Effects Of Short Photoperiod Research Articles

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.

Differential effects of cryptorchidism and short photoperiod on testicular prolactin and LH/human chorionic gonadotrophin receptors in the golden hamster.

Gonadal atrophy induced by short photoperiods in male golden hamsters is accompanied by a decrease in the total content of testicular prolactin and LH/human chorionic gonadotrophin (LH/hCG) receptors and a concomitant rise in the concentrations of LH receptors. Atrophic testes are typically abdominal. In this study, we have compared the effects of experimentally induced cryptorchidism and the effects of a short photoperiod on testicular prolactin and LH/hCG receptors. Cryptorchidism produced the expected decrease in testicular weight and an increase in plasma FSH concentrations, without altering plasma concentrations of LH or prolactin and with a relatively small decrease in plasma testosterone. It also produced an increase in the concentration of prolactin and LH/hCG receptors without significant changes in their total content. Exposure to a short photoperiod decreased weights of testes and seminal vesicles and plasma levels of prolactin and testosterone, with no significant effects on plasma gonadotrophin levels. Short photoperiod also increased the concentration of LH/hCG receptors but, in contrast to the effects of cryptorchidism, it produced a precipitous decline in the total content of testicular receptors for both prolactin and LH/hCG. We conclude that changes in prolactin and hCG binding measured in membrane preparations from decapsulated testes of hamsters exposed to a short photoperiod cannot be explained by the abdominal position of the gonads, abnormalities of Sertoli cell function or changes in the relative proportion of Leydig cells in the atrophic testes.

Olfactory bulbectomy prevents the gonadal regression associated with short photoperiod in male golden hamsters

In male rats, pre-pubertal olfactory bulbectomy (BX) unmasks photoperiodic responsiveness so that maintenance of BX animals on short photoperiod results in a pineal gland mediated gonadal regression (Nelson and Zucker, Neuroendocrinology, 32 (1981) 266). The objective of the present study was to determine the effect of BX in Syrian hamsters, a species where short photoperiod alone induces a pineal gland induced testicular regression. Pre-pubertal (25-days old) Syrian hamsters underwent either sham BX, BX, or pinealectomy (PX) plus BX. One half of each group was then placed on an LD 14:10 photoperiod and the other half on LD 6:18. Thirteen weeks later all animals were decapitated. In the animals on LD 14:10, BX resulted in a slight but highly significant increase in testes weight but had no effect on other parameters examined. Sham BX hamsters on LD 6:18 had regressed testes and reduced serum testosterone levels, but these effects of short photoperiod were reversed in BX hamsters, so that the testes and seminal vesicles remained large. In addition, serum LH and testosterone levels were elevated following BX of the animals on LD 6:18. These results indicate that the olfactory bulbs tonically inhibit the reproductive system even in male hamsters maintained on long photoperiod and that olfactory bulbectomy prevents gonadal regression in male Syrian hamsters on short photoperiod, an effect which is the opposite of results obtained in rats on short photoperiod. Elucidation of the neural pathways involved and the nature of the relationship between the olfactory bulb and the pineal gland or photoperiodism remains for further investigation.

Pineal involvement in the effects of short photoperiods on thyroid follicular cells in the syrian hamster

Pineal involvement in the effects of short photoperiods on thyroid follicular cells in the syrian hamster

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.

Photoperiodic control of body weight and energy metabolism in Syrian hamsters (Mesocricetus auratus): role of pineal gland, melatonin, gonads, and diet.

The effects of photoperiod and the pineal hormone melatonin on the regulation of body weight and energy metabolism were examined in Syrian hamsters, Mesocricetus auratus. Short photoperiod-housed female and male hamsters showed increases in body weight gain, feed efficiency, carcass lipid, brown adipose tissue mass, and thermogenic capacity. These effects of short photoperiods were mimicked by afternoon melatonin injections to hamsters in long-day photoperiods and were exaggerated in hamsters fed high fat diets. To determine the role of the gonads in these effects, ovariectomized hamsters were treated similarly and found to exhibit changes in body weight and energy metabolism that were 80-90% of those in gonadally intact hamsters. The role of the pineal gland in short photoperiod-induced body weight gain was examined in sham-pinealectomized and pinealectomized hamsters. Short photoperiod-induced increases in body weight were seen in both pinealectomized and sham-pinealectomized hamsters. Thus, pinealectomy blocks the effects of short photoperiods on reproductive function and thyroid activity, but not on body weight regulation. These results suggest that the effects of short photoperiods on body weight and energy metabolism are mediated by multiple, redundant mechanisms involving decreases in gonadal hormone secretion, changes in melatonin secretion, and gonad- and pineal-independent changes. All of the effects of short photoperiods are exaggerated in hamsters fed a high fat diet. These changes may represent adaptive preparatory responses that enhance winter survival in Syrian hamsters.

