um, so...
The receptors that bind nicotine are distributed throughout the brain- including areas involved in learning and memory, vision, movement, thought, emotion, dreaming, and pleasure. They're there to respond to acetylcholine (the endogenous transmitter), but are by activated by nicotine as well. The blood plasma levels of nicotine in smokers (and probably vapers) aren't high enough to kill the cells that have the receptors. There are changes in the subtypes of the receptors to compensate, but not cell death. In specific experimental circumstances (cells in a dish), nicotine has been reported to be neuroprotective.