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Background and Purpose: P2X4 receptors (P2X4R) are ligand gated cation channels that are activated by extracellular ATP released by neurons and glia. The receptors are widely expressed in the brain and have fractional calcium currents comparable with NMDA receptors. Although P2X4Rs have been reported to modulate synaptic transmission and plasticity, their involvement in shaping neuronal network activity remains to be elucidated. Experimental Approach: We investigated the effects of P2X receptors at network and synaptic level using local field potential electrophysiology, whole cell patch clamp recordings and calcium imaging in fast spiking parvalbumin positive interneurons (PVINs) in rat and mouse hippocampal slices. The stable ATP analogue ATPγS, selective antagonists and P2X4R knockout mice were used. Key Results: The P2XR agonist ATPγS reversibly decreased the power of gamma oscillations. This inhibition could be antagonized by the selective P2X4R antagonist PSB‐12062 and was not observed in P2X4−/− mice. The phasic excitatory inputs of CA3 PVINs were one of the main regulators of the gamma power. Associational fibre compound excitatory postsynaptic currents (cEPSCs) in CA3 PVINs were inhibited by P2X4R activation. This effect was reversible, dependent on intracellular calcium and dynamin‐dependent internalization of AMPA receptors. Conclusions and Implications: The results indicate that P2X4Rs are an important source of dendritic calcium in CA3 PVINs, thereby regulating excitatory synaptic inputs onto the cells and presumably the state of gamma oscillations in the hippocampus. P2X4Rs represent an effective target to modulate hippocampal network activity in pathophysiological conditions such as Alzheimer's disease and schizophrenia. [ABSTRACT FROM AUTHOR]

Background and Purpose: Gamma oscillations are fast rhythmic fluctuations of neuronal network activity ranging from 30 to 90 Hz that establish a precise temporal background for cognitive processes such as perception, sensory processing, learning, and memory. Alterations of gamma oscillations have been observed in schizophrenia and are suggested to play crucial roles in the generation of positive, negative, and cognitive symptoms of the disease.Experimental Approach: In this study, we investigated the effects of the novel antipsychotic cariprazine, a D3 -preferring dopamine D3 /D2 receptor partial agonist, on cholinergically induced gamma oscillations in rat hippocampal slices from treatment-naïve and MK-801-treated rats, a model of acute first-episode schizophrenia.Key Results: The D3 receptor-preferring agonist pramipexole effectively decreased the power of gamma oscillations, while the D3 receptor antagonist SB-277011 had no effect. In treatment-naïve animals, cariprazine did not modulate strong gamma oscillations but slightly improved the periodicity of non-saturated gamma activity. Cariprazine showed a clear partial agonistic profile at D3 receptors at the network level by potentiating the inhibitory effects when the D3 receptor tone was low and antagonizing the effects when the tone was high. In hippocampal slices of MK-801-treated rats, cariprazine allowed stabilization of the aberrant increase in gamma oscillation power and potentiated resynchronization of the oscillations.Conclusion and Implications: Data from this study indicate that cariprazine stabilizes pathological hippocampal gamma oscillations, presumably by its partial agonistic profile. The results demonstrate in vitro gamma oscillations as predictive biomarkers to study the effects of antipsychotics preclinically at the network level. [ABSTRACT FROM AUTHOR]

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 μ m 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 μ m). 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. [ABSTRACT FROM AUTHOR]

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 μ m) combined with physostigmine (2 μ m). 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 p Ki values for 19 receptors and analysed for correlation. Our results indicated that 5-HT3 receptors have an enhancing effect on gamma oscillations whereas dopamine D3 receptors inhibit them. To test this prediction, m-chlorophenylbiguanide, PD 128907 and CP 809101, selective agonists at 5-HT3, D3 and 5-HT2C receptors were applied and revealed that 5-HT3 receptors indeed enhanced the gamma power whereas D3 receptors reduced it. As predicted, 5-HT2C receptors had no effects on gamma oscillations. CONCLUSION AND IMPLICATIONS Our data suggest that antipsychotics alter hippocampal gamma oscillations by interacting with 5-HT3 and dopamine D3 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. [ABSTRACT FROM AUTHOR]

