Adenosine A1 receptor-mediated suppression of carbamazepine-resistant seizure-like events in human neocortical slices.

OBJECTIVE: The need for alternative pharmacologic strategies in treatment of epilepsies is pressing for about 30% of patients with epilepsy who do not experience satisfactory seizure control with present treatments. In temporal lobe epilepsy (TLE) even up to 80% of patients are pharmacoresistant, and surgical resection of the ictogenic tissue is only possible for a minority of TLE patients. In this study we investigate purinergic modulation of drug-resistant seizure-like events (SLEs) in human temporal cortex slices. METHODS: Layer V/VI field potentials from a total of 77 neocortical slices from 17 pharmacoresistant patients were recorded to monitor SLEs induced by application of 8 mM [K(+) ] and 50 µm bicuculline. RESULTS: Activating A1 receptors with a specific agonist completely suppressed SLEs in 73% of human temporal cortex slices. In the remaining slices, incidence of SLEs was markedly reduced. Because a subportion of slices can be pharmacosensitive, we tested effects of an A1 agonist, in slices insensitive to a high dose of carbamazepine (50 µm). Also in these cases the A1 agonist was equally efficient. Moreover, ATP and adenosine blocked or modulated SLEs, an effect mediated not by P2 receptors but rather by adenosine A1 receptors. SIGNIFICANCE: Selective activation of A1 receptors mediates a strong anticonvulsant action in human neocortical slices from pharmacoresistant patients. We propose that our human slice model of seizure-like activity is a feasible option for future studies investigating new antiepileptic drug (AED) candidates.

Corticosterone and corticotropin-releasing factor acutely facilitate gamma oscillations in the hippocampus in vitro.

Stressful experiences do not only cause peripheral changes in stress hormone levels, but also affect central structures such as the hippocampus, implicated in spatial orientation, stress evaluation, and learning and memory. It has been suggested that formation of memory traces is dependent on hippocampal gamma oscillations observed during alert behaviour and rapid eye movement sleep. Furthermore, during quiescent behaviour, sharp wave-ripple (SW-R) activity emerges. These events provide a temporal window during which reactivation of memory ensembles occur. We hypothesized that stress-responsive modulators, such as corticosterone (CORT), corticotropin-releasing factor (CRF) and the neurosteroid 3α, 21-dihydroxy-5α-pregnan-20-one (THDOC) are able to modulate gamma oscillations and SW-Rs. Using in vitro hippocampal slices, we studied acute and subacute (2 h) impact of these agents on gamma oscillations in area cornu ammonis 3 of the ventral hippocampus induced by acetylcholine (10 µm) combined with physostigmine (2 µm). CORT increased the gamma oscillations in a dose-dependent fashion. This effect was mediated by glucocorticoid receptors. Likewise, CRF augmented gamma oscillations via CRF type 1 receptor. Lastly, THDOC was found to diminish cholinergic gamma oscillations in a dose-dependent manner. Neither CORT, CRF nor THDOC modulated gamma power when pre-applied for 1 h, 2 h before the induction of gamma oscillations. Interestingly, stress-related neuromodulators had rather mild effects on spontaneous SW-R compared with their effects on gamma oscillations. These data suggest that the alteration of hippocampal gamma oscillation strength in vitro by stress-related agents is an acute process, permitting fast adaptation to new attention-requiring situations in vivo.

Extracellular ATP differentially affects epileptiform activity via purinergic P2X7 and adenosine A1 receptors in naive and chronic epileptic rats.

PURPOSE: Adenosine is considered an endogenous anticonvulsant. However, much less is known about the putative effects of its precursor, ATP, on epilepsy. Therefore, we tested whether ATP and its receptors are able to modulate epileptiform activity in the medial entorhinal cortex of the rat. METHODS: Recurrent epileptiform discharges (REDs) were induced by elevating extracellular potassium concentration combined with application of bicuculline in brain slices from naive and pilocarpine-treated chronic epileptic rats. Field potentials were recorded from layer V/VI of the medial entorhinal cortex. KEY FINDINGS: REDs in slices from naive animals had a higher incidence and a shorter duration than in slices from chronic epileptic animals. Exogenous application of ATP reversibly reduced the incidence of REDs in naive and chronic epileptic slices via activation of adenosine A(1) receptors without discernible P2 receptor effects. This effect was stronger in slices from chronic epileptic rats. In slices from naive rats, the P2X7 receptor antagonist A 740003 slightly but significantly reduced the amplitude of slow field potentials of REDs. In slices from chronic epileptic rats, none of the P2 receptor antagonists affected the parameters of REDs. SIGNIFICANCE: Our results suggest that endogenously released ATP differentially modulates REDs by activation of A(1) and P2X7 receptors. Although it has a minor proepileptic effect by direct activation of P2X7 receptors, its metabolite adenosine reduces the epileptiform activity via activation of A(1) receptors. The exact effect of ATP on neural activity depends on the actual activity of ectonucleotidases and the expression level of the purinergic receptors, which both alter during epileptogenesis. In addition, our data suggest that P2X7 receptor antagonists have a minor antiepileptic effect.

