CBD works best as preventive epilepsy treatment, not after seizures start

Malformations of cortical development (MCD) are major causes of refractory epilepsies, particularly in children. Cannabidiol (CBD) has demonstrated efficacy in treatment of refractory pediatric epilepsy syndromes. However, preclinical studies addressing its developmental stage-dependent effects, particularly in experimental models of MCD, remain limited. We evaluated the effects of CBD on induced hyperexcitability in cortical brain slices from Wistar rats with and without MCD at distinct developmental stages and examined whether alterations in endocannabinoid system (ECS) components are associated with CBD responsiveness. MCD was induced by bilateral cortical freeze lesion at postnatal day (P0-1) to generate microgyria in the somatosensory cortex. Local field potentials were recorded from cortical slices of juvenile (P21-30) and adolescent (P35-60) Sham and MCD rats. CBD was applied under three different timing paradigms to assess its effects on epileptiform activity induced by modified artificial cerebrospinal fluid containing 4-aminopiridine (4-AP) and 0 Mg2+ (mACSF). Gene expression of ECS components was quantified in cortical tissue by RT-qPCR at both developmental stages. CBD co-applied with mACSF reduced short (>2-10 s) ictal events in slices from Sham and decreased prolonged (>100 s) ictal events in slices mainly from MCD animals at both ages. CBD did not attenuate pre-established hyperexcitability. However, pre-exposure to CBD delayed ictal onset, reduced overall ictal events frequency, particularly in juvenile Sham animals, and abolished long-lasting ictal events in slices from adolescent animals. Cortical samples from juvenile MCD animals exhibited increased gene expression of NAPE-PLD, MGLL, CB1R and CB2R, whereas DAGL was reduced in adolescence. CBD exerted age- and context-dependent modulatory effects on cortical hyperexcitability, with stronger preventive than therapeutic actions. Developmental stage, cortical organization and alterations in ECS components may influence CBD responsiveness. These findings highlight the importance of maturational, cortical network and molecular context when evaluating cannabinoid-based strategies for MCD-related refractory epilepsies.