Day Of Estrus Research Articles

The effect of changes in feed intake around the time of insemination on systemic progesterone and embryo development and survival in cattle.

AbstractEarly embryo loss is the major cause of reproductive failure in cattle. The objective of this study was to investigate the effect of changes in feed intake around the time of insemination on systemic progesterone and on embryo development and survival and in cattle. Nutrition treatments were designed to provide 0.8 times (Low, L) or twice (High, H) maintenance energy requirements. Oestrus was synchronised in heifers (n=314) using two injections of prostaglandin (PG; 50 μg Cloprostenol, Estrumate) administered 10 days apart. On the day of oestrus following the first PG injection, heifers were randomly allocated to L or H (pre-AI). At the oestrus following the second PG injection, heifers were inseminated with semen from the same Limousin bull and on the following day were randomly allocated to either L or H until embryo recovery at day 8 (n=25), 14 (n=57) or 16 (n=71) or pregnancy diagnosis at day 30 (n=161). Hence there were four nutrition treatments; L-L, L-H, H-H and H-L. There was no significant difference in embryo survival rate determined at day 14, 16 or 30 and so the data were combined for analysis. Overall embryo survival rate was significantly lower (P<0.001) in H-L (0.37) than L-L (0.70), L-H (0.71; P<0.001) or H-H (0.68; P<0.01) treatment groups. Nutrition treatment did not affect systemic progesterone measured on days 4, 5, 6 or 7 of the pre- or post-AI oestrous cycle. The total cell number of 8-day-old blastocysts was not significantly affected by nutrition treatment neither was the length, diameter or estimated total protein content of 14-day-old embryos. Reducing energy intake immediately after AI reduced embryo survival rate but there was no evidence that this effect was mediated through changes in systemic progesterone.

Luteolytic effect of prolactin is dependent on the degree of differentiation of luteal cells in the rat.

We studied the morphological and quantitative changes in cyclic corpora lutea (CCL) and in CL of pregnancy (CLP) during structural luteolysis. Elimination of CCL takes several cycles, and cell death occurs as successive apoptotic bursts, from 2100 h in proestrus to 1300 h in estrus. Each apoptotic burst determined a 60% decrease in the CL volume and an 80% decrease in the number of steroidogenic cells (SC). All these changes were inhibited by blocking the preovulatory prolactin (PRL) surge with bromocryptine (CB154). Neither apoptotic cells nor changes in the number of SC were found in regressing CLP from Day 21 of pregnancy to Day 2 postpartum, although there was a 50% decrease in the CLP volume and a 30% decrease in the mean cross-sectional area of SC. Treatment with CB154 on the day of parturition did not modify these regressive changes. On Day 5 postpartum, the volume of the CLP and the number of SC were equivalent in lactating rats (showing high PRL concentrations induced by pup suckling) and nonlactating noncycling rats (in which cyclicity and, therefore PRL surges, were blocked by treatment with LHRH antagonist). However, on Day 10 postpartum, the CLP volume and the number of SC were significantly decreased in lactating rats, and apoptotic cells were frequent. In postpartum cycling rats, the CLP did not show apoptotic cells on the day of the second postpartum estrus (on Day 5 postpartum), whereas on the day of the third postpartum estrus (on Day 9 postpartum), apoptotic cells were abundant. These results indicate that PRL does not induce apoptosis in the CLP before Day 5 postpartum and strongly suggest that the proapoptotic effect of PRL is dependent on the degree of differentiation of luteal cells.

