Temporal modulation of the canonical clockwork in the suprachiasmatic nucleus and olfactory bulb by the mammary pheromone 2MB2 in pre-visual rabbits

Abstract

During the early stages of development, the olfactory system plays a vital role in the survival of altricial mammals. One remarkable example is the Oryctolagus cuniculus, whose mother-young interaction greatly depends on the 2-methylbut-2-enal (2MB2) pheromone that triggers nipple search and grasping behaviors. Olfactory stimulation with 2MB2 regulates the expression of the core body temperature and locomotor activity rhythms in rabbit pups, indicating the modulation of the circadian system by this volatile cue. To address this issue, in the present study, we determined the effect of stimulation with pulses of 2MB2 on the molecular circadian clockwork in the suprachiasmatic nucleus (SCN) and in the main olfactory bulb (MOB). For this purpose, 7-day-old rabbits were stimulated with distilled water (CON), with ethyl isobutyrate (ETHYL) or with the pheromone (2MB2) at different times of the cycle, and 1h later, the expression of the activity marker C-FOS and of the clock proteins PER1, CRY1 and BMAL1 was evaluated in the SCN and in the three layers of the MOB. The clock proteins were abundantly expressed in both structures; nevertheless these showed diurnal rhythmicity only in the MOB, confirming that central pacemakers exhibit a heterochronical development of the molecular clockwork. C-FOS expression in the SCN and in the MOB was modulated by exposure to ETHYL and to 2MB2 only when these stimulants were presented at ZT00 and at ZT18. In contrast, the clock proteins were essentially modulated by 2MB2 at ZT00 and at ZT06 in both structures. In addition, the PER1 and CRY1 proteins exhibited differential responses to stimulation in the three layers of the MOB. For the first time, we report a modulatory and time-dependent effect of the mammary pheromone 2MB2 on the expression of the core clock proteins in the SCN and in the MOB in rabbits during pre-visual stages of development.

Keywords: circadian rhythms; clock proteins; main olfactory bulb; mammary pheromone; non-photic synchronization; suprachiasmatic nucleus.