Figure 1.

Mutual relationship between the biological circadian clock, stress and orexigenic peptide systems. Circadian clock structures in the brain are under direct influence of the stress HPA-axis mediators: corticotropin-releasing hormone (CRH), adrenocorticotropic hormone (ACTH) and glucocorticoids (GCs), therefore excessive exposure to stress disrupts the circadian rhythmicity of the organism. Coincidently, chronic stress through excessive release of HPA mediators deregulates the synthesis and action of orexigenic brain peptides, which can lead to overconsumption of food, weight gain, obesity and stress-related eating disorders. The control of orexigenic peptide synthesis during prolonged stress exposure is dysregulated at several levels, since excessive stress disrupts circadian rhythmicity, which directly controls both neuropeptide release and HPA-axis function. The cycle of excessive stress influences on food intake-promoting peptide system activity and circadian clock structures is closed by the sensitivity of both HPA-axis and clock structures to orexigenic peptide system mediators.