Plasma Inhibin Levels in Relation to Steroids and Gonadotrophins during Oestrous Cycle in Buffalo

The study was conducted on six Murrah buffalo synchronized and induced to oestrus. An indwelling catheter was placed in the jugular vein of each buffalo 4 days before the expected onset of the oestrus following the induced oestrus and blood samples were collected at 8 h intervals from each animal throughout the oestrous cycle. Plasma immunoreactive inhibin, follicle-stimulating hormone (FSH), luteinizing hormone (LH), estradiol-17 beta and progesterone were estimated by radioimmunoassay to study the variations in the peripheral levels of these hormones and their inter-relationships in order to elucidate the feedback systems controlling them during the oestrous cycle of buffalo. Plasma inhibin levels ranged between 391.25 and 631.97 pg/ml during various phases of the oestrous cycle and were found to be higher than reported in cows. Peak LH and FSH levels during oestrus were 38.40 +/- 9.21 and 24.04 +/- 4.75 ng/ml, respectively and estradiol-17 beta and progesterone were 19.50 +/- 5.51 pg/ml and 0.61 +/- 0.25 ng/ml, respectively. The mean plasma inhibin concentration on the day of oestrus was 562.5 +/- 18.9 pg/ml. Levels of FSH in the plasma showed three mid-cycle elevations which corresponded to comparatively lower inhibin and elevated estradiol-17 beta levels during the same period. From this observation it was deduced that both inhibin and estradiol-17 beta have a feed-back regulatory effect on FSH secretion in buffalo.

Estrogen receptor beta in the sheep ovary during the estrous cycle and early pregnancy.

Objectives were to sequence and examine the expression of the estrogen receptor beta (ERbeta) in the sheep ovary. The sequence of the ovine ERbeta (oERbeta) was determined using reverse-transcription polymerase chain reaction (RT-PCR) and cloning techniques. The reading frame of oERbeta contained 527 amino acids and exhibited high overall homology with cow (98%), rat (88%), and human (88%) ERbeta. In addition, an oERbeta isoform having a 139-base pair deletion (oERbeta1) was identified. The predicted amino acid sequence of this isoform is lacking the ligand-binding and carboxyl-terminal transactivation domains. The oERbeta protein and mRNA were determined in ovaries obtained from ewes on Days 0 (first day of estrus), 2, 6, and 10 of the estrous cycle and Day 30 of gestation. Immunohistochemistry showed that oERbeta protein was located in granulosa cells, the ovarian surface epithelium, endothelium, and Day 2 corpus luteum (CL). Weak immunostaining for ERbeta was detected in the theca interna. Relative steady-state amounts of oERbeta mRNA in the CL were determined using semiquantitative RT-PCR. Amounts of oERbeta mRNA were greater (P < 0.05) during CL formation (Day 2) than at later stages. The oERbeta to oERbeta1 mRNA ratio was lower (P < 0.05) on Day 2 than on Day 10 or Day 30 due to a decrease in amounts of oERbeta1. Results indicate that the oERbeta is a 527-amino acid protein expressed in specific cells of the ovary. Changes in relative amounts of full-length oERB and a deletion isoform in CL occurred during the estrous cycle, suggesting that these two types of ERbeta might regulate estrogen actions during early CL development in sheep.

