Fig 1: 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.