Lesions of the medial prefrontal cortex enhance the early phase of psychogenic fever to unexpected sucrose concentration reductions, promote recovery from negative contrast and enhance spontaneous recovery of sucrose-entrained anticipatory activity.

Two groups of rats, one bearing bilateral excitotoxic lesions of the medial prefrontal cortex (mPFC) and one sham-lesioned group, were run in a successive negative contrast paradigm. Both groups had telemeters implanted to monitor core temperature and activity. After ad libitum baseline and food restriction to 85% body weights, rats received a sucrose solution once daily for 5 min and 30 s at 10:30 h. They received their preshift 32% sucrose solution for 14 days followed by a sucrose concentration reduction (downshift) to 4% sucrose for 12 days. Rats were then upshifted to 32% for six additional days before being downshifted to 4% for the next 6 days. There were no differences in intake of the 32% sucrose during the preshift. All rats showed profound suppression of intake upon the shift to 4% sucrose. On the first day of the unexpected 4% sucrose, lesioned rats showed an enhanced psychogenic fever compared with Shams, whereas on the second day of 4% sucrose they showed an impaired ability to blunt that fever compared with Shams. In addition, lesioned rats showed greater rates of recovery and asymptotic drinking of the subsequent 4% sucrose solution than Shams, indicating impairments in the encoding or retrieval of the shift. In addition, lesioned rats showed enhanced entrainment to the 32% sucrose meals, normal damping of anticipation, and enhanced spontaneous recovery of anticipatory thermal responses to the calorically impoverished 4% solutions. These failures to inhibit responding point to a failure in interference learning in rats bearing lesions of the mPFC.