Anticipatory activity to a daily palatable stimulus is accelerated in free-feeding rats housed in an enriched environment.

Abstract

In addition to the light-dark cycle, non-photic cues oscillating every 24 h can entrain central and peripheral circadian oscillators. When rodents receive a daily palatable food, they exhibit a pre-feeding increase in locomotor activity known as anticipatory activity (AA). The emergence of AA requires multiple conditioning cycles and persists following stimulus withdrawal, implicating learning and memory processes in its regulation. Environmental enrichment enhances neuroplasticity, learning, and memory capacities; however, its effects on non-photic circadian entrainment remain unexplored. For this purpose, male Wistar rats were reared from weaning under standard or enriched housing conditions for 60 days. Subsequently, locomotor activity was continuously recorded to assess AA to a daily chocolate piece administered during the light phase for 12 consecutive days. Anxiety-like behavior (elevated plus-maze and open field tests), chocolate consumption and motivation (chocolate binge and motivation for enclosed chocolate tests), and preference for other rewarding stimuli (sucrose preference test) were also assessed to determine whether differences in AA expression were attributed to these features. Both groups exhibited robust AA after repeated chocolate exposure; however, enriched rats developed AA approximately two days earlier than standard rats. Additionally, enriched animals displayed enhanced temporal precision of anticipatory onset and shorter post-chocolate activity. No differences were found between housing conditions in anxiety-like behavior, chocolate consumption, motivation to obtain chocolate, or sucrose preference. Our findings suggest that an enriched environment may influence specific temporal features of anticipatory activity induced by a palatable stimulus, without altering hedonic or motivational responses.