As discussed in greater detail in this special issue, the expression profile of CB1Rs evolves over time and across regions from a predominantly white matter distribution in embryonic brain to a definitive pattern in gray matter areas in the adult brain. Neurogenesis involves the proliferation of progenitor cells, migration, neuronal specification, final positioning, and synaptogenesis. Emerging evidence suggests that the endocannabinoid system influences these processes in fundamental ways [6, 20, 21, 64, 70, 85, 109, 162, 232]. The cannabinoid system has been shown to regulate neural progenitor proliferation, differentiation, and migration, thus contributing to determining the final positions and densities of immature pyramidal cells. Endocannabinoids are developmental cues that help determine neuronal identity at both the cellular and neuronal network levels. Thus, endocannabinoid signaling influences the process by which developing neurons differentiate into both glutamatergic [162] and GABAergic phenotypes [20]. Furthermore, the cannabinoid system plays a key role in dendrite arborization, neurite outgrowth or retraction, axonal specification, axonal elongation, axonal fasciculation, axonal navigation, migration, and positioning of inhibitory GABAergic interneurons and excitatory glutamatergic neurons [20, 21, 232].
