Long-day Period Research Articles

The irritable male syndrome.

The irritable male syndrome (IMS) is a behavioural state of nervousness, irritability, lethargy and depression that occurs in adult male mammals following withdrawal of testosterone (T). The negative mood state has been described in men following withdrawal of androgens and is a striking feature in male seasonally breeding mammals associated with the end of the mating season. The Soay ram provides an animal model for IMS. Rams exposed to alternating 16-week periods of long and short days inactivate the reproductive axis in response to the switch to long days; the rapid decrease in T secretion provokes the symptoms of IMS. The animals appear agitated and fearful, and the incidence of physical wounding owing to fractious inter-male fighting peaks at this time. Androgen and oestrogen receptors expressed in cells in the preoptic area and ventromedial/arcuate nuclei appear to relay the effects of T on behaviour and gonadotrophin secretion, and melatonin receptors expressed in the premammillary area relay the effects of melatonin/photoperiod. Changes in the activity of hypothalamic opioidergic, dopaminergic and serotonergic neural networks may dictate the interactive effects of T and photoperiod. The working hypothesis is that IMS is a transition state associated with low hypothalamic amine levels triggered, in part, by the withdrawal of opioid peptides.

Seasonal morphology of the domestic quail (Coturnix coturnix japonica) testis.

A histological study was conducted on the testes of adult domestic quails (Coturnix coturnix japonica) over a year. The results revealed a clear variation of testicular weight, seminiferous tubule diameter, and the thickness and composition of the germinal epithelium over the year. The highest testicular weights were detected at the end of the autumn and during the winter (short-day period), reaching a maximum, together with spermatogenic activity, in September (long-day period in the southern hemisphere). In contrast, both testicular weight and spermatogenic activity were markedly decreased at the end of spring and during summer (long-day periods in the southern hemisphere).

Seasonal cyclic pituitary and testicular activities in rams

Adult rams were subjected to various photoregimes for more than 4 years to determine whether pituitary and testicular activities are inherently cyclic. Adult rams (three treatment groups, each with 12 rams) of the Arcott breeds were housed in environmental rooms kept at 15°C and exposed to short days (8 h of light and 16 h of darkness) for 1 year to dissipate the possible influence of normal environmental changes. The rams were then exposed to long days (16 h of light and 8 h of darkness) for 3 months to induce testicular regression. Subsequently, rams in Treatment Group 1 were exposed to short days for 39 months. Rams in the other treatment groups were exposed either to alternating 4-month periods of short days and long days for 16 months followed by 21 months of short days (Treatment Group 2), or to alternating 4 month periods of short days and 2 month periods of long days for 12 months followed by 4 months of short days, and then a reversal in daylength to 21 months of long days (Treatment Group 3). Exposure to the fixed daylength photoregime was followed with a change in daylength to test the retention of photosensitivity in the rams. Scrotal circumference and serum concentrations of follicle stimulating hormone (FSH), testosterone and prolactin were measured every 2 weeks throughout the study. In the rams exposed to short days only (Treatment Group 1), no cyclic change in hormone levels or scrotal size was apparent; FSH levels, testosterone levels and scrotal size all rose significantly early in the 39 months period and remained above basal levels. In the rams of Treatment Groups 2 and 3, the changes in the photoperiod cycles induced rhythmic pituitary and testicular activities which persisted for the first year of constant daylength, faded or disappeared thereafter. Prolactin levels in each treatment depended on the light regime, with levels being depressed or elevated during short or long days, respectively ( P < 0.01). All rams responded to the final change in photoperiod with an appropriate increase or decrease in the pituitary and testicular activities. These observations indicate that persistent memory of previous photoperiod change accounts for the `apparently spontaneous' rhythms in pituitary and testicular activities in the short term, but the decline of the regular changes as the memory fades does not support the existence of inherent cyclicity in reproductive functions in rams of the Arcott breeds. 5 Authors: G.A. Langford, L.M. Sanford, G.J. Marcus and J.N.B. Shrestha. For the Department of Agriculture and Agri-Food Canada, Government of Canada, © Minister of Public Works and Government Services Canada (1998). 5

The effect of different periods of constant short days on smoltification in juvenile Atlantic salmon ( Salmo salar).

