Seasonal and acute changes in adrenocortical responsiveness in an arctic-breeding bird

The Lapland longspur, Calcarius lapponicus, times its breeding season so that chicks hatch coincident with the brief period of food abundance in the high arctic. This synchronization requires that all reproductive activities occur in over a much shorter period than at lower latitudes. Because of the known influence of stress hormones on delaying breeding in temperate-zone birds and the detrimental effects of such delays in the arctic, we expected the performance of the hypothalamic-pituitary-adrenal (HPA) axis of arctic-breeding birds to show less sensitivity to environmental stress than their mid-latitude counterparts. We found that adrenocortical responsiveness to the standardized stress of capture and handling, measured by taking five serial blood samples for corticosterone during the course of a 1-hr period, was similar to many temperate passerines and was also similar both between male and female longspurs and between the migratory and reproductive phases. However, the profile of plasma corticosterone during capture stress was significantly damped in longspurs sampled as they began their postnuptial molt. In addition, we had the opportunity to examine endocrine responses to a natural environmental stress in 1989 during a 3-day snowstorm which concealed available food resources. During this storm longspurs formed progressively larger flocks each day, with females abandoning incubation duties by the third day. Birds captured during the storm showed highly significant increases in both the rate of plasma corticosterone increase during capture and the peak postcapture level compared with birds sampled before the storm. This increased adrenal potential suggests increased activity of the HPA axis in response to severe conditions and is reminiscent of the response to fasting. Although the storm occurred during incubation, and reproductive hormone levels had begun to decline, we measured significant reductions in luteinizing hormone in both males and a subset of females captured during the storm.     

Long-term hypothyroidism causes decreased bone competence in male European starlings, Sturnus vulgaris

Male European starlings were thyroidectomised and held on either short or long day photoperiods. Intact euthyroid control birds were also held on either short or long days to control for differences in reproductive condition. Femora of birds from each group were sampled following plasma thyroxine measurement. Hypothyroidism caused decreased bone mechanical competence in starlings, as determined by Vickers microhardness testing. It was also found that transfer from short to long daylengths caused increased plasma thyroxine concentration, but that this did not affect bone mechanical competence. The finding that hypothyroidism causes decreased bone mechanical competence agrees with another animal study and a number of human studies, and we conclude that bone quality and mechanical competence can be adversely affected by abnormal thyroxine concentrations.     

Laparoscopic management of an intramural pregnancy

Adult cat fleas, Ctenocephalides felis (Bouché), survive and reproduce when fed human blood through an artificial membrane system. When a dog hair substrate was included in cages with the fleas, mean adult mortality was 2.4 after 12 d of bloodfeeding. Egg production began after 3 d and was continuous for 12 d, ranging from 3 to 4 eggs per female per day. In cages without hair, mean adult mortality was 61.2% after 12 d of bloodfeeding. Egg production began after 2 d, reached a maximum of two eggs per female per day after 7 d, and decreased thereafter. No significant differences in egg hatch were seen in treatment groups sampled from 5 to 7 d after the onset of bloodfeeding. After 7 d, however, egg hatch for fleas maintained in cages without hair was significantly lower than in cages where fleas were maintained on dog hair. Adult emergence from these larvae did not differ significantly between the two groups. Egg hatch and adult emergence in both groups of fleas fed on human blood did not differ significantly from egg hatch and adult emergence in fleas fed on colony cats.     

Effects of amino acid restriction during starter and grower periods on subsequent performance and incidence of leg disorders in two strains of male large white turkeys

