Monosodium glutamate induced convulsions in rats: Influence of route of administration, temperature and age

The Role of Glycogen Synthase Kinase-3β in the Zinc-Mediated Neuroprotective Effect of Metformin in Rats with Glutamate Neurotoxicity

Metformin has been suggested to have protective effects on the central nervous system, but the mechanism is unknown. The similarity between the effects of metformin and the inhibition of glycogen synthase kinase (GSK)-3β suggests that metformin may inhibit GSK-3β. In addition, zinc is an important element that inhibits GSK-3β by phosphorylation. In this study, we investigated whether the effects of metformin on neuroprotection and neuronal survival were mediated by zinc-dependent inhibition of GSK-3β in rats with glutamate-induced neurotoxicity. Forty adult male rats were divided into 5 groups: control, glutamate, metformin + glutamate, zinc deficiency + glutamate, and zinc deficiency + metformin + glutamate. Zinc deficiency was induced with a zinc-poor pellet. Metformin was orally administered for 35 days. D-glutamic acid was intraperitoneally administered on the 35th day. On the 38th day, neurodegeneration was examined histopathologically, and the effects on neuronal protection and survival were evaluated via intracellular S-100β immunohistochemical staining. The findings were examined in relation to nonphosphorylated (active) GSK-3β levels and oxidative stress parameters in brain tissue and blood. Neurodegeneration was increased (p < 0.05) in rats fed a zinc-deficient diet. Active GSK-3β levels were increased in groups with neurodegeneration (p < 0.01). Decreased neurodegeneration, increased neuronal survival (p < 0.01), decreased active GSK-3β (p < 0.01) levels and oxidative stress parameters, and increased antioxidant parameters were observed in groups treated with metformin (p < 0.01). Metformin had fewer protective effects on rats fed a zinc-deficient diet. Metformin may exert neuroprotective effects and increase S-100β-mediated neuronal survival by zinc-dependent inhibition of GSK-3β during glutamate neurotoxicity.

Ontogenetic differences in convulsive action and cerebral uptake of uremic guanidino compounds in juvenile mice

Guanidinosuccinate (GSA) and methylguanidine (MG) are endogenous, convulsant guanidino compounds which have been shown to be greatly increased in uremic patients. In the present study, we have investigated the age-related differences in convulsive action and cerebral uptake of these compounds in juvenile mice of 7, 14 and 21 days old. An age-dependent decrease was apparent in the severity of the GSA- and MG-induced convulsions and toxicity. Mean latency for the appearance of clonic convulsions increased with increasing age. Two hours following the i.p. injection of GSA or MG in a dose of 250 mg/kg, the resulting brain concentration decreased with increasing age of the animals. This effect was more pronounced in the case of MG. Neither for GSA, nor for MG was this age-dependent effect apparent after 30 min. GSA and MG serum as well as brain concentrations were lower in 21-day-old mice than in 7-day-old ones. However, the brain/serum concentration ratios of GSA and of MG were significantly lower in 21-day-old mice than in 7-day-old ones, indicating that at least part of the difference in brain level can be explained by higher permeability of the immature blood-brain barrier to these uremic guanidino compounds. In addition, brain/serum ratios of GSA in mice of 7 days old and in mice of 21 days old were significantly lower than the ratios of MG in these age groups, indicative of lower overall blood-brain barrier permeability to GSA than to MG.(ABSTRACT TRUNCATED AT 250 WORDS)