To study how meth and the immune system interact and regulate dopamine levels, we measured the electrical and chemical activity of dopamine neurons in mouse brain specimens treated with either meth or an immune molecule called TNF-α. This molecule is known to induce inflammation in the body.

We found that meth and TNF‑α converge in a part of the brain called the ventral tegmental area, a key reward hub that produces dopamine. In this area of the mouse brain, TNF‑α increased dopamine levels and neuronal activity in similar ways as meth.