Biomedical subjects
Publications and source records attributed to S M Reppert.
The [14C]labeled deoxyglucose method was used to monitor the daily pattern of glucose utilization in the suprachiasmatic nuclei of the squirrel monkey during late fetal development. The findings suggest that a circadian clock is functioning prenatally in the primate suprachiasmatic nuclei and that the maternal circadian system coordinates the timing of the fetal clock to ambient lighting.
A prospective study of the hormonal effects of a moderate exercise training program (4-wk control, 8-wk training) was conducted in seven young women. Sixty-minutes continuous bicycle ergometer tests of fixed relative intensity were performed at the beginning, middle, and end of the training period. The capacity of these acute bouts of exercise to affect circulating levels of stress markers, reproductive hormones, and hormones with possible antireproductive potential was measured. In addition, the urinary excretion of reproductive hormones was monitored continuously via serial overnight urine collections. Within testing sessions, plasma concentrations of all stress markers and antireproductive hormones rose significantly. Across testing sessions, only beta-endorphin + beta-lipotropin and cortisol exhibited an increment in peak responses as training progressed. Plasma reproductive hormone levels showed insignificant acute changes, and cyclic menstruation and preovulatory gonadotropin surges continued in all subjects. However, ovarian function was disturbed in four subjects as evidenced by a decreased excretion of estriol, free progesterone, or both. Transient infertility is a known clinical accompaniment of hormonal changes of comparable subtlety.
Pineal N-acetyltransferase (NAT) activity in 10-day-old rat pups was used to examine several aspects of the developing circadian timing system. When born and reared under constant darkness, 10-day-old animals manifested a clear daily rhythm of NAT activity whose phase was in time with the estimated circadian time of the mother (set by the lighting cycle during pregnancy). When pups were reared in constant darkness from birth by a foster mother whose circadian time was 180 degrees (12 h) out of phase with that of the natural mother, the resulting population profiles of NAT activity were arrhythmic. Analysis of the individual litter profiles from this experiment showed a variable postnatal influence of the maternal circadian system on the timing of the developing circadian system. Neither cross-fostering per se nor social interactions among litter mates contributed significantly to the apparent maternal influence. The magnitude of the postnatal maternal influence was not the same throughout development, but was most apparent during the first 5 days of life. Neonatal blinding (within 24 h of birth) did not appreciably alter the maternal influence. Extraretinal photoreception does not contribute to entrainment of the circadian clock during postnatal development, and retina-mediated photic entrainment is present by 10 days of age. The results indicate that pineal NAT activity monitored in 10-day-old rats provides a useful paradigm for studying the developing circadian system.
The circadian clock located in the suprachiasmatic nuclei (SCN) was characterized in the fetal rat by using 14C-labeled deoxyglucose to monitor glucose utilization (metabolic activity) of the nuclei. A clear day-night oscillation of metabolic activity was detectable in the fetal SCN from the 19th through the 21st days of gestation; the nuclei were metabolically active during the subjective day and metabolically inactive during the subjective night. During the subjective day on gestational day 21, the fetal SCN were found to manifest high metabolic activity for most of the subjective day. We were able to acutely dissociate SCN metabolic activity in the mother rat from that in the fetus by exposing the pregnant animals to light during the normal dark period of diurnal lighting on gestational day 20. The results show the utility of the deoxyglucose method for directly investigating prenatally the function of the biological clock located in the SCN.
In vivo glucose utilization was measured in the suprachiasmatic nuclei (SCN) of the rat, monkey, and cat using the 14C-labeled deoxyglucose technique. SCN metabolic activity in all species was endogenously rhythmic with high levels during the subjective daylight portion of the 24 h day. Such phase conservation across night-, day-, and randomly-active species is in agreement with formal analyses of the properties of entrainable circadian oscillators, and our data suggest that the biochemical processes which underlie the activity of this circadian clock are similar in mammals with differing patterns of expressed circadian rhythmicity.
