Eyelid conditioning, including delay eyelid conditioning and trace eyelid conditioning, has been used extensively to study neural structures and mechanisms of learning and memory as a form of associative learning. In the present study, microcurrent electrical stimulation was used to stimulate the medial prefrontal cortex (mPFC) to induce delay eyelid conditioning in guinea pigs. The acquisition rate and relative latency of the conditioned eyelid response (CR) and the startle eyelid response (SR) were analyzed. The mPFC sites in the guinea pigs were examined under a light microscope following Nissl staining. In addition, the expression of Fos protein in neurons was detected using immunohistochemistry and western blot analysis. The results indicated that the acquisition rates of CR and SR were increased significantly (P<0.05), whilst the relative latencies of CR and SR were decreased significantly (P<0.05). Lesions were observed in the mPFC regions in the training group when compared with the control group. In addition, immunohistochemistry and western blot analysis revealed that Fos expression was significantly increased in the training group when compared with the sham group for the control and resident-intruder test guinea pigs (P<0.05). Therefore, the enhancement of delay eyelid conditioning by microcurrent electrical stimulation of the mPFC in guinea pigs was triggered by the expression of Fos protein. The observations of the present study further expand the understanding of conditioned reflexes and may aid future investigations into the formation of eyelid conditioning and the mechanisms underlying the circuit in various conditions.
Keywords: Fos protein; delay eyelid conditioning; guinea pigs; medial prefrontal cortex.