Short Photoperiod Conditions Research Articles

Thermoregulation in the female hedgehog, Erinaceus europaeus, during the breeding season.

The body temperatures of 3 breeding and 7 non-breeding female hedgehogs were monitored during 3 years. Lactating females had significantly higher and less variable body temperatures than did pregnant and non-breeding hedgehogs. Breeding females had circadian body temperature cycles that were more biphasic than those of non-breeders. Females maintaining higher mean daily body temperatures showed less variability about the mean than those exhibiting lower mean daily body temperatures. The rate at which body temperatures became more variable as mean daily body temperatures fell was 4.6 times more rapid in non-breeding females than in pregnant and lactating hedgehogs. With the exception of a single female in late gestation, hedgehogs readily became torpid under conditions of low ambient temperature and short photoperiod during summer, particularly when their food intake was restricted.

The effect of melatonin administration and short exposures to cold on body temperature of the blind subterranean mole rat (Rodentia, Spalax ehrenberghi, Nehring).

Improvement of the cold resistance capacity of the mole rat (Spalax ehrenbergi, Nehring), a blind subterranean rodent, was achieved following subcutaneous melatonin administration. Melatonin-treated mole rats exhibited reduction both in initial body temperature (Tbo) and in the decrease of body temperature (delta Tb) after 6 hours of exposure to cold. The tested mole rats were acclimated to and kept during the experiment, under long (16L/8D) photoperiod schedule while the effects of melatonin administration on body temperature simulated the effects of short photoperiod conditions. These results suggest that in mole rats, melatonin biochemically mediates photoperiodic information into body temperature physiological response. As a byproduct of the original experiment, it was found that frequently repeated short (6 hours) exposure to cold (Ta = 5 +/- 1 degrees C) can in itself initiate an improvement of cold resistance capacity similar to the effect of melatonin administration. This supports the idea that mole rats may improve their cold resistance in response to either photoperiodic or climatic changes.

Effects of afternoon injections of melatonin in hypothyroid male Syrian hamsters.

Male Syrian hamsters were kept under either 14 h light/10 h dark (lights on at 06.30 h) or 2 h light/22 h dark (lights on at 14.30 h) photoperiods. Groups of hamsters under each photoperiod were rendered hypothyroid by addition of 0.4% thiourea to the drinking water. These hamsters received, in addition, either a daily evening injection of saline or a daily injection of 25 micrograms melatonin in saline. Groups of intact controls and pinealectomized control hamsters were also maintained under the two photoperiodic conditions. After 10 weeks under the different conditions the hamsters were killed by decapitation, and serum samples assayed for thyroxin, thyroid-stimulating hormone (TSH), and prolactin (PRL). Pituitary extracts were assayed for TSH and PRL. Hypothyroidism in hamsters receiving thiourea was confirmed by radio-immunoassay data showing low serum thyroxin and greatly elevated serum TSH concentrations. Melatonin injections resulted in significant depression of serum TSH in thiourea-treated hamsters under short photoperiod compared to saline-injected controls. Both melatonin injections and short photoperiod resulted in a significant reduction of pituitary TSH in hamsters on thiourea compared to values obtained from similarly treated animals under the 14 h light/10 h dark photoperiod. Hypothalamic concentrations of thyrotropin-releasing hormone (TRH) were significantly elevated by melatonin injections and by short photoperiodic conditions, but not by thiourea administration. The short photoperiod resulted in testicular involution which was completely reversed by pinealectomy and partially reversed (to 53% of controls) by thiourea treatment. Involution of gonads was complete in thiourea-treated animals under short photoperiod, if they received melatonin injections.(ABSTRACT TRUNCATED AT 250 WORDS)

Interactions of testosterone and short-photoperiod exposure on the neuroendocrine axis of the male Syrian hamster.