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.

Effect of Photoperiod at Different Growth Stages on the Initiation of Spikelet Primordia in Wheat

Leaf and spikelet initiation of wheat (Triticum aestivum L.) was studied on plants grown in cabinets under a range of constant photoperiod regimes and on plants transferred, at different growth stages, between these regimes. The existence of genotypically specific limits to the effects of short photoperiods on the delay in floral initiation and on the increase in the number of spikelets was demonstrated. A long photoperiod applied after the onset of apex elongation, but not earlier, induced the differentiation of spikelets in the axils of already existing primordia, which under a short photoperiod would have developed into leaves. The initiation of the terminal spikelet was induced by a long photoperiod applied not later than the double ridge stage. The final number of spikelets had been determined by the time of swelling of the spikelet primordia in the central portion of the spike.

Effects of short photoperiod on the ability of golden hamster pituitaries to secrete prolactin and gonadotropins in vitro.

Transfer of male golden (Syrian) hamsters from a 14L:10D (light:dark) to a 5L:19D photoperiod induced significant changes in pituitary function tested in vitro. Within 27 days after transfer to a 5L:19D photoperiod, basal prolactin (Prl) release was significantly depressed and response to dopamine (DA) was significantly enhanced as compared to Prl release by pituitaries from 14L: 10D hamsters. Follicle-stimulating hormone (FSH) release tended to be depressed after 9 or 27 days of 5L:19D exposure, but the effect was not significant. After 77 days of 5L:19D exposure, Prl release was further suppressed, while FSH release surpassed that seen in 14L:10D pituitaries. In vitro FSH response to luteinizing hormone releasing hormone (LHRH) was also enhanced at this time. After 15 weeks of exposure to a short photoperiod, FSH secretion was still elevated above control levels, but Prl release and Prl response to DA were no longer different from that of 14L: 10D controls. Secretion of luteinizing hormone (LH) in vitro, either basal or LHRH stimulated, was not affected by photoperiod at any time tested. From these results, we conclude that short photoperiod exposure does not reduce the pituitary's ability to secrete LH or FSH, although secretion of Prl is severely attenuated.

Photoperiod and melatonin influence seasonal gonadal cycles in the grasshopper mouse (Onychomys leucogaster).

Development of the reproductive apparatus was delayed in grasshopper mice maintained from birth in short photoperiods (10 h light/day). The inhibitory effects of short photoperiods on sexual maturation eventually waned and mice in 10L:14D became reproductively active. Adult mice transferred from long (14 h light/day) to short photoperiods underwent testicular regression after 10 weeks and complete gonadal redevelopment after 30 weeks. A similar phenomenon was observed in adult female mice; oestrous cycles ceased within 3 weeks and resumed after 13 weeks in the short photoperiod. The regressive effects of short photoperiods on the male reproductive system were mimicked by daily injections of melatonin administered to mice housed in 14L:10D. Responsiveness of the female reproductive system to melatonin was reduced among photorefractory as compared to photosensitive mice. We suggest that the initial rate of sexual maturation and the timing of seasonal breeding in adult mice are regulated by photoperiod; effects of short daylengths on the neuroendocrine-reproductive axis appear to be mediated by the pineal gland.

Regulation in pregnant mink (Mustela vison) of plasma progesterone and prolactin concentrations and regulation of onset of the spring moult by daylight ratio and melatonin injections

In pregnant or pseudopregnant mink maintained under natural daylight conditions and mated early in March, plasma prolactin and progesterone levels began to increase after the vernal equinox. The onset of spring moult was observed a few days later. When the females were transferred to a 15 h light (L): 9 h dark (D) photoperiod just after mating, prolactin and progesterone increase was advanced by several days; when the mink were transferred to an 11 h L: 13 h D schedule, these increases, as well as the onset of spring moult, were delayed or inhibited. A daily afternoon injection of melatonin mimicked the effects of short photoperiod. A positive relation was observed between plasma prolactin on the one hand and progesterone secretion or onset of moulting on the other. These results suggest that short photoperiod or melatonin effects might act by inhibiting prolactin secretion.

Photoperiodic regulation of body mass, food intake, and reproduction in meadow voles.

