Abstract
Circadian activity rhythms are jointly controlled by a master pacemaker in the hypothalamic suprachiasmatic nuclei (SCN) and by food-entrainable circadian oscillators (FEOs) located elsewhere. The SCN mediates synchrony to daily light-dark cycles, whereas FEOs generate activity rhythms synchronized with regular daily mealtimes. The location of FEOs generating food anticipation rhythms, and the pathways that entrain these FEOs, remain to be clarified. To gain insight into entrainment pathways, we developed a protocol for measuring phase shifts of anticipatory activity rhythms in response to pharmacological probes. We used this protocol to examine a role for dopamine signaling in the timing of circadian food anticipation. To generate a stable food anticipation rhythm, rats were fed 3h/day beginning 6-h after lights-on or in constant light for at least 3 weeks. Rats then received the D2 agonist quinpirole (1 mg/kg IP) alone or after pretreatment with the dopamine synthesis inhibitor α-methylparatyrosine (AMPT). By comparison with vehicle injections, quinpirole administered 1-h before lights-off (19h before mealtime) induced a phase delay of activity onset prior to the next meal. Delay shifts were larger in rats pretreated with AMPT, and smaller following quinpirole administered 4-h after lights-on. A significant shift was not observed in response to the D1 agonist SKF81297. These results provide evidence that signaling at D2 receptors is involved in phase control of FEOs responsible for circadian food anticipatory rhythms in rats.
Highlights
In mammals, daily rhythms of physiology and behavior are jointly controlled by a master light-entrainable circadian pacemaker in the suprachiasmatic nuclei (SCN) of the hypothalamus, and by food-entrainable oscillators (FEOs) located elsewhere
The SCN are critical for entrainment of daily rhythms to LD cycles, while FEOs are responsible for generating the daily rhythm of food anticipatory activity that emerges when rodents are restricted to one or two daily meals at a fixed time of day
Food anticipation onset was advanced in both the vehicle and the drug condition, compared to the immediately preceding days and to the ZT11 injection condition, but this is attributable to increased hunger due to food depriving the rats on the day of the injection
Summary
Daily rhythms of physiology and behavior are jointly controlled by a master light-entrainable circadian pacemaker in the suprachiasmatic nuclei (SCN) of the hypothalamus, and by food-entrainable oscillators (FEOs) located elsewhere. Anticipatory activity rhythms can be induced by daily schedules of access to other reward stimuli, including water [6], mates [7,8], drugs of abuse [9] and palatable food without caloric restriction [10,11,12]. These findings raise the possibility that neural correlates of reward can entrain circadian oscillators that drive food anticipatory rhythms [13]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
