Effects of A1 receptor agonist/antagonist on spontaneous seizures in pilocarpine-induced epileptic rats.

Adenosine is an endogenous anticonvulsant that activates pre- and postsynaptic adenosine A1 receptors. A1 receptor agonists increase the latency for the development of seizures and status epilepticus following pilocarpine administration. Although hippocampal adenosine is increased in the chronic phase of the pilocarpine model, it is not known whether the modulation of A1 receptors may influence the frequency of spontaneous recurrent seizures (SRS). Here, we tested the hypothesis that the A1 receptor agonist RPia ([R]-N-phenylisopropyladenosine) and the A1 antagonist DPCPX (8-Cyclopentyl-1,3-dipropylxanthine) administered to chronic pilocarpine epileptic rats would respectively decrease and increase the frequency of SRS and hippocampal excitability. Four months after Pilo-induced SE, chronic epileptic rats were video-monitored for the recording of SRS before (basal) and after a 2-week treatment with RPia (25µg/kg) or DPCPX (50µg/kg). Following sacrifice, brain slices were studied with electrophysiology. We found that rats given RPia had a 93% nonsignificant reduction in the frequency of seizures compared with their own pretreatment baseline. In contrast, the administration of DPCPX resulted in an 87% significant increase in seizure rate. Nontreated epileptic rats had a similar frequency of seizures along the study. Corroborating our behavioral data, in vitro recordings showed that slices from animals previously given DPCPX had a shorter latency to develop epileptiform activity, longer and higher DC shifts, and higher spike amplitude compared with slices from nontreated Pilo controls. In contrast, smaller spike amplitude was recorded in slices from animals given RPia. In summary, the administration of A1 agonists reduced hippocampal excitability but not the frequency of spontaneous recurrent seizures in chronic epileptic rats, whereas A1 receptor antagonists increased both.

The Effect of Low Magnesium Concentration on Ictal Discharges In A Non-Synaptic Model.

Magnesium (Mg[Formula: see text] is an essential mineral for several cellular functions. The concentration of this ion below the physiological concentration induces recurrent neuronal discharges both in slices of the hippocampus and in neuronal cultures. These epileptiform discharges are initially sensitive to the application of [Formula: see text]-methyl-D-aspartate (NMDA) receptor antagonists, but these antagonists may lose their effectiveness with prolonged exposure to low [Mg[Formula: see text]], when extracellular Ca[Formula: see text] reduction occurs, typical of ictal periods, indicating the absence of synaptic connections. The study herein presented aimed at investigating the effect of reducing the [Mg[Formula: see text]] during the induction of Nonsynaptic Epileptiform Activities (NSEA). As an experimental protocol, NSEA were induced in rat hippocampal dentate gyrus (DG), using a bath solution containing high-K[Formula: see text] and zero-added-Ca[Formula: see text]. Additionally, computer simulations were performed using a mathematical model that represents electrochemical characteristics of the tissue of the DG granular layer. The experimental results show that the reduction of [Mg[Formula: see text]] causes an increase in the duration of the ictal period and a reduction in the interictal period, intensifying epileptiform discharges. The computer simulations suggest that the reduction of the Mg[Formula: see text] level intensifies the epileptiform discharges by a joint effect of reducing the surface charge screening and reducing the activity of the Na/K pump.

Modification of the natural progression of epileptogenesis by means of biperiden in the pilocarpine model of epilepsy.

Brain injuries are often associated with the later development of epilepsy. Evidence suggests that morphological and functional changes occur in the remaining neural tissue during a silent (or latent) period in which no seizures are expressed. It is believed that this silent (reorganization) period may provide a therapeutic window for modifying the natural history of disease progression. Here we provide evidence that biperiden, a muscarinic anticholinergic agent, is able to alter disease progression in an animal model of epilepsy. We observed that biperiden was capable of slowing the manifestation of the first spontaneous epileptic seizure and effectively reduced the severity and number of recurrent, spontaneous epileptic seizures during the animals' lifespan. Biomolecular (microdialysis) and electrophysiological (extracellular field recordings) studies determined that biperiden was capable of elevating the threshold of hippocampal excitability, thereby making the hippocampal glutamatergic pathways less responsive to stimuli when high concentrations of potassium were used in vivo or in vitro. Notably, there was no hindrance of long-term memory or learning (a potential problem given the amnestic nature of biperiden). We conclude that biperiden has antiepileptogenic potential and may represent an opportunity for the prevention of post-traumatic epilepsy.

Effects of anterior thalamic nucleus deep brain stimulation in chronic epileptic rats.

Deep brain stimulation (DBS) has been investigated for the treatment of epilepsy. In rodents, an increase in the latency for the development of seizures and status epilepticus (SE) has been reported in different animal models but the consequences of delivering stimulation to chronic epileptic animals have not been extensively addressed. We study the effects of anterior thalamic nucleus (AN) stimulation at different current intensities in rats rendered epileptic following pilocarpine (Pilo) administration. Four months after Pilo-induced SE, chronic epileptic rats were bilaterally implanted with AN electrodes or had sham-surgery. Stimulation was delivered for 6 h/day, 5 days/week at 130 Hz, 90 µsec. and either 100 µA or 500 µA. The frequency of spontaneous recurrent seizures in animals receiving stimulation was compared to that recorded in the preoperative period and in rats given sham treatment. To investigate the effects of DBS on hippocampal excitability, brain slices from animals receiving AN DBS or sham surgery were studied with electrophysiology. We found that rats treated with AN DBS at 100 µA had a 52% non-significant reduction in the frequency of seizures as compared to sham-treated controls and 61% less seizures than at baseline. Animals given DBS at 500 µA had 5.1 times more seizures than controls and a 2.8 fold increase in seizure rate as compared to preoperative values. In non-stimulated controls, the average frequency of seizures before and after surgery remained unaltered. In vitro recordings have shown that slices from animals previously given DBS at 100 µA had a longer latency for the development of epileptiform activity, shorter and smaller DC shifts, and a smaller spike amplitude compared to non-stimulated controls. In contrast, a higher spike amplitude was recorded in slices from animals given AN DBS at 500 µA.