Circadian characteristics of Djungarian hamsters: effects of photoperiodic pretreatment and artificial selection

Abstract

Bidirectional artificial selection for (High Line) and against (Low Line) photoresponsiveness altered the percent of photoresponsive hamsters within lines and affected circadian function of hamsters identical in photoresponsiveness. For example, free-running period was shorter in responsive relative to nonresponsive hamsters. Between-line differences for responders and nonresponders were also found: hamsters from the High Line had a shorter free-running period relative to Low Line hamsters. However, phase angle of entrainment to long and short days was not affected. In general, expression of circadian rhythmicity was extraordinarily inflexible in photononresponsive hamsters from both lines: 1) phase angle of entrainment to lights on was similar under short and long day; 2) activity duration was similar under long and short days, although some decompression occurred in constant dark; 3) aftereffects on the free-running period were absent; and 4) amplitude of the phase-response curve was small (+/- 1 h) and present only at circadian times 10-24. We propose that selection for or against photoresponsiveness may have affected the interaction of component oscillators underlying circadian rhythmicity.

Mice lacking the PACAP type I receptor have impaired photic entrainment and negative masking

“…We preferred the Aschoff type II to the type I procedure (20) to generate a light PRC, since it eliminates possible confounding effects of chronic DD, including a more light-sensitive system compared with the LD cycle experiment (25)(26)(27)29) and permits simultaneous light stimulation (since all animals are entrained) at a given clock time. Using the type II procedure, we found that the response to light stimulation in PAC1 KO mice differed from our previously obtained results using the type I regime (11).…”

Enhanced circadian photoresponsiveness after prolonged dark adaptation in seven species of diurnal and nocturnal rodents

“…For species that exhibit strong reproductive seasonality (such as the Siberian hamster), however, LD 12:12 does not provide sufficient daily illumination to prevent reproductive inhibition. This was deemed to be an acceptable cost for the institution of a uniform LD cycle for all species, particularly because exposure to short photoperiods enhances (i.e., does not inhibit) circadian photoresponsiveness in Siberian hamsters [26].…”

“…By convention, the time of activity onset is designated as CT 0 for diurnal species and as CT 12 for nocturnal species. In order to achieve the largest expected phase delay of the activity rhythm, pulses were presented at CT 14 for Nile grass rats [30], laboratory rats [41], and Syrian hamsters [33], at CT 15 for degus [16] and Siberian hamsters [26], and at CT 16 for mice [18]. Because no phase-response curve has been published for Mongolian gerbils, CT 15 was chosen as a tentative optimal circadian time for this species.…”

“…In many studies, animals were kept in darkness for the duration of the study and were repeatedly exposed to light pulses at intervals of 10 to 46 days without intermediary re-entrainment to a light-dark cycle [6,[18][19][20][21]25,26,33,34,40,41], so that the actual state of dark adaptation of the animals at the time of each pulse could not be ascertained. In other studies, light-pulse tests were consistently preceded by a standardizing light-dark cycle but the interval in darkness prior to the pulse ranged from 5 to 21 days across studies [4,5,9,10,22,30,39,42,43].…”

Seasonal variations in daily rhythms of activity in athletic horses

“…In temperate zones, the photoperiod markedly changes across seasons and affects mammalian physiology and behaviour (Sumova et al, 2004). For instance, in nocturnal rodents, the duration of locomotor activity reflects the photoperiod as being shorter on long summer than on -E-mail: giuseppe.piccione@unime.it short winter days (Puchalski and Lynch, 1991;Elliott and Tamarkin, 1994). The rhythmic production of the pineal hormone melatonin, which is a part of the timekeeping system, is also highly photoperiod-dependent, both in nocturnal and in diurnal animals; the high nocturnal melatonin production is shorter on long summer than on short winter days (Illnerová , 1991).…”