Diazepam's Impact on Self-Stimulation but Not Stimulation-Escape Suggests Hedonic Modulation

In rats that self-administered lateral hypothalamic (LH) stimulation through chronically implanted electrodes, ip diazepam (DZ) increased rates and decreased thresholds of self-stimulation (SS) in a dose-related manner. Stimulation-escape (SE), however, was refractory to the drug. There was a complete dichotomy in electrode placements along the anterior/posterior plane. Every pure-reward electrode location was posterior to every reward-escape electrode. DZ-sensitive SS appears to be mediated by a reward substrate common to both pure-reward and reward-escape rats, whereas SE is supported by an aversive system unaffected by DZ and stimulated only in those rats with anterior placements. The lack of control over SE suggests that the drug's effect on stimulation-induced conduct is to increase reward rather than to decrease aversion. This hypothesis is discussed in the context of DZ's interactions with drugs of abuse.