Opposite effects of shell or core stimulation of the nucleus accumbens on long-term potentiation in dentate gyrus of anesthetized rats

Hippocampal long-term potentiation (LTP) is a long-lasting increase in synaptic efficacy which is considered a cellular correlate of learning and memory. It has been shown that both, stimuli with emotional/motivational content and the electrical stimulation the basolateral amygdala, can modulate hippocampal LTP. The nucleus accumbens is part of the ventral striatum and is composed of two main regions: core and shell. Core and shell share a similar cellular composition, but differ in their connectivity with other brain areas. Considering that the nucleus accumbens is related to motivation and that it receives a strong projection from the basolateral amygdala, we have studied the effect of stimulating accumbens shell or core on medial perforant path-granule cells' LTP in anesthetized male Wistar rats. We found that electrical stimulation of the shell enhances the magnitude of LTP while the stimulation of the core completely prevents LTP induction. The stimulation of the accumbens shell or core alone produced no apparent, direct field potential in dentate gyrus. Additionally, the co-stimulation of the shell or core with the medial perforant path does not modify the input-output curves obtained using stimulation of the perforant path only. These results demonstrate that electrical stimulation of the accumbens shell or core has a bidirectional effect on LTP induction at the dentate gyrus.