Diurnal Clock Gene Expression in the Olfactory Bulb of Newborn Rabbits

*Corresponding author e-mail: oscarhcdf@hotmail.com Introduction: In the European rabbit ( Oryctolagus cuniculus ) the once-daily nursing acts as an effective non-photic entraining signal for the newborn circadian system relevant for pups’ survival. Rabbits only nurse for a few minutes once every 24 h and previous studies have shown that the pups, blind at birth, display endogenous circadian rhythms in behavior (locomotor activity), physiology (temperature) and molecular (clock gene expression in the suprachiasmatic nucleus) entrained by this regular daily event. Furthermore, the young are able to anticipate the time of nursing, and this persists even during fasting conditions. Methods: In order to understand the neural organization of the rabbits early circadian system, we investigated the 24-h pattern of expression of the clock genes Per 1, Cry 1 and Bmal1 in the olfactory bulb (OB; a potential circadian oscillator in mammals). We used 43 pups from seven litters maintained in constant darkness and entrained by nursing, allowing to the newborn pups the access to a lactating female every 24-h, from the postnatal day 1 to 7 (PI- P7). After nursing on P7, pups were killed in the dark at 3-h intervals so as to obtain eight groups ( n =5–6 pups/group) distributed evenly across the 24 h before the next scheduled nursing. Profiles in the expression of the clock genes Per1 , Cry1 and Bmal1 were determined using in situ hybridization in sections containing the OB. Results: We report for the first time; 1) that Per1 , Cry1 and Bmal1 are all expressed in the OB of the newborn rabbits, 2) the expression take place mainly in the mitral cell layer, and 3) the expression of the clock genes shows diurnal rhythmicity in the OB. Conclusion: Our findings suggest that the OB is a potential part of the newborn rabbit’s circadian system. Nevertheless, is important to dilucidate if the OB of newborn rabbits displays an endogenous circadian rhythm and if is possible to synchronize it by non-photic cues associated with the mothers daily nursing visit. Support: CONACyT 48504, PAPIIT IN226107. Publication History Article published online: 16 June 2026 © 2009. Brazilian Sleep Academy. This is an open access article published by Thieme under the terms of the Creative Commons Attribution-NonDerivative-NonCommercial License, permitting copying and reproduction so long as the original work is given appropriate credit. Contents may not be used for commercial purposes, or adapted, remixed, transformed or built upon. (https://creativecommons.org/licenses/by-nc-nd/4.0/) Thieme Revinter Publicações Ltda. Rua Rego Freitas, 175, loja 1, República, São Paulo, SP, CEP 01220-010, Brazil