Mice lacking neuropeptide Y show increased sensitivity to cocaine.

@article{Srensen2012MiceLN,
  title={Mice lacking neuropeptide Y show increased sensitivity to cocaine.},
  author={Gunnar S{\o}rensen and David P. D. Woldbye},
  journal={Synapse},
  year={2012},
  volume={66 9},
  pages={
          840-3
        }
}
There is increasing data implicating neuropeptide Y (NPY) in the neurobiology of addiction. This study explored the possible role of NPY in cocaine-induced behavior using NPY knockout mice. The transgenic mice showed a hypersensitive response to cocaine in three animal models of cocaine addiction. Whether this is due to an observed compensatory increase in striatal dopamine transporter binding or an anxiogenic phenotype of the transgenic mice remains to be determined.