In vitro effect of TNF-alpha and IFN-gamma in retinal cell infection with Toxoplasma gondii.

PURPOSE: Toxoplasma gondii is an intracellular protozoan parasite and the most common cause of infectious uveitis. This study was conducted to evaluate the in vitro effect of tumor necrosis factor (TNF)-alpha and interferon (IFN)-gamma in rat retinal cells infected with T. gondii. METHODS: Rat retinal cells, retinal pigment epithelial (RPE) cells, and retinal Müller glial (RMG) cells were in vitro infected with T. gondii RH strain tachyzoites. Cultured cells were stimulated with various concentrations of TNF-alpha and IFN-gamma. The effect of TNF-alpha and IFN-gamma in T. gondii invasion and replication between retinal cells was determined through two different methods: measuring [(3)H]-uracil incorporation and counting infected cells by microscopic examination. RESULTS: Infection by T. gondii was lesser within RPE cells than within RMG cells. IFN-gamma significantly inhibits [(3)H]-uracil incorporation in RMG and RPE cells (respectively, 35%, 83%, and 87% inhibition at 0.1, 1, and 10 ng/mL for RMG cells and 0%, 30%, and 75% for RPE cells). TNF-alpha significantly inhibits [(3)H]-uracil incorporation in RPE cells (23% and 38% inhibition at 1 and 10 ng/mL), but not in RMG cells. These results were confirmed by confocal microscopic data. The percentage of infected cells decreased from 20% to 7% after IFN-gamma stimulation. CONCLUSIONS: Both cytokines IFN-gamma and TNF-alpha inhibited T. gondii replication in the RPE cells, whereas only IFN-gamma had an anti-Toxoplasma activity within the RMG cells. The differences in cytokine response may be the reason that RPE cells are less efficiently infected by T. gondii than are RMG cells.

Dopaminergic modulation of long-term synaptic plasticity in rat prefrontal neurons.

In rat prefrontal cortex (the prelimbic area of medial frontal cortex), the induction of long-term depression (LTD) and long-term potentiation (LTP) of glutamatergic synapses is powerfully modulated by dopamine. The presence of dopamine in the bathing medium facilitates LTD in slice preparations, whereas in the anesthetized intact brain, dopamine released from dopaminergic axon terminals in the prefrontal cortex facilitates LTP. Dopaminergic facilitation of LTD is at least partly achieved by postsynaptic biochemical mechanisms in which enzymatic processes triggered by dopamine receptor activation cooperate with those triggered by glutamate metabotropic receptor activation. Evidence suggests that dopamine facilitates LTP also in the slice condition. In this case, dopamine receptors must be pre-stimulated ('primed') before the application of high-frequency stimuli in the presence of dopamine. This procedure may mimic baseline stimulation of dopamine receptors that occurs under physiological conditions.

Direct and indirect interactions between cannabinoid CB1 receptor and group II metabotropic glutamate receptor signalling in layer V pyramidal neurons from the rat prefrontal cortex.

At proximal synapses from layer V pyramidal neurons from the rat prefrontal cortex, activation of group II metabotropic glutamate receptors (group II mGlu) by (2S,2'R,3'R)-2-(2',3'-dicarboxycyclopropyl) glycine (DCG IV) induced a long-lasting depression of excitatory postsynaptic currents. Paired-pulse experiments suggested that the depression was expressed presynaptically. Activation of type 1 cannabinoid receptors (CB1) by WIN 55,212-2 occluded the DCG IV-induced depression in a mutually occlusive manner. At the postsynaptic level, WIN 55,212-2 and DCG IV were also occlusive for the activation of extracellular signal-regulated kinase. The postsynaptic localization of active extracellular signal-regulated kinase was confirmed by immunocytochemistry after activation of CB1 receptors. However, phosphorylation of extracellular signal-regulated kinase in layer V pyramidal neurons was dependent on the activation of N-methyl-d-aspartate receptors, consequently to a release of glutamate in the local network. Group II mGlu were also shown to be involved in long-term changes in synaptic plasticity induced by high frequency stimulations. The group II mGlu antagonist (RS)-alpha-methylserine-O-phosphate monophenyl ester (MSOPPE) favoured long-term depression. However, no interaction was found between MSOPPE, WIN 55,212-2 and the CB1 receptor antagonist SR 141716A on the modulation of long-term depression or long-term potentiation and the effects of these drugs were rather additive. We suggest that CB1 receptor and group II mGlu signalling may interact through a presynaptic mechanism in the induction of a DCG IV-induced depression. Postsynaptically, an indirect interaction occurs for activation of extracellular signal-regulated kinase. However, none of these interactions seem to play a role in synaptic plasticities induced with high frequency stimulations.