Male turkeys of two commercial Large White strains (Nicholas 88, BUT 6) were subjected to growth restriction by means of reducing amino acid (AA) content of diets to a minimum of 75% of NRC (1994) suggested levels. There were three periods when diets containing 75% of NRC recommended AA for that age period were fed ad libitum: 0 to 3 wk, 0 to 6 wk, or 6 to 12 wk. A fourth (control) group was not restricted in AA content at any time. When turkeys were not fed the AA-restricted diets they were fed diets formulated to meet a minimum of 100, 110, or 120% of NRC (1994) AA recommendations, which resulted in a 3 x 4 factorial arrangement of treatments with three AA levels by four restriction times. Four pens of 12 males each were fed each AA by restriction time combination. At 18 wk, all birds were scored individually for leg condition and representative samples of turkeys were processed for parts yield. Birds fed restricted diets from 0 to 6 or 6 to 12 wk had significantly lower BW at 18 wk than control birds. Birds fed the restricted diets from 0 to 3 wk did not differ significantly in 18-wk BW compared to control birds but the magnitude of difference was similar to that observed at the end of the restriction period. Feed utilization was not improved by early AA restriction. Restricting early growth resulted in a significantly higher incidence of birds with no leg disorders and a lower incidence of birds with moderate leg disorders than control birds. Feeding higher AA levels during realimentation resulted in a greater severity of leg disorders. Breast meat yield was depressed significantly as severity of early restriction increased. Increasing dietary AA above NRC (1994) recommended levels generally improved performance during realimentation but was not able to compensate for reduced gains during restriction.     

The chronic infusion of nicotine into the developing chick embryo does not alter the density of (-)-[3H]nicotine-binding sites or vestibular function

(-)-Nicotine (1.2 mg/day) or saline was infused into chick embryos (Gallus domesticus) for 10 days beginning 12 h beyond the eight day of incubation (E8 + 12 h). Twelve h beyond the eighteenth day of incubation (E18 + 12 h), the eggs were opened to access the embryos and subcutaneous skull electrodes placed. Short latency vestibular response thresholds and input/output functions were determined to assess neurophysiological consequences of chronic nicotine administration. Samples of serum and extraembryonic (amniotic and albumen) fluid were analyzed by gas chromatography-mass spectrometry to determine the levels of nicotine and its major metabolite, cotinine. The brains were removed and divided into diencephalon and mesencephalon and the density of (-)-[3H]nicotine binding sites in each brain area was measured. Nicotine and cotinine were found in the serum and extraembryonic fluid, but nicotinic receptors were not up-regulated in the brains of animals infused with nicotine in comparison to controls. Vestibular response thresholds also did not differ between nicotine-treated and control animals.     

Inhalation teratology and reproduction studies with 1,1-dichloro-2,2,2-trifluoroethane (HCFC-123)

HCFC 123 is one of the chemicals being developed as a replacement for CFC 11 in refrigerant and solvent applications. Supplementing earlier rat teratology studies, a rabbit inhalation teratology study was conducted. In addition, one-generation and two-generation inhalation reproduction studies were conducted. In the teratology study, the pregnant rabbits were exposed to levels of 0 (control), 500, 1500, and 5000 ppm, 6 hr per day from Days 6 through 18 of gestation. Slight body weight losses and reduced food consumption were seen in does in all three exposure level groups. This response followed an exposure-related pattern. There were no other signs of maternal toxicity. There was also no evidence of treatment-related effects on the kits. A probe one-generation reproduction study was conducted. In this study four groups of 12 male and 12 female rats were exposed to vapors of HCFC 123 6 hr per day, 7 days per week from 4 weeks prior to mating through weaning of their offspring. The exposure levels for this study were 0 (control), 300, 1000, and 5000 ppm. There were no effects on mating and fertility, or on pup survival or birth weight. A two-generation study was subsequently conducted. In this study, five groups of 32 male and female rats were exposed to HCFC 123 from 6 weeks of age through weaning. From the offspring of these animals, groups of 28 males and females were selected for the F1 generation. These animals were exposed to HCFC 123 from weaning (4 weeks of age) through weaning of the F1 generation. All exposures were 6 hr per day, 7 days per week. The exposure levels for this study were 0 (control), 30, 100, 300, and 1000 ppm. There were no effects on any of the fertility or reproductive indices measured. As with prior studies, decreases in serum triglyceride levels were seen. Pup survival and birth weight were unaffected by treatment. Pup body weight gain was lower in all treatment groups during nursing, following an exposure-related pattern. Since weight gain for the F1 animals was normal following weaning, this depression of body weight gain may be related to the depression of serum triglycerides. In addition, liver weights of the adult rats exposed to levels of 100 ppm and higher of HCFC 123 were higher than controls, histological examination revealed only hepatic enlargement and vacuolation. It was concluded that exposure to HCFC 123 did not cause reproductive effects although it did effect the body weight gain of the offspring during lactation.     

