Prior light alters the circadian clock in the chick pineal gland

Roles of Direct Photoreception and the Internal Circadian Oscillator in the Regulation of Melatonin Secretion in the Pineal Organ of the Domestic Turkey: A Novel In Vitro Clock and Calendar Model

The regulation of melatonin secretion in the avian pineal organ is highly complex and shows prominent interspecies differences. The aim of this study was to determine the roles of direct photoreception and the internal oscillator in the regulation of melatonin secretion in the pineal organ of the domestic turkey. The pineal organs were collected from 12-, 13- and 14-week-old female turkeys reared under a 12 L:12 D cycle with the photophase from 07.00 to 19.00, and were incubated in superfusion culture for 3-6 days. The cultures were subjected to different light conditions including 12 L:12 D cycles with photophases between 07.00 and 19.00, 13.00 and 01.00 or 01.00 and 13.00, a reversed cycle 12 D:12 L, cycles with long (16 L:8 D) and short (8 L:16 D) photophases, and continuous darkness or illumination. The pineal organs were also exposed to light pulses of variable duration during incubation in darkness or to periods of darkness during the photophase. The secretion of melatonin was determined by direct radioimmunoassay. The turkey pineal organs secreted melatonin in a well-entrained diurnal rhythm with a very high amplitude. Direct photoreception as an independently acting mechanism was able to ensure quick and precise adaptation of the melatonin secretion rhythm to changes in light-dark conditions. The pineal organs secreted melatonin in circadian rhythms during incubation in continuous darkness or illumination. The endogenous oscillator of turkey pinealocytes was able to acquire and store information about the light-dark cycle and then to generate the circadian rhythm of melatonin secretion in continuous darkness according to the stored data. The obtained data suggest that the turkey pineal gland is highly autonomous in the generation and regulation of the melatonin secretion rhythm. They also demonstrate that the turkey pineal organ in superfusion culture is a valuable model for chronobiological studies, providing a highly precise clock and calendar. This system has several features which make it an attractive alternative to other avian pineal glands for circadian studies.

Duration of melatonin regulates seasonal changes in song control nuclei of the house sparrow, Passer domesticus: independence from gonads and circadian entrainment

Avian behavior and physiology are temporally regulated by a complex circadian clock on both a daily and an annual basis. The circadian secretion of the hormone melatonin is a critical component of the regulation of circadian/daily processes in passerine birds, but there is little evidence that the gland regulates annual changes in primary reproductive function. Here it is shown that locomotor rhythms of house sparrows, Passer domesticus, which are made arrhythmic by either pinealectomy or maintenance in constant light, can be synchronized by daily administration of melatonin of different durations to simulate the melatonin profiles indicative of long and short photoperiods. Pinealectomized male sparrows maintained in constant darkness were entrained by both melatonin regimens. In both cases, testes were regressed and the song control nuclei were small. Intact male house sparrows maintained in constant light were also entrained to both melatonin regimens. However, sparrows that received a long duration melatonin cycle exhibited small song control nuclei, while sparrows that received short duration melatonin or no melatonin at all exhibited large song control nuclei. The data indicate that seasonal changes in melatonin duration contribute to the regulation of song control nuclei.

Nighttime Oxygen Desaturation and Symptoms of Sleep-Disordered Breathing in Long-Stay Nursing Home Residents

BACKGROUND

Sleep-disordered breathing (SDB) is common in older adults and has been implicated as a cause of decreased quality of life and even death. Sparse data exist on SDB in the nursing home setting. The authors evaluated SDB (using attended nocturnal pulse oximetry) in nursing home residents with daytime sleepiness and nighttime sleep disturbance.

METHODS

Pulse oximetry was used to estimate the prevalence of nighttime oxygen desaturation in 109 long-stay nursing home residents (mean [standard deviation] age = 86.2 [9.2] years; 74% women). Pulse oximetry findings were compared to a structured observational measurement of symptoms of SDB, the Observational Sleep Assessment Instrument. Seventy-one participants had concurrent wrist actigraphy to estimate total sleep time during oximetry recording.

RESULTS

Using the oxygen desaturation index (ODI; average number of oxygen desaturations 4% or more below the baseline level per hour), the authors found that 40% of the residents had abnormal ODI (ODI more than 5, which is suggestive of SDB). Of all observational variables assessed, only loud breathing during sleep was significantly correlated with ODI (r =.284; p =.003). When ODI was adjusted for estimated total sleep time, higher adjusted ODI was associated with higher body mass index (kg/m(2)).

CONCLUSIONS

Abnormal ODI is common in nursing home residents. Observed loud breathing at night and high body mass index may suggest that further assessment of SDB is indicated. Future research should determine the importance of SDB and abnormal nocturnal oxygen desaturation on functioning and quality of life in nursing home residents.

Ontogeny of N-acetyltransferase activity rhythm in pineal gland of chick embryo

1. N-acetyltransferase was present in pineal glands of 14-day-old chick embryos though no rhythm either in LL, DD or LD 12:12 was observed in this age. 2. Daily rhythm in pineal NAT activity was found in 18-day-old embryos incubated under LD 12:12 and LD 16:8 but no NAT rhythm was detected in DD or LL. 3. NAT rhythm persists for 2 days in constant darkness and it may be circadian in nature. 4. Presence of melatonin (85 +/- 8 pg/mg tissue) was detected in pineals of 18-day-old chick embryos.

