Characterization of diurnal core clock gene expression across brain regions of mice with differential degree of glucocorticoid receptor knockout

Characterization of diurnal core clock gene expression across brain regions of mice with differential degree of glucocorticoid receptor knockout" (2015). Undergraduate Honors Theses. Paper 975. Abstract Circadian rhythms are maintained through the self-regulatory, oscillatory molecular clock, which includes Per1, Per2, and Bmal1 clock genes, among others. Disruptions to clock gene expression have been associated with numerous disorders including major depressive disorder, anxiety disorders, and bipolar disorders. The molecular clock has been well characterized in the hypothalamic suprachiasmatic nucleus (SCN), the master clock of the body. Many peripheral tissues and extra-SCN brain regions have also been shown to express these core clock genes rhythmically, but as the SCN has few direct projections to extra-hypothalamic regions, the question remains as to how the SCN communicates to extra-SCN molecular clocks. Glucocorticoids (CORT) are a promising candidate by which the SCN signals to other brain and body regions, as glucocorticoid receptors (GR) are found ubiquitously throughout the body, with the notable exception of the SCN. Furthermore, CORT is released in a circadian manner, with peak plasma levels occurring at the beginning of the animal's active phase. Interestingly, there is a hypersensitive glucocorticoid response element (GRE) in the promoter region of the Per1 gene, which may be a mechanism by which CORT can modulate the molecular clock. We compared clock gene expression in mice that had a conditional forebrain glucocorticoid receptor knockout (FBGRKO) to expression in GR floxed mice (control genotype comparison) to determine the necessity of GRs in diurnal core clock gene expression. FBGRKO (C57BL/6 pure strain of the T29-1 founder line containing Cre+ recombinase transgene) mice have been previously well characterized to have disruptions in GR expression in the forebrain including the hippocampus (HPC), amygdala (AMY), cortex, and nucleus accumbens, while the central nucleus of the amygdala (CEA) had a 50% deletion and the paraventricular nucleus (PVN) was not affected. Mice were sacrificed under basal conditions in the light phase (zeitgeber time, ZT, 1.5) or dark phase (ZT13). In situ hybridization was used to measure mRNA expression. Our results show there is a time of day difference for Per1, Per2, and Bmal1 clock genes mRNA expression in the SCN and for Per1 and Bmal1 mRNA in the PVN. Only Bmal1 mRNA showed a time of day difference in subregions of the prefrontal cortex (PFC; anterior cingulate, prelimbic, infralimbic, ventral orbital), insula, subregions of the HPC (CA1, CA3, supra dentate gyrus, infra dentate gyrus), …