Duration of fertility in ad libitum and feed-restricted caged broiler breeders

It has been shown in previous studies that fertility can be reduced in overweight broiler breeder (BB) flocks. In an effort to determine the effect of ad libitum feeding on the duration of fertility in BB hens, 60 52-wk-old Shaver Starbro hens were randomly assigned to one of two treatments, ad libitum feeding (F) or restricted feeding (R) to maintain breeder target weights. All hens were reared to 52 wk under conditions of feed restriction. All birds were weighed individually on a weekly basis. At the beginning of each of two 4-wk study periods (56 to 60 wk and 60 wk to 64 wk), all birds were inseminated on 2 consecutive d with 0.05 mL pooled BB semen. All eggs were weighed and placed in a forced air incubator the same day that they were laid. After 7 to 10 d of incubation, the eggs were broken out and scored macroscopically as fertile with live embryo, fertile with dead embryo (early embryonic death), or clear (assumed infertile). The duration of fertility was defined as the number of days from the day after the second insemination to the last fertile egg before two consecutive interfile eggs. Hen BW were significantly different between treatments within each of the two 4-wk studies. The mean BW of the F hens was 4,261 g in Study 1 and 4,448 g in Study 2. The BW of the R hens were 3,459 g in Study 1 and 3,565 g in Study 2. Egg production levels and average egg weight was not different between treatments in either study. In Study 1, the duration of fertility for the F hens (12.7 d) and the R hens (12.7 d) were not different. In Study 2, the durations of fertility were significantly higher (P < 0.05) in the R hens (12.7 d) than in the F hens (10.0 d). These results support the theory that overweight BB have a reduced duration of fertility that may contribute to a reduced fertility in artificially inseminated and naturally mated flocks.     

Organoleptic evaluation of eggs produced by laying hens fed diets containing graded levels of flaxseed and vitamin E

Eighteen-week-old laying hens were fed diets containing 0, 10, or 20% ground flaxseed and 10 or 100 IU vitamin E/kg diet, in a factorial arrangement. When birds were 60 wk of age, eggs were collected from various treatments and used in taste panel studies. All studies involved freshly boiled eggs. In Experiment 1, four separate panels were conducted to obtain information on egg aroma, egg flavor, presence of any off-flavor, and overall acceptability of the egg. Pooled data showed a very significant difference among panelists for all attributes tested (P < 0.01) and off-flavors were detected in eggs from hens fed 10 and 20% flaxseed with 10 mg vitamin E/kg. In Experiment 2 panelists were asked to evaluate egg aroma, yolk flavor, and overall acceptability in eggs from birds fed the lowest level of vitamin E with 0 or 10% flaxseed, and birds fed 20% flaxseed and 10 or 100 mg vitamin E/kg. The highest ratings for egg aroma, yolk flavor, and overall acceptability were for the control eggs. There was a significant reduction in overall acceptability as flaxseed concentration increased (P < 0.05) and an interesting and significant (P < 0.05) decline in overall acceptability for birds fed 100 vs 10 IU vitamin E/kg diet in eggs for birds fed 20% flaxseed. In a third study, there was an indication of preference for eggs from birds not fed flaxseed, when the diet contained 10, rather than 100 IU vitamin E/kg diet. These data suggest that high (> 10%) levels of flaxseed used in the bird's diet will result in some decrease in overall egg acceptability as assessed by aroma and flavor. These effects seem to be accentuated by using high levels of vitamin E in the bird's diet.     