The present study investigated the differential effects of a range of constant photoperiods on the development of biomodality and hypoosmoregulatory ability and the changes in coloration and morphology which occur during the process of smoltification in the Atlantic salmon. The aim being to determine the photoperiod conditions required for the successful production of out-of-season (0+) smolts. In 2 separate experiments, groups of parr reared from hatch under a long day (LL or LD 23:1) and in heated water (10°C or 13°C) were subjected to a short day photoperiod (LD 8:16 or LD 10:14) for periods of 4, 5, 6, 7, 8 or 12 weeks starting at varying times from July through to September after which the groups were then returned to a long day (LD 19.5:4.5 or LD 20:4). Control groups of fish were held under a natural photoperiod and also constant long days (LD 19.5:4.5). The timing of the changes from long to short and short to long daylengths in different photoperiod regimes induced differences in seasonal profile of the various parr–smolt changes in morphology and hypo-osmoregulatory ability. The development of bimodality was related to the timing of the decrease in photoperiod, whereas hypoosmoregulatory ability and smolt coloration appeared related to the increase. The regimes which included periods of 6 or more weeks of short days advanced smoltification compared to the group under ambient photoperiod. By contrast, smoltification was not completed in the groups exposed to 4 or 5 week periods of short days or constant long days. Under all the artificial photoperiod regimes there was some degree of desynchronisation of the various constituent processes of smoltification. Collectively, these data provide information on the specific components of photoperiod regimes which are necessary for the successful production of out-of-season smolts; they also suggest that smoltification is controlled by a series of interrelated endogenous rhythms or clocks.

Reproductive hormone levels of early postpubertal ram lambs in relation to breed, adult testis size and semen quality

To evaluate the usefulness of early postpubertal endocrine characteristics for predicting reproductive potential, blood serum levels of testosterone, luteinizing hormone (LH), follicle stimulating hormone (FSH) and prolactin were determined in rams at 6, 8 and 12 months of age. Two years later, scrotal size and semen quality were measured. The rams, housed indoors year-round were of a meat-type sire (Canadian Arcott), two fecund-type dams (Outaouais and Rideau Arcotts) and Finnish Landrace breeds. Daylength was maintained at 16-h light and 8-h darkness (long days) from weaning to 6 months. At that time, daylength was reduced to 9-h light per day (short days) until the rams reached 3 years of age. The lighting regimen was then changed again to long days for 3 months, then back to short days (8 h of light). Indices of semen quality and testis size in adult rams were calculated from 10 records, collected biweekly, beginning at the end of a period of long days. Hormone levels, adult testis size and semen quality varied with breed. In general, young Canadian rams had significantly lower testosterone and FSH levels than Finnish Landrace rams but as adults had a larger scrotal circumference and produced more sperm per ejaculate (42.2 cm and 7.0×10 9 compared to 33.0 cm and 3.3×10 9). Outaouais and Rideau rams had hormone levels similar to those of Finnish Landrace rams but testicular size and sperm production were intermediate between those of Canadian and Finnish Landrace rams. There were no breed differences among ram lambs in LH or prolactin levels. FSH levels, at all ages, were correlated negatively with scrotal size ( P<0.01). These findings indicate that FSH levels in ram lambs may be useful for predicting adult testis function.

Effect of Irradiance Level and Paclobutrazol on Reducation of Leaf Damage in Begonia × cheimantha

Begonia × cheimantha (Christmas or Lorraine begonia) is a popular holiday crop in Europe, with certain cultivars having outstanding postharvest characteristics. Its commercial production in the southern United States has been limited by the occurrence of mottled leaf chlorosis and necrosis, apparently due to environmental stress. In this study, B. × cheimantha `Emma' was grown in the fall in a glass greenhouse at College Station, Texas, under either 0%, 60%, or 87% polyethylene shade cloth. Leaf chlorosis and necrosis was very severe on plants grown in full sun (≈650 mol·m–2·s–1), with slight chlorosis on plants under 60% shade. Plants under full sun, however, were more compact, flowered earlier, and had shorter peduncles with more flowers than those grown under shade. Reducing the vegetative long-day treatment period from 7 to 4 weeks had no effect on leaf damage development. Plants treated with paclobutrazol were shorter and had less leaf damage than untreated plants. Leaves of treated plants had a relatively higher concentration of soluble protein, chlorophyll, and enhanced activities of ascorbate peroxidase (AsA), dehydroascorbate (DHA) reductase, and monodehydro-ascorbate (MDHA) reductase than untreated plants. For Texas growing conditions, these preliminary studies indicate that B. × cheimantha should be grown under reduced light intensities, with excessive height and leaf damage being controlled with growth retardants such as paclobutrazol.

