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PubMed1976

Regulation of serum gonadotropins by photoperiod and testicular hormone in the Syrian hamster.

Male hamsters were maintained on long (14L:10D) or short (10L:14D) photoperiods. The serum concentrations of LH and FSH were reduced in the animals kept on the short photoperiod, and these animals had atrophied testes and sex accessories. Serum gonadotropin concentrations increased following castration in both long and short photoperiods, but gonadotropin secretion was inhibited by much smaller doses of testosterone in the males maintained on the short photoperiod as compared to males kept on a long photoperiod. The levels of testosterone required to suppress serum gonadotropin levels in castrated animals corresponded reasonably well with the serum androgen levels observed in intact males, suggesting that serum androgen is a major regulator of gonadotropin secretion in the male hamster.

Androgens↗

PubMed1975

Photoperiodic control of LH release in the ram. II. Light-androgens interaction.

The intensity of negative feedback of androgens on hypothalamo-hypophyseal activity was compared in two groups of castrated rams under 8.00 or 16.00 h of daily illumination respectively following a conditioning period. In experiment I, two groups of 15 rams under each light photoperiod were slaughtered at different times after a 200 mg testosterone propionate (TP) intramuscular injection. Animals receiving the vehicle only acted as controls. The hypophyseal LH concentration, which increases when there is temporary inhibition of the release into the blood, was taken as a criterion of the inhibition due to TP. In both groups of rams the LH concentration increased in the pituitary following TP treatment. A return to the pre-injection level was observed 48 h later only in animals under a 8.00 h light photoperiod, indicating a shorter negative effect of the injection than in the case of rams under 16.00 h light photoperiod. In experiment II, the inhibitory effect of TP was assessed at two doses, i. e. 300 and 600 mg, by the decrease in the plasma LH level following an intramuscularly injection. In both cases the decrease in LH release was more pronounced in rams under 16.00 h of daily illumination than in those under 8.00 h (mean decrease in LH release: 21.2 and 33.2% respectively in 300 and 600 mg treated rams under 16.00 h daylight as against 9.2 and 14.8% in rams under 8.00 h). Thus it appears that to the intrinsic action of the photoperiod is superposed on a modulatory effect of steroid action on the hypothalamo-hypophyseal activity. The hypothesis is therefore presented that, in rams a decreasing light photoperiod acts in two ways: 1) by stimulating the activity of the hypothalamo-hypophyseal system, 2) by decreasing the intensity of the negative feedback effect of steroids.

Animals↗

PubMed1978

Rate of testicular maturation, in relation to gonadotrophin and testosterone levels, in quail exposed to various artificial photoperiods and to natural daylengths.

Rates of testicular growth and plasma levels of FSH, LH and testosterone were determined in Japanese quail exposed to various fixed photoperiods (number of hours of light: number of hours of darkness): 12L : 12D, 13L : 11D, 14L : 10D, 16L : 8D and 20L : 4D and to natural daylengths. All five artificial photoperiods stimulated spermatogenesis, with the testes reaching maturity after 30-40 days. Maximum rates of testicular growth occurred with 14L : 10D, 16L : 8D or 20L : 4D but the rate was reduced by 50% in birds exposed to 12L : 12D.. This reduction was due to decreased growth in the seminiferous tubule epithelium (and hence in tubule diameter); the duration of spermatogenesis hardly being affected. Near maximum growth rates occurred with 13L : 11D. The hormone profiles offer an explanation for the differential rates of testicular growth. In the three longest photoperiods, FSH rose from 20 ng/ml to peak levels of 300-400 ng/ml after 10 days. As the testes matured, so the level of FSH decreased to 50-100 ng/ml. This pattern was not seen under 12L : 12D ; the level of FSH rose slowly to about 100 ng/ml and showed no peak of secretion. With 13L : 11D a small peak was found, which decreased at maturity. In quail with testes is greater than 1500 mg, the level of FSH was invariably about 100 ng/ml. Patterns of LH secretion were rather similar with all treatments, but testosterone was affected by photoperiod; lower levels were found under 12L : 12D than 20L : 4D. The rate of photoperiodically induced testicular growth was proportional to the levels of FSH, and possibly also testosterone, in the circulation. Outdoors, testicular growth began when daylengths reached about 12 h. Maturity occurred within the next 40 days. The levels of FSH rose steadily but did not show a peak of secretion. In general, the highest levels of hormone were found in July just before gonadal regression which occurred when the daylengths were still quite long.

