Research reportIntracranial self-stimulation facilitates active-avoidance retention and induces expression of c-Fos and Nurr1 in rat brain memory systems

- ICSS given after active avoidance (TWAA) acquisition improves 48 h retention.
- Does this ICSS effect involve c-Fos and Nurr1 expression in brain memory areas?
- ICSS increases IEGs expression in amygdala, HPC, CPu and LH.
- Acquisition increased both IEGs in HPC (CA), while retention only Nurr1 in amygdala.
- We concluded that post-TWAA ICSS results in IEG changes in memory regions (as CA3).

Intracranial self-stimulation (ICSS), a special form of deep brain stimulation in which subjects self-administered electrical stimulation in brain reward areas as the lateral hypothalamus, facilitates learning and memory in a wide variety of tasks. Assuming that ICSS improves learning and memory increasing the activation of memory-related brain areas, the present work examined whether rats receiving an ICSS treatment immediately after the acquisition session of a two-way active avoidance conditioning (TWAA) show both an improved retention and a pattern of increased c-Fos and Nurr1 protein expression in the amygdala, hippocampus, dorsal striatum and/or lateral hypothalamus. The response of both activity-induced IEGs to ICSS was examined not only as markers of neural activation, but because of their reported role in the neural plasticity occurring during learning and memory formation. Results showed that the TWAA conditioning alone increased the expression of the two analysed IEGs in several hippocampal areas, and TWAA retention increased Nurr1 expression in amygdala. ICSS treatment increased the number of c-Fos and Nurr1 positive cells in almost all the brain regions studied when it was measured 70 min, but not 48 h, after the stimulation. Post-training ICSS treatment, as expected, facilitated the 48 h retention of the conditioning. It is noteworthy that in CA3 conditioning and ICSS separately increased c-Fos expression, but this increasing was greater when both, conditioning and ICSS, were combined. Present results suggest that rapid and transient increased expression of these two synaptic plasticity and memory related IEGs in some hippocampal areas, such as CA3, could mediate the facilitative effects of ICSS on learning and memory consolidation.