The annual testicular cycle of the domestic quail (Coturnix coturnix japonica).

A morphometric study was conducted on the testis of the domestic quail Coturnix coturnix japonica to determine testicular kinetics. We investigated the variability along the year of testicular parameters such as seminiferous tubule diameter, germinal epithelium height and amount of meiotic figures of maturing spermatids in the seminiferous epithelium and of sperm in the tubular lumen. The results of morphometric analysis showed the occurrence of an annual testicular cycle defined by four distinct phases: a resting phase (at the end of summer), a recrudescence phase (in the fall), a proliferative phase (at the end of winter and beginning of spring), and a regression phase (spring and summer). We also observed that the testes of adult quails present elevated and maximal spermatogenic activity in fall-winter (short-day period) and at the beginning of spring, respectively, and lower values in spring and summer (long-day periods), with minimum values at the end of summer.

'Hamster-like' cycles in testicular size in the absence of gonadotrophin secretion in HPD rams exposed to long-term changes in photoperiod and treatment with melatonin.

Long term changes in the secretion of FSH, LH and testosterone, and the size of the testis were measured in groups of hypothalamo-pituitary disconnected Soay rams (HPD rams, n = 8) and control Soay rams (HPD-sham operated and unoperated, total n = 8) while exposed to an artificial lighting regimen of alternating 16-weekly periods of long days (16L: 8D) and short days (8L: 16D), and when treated with a constant-release implant of melatonin given under long days (total study: 136 weeks). Short term provocation tests using NMDA (glutamate receptor agonist), GnRH and LH were used to assess functionality of the hypothalamus, pituitary gland and testis, respectively. Control rams expressed normal photoperiod-induced cycles in the reproductive axis. Blood concentrations of FSH, LH and testosterone were significantly increased under short days, and decreased under long days with parallel changes in testicular diameter. Treatment with implants of melatonin under long days mimicked the effect of short days and induced rapid reactivation of the reproductive axis. In the HPD rams the blood concentrations of FSH, LH and testosterone declined immediately after the HPD surgery and values remained close to the lower limit of detection of the radioimmunoassays throughout the experiment. LH pulses were absent in the HPD rams and NMDA failed to induce LH secretion consistent with functional disconnection of the pituitary gland from the hypothalamus. The testes regressed to a significantly smaller size in the HPD rams compared with controls even at the nadir of the sexual cycle (testis diameter: 30.2 +/- 0.7 vs 41.3 +/- 0.8 mm, HPD vs control rams, respectively). A low amplitude cycle in testicular diameter (peak to nadir: 5.0 +/- 0.7 mm) persisted in the HPD rams with a temporal pattern opposite to the controls (growth under long days instead of short days; 'hamster like'). In the HPD rams, the treatment with melatonin blocked the long day-associated increase in testicular size, without effects on FSH, LH and testosterone secretion, pituitary responsiveness to GnRH (LH increment) or testicular responsiveness to LH (testosterone increment). This was in contrast to the cyclical changes in all parameters induced by melatonin in the control rams. At post-mortem, the reproductive tract in HPD rams was markedly regressed compared with the controls. The efficiency of spermatogenesis was reduced with few germ cells maturing beyond primary spermatocytes. Immunocytochemical staining, however, revealed the maintenance of androgen receptor expression in Sertoli cells, pertibular cells and Leydig cells, and steroid activity as measured by 17 alpha-hydroxylase expression in Leydig cells. Overall, the absence of photoperiod-induced changes in gonadotrophin secretion in the HPD rams illustrates the dependence on regulation by the hypothalamus, presumably through the secretion of GnRH. The residual cycle in the size of the testes in the HPD rams was closely correlated with the photoperiod-induced changes in prolactin secretion which persisted in these animals (summary of previous published data included). The combined results support the view that melatonin acts in the hypothalamus to mediate effects of photoperiod on gonadotrophin secretion and in the pituitary gland to mediate effects on prolactin secretion (dual site hypothesis), and that FSH, LH and prolactin act synergistically to regulate the long-term cycle in testicular activity in the ram.