Exposure of adult male golden hamsters to short days (less than 12.5 h light/day) leads to suppression of gonadal function which is secondary to reductions in gonadotropin and prolactin (PRL) secretion. Short-day (SD) exposure also leads to a reduction in hypothalamic norepinephrine (NE) and dopamine (DA) metabolism and an increase in hypothalamic LHRH content which appears to be related to a decrease in LHRH release. To determine whether SD-induced changes in NE and DA metabolism are dependent or independent of changes in circulating testosterone (T) levels and thus possible mediators of photoperiod effects on gonadotropin secretion, the effects of castration and steroid replacement on hypothalamic amine metabolism were studied in male hamsters maintained under long or short photoperiod conditions. The presence of Silastic T-implants resulted in a greater suppression of LH and FSH in SD than in long-day (LD) hamster, but increased median eminence (ME) LHRH content in both groups. Exposure of castrate hamsters to short days led to a reduction of NE turnover in the ME and medial preoptic-suprachiasmatic area (MPOA) and a decrease in serum FSH levels. LH levels tended to be lower, but not significantly so. The decrease in ME NE turnover was potentiated by T replacement, but in the MPOA-SCN, T-implants reversed the effects of short days. NE turnover in the MBH was reduced by T in both LD and SD animals, but the effect was much greater in the SD animals. SD exposure also caused a decrease in ME DA metabolism that was reversed by T replacement.(ABSTRACT TRUNCATED AT 250 WORDS)

Prevention by pinealectomy of short-photoperiod-induced ultrastructural changes in the hamster Harderian gland.

Harderian gland ultrastructure was examined at biweeky intervals for 16 weeks after either pinealectomy or sham-operation of male and female hamsters kept in 1L:23D and 14L:10D photoperiods. Female characteristics such as membrane formations and extensive smooth endoplasmic reticulum appeared in the males kept under short photoperiod conditions. Similarly, male characteristics such as the tubular clusters appeared in the glands of females kept in the short photoperiod. When male and female hamsters were pinealectomized and exposed to the short photoperiod, the glands in each sex retained the characteristics typical of that sex. Atrophy of the testes and uteri was also observed in the sham-operated hamsters maintained under short photoperiods, but not in the pinealectomized animals. The changes observed in the Harderian glands and reproductive organs of hamsters kept in the short photoperiod were not observed in the hamsters maintained in the long photoperiod. The photoperiod-induced ultrastructural changes in the hamster Harderian glands are most likely due to changes in hormonal levels brought about by the regression of reproductive organs and can be prevented by pinealectomy.

The influence of natural short photoperiodic and temperature conditions on plasma thyroid hormones and cholesterol in male Syrian hamsters.

Adult male Syrian hamsters were subjected to 1, 3, 5, 7 or 11 weeks of either natural winter conditions or rigorously controlled laboratory conditions (LD 10∶14; 22 ± 2‡C). Although both groups of hamsters gained weight over the course of the experiment, hamsters housed indoors were significantly heavier after 5 weeks of treatment compared to their outdoors counterparts. Animals housed under natural conditions exhibited a significant decrease in circulating levels of thyroxine (T4) and a rapid rise in triiodothyronine (T3) levels; the free T4 and free T3 index (FT4I and FT3I) mirrored the changes in circulating levels of the respective hormones. Laboratory-housed animals had a slight rise in T4 and FT4I at 3 weeks followed by a slow steady decline in these values; T3 and FT3I values did not change remarkably in these animals. Plasma cholesterol declined steadily over the course of the experiment in laboratory-maintained animals but increased slightly during the first 5 weeks in animals under natural conditions. Since the photoperiodic conditions were approximately of the same duration in these 2 groups, it is concluded that the major differences in body weight, thyroid hormone values and plasma cholesterol are due to some component (possibly temperature) in the natural environment.

Effect of short photoperiod on hypothalamic methionine-enkephalin and LHRH content and serum beta-endorphin-like immunoreactivity (beta-end LI) levels in golden hamsters.

