• Circadian rhythms
• Reptile sleep
• Proto-mammalian sleep
• Unihemispheric sleep in marine mammals and birds
• Dorsal and ventral streams and a proposal for the function of SWS.

1. Conclusions
2. Remaining questions

Questions:

1. How does the clock work? A circular link of cause and effect.
2. How is it brought in synchrony with the world?
3. How does it bring about changes in behavior?

1. Negative feedback loops involving transcription, translation and post-translational processes.
2. Photoreceptors signal (synaptically in mammals, but not in birds) to the circadian oscillator, elevating the level of a clock component and thus resetting the clock.
3. Output mechanisms vary across species. Protein level regulation by clock components.

Immortal time: Circadian clock properties of rat suprachiasmatic cell lines
Earnest DJ, Liang FQ, Ratcliff M, Cassone VM
SCIENCE

283: (5402) 693-695 JAN 29 1999

Abstract:
Cell lines derived from the rat suprachiasmatic nucleus (SCN) were screened for circadian clock properties distinctive of the SCN in situ. Immortalized SCN cells generated robust rhythms in uptake of the metabolic marker 2-deoxyglucose and in their content of neurotrophins. The phase relationship between these rhythms in vitro was identical to that exhibited by the SCN in vivo. Transplantation of SCN cell lines, but not mesencephalic or fibroblast Lines, restored the circadian activity rhythm in arrhythmic, SCN-lesioned rats. Thus, distinctive oscillator, pacemaker, and clock properties of the SCN are not only retained but also maintained in an appropriate circadian phase relationship by immortalized SCN progenitors.

How temperature changes reset a circadian oscillator
Liu Y, Merrow M, Loros JJ, Dunlap JC
SCIENCE

281: (5378) 825-829 AUG 7 1998

Abstract:
Circadian rhythms control many physiological activities. The environmental entrainment of rhythms involves the immediate responses of clock components. Levels of the clock protein FRQ were measured in Neurospora at various temperatures; at higher temperatures, the amount of FRQ oscillated around higher Levels. Absolute FRQ amounts thus identified different times at different temperatures, so temperature shifts corresponded to shifts in clock time without immediate synthesis or turnover of components. Moderate temperature changes could dominate Light-to-dark shifts in the influence of circadian timing. Temperature regulation of clock components could explain temperature resetting of rhythms and how single transitions can initiate rhythmicity from characteristic circadian phases.

Natural variation in a Drosophila clock gene and temperature compensation
Sawyer LA, Hennessy JM, Peixoto AA, Rosato E, Parkinson H, Costa R, Kyriacou CP
SCIENCE

278: (5346) 2117-2120 DEC 19 1997

Abstract:
The threonine-glycine (Thr-Gly) encoding repeat within the clock gene period of Drosophila melanogaster is polymorphic in length. The two major variants (Thr-Gly)17 and (Thr-Gly)20 are distributed as a highly significant latitudinal dine in Europe and North Africa. Thr-Gly length variation from both wild-caught and transgenic individuals is related to the flies' ability to maintain a circadian period at different temperatures. This phenomenon provides a selective explanation for the geographical distribution of Thr-Gly lengths and gives a rare glimpse of the interplay between molecular polymorphism, behavior, population biology, and natural selection.

• Bees show circadian periodicity in locomotor activity with a period slightly less than 24 hs. in the dark.
• Optomotor interneurons show circadian variability in response to pattern movement. Kaiser & Steiner-Kaiser, 1983.

Fig. 51, Hobson 1995.

Dolphins have complete optical decussations and poorly developed corpus callosum (cc). Is this the unihemispheric sleep enabler?

• Unihemispheric sleep occurs in birds with binocular vision.
• Unihemispheric sleep is also observed in regions below the hemispheres (e.g. the thalamus).
• Opposum and other mammals with poorly developed cc have no unihemispheric sleep.
• Mammals with severed cc carry on with bihemispheric sleep.

• The amazonian manatee (Sirenia) shows SWS for 27% and paradoxical sleep for 1% of recording time.
• Paradoxical sleep was identified as flat neck EMG with desynchronized EEG. No REM or muscle twitches were found.
• These periods were 20-253 s long.
• 25% of SWS was asymmetrical.
• Sleep was briefly interrupted to breathe.
• Some seals show USWS; others do not. Seals show prolonged (15-30 mins) breath holding during sleep.

• 17% of sleep in the glaucous winged gull is USWS (Amlaner et al, in Horne 1988).
• Unihemispheric sleep in ducks is accompanied by asynchronous contralateral eye closure (Rattenborg et al, 1999).
• Perhaps used in transoceanic flights, although this remains untested (Rattenborg, personal communication).

References

• CASTELLINI MA, MILSOM WK, BERGER RJ, COSTA DP, JONES DR, CASTELLINI JM, REA LD, BHARMA S, HARRIS M (1994): PATTERNS OF RESPIRATION AND HEART-RATE DURING WAKEFULNESS AND SLEEP IN ELEPHANT SEAL PUPS. AMERICAN JOURNAL OF PHYSIOLOGY 266: (3) R863-R869, Part 2.