Cannabinoids in the Treatment of Epilepsy.

Endocannabinoids are key modulators of synaptic function. By activating cannabinoid receptors expressed in the central nervous system, these lipid messengers can regulate several neural functions and behaviors. As experimental tools advance, the repertoire of known endocannabinoid-mediated effects at the synapse, and their underlying mechanism, continues to expand. Retrograde signaling is the principal mode by which endocannabinoids mediate short- and long-term forms of plasticity at both excitatory and inhibitory synapses. However, growing evidence suggests that endocannabinoids can also signal in a nonretrograde manner. In addition to mediating synaptic plasticity, the endocannabinoid system is itself subject to plastic changes. Multiple points of interaction with other neuromodulatory and signaling systems have now been identified. In this Review, we focus on new advances in synaptic endocannabinoid signaling in the mammalian brain. The emerging picture not only reinforces endocannabinoids as potent regulators of synaptic function but also reveals that endocannabinoid signaling is mechanistically more complex and diverse than originally thought. Copyright © 2012 Elsevier Inc. All rights reserved.

Abnormally high spiking activity can damage neurons. Signaling systems to protect neurons from the consequences of abnormal discharge activity have been postulated. We generated conditional mutant mice that lack expression of the cannabinoid receptor type 1 in principal forebrain neurons but not in adjacent inhibitory interneurons. In mutant mice,the excitotoxin kainic acid (KA) induced excessive seizures in vivo. The threshold to KA-induced neuronal excitation in vitro was severely reduced in hippocampal pyramidal neurons of mutants. KA administration rapidly raised hippocampal levels of anandamide and induced protective mechanisms in wild-type principal hippocampal neurons. These protective mechanisms could not be triggered in mutant mice. The endogenous cannabinoid system thus provides on-demand protection against acute excitotoxicity in central nervous system neurons.

Cannabidiol (CBD), a major nonpsychotropic constituent of Cannabis, has multiple pharmacological actions, including anxiolytic, antipsychotic, antiemetic and anti-inflammatory properties. However, little is known about its safety and side effect profile in animals and humans. This review describes in vivo and in vitro reports of CBD administration across a wide range of concentrations, based on reports retrieved from Web of Science, Scielo and Medline. The keywords searched were "cannabinoids", "cannabidiol" and "side effects". Several studies suggest that CBD is non-toxic in non-transformed cells and does not induce changes on food intake, does not induce catalepsy, does not affect physiological parameters (heart rate, blood pressure and body temperature), does not affect gastrointestinal transit and does not alter psychomotor or psychological functions. Also, chronic use and high doses up to 1,500 mg/day of CBD are reportedly well tolerated in humans. Conversely, some studies reported that this cannabinoid can induce some side effects, including inhibition of hepatic drug metabolism, alterations of in vitro cell viability, decreased fertilization capacity, and decreased activities of p-glycoprotein and other drug transporters. Based on recent advances in cannabinoid administration in humans, controlled CBD may be safe in humans and animals. However, further studies are needed to clarify these reported in vitro and in vivo side effects.