Tuberous sclerosis complex (TSC), caused by dominant mutations in either TSC1 or TSC2 tumour suppressor genes is characterized by the presence of brain malformations, the cortical tubers that are thought to contribute to the generation of pharmacoresistant epilepsy. Here we report that tuberless heterozygote Tsc1(+/-) mice show functional upregulation of cortical GluN2C-containing N-methyl-D-aspartate receptors (NMDARs) in an mTOR-dependent manner and exhibit recurrent, unprovoked seizures during early postnatal life (<P19). Seizures are generated intracortically in the granular layer of the neocortex. Slow kinetics of aberrant GluN2C-mediated currents in spiny stellate cells promotes excessive temporal integration of persistent NMDAR-mediated recurrent excitation and seizure generation. Accordingly, specific GluN2C/D antagonists block seizures in Tsc1(+/-) mice in vivo and in vitro. Likewise, GluN2C expression is upregulated in TSC human surgical resections, and a GluN2C/D antagonist reduces paroxysmal hyperexcitability. Thus, GluN2C receptor constitutes a promising molecular target to treat epilepsy in TSC patients.

Altered development of the human cerebral cortex can cause severe malformations with often intractable focal epileptic seizures and may participate in common pathologies, notably epilepsy. This raises important conceptual and therapeutic issues. Two missense mutations in the sushi repeat-containing protein SRPX2 had been previously identified in epileptic disorders with or without structural developmental alteration of the speech cortex. In the present study, we aimed to decipher the precise developmental role of SRPX2, to have a better knowledge on the consequences of its mutations, and to start addressing therapeutic issues through the design of an appropriate animal model. Using an in utero Srpx2 silencing approach, we show that SRPX2 influences neuronal migration in the developing rat cerebral cortex. Wild-type, but not the mutant human SRPX2 proteins, rescued the neuronal migration phenotype caused by Srpx2 silencing in utero, and increased alpha-tubulin acetylation. Following in utero Srpx2 silencing, spontaneous epileptiform activity was recorded post-natally. The neuronal migration defects and the post-natal epileptic consequences were prevented early in embryos by maternal administration of tubulin deacetylase inhibitor tubacin. Hence epileptiform manifestations of developmental origin could be prevented in utero, using a transient and drug-based therapeutic protocol.

Acid-sensing ion channels (ASICs) are widely expressed in mammalian sensory neurons and supposedly play a role in nociception and acid sensing. In the course of functioning the redox status of the tissue is subjected to changes. Using whole-cell patch-clamp/concentration clamp techniques we have investigated the effect of redox reagents on the ASIC-like currents in the sensory ganglia and hippocampal neurons of rat. The reducing agent dithiothreitol (DTT), when applied in the concentrations 1–2 mM, reversibly potentiates proton-activated currents, while the oxidizing reagent 5,5′-dithio-bis-(2-nitrobenzoic acid) (DTNB) causes their inhibition. The EC50 and Hill coefficient for the activation of ASIC-like currents by protons are not affected by DTT. Redox modulation of proton-activated currents is independent on the membrane potential and on the level of pH used for the current activation. The endogenous antioxidant tripeptide glutathione (its reduced form, g-l-glutamyl-l-cysteinyl-glycine, GSH) also potentiates proton-activated currents. Our results indicate that ASIC-like currents are susceptible to regulation by redox agents.

At many central synapses, endocannabinoids released by postsynaptic cells act retrogradely on presynaptic G-protein-coupled cannabinoid receptors to inhibit neurotransmitter release. Here, we demonstrate that cannabinoids may directly affect the functioning of inhibitory glycine receptor (GlyR) channels. In isolated hippocampal pyramidal and Purkinje cerebellar neurons, endogenous cannabinoids anandamide and 2-arachidonylglycerol, applied at physiological concentrations, inhibited the amplitude and altered the kinetics of rise time, desensitization, and deactivation of the glycine-activated current (IGly) in a concentration-dependent manner. These effects of cannabinoids were observed in the presence of cannabinoid CB1/CB3, vanilloid receptor 1 antagonists, and the G-protein inhibitor GDPβS, suggesting a direct action of cannabinoids on GlyRs. The effect of cannabinoids on IGly desensitization was strongly voltage dependent. We also demonstrate that, in the presence of a GABAA receptor antagonist, GlyRs may contribute to the generation of seizure-like activity induced by short bursts (seven stimuli) of high-frequency stimulation of inputs to hippocampal CA1 region, because this activity was diminished by selective GlyR antagonists (strychnine and ginkgolides B and J). The GlyR-mediated rhythmic activity was also reduced by cannabinoids (anandamide) in the presence of a CB1 receptor antagonist. These results suggest that the direct inhibition of GlyRs by endocannabinoids can modulate the hippocampal network activity.

Numerous data indicate that nonsynaptic release of glutamate occurs both in normal and pathophysiological conditions. When reaching receptors in the postsynaptic density (PSD), glutamate (Glu) could affect the synaptic transmission. We have tested this possibility in the hippocampal CA1 synapses of rats, either by applying exogenous Glu to the CA1 neurons or by disruption of Glu transporter activity. L-Glu (400 microM) was directly applied to the hippocampal slices acutely isolated from the rats. It produced a strong inhibition of both ortho- and antidromically elicited action potentials fired by CA1 neurons while the excitatory postsynaptic current (EPSC) measured in these neurons remained totally unaffected. The optical isomer D-Glu which is not transported by the systems of Glu uptake inhibited not only orthodromic and antidromic spikes, but also EPSC. Non-specific glutamate transporter inhibitor DL-threo-beta-hydroxyaspartic acid (THA, 400 microM) mimicked the effects of exogenous Glu and produced strong inhibition of both orthodromic and antidromic spikes, without any influence on the amplitude of EPSCs. Dihydrokainate (DHK, 300 microM), selective inhibitor of GLT-1 subtype of glutamate transporter, exerted a significant inhibitory action on the orthodromically evoked spikes and also on the EPSC. Our results indicate that extrasynaptic and PSD membranes of CA1 neurons form separate compartments differing in the mechanisms and efficiency of external Glu processing: the protection of PSD markedly prevails.

