Weeks In Short Photoperiod Research Articles

Short Photoperiod-Dependent Enrichment of Akkermansia spec. as the Major Change in the Intestinal Microbiome of Djungarian Hamsters (Phodopus sungorus)

The Djungarian hamster (Phodopus sungorus) is a prominent model organism for seasonal acclimatization, showing drastic whole-body physiological adjustments to an energetically challenging environment, which are considered to also involve the gut microbiome. Fecal samples of hamsters in long photoperiod and again after twelve weeks in short photoperiod were analyzed by 16S-rRNA sequencing to evaluate seasonal changes in the respective gut microbiomes. In both photoperiods, the overall composition was stable in the major superordinate phyla of the microbiota, with distinct and delicate changes of abundance in phyla representing each <1% of all. Elusimicrobia, Tenericutes, and Verrucomicrobia were exclusively present in short photoperiod hamsters. In contrast to Elusimicrobium and Aneroplasma as representatives of Elusimicrobia and Tenericutes, Akkermansia muciniphila is a prominent gut microbiome inhabitant well described as important in the health context of animals and humans, including neurodegenerative diseases and obesity. Since diet was not changed, Akkermansia enrichment appears to be a direct consequence of short photoperiod acclimation. Future research will investigate whether the Djungarian hamster intestinal microbiome is responsible for or responsive to seasonal acclimation, focusing on probiotic supplementation.

Initial expression of the common alpha-chain in hypophyseal pars tuberalis-specific cells in spontaneous recrudescent hamsters.

When exposed to short-day conditions, hamsters and other long-day breeders undergo gonadal regression. With chronic exposure to short days, however, the animals become photorefractory and gonadal recrudescence occurs. The underlying mechanism for this insensitivity is still unknown. There is growing evidence, however, that specific cells of the pituitary pars tuberalis (PT) mediate these photoperiod/nonphotoperiod-dependent changes as a direct or indirect "Zeitgeber" for the endocrine system. We investigated messenger RNA (mRNA)/protein formation for several hypophyseal hormones (beta-TSH, beta-LH, PRL, common alpha-chain) in the pars distalis (PD) and PT of female Djungarian hamsters in long photoperiod (LP) and after 18, 28, and 38 weeks of short photoperiod (SP). As indicated by gonadal and body weight, the hamsters displayed gonadal regression after 18 and 28 weeks of SP; after 38 weeks of SP, all animals showed recrudescence. At 18 and 28 weeks of SP, only PRL mRNA and protein levels were significantly reduced in the PD and returned to LP values after 38 weeks of SP. The expression of hypothalamic tyrosine hydroxylase in the arcuate nucleus that was determined by immunocytochemistry and by in situ hybridization was also down-regulated in SP18 and SP28 with increasing levels at SP38. Urinary 6-sulfatoxymelatonin levels were elevated in SP with highest levels in the SP18 group. In the PT, beta-TSH mRNA and protein were not detectable in all SP groups compared with the moderate signal intensity in LP. The common alpha-chain mRNA and protein, however, which were also reduced in the animals of the SP18 group, were already elevated after 28 weeks of SP and nearly reached LP-levels after 38 weeks of SP. These results show that, in contrast to LH and TSH, PRL expression in the PD is a sensitive indicator for photoperiod dependent changes of the endocrine system and seems to be tyrosine hydroxylase independent. The increase of common alpha-chain expression in PT-specific cells depending upon duration of SP that precedes the hormonal changes in the PD leads us to speculate that PT-specific cells initiate spontaneous recrudescence via a PT-PD pathway.

Photoperiod nonresponsive Siberian hamsters: effect of age on the probability of nonresponsiveness.

Groups from three different breeding lines of Siberian hamsters (UNS = general colony animals, PNRa = selected for photoperiod nonresponsiveness as adults, PNRj = selected for photoperiod nonresponsiveness as juveniles) were exposed to short days at weaning and again as adults (Experiment 1) or only as adults (Experiment 2). The proportion of photoperiod nonresponsive individuals in each line was determined by measuring testis length after 6 weeks of exposure to short days (juveniles) or by paired testis weights after 12 weeks in short photoperiod (adults). Adults were blood sampled on the day of sacrifice (Experiment 1) or on Weeks 3, 4, 5, 6, 8, 10, and 12 (Experiment 2) for determination of serum prolactin (PRL) and follicle-stimulating hormone (FSH) concentrations. Nonresponsive individuals were present in all three lines of hamsters. Furthermore, all three lines of hamsters showed an increase in the proportion of nonresponders with age; some individuals are responsive to short days as juveniles, but become nonresponsive in adulthood. The two PNR lines exhibited a greater proportion of nonresponders at both ages compared to the UNS line, with the PNRj line exhibiting the greatest proportion of nonresponders at each age. During exposure to short days, nonresponders exhibited significantly higher serum PRL and FSH concentrations that did the UNS line; nonresponders also exhibited larger testis size, and fewer animals molted to winter-type pelage. The results indicate that (a) in all three lines, a significantly higher proportion of animals are nonresponsive to short photoperiod as adults than as juveniles; (b) selection for nonresponsiveness as juveniles can produce a line of hamsters that, as adults, are nearly all nonresponsive to short days; and (c) some individuals from each line are responsive to short photoperiod early in life, but become nonresponsive as adults.

