MIN6 is one of the few pancreatic ␤ cell lines that respond to physiological concentrations of glucose by secreting insulin, and little is known about the triggered molecular mechanisms. We report below that the response to glucose in the MIN6 cells includes an activation of the p42 and p44 mitogen-activated protein (MAP) kinases (ERK2 and ERK1). This activation also occurred with the antidiabetic sulfonylurea glibenclamide and kainate, a specific agonist of a subtype of the ionotropic glutamate receptors, which depolarize the cytoplasmic membrane. The requirement for a calcium entry through the L-type voltage-gated channels and other characteristics of the regulation of the MAP kinase activity, such as the effect of the elevation of the cAMP concentration by forskolin, were similar to those of the secretion of insulin. However, the activation of the MAP kinases is not required for the secretion of insulin, inasmuch as this effect of glucose was not abolished when the MAP kinases were prevented from activation by PD098059, an inhibitor of the MAP kinase kinase. However, as the MAP kinases were translocated into the nucleus, they might be implicated in the calcium-dependent transcriptional response of the cells to glucose and thus regulate the expression of the insulin gene.

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Infection by Toxoplasma gondii is asymptomatic, leading to an immune response that controls the disease. In immune-compromised patients, however, quiescent cysts can reactivate, leading to toxoplasmic encephalitis. We studied the infection of cells of the central nervous system in an attempt to understand the process leading to this complication. Primary cultures of rat hippocampal glial cells and neurons were infected with the virulent strain RH and examined by immunofluorescent microscopy after fixation of cells and staining with antibodies specific to the different cell types. After 24 h of infection, glial cells were highly infected and showed active division of the parasite. Neurons, on the other hand, were much less efficiently infected than glial cells, but actual penetration of the parasites was demonstrated by confocal microscopy. Whereas glial cells contained vacuoles with several parasites, the vacuoles observed in neurons usually contained one parasite or, rarely, two, indicating that the parasites inside neurons did not undergo active division. This was corroborated by determination of the incorporation of [3H]-uracil. Little is known about the mechanism of neuronal infection by Toxoplasma. The experimental setup used in this study should help to improve our understanding of neuronal infection and bring insight into the physiopathology of toxoplasmic encephalitis.

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