A new substance (R,S)-(3,4-dihydro-6,7-dimethoxyisoquinoline-1-yl)-2-cyclohexyl-N-(3,3-diphenylpropyl)-acetamide hydrochloride (BIIA388Cl), which demonstrates neuroprotective properties in animal models, was examined for its action on K+ currents in acutely isolated rat hippocampal neurons using the patch–clamp/concentration clamp techniques in the whole-cell configuration. The delayed rectifier K+-current (IDR) was strongly inhibited by externally applied BIIA388Cl, while the transient A-current (IA) remained virtually unaffected. Block of IDR by the pre-applied BIIA388Cl was revealed as a rapid decay of the current indicating direct interaction of the drug with the open state of the channel. The removal of the block upon repolarization was also rapid (τ=22 ms). The dose–response relationship for the blocking action of BIIA388Cl revealed an IC50 value of 300 nM for the peak IDR, whereas the IC50 value for IDR measured 300 ms after the onset of depolarization was 120 nM. The blocking action of BIIA388Cl on IA was at least 200 times less potent. These data allow us to conclude that BIIA388Cl is an effective and selective blocker of IDR. This current is the main pathway for the loss of intracellular potassium by depolarized neurons. Selective obstruction of this pathway could be useful for neuroprotection.

Despite almost forty years of widespread use of antidepressant drugs, their mode of action is still unknown. Hyperforin, a phloroglucinol derivative, is a major pharmacologically and therapeutically active constituent of Hypericum perforatum extract that is widely used as an herbal antidepressant drug. However, the mechanism or mechanisms of action of these naturally abundant, non-toxic extracts remain unclear. Enzymatically isolated patch-clamped rat central and peripheral neurons exposed to rapid changes in the composition of external medium (concentration clamp) were used in our experiments to investigate the modulation of the various voltage- and ligand-gated channels by hyperforin, as well as by other constituents of Hypericum perforatum. At nanomolar concentrations, hyperforin induced significant inhibition of various ion channels. In the case of P-type Ca2+ channels, we established that hyperforin acts via interaction with calmodulin or through calmodulin-activated pathways involving at least one second messenger. The results presented here indicate that multiple mechanisms and extract constituents may be involved in the antidepressant action of Hypericum extracts, and that they could also possess neuroprotective and analgesic effects.

Using an in situ patch clamp in hippocampal CA1 mini-slices, we measured excitatory postsynaptic currents (EPSC) by varying the strength of the stimulus applied to the axons of CA3 neurones. The kinetics of the EPSC was initially independent of the stimulus strength. Post-ischaemic potentiation of the EPSC was observed 60-80 min after brief periods (10 min) of anoxia/aglycaemia. The decay of the EPSC slowed significantly in most of the examined neurones. In 11 of 17 cells the EPSC kinetics became dependent on stimulus strength: a slower decay corresponded to a stronger stimulus. This effect was not abolished by N-methyl-D-aspartate (NMDA) or a non-NMDA receptor blocker (D-2-amino-5-phosphonovaleric acid or 6-cyano-7-nitroquinoxaline-2,3-dione respectively) indicating the polysynaptic nature of the modified EPSC: transient ischaemia led to the long-term recruitment of previously inactive, possibly latent NMDA synapses between CA1 neurones.

When performed at increased external [Ca2+]/[Mg2+] ratio (2.5 mM/0.5 mM), temporary block of Al adenosine receptors in hippocampus [by 8-cyclopentyltheophylline (CPT)] leads to a dramatic and irreversible change in the excitatory postsynaptic current (EPSC) evoked by Schaffer collateral/commissural (SCC) stimulation and recorded by in situ patch clamp in CA1 pyramidal neurons. The duration of the EPSC becomes stimulus dependent, increasing with increase in stimulus strength, The later occurring component of the EPSC is carried through N-methyl-D-aspartate (NMDA) receptor-operated channels but disappears under either the NMDA antagonist 2-amino-5-phosphonovaleric acid (APV) or the non-NMDA antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). These findings indicate that the late component of the SCC-evoked EPSC is polysynaptic: predominantly non-NMDA receptor-mediated SCC inputs excite CA1 neurons that recurrently excite each other by predominantly NMDA receptor-mediated synapses. These recurrent connections are normally silent but become active after CPT treatment, leading to enhancement of the late component of the EPSC, The activity of these connections is maintained for at least 2 hr after CPT removal, When all functional NMDA receptors are blocked by dizocilpine maleate (MK-801), subsequent application of CPT leads to a partial reappearance of NMDA receptor-mediated EPSCs evoked by SCC stimulation, indicating that latent NMDA receptors are recruited. Altogether, these findings indicate the existence of a powerful system of NMDA receptor-mediated synaptic contacts in SCC input to hippocampal CA1 pyramidal neurons and probably also; in reciprocal connections between these neurons, which in the usual preparation are kept latent by activity of A(1) receptors.