Seasonal regulation of melatonin receptors in rodent pars tuberalis: correlation with reproductive state.

Using quantitative autoradiography, we have studied the relationship between melatonin receptor density in the pars tuberalis (PT) and photoperiodic changes in sexual activity in a photoperiodic (Syrian hamster), and a non photoperiodic (rat) rodent. Syrian hamsters exposed to short photoperiod (SP) for 13 weeks or kept in long photoperiod (LP) with daily melatonin injections for 8 weeks, had both gonadal regression and a significant decrease in 2-125I-melatonin binding site density in the PT when compared to controls. In contrast, when the animals were sexually active, photorefractory Syrian hamsters exposed to SP for 27 weeks, or rats kept for 13 weeks in SP, the PT melatonin receptor density was similar to that of control animals kept in LP. These results show clearly that a correlation exists between gonadal status and density of melatonin receptors in the PT and suggest that the PT could be the site where melatonin mediates its effects on seasonal function.

Seasonal patterns and environmental regulation of frost hardiness in shoots of seedlings of Thuja plicata, Chamaecyparis nootkatensis, and Picea glauca

Seasonal patterns of frost hardiness and the effects of photoperiod, water stress, and low temperature on hardiness development were examined in shoots of 1st-year seedlings of western red cedar (Thuja plicata Donn), yellow cedar (Chamaecyparis nootkatensis (D. Don) Spach), and white spruce (Picea glauca (Moench) Voss). Under natural conditions, spruce hardened in two stages starting in early August, first at a slow rate in response to shortening photoperiod, then at a faster rate in response to decreasing temperatures. Western red cedar and yellow cedar started hardening in late October to early November when the photoperiod was already less than 11 h and daily maximum temperatures less than 15 °C. Seedlings of these two species attained a greater degree of frost hardiness when exposed to persistent subfreezing temperatures. Under controlled conditions, 4 weeks of short photoperiod at warm temperatures (9 h light:15 h dark, 20:15 °C) had little effect on hardiness of the two cedars but increased hardiness in spruce to about −15 °C. Water stress increased hardiness in spruce under long photoperiod (18 h light: 6 h dark, 20:15 °C) but only marginally in western red and yellow cedar. Low temperatures (7:3 °C, light:dark, 9-h photoperiod) increased hardiness in all species. Exposure to 2 and −3 °C (light:dark, 9-h photoperiod) increased the rate of hardening in western red and yellow cedar but not in white spruce. The ability to deharden in white spruce was related to chilling requirements and not necessarily exposure to warm temperatures. The induction and maintenance of hardiness in the three species appear to be controlled by different environmental signals. Key words: photoperiod, low temperature, water stress, dormancy, dehardening.

Increased FSH Levels Precede Short Photoperiod‐Induced Anestrus in Intact and Unilaterally Ovariectomized LSH/SsLak Hamsters

Anestrus brought about after 2-4 weeks of short photoperiod (SP) exposure in LSH/SsLak hamsters is preceded by impaired follicular development. Since the latter is critically dependent on adequate FSH levels, this study tested the hypothesis that SP might alter baseline or compensatory FSH levels prior to the onset of anestrus. Regularly cycling females in 141:10 (LP) were transferred to SP (8L:16D). Between 0800 and 0900 h on days 20 through 24 of SP exposure, half of the animals in diestrus II were unilaterally ovariectomized (UO), and the remaining animals were sham-operated (Sham-UO). Seven hours after surgery, blood samples were taken via cardiac puncture. All animals were killed the following morning at 0900 h. Uterine weights were significantly reduced in SP-exposed hamsters, yet the compensatory increase in FSH following unilateral ovariectomy was not affected; a tendency for higher levels was noted. On proestrus, serum and pituitary FSH levels of SP-exposed Sham-UO animals were significantly elevated over similarly treated LP-exposed hamsters. Interestingly in animals with severe follicular impairment, the highest FSH levels correlated with the lowest uterine weights. The data suggest that SP exposure does not impair compensatory FSH release or the ability of the ovaries to respond to UO. SP-induced elevations in FSH levels may result from reduced follicular secretion and reduced inhibin and/or estrogen levels.

