The dorsal hippocampus (DH) is primarily involved in
the formation
of contextual fear-conditioned (CxFC) memory. However, CxFC memory
can be formed even in the absence of the DH. In addition to the DH,
the infralimbic cortex (IL), a sub-region of the medial prefrontal
cortex (mPFC), also plays an important role in the consolidation of
CxFC memory. However, role of IL in the development of compensatory
CxFC memory is not known. Here, we have examined (a) the development
of the compensatory circuitry of CxFC memory within 3 days after the
first test in the absence of the DH and (b) the role of IL in the
induction of compensatory CxFC memory in the absence of the DH. The
DH-lesioned rats re-trained for CxFC 1 day after the first testing
exhibited significantly less freezing compared to the control group.
However, the DH-lesioned rats, re-trained for CxFC 3 days after the
first testing, showed a robust freezing response. It suggests that
the fully functional compensatory circuitry of contextual fear memory
develops after multiple training separated by 3 days. Furthermore,
we observed that reversible inactivation of the IL of the DH-lesioned
rats during the first training waned the formation of compensatory
CxFC. It suggests that (a) the IL receives contextual fear memory
information during the first trial in the absence of the DH and (b)
perturbation in fear memory information encoding in the IL during
the first trial impairs the development of the compensatory network
in the absence of the DH.
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