Adult female golden hamsters were used to study the effect of short photoperiod on the endogenous opioid system and the effect of pinealectomy on the serum beta-endorphin-like immunoreactivity (beta-end LI) levels. Hamsters were housed under either long photoperiod (14L:10D) or short photoperiod (2L:22D) and the regularity of the estrous cycles was determined by daily vaginal exfoliative cytology. Hamsters under short photoperiod became acyclic after about 7 wk. At the end of 8 wk, all the hamsters were decapitated and medial basal hypothalamic (MBH) content of LHRH and methionine-enkephalin (met-enkephalin) were measured by specific radioimmunoassays (RIA). Both LHRH and met-enkephalin levels of the MBH were significantly elevated in the short-photoperiod hamsters as compared to the normally cycling control animals under long photoperiod. In a second experiment, the effect of pinealectomy (PNX) on the serum levels of beta-end LI in the short-photoperiod hamsters was determined. The serum beta-end LI levels were increased approximately threefold in the noncyclic hamsters housed under 8 wk of short-photoperiod conditions. Pinealectomized hamsters kept under 8 wk of short-photoperiod exhibited lower serum beta-end LI levels similar to those of normally cycling hamsters kept under long photoperiod. These results indicate a possible functional relationship between increased pineal activity (as a result of short photoperiod) and increased MBH met-enkephalin, LHRH, and serum beta-end LI levels.

Interactions of pinealectomy and short-photoperiod exposure on the neuroendocrine axis of the male Syrian hamster.

The effect of pineal gland removal on neuroendocrine function of male Syrian hamsters housed under long (14 h light:10 h dark) or short (5 h light 19 h dark) photoperiod conditions was tested. In sham-operated, but not in pinealectomized, animals, exposure to the short photoperiod resulted in a significant reduction in testicular weight. Median eminence (ME), medial basal hypothalamus (MBH), and medial preoptic-suprachiasmatic (MPOA-SCN) norepinephrine (NE) turnover was significantly reduced in 5 L:19 D sham-operated animals as compared to 14 L:10 D sham-operated or 14 L:10 D pinealectomized controls. The effects of short photoperiod on ME and MPOA-SCN NE turnover were reversed by pinealectomy, but reductions in MBH NE turnover were not dependent on the presence of the pineal gland. Pineal-dependent decreases in MBH and increases in MPOA-SCN dopamine turnover were also observed after transfer of hamsters from long to short photoperiods. Both ME and MBH luteinizing hormone-releasing hormone (LHRH) levels were increased after short-photoperiod exposure, but pineal removal prevented these increases of LHRH levels only in the MBH of the 5 L:19 D hamsters. Levels of serotonin or its metabolite, 5-hydroxyindole-acetic acid, were not affected by pinealectomy and/or short-photoperiod exposure. We conclude that short-photoperiod-induced gonadal atrophy in the Syrian hamster is associated with pineal-dependent and pineal-independent changes in hypothalamic neurotransmitter turnover and hypothalamic LHRH content.

Failure of inbreeding to influence pineal-induced gonadal regression in short day exposed hamsters.

The rate of testicular degeneration and the drop in plasma testosterone levels were compared in what were referred to as short-term domesticated (STD) and long-term domesticated (LTD) Syrian hamsters when they were maintained under short photoperiodic conditions (light:dark cycles of 10:14). STD hamsters were derived from wild stock captured in 1971; LTD animals were derived from the original stock captured in 1930. The rate of testicular degeneration as well as the fall in plasma testosterone levels were similar in both groups of animals. After 26 weeks exposure to short days, the testes and accessory sex organs regenerated to the fully mature state in both the STD and LTD animals; likewise, plasma testosterone levels had returned to normal in both groups. Pineal melatonin levels of STD and LTD female hamsters were compared during both the light phase (2000 and 0800hr) and dark phase (0200 and 0400hr) of the daily light:dark cycle. These animals were kept under photoperiodic conditions of 14:10 with lights on daily from 0600-2000hr. Day- and night-time levels of pineal melatonin were similar in both groups of hamsters. The results indicate that inbreeding does not influence the atrophic response of the reproductive organs of male hamsters to short day exposure or the ability of the pineal gland to produce melatonin.