Deoxyglucose labeled with carbon-14 was used in studying the utilization of glucose in the suprachiasmatic nuclei of fetal rats. The results showed that an entrainable circadian clock is present in the suprachiasmatic nuclei during fetal development and that the maternal circadian system coordinates the phase of the fetal clock to environmental lighting conditions.
Cerebrospinal fluid (CSF) was serially withdrawn in individual, unanesthetized, unrestrained rats and assayed for vasopressin using a sensitive and specific radioimmunoassay. A prominent daily rhythm in the CSF concentrations of this peptide was found under diurnal lighting conditions. Low levels during the dark period alternated with high values during the light period; the rhythm appeared to anticipate the artificial 'dawn' and 'dusk' by a few hours. An 8-h phase shift in diurnal lighting caused a corresponding phase shift in the CSF rhythm. In addition, the rhythm persisted for at least 10 days in the absence of periodic environmental lighting cues in animals blinded by bilateral orbital enucleation; the rhythm was disrupted after 10 days of constant light. Blood vasopressin concentrations did not show a daily rhythm. Our results indicate that the daily vasopressin rhythm in rodent CSF is endogenously generated and that its phase is synchronized to the environmental light-dark cycle.
The temporal profiles of oxytocin were examined in the cerebrospinal fluid (CSF) of the cat and rat. Unlike the marked daily rhythm of oxytocin concentrations recently described in the CSF of the rhesus monkey, no daily rhythm of the peptide was evident in the CSF of either the cat or rat. The apparent species specificity of the CSF oxytocin profiles among these mammals is contrasted with the consistent expression of a daily rhythm of arginine-vasopressin in the CSF of each of the three species.
By monitoring two time points (one at mid-light and the other at mid-dark), the day-night variation of melatonin content in the retina of 19-day-old chicks was characterized. Melatonin was detected in the retina plus attached pigment epithelium by a specific radioimmunoassay, and its identity was verified by high performance liquid chromatography with electrochemical detection. Melatonin content in the posterior pole of the eye showed a fivefold day-night variation, with high levels during the dark period of diurnal lighting. Light exposure during the dark period lowered the normally high nighttime value; maintenance of darkness during the normal light period did not alter the low melatonin values typical of mid-light. Pineal melatonin content responded similarly to the above lighting manipulations. Neither pinealectomy nor optic nerve transection had an effect on retina-pigment epithelium melatonin or its light-dark rhythm. We next examined the relative contributions of retinal and pineal melatonin to blood levels. Pinealectomy reduced the normally high mid-dark plasma melatonin value by 80%. The addition of bilateral enucleation reduced the mid-dark value by another 9% of control values. The day-night variation of retina-pigment epithelium melatonin was first evident in the embryo 2 days prior to hatching and persisted through adulthood. It was concluded that the chick retina from the latter stages of embryonic development is capable of rhythmically synthesizing melatonin; that retinal melatonin content displays a photically controlled circadian rhythm in phase with, but independent of, the pineal gland; and that the retinal rhythm is not regulated by afferent optic nerve fibers. The pineal gland is the major source of plasma melatonin in the intact chick, with at most a small contribution from the retina.
The concentrations of oxytocin, arginine vasopressin, and estrogen stimulated neurophysin in cerebrospinal fluid of monkeys showed a daily fluctuation with high concentrations occurring during the light period. The patterns of oxytocin and estrogen-stimulated neurophysin in the cerebrospinal fluid were not observed in the plasma nor were they altered after the administration of a dose of estradiol that increased concentrations of estrogen-stimulated neurophysin in plasma. The disassociation between these cerebrospinal fluid and plasma patterns and values suggests that the secretory activity of neurons that release estrogen-stimulated neurophysin and oxytocin into the cerebrospinal fluid is controlled by mechanisms different from those that control their release into the plasma.