Effects of prenatal exposure to 5-fluoro-2'-deoxyuridine on developing central nervous system and reproductive function in male offspring of mice

The effect of 5-fluoro-2'-deoxyuridine (FrdU) on the developing brain and postpubertal reproductive function of male mouse offspring treated prenatally was investigated. FrdU was administered intraperitoneally to pregnant ICR mice at 1.5, 3, 6, 12.5, 25, and 50 mg/kg/day on days 8 through 13 of gestation or 12.5, 25, and 50 mg/kg/day on days 14 through 18 of gestation. Dams were allowed to deliver spontaneously. Dams treated with FrdU at 12.5, 25, and 50 mg/kg/day on days 8 through 13 of gestation did not deliver because of entire intrauterine death of embryos. Male offspring were aged for 10 or 15 weeks and then cohabited with untreated female mice for assessment of reproductive performance. Histological examination of the testis, epididymis, prostate, and seminal vesicle of offspring at 12 weeks of age, and sperm analysis of offspring at 12 or 17 weeks of age were performed. Dose-dependent decreases in body weight gain were noticed throughout the life of offspring. A marked decrease in the copulation rate was noted in the group treated with FrdU at 6 mg/kg/day on days 8 through 13 of gestation. However, neither histological examination of testes and sex-accessory glands nor sperm analysis revealed adverse effects of FrdU on the reproductive function in the male offspring of dams treated with FrdU at 6 mg/kg/day on days 8 through 13 of gestation. There were no significant differences in the relative weight of testes and epididymides between the group treated with FrdU at 6 mg/kg/day on days 8 through 13 of gestation and the control group. Absolute brain weight in the groups treated with FrdU on days 8 through 13 of gestation significantly decreased, while relative brain weight increased in the group treated at 6 mg/kg/day on days 8 through 13, and at 25 and 50 mg/kg/day on days 14 through 18 of gestation. Dilatation of the lateral and third ventricles was observed in all of the male offspring of dams treated with FrdU at 6 mg/kg/day on days 8 through 13 of gestation, when inspected at 12 and 17 weeks of age. In the subsequent study, ICR mice were treated intraperitoneally with FrdU at 6.25-100 mg/kg on day 12 of gestation, and the fetuses obtained 24 h after treatment. Histological observation was performed in the ventricular zone of telencephalon, and in the ependymal and mantle layers of diencephalon in the fetal brain. The incidence of pyknotic cells in these areas was increased linearly with increasing FrdU dose. From these results and our previous findings, we suggest that damage to the central nervous system, a substantial neuronal deficit, resulting from excessive cell death in the developing brain may lead to reproductive dysfunction after puberty.     

Net transfer and incorporation of yolk n-3 fatty acids into developing chick embryos

The effect of egg yolk fatty acid composition on the uptake and utilization of essential n-6 and n-3 fatty acids by the developing chick embryo was studied. Eggs were enriched with n-9, n-3, or n-6 fatty acids by incorporating sunflower seed high in oleic acid (C18:1 n-9), flax seed rich in linolenic acid (C18:3 n-3), or sunflower seed high in linoleic acid (C18:2 n-6) into the laying hen diets. Fertile eggs were collected and incubated. The fatty acid composition of eggs and newly hatched chicks were compared. Feeding diets containing flax seed increased (P < .05) total n-3 fatty to 528.4 mg compared with 53.9 and 39.3 mg for eggs from hens fed diets with high oleic acid or regular sunflower seed, respectively. Levels of C18:2 n-6 and monounsaturated fatty acids were higher in eggs from hens fed diets containing regular or high oleic acid sunflower seeds. Dietary fat did not influence the total lipid content of the egg yolk or total lipids of chick tissues. The fatty acid composition of the hatched progeny was significantly altered by egg yolk lipids. However, the percentage incorporation of essential n-6 and n-3 fatty acids into the progeny increased when yolk sources of these fatty acids were low. The developing chick embryo appeared to preferentially take up docosahexaenoic acid and arachidonic acid from the yolk lipids. Evidence also suggests that conversion of C18:2 n-6 and C18:2 n-3 to longer chain n-3 or n-6 fatty acids occurs during the incubation period.     

Role of gonadal hormones in incubation behavior of male ring doves (Streptopelia risoria).