Animals↗

PubMed1979

Influence of the pineal gland, olfactory bulbs and photoperiod on surges of plasma prolactin in the female rat.

The role of the pineal gland, olfactory bulbs and photoperiod in the regulation of the two daily surges of plasma prolactin in the pseudopregnant rat has been investigated. Pinealectomy had no effect on the surges of prolactin in pseudopregnant rats maintained on either a long (14 h light : 10 h darkness; 14L : 10D) or a short (2L : 22D) photoperiod, but olfactory bulbectomy decreased the nocturnal surge in animals maintained on 14L : 10D. This effect of bulbectomy was eliminated if the rats maintained on 14L : 10D were also pinealectomized. After cervical stimulation, bulbectomized rats maintained on a 2L : 22D photoperiod had nocturnal-type prolactin surges similar to those of intact rats maintained on the same photoperiod. These results indicate that the pineal gland andlength of photoperiod are not involved in the regulation of the surges of plasma prolactin in pseudopregnant rats but that the olfactory bulbs may enhance the nocturnal surge.

Animals↗

PubMed1979

Variables associated with peripartum traits in dairy cows. IV. Seasonal relationships among temperature, photoperiod, and blood plasma prolactin.

Concentrations of prolactin in plasma were measured in 176 dairy cows and heifers from 13 days before calving to 2.5 days after calving over 21 mo. Prolactin averaged 35.1, 115.0, and 34.4 ng/ml prepartum (days -13 to -2), peripartum (days -1.0 to +.5), and postpartum (days +1.5 and +2.5). Season of the year affected prolactin in all periods. The linear covariate of daily photoperiod (hours of daylight per 24 h) accounted for as much variation in prolactin prepartum and postpartum as did linear covariates of both photoperiod and average daily temperature. However, it was possible to account for additional seasonal variation in prolactin peripartum by addition of the temperature covariate to the photoperiod covariate. Although photoperiod was related either directly or indirectly more than temperature to factors affecting prolactin seasonally, these statistical inferences cannot prove that prolactin is more dependent on photoperiod than on temperature because the two metereorological measures were correlated (r = .84). When the data were grouped for correlation analysis by months, correlations between temperature and prolactin among prepartum samples collected in the spring and in the fall were positive, small but significant.

Animals↗

PubMed1979

Photoperiodic control of rat pineal serotonin N-acetyl-transferase activity.

Adult male albino rats were acclimated to constant light (light:dark-LD-24:0) or to darkness interrupted with brief periods of light at 6 h intervals (LD 1/4:5 3/4 X 4) concurrently with rats maintained in a LD 14:10 photoperiodic cycle. The activity and rhythmicity of pineal serotonin N-acetyltransferase (NAT) was examined at regular intervals for 24 hours in rats maintained in the experimental photoperiods and compared to pineal NAT activity and rhythmicity in rats maintained in the LD 14:10 photoperiod. The results indicate that constant light is capable of depressing nocturnal levels of rat pineal NAT and obliterating the pineal NAT rhythm. Likewise, rats subjected to darkness interrupted with brief periods of light at 6 h intervals experienced a similar response in pineal NAT activity to animals subjected to constant light, i.e., pineal NAT activity was persistently low and the rhythmicity was obliterated. The results are discussed relative to the hypothesis that the pineal NAT activity responds to an endogenous rhythm in photoperiodic time measurement. The evidence herein suggests that the time of occurrence of environmental light in the photoperiod is more important in determining pineal NAT activity and/or rhythmicity than is the total amount of darkness or the dark to light ratio to which animals may be subjected.

