Altered SWD stopping mechanism in WAG/Rij rats subchronically treated with the cannabinoid agonist R(+)WIN55,212-2.

A single injection of the cannabinoid agonist R(+)WIN55,212-2 (WIN) is known to cause an increase of the mean duration of spontaneously occurring spike-and-wave discharges (SWDs) in rats of the WAG/Rij strain, a genetic model for absence epilepsy. The aim of the present study was to establish whether repeated activation of CB1 receptors with WIN leads to tolerance in its effect on SWD parameters, spectral density, and behavior over time. Adult male WAG/Rij rats (n = 16) were treated with WIN (6 mg/kg) or vehicle (olive oil). Injections (s.c.) took place 3 times per week during 2 weeks. Electroencephalogram (EEG) recordings, each lasting 24 h, were made 3 times: immediately before the first injection (baseline), immediately after the first injection (acute treatment), and after 2 weeks of treatment (subchronic treatment). The recordings were analyzed regarding incidence, durations of SWDs, and hazard rates of the durations of SWDs, the latter to describe SWD stopping probabilities. Putative changes in the spectral content of the EEG before and after WIN during active and passive behaviors were additionally investigated. Spike-and-wave discharge incidence was not affected by the acute and subchronic treatments. The mean duration of the SWDs was significantly longer than controls in the acute WIN-treated animals [11.9-s standard error of the mean (SEM): 0.64 compared with 8.4-s SEM: 0.25] as well as in subchronically treated animals (11.5-s SEM: 1.00 compared with 8.4-s SEM: 0.25). Hazard rates were significantly lower for WIN-treated animals at SWD durations in the 5.04-20.16-s range on both occasions. No effects of WIN on the frequency spectrum of the ongoing EEG were found, neither acutely nor after repeated administration. Evidence for tolerance was not found. The results on the mean duration and hazard rates suggest that stimulating the endocannabinoid system affects the SWD stopping mechanism, resulting in more long SWDs. We speculate that this effect is likely to be a direct result of CB1 receptor agonism and a subsequent decrease in the availability of gamma-aminobutyric acid (GABA) in the reticular thalamic nucleus, which further weakens, in WAG/Rij rats already disturbed, the stopping mechanism of the SWDs.

The "Twin Peaks" method of automated Spike-Wave detection: A two-step, two-criteria Matlab application.

BACKGROUND: There are many automated spike-wave discharge detectors, but the known weaknesses of otherwise good methods and the varying working conditions of different research groups (mainly the access to hardware and software) invite further exploration into alternative approaches. NEW METHOD: The algorithm combines two criteria, one in the time-domain and one in the frequency-domain, exploiting morphological asymmetry and the presence of harmonics, respectively. The time-domain criterion is additionally adjusted by normal modelling between the first and second iterations. RESULTS: We report specificity, sensitivity and accuracy values for 20 recordings from 17 mature, male WAG/Rij rats. In addition, performance was preliminary tested with different hormones, pharmacological injections and species (mice) in a smaller sample. Accuracy and specificity were consistently above 91 %. The number of automatically detected spike-wave discharges was strongly correlated with the numbers derived from visual inspection. Sensitivity varied more strongly than specificity, but high values were observed in both rats and mice. COMPARISON WITH EXISTING METHODS: The algorithm avoids low-voltage movement artifacts, displays a lower false positive rate than many predecessors and appears to work across species, i.e. while designed initially with data from the WAG/Rij rat, the algorithm can pick up seizure activity in the mouse of considerably lower inter-spike frequency. Weaknesses of the proposed method include a lower sensitivity than several predecessors. CONCLUSION: The algorithm excels in being a selective and flexible (based on e.g. its performance across rats and mice) spike-wave discharge detector. Future work could attempt to increase the sensitivity of this approach.

Immediate versus late effects of vigabatrin on spike and wave discharges.

Vigabatrin increases GABA concentrations by inhibiting GABA transaminase. In previous studies, it was shown that vigabatrin increases the incidence of Spike and Wave Discharges (SWD) in the WAG/Rij rat model for absence epilepsy. Since following a single dose of vigabatrin GABA concentrations are known to be increased for several days, the present study sheds light on how the previously described changes in SWD characteristics develop over a longer time frame. To achieve this, we injected adult WAG/Rij rats with 500 mg/kg and recorded their EEG for 48 h. SWD were quantified, and their peak frequencies were calculated. Our results showed three rapid onset effects: a sharp increase in SWD incidence, from 12.5 /hour to 133/hour), this increase lasted only 4.4 h, an increase in mean SWD duration, from 4.6 s to 8.1 s and a drop in peak frequency, from 8 to 6 Hz. Since it takes several hours before GABA concentrations are sufficiently increased, we propose that these immediate effects are caused by direct stimulation of both GABAA and GABAB receptors by the molecule vigabatrin. Next, the mean SWD duration decreased below baseline values after 4.4 h. Hazard rate analysis showed that this is caused by an increased probability of short SWD. We argue that these changes are caused by increased activation of both GABAA and GABAB receptors in the frontal cortex and the thalamus, and more specifically, in the Reticular Thalamic Nucleus (RTN). After approximately 34 h, the probability of short SWD returned to normal. This suggests the occurrence of downregulation of GABA receptors. The decrease in peak frequency was still present 48 h after injection. It has been argued that the balance between GABAA and GABAB receptor-mediated activity in the RTN is crucial for controlling this SWD characteristic. It can be concluded that a single dose of vigabatrin results in remarkable and opposite effects over time: an initial, proabsence effect is followed by an antiabsence effect.

