Constitutive and Conditional Deletion of Type 1 Dopamine Receptor (Drd1) to Study Food Anticipatory Activity

A structure within the hypothalamus, known as the suprachiasmatic nucleus (SCN), acts as a central clock for the body. It regulates biological rhythms that occur with a near 24-hour period, otherwise known as circadian rhythms. These rhythms, such as sleep, activity, hormone release, and appetite are regulated at the cellular level by a transcriptional-translational feedback loop. The major circadian entraining stimulus is blue wavelengths of light received by a special class of neurons in the retina. Interestingly, circadian rhythms can also be influenced by non-photic stimuli such as feeding. Scavenging for food is a major part of survival for organisms. The activity preceding scheduled mealtimes, or food anticipatory activity (FAA), can be initiated in rodent models when fed a limited amount at the same time daily and is thought to be the output of an as yet unidentified food entrained oscillator. Previous studies, using gene deletion and receptor pharmacology, implicated dopamine type receptor 1 (D1R) signaling in the dorsal striatum as necessary for FAA in mice. To further understand the association of D1R with FAA on a calorie-restricted feeding schedule, we have attempted to create several different cell-type specific conditional deletions of D1R using the Cre-lox system. While the Cre-mediated deletions were being created, we re-tested the initial D1R knockout line and observed only a subtle impairment in FAA compared to our prior results. We also obtained and tested a new D1R KO line created by the Knockout Mouse Project. Interestingly, this line of D1R KO mice had a significant impairment in FAA but overall this impairment was subtle and diminished after 4 weeks of timed, calorie restricted feeding. We were unsuccessful in obtaining conditional deletion of D1R mutants when using a tamoxifen-inducible Cre or a transgenically driven D1R-Cre. Finally, we were successful in conditionally deleting D1R using a gamma-aminobutyric acid vesicular transporter (vGat)-Cre line. These studies are not yet completed, but preliminary evidence suggests that deletion of D1R by vGat-Cre does not substantially impair FAA. Taken together, our results suggest that the lack of reproducibility of the defect in D1R knockout mice may be due to 1) a spontaneous suppressor mutation, 2) genetic drift of non-isogenic alleles, 3) changes in environmental conditions, or 4) or the fact that D1R is not a major modifier of FAA in mice and that previous results were spurious.