Acetyltransferases↗

PubMed2026

Long-day photoperiod promotes growth of pea (Pisum sativum L.) via auxin biosynthesis and polar transport.

Photoperiodic sensitivity is an essential factor that may affect agricultural practices under current climate scenarios. This study used pea (Pisum sativum) to examine effects of varying photoperiods on growth and photosynthetic parameters and then reveal the mechanistic basis of this process by linking them with tissue-specific distribution of auxin and regulation of related genes. This was achieved by transcriptome sequencing, genome-wide gene family identification, and expression pattern analysis. Best results in terms of growth and yield were obtained with a 20 h/4 h light/dark photoperiod and these plants had the highest content of endogenous indole-3-acetic acid (IAA) in both the shoot apex and the root. Genes consistently upregulated with prolonged light exposure were significantly enriched in pathways related to light signal transduction, photosynthetic carbon metabolism, and phytohormone signal transduction. Through genome-wide identification, we characterized the TAA/TAR and YUCCA families (key gene families involved in auxin biosynthesis) as well as the PIN family (responsible for auxin polar transport) in pea. Extending the light duration positively affected expression of several genes related to auxin biosynthesis and transport, among them members of the Elongated Hypocotyl (HY) and Phytochrome-Interacting Factor (PIF) families being key light-induced transcription factors, PsTAR2, the principal gene regulating auxin biosynthesis, as well as PsPIN4, PsPIN5, PsPIN11, and PsPIN13 which mediate polar auxin transport. By elucidating mechanisms underlying the coordinated regulation of pea growth by light and auxin, this work provides a significant reference for photoperiod research on long-day crops for both protected- and field-based horticulture.

Auxin↗

PubMed1977

Effect of extended photoperiod on the spermatogenic activity of chicken-pheasant hybrids.

1. Males of chicken-pheasant hybrids and non-breeding pheasants were exposed to photoperiods of 10 or 20 h/d to test the effect of light on spermatogenic activity. 2. Testicular weights of hybrids and pheasants exposed to 10 h/d were similar and extending the photoperiod did not increase this in hybrids, although it caused a 48-fold increase, and complete recovery of spermatogenic activity, in pheasant. 3. Extending the photoperiod caused an increase in the number of primary spermatocytes and a corresponding decrease in the number of spermatogonia in hybrids, however, stages beyond primary spermatocytes were not present. This suggests that the stimulus of extending the photoperiod, while sufficient to induce meiosis in existing germ cells, is not enough to effect proliferative bursts or to overcome the meiotic arrest in the hybrids.

Animals↗

PubMed1978

The photoperiodic effect of ahemeral light-dark cycles which entrain circadian rhythms.

1. A 27-h cycle of light and dark provides a greater gonadotrophic stimulus to the laying fowl, as judged by sexual maturity and rate of lay, than a 24-h cycle incorporating the same photoperiod. 2. An hypothesis put forward to account for these effects states that Effective Photoperiod equal p + c - b, where p = actual photoperiod, c = cycle length and b = the period of the endogenous biological clock. 3. Two experiments designed to test this hypothesis have yielded results which are consistent with it. 4. A poultryman who use an ahemeral cycle to alter egg weight or shell thickness and then whishes to transfer his flock back to a 24-h cycle should calculate the difference between the two cycle lengths and then add this quantity to the prevailing photoperiod to find the appropriate amount of light to be used in the 24-h cycle.

Animals↗

PubMedDate not supplied

Evidence for a circadian oscillation in the gonadal response of the tropical weaver bird (Ploceus philippinus) to programmed photoperiod.