Using a method for continuous removal of cisternal cerebrospinal fluid (CSF) from freely moving cats, we delineated the circadian nature of the daily rhythm in CSF arginine vasopressin. The daily melatonin rhythm was also monitored in CSF as another marker of circadian function. Under diurnal lighting conditions, both hormones exhibited prominent daily rhythms; the CSF vasopressin rhythm was characterized by high daytime values, whereas the CSF melatonin rhythm was characterized by high nighttime levels. In contrast, drinking behavior exhibited a 24-h component in only one of four animals studied. Daily CSF rhythms of vasopressin and melatonin persisted for over 78 days of study in constant light. The vasopressin rhythm clearly free-ran in this environment, manifesting cycle lengths of slightly greater than 24 h. The daily melatonin pattern split into several components with increasing time in constant light. An acute 8-h phase delay in the daily light-dark cycle resulted in corresponding but gradual phase shifts in both rhythms. These results indicate that both the vasopressin and melatonin rhythms in cat CSF are endogenously generated and are entrained by the daily light-dark cycle.
A rabbit antiserum to somatostatin was used to develop radioimmunoassay methods for measuring somatostatin in monkey cerebrospinal fluid (CSF). By gel permeation chromatography, at least five molecular weight forms of immunoreactive somatostatin (IRS) were identified in monkey CSF; two of these species co-migrated with either synthetic somatostatin-14 or somatostatin-28. The 24-hr profile of CSF somatostatin immunoreactivity was obtained from five monkeys during diurnal lighting, constant light, and constant darkness. During diurnal lighting, all five monkeys had a clear ultradian component in CSF IRS of 4 to 5 hr duration; this pattern was not affected significantly by constant light or dark. In addition, there of the five monkeys exposed to diurnal lighting showed a diurnal rhythm in CSF IRS, with higher hormone levels during darkness. In some animals, this diurnal rhythm also could be demonstrated during constant light or dark.
The circadian characteristics of the daily rhythm in oxytocin (OT) concentrations in cerebrospinal fluid (CSF) were studied in the rhesus monkey. Monkeys subjected to constant light or constant dark for periods of 3 to 6 days manifested persistence of the CSF OT rhythm. A 12-hr phase shift in the light-dark cycle resulted in a resynchronization of the rhythm to the new lighting schedule within 3 to 4 days. Altering the daily feeding and care schedule during a period of constant darkness did not alter the expression or timing of the CSF OT rhythm significantly. These results suggest that the OT rhythm is endogenously generated and that the daily light-dark cycle normally synchronizes the rhythm to the 24-hr cycle.
The effects of alterations in environmental lighting on the daily rhythm in cerebrospinal fluid concentrations of melatonin were studied in the rhesus monkey. It was found that acute exposure to darkness during the day did not markedly increase normally low daytime CSF melatonin levels, that light suppressed the normally high CSF melatonin values at night, and that 12-h phase shifts in the diurnal lighting cycle caused 12-h phase shifts in the rhythm. The daily rhythm persisted for 6.5 days of study in constant darkness and the phase of the rhythm was not affected in constant darkness by a 12-h phase shift in the daily delivery of food and daily care of the animals. These results support the notion that the melatonin rhythm in this primate species is endogenous in nature, and that light can act to both coordinate the rhythm to the 24-h day and to acutely suppress melatonin production.
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Cerebrospinal fluid was continuously collected from the cisternal-cervical subarachnoid space of chair-restrained rhesus monkeys. The concentrations of melatonin and cortisol were measured in the cerebrospinal fluid. Under diurnal lighting (light:dark, 12:12 h) melatonin concentrations were elevated during darkness and low during illumination. The melatonin rhythm persisted in constant darkness but was suppressed in constant illumination. Under diurnal lighting, cortisol concentrations were elevated in the early portion of the light period. This daily rhythmicicty of cortisol secretion was not altered by constant illumination or constant darkness. The differential response of the two hormones to constant light suggest that the daily fluctuation of melatonin secretion was not responsible for the daily rhythmicity of cortisol secretion in the rhesus monkey.
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Melatonin was measured in plasma of seven women volunteers before and after serial acute submaximal exercise tests performed during the course of a two-month, progressive endurance training program. Plasma melatonin increased during all exercise sessions and declined towards baseline values when re-measured thirty minutes after completion of each exercise. This finding indicates that vigorous physical activity elicits transient increases in plasma melatonin in both sedentary and trained women.