Photoperiod modifies daily maps of light and dark sensitivity for N-acetyltransferase activity in pineal glands of 3-week old Gallus domesticus

N-acetyltransferase (NAT) activity in pineal glands exhibits a circadian rhythm with peak activity occurring in the dark-time. We previously showed that in Gallus domesticus chicks pretreated with LD12:12, NAT activity was increased by dark exposure (peak dark sensitivity occurred during the expected dark-time) or decreased by light at night (peak light sensitivity occurred early in the night during the time of dark sensitivity). In this study we mapped dark sensitivity vs time (for NAT activity increase in response to 2 h dark pulses), and light sensitivity vs time (for NAT activity decrease in response to 10 min or 30 min light pulses) over a cycle for 3-week old chicks, Gallus domesticus, pretreated with long (LD16:8) or short photoperiod (LD8:16). Sensitivity to light was increased in the second 8 h after L/D by LD8:16. Sensitivity to dark was increased in the first 8 h after L/D by LD16:8.

Examination of in vitro melatonin secretion from superfused trout (Salmo gairdneri) pineal organs maintained under diel illumination or continuous darkness

Melatonin secretion was measured from rainbow trout (Salmo gairdneri) pineal organs maintained individually under flow-through whole organ culture (superfusion) conditions. Radioimmunoassay of perfusate fractions collected during controlled photic conditions demonstrated that melatonin secretion in vitro remained basal during the photophase and underwent increases in titer during the scotophase. While amounts of melatonin (mel) secreted were characteristic of individual pineal organs, photophase values ranged between 0.25 and 0.75 ng mel/ml and scotophase values ranged from 6 to 10 ng mel/ml of perfusate. Diel melatonin secretion profiles reflected the illumination regimen, with light associated with low melatonin titer in the perfusate and darkness associated with high titer. Light pulses during a normal scotophase resulted in a depression in melatonin secretion regardless of whether it was administered early or late in the dark period. Pulses of darkness given early or late in a normal photophase resulted in increased melatonin secretion. Superfused trout pineal organs did not display endogenous rhythmicity in melatonin secretion when subjected to prolonged exposure to continuous darkness (DD), whether first exposed to entraining light/dark (LD) cycles prior to DD or exposed to DD at the initiation of superfusion. In both studies, elevated melatonin secretion gradually declined over time. But exposure to a 4:4LD cycle after DD resulted in decreased (with light) and increased (with darkness) melatonin secretion. These results demonstrate that the trout pineal organ can be maintained for extended periods of time in superfusion culture, that the trout pineal organ is very responsive to light or dark for regulating melatonin synthesis, and that an endogenous rhythm in melatonin synthesis when organs were maintained in DD was not detectable.

Rapid adjustment of the pineal N-acetyltransferase rhythm to change from long to short photoperiod in the Japanese quail (Coturnix coturnix japonica)

The dynamics of adjusting the pineal N-acetyltransferase rhythm from long to short photoperiod was assessed in the Japanese quail (Coturnix coturnix japonica). The transition from LD 16:8 to LD 8:16 was accomplished by symmetrical prolongation of the dark period. In LD 16:8, the period of elevated nocturnal activity lasted approximately 7 hours. During the first prolonged night, the evening N-acetyltransferase rise advanced by almost 3 hours relative to the rise in LD 16:8 and occurred at the same time as during the 3rd, 7th, and 14th day after the transition. The morning N-acetyltransferase decline did not shift during the first long night; during the third night it was delayed relative to the decline in LD 16:8 by more than 2 hours and occurred at the same time as during the 7th and 14th night following the LD 16:8 to LD 8:16 transition. Three, 7, and 14 days after the transition, the period of elevated N-acetyltransferase activity lasted approximately 12 hours. Hence extension of the N-acetyltransferase rhythm profile proceeded first into the evening and then only into the morning hours, and it was accomplished within 2 to 3 days.

Circadian rhythm in pineal N-acetyltransferase activity: rapid phase reversal and response to shorter than 24-hour cycles (IV)

N-Acetyltransferase (NAT) is an enzyme whose rhythmic activity in the pineal gland and retina is responsible for circadian rhythms in melatonin. The NAT activity rhythm has circadian properties such as persistence in constant conditions and precise control by light and dark. Experiments are reported in which chicks (Gallus domesticus), raised for 3 weeks in 12 h of light alternating with 12 h of dark (LD12:12), were exposed to 1-3 days of light-dark treatments during which NAT activity was measured in their pineal glands. (a) In LD12:12, NAT activity rose from less than 4.5 nmol/pineal gland/h during the light-time to 25-50 nmol/pineal gland/h in the dark-time. Constant light (LL) attenuated the amplitude of the NAT activity rhythm to 26-45% of the NAT activity cycle in LD12:12 during the first 24 h. (b) The timing of the increase in NAT activity was reset by the first full LD12:12 cycle following a 12-h phase shift of the LD12:12 cycle (a procedure that reversed the times of light and dark by imposition of either 24 h of light or dark). This result satisfies one of the criteria for NAT to be considered part of a circadian driving oscillator. (c) In less than 24-h cycles [2 h of light in alternation with 2 h of dark (LD2:2), 4 h of light in alternation with 4 h of dark (LD4:4), and 6 h of light in alternation with 6 h of dark (LD6:6)], NAT activity rose in the dark during the chicks' previously scheduled dark-time but not the previously scheduled light-time of LD12:12. In a cycle where 8 h of light alternated with 8 h of dark (LD8:8), NAT activity rose in both 8-h dark periods, even though the second one fell in the light-time of the prior LD12:12 schedule.(ABSTRACT TRUNCATED AT 250 WORDS)