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

Abstract

SUMMARYPurpose: 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.

Combined electrophysiological and biosensor approaches to study purinergic regulation of epileptiform activity in cortical tissue

“…This minor role was echoed by ATP biosensor measurements, which showed little appreciable release of ATP during either evoked seizure activity or spontaneous seizures caused by the elevation of extracellular K + to 6 mM, both of which were capable of provoking considerable adenosine release (Figure 6). Thus, under these conditions there seems to be both little ATP release and little P2 receptor involvement in modulating epileptiform activity, observations confirmed by others (Klaft et al, 2012). However, these findings do not preclude the potential importance of ATP release and P2 receptors in other seizure models or conditions (Burnstock et al, 2011).…”

Silencing of P2X7R by RNA interference in the hippocampus can attenuate morphological and behavioral impact of pilocarpine-induced epilepsy

“…P2X7R have been shown to modulate mechanisms involved with apoptosis/necrosis and neuronal differentiation of NPCs [87][88][89][90], while P2Y1 receptors modulate proliferation and migration of NPCs [91][92][93]. Klaft et al [94] also found that P2X7R antagonists had a minor antiepileptic effect in medial entorhinal cortex on rats subjected to pilocarpine-induced epilepsy.…”

The Antiepileptic Potential of Nucleosides

“…It has also been demonstrated in the hippocampus that glutamate increases the Ado level via NMDA receptor activation, which may inhibit glutamate release presynaptically via A 1 receptors [102]. The inhibition by Ado may be sufficient (i) to regulate the spreading of seizures, (ii) to decrease epileptic activity ( Table 3) and (iii) for seizure termination [96,101,[103][104][105][106][107][108]. An increase in the Ado level in epileptic brain tissue has been demonstrated [109][110][111][112].…”