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 A1 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 A1 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 A1 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. [ABSTRACT FROM AUTHOR]

Mixed striatal cell cultures containing neurons and glial cells were grown either in neurobasal medium (NBM) or Dulbecco's modified Eagle's medium (DMEM). Whole-cell patch-clamp recordings indicated that, if at all, only a single, low amplitude spike was evoked shortly after starting the injection of a depolarizing current pulse into NBM neurons. In contrast, DMEM neurons fired series of high amplitude action potentials, without apparent spike frequency adaptation. The possible reason for the observed action potential failure in NBM neurons was a low density of Na+ channels per unit of membrane surface area. However, both in NBM and DMEM neurons, ATP did not induce inward current responses via P2X receptor-channels, although GABAA and N-methyl-D-aspartate (NMDA) receptor-channels could be activated by muscimol and NMDA, respectively. Ca2+ imaging experiments by means of the Fura-2 method were utilized to measure intracellular Ca2+ ([Ca2+]i) in neurons and glial cells. NBM, but not DMEM neurons responded to ATP with [Ca2+]i transients; glial cells grown in either culture medium were equally sensitive to ATP. ATP caused an increase of [Ca2+]i by a mechanism only partly dependent on external Ca2+; the residual ATP effect was blocked by cyclopiazonic acid (CPA) and was therefore due to the release of Ca2+ from its intracellular pools. The receptor involved was characterized by P2 receptor antagonists (PPADS, MRS 2179, AR-C69931MX) and was found to belong to the P2Y1 subtype. CPA caused an early [Ca2+]i response due to release from intracellular storage sites, followed by a late [Ca2+]i response due to the influx of this cation from the extracellular space, probably triggered by the opening of store-operated channels (SOCs) in the plasma membrane. It is concluded that in partial analogy with the effect of CPA, ATP releases [Ca2+]i via the Gq/phospholipase C/inositoltrisphosphate (IP3) pathway, thereby opening SOCs. It is hypothesized that this effect of ATP may have an important role for the proliferation and migration of striatal neuronal progenitors. J. Cell. Physiol. 209: 81–93, 2006. © 2006 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

1: N-type Ca2+ channel modulation by an endogenous P2Y receptor was investigated by the whole-cell patch-clamp method in HEK 293 cells transfected with the functional rabbit N-type calcium channel. 2: The current responses (ICa(N)) to depolarizing voltage steps were depressed by ATP in a concentration-dependent manner. Inclusion of either guanosine 5'-O-(3-thiodiphosphate) or pertussis toxin into the pipette solution as well as a strongly depolarizing prepulse abolished the inhibitory action of ATP. 3: In order to identify the P2Y receptor subtype responsible for this effect, several preferential agonists and antagonists were studied. Whereas the concentration-response curves of ADP and adenosine 5'-O-(2-thiodiphosphate) indicated a higher potency of these agonists than that of ATP, a,ß-methylene ATP, UTP and UDP were considerably less active. The effect of ATP was abolished by the P2Y receptor antagonists suramin and N6-(2-methylthioethyl)-2-(3,3,3-trifluoropropylthio)-ß,?-dichloromethylene-ATP, but not by pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid, 2'deoxy-N6-methyladenosine-3',5'-diphosphate or 2-methylthio AMP. 4: Using reverse transcription and polymerase chain reaction, mRNA for the P2Y1, P2Y4, P2Y6, P2Y11 and P2Y13 receptor subtypes, but not the P2Y2, and P2Y12 subtypes, was detected in HEK 293 cells. 5: Immunocytochemistry confirmed the presence of P2Y1, and to a minor extent that of P2Y4, but not of P2Y2 receptors. 6: Hence, it is tempting to speculate that P2Y13 receptors may inhibit N-type Ca2+ channels via the ß? subunits of the activated Gi protein.British Journal of Pharmacology (2004) 141, 141-151. doi:10.1038/sj.bjp.0705588 [ABSTRACT FROM AUTHOR]