Figure 5.

Fluorescence in situ hybridization (FISH) of let-7 before and after the treatment with morphine (75 mg/pellet/mouse). The brain cortex was used for the analysis of let-7 mRNA by FISH. Samples were costained using anti-MOR antibody (1:5000) to determine the level of let-7 in MOR-expressing cells. The let-7 transcript was increased after morphine treatment. Moreover, the increase was observed in MOR-expressing cells (arrows indicate representative cells with costaining of MOR and let-7), but not in MOR-negative cells (only DAPI nuclear staining, but no MOR staining). Fifteen prefrontal cortex slices from 3 mice were studied for each condition. In the control group, 78 MOR-expressing cells and 60 MOR-negative cells were imaged. In the morphine group, let-7 upregulation occurred in 78/85 MOR-expressing cells; no cell showed let-7 response in MOR-negative cells (0/65).