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Purpose: Thresholds to pentylenetetrazol (PTZ) seizures were usually based only on clinical symptoms. Our purpose was to use electroclinical patterns to assess the efficacy of a ketogenic and/or calorie-restricted diet on PTZ-induced seizures.
Methods: Forty 50-day-old rats were divided in four weight-matched groups and fed controlled diets: normocalorie carbohydrate (NC), hypocalorie carbohydrate (HC), normocalorie ketogenic (NK), and hypocalorie ketogenic (HK). After 21 days, blood glucose and β-hydroxybutyrate levels were determined and seizures were induced by continuous infusion of PTZ. The clinical and EEG thresholds to each seizure pattern were compared between the different groups.
Results: The electroclinical course of PTZ-induced seizures was similar in all groups. The HK group exhibited higher thresholds than the other ones for most clinical features: absence (p = 0.003), first overt myoclonia (p = 0.028), clonic seizure (p = 0.006), and for EEG features: first spike (p = 0.036), first spike-and-wave discharge (p = 0.014), subcontinuous spike-and-wave discharges (p = 0.005). NK, HC, and NC groups were not significantly different from each other. Blood glucose and β-hydroxybutyrate levels were not correlated with electroclinical seizure thresholds. After the clonic seizure, despite stopping PTZ infusion, a tonic seizure occurred in some animals, without significant difference regarding the diet.
Conclusion: This approach permitted a precise study of the electroclinical course of PTZ-induced seizures. In addition to the usually studied first overt myoclonia, we clearly demonstrated the efficiency of a calorie restricted KD in elevating thresholds to most electroclinical seizure patterns. We confirmed the lack of efficiency of the KD to reduce seizure severity once the seizure has started.
The KD is a high-fat, low-protein, and low-carbohydrate diet with a usual ratio of 4:1 of fats to carbohydrates + proteins (by weight). Seizure control appears to be more effective with high lipid/carbohydrate + protein ratios both in clinical (Freeman et al., 2000) and experimental settings (Bough et al., 2000b). In rodents, maximal anti-seizure efficacy is achieved at about 1–2 weeks after initiation of the KD (Appleton and DeVivo, 1974; Bough and Eagles, 1999; Rho et al., 1999; Bough et al., 2006) and the same delay for maximal efficacy was reported in humans (Freeman et al., 2000). In humans, the outcome of treatment with the KD seems to be unrelated to age, sex, seizure type, or frequency and at least 50% of the patients treated with the KD undergo 50% or more reduction of seizure number (Schwartz et al., 1989a; Freeman et al., 1998; Vining et al., 1998). In animals, the effects of the KD are more modest. Increases of only 15–20% in seizure thresholds have been reported in mice and rats (Appleton and DeVivo, 1974; Bough et al., 1999b; Rho et al., 1999). KDs are effective in both young (Uhlemann and Neims, 1972; Otani et al., 1984; Bough et al., 1999b) and adult rodents (Appleton and DeVivo, 1974; Muller-Schwarze et al., 1999).
Recently, it was also reported that calorie restriction in a normal carbohydrate diet is able to increase seizure threshold (Bough et al., 2003). A 50% calorie restriction appears as effective as the KD with a significantly lower ketonemia (Eagles et al., 2003). These data are in line with clinical reports, both during the initiation period of the KD and beyond if seizures cluster (Freeman and Vining, 1999). In fact, classically, calorie restriction is an integral part of the KD in humans (Bough et al., 2000a, 2000b; Greene et al., 2001, 2003).
Several earlier studies measured the threshold to pentylenetetrazol (PTZ)-induced seizures in rats fed a KD (Bough et al., 2000a, 2000b; Nylen et al., 2005) or subjected to calorie restriction (Bough et al., 1999b; Eagles et al., 2003) but these studies were only based on the observation of clinical seizure symptoms. In the present work, we used either a KD and/or calorie-restricted diet in rats receiving a PTZ infusion in the tail vein but we performed threshold measurements under EEG recording. Indeed, progressively increasing doses of PTZ lead first to spike-and-wave discharges that are followed by myoclonic, clonic, and tonic–clonic seizures by increasing the dosage of the convulsant (Andre et al., 1998). Our purpose was to control whether the efficacy of the KD and/or calorie restriction was similar on the different types of seizures induced by PTZ and whether clinical signs of seizure activity can be considered as reliable and sufficient indexes to assess seizure activity.