Endokannabinoide sistemaren parte-hartzea arratoien garuntxoaren jaio osteko garapenean

Abstract

The endocannabinoid system (ECS) is widely distributed throughout the organism. This system influences brain development and suppresses neurotransmitter release in the mature brain, thus intervening in brain circuit formation and neural communication. Because of methodological limitations, most investigations focused on the study of the embryo development have been carried out in cell culture. In the central nervous system, the ECS is highly expressed in the cerebellar cortex where it plays a crucial role in the postnatal development of the granule cells. However, little is known about how the precise localization of the components of the ECS takes place during the early postnatal development, which is needed for the correct wiring of the cerebellar circuits. In this study, we used high resolution immunoelectron microscopy to investigate the subcellular localization of the cannabinoid CB₁ receptor and the main enzymes for the synthesis and degradation of the endocannabinoid 2-arachidonoyl-glycerol (2-AG), diacylglycerol lipase (DAGL-α) and monoacylglycerol lipase (MAGL), respectively, in the granule cells during the early postnatal development of the cerebellum. The CB₁ receptor, DAGL-α and MAGL were localized at the granule cell axons, the parallel fibers, during granule cell migration and axon elongation occurring at early postnatal age. Moreover, CB₁ receptor and DAGL-α immunoparticles were placed in the parallel fiber membranes, while MAGL labeling was at the parallel fiber membranes and cytoplasm. At postnatal day 12, when parallel fibers make already synapses with the Purkinje cell dendritic spines, the CB₁ receptor exhibited the typical presynaptic localization in parallel fiber terminal membranes, and MAGL was close to the membrane and in the cytoplasm of the parallel fiber terminals. However, DAGL-α was excluded from the parallel fiber terminals but it was expressed at postsynaptic sites. Altogether, the expression of CB₁ receptors, DAGL-α, and MAGL in the granule cell parallel fibers starts at early stages of the postnatal development. Later on, the CB₁ receptors and MAGL remain in the mature parallel fiber synapses, while DAGL-α disappears from them and switches to the postsynaptic dendritic spines of the Purkinje cells. These structural changes correlate with the functions in which the ECS is involved during postnatal development. Hence, the identification of the specific localization of the components of the ECS in the developing cerebellum is crucial for understanding the structural, functional and behavioral changes taking place in the brain by cannabis consume. Furthermore, this knowledge could be exploited therapeutically as the ECS manipulation might have potential clinical applications in the treatment of brain diseases caused by abnormal development of the brain.