This proposal focuses on examining the mechanism of cannabidiol (CBD), a non-psychoactive component of cannabis with documented anti-seizure effects in several pre-clinical studies(1, 2) and a recent double-blinded, multicenter phase III clinical trial in patients with treatment-resistant epilepsy(3, 4). Despite centuries of clinical usage, the mechanism of action of CBD remains ambiguous. Further exploring the pharmacology of CBD may provide benefit to the 1/3 of epilepsy patients with seizures resistant to current treatments (10). In one leading hypothesis, CBD acts as a competitive antagonist at the G-protein coupled receptor, GPR55, inhibiting binding of a membrane phospholipid, lysophosphatidylinositol (LPI). CBD blocks LPI- mediated increases in presynaptic Ca2+ and vesicular release, thus reducing excitability at axon terminals (12). However, the function of LPI-GPR55 signaling at inhibitory synapses, as well as potential postsynaptic effects, remains to be explored. Using a multidisciplinary approach with ex vivo whole cell patch clamp electrophysiology, and in vitro immunocytochemistry and molecular biology, I discovered that LPI had unique effects at excitatory and inhibitory synapses, both at the pre- and postsynapse. At 5-10 minutes post application, LPI increased the frequency of vesicular release in CA1 hippocampus, consistent with previous reports of presynaptic locus of GPR55 action(12). However, contrary to prior studies, I identified prominent GPR55 staining in the cell bodies of CA1 pyramidal neurons, and a postsynaptic LPI effect of increased GluA1 AMPAR expression at 50-60 minutes post application. I also determined that LPI reduced inhibitory postsynaptic strength, in part by reducing GABAAR ?2 subunit expression. Taken together, these results suggest that LPI increases the excitatory / inhibitory ratio in hippocampal neuronal networks by a dual mechanism: enhancing excitatory transmission and attenuating inhibition. This predicts that CBD, by opposing LPI action, may exert its beneficial anti-seizure effects on both excitatory and inhibitory synapses through actions at GPR55. I plan to explore these possibilities by repeating these experiments with CBD pre-treatment and GPR55-/- mice as controls. To supplement these experiments at the circuit level, I plan to investigate how LPI and CBD regulate evoked transmission and short-term plasticity in CA3-CA1 hippocampal circuits. At the in vivo level, I will use both acute and chronic seizure models to determine seizure susceptibility in GPR55-/- mice. Based on surprising preliminary results, I discovered that seizure activity upregulates GPR55 membrane expression, producing a biomarker for prolonged seizures and potentiating the effects of LPI. In all, as part of this fellowship, I propose to combine my clinical training and scientific experience to elucidate the mechanisms of this intriguing therapeutic target for epilepsy, and help stratify subpopulations for targeted treatment.

Public Health Relevance

Current anti-seizure targets are unsuccessful in 1/3 of patients with epilepsy, demonstrating a critical need for novel, targeted therapeutics. Recent pre-clinical and clinical evidence suggests that cannabidiol (CBD) may provide an effective, tolerable alternative to current therapeutics, however its mechanism of action is unclear. In this study, I will examine a newly described proposed target for cannabidiol, and examine potential pathways by which CBD controls seizure activity at the synaptic, systems, and in vivo level.

National Institute of Health (NIH)
National Institute of Neurological Disorders and Stroke (NINDS)
Individual Predoctoral NRSA for M.D./Ph.D. Fellowships (ADAMHA) (F30)
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Neurological Sciences Training Initial Review Group (NST)
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Whittemore, Vicky R
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New York University
Schools of Medicine
New York
United States
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French, Jacqueline A; Koepp, Matthias; Naegelin, Yvonne et al. (2017) Clinical studies and anti-inflammatory mechanisms of treatments. Epilepsia 58 Suppl 3:69-82
Rosenberg, Evan C; Louik, Jay; Conway, Erin et al. (2017) Quality of Life in Childhood Epilepsy in pediatric patients enrolled in a prospective, open-label clinical study with cannabidiol. Epilepsia 58:e96-e100
Rosenberg, Evan C; Patra, Pabitra H; Whalley, Benjamin J (2017) Therapeutic effects of cannabinoids in animal models of seizures, epilepsy, epileptogenesis, and epilepsy-related neuroprotection. Epilepsy Behav 70:319-327
Rosenberg, Evan C; Tsien, Richard W; Whalley, Benjamin J et al. (2015) Cannabinoids and Epilepsy. Neurotherapeutics 12:747-68