Neonatal exposure to AY-9944 increases typical spike and wave discharges in WAG/Rij and Wistar rats.

Absence-epileptic seizures appear in the EEG as Spike and Wave Discharges (SWDs). Typical SWDs develop spontaneously in WAG/Rij rats, an inbred Wistar strain. Atypical SWDs however were reported in studies in which the cholesterol synthesis inhibitor AY-9944 was administered to neonatal Wistar rats, causing absence-like seizures later in life. Atypical SWDs seemed to differ from typical SWDs in 3 aspects: lower peak frequency, longer duration, and involvement of the hippocampus. The aim of the present study was to investigate the effect of AY-9944 on typical SWDs. Male Wistar and WAG/Rij rats were injected with 7.5 mg/kg AY-9944 or saline postnatally. After 6 months, EEGs were recorded from the cortex and the hippocampus. Incidence, duration and peak frequency of the SWDs were determined. The SWD stopping probability was estimated by hazard rate analysis. Hippocampal involvement was assessed by cross correlation analysis of the hippocampus and cortex channels. The Wistar rats unexpectedly showed a high incidence of spontaneous SWDs. The AY-treatment increased the total SWD duration in both Wistar and WAG/Rij rats: the incidence was 1.6 times higher and the mean SWD duration was 1.4 times longer than in the saline-treated rats. The peak frequency of the SWDs did not change. The hazard rates were lower in the AY-treated rats, so some very long SWDs were observed. Cross correlations of spiky activity in the hippocampus pointed to volume conduction rather than to genuine SWD activity in this area. In summary, we found no indication that SWDs in AY-treated animals differ from typical SWDs. However, since saline-treated rats had many spontaneous SWDs, other rat strains might respond differently. With respect to the mechanism, the appearance of long SWDs suggests that the SWD stopping mechanism is affected by the treatment. We speculate that this effect is due to changes in the distribution of GABA-ergic and glutamatergic receptors in lipid rafts.

Cannabinoid antagonist SLV326 induces convulsive seizures and changes in the interictal EEG in rats.

Cannabinoid CB1 antagonists have been investigated for possible treatment of e.g. obesity-related disorders. However, clinical application was halted due to their symptoms of anxiety and depression. In addition to these adverse effects, we have shown earlier that chronic treatment with the CB1 antagonist rimonabant may induce EEG-confirmed convulsive seizures. In a regulatory repeat-dose toxicity study violent episodes of "muscle spasms" were observed in Wistar rats, daily dosed with the CB1 receptor antagonist SLV326 during 5 months. The aim of the present follow-up study was to investigate whether these violent movements were of an epileptic origin. In selected SLV326-treated and control animals, EEG and behavior were monitored for 24 hours. 25% of SLV326 treated animals showed 1 to 21 EEG-confirmed generalized convulsive seizures, whereas controls were seizure-free. The behavioral seizures were typical for a limbic origin. Moreover, interictal spikes were found in 38% of treated animals. The frequency spectrum of the interictal EEG of the treated rats showed a lower theta peak frequency, as well as lower gamma power compared to the controls. These frequency changes were state-dependent: they were only found during high locomotor activity. It is concluded that long term blockade of the endogenous cannabinoid system can provoke limbic seizures in otherwise healthy rats. Additionally, SLV326 alters the frequency spectrum of the EEG when rats are highly active, suggesting effects on complex behavior and cognition.

Endocannabinoid system protects against cryptogenic seizures.

Effects of the cannabinoid antagonist rimonabant on the EEG were investigated in healthy, non-epileptic rats. The drug was administered orally at 30 mg/kg/day for 3 weeks. The EEG was recorded continuously. In 3 out of 13 rats, limbic convulsive seizures, which were not related to the time of drug administration, were observed after 5-8 days. We hypothesize that an accumulation of micro-injuries in the brain is responsible for these "spontaneous" seizures.