The effect of an asymmetrical skeleton photoperiod scheduleee was studied on the gonadal development in a tropical finch, the weaver bird (Ploceus philippinus). The schedul comprised a short nonstimulatory primary photoperiod of 6 hrs and a secondary much shorter lightperiod given as a 15-min light pulse at different times in the dark period. The light pulse 11 hrs after the basic period resulted in gonadal stimulation, while light pulse in contimuation with the basic period or 8, 14 or 21 hrs after the basicperiod was not stimulatory. The "photoinducible phase" was much more precisely outlined by shifting the birds from an 8-h to a 10-h pulse, and from an 11-h to 12-h pulse and was found to be very short, lasting about an hour falling between 11 and 12 hrs after the primary light period. The short photoinducible phase may be of an adaptive value since in the tropics the difference between the shortest and the longest daylength is also rather small (3 hrs and 15 min at Varanasi, 25degrees N). Clearly the weaver bird possesses a fine time-measuring device involving an endogenous circadian rhythm in photosensitivity. In nature, spermatogenesis in this bird also begins in March when the daylength exceeds 11 hrs (thus perhaps coinciding with the photoinducible phase). In rather small, photoperiod may not serve as a cue to trigger seasonal reproductive periodicity, it seems that photoperiod can act as a Zeitgeber for the initiation of spermatogenesis in the weaver bird at least.

Animals↗

PubMed1992

Entrainment of the circadian rhythm in the rat pineal N-acetyltransferase activity by melatonin is photoperiod dependent.

Entraining effect of melatonin on the circadian rhythm in rat pineal N-acetyltransferase (NAT) activity was studied under various photoperiods. Melatonin administration prior to dark onset for 5 successive days phase-advanced the evening NAT rise under the light:dark (LD) cycle of either LD 10:14 or LD 8:16, but not under LD 12:12. It is assumed that under the latter regime, the end of a light period exhibited a phase-delaying effect on the NAT rise. The light exposure appeared to be a stronger Zeitgeber than melatonin itself. Data show that melatonin applied in the late light period advances the evening NAT rise under a short photoperiod only; under a longer photoperiod, the phase-advancing effect of melatonin may conflict with a phase-delaying effect of the end of a light period, and the effect of light exposure overrides that of melatonin.

Animals↗

PubMed1976

Response of the ovary in the catfish, Heteropneustes fossilis (Bloch), to various combinations of photoperiod and temperature.

Responses of the ovary of the catfish, Heteropneustes fossilis, to various regimes of photoperiod and temperature, were studied during the different periods of the annual ovarian cycle. During the preparatory and post-spawning periods moderate temperatures of 25 degrees C and above, regardless of photoperiod, were more favorable for the formation of yolky (stage III) oocytes than coller temperatures (below 23 degrees C). Even under conditions of continuous dark or light, ovarian development occurred as a function of warm temperatures. Gravid ovaries were maintained beyond the spawning period only with a temperature of 30 degrees C, photoperiod notwithstanding. Nevertheless, moderate or cool temperatures did not prevent the ovarian regression that occurred by the first week of October in the post-spawning period. Regulation of ovarian activity at least in part by an endogenous circannual rhythm appears possible.

Animals↗

PubMed1978

The effects of photoperiod on androgen-induced reproductive behavior in male ring doves, Streptopelia risoria.

The effect of photoperiod on reproductive behavior in male ring doves (Streptopelia risoria) was studied in androgen-injected castrates maintained under long (16L:8D) or short (86:16D) photoperiods. Behavioral recordings were made over a 2-week period during which each male was paired with a female for 6.5 hr/day. There was some indication that males held on long days display higher levels of courtship activity during the initial period following pairing, but the evidence was not conclusive. Day length had no effect upon copulatory behavior. Long-day males exhibited consistently higher levels of nest building than short-day males, indicating that photoperiod affects building through some mechanism other than changes in endogenous androgen levels.

Animals↗

PubMed1976

A metabolic indicator of photoperiodic timing.

Characteristics of CO2 output patterns of axenic cultures of Lemna perpusilla are being sought that would serve as biochemically definable indicators of the crucial photoperiodic events during inductive light/dark schedules, using cycles with skeleton main light periods and overall periodicities of 24 hr. As the length of the main light period is increased over the range 4-10 hr, the daily times of maximal output on nitrate or ammonium media shift about 2.5 hr; there is a precisely parallel shift in the time of maximal photoperiodic sensitivity of flowering to a night interruption. These times do not depend on either a "drawn" or a "dusk" signal alone, but are functions of both. The time of maximal daily CO2 output on aspartate medium reflects only the dawn signal, suggesting that the display of some component of CO2 flux coupled to the photoperiodic timing mechanism can be controlled by modifying nitrogen metabolism.