Examined the role of testicular hormones in the incubation behavior of 85 male ring doves. Intramuscular injection of testosterone propionate (TP) at 100 mg/day to intact or castrated Ss throughout a reproductive cycle had no deleterious effects on sitting or crop-sac growth. Similarly, castrated Ss given TP only until the start of a reproductive cycle incubated normally. Thus, changes in androgen titer following courtship do not affect incubation behavior. In contrast, progesterone administered to intact Ss at 100 mg/day throughout a reproductive cycle interfered with both sitting behavior and crop-sac growth. It is concluded that high levels of progesterone (whether of gonadal or adrenal origin) would be incompatible with maintenance of incubation, possibly because of interference with prolactin secretion. (22 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Copulation rate and sperm use by female bearded tits, Panurus biarmicus

We examined functional and mechanistic aspects of sperm competition in the bearded tit by determining (1) the variation in copulation rate between birds breeding alone or with other males present, and (2) the number of sperm present in the female reproductive tract estimated from the number of sperm trapped on the perivitelline layers of eggs. Females copulated at a higher rate with their partner when other males were present, but this did not translate into more sperm on eggs, possibly because insemination rates exceeded the female's sperm storage capacity. The rate of sperm loss from the female's reproductive tract, which is an important variable of sperm competition models, was obtained for the first time for a wild bird and was relatively high compared with other birds. This suggests that bearded tits copulate frequently because a single insemination is insufficient to fertilize the whole clutch, and females thus have to copulate during the egg-laying period to avoid infertile eggs. This finding is the first empirical support for the fertility insurance hypothesis. In line with this we discuss the significance of the interspecific variation in rate of sperm loss in relation to mating strategies in general, and the evolution of multiple mating rather than improved sperm storage in bearded tits with particular regard to the pronounced extrapair copulation behaviour of females. Copyright 1998 The Association for the Study of Animal Behaviour.     

Efficacy of various therapeutic regimens in eliminating Pasteurella pneumotropica from the mouse

Pasteurella pneumotropica, a gram-negative opportunistic pathogen, can be isolated from the oropharynx, intestinal tract, and reproductive tract of clinically normal mice and has been associated with various clinical syndromes, including conjunctivitis, infections of the reproductive tract, otitis, and subcutaneous abscess formation. Enrofloxacin, a fluoroquinolone bactericidal antimicrobial, has been shown to be effective in eliminating P. multocida from rabbits. We sought to determine whether enrofloxacin would eliminate P. pneumotropica from mice known to be asymptomatically infected with the agent. Pasteurella pneumotropica-positive (culture and immunofluorescence assay) male (n = 55) and female (n = 55) C57BL/6N mice were randomly assigned to one of seven treatment groups or to a control group. These groups were designed to evaluate the efficacy of enrofloxacin administered orally via the drinking water or parenterally at three dosages (8.5, 25.5, and 85.0 mg/kg of body weight per day) over a 14-day treatment period. A tetracycline-treated group (60 mg/kg per day) and an untreated control group were included for comparisons. Repeated oropharyngeal swab and fecal specimens were obtained for culture through posttreatment day 30, and specimens from numerous enteric and reproductive organs collected during necropsy were used to evaluate group differences. Enrofloxacin eliminated evidence of P. pneumotropica from all sites when administered at 25.5 or 85 mg/kg but not at 8.5 mg/kg by either route for at least 30 days after treatment. Tetracycline-treated and control groups remained consistently culture-positive throughout the study. We concluded that the oral route may be a more practical method for treating large numbers of mice. Enrofloxacin may be a practical and inexpensive alternative to cesarian rederivation or embryo transfer for the elimination of P. pneumotropica in mice.     

