Hyperactive when young, hypoactive and overweight when aged: Connecting the dots in the story about locomotor activity, body mass, and aging in Trpv1 knockout mice

We have recently found that, at a young age, transient receptor potential vanilloid-1 (Trpv1) knockout (⁻/⁻) mice have a higher locomotor activity than their wild-type littermates (⁺/⁺). We have also found that, with age, Trpv1^−/− mice become substantially heavier than Trpv1^+/+ controls, thus forming a paradoxical association between locomotor hyperactivity and overweight. The present study solves this contradiction. By using two experimental paradigms, we show that aged Trpv1^−/− mice have not an increased, but a decreased, locomotor activity, as compared to age-matched Trpv1^+/+ controls. We also confirm that aged Trpv1^−/− mice are overweight. We conclude that TRPV1 channels are involved in the regulation of both general locomotor activity and body mass in an age-dependent manner.