Agronomic and economic evaluation of Sesbania rostrata green manure establishment in irrigated rice

Research on crop establishment methods may improve green manure performance, reduce costs, and increase the adaptability of pre-rice green manure technology in lowland rice-based cropping systems. A two-season field experiment was conducted at the International Rice Research Institute (IRRI) in Los Baños, Philippines in 1991–1992 to compare four establishment practices of Sesbania rostrata green manure (zero tillage, with tillage, relay cropping in rice for 2 or 4 weeks) with four mineral N fertilizer levels (0, 30, 60, and 90 kg urea N/ha) in an intensive irrigated lowland system with three rice crops per year. S. rostrata was grown twice a year during the 43-day dry-wet and wet-dry transition periods between the wet and dry season rice crops. Grain yield potential and fertilizer responsiveness of rice was generally highest in the dry season. On the other hand, S. rostrata growth was more vigorous in the wet season (long-day period) than in the dry season, regardless of establishment method. Green manure N accumulation was lowest with zero tillage (30 and 90 kg N/ha in dry and wet season, respectively) and highest when it was relay-cropped for two weeks (60 and 180 kg N/ha in dry and wet season, respectively). Land preparation for Sesbania ensured best green manure stand (> 100 plants/m 2 vs 20–40 plants/m 2 at no-till establishments) but increased costs of green manuring by US$16/ha compared with other establishment methods. A quadratic response function between mineral fertilizer equivalence and green manure N indicated that up to 75 kg N/ha, lowland rice uses green manure N more efficiently than urea. Depending on season and establishment method, S. rostrata substituted for 35 to 90 kg of split-applied urea N. Benefit-cost ratios indicated that pre-rice green manure use in the wet season under the current fertilizer and labor prices in the Philippines was a less attractive economic option than mineral N fertilizer. This was true for all establishment methods. In the dry season, S. rostrata established by relay cropping gave the highest rate of return. The 2-week relay cropping of green manure with irrigated rice gave highest green manure N accumulation and rice grain yield, and may be economically viable where fertilizer prices are higher or labor costs are lower than in the Philippines.

Seasonal and photoperiod-induced changes in the secretion of alpha-melanocyte-stimulating hormone in Soay sheep: temporal relationships with changes in beta-endorphin, prolactin, follicle-stimulating hormone, activity of the gonads and growth of wool and horns.

Blood plasma concentrations of alpha-melanocyte-stimulating hormone (alpha-MSH), beta-endorphin (beta-END), prolactin and follicle-stimulating hormone (FSH), and associated changes in the size of the testes, and growth of the horns and pelage were measured in male (n = 8), castrated male (n = 5) and female (n = 9) Soay sheep. The animals were born in April and kept outdoors near Edinburgh (56 degrees N) during the first two years of life. In all groups there was a close association between the weekly changes in the plasma concentrations of alpha-MSH and beta-END; the molar ratio in mean concentrations was close to 1:1. The blood plasma concentrations of both hormones varied markedly with season with a 3- to 10-fold increase in concentrations from the minimum in winter to the maximum in autumn. The seasonal peak occurred in September in the first year of life as juveniles, and between July (males) and September (females) in the second year when the animals were sexually mature. The plasma concentrations of ACTH did not vary in parallel with the seasonal changes in the concentrations of alpha-MSH (measured only in males); the molar ratio for the concentrations of alpha-MSH:ACTH was 1:0.12. The seasonal increase in the concentrations of alpha-MSH occurred 1-3 months after the seasonal increase in the concentrations of prolactin and the associated growth in horns and pelage, and slightly before, or coincident with the seasonal increase in the concentrations of FSH and the growth in the testes. In a second experiment, the same parameters were measured in a group of adult male Soay sheep (n = 8) housed indoors under an artificial lighting regimen of alternating 16-week periods of long (16 h light: 8 h darkness) and short days (8 h light: 16 h darkness). In this situation, there was a clearly defined photoperiod-induced cycle in the plasma concentrations of alpha-MSH with a 25-fold increase from a minimum under long days to a maximum under short days. The concentrations of beta-END varied in close parallel with the changes in alpha-MSH, and the temporal associations with the changes in the other pituitary hormones were similar to those observed in animals housed outdoors. Overall, the results support the view that alpha-MSH is co-secreted with beta-END from the melanotrophs in the pars intermedia of the pituitary gland, and that the secretory activity of the melanotrophs changes markedly with season, increasing in summer and autumn, and decreasing in winter and spring.(ABSTRACT TRUNCATED AT 400 WORDS)

Active immunization against melatonin in Ile-de-France ewes and photoperiodic control of prolactin secretion and ovulatory activity.