Hyperprolactinemia prevents short photoperiod-induced changes in brown fat.

Previous studies demonstrated that short photoperiod exposure significantly decreases circulating prolactin levels. The present study investigated the possibility that concomitant changes in brown fat tissue mass, protein content, thermogenic capacity, and carcass composition are dependent on this change in prolactin levels. Male golden (Syrian) hamsters were sham operated and exposed to a short (10L:14D) or long (14L:10D) photoperiod. A third group was implanted with exogenous pituitaries under the right kidney capsule and exposed to a short photoperiod. In experiment I, 4 wk of short- vs. long-photoperiod exposure did not result in significant changes in circulating prolactin levels, nor was there an increase in brown fat mass, protein content, or thermogenic capacity. Four weeks of short-photoperiod exposure did significantly increase carcass lipid content. However, this increase did not occur in hamsters exposed to 4 wk of short photoperiod but made hyperprolactinemic (implanted with two exogenous pituitaries). Ten weeks of short photoperiod significantly reduced circulating prolactin levels. Concomitantly, brown fat mass, protein content, and thermogenic capacity, as well as carcass fat, were increased. These short-photoperiod-induced changes were not observed in similarly exposed hamsters that were made hyperprolactinemic via two implanted pituitaries. In experiment II, similar changes in brown fat and body composition occurred in sham-operated hamsters exposed to 10 wk of short photoperiod. These changes were prevented in hamsters exposed to 10 wk of short photoperiod but made hyperprolactinemic via only one implanted pituitary. These results suggest that decreased prolactin is a necessary condition for the increased brown fat mass, protein content, and thermogenic capacity that occurs when golden hamsters are exposed to short photoperiod.

Early short photoperiod effects in female LSH/SsLak Syrian hamsters.

Previous experiments showed that LSH/SsLak female hamsters cease ovarian cyclicity after 2-4 weeks of short photoperiod (SP) treatment. This study was designed to reveal early hormonal and histological changes on day 1 of the estrous cycle (estrus) in SP-treated animals and changes brought about by the SP-induced acyclic condition. Groups of 8-10 animals were killed on day 1 after 0, 4, 8, 12, and 16 days of SP treatment; sera and pituitaries were saved for hormone determinations, and ovaries were prepared for histological analysis. Intraatrial cannulae were inserted into anovulatory animals, and blood samples were withdrawn on the first and second postoperative days; the animals were killed on the third postoperative day. PRL levels were significantly reduced in cycling animals after 16 days of SP exposure and diminished further in acyclic animals. Pituitary PRL did not change in cycling animals, although it was highly depressed in SP-treated acyclic animals. The estrous FSH surge, serum LH levels, and pituitary gonadotropin contents were not affected by SP in cycling animals; in anovulatory animals, pituitary gonadotropin contents were significantly increased, and daily afternoon gonadotropin surges were observed. Uterine weights were reduced in cycling animals and underwent a further reduction after cyclicity ceased. Ovarian analysis revealed that all cycling animals had the same number of recruited follicles, yet significantly fewer corpora lutea and an apparent increase in atretic antral follicles were observed after 16 days of SP exposure. These results suggest that SP-induced cessation of estrous cyclicity occurs abruptly. SP does not alter the secondary FSH surge, but might adversely affect maintenance of follicular growth and depress serum PRL levels.

Suppression of sympathetic nervous system by short photoperiod and melatonin in the Syrian hamster

Exposure to short photoperiod or melatonin treatment brings about gonadal regression in Syrian hamsters. The possible influence of these treatments on the sympathetic nervous system (SNS) in these animals was investigated. Male Syrian hamsters were exposed to either long or short photoperiod or subjected to administration of melatonin or its vehicle solution. Exposure of hamsters to 10 weeks of short photoperiod, significantly reduced the noradrenaline (NA) turnover in the heart. Daily administration of melatonin for 8 weeks also resulted in a similar suppression of NA turnover in the heart. Hamsters that were treated with melatonin maintained a lowered metabolic rate as well, at and below thermaneutral temperature. These findings suggest that in a deep hibernator, short photoperiod could suppress the peripheral sympathetic activity and that melatonin may act as the endogenous mediator.

Effects of inhibitory and stimulatory photoperiods and sexual maturation on the ability of hamster testes to respond to hCG in vitro.

