Adaptation of physiology and behavior to seasonal changes in the environment are for many organisms essential for survival. Most of our knowledge about the underlying mechanisms comes from... Show moreAdaptation of physiology and behavior to seasonal changes in the environment are for many organisms essential for survival. Most of our knowledge about the underlying mechanisms comes from research on photoperiodic regulation of reproduction in plants, insects and mammals. However, even humans, who mostly live in environments with minimal seasonal influences, show annual rhythms in physiology (e.g., immune activity, brain function), behavior (e.g., sleep–wake cycles) and disease prevalence (e.g., infectious diseases). As seasonal variations in environmental conditions may be drastically altered due to climate change, the understanding of the mechanisms underlying seasonal adaptation of physiology and behavior becomes even more relevant. While many species have developed specific solutions for dedicated tasks of photoperiodic regulation, we find a number of common principles and mechanisms when comparing insect and mammalian systems: (1) the circadian system contributes to photoperiodic regulation; (2) similar signaling molecules (VIP and PDF) are used for transferring information from the circadian system to the neuroendocrine system controlling the photoperiodic response; (3) the hormone melatonin participates in seasonal adaptation in insects as well as mammals; and (4) changes in photoperiod affect neurotransmitter function in both animal groups. The few examples of overlap elaborated in this perspective article, as well as the discussion on relevance for humans, should be seen as encouragement to unravel the machinery of seasonal adaptation in a multitude of organisms. Show less
The experimental research in this thesis aims to gain more understanding of how the SCN network is organized and what is needed for network changes. More specifically, this work focused on the... Show moreThe experimental research in this thesis aims to gain more understanding of how the SCN network is organized and what is needed for network changes. More specifically, this work focused on the potential role of GABA and the GABAeric E/I balance in SCN network plasticity. Communication and synchronization in the SCN are important for the generation of a strong and coherent output signal. Under certain conditions, like long photoperiod, the phases of the individual SCN cells are more dispersed over the 24 hour cycle as evidenced by measurements of electrical activity and clock gene expression. Aging is also known to affect the network organization of the SCN with deterioration in synchronization among the individual SCN neurons. In this thesis, I present work that contributes to research questions regarding the effect of light exposure and/or aging on several characteristics of SCN network plasticity. Show less
The suprachiasmatic nucleus (SCN) functions as a circadian clock that drives 24-hour rhythms in physiology and behavior. The SCN neurons function as cell-autonomous oscillators, and the... Show more The suprachiasmatic nucleus (SCN) functions as a circadian clock that drives 24-hour rhythms in physiology and behavior. The SCN neurons function as cell-autonomous oscillators, and the production of a coherent SCN rhythm is dependent upon synchronization among single cells. We investigated how changes in phase-synchronization between individual cells effect the ability of the SCN to phase-shift its rhythm. Empirical and modelling studies revealed larger phase-shifts in synchronized SCN than in desynchronized SCN. The major external stimulus affecting the SCN is light. We explored the ability of melanopsin and rod- and cone photoreceptors to mediate the effects of light on SCN discharge, and found that melanopsin and cones are able to mediate light responses of the SCN. Studies performed in nocturnal species have indicated that the SCN’s rhythmicity is also influenced by the animal’s own behavioral activity. We assessed the effect behavioral activity on the amplitude of the circadian rhythm in SCN electrical discharge rate in the day-active Arvicanthis ansorgei. The results showed acute enhancements of SCN discharge during episodes of behavioral activity. The studies described in this thesis indicate that the SCN is part of a brain network that includes the retina and areas involved in behavioral activity and sleep. Show less
Many organisms have developed an internal clock to cope with the daily and seasonal cycles in the environment. In mammals, suprachiasmatic nuclei (SCN) of the hypothalamus control circadian rhythms... Show moreMany organisms have developed an internal clock to cope with the daily and seasonal cycles in the environment. In mammals, suprachiasmatic nuclei (SCN) of the hypothalamus control circadian rhythms in behavior and physiology. Evidence links the proper function of circadian clock to mental and physical health. Aging disturbs the accurate function of the SCN and impairs many rhythms such as sleep-wake cycle. Hence improvement of clock function can aid healthy aging. In chapters 3 and 4 I show the ensemble output of the SCN neuronal network is more robust than individual cells__ output suggesting a compensatory role of the network in aging. Seasonal changes affect the physiology and reproduction success of many organisms. The SCN encodes for day-length by adjusting the pattern of its electrical activity rhythm.. In chapters 5 and 6 I reveal that plasticity in interneuronal and cell-intrinsic functions in the SCN helps the organism to adjust to yearly natural changes in photoperiod. These results imply that extensive artificial light in modern society may alter neurotransmitters action in the SCN. A better understanding of SCN network function and cellular properties facilitate alleviation of modern life-related diseases caused by circadian disturbances and aging. Show less