An experiment was conducted to determine whether active immunization against melatonin could modify the perception of abrupt photoperiodic changes in ewes. Two groups each containing six intact Ile-de-France ewes were submitted to alternate periods of short days for 2.5 months and long days for 2.5 days for about 70 weeks. Three series of active immunizations against a melatonin conjugate were carried out during the first of the three long-day periods. Control ewes were actively immunized at the same time against human serum albumin. Blood samples were taken once a week throughout the experiment to measure antibody titre and affinity, and prolactin and progesterone concentrations. Sera of all treated ewes demonstrated higher antibody titres than those of control ewes. Antisera were highly specific, as evidenced by the absence of displacement of iodinated melatonin in the presence of ten melatonin metabolites. Significant effects of photoperiod and of the interaction between treatment and photoperiod on prolactin concentration were detected. Prolactin concentrations in plasma of the control ewes were high during long days and low during short days. However, in the treated ewes, with the exception of the first period of long days, prolactin concentrations were not influenced by photoperiodic changes. Ovulatory activity of control ewes, as demonstrated by progesterone measurements, was stimulated by short days and inhibited by long days. In contrast, ovulatory activity of treated ewes, after a response identical to that of control ewes after the first photoperiodic shift from long to short days, showed a complete desynchronization of ovulatory activity relative to photoperiodic changes.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of placing micro-implants of melatonin in the pars tuberalis, pars distalis and the lateral septum of the forebrain on the secretion of FSH and prolactin, and testicular size in rams

Previous studies involving the placement of microimplants of melatonin in the brain in sheep exposed to long days have provided evidence that melatonin acts within or close to the mediobasal hypothalamus (MBH) to mediate the effects of daylength on cycles in reproduction, moulting and other seasonal characteristics. To extend these observations, groups of Soay rams have now been treated with micro-implants of melatonin placed in the pars tuberalis (PT) and pars distalis (PD) of the pituitary gland, and in the lateral septum of the forebrain (septum). The PT and septum are potential target sites for the action of melatonin based on the localized binding of iodomelatonin assessed by in situ autoradiography. The animals were initially exposed to alternating 16-week periods of long days (16 h light: 8 h darkness; 16L:8D) and short days (8L:16D) to entrain the seasonal cycles. The treatments were started at 10 weeks into a period of long days when the animals had a physiology normally observed in summer (low blood plasma concentrations of FSH and high concentrations of prolactin), and they remained under long days throughout the experiments. In experiment 1, animals received micro-implants of melatonin placed in the PT (n = 6) or PD (n = 4), or received empty implants in similar sites (n = 4) or no surgery (n = 4; total control, n = 8). In experiment 2, groups of animals received microimplants of melatonin placed in the lateral septum (septum, n = 7) or received corresponding control treatments (total control, n = 8). The micro-implants consisted of 22 gauge stainless-steel needles with melatonin fused inside the tip. They were inserted bilaterally in the selected sites and left in place for 14 weeks. The biological effects of the treatments were assessed by measuring the changes in the blood plasma concentrations of FSH and prolactin, growth of the teses and moulting of the pelage over a period of 28 weeks (14 weeks treatment and 14 weeks post-treatment). The administration of melatonin in the PT, but not in the PD or septum, affected the photoperiodically induced cycle in the secretion of FSH and prolactin. In the PT group there was no significant change in the plasma concentrations of FSH during the treatment with melatonin, but there was a significant (P < 0.001, ANOVA) decrease in the levels of FSH after the treatment associated with premature regression of the testes.(ABSTRACT TRUNCATED AT 250 WORDS)

Photoperiodically-induced cycles in the secretion of prolactin in hypothalamo-pituitary disconnected rams: evidence for translation of the melatonin signal in the pituitary gland.