The decrease in gonadal weight produced in adult golden hamsters by exposure to short photoperiods was accompanied by a marked reduction in the ability of the testes to produce testosterone from endogenous precursors in vitro, both without and with hCG stimulation. These changes were significant after 4-7 weeks in short photoperiod (5L: 19D) and were even more pronounced after 17-20 weeks. Production of testosterone in vitro by testes of immature hamsters was comparable to values obtained in adult animals with short photoperiod-induced gonadal atrophy. Delay of sexual maturation induced by daily injections of bromocriptine was accompanied by a further decrease in testicular testosterone production in vitro. Exposure of gonadally-regressed adult hamsters to a long, stimulatory photoperiod (14L: 10D) produced a rapid and marked increase in testicular testosterone production, which was coincident with the previously demonstrated increase in serum gonadotrophin levels after 1-5 days of photostimulation. Furthermore, testosterone production in vitro by regressed testes of animals exposed to short photoperiod was increased significantly by one large dose of hCG administered 26 h before killing the animals. It is concluded that the suppressive effects of short photoperiods on the ability of the hamster testis to produce testosterone and to respond to hCG stimulation are due to reductions in endogenous LH, FSH and prolactin release, with a consequent loss of testicular LH/hCG receptors and decreased activity of enzymes involved in the biosynthesis of testosterone.

Modification of testicular and thyroid function by chronic exposure to short photoperiod: A comparison in four rodent species

1. 1. Exposure of male Syrian hamsters ( Mesocricetus auratus) for 10 weeks to short photoperiod (SP) providing 10hr light:14hr darkness (10:14 LD) produced a significant reduction in the weights of the reproductive organs, plasma thyroxine (T 4) levels and free T 4 index (FT 4I) compared to the values of animals exposed to long photoperiod (LP, 14:10 LD). 2. 2. C57bl male house mice ( Mus musculus) kept in SP (10:14 LD) had reproductive organ weights equivalent to those of mice kept in long days (14:10 LD) and lower T 3 uptake (T 3U) values. 3. 3. Male gerbils ( Meriones unguiculatus) exposed to 13 weeks of SP (10:14 LD) had lower body weights, testes and seminal vesicle weights and higher T,U values compared to LP (14:10 LD) controls. However, no effect was seen on plasma T 4 and triiodothyronine (T 3,) values nor the FT 4I and free T 3 index (FT 3,I). 4. 4. White-footed male mice ( Peromyscus leucopus) exposed to SP (8:16 LD) had significantly lower testes and seminal vesicle weights while plasma T 4 and T 3 levels were unaffected. 5. 5. Snell strain house mice ( Mus musculus) exposed to SP (8:16 LD) had normal reproductive organ weights compared to the values of LP-exposed (16:8 LD) control animals. However, there was a significant depression in T 3 and in the FT 3I in the SP animals.

Plasma prolactin concentrations and testicular human chorionic gonadotropin binding sites during short photoperiod-induced testicular regression and recrudescence in the golden hamster.

Experiments were conducted in the golden hamster to determine temporal relationships and statistical correlations between plasma PRL concentrations and unoccupied testicular hCG binding sites during short photoperiod-induced testicular regression and spontaneous recrudescence. Although two experiments provided statistically significant (P<O.02) correlations between plasma PRL concentrations and testicular hCG binding, variability in onset of increased plasma PRL during recrudescence prevented any definite conclusions concerning a possible cause-and-effect relationship. Hence, the data do not indicate that a period of increased PRL secretion either initiates, or is initially necessary for, spontaneous recrudescence or changes in testicular hCG binding occurring during spontaneous recrudescence. Time of initiation of spontaneous testicular recrudescence was variable, but was always associated with increases in plasma concentrations of LH, FSH, and PRL. Testes from hamsters maintained in either short or long photoperiod had a single class of high affinity hCG binding sites with an average equilibrium association constant (Ka) of 3.06 × 1010 M−1. During the first 4 weeks of short photoperiod, when no changes in testicular weights were found, there were significant decreases in both concentration (fmol/mg protein) and total content (fmol/testes) of testicular hCG binding sites. However, after 10 weeks of short photoperiod and continuing through 16–18 weeks, the concentration of hCG binding sites was increased, while total content remained depressed, in regressed testes when compared with testicular hCG binding found in long photoperiod hamsters. Use of either [125I] iodo-hCG or [125I] iodo-hLH gave identical results. This increased concentration of unoccupied hCG/hLH binding sites may represent 1) an increase in binding sites per Leydig cell; 2) decreased occupancy or decreased loss of testicular hCG binding sites commensurate with decreased plasma LH concentrations; or 3) a relative increase in numbers of Leydig cells compared with other testicular components as testes undergo regression.