Dissociation of limbic structures by pharmacological effects of diazepam on electrical self-stimulation in the mouse

The effect of diazepam was tested on self-stimulation (SS) in 21 mice implanted with a bipolar electrode in the lateral hypothalamus (LH), the dorsolateral hippocampus (HPC) or the lateral entorhinal cortex (LEC). Diazepam, injected i.p. in doses of 0.5, 1 and 2 mg/kg, significantly increased SS rates with electrodes in LH while 4 and 8 mg/kg of diazepam had no significant effect. At low doses, similar increases were seen in mice with LEC electrodes but high doses produced a significant suppression. HPC animals showed an almost total suppression of SS beginning at 2 mg/kg of diazepam; lower doses had no significant effect. The results indicate that entorhinal and hippocampal SS are at least partly independent phenomena; in addition, the suppression of SS by moderate doses of diazepam remains specific to the HPC among the brain structures studied to date.