Values of net compensation irradiation and their dependence on photosynthetic efficiency and respiration in marine unicellular algae

Daily compensation irradiation for net photosynthetic rates (ΣIcomp) of Skeletonema costatum (Greville) Cleve, Chaetoceros ceratosporum Ostenfeld, Nitzschia sp., Thalassiosira nordenskioldii Cleve, and Chroomonas salina (Wislouch) Butcher were measured during 1979 to obtain values for use in ecological models describing compensation and critical depths of marine phytoplankton. Batch cultures of these unicellular algae were exposed to temperatures and photoperiods varying from 6° to 15°C and 8.4 to 16.0 h, conditions typical of surface water in Saanich Inlet, a fjord in Vancouver Island, British Columbia, Canada. Results obtained with S. costatum and T. nordenskioldii provided estimates of ΣIcomp varying between 1.8 and 13 J cm-2 d-1, from which a mean value of 7.0 J cm-2 d-1 was calculated for use in ecological models with neritic phytoplankton. No seasonal variation in compensation irradiation was noted because photosynthetic efficiencies, which increased as division rates increased, were balanced by respiration rates, which increased as temperature increased. Results obtained with Chaetoceros ceratosporum, Nitzschia sp., and Chroomonas salina were difficult to interpret, because respiration rates were stimulated and depressed by light, respectively, for the first two species and the last one. This light effect was greatest when cells grew under conditions of low temperature and short photoperiod. Also, under winter and spring conditions, cells of Nitzschia sp. appeared to fix CO2 in the dark and with low irradiances by mechanisms other than photosynthesis.

Variations in plasma cortisol concentrations over a 24-hour period in the rainbow trout Salmo gairdneri

Plasma cortisol was measured in rainbow trout ( Salmo gairdneri), killed at intervals over 24-hr periods. In trout killed at a fish farm in July, under a long photoperiod, plasma cortisol titres were higher at night than in the light hours, with maximum levels at 2400 hr. No circadian variations were apparent in trout killed at the farm in December, under short photoperiod conditions when cortisol levels were lower than in summer fish. Trout were also maintained in small tanks in an aquarium under similar photoperiods and temperature as in the field. Basal cortisol concentrations remained low. In July, the peak of plasma cortisol seen at 2400 hr in the field continued to be expressed, in exaggerated form, at the beginning of the light period in the morning. In June, maintenance in constant light appeared to advance the 2400 hr peak to 1800 hr and to raise cortisol levels in general, but firm interpretation of these observations awaits further work.

Control of contour feather growth of Japanese quail

AbstractGrowth of a contour feather on a dorsal spinal tract of Japanese quail was investigated using a logistic model, in which feather length is determined by two factors, growth rate and growth period. Final feather lengths were constant under most experimental conditions including those under which the growth rate decreased while the growth period increased. Another experimental condition was discovered in which a feather elongated owing to an increase in growth period.Once a feather had fully grown, its length remained constant. After plucking a feather, a new feather grew and its final length was correlated with the old one. Shortening a growing feather by cutting off a distal part did not affect its growth pattern. In addition, shortening a fully grown feather by cutting off the distal part did not activate its follicle. Plucking a feather during growth stopped and erased the present growing phase and initiated feather growth from the beginning to form a complete feather. Repetition of plucking four or five times did not affect the final length of a feather, but did decrease the growth rate, which was complemented by an elongation of the growth period. Feather formation under a short photoperiod condition (8L:16D) resulted in a longer feather which resulted from elongation of the growth period while the growth rate remained constant.

Grasses more sensitive to SO2 pollution in conditions of low irradiance and short days

Research into the effects of low levels of SO2 on grasses has revealed no direct correlation between the dose of this pollutant and the plant's response1. Authors have suggested that environmental factors are of prime importance in the control of the response, because in many cases damage was most severe during the winter2,3. I have investigated the influence of total irradiance on the sensitivity of grasses to SO2, and shown that the effect of the pollutant was greatest in conditions of low irradiance and short photoperiod. Together, these factors may contribute to the increased sensitivity of plants during winter exposures to pollutants.