Dopamine D3 Receptors Inhibit Hippocampal Gamma Oscillations by Disturbing CA3 Pyramidal Cell Firing Synchrony.

Cortical gamma oscillations are associated with cognitive processes and are altered in several neuropsychiatric conditions such as schizophrenia and Alzheimer's disease. Since dopamine D3 receptors are possible targets in treatment of these conditions, it is of great importance to understand their role in modulation of gamma oscillations. The effect of D3 receptors on gamma oscillations and the underlying cellular mechanisms were investigated by extracellular local field potential and simultaneous intracellular sharp micro-electrode recordings in the CA3 region of the hippocampus in vitro. D3 receptors decreased the power and broadened the bandwidth of gamma oscillations induced by acetylcholine or kainate. Blockade of the D3 receptors resulted in faster synchronization of the oscillations, suggesting that endogenous dopamine in the hippocampus slows down the dynamics of gamma oscillations by activation of D3 receptors. Investigating the underlying cellular mechanisms for these effects showed that D3 receptor activation decreased the rate of action potentials (APs) during gamma oscillations and reduced the precision of the AP phase coupling to the gamma cycle in CA3 pyramidal cells. The results may offer an explanation how selective activation of D3 receptors may impair cognition and how, in converse, D3 antagonists may exert pro-cognitive and antipsychotic effects.

Purinergic P2X, P2Y and adenosine receptors differentially modulate hippocampal gamma oscillations.

The present study was designed to investigate the role of extracellular ATP and its receptors on neuronal network activity. Gamma oscillations (30-50 Hz) were induced in the CA3 region of acute rat hippocampal slices by either acetylcholine (ACh) or kainic acid (KA). ATP reduced the power of KA-induced gamma oscillations exclusively by activation of adenosine receptors after its degradation to adenosine. In contrast, ATP suppressed ACh-induced oscillations through both adenosine and ATP receptors. Activation of adenosine receptors accounts for about 55%, activation of P2 receptors for ∼45% of suppression. Monitoring the ATP degradation by ATP biosensors revealed that bath-applied ATP reaches ∼300 times lower concentrations within the slice. P2 receptors were also activated by endogenous ATP since inhibition of ATP-hydrolyzing enzymes had an inhibitory effect on ACh-induced gamma oscillations. More specific antagonists revealed that ionotropic P2X2 and/or P2X4 receptors reduced the power of ACh-induced gamma oscillations whereas metabotropic P2Y(1) receptor increased it. Intracellular recordings from CA3 pyramidal cells suggest that adenosine receptors reduce the spiking rate and the synchrony of action potentials during gamma oscillations whereas P2 receptors only modulate the firing rate of the cells. In conclusion, our results suggest that endogenously released ATP differentially modulates the power of ACh- or KA-induced gamma oscillations in the CA3 region of the hippocampus by interacting with P2X, P2Y and adenosine receptors. This article is part of a Special Issue entitled 'Post-Traumatic Stress Disorder'.

First and second generation antipsychotics influence hippocampal gamma oscillations by interactions with 5-HT3 and D3 receptors.

BACKGROUND AND PURPOSE: Disturbed cortical gamma band oscillations (30-80 Hz) have been observed in schizophrenia: positive symptoms of the disease correlate with an increase in gamma oscillation power, whereas negative symptoms are associated with a decrease. EXPERIMENTAL APPROACH: Here we investigated the effects of first and second generation antipsychotics (FGAs and SGAs, respectively) on gamma oscillations. The FGAs haloperidol, flupenthixol, chlorpromazine, chlorprothixene and the SGAs clozapine, risperidone, ziprasidone, amisulpride were applied on gamma oscillations induced by acetylcholine and physostigmine in the CA3 region of rat hippocampal slices. KEY RESULTS: Antipsychotics inhibited the power of gamma oscillations and increased the bandwidth of the gamma band. Haloperidol and clozapine had the highest inhibitory effects. To determine which receptor is responsible for the alterations in gamma oscillations, the effects of the antipsychotics were plotted against their pK(i) values for 19 receptors and analysed for correlation. Our results indicated that 5-HT(3) receptors have an enhancing effect on gamma oscillations whereas dopamine D(3) receptors inhibit them. To test this prediction, m-chlorophenylbiguanide, PD 128907 and CP 809101, selective agonists at 5-HT(3) , D(3) and 5-HT(2C) receptors were applied and revealed that 5-HT(3) receptors indeed enhanced the gamma power whereas D(3) receptors reduced it. As predicted, 5-HT(2C) receptors had no effects on gamma oscillations. CONCLUSION AND IMPLICATIONS: Our data suggest that antipsychotics alter hippocampal gamma oscillations by interacting with 5-HT(3) and dopamine D(3) receptors. Moreover, a correlation of receptor affinities with the biological effects can be used to predict targets for the pharmacological effects of multi-target drugs.