Long term changes in the secretion of prolactin were monitored in groups of hypothalamo-pituitary disconnected rams (HPD rams, n = 8) and control rams (HPD sham-operated and unoperated, n = 8) while exposed to an artificial lighting regimen of alternating 16-weekly periods of long days (16L:8D) and short days (8L:16D) for 72 weeks, and during a treatment with subcutaneous constant-release implants of melatonin under long days. The HPD rams showed all the clinical characteristics of complete pituitary disconnection (diabetes insipidus, gonadal regression and slight obesity), and were unresponsive to a range of provocation tests (exposure to a barking sheep dog, cannulation of the jugular vein, injection of serotonin and NMDA) which caused acute changes in the blood plasma concentrations of prolactin in the controls. Nevertheless, there was a clearly defined cycle in the blood concentrations of prolactin in the HPD rams related to the imposed lighting regimen with values 10-fold higher under long days compared to short days (HPD mean +/- SEM: 90.1 +/- 24.7 vs 9.4 +/- 2.0 micrograms/l, long vs short day respectively, P < 0.001). The temporal pattern was very similar to that observed in the controls, although the concentrations of prolactin were higher in the HPD rams and more variable (control mean +/- SEM: 55.6 +/- 3.6 vs 3.0 +/- 0.5 micrograms/l, long vs short day, P < 0.001). There was a corresponding cycle in the growth and moulting of the wool in the HPD rams consistent with a biological response to the photoperiodically-induced changes in the secretion of prolactin. The diurnal rhythm in the blood concentrations of prolactin was absent in the HPD rams, but there was a normal rhythm in the secretion of melatonin. The treatment of the animals with constant-release implants of melatonin under long days caused a marked decrease in the blood concentrations of prolactin in both the HPD and control rams. The overall conclusion is that the endogenously generated daily melatonin signal which encodes daylength acts directly in the pituitary gland to mediate the effects of photo-period on the secretion of prolactin. The photo-period transduction pathway thus by-passes the hypothalamus.

Climate, trophic factors, and breeding patterns of the Nile grass rat (Arvicanthis niloticus solatus): a 5-year study in the Sahelian region of Burkina Faso (formerly Upper Volta)

From 1984 to 1989, five populations of the Nile grass rat, Arvicanthis niloticus solatus, living in five different habitats of the Sahelian region were studied in northern Burkina Faso (Oursi, 14°N). The following were investigated: (i) seasonal variations in the percentages of sexually active males and females and the percentage of the population less than 6 weeks old, and (ii) seasonal variations in testis and seminal vesicle masses and plasma testosterone levels in adults. Both the large form of A. niloticus occupying habitats with stable trophic resources and the small form of the species occupying habitats with fluctuating resources showed seasonal breeding, mainly in the dry season, in contrast with what we have observed elsewhere in other species in this region. In dry years with normal rainfall (rains between June and September), breeding occurred from mid-October to mid-July in habitats with constant trophic resources and from mid-October to mid-April in habitats with fluctuating resources. In 1986, a year with exceptional rainfall (additional rains in January), breeding was continuous in habitats where this climatic disturbance caused a reappearance of primary production and there was a population outbreak of A. n. solatus. Relationships between (i) breeding cycles, (ii) long-day periods, which have a gonadoinhibitory effect, (iii) seasonal variations in relative humidity and temperature, and (iv) dietary characteristics of A. n. solatus suggest that this subspecies is capable of breeding throughout the year. This is due to its adaptable dietary habits, which allow it to take advantage of resources that are either constant (insects, harvest wastes, and the water-rich bark of certain woody plants) or seasonal (rain-dependent herbaceous plants and farm vegetables). The end of breeding appears to be related to the relative timing of the stimulatory effect of certain foods and the inhibitory effects of photoperiod, temperature, and humidity. Under this hypothesis, the gonadoinhibitory effect of long days was masked in 1986 by an earlier stimulatory effect related to the reappearance of vegetation following the exceptionally heavy rainfall in January.

Photoperiod-mediated increases in serum concentrations of inhibin, follicle-stimulating hormone, and luteinizing hormone are accentuated in adult shortened-scrotum rams without corresponding decreases in testosterone and estradiol.

