Fig 2: Immunohistochemical staining sections of the brain cortex of six groups showing positive cytoplasmic expression of CHOP antibodies in all groups, including G6 (normal control). Negative expression of caspase-8 antibodies in all groups except mild expression in G4 (nicotine) and G1 (high-dose tramadol). P53 is expressed in all groups with the lowest positivity in G3 (nicotine+tramadol) and G6 (normal control) (×400 all).

Fig 3: Western blot protein expression of the CHOP endoplasmic reticulum stress (ER stress) marker in rats' brains. The figure also demonstrated Caspase-8 expression, the other BIP ER stress marker, and B-actin as reference protein. As regards CHOP expression, the highest expression was recorded in the nicotine group. The lowest expression was noticed in the high Tramadol group. The combined category showed less CHOP expression than nicotine alone.

Fig 4: Immunohistochemical staining sections of the brain hippocampus of six groups showing different expressions of CHOP antibodies with the lowest expression in G1 (high-dose tramadol) and G6 (normal control). Caspase-8 antibody is negative in all groups showing only focal positivity in G1 (high-dose tramadol) and G6 (normal control). P53 antibody is negative in all groups except showing mild positivity in G4 (nicotine) and G5 (Olanzapine). (×400 all).