Influence of Photoperiod and Neonatally Administered Androgen on Estrous Cycles and Behavior in Hamsters1, 2

Transient or permanent disruptions of estrous cycles were studied in golden hamsters injected with oil, 1 or 10 μg testosterone propionate 4 days after birth and reared in rooms maintained on short (6L:18D or 12L:12D) or long (14L:10D) photoperiods. The duration of 2 transient episodes of vaginal acyclicity, one related to age and the other to season, was longer in the animals reared in the short photoperiod conditions and independent of exogenous hormone administered neonatally. A more enduring acyclicity, detected in vaginal smears, started at 250 days. Its age of occurrence was related directly to androgen dosage and inversely to the light/dark ratio. Degree of receptivity, measured after ovariectomy and injection of estradiol benzoate and progesterone, was lower in hamsters injected neonatally with androgen than with oil and in those in short than in long photoperiods. Ovaries of acyclic animals were devoid of corpora lutea; a few were polyfollicular in 14L:10D or 6L:18D conditions. Thus, neonatal administration of androgen induces premature absence of cyclicity in hamsters as it does in rats. Short photoperiods instigate both temporary and permanent loss of estrous cycles. Vaginal smears similar to those of the diestrous stage in combination with ovarian cells with a luteinized appearance suggest that progesterone levels are higher in the acyclic hamster than in the acyclic rat.

The effects of blinding, pinealectomy and exposure to constant dark conditions on gonadal activity in the female goldfish, Carassius auratus

The effects of pinealectomy, blinding, and exposure to constant darkness were examined in female goldfish during different seasons. Neither blinding nor pinealectomy under short or decreasing photoperiod conditions, nor exposure to constant darkness had an effect on ovarian activity in goldfish during fall and winter. In spring, constant darkness has an inhibitory effect on ovarian activity. Pinealectomy under increasing photoperiod conditions partially inhibits reproductive activity, but not to the extent of constant darkness. Blinding, under the same regime also inhibited to some extent the ovarian response to increasing photoperiod. Our data suggest that retinal pathways and the pineal organ are involved in the photosexual response to increasing day lengths.

The effects of pinealectomy on pituitary and plasma gonadotropin levels in Carassius auratus exposed to various photoperiod–temperature regimes

The effects of pinealectomy on pituitary and plasma gonadotropin levels and gonadal development in female goldfish exposed to various photoperiod‐temperature regimes during different seasons were examined. Pinealectomy during autumn had no effect on either pituitary or plasma hormone levels or gonadal development. When goldfish are pinealectomized in spring and exposed to long photoperiod conditions, the ovaries regress and plasma gonadotropin levels are significantly depressed compared to sham operated animals. Sham operated goldfish exposed to short photoperiod conditions in spring had regressing ovaries whereas pinealectomized animals under this regime either spawned or had ovaries in the late vitellogenic phase. Plasma gonadotropin titres in the pinealectomized group were significantly lower than those of sham operated animals. The pineal can be either stimulatory or inhibitory to gonadal development depending on the photoperiod regime to which the animals are exposed. The pineal apparently influences gonadal activity by modulating gonadotropin secretion. A diurnal variation in plasma gonadotropin levels was also observed in both sham operated and pinealectomized goldfish exposed to a long photoperiod warm‐temperature regime in spring.

Effects of pinealectomy and melatonin injections at different seasons on ovarian activity in the lizard Anolis carolinensis

AbstractThe short‐term effects of pinealectomy and melatonin treatment on ovarian activity in the lizard, Anolis carolinensis were examined at various times of the year. Animals were maintained under short photoperiod (6L:18D) at a constant temperature of 31 ± 1°C.Destruction of the epiphysis by heat cautery in November and January caused significant follicular development within 14 days. Daily administration of 10 μg synthetic melatonin blocked ovarian stimulation resulting from pinealectomy. Ovarian sensitivity to pinealectomy decreased with the onset of seasonal reproductive activity and was absent at the end of the normal breeding season, i.e., September.These observations support the hypotheses that, under conditions of short photoperiod and high environmental temperature, (a) the pineal organ can modify ovarian activity in Anolis; (b) there exists a definite seasonal sensitivity to this influence; and (c) melatonin may be an active agent of pineal function.

