Chronobiology & Neuroendocrinology Lab
What We Do

Chronobiology and Neuroendocrinology lab research examines the neural and behavioral features of circadian rhythms in the day-active Octodon degus, an animal model with circadian properties similar to humans. Currently,the lab is particularly interested in the interaction between stress and the circadian system, development of sex differences in the use of photic and non-photic entraining cues, and the anatomical system which supports the use of both types of entraining signals. The lab has recently begun a new line of research exploring the role of prenatal steroid hormones on the development of gender-specific behavior and physiology across the lifespan, using sheep as the animal model.

Current and On-Going Research
  • the function of the circadian clock just before and early during puberty in the diurnal degu
  • the circadian rhythms of rats exposed to stress during the last trimester of gestation and then were either allowed to self-administer cocaine or exposed to acute stressors (in collaboration with Dr. Jill Becker and Dr. Seema Bhatnagar
  • the effect of adolescent exposure to drugs of abuse on circadian rhythms
  • the development of sex differences in the rat circadian function
  • the effect of developmental disruptions like stress or cocaine exposure on reproductive function of female rats (in collaboration with Dr. Robert Thompson)
  • the circadian control over reproduction in the diurnal degu (in collaboration with Dr. Megan Mahoney)
  • the attention control of circadian entrainment (in collaboration with Dr. Martin Sarter)
  • the similarities and differences in male and female diurnal sleep, how it is altered by jet lag treatments, and whether sleep in juvenile animals without a mature circadian system is different from that of adults
  • the effects of endocrine disruptors on dominance and reproductive behaviors over the lifespan (in collaboration with Reproductive Sciences)
  • the behavior of inter-sex individuals (in collaboration with Reproductive Sciences)
2009
Interactions between cognition and circadian rhythms: Attentional Demands modify circadian entrainment

Animals and humans are able to predict and synchronize their daily activity to signals present in their environments. Environmental cues are most often associated with signaling the beginning or the end of a daily activity cycle, but they can also be used to time the presentation or availability of scarce resources.
If the signal occurs consistently, animals can begin to anticipate its arrival and ultimately become entrained to its presence. While many stimuli can produce anticipation for a daily event, these events rarely lead to changes in activity patterns during the rest of the circadian cycle. Here the authors demonstrate that performance of a task requiring sustained attention not only produces entrainment, but produces a robust modification in the animals’ activity throughout the entire circadian cycle. In particular, normally nocturnal rats, when trained during the light phase (ZT 4) adopted a significant and reversible diurnal activity pattern. Of importance, control experiments demonstrated that this entrainment could not be attributed to the noncognitive components of task performance, such as handling, water
deprivation, access to water used as a reward, or animal activity associated with operant training. These findings additionally indicate that levels of cognitive performance are modulated by the circadian cycle and that such activity can act as a highly effective entrainment signal. These results form the basis for future research on the role of neuronal systems mediating interactions between cognitive activity and circadian rhythms.

Adolescent changes in the homeostatic and circadian regulation of sleep

Sleep deprivation among adolescents is epidemic. We argue
that this sleep deprivation is due in part to pubertal changes
in the homeostatic and circadian regulation of sleep. These
changes promote a delayed sleep phase that is exacerbated
by evening light exposure and incompatible with aspects of
modern society, notably early school start times. In this review
of human and animal literature, we demonstrate that
delayed sleep phase during puberty is likely a common phenomenon in mammals, not specific to human adolescents,
and we provide insight into the mechanisms underlying this
phenomenon.

period gene expression in the diurnal degu (octodon degus) differs from the nocturnal laboratory rat (rattus norvegicus)

Recent data suggest that both nocturnal and diurnal mammals generate circadian rhythms using similarly phased feedback loops involving Period genes in the suprachiasmatic nuclei (SCN) of the hypothalamus. These molecular oscillations also exist in the brain outside of the SCN, but the relationship between SCN and extra-SCN oscillations is unclear. We hypothesized that a comparison of “diurnal” and “nocturnal” central nervous system Per rhythms would uncover differences in the underlying circadian mechanisms between these two chronotypes. Therefore, this study compared the 24-h oscillatory patterns of Per1 and Per2 mRNA in the SCN and putative striatum and cortex of Octodon degus (degu), a diurnal hystricognath rodent, with those of the nocturnal laboratory rat, Rattus norvegicus. The brains of adult male degus and rats were collected at 2-h intervals across 24 h in entrained light-dark and constant darkness conditions, and sections were analyzed via in situ hybridization. In the SCN, degu
Per1 and Per2 hybridization signal exhibited 24-h oscillatory patterns similar in phasing to those seen in other rodents, with peaks occurring during the light period and troughs during the dark period. However, Per1 remained elevated for five fewer hours in the degu than in the rat, and Per2 remained elevated for two fewer hours in the degu. In brain areas outside of the SCN, the phase of Per2 hybridization signal rhythms in the degu were 180° out of phase with those found in the rat, and Per1 hybridization signal lacked significant rhythmicity. These results suggest that, while certain basic components of the transcriptional-translational feedback loop generating circadian rhythms are similar in diurnal and nocturnal mammals, there are variations that may reflect adaptations to circadian niche

the response of per1 to light in the suprachiasmatic nucleus of the diurnal degu (octodon degus)

Several studies suggest that the circadian systems of diurnal mammals respond differently to daytime light than those of nocturnal mammals. We hypothesized that the photosensitive “clock” gene Per1 would respond to light exposure during subjective day in the suprachiasmatic nucleus of the diurnal rodent, Octodon degus. Tissue was collected 1.5–2 h after a 30 min light pulse presented at five timepoints across the 24 h
day and compared to controls maintained under conditions of constant darkness. Per1 mRNA was quantified using in situ hybridization. Results showed that the rhythmicity and photic responsiveness of Per1 in the degu resembles that of nocturnal
animals
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