Peripheral T cells from multiple sclerosis patients trigger synaptotoxic alterations in central neurons.

AIMS: The crucial step in the pathogenic events that lead to the development and the progression of multiple sclerosis (MS) is the infiltration of autoreactive T cells in the brain. Data from experimental autoimmune encephalomyelitis (EAE) mice indicate that, together with microglia, T cells are responsible for the enhancement of the glutamatergic transmission in central neurons, contributing to glutamate-mediated excitotoxicity, a pathological hallmark of both EAE and MS brains. Here, we addressed the synaptic role of T cells taken from MS patients. METHODS: A chimeric model of human T cells and murine brain slices was established to record, by Patch Clamp technique, the glutamatergic transmission in the presence of T cells isolated from the peripheral blood of healthy subjects (HS), active (a) and nonactive (na) relapsing remitting MS patients. Intracellular staining and flow cytometry were used to assess tumour necrosis factor (TNF) expression in T cells. RESULTS: Chimeric experiments indicated that, compared to HS and naMS, T cells from aMS induced an increase in glutamatergic kinetic properties of striatal neurons. Such alteration, reminiscent of the those induced by EAE T cells, was blocked by incubation of the slices with etanercept, a TNF receptor antagonist. Of note, T cells from aMS expressed more TNF than naMS patients and HS subjects. CONCLUSION: These data highlight the synaptotoxic potential retained by MS T cells, suggesting that during the inflammatory phase of the disease infiltrating T cells could influence the neuronal activity contributing to the TNF-mediated mechanisms of glutamate excitotoxicity in central neurons.

A novel crosstalk within the endocannabinoid system controls GABA transmission in the striatum.

The N-palmitoylethanolamine (PEA) is an endogenous member of the endocannabinoid system (ECS) with several biological functions, including a neuromodulatory activity in the central nervous system. To shed light on the neuronal function of PEA, we investigated its involvement in the control of both excitatory and inhibitory transmission in the murine striatum, a brain region strongly modulated by the ECS. By means of electrophysiological recordings, we showed that PEA modulates inhibitory synaptic transmission, through activation of GPR55 receptors, promoting a transient increase of GABAergic spontaneous inhibitory postsynaptic current (sIPSC) frequency. The subsequently rundown effect on sIPSC frequency was secondary to the delayed stimulation of presynaptic cannabinoid CB1 receptors (CB1Rs) by the endocannabinoid 2-AG, whose synthesis was stimulated by PEA on postsynaptic neurons. Our results indicate that PEA, acting on GPR55, enhances GABA transmission in the striatum, and triggers a parallel synthesis of 2-AG at the postsynaptic site, that in turn acts in a retrograde manner to inhibit GABA release through the stimulation of presynaptic CB1Rs. This electrophysiological study identifies a previously unrecognized function of PEA and of GPR55, demonstrating that GABAergic transmission is under the control of this compound and revealing that PEA modulates the release of the endocannabinoid 2-AG.

Electrophysiological and amperometric evidence that modafinil blocks the dopamine uptake transporter to induce behavioral activation.

Although the wake-promoting drug modafinil has been shown to bind quite exclusively to the dopamine transporter (DAT), its action in the brain has been thought to be partially independent from the facilitation of the dopaminergic signals. Here we used electrophysiological and amperometric techniques to investigate the effects of modafinil on the dopaminergic neurons of the substantia nigra pars compacta (SNpc) and on the synaptic overflow of dopamine in the dorsal striatum from the sliced tissue of wild-type and cocaine-insensitive genetically modified mice (DAT-CI). Moreover, we examined the consequences of modafinil administration on the locomotor behavior of wild-type and DAT-CI mice. In in vitro experiments, modafinil inhibited the spontaneous firing discharge of the dopaminergic neurons. More consistently, it potentiated firing inhibition and the membrane responses caused by exogenously applied dopamine on these cells. Furthermore, it augmented the stimulus-evoked outflow of DA in the striatum. Noteworthy, modafinil caused locomotor activation in wild-type mice. On the other hand, neither the electrophysiological nor the behavioral effects of modafinil were detected in DAT-CI animals. These results demonstrate that modafinil potentiates brain dopaminergic signals via DAT inhibition by acting at the same binding site of cocaine. Therefore, this mechanism of action explains most of the pharmacological properties of this compound in the clinical setting.