Ca2+-assisted receptor-driven endocannabinoid release:: mechanisms that associate presynaptic and postsynaptic activities

Endogenous cannabinoids (endocannabinoids) serve as retrograde messengers at synapses in various regions of the brain. They are released from postsynaptic neurons and cause transient and long-lasting reduction of neurotransmitter release through activation of presynaptic cannabinoid receptors. Endocannabinoid release is induced either by increased postsynaptic Ca2+ levels or by activation of G(q/11)-coupled receptors. When these two stimuli coincide, endocannabinoid release is markedly enhanced, which is attributed to the Ca2+ dependency of phospholipase C beta (PLC beta). This Ca2+-assisted receptor-driven endocannabinoid release is suggested to participate in various forms of synaptic plasticity, including short-term associative plasticity in the cerebellum and spike-timing-dependent long-term depression in the somatosensory cortex. In these forms of plasticity, PLC beta seems to function as a coincident detector of presynaptic and postsynaptic activities.