Aus dem Institut für Neurophysiologie der Medizinischen Fakultät Charité – Universitätsmedizin Berlin DISSERTATION Pharmacological modulation of physiological and pathophysiological neuronal network activities: special emphasis on purinergic ATP receptors

The present studies (Schulz et al., 2012a, 2012b; Klaft et al., 2012) were designed to investigate the role of extracellular ATP and its receptors on physiological and pathophysiological activities of neuronal networks and to elucidate how the neuronal network is modulated by approved multi-target antipsychotics. Persistent gamma oscillations (30-100 Hz) were induced in the CA3 region of acute rat hippocampal slices by the application of 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 via both adenosine and P2 receptors. The latter were also activated by endogenous ATP since blockade of ATP-hydrolyzing enzymes also inhibited gamma oscillations. More specific antagonists revealed that ionotropic P2X2 and/or P2X4 receptors reduced the power of ACh-induced gamma oscillations whereas metabotropic P2Y1 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 pyramidal cells. As a model of hypersynchronous pathophysiological network activity, we induced recurrent epileptiform discharges (REDs) in slices from naïve and pilocarpine-treated rats by elevating extracellular potassium concentration in combination with bicuculline. Application of ATP reversibly reduced the incidence of REDs in naïve and chronic epileptic slices via activation of adenosine A1 receptors without discernible P2 receptor effects. In slices from naïve 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. Because disturbances in neuronal network activities are also related to psychotic symptoms, we investigated the effects of first and second generation antipsychotics on ACh/Physo-induced gamma oscillations. Several antipsychotics inhibited the power of gamma oscillations and increased the bandwidth of the gamma band. To elucidate which receptors of these multi-target drugs are responsible for the alterations of gamma oscillations, the effects of the antipsychotics were correlated to their pKi values for 19 receptors. We found that 5-HT3 receptors may have an enhancing effect on gamma oscillations whereas D3 receptors may inhibit them. This in silico predictions were confirmed by specific agonists. In conclusion, we found that (a) adenosine receptors dampen neuronal network activity both in models of physiological gamma oscillations and pathophysiological recurrent epileptiform discharges, (b) P2Y1 receptors support gamma oscillations, (c) P2X2 and P2X4 receptors suppress gamma activity, (d) P2X7 receptors show a minor proepileptic effect, and (e) antipsychotics influence gamma oscillations by interacting with 5-HT3 and D3 receptors.