A high-fat diet impairs learning that is dependent on the dorsal hippocampus but spares other forms of learning

Two experiments were conducted to evaluate the effects of a high-fat diet (HFD) on two tasks that were either dependent on the dorsal hippocampus (DH) or independent of the DH. A total of 80 adult male Sprague Dawley rats were administered either a lard-based HFD (60% of calories from fat) or a control diet (10% of calories from fat) for 8 weeks, and then were trained and tested on either the latent cue preference (LCP) task or the conditioned cue preference (CCP) task in a 3-compartment box apparatus (2 end-compartments and 1 middle-compartment). The end compartments of the box apparatus contained either a single environmental cue (DH-independent) or multiple environmental cues (DH-dependent). During training trials for the LCP and CCP tasks, on alternating days, rats were given access to water in 1 of the 2 end compartments and no water in the opposite end compartment. Rats were water-replete during LCP training and were water-deprived during CCP training. During testing for both tasks, all rats were water-deprived and given free access to all compartments while the amounts of time spent in each compartment were recorded. Results showed that rats given the HFD demonstrated no compartment preferences during both LCP and CCP testing when the compartments contained multiple cues, while rats fed the control diet demonstrated normal compartment preference behavior. However, when the compartments contained a single environmental cue, rats given either the HFD and control diet demonstrated normal LCP and CCP learning. These results demonstrate that consumption of a HFD disrupted both LCP and CCP learning in a multiple-cue (DH-dependent) environment, but did not impair either type of learning in a single-cue (DH-independent) environment. This may be due to selective impairment of the DH caused by increased oxidative stress, inflammation, and/or disrupted neurotransmission produced by consumption of the HFD.