The Calcineurin Inhibitor Ascomicin Interferes with the Early Stage of the Epileptogenic Process Induced by Latrunculin A Microperfusion in Rat Hippocampus

Abstract

Latrunculin A microperfusion in rat hippocampus has shown to be an effective model of acute and chronic seizures for neurochemical studies. The intervention over early synaptic plasticity changes after the epileptogenesis onset represents a big challenge on the design of a suitable therapy to impair the epilepsy development. We previously suggested that receptor location might be essential for controlling neuronal excitability, and that disruption of local cytoskeletal dynamics followed by drastic changes in the synaptic/extrasynaptic ratio of NMDA, AMPA receptors and their subsequent downstream signalling may play an important role in the pathogenesis of seizures. In the present study, we performed a pharmacological intervention in the Latrunculin model by using Ascomicin (ASC) and Phenytoin (PHT). We pointed out the inhibitory action of ASC over the protein phosphatase 2B (PP2B). PP2B pathological mechanism involves changes in actin cytoskeleton and showed to avoid those subsequent changes previously observed in PSD components. On the contrary, PHT didn't seem to modify the F-actin depolymerization process induced, showing a similar redistribution pattern from the PSD towards the extrasynaptic site of several molecular components with more or less dependence on actin for their location, including glutamate receptors. Overall, we propose that the early intervention over changes on the synapse during the epileptogenic process might represent the best approach to avoid the onset of chronic refractory seizures our model. On this regard, the therapeutic potential of ASC, FK506 and derivatives should be further explored as a possible tool in the intervention over epilepsy and other brain diseases.

Partial seizures induced by latrunculin A microperfusion in the mouse hippocampus: Role of extracellular glutamate and NMDA receptors

“…These results are consistent with our observations in rats. [27] Taken together with the effect of the increase in extracellular glutamate concentrations on latrunculin A pre-treated mice reported here and the previously reported results in rats [20] , they suggest that actin depolymerization might be not only a consequence but also a cause of epileptic seizures.…”

“…[9] Alterations in several actin-related proteins, such as acidic calponin [29] and calpain [30] have been linked to epileptic seizures in different experimental models. We have recently shown that latrunculin A microperfusion has a significant effect on components of the MAPK signaling pathways such as ERK 1/2 and pp38 [27] . Substantial evidence suggests the involvement of actin cytoskeleton in the excitability upregulation of postsynaptic neurons resulting from an increase in glutamate excitatory action [31] .…”

Molecular Targets on Antiepileptogenic Therapy Research: Deconstructing the Network for Translational Purposes

“…22 The beneficial effect of the introduction, as part of some refractory epilepsy therapies, of compounds like corticosteroids, immunoglobulins and monoclonal antibodies (Rituximab, Efalizumab and Natalizumab) or immunosupressors (Cyclosporine A, Tacrolimus and Rapamycin), confirms the important influence on epileptogenesis of this associated processes and thus postulating new molecular targets on the initiated immune/inflammatory cascades. 19,24,29 On the other hand, it is well known that glial cells play an important role in generating seizures by modulating synaptic transmission and, in the long term, contributing to the epileptic process by inducing inflammatory milieu around neurons. Particularly, astrocytes and microglia, are considered key players on initiating this inflammatory response after a brain insult.…”

“…This accumulation of glutamate in extracellular areas, in addition to the previously described changes on expression and redistribution pattern of excitatory glutamate receptors to the extrasynaptic compartment on the cell membrane, would facilitate the synchronization of hyperexcitable networks as the main consequence of brain circuitry rearrangement after the epileptogenic insult. 8,19 On the same line, Neuropeptides are signaling molecules participating in the modulation of synaptic transmission. These peptides are released after neural excitation in the extracellular space and exert their action on G-protein coupled receptors pre and postsynaptically.…”

“…On this regard, not only molecular targets like ion channels, [10][11][12] Glutamate AMPA and NMDA and GABA receptors [13][14][15][16] but also key proteins responsible for postsynaptic structure rearrangement after brain injury are been focus of study. Some examples include: cytoskeletal proteins, like F-actin; 17,18 accessory proteins for receptor and vesicle trafficking, like Stargazing and Synaptin; 9,17,19 Scaffold proteins like PSD-95, Kalirin-7/Trio among others. 20,21 In addition, at the intracellular level, there are also been reported elements responsible for postsynaptic cell transduction pathways taking part on the epileptogenesis mechanism highlighting the ERK/MAP kinase cascade and the activation of CREB-based gene expression.…”