-positive catecholaminergic cell bodies and axons and dopamine-D1 receptor expressing RGCs along the ventricular surface of telencephalon, a site of active neurogenesis. A primary cell culture model was established and immunofluorescence analysis indicates that in vitro RGCs from female goldfish retain their major characteristics in vivo, including expression of glial fibrillary acidic protein and brain lipid binding protein. The estrogen synthesis enzyme aromatase B is exclusively found in RGCs, but this is lost as cells differentiate to neurons and other glial types in adult teleost brain. Pharmacological experiments using the cultured RGCs established that specific activation of dopamine D1 receptors up-regulates aromatase B mRNA through a cyclic adenosine monophosphate-dependent molecular mechanism. These data indicate that dopamine enhances the steroidogenic function of this neuronal progenitor cell.