The role of the suprachiasmatic nuclei in the generation of circadian rhythms in the golden hamster,Mesocricetus auratus

To establish whether the suprachiasmatic nuclei (SCN) of the Ruin lizard ( Podarcis sicula) play a role in entrainment of circadian rhythms to light, we examined the effects of exposure to 24-h light-dark (LD) cycles on the locomotor behavior of lizards with SCN lesions. Lizards became arrhythmic in response to complete SCN lesion under constant temperature and constant darkness (DD), and they remained arrhythmic after exposure to LD cycles. Remnants of SCN tissue in other lesioned lizards were sufficient to warrant entrainment to LD cycles. Hence, the SCN of Ruin lizards are essential both to maintain locomotor rhythmicity and to mediate entrainment of these rhythms to light. We also asked whether light causes expression of Fos-like immunoreactivity (Fos-LI) in the SCN. Under LD cycles, the SCN express a daily rhythm in Fos-LI. Because Fos-LI is undetectable in DD, the rhythm seen in LD cycles is caused by light. We further showed that unilateral SCN lesions in DD induce dramatic period changes. Altogether, the present data support the existence of a strong functional similarity between the SCN of lizards and the SCN of mammals.

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Role of learning in the selection of dietary protein in the golden hamster (Mesocricetus auratus).

Behavioral Neuroscience ◽

10.1037/0735-7044.113.3.574 ◽

1999 ◽

Vol 113 (3) ◽

pp. 574-586 ◽

Cited By ~ 15

Author(s):

David DiBattista ◽

Sharon Mercier

Keyword(s):

Dietary Protein ◽

Golden Hamster ◽

Mesocricetus Auratus ◽

Selection Of

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Seasonality and role of SCN in entrainment of lizard circadian rhythms to daily melatonin injections

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.1998.274.4.r1004 ◽

1998 ◽

Vol 274 (4) ◽

pp. R1004-R1014 ◽

Cited By ~ 2

Author(s):

Cristiano Bertolucci ◽

Augusto Foà

Keyword(s):

Circadian Rhythms ◽

Locomotor Behavior ◽

Suprachiasmatic Nuclei ◽

Primary Target ◽

Podarcis Sicula ◽

Injection Period ◽

Target Sites ◽

Locomotor Rhythms ◽

First Time

To establish whether the capability of daily melatonin injections to entrain circadian rhythms varies with season, we examined in constant conditions the locomotor behavior of lizards Podarcis sicula collected and subjected to daily melatonin injections at different times of the year. Although in summer locomotor rhythms of both pineal-intact and pinealectomized lizards became entrained to the 24-h injection period, in the other seasons their rhythms did not entrain to the injection period. To establish whether the suprachiasmatic nuclei (SCN) mediate summer entrainment of locomotor rhythms to melatonin, we examined the behavioral effects of daily melatonin injections in lizards subjected to either bilateral (SCN-X) or unilateral (USCN-X) ablation of the SCN. SCN-X lizards became behaviorally arrhythmic, and daily melatonin injections did not restore rhythmicity. USCN-X lizards remained rhythmic, and their locomotor rhythms did entrain to the injections. Besides demonstrating for the first time in a vertebrate that daily melatonin injections are capable of entraining circadian rhythmicity in only one season (summer), the present results support the view that the SCN (and not the pineal gland) are the primary target sites of melatonin in the circadian system of P. sicula.

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