Carcass traits and reproductive development at the onset of lay in two lines of female turkeys

A study was conducted comparing ovary and oviduct development following photostimulation in two lines of turkey breeder stocks (female line and male line). Birds were euthanatized for assessment of reproductive organ morphology at 3-d intervals following photostimulation (203 d of age) to 245 d and on the day following their first oviposition. The age at first oviposition was similar for both lines. Male line birds were 3 to 4 kg heavier than female line birds throughout the study, but had lower abdominal fat pad weights when expressed as a percentage of BW. Female line birds had significantly more total carcass lipid as a percentage of BW than male line birds (24.76 vs 22.79%, respectively). Male line birds had significantly more large ovarian follicles with a greater proportion in a triple or greater hierarchical arrangement at first egg. To determine the incidence of unreconciled ovulations (presumed to be internally ovulated follicles and defined as ovulations occurring prior to first oviposition), postovulatory follicles on the ovary were reconciled with observed ovipositions and the developing eggs that were in the oviduct at the time of study. On average, male line hens had 3.0 unreconciled postovulatory follicles at first egg, whereas the female line hens had 1.6. The incidence of birds with physical remnants of internal ovulation was correlated (r = 0.44) to the number of unreconciled ovulations. The developing oviduct of the female line birds reached its mature weight (84.8 g) 3 d earlier than the ovary did. The developing ovary and oviduct of the male line hens reached their mature weights on the same day. The development of the male line oviduct is seemingly accelerated relative to that of the ovary, resulting in lost ovulations early in lay.     

Breeding biology of Muscovy duck Cairina moschata in natural incubation: the effect of nesting behavior on hatchability

A breeding biology study of a genetically unselected variety of Muscovy duck Cairina moschata was conducted in an experimental duck unit in Maputo, Mozambique (25 degrees 58' S, 32 degrees 35' E), to gain insight into factors affecting hatchability during natural incubation. Nesting and incubation behaviors were recorded by daily nest visits. Of 1,338 nests investigated, 70% were incubated until hatching. In 23% of the incubated nests, eggs were laid by more than one duck in the same nest, indicated as dump nests. Artificial dump nests (15% of the incubated nests) were created by adding eggs (690 eggs) from nests abandoned by the duck before incubation had started. A total of 37% of the incubated nests contained eggs that were laid after the onset of incubation (nonterm eggs). Similar hatching rate was found between ducks raised in parks with or without access to swimming water. No significant difference was found in hatchability between normal (0.76) and dump nests (0.77). Artificial dump nests showed higher hatching rates than nests containing nonterm eggs. Dump nesting appears to be a reproductive strategy used by the Muscovy duck to enhance duckling production. Hatching rate was strongly influenced by the length of laying period (period between the ovoposition of the first egg until the onset of incubation) and reproduction cycle (laying period and incubation period). Hatchability was higher for clutches with a shorter reproduction cycle. It is concluded that nesting behavior of the domesticated Muscovy duck is similar to that of its wild ancestor.     

A test for photorefractoriness in high-producing stocks of laying pullets

1. Pullets of 2 high-producing commercial stocks (both brown-egg layers) were exposed to 5 different lighting patterns between 18 and 72 weeks to test the hypothesis that photoperiods used in commercial lighting programmes early in the laying year may be unnecessarily long and, by accelerating the development of photorefractoriness, may contribute to the decline in egg production observed after the initial peak. Two rooms of 288 pullets were allocated to each treatment. 2. The rate of lay observed with a Step-Up treatment which gave increases in photoperiod from 8L:16D at 18 weeks to 15L:9D at 27 weeks of age was not significantly different from that of treatments which held the birds on 11L:13D during peak egg production but gave increments up to 15L:9D later in the laying year. 3. A control group maintained on 11L:13D from 20 to 72 weeks laid 295 eggs per bird housed and a further group held on 8L:16D from 0 to 72 weeks laid 284 eggs per bird. These yields were lower than the Step-Up treatment (299 eggs) but show the potential of modern hybrid stocks to lay prolifically even without light stimulation. 4. It is concluded that the stocks tested in this experiment showed no advantage when given lighting programmes in the first laying year which were designed to minimise the adverse effects of photorefractoriness.     

The onset of incubation in birds: can females control hatching patterns?

