Diet-induced obesity (DIO) mice models are commonly used to investigate obesity-related health problems. Until now, only sparse data exist on the influence of DIO on behavior and stress hormones in mice. The present study investigates high-fat DIO with two different feeding regimes on behavioral parameters in mice. Various behavioral tests (open field, elevated plus maze, social interaction, hotplate) were performed with female BALB/c and male C57BL/6 mice after a feeding period of twelve weeks (restrictive vs. ad libitum and normal-fat diet vs. high-fat diet) to investigate levels of anxiety and aggression. BALB/c mice were DIO-resistant and therefore the prerequisite for the behavior analyses was not attained. C57BL/6 mice fed a high-fat diet had a significantly higher body weight and fat mass compared to C57BL/6 mice fed a control diet. Interestingly, the DIO C57BL/6 mice showed no changes in their aggression- or anxiety-related behavior but showed a significant change in the anxiety index. This was probably due to a lower activity level, as other ethological parameters did not show an altered anxiety-related behavior. In the ad libitum-fed DIO group, the highest corticosterone level was detected. Changes due to the feeding regime (restrictive vs. ad libitum) were not observed. These results provide a possible hint to a bias in the investigation of DIO-related health problems in laboratory animal experiments, which may be influenced by the lower activity level.

This study examines the effects of neurotensin (NT) receptor sites on the sensation of visceral pain. Previous work by researchers has found, through the use of NT analogs, that visceral pain is closely associated with NT receptor 2 (NTSR2). This study tested 70 genetically modified mice. The mice were either missing NTSR1, NTSR2, or were wild-type (WT) mice that were not missing any NT receptors. The mice were injected intraperitoneally with either saline or acetic acid then observed for a 60 minute period and writhing behavior was recorded. Twenty four hours later activity levels were recorded in the open field assay. We found that contrary to previous research, NTSR2 is not solely responsible in the sensation of visceral pain. We also found that NTSR1 plays a more significant role than NTSR2, contrary to previous research. Additionally, we found that the NT receptors may be affected by age related factors. The findings of this study suggest that NTSR2 does in fact play a role in the sensation of visceral pain but that NTSR1 may modulate the degree of activation of NTSR2. It can also be concluded that age may have a role in the effectiveness of NTSR sites in visceral pain. This information allows for further research to analyze possible age-dependent effects of NT receptor sites that could alter the possible usefulness of NT analogues in the future.