Abstracts

Rationale: The endocannabinoid (eCB) system serves a central function in regulating neuronal plasticity. Thus, the eCB system can be considered a putative target for central nervous system diseases including epilepsies. In this study, we modulated the cascade genetically and pharmacologically and analyzed the impact on epileptogenesis and ictogenesis. Methods: Twenty male conditional cannabinoid (CB)-1 receptor knockout (KO)-mice (CB^{1f/f;CaMKIIαCre}) along with littermate controls (CB^1f/f) and twenty male NMRI mice, for the genetic and pharmacological studies respectively, were stimulated once daily via an implanted depth electrode. NMRI mice received i.p. injections of either the selective CB1 receptor-antagonist SR-141716 (5mg/kg i.p.) or vehicle thirty minutes prior to each kindling stimulation. Following kindling we analyzed locomotion, exploratory and anxiety-like behaviors in the Black and White Box (BWB) and the Open Field (OF). Neuronal progenitor cells were stereologically assessed based on immunohistological labeling of doublecortin. Results: Both the lack of CB1 receptors in KO mice (n=10) as well as antagonism at CB1 receptors (n=11) caused no differences in the development of generalized seizures but resulted in significantly longer seizure durations. Lower initial thresholds were detected in KO-mice as compared to littermate controls (p=0.0281, n=10). In the OF, KO mice spent less time in the center (non-kindled n= 8, p=0.0421; kindled n=9, p=0.0374) and more time engaging in thigmotaxis (p=0.0111 and p=0.012) as compared to littermate controls (non-kindled n= 8, kindled n=10). The two-way ANOVA revealed a significant impact of the genotype (p<0.0001) on anxiety-related behavior. In contrast, there was no inter-group difference between vehicle-treated (non-kindled n=11, kindled n=9) and SR-141716-treated mice (kindled n=11). In the BWB, kindled KO mice spent a significantly longer time in the white compartment (p=0.012) and had 41% more transitions (p=0.0025) than non-kindled controls (p=0.012; kindled n=10, non-kindled n=9). No significant inter-group differences in the pharmacological modulation of the eCB system were observed (vehicle non-kindled n=11, vehicle kindled n=9, kindled SR-141716 n=10). Compared to the non-stimulated control, kindling resulted in an increased hippocampal density of neuronal progenitor cells without any genotype-dependent differences. Conclusions: The study demonstrated that the eCB cascade affects seizure susceptibility as well as endogenous termination of seizure activity, but fails to influence kindling acquisition. Thus, eCB signaling seems to play a role in ictogenesis but not epileptogenesis. We are grateful to Prof. Dr. Beat Lutz for generating and providing the conditional knock-out mice. In addition we thank Marion Fisch, Barbara Kohler, Andrea Wemeyer and Angela Vicidomini for their excellent technical assistance. The authors are grateful for a scholarship from the Elitenetzwerk Bayern for E.-L. von Rüden.