Adult male voles were maintained for 10 wk in long or short photoperiods (14 or 10 h of light/day). A third group of animals housed in the long photoperiod was implanted with capsules containing melatonin. Body weight and food intake were measured weekly; various tissues were weighed and analyzed at the time of autopsy. After 10 wk, voles in the short photoperiod weighed 20% less and consumed 30% less food than those housed in the long photoperiod. Total body water and lean body mass were reduced in the short-day animals, although the size of the brown adipose tissue was not affected. White adipose tissue lipoprotein lipase (LPL) activity was markedly reduced in the short-day voles who also manifested gonadal regression and suppression of spermatogenesis. Melatonin mimicked the effects of short photoperiods on LPL activity and on lean body mass; other parameters for melatonin-treated animals were intermediate between those of untreated long- and short-day voles. We hypothesize that winter weight losses experienced by meadow voles in the field are mediated by decreases in the duration of the daily photophase and that the reduction in body mass permits overwintering voles to reduce their energy requirements and the amount of time devoted to foraging. At least part of the seasonal decline in body mass appears due to a decrease in gonadal hormone secretion.

Pineal influences hypothalamic Gn-RH content in the vole, Microtus agrestis.

Summary. Male voles reared in a stimulatory (long) photoperiod have significantly greater contents of hypothalamic Gn-RH and pituitary LH and greater testicular and seminal vesicle weights than do voles reared in inhibitory (short) photoperiods. The inhibitory effects of short photoperiod were reversed by pinealectomy.

Effect of 5-methoxytryptamine on testicular atrophy induced by experimental or natural short photo-periods in the golden hamster (Mesocricetus auratus).

Subcutaneous implantation of 5-methoxytryptamine-filled silastic capsules overcomes, in natural as well as in experimental conditions, the inhibitory effect of short photoperiod on the gonadal axis. The results obtained are similar to those obtained after pinealectomy. They indicate that 5-methoxytryptamine when constantly available presents, like melatonin, a progonadal (or counter-antigonadal) effect. Evidently, 5-methoxytryptamine, like melatonin, is involved in the control of the reproductive function.

Effects of short photoperiod on pituitary and testicular function in the Chinese hamster, Cricetulus griseus.

Effects of short photoperiod on pituitary and testicular function in the Chinese hamster, Cricetulus griseus.

Gonadotropin secretion during reproductive cycles in teleosts: Influences of environmental factors

Blood levels of the “Con A-II” or “maturational” gonadotropin (GtH) in teleosts are low in sexually immature fish, but sexually regressed fish may have high levels if the temperature is warm. In some species a temporary increase in blood GtH levels may occur at the initiation of gametogenesis, and in most species a gradual increase generally occurs as gametogenesis proceeds. A further increase in blood levels of GtH occurs at the time of oocyte maturation; in goldfish a “surge” in blood levels of GtH induces oocyte maturation and ovulation. A long postovulatory surge of GtH occurs in rainbow trout if ovulated oocytes are retained. In males there are increases in blood levels of GtH at the time of spermiation, and in goldfish and carp an additional increase occurs during actual spawning. A rise in temperature generally causes an increase in blood levels of GtH. At warm temperatures, gonadal activity is not necessarily stimulated and gonadal regression can occur in spite of the relatively high blood levels of GtH. Female goldfish that are mature (completed vitellogenesis) or undergoing ovarian recrudescence generally have a significant daily cycle in serum levels of GtH, whereas sexually regressed females do not. Temperature, photoperiod, feeding, and length of exposure to the environmental conditions each influence the daily cycle of serum GtH levels; disappearance of a significant cycle is usually correlated with the onset of oocyte atresia. These findings support the hypothesis that a daily cycle of blood levels of GtH is of importance in stimulating and maintaining gonadal activity. There are daily variations in ovarian responsiveness to injected GtH in goldfish, indicating that GtH receptors in the ovary may also have a daily cycle. In spring-spawning teleosts, the pineal, and in some species also the eyes, are involved in mediating the stimulatory effects of long photoperiods and the inhibitory effects of short photoperiods on gonadal growth in the spring. Pinealectomy, and in some cases blinding, influence the daily cycle of blood levels of GtH in female goldfish and, via this route, gonadal activity is presumably affected. Melatonin, a pineal factor, may act on the hypothalamus to mediate these actions. Temperature influences the metabolic clearance rate and pituitary secretion rate of GtH. Whether the effects of temperature are via actions directly on the tissues at each level of the hypothalamo-hypophysial-gonadal axis or via input to the neuroendocrine system from temperature receptors is not known.

