Adolescent ethanol intake alters cannabinoid type‐1 receptor localization in astrocytes of the adult mouse hippocampus

Cannabinoid type‐1 (CB 1 ) receptors are widely distributed in the brain and play important roles in astrocyte function and the modulation of neuronal synaptic transmission and plasticity. However, it is currently unknown how CB 1 receptor expression in astrocytes is affected by long‐term exposure to stressors. Here we examined CB 1 receptors in astrocytes of ethanol (EtOH)‐exposed adolescent mice to determine its effect on CB 1 receptor localization and density in adult brain. 4–8‐week‐old male mice were exposed to 20 percent EtOH over a period of 4 weeks, and receptor localization was examined after 4 weeks in the hippocampal CA1 stratum radiatum by pre‐embedding immunoelectron microscopy. Our results revealed a significant reduction in CB 1 receptor immunoparticles in astrocytic processes of EtOH‐exposed mice when compared with controls (positive astrocyte elements: 21.50 ± 2.80 percent versus 37.22 ± 3.12 percent, respectively), as well as a reduction in particle density (0.24 ± 0.02 versus 0.35 ± 0.02 particles/μm). The majority of CB 1 receptor metal particles were in the range of 400–1200 nm from synaptic terminals in both control and EtOH. Altogether, the decrease in the CB 1 receptor expression in hippocampal astrocytes of adult mice exposed to EtOH during adolescence reveals a long lasting effect of EtOH on astrocytic CB 1 receptors. This deficiency may also have negative consequences for synaptic function.