A role for Src kinase in spontaneous epileptiform activity in the CA3 region of the hippocampus

Abstract

Members of the Src family of nonreceptor protein tyrosine kinases (PTKs) have been implicated in the regulation of cellular excitability and synaptic plasticity. We have investigated the role of these PTKs in in vitro models of epileptiform activity. Spontaneous epileptiform discharges were induced in vitro in the CA3 region of rat hippocampal slices by superfusion with the potassium channel blocker 4-aminopyridine in Mg 2؉ -free medium. In hippocampal slices treated in this fashion, Src kinase activity was increased and the frequency of epileptiform discharges could be greatly reduced by inhibitor of the Src family of PTKs, 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo T he epilepsies are heterogeneous disorders characterized by recurrent synchronous discharges of large neuronal populations. Prominent features of the natural history of these pathologies are functional changes leading to the development of areas of low seizure threshold (epileptic foci) and the evolution toward more pervasive and malignant forms. In the present study, we investigated the role of nonreceptor protein tyrosine kinases (PTKs) of the Src family in the generation of spontaneous epileptiform activity in the CA3 region of rat hippocampal slices. Members of this family of PTKs are expressed in the central nervous system and have been implicated in the regulation of glutamate N-methyl-D-aspartate (NMDA) receptors, affecting in turn neural excitability and plasticity (1-3). In fact, phosphorylation of certain NMDA NR2 subunits by Src and the related nonreceptor PTK Fyn has been shown to increase NMDA receptor channel activity (1, 4). Enhanced NMDA responses have been observed in the kindling model of epilepsy (5-8) and in human epilepsy (9). Activation of Src also induces potentiation of non-NMDA glutamate receptor responses in an NMDAand Ca 2ϩ -dependent manner (1). Observations with mice in which Fyn was either genetically deleted or overexpressed also support a role for Src-family PTKs in the induction of kindling (10, 11), a process in which NMDA receptors have been shown to play a critical role (12, 13).Depletion of extracellular Mg 2ϩ from hippocampal slices results in enhancement of synaptically evoked responses in CA1 and CA3 and the appearance of spontaneous paroxysmal depolarization shifts in both areas (5, 14-16), whereas 4-aminopyridine (4-AP) induces epileptiform activity by enhancing the release of excitatory and inhibitory amino acids (17-19). We induced epileptiform activity in rat hippocampal slices with Mg 2ϩ -free medium in the presence of the potassium channel blocker 4-AP, a model of epileptogenesis previously used in neocortical slice preparations (17).Application of Mg 2ϩ -free medium and 4-AP induced robust bursting in the CA3. Src kinase activity was induced in such a model, and spontaneous epileptiform activity could be strongly reduced by the Src-family PTK inhibitor (4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo [3,4-d]pyrimidine (PP2) also known as AG 1879 (20). In some experiments, hippocampal slices were tr...

Unique domain anchoring of Src to synaptic NMDA receptors via the mitochondrial protein NADH dehydrogenase subunit 2

“…LTP at Schaffer collateral-CA1 synapses is the prototypic example of NMDAR-dependent enhancement of excitatory synaptic transmission observed at numerous types of glutamatergic synapses throughout the CNS (48). In addition, Src is implicated in NMDAR-dependent seizures (49), chronic pain (50), and neurotoxicity (51). Thus, our discovery of the Src-ND2 interaction at NMDARs defines a protein-protein interaction of general relevance to regulation of neuronal function, synaptic plasticity, and pathophysiology in the CNS.…”

Extracellular Signal-Regulated Kinase 1/2 Is Required for the Induction of Group I Metabotropic Glutamate Receptor-Mediated Epileptiform Discharges

“…In addition, it has been shown that inhibition of the ERK1/2 pathway attenuates the frequency and duration of epileptiform discharges (Murray et al, 1998;Sanna et al, 2000). However, available data also suggested that the suppression of ERK1/2 activities in the pilocarpine-model of epilepsy did not prevent seizures (Berkeley et al, 2002).…”

Tyrosine phosphorylation of synapsin I by Src regulates synaptic-vesicle trafficking

“…High-frequency synaptic stimulation, epileptiform activity and spatial learning trials activate Src kinases and promote their association with interacting and/or substrate proteins, including synapsin I (Lauri et al, 2000;Sanna et al, 2000;Zhao et al, 2000). Moreover, studies using specific Src inhibitors indicate that Src-family kinases directly modulate neurotransmitter release by interfering with activity-dependent Ca 2+ entry, actin dynamics and SV exocytosis.…”