Biological Clocks↗

PubMed1979

Variations in plasma prolactin, thyroid hormones, gonadal steroids and growth hormone in turkeys during the induction of egg laying and moult by different photoperiods.

1. Concentrations of prolactin, growth hormone, testosterone, progesterone, thyroxine and triiodothyronine were measured in the blood plasma of female turkeys during successive periods of egg laying, a decline in lay, a moult induced by a short photoperiod (6 light: 18 dark) and a resumption of egg laying induced by a long photoperiod (16L:8D). 2. Concentrations of prolactin, growth hormone, testosterone and progesterone were higher in laying birds than in birds which were moulting or not laying. 3. The concentration of testosterone, but not of the other hormones studied, increased significantly during the period of profuse moult. 4. Concentrations of the thyroid hormones did not change with the varying physiological condition of the birds. However, the concentration of thyroxine was depressed by the long photoperiod.

Animals↗

PubMed1978

The effects of pinealectomy on pituitary prolactin levels in Carassius auratus exposed to various photoperiod-temperature regimes.

Pinealectomy has an influence on pituitary prolactin levels in goldfish maintained under certain photoperiod-temperature regimes. The effects of pinealectomy on pituitary prolactin content depend on photoperiod and time of sampling. Thus, differences between pinealectomized and sham operated animals may be due to a shift of a daily variation in pituitary prolactin levels. The pineal in fishes may thus be involved in photoperiod influences on daily prolactin rhythms.

Acclimatization↗

PubMed1976

Entrainment of the adrenal rhythm to photoperiod prior to puberty: effects of early experience on the adrenal rhythm and puberty.

The purpose of this study was to determine whether exposure to a cycle of light and dark before the onset of the adrenal rhythm would be necessary in order for rats to develop a normal rhythm of peripheral corticosterone when placed in a test photoperiod at weaning age. Rats were reared in constant light (LL) until weaning age, at which time they were placed in a cycle of 14 h light, 10 h dark (14:10). Females born and reared in 14:10 had peak corticosterone values at 14.00 h on days 22 and 26, and at 18.00 h on days 32 and 36. Males did not display a clear-cut rhythm at 22 or 26 days but had peak corticosterone at 18.00 h on days 32 and 36. Males and females reared in LL until weaning had no rhythm as a group in 14:10 at 24 days of age, but had a corticosterone peak at 18.00 h on days 28 and 40. Females born and reared in LL and exposed to 14:10 for 1 day developed an adrenal rhythm regardless of the age at exposure, but only 25 day old animals showed a normal pattern for their age group. Puberty was advanced in rats exposed to a single day of 14:10 at 25 days of age, but was delayed in younger rats (22 days old), and was unaffected by light exposure in older rats (28 days of age). It can be concluded that early exposure to light-dark cycles is not required for the normal development of an adrenal rhythm in the weanling rat, and that the setting of the corticosterone rhythm to the photoperiod can occur quite rapidly. Rats at 25-26 days of age are able to respond differently to a light cycle challenge than younger rats. A photoperiodic stimulus at that time can advance the onset of puberty.

Adrenal Glands↗

PubMed1975

Primate breeding season: photoperiodic regulation in captive Lemur catta.

Under natural light in Portland, Oreg., captive ring-tailed lemurs (Lemur catta) experience a breeding season that differs by nearly half a year from the season in Madagascar. A series of experimental day length changes from 1971 to 1974 demonstrated the ability of both temperate and tropical photoperiod cycles to induce estrous cycles in quiescent animals. After photoperiodic activation, most impregnated females failed to resume estrous cycles even after infant separations unless they received additional photoperiod changes. Unimpregnated females, on the other hand, showed no significant decline in the incidence of estrous cycles under prolonged exposure to a constant day length regimen (12.OL:12.OD) for over a year.

Animals↗