Neurotoxic effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin in cerebellar granule cells

An environmental pollutant, tetrachloro dibenzo dioxin (TCDD) is known to illicit the cognitive disability and motor dysfunction in the developing brain. TCDD induced effects leading to neurodevelopmental and neurobehavioral deficit may have been defined, however underlying molecular mechanism and possible intracellular targets remain to be elucidated. In this study, we attempted to analyze TCDD-induced neurotoxic effects in the granule cells from cerebellum where certain cognitive abilities and motor function command are known to be excuted. [3H]PDBu, (phorbol 12,13-dibutyrate) binding assay indicated that TCDD induced a dose-dependent increase of total PKC activity and its induction was the aryl hydrocarbon receptor (AhR) dependent and N-methyl-D-aspartate receptor (NMDAR) independent. TCDD also caused the translocation of both PKC-alpha and -epsilon in a dose-dependent manner but associated with different receptors; PKC-alpha via AhR but not PKC-epsilon indicating an isozyme-specific pattern of the induction. Increase of the ROS formation was also observed in the cells treated with TCDD in a dose-dependent and an AhR-dependent manner. The treatment of the cells with the diamino dicyano-bis(2-aminophenylthio) butadiene (U0126, MEK-1/2 inhibitor), dizocilpine maleate (MK-801, non-competitive N-methyl-D-aspartate glutamate receptor antagonist) and vitamin E attenuated the TCDD-induced ROS production indicating that TCDD-induced ROS formation may be associated with activation of ERK-1/2 in the MAP kinase pathway or the NMDA receptor. TCDD also increased [Ca2+]i, which is associated with ROS formation and PKC activation in the cerebellar granule cells. It is suggested that TCDD activates the NMDA receptor, which may induce a sustained increase of [Ca2+]i in neurons followed by the ROS formation. Our findings may contribute to understanding the mechanism of TCDD-related neurotoxicity, thereby improving the health risk assessment of neurotoxic compounds in humans.

STUDIES ON THE RELATION BETWEEN INHIBITORY EFFECT OF MYELIN MEMBRANE PROTEINS ON NEURITE OUTGROWTH AND cAMP LEVELS IN NEURONS / 解剖学报

Objective To study the relationship between the inhibitory effects that myelin membrane proteins exerted on nerve regeneration and the changes of intracellular cAMP levels in neurons. Methods To observe the effects of myelin membrane proteins extracted from central nervous system(CNS) by density centrifugation on the outgrowth of neurite of cerebella granule cells in culture and detect the changes of intracellular cAMP levels of the neurons with radioimmunoassay. Results 1^Myelin membrane proteins of CNS inhibited neurite outgrowth of cultured cerebella granule cells. 2^The cAMP level in neurons decreased in 5 minutes after contacting myelin membrane proteins and reached to the lowest level in 12 hours of contacting. Conclusion The inhibitory effects of myelin membrane proteins on the outgrowth of neurites may be related to the inhibitory factors which cause the decrease of cAMP level in neuron through the passway of signal transduction pathway. [