Relationships between "seasonal" changes in the secretion of gonadotropic (FSH, LH) and gonadal feedback (inhibin, testosterone, estradiol) hormones were examined in the adult ram. Eight Dorset x Leicester x Suffolk rams were kept in photoperiod-controlled rooms for 2 yr and subjected to alternating 4-mo periods of stimulatory (8 h light) and inhibitory (16 h light) day-lengths. The scrota of four rams were shortened at the outset to elevate testicular temperature and presumably impair inhibin secretion by Sertoli cells. Blood samples were collected serially from the jugular vein every 3 wk, and scrotal circumference of the four control rams were measured every 2 wk. Testicular recrudescence and regression were completed in the second month of the short- and long-day periods, respectively. Mean serum concentrations of testosterone and estradiol varied in synchrony across months (r = 0.42) and were similar between the groups of rams, except early in the short-day periods when testosterone was 50% lower in the shortened-scrotum rams because of smaller "seasonal" increases in testosterone pulse amplitude and baseline concentration. Increases in the secretion of gonadotropic hormones during testicular recrudescence were greater in magnitude (FSH) and/or of longer duration (FSH, LH pulse amplitude, and baseline LH) in rams with shortened scrota. In fact, mean FSH concentration was an average of 250% higher in the shortened-scrotum vs. the control rams throughout the last two photoperiod cycles. Mean inhibin concentration varied with month in accordance with FSH (r = 0.52) and either remained normal or was higher than usual (e.g., 55% during testicular regression) in the shortened-scrotum rams.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of photoperiod on the annual cycle of testis growth in a tropical mammal, the little red flying fox, Pteropus scapulatus.

Little red flying foxes (Pteropus scapulatus) are seasonal breeders: they mate in late spring/early summer, and young are born the following autumn. In captivity, males housed outdoors in a normal breeding colony in natural daylight showed a single cycle of testis growth and regression each year. During reproductive quiescence, testicular volume was approximately 2 cm3; recrudescence began soon after the winter solstice; testicular volume was maximum at approximately 6.5 cm3 at the spring equinox; and regression was complete by the end of summer. To test whether photoperiod entrains or synchronizes the cycle, groups of males were housed indoors, without females, at constant temperature, and artificial lighting was timed to either mimic naturally changing daylength or provide alternating 3-month periods of short (11 h light:13 h dark) or long (16 h light:8 h dark) days (two groups, three months out of phase with each other). During 18 months, the applied photoperiod protocol had no effect on the frequency of testicular cycles (which remained at one per year), the time course of recrudescence and regression (as described above for normal outdoor control males), or the completeness of growth and regression stages. These results suggest that male P. scapulatus are not reproductively photoresponsive.

Effects of Early-Cutting Management on Forage Yield and Quality of Alfalfa in Northeast Kansas (1993)

Alfalfa cutting management has been a topic of interest and concern in Kansas and other regions of the United States. Current recommendations for cutting schedules in Kansas are based on a combination of plant and crown-bud development. This is critical because Kansas has a highly variable climate, and alfalfa forage is harvested during both shortand long-day periods throughout the production season. Depending on the point of the cutting cycle and the existing environmental conditions, the first regrowth at the harvest indicator can occur at or prior to the 10%-bloom stage throughout the season. The maturity stage at which alfalfa is initially harvested in the spring is important for several reasons. The new growth initiates from the crown buds, which depletes total nonstructural carbohydrate (TNC) root/crown reserves. Depending on the previous year's fall-cutting management and severity of winter and/or spring weather, an alfalfa field can be stressed early in the spring. Also, insect and 105

Reproductive effects of placing micro-implants of melatonin in the mediobasal hypothalamus and preoptic area in rams.

