Plasticity in the propagation of hippocampal stimulation-induced activity: a [14C]2-deoxyglucose mapping study

Previous work has suggested that the rewarding effect of hippocampal stimulation develops only as a consequence of neuroplastic change resulting from repeated stimulation experience: naive rats will not initiate self-stimulation for several days, but a prior program of hippocampal kindling greatly facilitates acquisition of self-stimulation. In the current study, the metabolic tracer [14C]2-deoxyglucose was used to measure functional activity during a session of repeated electrical stimulation of the hippocampus to determine whether the resulting activation propagates more widely in experienced hippocampal self-stimulators than in naive rats receiving the same programmed stimulation. A control group of naive unstimulated rats was also included. The results indicated that dorsal CA3 stimulation in naive rats failed to increase metabolic activity in the hippocampus, while in experienced rats, the stimulation produced significant bilateral activation of CA1, CA3, and the ventral subiculum. These results provide support for the hypothesis that development of the rewarding effect of hippocampal stimulation is associated with more widespread propagation of stimulation-induced activity.