Endocannabinoids: a new family of lipid mediators involved in the regulation of neural cell development.

The endocannabinoids (eCBs) anandamide and 2-arachidonoylglycerol are important retrograde messengers that inhibit neurotransmitter release via presynaptic CB1 receptors. In addition, cannabinoids are known to modulate the cell death/survival decision of different neural cell types, leading to different outcomes that depend on the nature of the target cell and its proliferative/differentiation status. Thus, cannabinoids protect primary neurons, astrocytes and oligodendrocytes from apoptosis, whereas transformed glial cells are prone to apoptosis by cannabinoid challenge. Moreover, a potential role of the eCB system in neurogenesis and neural differentiation has been proposed. Recent research shows that eCBs stimulate neural progenitor proliferation and inhibit hippocampal neurogenesis in normal adult brain. Cannabinoids inhibit cortical neuron differentiation and promote glial differentiation. On the other hand, experiments with differentiated neurons have shown that cannabinoids also regulate neuritogenesis, axonal growth and synaptogenesis. These new observations support that eCBs constitute a new family of lipid signaling cues responsible for the regulation of neural progenitor proliferation and differentiation, acting as instructive proliferative signals through the CB1 receptor.