nicotine, neuro-pharmacologically,
nicotine plugs into dopamine receptors in your brain's reward centers - nucleus accumbens, ventral striatum region, Ventral tegmental area, etc... so indirectly this dopamine agonist, among other neuro-cascade effects, and 2nd messenger effects, triggers your norepinephrine and epinephrine release, triggering stimulating fight or flight reflexes, thus keeping you awake