Adolescent Ethanol Intake Alters Cannabinoid Type-1 Receptor Localization in Astrocytes of the Adult Mouse Hippocampus

Cannabinoid type-1 (CB ) 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 receptor expression in astrocytes is affected by long-term exposure to stressors. Here we examined CB receptors in astrocytes of ethanol (EtOH)-exposed adolescent mice to determine its effect on CB 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 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 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 receptor expression in hippocampal astrocytes of adult mice exposed to EtOH during adolescence reveals a long lasting effect of EtOH on astrocytic CB receptors. This deficiency may also have negative consequences for synaptic function.