Gender differences in the rat corpus callosum: An ultrastructure study

Melamine regulatory assessment for endocrine disruption

Melamine has several domestic and industrial uses as a flame retardant or in the manufacture of melamine-formaldehyde resins. Based on available scientific literature data, the French Agency for Food, Environmental and Occupational Health & Safety (ANSES) included this substance in the list of "chemicals that may present endocrine disruptor (ED) properties", and the substance was prioritized to assess whether it should be classified as an ED in European Union (EU) regulations for hazard identification. This review reports the assessment of melamine based on relevant studies from the registration dossier under REACH, and peer-reviewed literature. Among the various adverse effects, reproductive, neurodevelopmental, and thyroid effects were analyzed in particular, because they could be the consequence of an endocrine disruption. The different modes of action (endocrine or non-endocrine) potentially leading to these effects were scrutinized to understand whether the WHO definition for ED and the criteria for hazard identification were met. It was concluded that the reproductive effect on spermatogenesis was not a consequence of endocrine activity. A biologically plausible link between this effect and endocrine activity was not established, and other modes of action (oxidative stress or altered energy metabolism) could be involved. Similarly, thyroid and neurodevelopmental effects appeared at higher doses than those leading to renal toxicity. Our assessment confirms that melamine is a reprotoxic substance but does not support ED classification. This assessment illustrates the scientific and regulatory challenges in differentiating specific endocrine disruption from an indirect endocrine effect resulting from non-ED mediated systemic toxicity.

Diffusion Tensor Imaging Detects Acute and Subacute Changes in Corpus Callosum in Blast-Induced Traumatic Brain Injury

There is a critical need for understanding the progression of neuropathology in blast-induced traumatic brain injury using valid animal models to develop diagnostic approaches. In the present study, we used diffusion imaging and magnetic resonance (MR) morphometry to characterize axonal injury in white matter structures of the rat brain following a blast applied via blast tube to one side of the brain. Diffusion tensor imaging was performed on acute and subacute phases of pathology from which fractional anisotropy, mean diffusivity, axial diffusivity, and radial diffusivity were calculated for corpus callosum (CC), cingulum bundle, and fimbria. Ventricular volume and CC thickness were measured. Blast-injured rats showed temporally varying bilateral changes in diffusion metrics indicating persistent axonal pathology. Diffusion changes in the CC suggested vasogenic edema secondary to axonal injury in the acute phase. Axonal pathology persisted in the subacute phase marked by cytotoxic edema and demyelination which was confirmed by ultrastructural analysis. The evolution of pathology followed a different pattern in the cingulum bundle: axonal injury and demyelination in the acute phase followed by cytotoxic edema in the subacute phase. Spatially, structures close to midline were most affected. Changes in the genu were greater than in the body and splenium; the caudal cingulum bundle was more affected than the rostral cingulum. Thinning of CC and ventriculomegaly were greater only in the acute phase. Our results reveal the persistent nature of blast-induced axonal pathology and suggest that diffusion imaging may have potential for detecting the temporal evolution of blast injury.