Childhood absence epilepsy (CAE) is characterized by frequent seizures consisting of spike–wave discharges (SWDs) and motor arrest that arise from dysfunctional cortico‐thalamic networks [1]. Although CAE has long been considered a relatively benign epilepsy, up to one third of patients are pharmaco‐resistant and many develop long‐lasting neuropsychiatric comorbidities, including attentional and memory deficits, anxiety, and mood disorders [1]. These limitations underscore the need for mechanism‐based therapeutic strategies targeting network dysfunction rather than seizure suppression alone.

Among emerging targets, the endocannabinoid system (ECS) has attracted increasing attention because of its central role in regulating neuronal excitability, synaptic transmission, and activity‐dependent plasticity [2, 3, 4]. Endocannabinoids (eCBs) act as retrograde messengers that constrain excessive neurotransmitter release and stabilize network activity. Despite the clinical success of cannabidiol (CBD) in Dravet and Lennox–Gastaut syndromes [5], evidence supporting cannabinoid‐based therapies in CAE remains limited and conflicting [3]. Notably, direct activation of cannabinoid type‐1 receptors (CB1Rs) using Δ9‐tetrahydrocannabinol or synthetic agonists consistently exacerbates absence seizures (ASs) in genetic absence epilepsy models, including WAG/Rij and GAERS rats (see [3] and reference therein).

In contrast, a growing body of preclinical evidence indicates that circuit‐restricted enhancement of endogenous cannabinoid signaling suppresses absence seizures. Focal administration of anandamide (AEA), palmitoylethanolamide (PEA), or CB1R agonists into thalamic or cortical nodes of the SWD‐generating network reduces seizure activity in WAG/Rij rats [6]. Similarly, CB1R positive allosteric modulators attenuate ASs in GAERS without producing the pro‐absence effects associated with orthosteric agonists (see [3] and reference therein). These observations suggest that the outcome of ECS modulation critically depends on both anatomical localization and mode of receptor engagement.

Here, we provide electrophysiological in vivo evidence that selective enhancement of endogenous cannabinoid tone via inhibition of fatty acid amide hydrolase (FAAH) robustly suppresses absence seizures in GAERS rats. All procedures were approved by the Cardiff University Animal Ethics Committee and conducted in accordance with ARRIVE guidelines, the Basel Declaration (3Rs), and UK Home Office regulations. Using video‐EEG recordings combined with automated detection and blinded manual validation of SWDs, we assessed the effects of the irreversible FAAH inhibitor PF‐04457845 [7] following acute (Figure 1A–G) and subchronic (7 days) systemic administration (Figure 1H–N), as well as focal bilateral microinfusion into the ventrobasal (VB) thalamus (Figure 2A–G). Across all experimental paradigms, FAAH inhibition consistently reduced ASs, primarily by decreasing seizure number and total time spent in seizures, while exerting minimal effects on mean seizure duration (Figures 1, 2).

Acute intraperitoneal administration of PF‐04457845 (1–3 mg/kg, i.p.) produced a clear, time‐dependent reduction in SWDs, evident within 1–3 h after injection (Figure 1A–G). Quantitative EEG analyses demonstrated a significant decrease in both seizure frequency and cumulative seizure time compared with vehicle‐treated controls. Notably, the magnitude of the anti‐absence effect was comparable at both doses, suggesting that near‐complete FAAH inhibition may already be achieved at the lower dose, consistent with the high potency and irreversible mechanism of PF‐04457845 [7]. At higher doses, compensatory mechanisms such as CB1R desensitization or synaptic saturation [4] within thalamocortical circuits may further limit efficacy.

Repeated systemic administration of PF‐04457845 (1 mg/kg, i.p. for 7 days) resulted in a more pronounced suppression of ASs, with no evidence of tolerance (Figure 1H–N). This subchronic treatment significantly reduced seizure number and total seizure time across the recording period, again without consistently affecting seizure duration. These findings indicate that FAAH inhibition produces sustained anti‐absence efficacy and may be compatible with chronic therapeutic use, an important consideration for CAE.

To determine whether thalamic FAAH inhibition is sufficient to suppress ASs, PF‐04457845 was microinfused bilaterally into the VB. Focal VB administration markedly reduced seizure number and total seizure time (Figure 2A–G), closely mirroring the effects observed after systemic treatment. This result demonstrates that enhancement of endogenous cannabinoid signaling within the VB alone is sufficient to attenuate pathological thalamocortical oscillations underlying ASs. Given the central role of VB thalamocortical neurons in the generation of pASs [1], these data highlight the VB as a critical site for ECS‐mediated seizure control.

The present findings are mechanistically relevant in view of previous evidence indicating altered ECS signaling in experimental ASs. GAERS and WAG/Rij rats display region‐specific changes in CB1R expression and endocannabinoid levels within cortico‐thalamic circuits [8]. Importantly, FAAH inhibition enhances on‐demand AEA signaling while preserving the spatial and temporal specificity of endogenous eCB release, thereby avoiding the widespread receptor activation produced by direct CB1R agonists. This distinction likely explains why FAAH inhibition suppresses ASs, whereas orthosteric agonists exacerbate them.

From a translational perspective, PF‐04457845 has been extensively evaluated in humans and shown to be safe and well tolerated, producing near‐complete FAAH inhibition and robust elevation of AEA levels without major adverse effects [9]. Although clinical trials did not demonstrate efficacy for chronic pain [10], PF‐04457845 reduced cannabis withdrawal symptoms and cannabis use [9], supporting its CNS penetration and functional engagement of FAAH inhibition in humans. Importantly, the absence of overt psychoactive effects [3] distinguishes FAAH inhibition from direct cannabinoid receptor agonism and represents a major advantage for potential use in pediatric epilepsies such as CAE.

Beyond its immediate translational relevance, FAAH inhibition also provides a valuable experimental tool to dissect the contribution of endogenous cannabinoid signaling to cortico‐thalamic network dynamics. By selectively amplifying activity‐dependent endocannabinoid release, FAAH inhibition allows endogenous circuits to retain control over the spatial and temporal domain of cannabinoid signaling. This property is particularly relevant in absence epilepsy, where pathological oscillations emerge from highly structured cortico‐thalamic loops and are exquisitely sensitive to small changes in synaptic balance [1].

In conclusion, we provided EEG‐based functional evidence that circuit‐selective enhancement of endogenous cannabinoid signaling via FAAH inhibition suppresses ASs in GAERS rats. By preferentially reducing seizure initiation without altering seizure duration, FAAH inhibition offers a mechanistically distinct approach compared with existing therapies and reconciles previously conflicting results of cannabinoids' effects on ASs. These results support further preclinical and clinical evaluation of FAAH inhibitors as potential treatments for CAE.