Dissociation of circadian rhythms in adolescent rats affects object recognition and spatial recognition memories

Abstract

The T22 protocol is an animal model of forced internal desynchronization, in which rats are exposed to an 11:11 light-dark (LD) cycle. This non-invasive protocol induces the dissociation of circadian rhythms in adult rats, making it possible to study the effects of circadian disruption on physiological and behavioral processes such as learning, memory, and emotional responses. However, the effects of circadian dissociation during other developmental stages, such as adolescence, remain unexplored. Adolescence is a period marked by significant changes in sleep patterns and increased exposure to bright light at night, making it essential to investigate how circadian dissociation may affect this phase of development. This study aimed to evaluate the circadian rhythmicity, cognitive performance and anxiety-like behavior in adolescent Wistar rats under the alignment (aligned T22 group) or misalignment (misaligned T22 group) phases of the T22 cycle. A third group of adolescent rats was maintained in a normal 12:12 LD cycle during the experiment and was used as control group (T24 group). Compared to the control group, adolescent rats under both phases of the T22 cycle exhibited a dissociated circadian rhythm of the locomotor activity and deficits in object recognition memory tasks, without impairments in tasks related to emotional responses. These findings indicate that forced desynchronization impairs recognition memory in adolescent rats, suggesting potential cognitive consequences of internal desynchronization during this critical developmental phase, with relevant implications for public health discussions.

Keywords: Adolescence; Circadian rhythm; Internal desynchronization; Locomotor activity; Memory; Rat.