Circadian organization of the diurnal Caviomorph rodent,Octodon degus

Abstract

The Octodon degus, or degu, is an excellent animal model for studying the theoretical and neural underpinnings of diurnality. The power of this model comes from their unique evolutionary lineage, long lives, and relative ease of care in the laboratory for a non-domesticated species. We have summarized the field and laboratory data indicating the critical variables that influence the degus' phase preference and the possible mechanisms for the phase flexibility observed in the field and laboratory. We also review studies examining the physiology and anatomy of light and non-photic inputs to the degu circadian system and studies of the circadian pacemaker itself, with particular emphasis placed on characteristics that appear to be convergent adaptations to a diurnal niche. Finally, we begin to seek the origin for the diurnally-phased activity output of the degu, although we conclude that significant work remains to be done.

Adolescent Changes in the Homeostatic and Circadian Regulation of Sleep

“…Rhythms in deoxyglucose metabolism, photic sensitivity , and neuropeptide expression (e.g. AVP and VIP) in the SCN are also similar in diurnal and nocturnal species [53,54] . Therefore, the downstream coupling (or phase relationship) between the circadian pacemaker and central or peripheral systems plays an important role in determining the phase of behavioral and endocrine rhythms.…”

“…Substantial evidence now indicates that adult diurnal and nocturnal species have a similar phasing of many aspects of SCN physiology [53,54] . For example, the phase of the transcriptional-translational clock gene feedback loop in the SCN that generates 24 h of oscillation is very similar in the nocturnal rat and diurnal degu [55] .…”

The Substructure of the Suprachiasmatic Nucleus: Similarities between Nocturnal and Diurnal Spiny Mice

“…In diurnal species the circadian system drives sleep during the night and wakefulness during the day, whereas masking by light at night directly stimulates activity, and by darkness during the day decreases it. Both systems have the opposite effects in nocturnal species [Mrosovsky, 1999;Hagenauer and Lee, 2008].…”

“…Some animals, however, are very plastic and can be diurnal in some environmental conditions and nocturnal in others Dayan, 2003, 2008]. Examples include microtine rodents that are diurnal in winter and nocturnal in the summer [Rowsemitt et al, 1982] and cotton rats in which patterns differ across individuals and change over time [Camerson and Spencer, 1981;Johnston and Zucker, 1983;Hoogenboom et al, 1984;Hagenauer and Lee, 2008]. Plasticity can be promoted by changes in masking or in circadian mechanisms [Mrosovsky and Hattar, 2005].…”

The first observation of seasonal affective disorder symptoms in Rhesus macaque

“…Another major difference is the behavioral responses to light and darkness. Specifically, diurnal animals become more active in response to light and less active in response to darkness, while nocturnal ones have opposite patterns of response [19][20][21][22][23]. Moreover, the hypothalamus-pituitary-adrenal (HPA) axis activity starts to rise at the end of the night in diurnal mammals, whereas in nocturnal animals it occurs at the end of the day [24].…”