Astrocyte CB1 receptors are required for inhibitory maturation and ocular dominance plasticity in the mouse visual cortex

Abstract

Neuronal circuits are shaped by experience. This happens much more readily in the young compared to the adult brain. The unique learning capacity of the young brain is regulated through postnatal critical periods, during which the ability of neuronal networks to re-wire is greatly enhanced. Endocannabinoids, which signal through the cannabinoid CB1 receptor (CB1R), regulate several forms of neuronal plasticity. In the developing neocortex, CB1Rs play a key role in the maturation of inhibitory circuits. For example, interfering with CB1R signaling during development disrupts inhibitory maturation in the prefrontal cortex. In developing primary visual cortex (V1), endocannabinoid-mediated plasticity at inhibitory synapses regulates the maturation of inhibitory synaptic transmission, shifting synapses from an immature state characterized by strong short-term depression to a mature state with reduced short-term depression. This maturation step correlates with the timing of the critical period. While CB1Rs were originally thought to reside mainly on presynaptic axon terminals, recent studies have highlighted an unexpected role for astrocytic CB1Rs in endocannabinoid mediated plasticity. Here, we investigate the impact of cell-type specific removal of CB1Rs from interneurons or astrocytes on development of inhibitory synapses and network plasticity of V1. We show that removing CB1Rs from astrocytes interferes with maturation of inhibitory synaptic transmission in V1. In addition, it strongly reduces ocular dominance (OD) plasticity during the critical period. In contrast, removing interneuron CB1Rs leaves these processes intact. Our results reveal an unexpected role of astrocytic CB1Rs in critical period plasticity in V1, and highlight the involvement of glial cells in the plasticity and synaptic maturation of sensory circuits.