The Lack of Light-Dark and Feeding-Fasting Cycles Alters Temporal Events in the Goldfish (Carassius auratus) Stress Axis

Abstract

Vertebrates possess circadian clocks, driven by transcriptional–translational loops of clock genes, to orchestrate anticipatory physiological adaptations to cyclic environmental changes. This work aims to investigate how the absence of a light-dark cycle and a feeding schedule impacts the oscillators in the hypothalamus-pituitary-interrenal axis of goldfish. Fish were maintained under 12L:12D feeding at ZT 2; 12L:12D feeding at random times; and constant darkness feeding at ZT 2. After 30 days, fish were sampled to measure daily variations in plasma cortisol and clock gene expression in the hypothalamus-pituitary-interrenal (HPI) axis. Clock gene rhythms in the HPI were synchronic in the presence of a light-dark cycle but were lost in its absence, while in randomly fed fish, only the interrenal clock was disrupted. The highest cortisol levels were found in the randomly fed group, suggesting that uncertainty of food availability could be as stressful as the absence of a light-dark cycle. Cortisol daily rhythms seem to depend on central clocks, as a disruption in the adrenal clock did not impede rhythmic cortisol release, although it could sensitize the tissue to stress.

Daily Rhythms in the IGF-1 System in the Liver of Goldfish and Their Synchronization to Light/Dark Cycle and Feeding Time

“…In all experimental groups, food was provided by automatic feeders without altering either the light or dark conditions established at feeding time. The validity of this feeding protocol, which guarantees food intake within 30 min immediately after food delivery under 24D conditions, has been previously reported [ 43 ]. On the day of the experiment, fish were sampled every 4 h ( n = 7 fish/sampling time) throughout a 24-h cycle (ZT3, ZT7, ZT11, ZT15, ZT19 and ZT23).…”

REV-ERBα Agonist SR9009 Promotes a Negative Energy Balance in Goldfish

“…Daily locomotor activity was recorded during the subchronic SR9009 treatment as previously described [ 41 , 55 ]. In short, infrared photocells (Omron Corporation E3S-AD12, Kyoto, Japan) were fixed onto aquaria walls, two of them below the automatic feeder and four placed at 3–9 cm above the bottom, one on each aquaria wall.…”

“…mRNA abundance of npy , pomc , cartpt-I , hcrt , ghrelin , leptin-aI , and pepck was determined by RT-qPCR as previously described [ 41 , 55 ], with minor modifications. Tissues were mechanically homogenized, and RNA was isolated from the liver, hypothalamus, and intestine using the trizol/chloroform method (TRI ® Reagent, Sigma Chemical, Madrid, Spain), and treated with RQ1 RNAse-Free DNAse (Promega, Madison, WI, USA).…”

Nuclear Receptors (PPARs, REV-ERBs, RORs) and Clock Gene Rhythms in Goldfish (Carassius auratus) Are Differently Regulated in Hypothalamus and Liver

“…In fish, the effects of feeding time on physiological and behavioral aspects are well studied. Feeding time affects daily locomotor activity rhythms ( Aranda et al, 2001 ; Cavallari et al, 2011 ; Feliciano et al, 2011 ; Gómez-Boronat et al, 2018 ); clock genes expression in liver, gut, and brain ( López-Olmeda et al, 2009 ; López-Olmeda et al, 2010 ; Feliciano et al, 2011 ; Nisembaum et al, 2012 ; Tinoco et al, 2014 ; Gómez-Boronat et al, 2018 ); and daily profile of circulating cortisol ( Montoya et al, 2010 ; Cowan et al, 2017 ; Gómez-Boronat et al, 2018 ; Saiz et al, 2021 ). However, it is unknown whether feeding time, in addition to entrain clock genes, also drives daily rhythms in PPARs, REV-ERBs, and RORs transcription factors in teleost.…”