Quinine, a Blocker of Neuronal Cx36 Channels, Suppresses Seizure Activity in Rat Neocortex In Vivo

Abstract

Summary:Purpose: The selective contribution of neuronal gap junction (GJ) communication via connexin 36 (Cx36) channels to epileptogenesis and to the maintenance and propagation of seizures was investigated in both the primary focus and the mirror focus by using pharmacologic approaches with the 4-aminopyridine in vivo epilepsy model.Methods: ECoG recording was performed on anesthetized adult rats, in which either quinine, a selective blocker of Cx36, or the broad-spectrum GJ blockers carbenoxolone and octanol were applied locally, before the induction or at already active epileptic foci.Results: The blockade of Cx36 channels by quinine before the induction of epileptiform activity slightly reduced the epileptogenesis. When quinine was applied after 25-30 repetitions of seizures, a new discharge pattern appeared with frequencies >15 Hz at the initiation of seizures. In spite of the increased number of seizures, the summated ictal activity decreased, because of the significant reduction in the duration of the seizures. The amplitudes of the seizure discharges of all the patterns decreased, with the exception of those with frequencies of 11-12 Hz. The blockade of Cx36 channels and the global blockade of the GJ channels resulted in qualitatively different modifications in ictogenesis.Conclusions: The blockade of Cx36 channels at the already active epileptic focus has an anticonvulsive effect and modifies the manifestation of the 1-to 18-Hz seizure discharges. Our findings indicate that the GJ communication via Cx36 channels is differently involved in the synchronization of the activities of the networks generating seizure discharges with different frequencies. Additionally, we conclude that both neuronal and glial GJ communication contribute to the manifestation and propagation of seizures in the adult rat neocortex. Key Words: Gap junctions-Cx36-4-AP-induced seizure-EpileptogenesisIctogenesis-In vivo-Quinine-Carbenoxolone.Epilepsy is one of the most prevalent neurologic disorders worldwide, but pharmacologic therapy remains the best remedy for its treatment. One reason for the incomplete effectiveness of the currently available anticonvulsants is that they were identified by using the same classic epilepsy models, which mainly involve the same actions, without a consideration of the variations in the pathophysiologic mechanisms that result in epilepsy. Growing evidence indicates that, besides the chemical synapses, direct coupling via gap junction (GJ) channels provides a second major pathway, contributing to normal and abnormal physiologic rhythms both during development and in the adult brain (1-3).GJ channels mediating electrical signaling are involved in the physiologic synchronizing mechanism in the brain (3-5) and contribute to pathologic hypersynchrony in various in vitro (6-9) and in vivo (10-13) epilepsy models.

The Neuropharmacology of the Ketogenic Diet

“…Studies to determine whether brain levels of acetone during consumption of the diet are within the range of those known to confer seizure protection have not yet been conducted because of the difficulty of measuring acetone, but are feasible. In addition, it will be of interest to determine whether acetone protects against epileptiform activity in in vitro models through traditional mechanisms, or whether it acts on novel targets, such as gap junctions, which appear to mediate epilepti-form activity in some circumstances and are influenced by small molecules that are structurally similar to ketone bodies [86].…”

Anticonvulsant activity of quinine in rat models of seizure in comparison with valproate and phenytoin

“…5 Studies have demonstrated that quinine suppresses ictal activity without affecting normal neuronal function in both in-vitro (rat hippocampal slice preparation) 7 and in-vivo (4-aminopyridine induced epilepsy model) 3 conditions. Further, trimethylamine, a specific opener of GJ channels negates quinine's seizure protective activity.…”

“…5 Various studies have documented in-vitro and in-vivo anticonvulsant activity of quinine in animal models. 3,[6][7][8][9] However, there is a paucity of data wherein the anticonvulsant activity of quinine is compared with drugs currently used in treating epilepsy.…”

“…1 has been associated with juvenile myoclonic epilepsy. 3 Quinine is a selective and reversible blocker of Cx-36. 5 Various studies have documented in-vitro and in-vivo anticonvulsant activity of quinine in animal models.…”

Connexin-36 Knock-Out Mice have Increased Threshold for Kindled Seizures: Role of GABA Inhibition

“…However in most cases, these experiments with Cx expression and epilepsy were performed with already epileptic subjects [30][31][32][33]. Indeed, many studies have shown that GJs play a role in epilepsy, as seizures can be ameliorated by GJ blockers and exacerbated by GJ openers [31,[34][35][36][37][38][39][40]. For example, mice lacking neuron-specific Cx36 GJs evince reduced kainate-induced [41] and 4-aminopyridine-induced seizures [42].…”