Circadian activity rhythms during the last days of Nothobranchius rachovii’s life: A descriptive model of circadian system breakdown

Abstract

Several studies have been performed to identify age-related changes in the circadian system (CS) but the impairment of the CS and its chronodisruption at the end of an organism life have not been studied in depth. Aging commonly affects the input pathways into the biological clock or restraints their processing, therefore simplifying the system output, the overt rhythms. The purpose of this work was to do a complete characterization of changes that occurs in the CS in the last stage of a vertebrate organism life and to develop tools able to detect in which moment of the last days of life is the animal, using an overt rhythm, the rest-activity rhythm (RAR). For that, a fish species proposed as model for aging studies, Nothobranchius rachovii, has been used. A progressive and sequential CS breakdown has been described for the last 22 d of life of N. rachovii (∼7% of total life), suffering a general RAR impairment mainly reflected by changes in phase regularity, complexity, amplitude and the ability to stay synchronized to the LD cycle. Also, an equation of days remaining of life, based on the RAR description, has been calculated and proposed as a tool to identify close-to-death individuals which could be subjected to an adequate restoring treatment to enhance the CS function and improve their well-being.

• Aging model
• circadian system
• circadian system breakdown
• death
• locomotor activity
• Nothobranchius

Declaration of interest

This project was funded by the Seneca Foundation (12005/PI/09), Instituto de Salud Carlos III (RETICEF, RD12/0043/0011) and the Spanish Ministry of Science and Education (BFU2010-21945-C02-01), including FEDER co-funding. Pedro Francisco Almaida Pagán was funded by a Marie Curie Intra-European Fellowship within the 7th Community Framework Program (PIEF-GA-2011-297964, OLDMITO). All authors have contributed equally. The authors report no conflicts of interests.

Supplementary material available online

Supplementary Figure 1. Absolute SD of the period value for each N. rachovii and day. Grey and black dots indicate the two populations obtained by k-means clustering analysis, indicating a clear limit for each population, corresponding to day 12 before death. Each cross indicates the centroid of each population. Total variance: 41.77. Intra-class variance: 11.52.