The biological clock in mammals is located in the suprachiasmatic nucleus (SCN) and regulates daily and seasonal rhythms. The research presented in this thesis consists of behavioral and... Show moreThe biological clock in mammals is located in the suprachiasmatic nucleus (SCN) and regulates daily and seasonal rhythms. The research presented in this thesis consists of behavioral and electrophysiological experiments to investigate the SCN as a pacemaker of daily and seasonal rhythms. We investigated the activity of single neurons and small groups of neurons in the SCN and their role in photoperiodic adaptations. We found that single cells in the SCN do not code for the length of day, but that photoperiodic encoding is a property of the SCN neuronal network. Show less
In order to cope with and to predict 24-hour rhythms in the environment, most, if not all, organisms have a circadian timing system. The most important mammalian circadian pacemaker is located in... Show moreIn order to cope with and to predict 24-hour rhythms in the environment, most, if not all, organisms have a circadian timing system. The most important mammalian circadian pacemaker is located in the suprachiasmatic nucleus at the base of the hypothalamus in the brain. Over the years, it has become clear that the circadian system is complex and that additional oscillators exist, both within and outside the central nervous system. The aim of this thesis was to obtain insight in the hierarchical organization of the circadian timing system and to determine whether certain attributes arise at the tissue level. The data reveal that interactions between the SCN and the periphery, as well as interactions between subregions within the SCN, contribute significantly to the functioning of the circadian system. Another important finding is that the multiple components of the circadian system can, under certain circumstances, dissociate. The hierarchical organization of the circadian timing system, the interactions between and within organizational levels, and importantly, the ability of several components to dissociate, may provide the circadian system the required plasticity to adjust to biologically relevant changes in the environment. Show less
