Nicotine and cocaine modulate
self-stimulation behavior
In a self-stimulation experiment, rats were permitted to apply
microstimulation to themselves at will.  The rate at which they
applied microstimulation depended upon the stimulation frequency.
Strikingly, both cocaine and nicotine increase behavioral response
rate for a given stimulation frequency compared to baseline.  Thus,
cocaine and nicotine appear to enhance the pleasure produced by
self-stimulation.
PNS Fig. 51.9