Self-stimulation of the nucleus accumbens and some comparisons with hypothalamic self-stimulation

Rats were trained to respond for electrical stimulation of the nucleus accumbens (ACB) or lateral hypothalamus (HYP) in a shuttle-box apparatus. Whereas the HYP rats showed rapid acquisition and stabilization of performance, the ACB rats were slow to learn the task and commonly took longer than 20 daily sessions to stabilize. Once stabilized, both groups responded with similarly vigorous performance. All rats displayed a predominantly locomotor behaviour, which was almost totally devoid of exploratory behaviours typically associated with self-stimulation. The absence of stimulus-bound behaviours was particularly notable in the ACB group. These rats, but not the HYP rats, showed an increase in the latency to initiate stimulation during the daily 25-min test sessions. Depriving the animals of a single self-stimulation session caused a decrease in the latency of ACB rats to initiate on the following day while having no effect on the HYP rats. All ACB rats gradually developed convulsive seizures during the first 3 weeks of testing which subsequently became more frequent and severe. None of the HYP rats showed any involuntary motor effects. The results show that ACB self-stimulation is a very different phenomenon to HYP self-stimulation, and suggest that, in addition to reward and aversion, ACB self-stimulation may involve a stereotyped ritual controlled partly by adaptation and conditioning.