EFFECTS OF RESTRICTED PHOTOPERIOD AND MELATONIN ADMINISTRATION ON GONADAL WEIGHT IN THE JAPANESE KILLIFISH

Gonadal maturation, ovulation and spawning in the Japanese killifish, Oryzias latipes, are especially influenced by environmental changes of photoperiod (Egami, 1954; Yoshioka, 1962). Reduction in gonosomatic index (GSI: gonadal weight as a percentage of total body weight) is marked in fish maintained under continuous darkness or natural daylight (a short photoperiod) conditions during the period from October to December, but the index increases after pinealectomy (Urasaki, 1972). In Oryzias it is obvious that the reduced light period is effective in lowering gonadal weight, but the mechanism is still unknown. However, it is postulated that the pineal gland plays some role in the mechanism. The present investigation was carried out to study the mode of action of the pineal in inhibiting gonadal development in the fish. Adult specimens, 360–450 mg in body weight, of Oryzias latipes were used in the experiment. On 12 November (Expt 1) and on 20 January (Expt

A preliminary study of the seasonal geographic distribution and overwintering of Culex restuans Theobald and Culex salinarius Coquillet (Diptera: Culicidae).

A preliminary study was made of overwintering mechanisms and phenology of 2 common eastern United States mosquitoes: Culex restuans Theobald and Culex salinarius Coquillett. The seasonal distribution of adult activity of the 2 species was established by the month by month plotting of collection records gleaned from 170 published articles. Colonized females of each species were subjected to simulated fall conditions of temperature and photoperiod. C. restuans showed a marked reduction of blood feeding and exhibited gonotrophic dissociation in response to conditioning by short photoperiod and low temperature (15° and 20°C). C. salinarius females showed a significant reduction of blood-feeding under conditions of short photoperiod, but only at the lowest conditioning temperature (15°C) and did not exhibit gonotrophic dissociation. The authors suggest that both species undergo a true diapause but that qualitative and quantitative differences contribute to the generally more northern distribution of C. restuans. The implication of diapause to overwinter survival of arboviruses is discussed.

Initiation of Inflorescences in Cool‐season Perennial Grasses1

The objectives of this paper are to discuss pertinent literature and to present some recent research concerning induction of the vegetative primordia and initiation of floral development in perennial cool‐season grasses. The amount of exposure to short photoperiod and cool temperatures under field conditions necessary for induction of three forage grasses and four cultivars of Kentucky bluegrass (Poa pratensis L.) was studied. Plants were moved from the field at 15‐day intervals from September 15 to March 15 and grown under long photoperiod and warm temperatures for the production of inflorescences.The number of inflorescences produced indicated that a high level of induction for smooth bromegrass [Bromus inermis (Leyss.)], crested wheatgrass [Agropyro desertorum (Fisch. ex. Link) Schult.], and orchardgrass (Dactylis glomerata L.) had been reached by October 15, November 1, and November 15, respectively. The four Kentucky bluegrass cultivars showed a significant linear response to exposure. Inflorescence production increased as the exposure time increased. Seed production for Kentucky bluegrass cultivars followed essentially the same pattern as inflorescence production in response to exposure. The time required for inflorescence emergence for all cultivars and species had a negative association with the length of exposure to inductive conditions. If the rate of inflorescence emergence was used as the index, induction intensity was increasing up to March 15.Observations of dissected tillers at weekly intervals indicated the initiation of floral development for smooth bromegrass by February 12, and for orchardgrass and crested wheatgrass by February 19. The apices of the Kentucky bluegrass cultivars show a transition to floral primordia by January 22 for Delta and by February 5, 12, and 26 for Newport, Cougar, and Merion, respectively. Transition of vegetative apices to floral development occurred under conditions of cold temperature and short photoperiod for all species and cultivars.