Neurobiology and systems physiology of the endocannabinoid system

Endocannabinoids are synthesised from lipid precursors, are released from postsynaptic neurons in an activity-dependent way, and act as retrograde signalling messengers on specific G (i)-protein-coupled cannabinoid (CB (1)) receptors on presynaptic terminals. Hence, endocannabinoids are in a strategic position to regulate transmitter release. CB (1)-receptors are abundant on GABAergic, glutamatergic and dopaminergic synapses and play an essential role in a variety of cognitive processes and in the control of behaviour. The endocannabinoid system is not only the target of the psychoactive components of the hemp plant (tetrahydrocannabinol from hashish and marijuana) but has also been exploited for drugs acting as agonists (e.g. dronabinol) or antagonists (e.g. rimonabant) of the CB (1)-receptor. The former drugs exert orexigenic effects and can be used for the mitigation of anorexia e.g. in cancer patients, but have also been used for the treatment of multiple sclerosis. The latter have been used to treat adipositas. The role of the endocannabinoid system in the development of drug dependence has been discussed controversially, but recent evidence suggests that chronic stimulation of the endocannabinoid system may facilitate drug dependence.