Stress- and pellet-priming-induced reinstatement of food seeking and neuronal activation in c-fos-GFP transgenic female rats: Role of ovarian hormones

Relapse to maladaptive eating habits during dieting is often provoked by stress and acute re-exposure to palatable foods. Women may be particularly vulnerable to relapse due to fluctuations in ovarian hormones. Here, we evaluated the effects of ovariectomy and estrous cycle phase on yohimbine- or pellet-priming- induced reinstatement of food seeking and mPFC activation in c-fos-GFP transgenic female rats, which express GFP in strongly activated neurons. Food-restricted OVX or sham-operated rats were trained to lever-press for delivery of palatable food pellets that were paired with a tone-light cue. Pellet intake was then assessed after systemic injections of pharmacological stressor yohimbine (0.5- 2 mg/kg, i.p.). Subsequently, lever-pressing was extinguished and reinstatement of food seeking was assessed after yohimbine injections or pellet priming (1-4 non-contingent pellets). We also assessed the effect of estrous cycle phase on yohimbine- and pellet-priming-induced reinstatement of food-seeking, using the same training and extinction procedures described above. Compared to sham rats, OVX rats showed a modest decrease in pellet-priming-induced reinstatement, but not in yohimbine-induced increases in pellet intake or yohimbine-induced reinstatement. Both reinstatement manipulations were associated with increased GFP expression in dorsal and ventral mPFC in both groups. Additionally, the magnitude of yohimbine- or pellet-priming-induced reinstatement was not affected by estrous cycle phase. Results suggest that ovarian hormones do not play a role in stress-induced feeding or relapse in our rat model and confirm our previous findings using male rats on the role of mPFC in stress- and pellet-priming induced reinstatement of food seeking.