The reproductive effects of placing micro-implants of melatonin in the mediobasal hypothalamus (MBH) and preoptic area (POA) were monitored in Soay rams. Groups of animals were initially conditioned to alternating 16 weekly periods of long days (16 h light: 8 h darkness; 16L:8D) and short days (8L:16D) for at least 9 months to entrain the seasonal reproductive cycle. All experiments were then initiated at 10 weeks under long days when the animals were sexually inactive. In experiment 1, rams were exposed to short days for 14 weeks or maintained on long days to illustrate the photoperiodically induced re-activation and regression of the reproductive axis. In experiments 2-4, rams received micro-implants of melatonin in the MBH or POA, or received control treatments (sham-operated or no surgery) for 12-14 weeks while maintained on long days (total of 12 animals/treatment). The melatonin implants consisted of 22-gauge stainless-steel cannulae with melatonin fused inside the tip and were placed bilaterally in the brain. Incubation of the implants in Tricine-buffered saline (pH 8.0) at 37 degrees C showed that the release rate of melatonin was relatively constant after an initial peak in week 1 (means +/- S.E.M.: 3.42 +/- 0.43 micrograms/24 h). Rams with melatonin implants placed in the MBH, but not in the POA, showed a consistently earlier re-activation of the reproductive axis compared with the control animals in all three experiments (12/12 for MBH vs 2/12 for POA). The mean time to maximum testicular diameter was 12.2 +/- 0.9, 21.6 +/- 1.8 and 22.3 +/- 1.2 weeks for the MBH, POA and combined control groups respectively (MBH vs control, P less than 0.01; analysis of variance). The premature growth of the testes in the MBH group was associated with an earlier increase in the blood plasma concentrations of FSH and testosterone, and the appearance of the sexual skin coloration. Removal of the implants resulted in a decline in all reproductive parameters. The melatonin treatments did not cause a detectable increase in the peripheral concentrations of melatonin, or affect the diurnal rhythm in melatonin which reflected the long-day photoperiod. When implants containing 125I-labelled melatonin were introduced into the brain the associated radioactivity was localized to within 1 mm of the implants. The overall results demonstrate that the constant administration of melatonin into the MBH blocks the effect of the endogenous long-day melatonin signal and induces gonadal redevelopment.(ABSTRACT TRUNCATED AT 400 WORDS)

Leaf Unfolding Rate in Begonia × hiemulis

The rate of leaf unfolding as a function of temperature was determined for Begonia × hiemalis Fotsch under long-day (16 hours of light) conditions before flower initiation. Irradiance was maintained at 280 ± 20 μmol·m–2·s–1 (16.1 mol·m–2·day–l). The two cultivars Hilda and Ballet had similar rates of leaf unfolding in the range from 13 to 28C. The rate increased to a maximum of 0.116 leaves/day at 21C and then decreased at higher temperature. The following quadratic function (where T is the temperature in °C) was selected to describe initial long-day leaf unfolding rate in B. × hiemalis: leaves/day = -0.2083 + 0.03145 × T – 0.0007631 × T2, (r2 = 0.97). The leaf unfolding response to temperature varied for plants of `Hilda' and `Ballet' during short days (10 hours of light) following the initial long-day period. Plants of `Ballet' continued to unfold leaves at a similar rate as under initial long photoperiods, while the leaf unfolding rate for `Hilda' decreased to half the rate observed under long days.

Interrupted lighting of chrysanthemums: monitoring of average daily light integral as an aid to timing

Relationships were determined for six chrysanthemum cultivars between the number of short days (SD) required for floral commitment and the average daily light integral. This was done to improve the timing of interrupted lighting, a technique involving the intercalation of a period of long days (LD) into the SD phase of growing. Thirteen greenhouse trials were conducted at various times of year, some with shading, at a minimum maintained temperature of 17°C. The basipetal commitment to flowering in SD was determined by transferring plants at intervals from SD to LD and subsequently comparing numbers of leaves below the flower bud on the main stems and lateral shoots of the transferred plants with those on other plants maintained continuously in SD. Numbers of SD required for complete commitment were then related to light receipt in the greenhouse. Whilst the speed of commitment varied considerably with cultivar, the form of the relationship for each was similar; asymptotic above 1.0–1.5 MJ m −2 day −1 photosynthetically active radiation (approximately 4.6–6.9 mol m −2 day −1), and exponential at lower average daily light integrals. The main effect of low light was to slow the commitment of the terminal meristem; subsequent commitment of axillary buds appeared to be independent of light integral. Confidence bands were calculated around the lines of best fit and relationships based on the upper limits of these have been used subsequently in conjunction with light monitoring for advising when to begin interruption. Analysis of historical light records for Littlehampton indicate the degree of variation to be expected from year to year for a given cultivar starting SD on a particular date during winter. Some practical aspects of using light-integral monitoring for the timing of interrupted lighting are discussed.