We investigated intraspecific variation in incubation behaviour of wild Eurasian kestrels, Falco tinnunculus, in Finland and tested whether patterns of hatching asynchrony could be predicted from patterns of incubation. The timing of the onset of incubation varied considerably for 17 female kestrels. Eggs generally hatched in the order they were laid, and both total hatching span of the clutch and the pattern of eggs hatching on certain days corresponded well with incubation behaviour. This result was consistent with the idea that females have much control over hatching patterns. In the majority (65%) of cases, the proportion of daily incubation increased monotonically with the laying sequence, a pattern described previously in other birds. Unusual patterns of incubation (35%) were most common in females with poor body condition during incubation and may be the result of energy constraints during laying.Copyright 1998 The Association for the Study of Animal Behaviour. Copyright 1998 The Association for the Study of Animal Behaviour.     

Phase shifts in circadian rhythmicity of total, free corticosterone and transcortine plasma levels in hypothyroid male Japanese quails

Control, radiothyroidectomized, and methimasol-treated short day (6L:18D; beginning of light at 0700) male Japanese quails were studied with regard to their circadian rhythmicity of total, free corticosterone and transcortine plasma level. In the controls, the peak of total and free corticosterone coincided with the maximal corticosterone binding capacity of transcortine; these parameters can be characterized by similar daily rhythm. In hypothyroid birds a synchronous phase shift of these parameters has been observed. In methimasol-treated animals the phase shift of the circadian rhythmicity was 6-8 hr, and in the radiothyroidectomized group 12 hr, respectively. According to the degree of hypothyroidism the metabolic clearance rate (MCR) of corticosterone decreased. This effect leads to the phase shift of total corticosterone rhythm, and the shift includes not only free, but also transcortine concentration.     

Monoamine oxidase in developing chick retina

The developmental changes in monoamine oxidase (MAO) activities towards 5-hydroxytryptamine (5-HT) and beta-phenylethylamine (PEA) in chick retina were investigated. The whole pattern of the developmental changes in MAO activity towards 5-HT was similar to that towards PEA, even though the activity towards 5-HT was much lower than that towards PEA during the period from the 12th day of incubation to the 14th day after hatching. The MAO activities on the 12th day of incubation were low and increased remarkably until the 18th day of incubation. Then they remained unchanged until the 7th day after hatching; therefore, they decreased. The activities measured on the 14th day after hatching are on the same level as those of an adult. The multiplicity of MAO in the retinae of a chick on the 12th day of incubation and of an adult was also studied with specific inhibitors. The result showed that the major part of MAO in chick retina is type B enzyme; that type A MAO in the retina of an adult is, however, relatively higher than that in the retina of the embryo on the 12th day of incubation. It was found that an appreciable amount of MAO activity towards 5-HT in chick retina is due to type B MAO.     

Chick embryo development can be irreversibly altered by early exposure to weak extremely-low-frequency magnetic fields

Several reports have shown that weak, extremely-low-frequency (ELF), pulsed magnetic fields (PMFs) can adversely affect the early embryonic development of the chick. In this study, freshly fertilized chicken eggs were exposed during the first 48 h of postlaying incubation to PMFs with 100 Hz repetition rate, 1.0 microT peak-to-peak amplitude, and 500 microseconds pulse duration. Two different pulse waveforms were used, having rise and fall times of 85 microseconds (PMF-A) or 2.1 microseconds (PMF-B). It has been reported that, with 2 day exposure, these fields significantly increase the proportion of developmental abnormalities. In the present study, following exposure, the eggs were allowed to incubate for an additional 9 days in the absence of the PMFs. The embryos were taken out of the eggs and studied blind. Each of the two PMF-exposed groups showed an excess in the percentage of developmental anomalies compared with the respective sham-exposed samples. This excess of anomalies was not significant for the PMF-A-treated embryos (P = 0.173), whereas it was significant for the PMF-B-exposed group (P = 0.007), which showed a particularly high rate of early embryonic death. These results reveal that PMFs can induce irreversible developmental alterations and confirm that the pulse waveform can be a determinant factor in the embryonic response to ELF magnetic fields. The data also validate previous work based on the study of PMFs' effects at day 2 of embryonic development under field exposure.