The anovulatory hamster: a comparison of the effects of short photoperiod and daily melatonin injections on the induction and termination of ovarian acyclicity.

Cyclic female hamsters were rendered anovulatory by daily subcutaneous melatonin injections (25 microgram/0.1 ml oil) in 29 days or by transfer to a short light cycle, LD 6:18 (lights 1000-1600 hrs) in 33 days. Estrous cyclicity was reinitiated in these animals in 44 or 45 days following cessation of melatonin injections or transfer to long light cycles (LD 14:10, lights 0600-2000 hrs), respectively. Exposure of both groups to LD 6:18 after reinitiation of estrous cyclicity caused a second cessation of ovulation in 75 (melatonin group) or 61 (short light cycle group) days. Thus, although both treatments disrupted estrous cyclicity for nearly 6 weeks, this was not sufficient to induce photorefractoriness (failure to respond to short light cycles with continued estrous cyclicity). Rather, every animal responded to LD 6:18 and ceased ovulating. Melatonin-induced anovulatory hamsters showed daily gonadotropin release patterns identical to those reported in hamsters in other anovulatory states (lactating, prepubertal, and photoinduced anovulatory hamsters); that is, peak LH and FSH release at 1700 hrs daily.

Photoperiod, Pineal, Melatonin and Reproduction in Hamsters

Publisher Summary This chapter discusses the experiments done on male hamsters. It should be noted, however, that corresponding results have been obtained in females in nearly all cases, regardless of whether photoperiodic effects, the results after pineal manipulations or after application of melatonin are considered. Many mammalian species show a marked annual cycle of gonadal and other functions. In a number of cases it has been shown that the photoperiod, that is, the length of the daily light cycle and its changes, are involved in the regulation of this cycle. The pineal has been shown to participate in the transduction of photoperiodic effects of short photoperiods leading to regression and also of long photoperiods stimulating recrudescence. The latter effect is not only a suppression of antigonadotrophic effects from the pineal, but a positive stimulation. The exact role of melatonin in the photoperiodic mechanism and its site of action are still unclear. Strong effects of melatonin application have been found in photoperiodic mammals. Recent experiments suggest that not only the amount of melatonin, but its pattern of synthesis and release may be important in the conveyance of photoperiodic effects. No support for the assumption that the site of action of melatonin is the pineal itself has been found in experiments with pinealectomized animals.

Effects of short photoperiods on puberty, growth and moult in the Djungarian hamster (Phodopus sungorus).

Male Djungarian hamsters were raised from birth in either long (16L:8D) or short (8L:16D) photoperiods. In 16L:8D, testes were large (about 400 mg) and showed full spermatogenesis from 31 days of age, the cauda epididymidis contained motile spermatozoa from 35 days and the accessory glands were large and reached their final size at about 60 days of age. In 8L:16D, testes remained small (about 15 mg) and undeveloped up to an age of about 130 days; they then developed to reach normal size and full spermatogenesis. In 16L:8D body weight increased steadily up to an age of about 160 days, but in 8L:16D body weight increase was slower and reached normal values, after a plateua at about 80 days, at about 190--260 days. Most animals in 8L:16D moulted into winter pelage, and then into the summer pelage; those in 16L:8D kept the summer pelage throughout.

Photoperiodic influences on testicular regression, recrudescence and the induction of scotorefractoriness in male golden hamsters.

Hamstei testes which have undergone short photoperiod-induced atrophy become refractory to the effects of short photoperiod after spontaneous or light-induced recrudescence (Reiter, 1974). We have termed this phenomenon, “scotorefractoriness.” The present experiments assessed relations between photoperiod-induced testicular regression, recrudescence and scotorefractoriness. Experiment 1 established that mere testicular regression was not sufficient to induce scotorefractoriness. Testes of some animals which were regressed by 6 or 9 weeks of exposure to a LD 2:22 photoperiod (short days) and recrudesced by 9 weeks of exposure to a LD 14:10 photoperiod (long days) subsequently regressed again in response to a second 9 week exposure to LD 2:22; others appeared scotorefractory. Experiment 2 determined that animals which achieved complete testicular regression during 9 weeks of LD 2:22 were less sensitive to the stimulating effects of long days than were animals which were in LD 2:22 for 12–15 weeks. The transition from long to short days initiates gonadal atrophy, permits subsequent testicular recrudescence and also induces scotorefractoriness. Short day exposure initially decreases the sensitivity of the neuroendocrinetesticular axis to the effects of long days; the subsequent recovery of sensitivity to photostimulation may parallel processes involved in spontaneous testicular recrudescence.