EFFECTS OF DIETARY PROTEIN LEVEL UPON PERIPHERAL PLASMA PROGESTERONE CONCENTRATION AND CONCEPTION RATE IN DAIRY CATTLE

There have been concerns that high protein intake had a significant influence on blood components and uterine constituents in non-lactating dairy cows and on spcrmatozoal motility. There are study that show that as dietary crude protein (CP) is increased, there is a tendency of reduced fertility in dairy cows while other studies have suggested that there is no relationship between reproductive performance and dietary CP intake. The objective of the study was to investigate the effect of dietary CP intake on blood progesterone concentrations and conception rate in dairy cattle. Fourteen lactating Friesian cows were randomly divided into two equal groups, a control group - Low Protein (LP) and a treated - High Protein (HP) group. The cows’ oestrous cycles were synchronized and inseminated with frozen semen. Jugular blood samples were collected daily for at least 21 days after the first insemination starting on day of oestrus and then twice per week until they were 6-weeks of pregnant and then once per week until they were 12-weeks pregnant. The result showed that the progesterone concentrations in the control (LP) cows were significantly higher than in the treated (HP) cows during pre-conception oestrous cycles that did not result in pregnancy for 10 cows (5 in each group). Except on the last day of sampling (day 42), there were no differences in progesterone concentrations between the two groups of cows during first 6-weeks of pregnancy. The plasma progesterone concentrations were significantly lower in the HP group on days 45 and 52. However, dietary protein had no significant effect on overall group mean concentrations over this 6-week period (7 to 12 week) but the interaction, Group x time, was significant. The number of services per conception was lower for the cows fed the low CP diet. However, the median number of services per conception for the two groups was not statistically different. The results clearly indicated that cows fed the high CP rations had significantly reduced plasma progesterone concentrations when compared with those fed the low protein diet. The result also suggested that low progesterone concentrations particularly during the pre-conception oestrous cycle in the HP-fed groups were associated with a lower conception rate (32%) compared in the LP-fed group (54%).

Ovulation delay induced by blockade of the cholinergic system on dioestrus-1, is related to changes in dopaminergic activity of the preoptic anterior-hypothalamic area of the rat

One hour after the injection of 100 mg/kg of atropine-sulphate at 1300 h of dioestrus-1, there was an abrupt increase of 17β-oestradiol plasma level and a significant increase in dopaminergic neural activity in preoptic anterior-hypothalamic area, without changes in luteinizing hormone serum level, in comparison with the saline injected group. Animals injected with atropine-sulphate showed a second increase in dopaminergic neural activity in the preoptic anterior-hypothalamic at 1100 of dioestrus-2 (atropine-sulphate 0.471 ± 0.7 vs. saline 0.241 ± 0.03, p < 0.01). In this group of animals, the preovulatory surges of 17β-oestradiol and luteinizing hormone occurred simultaneously at 1700 h of the expected day of oestrus; spontaneous ovulation was delayed until the expected day of dioestrus-1. Present results suggest that during dioestrus-1 there is a functional relationship between the cholinergic and dopaminergic systems in preoptic anterior-hypothalamic area, regulating the release of luteinizing hormone resulting in ovulation.

Effect of dominant follicle removal before superstimulation of follicular growth, ovulation and embryo production in Holstein cows

This study was to investigate whether removing the dominant follicle 48 h before superstimulation influences follicular growth, ovulation embryo production in Holstein cows. After synchronization, ovaries were scanned to asses the presence of a dominant follicle by ultrasonography with a real-time linear scanning ultrasound system on Days 4, 6 and 8 of the estrus cycle (Day 0 = day of estrus). Twenty-six Holstein cows with a dominant follicle were divided into 2 groups in which the dominant follicle was either removed (DFR group, n=13) by ultrasound-guided follicular aspiration or left intact (control group, n=13) on Day 8 of the estrus cycle. Superovulation treatment was initiated on Day 10. All donors were superovulated with injections of porcine FSH (Folltropin ™) twice daily with constant doses (total: 4000 mg) over 4 d. On the 6 th and 7 th injections of Folltropin, 30 mg and 15 mg of PGF 2α (Lutalyse) were given. Donors were inseminated twice at 12 h and 24 h after the onset of estrus. Embryos were recovered on Day 6 or 7 after AI. During superstimulation, the number of follicles 2 to 5 mm (small), 6 to 9 mm (medium) and ≥ 10 mm (large) was determined by ultrasonography on a daily basis. At embryo recovery, the number of corpora lutea (CL) was also determined by ultrasonography and blood samples were collected for analysis of progesterone concentration. Follicular growth during superstimulation was earlier in the DFR group than in the control group. The number of medium and large follicles was greater (P < 0.01) in the DFR group than in the control group on Days 1 to 2 and Days 3 to 4 of superstimulation, respectively. The numbers of CL (9.6 ± 1.1 vs 6.1 ± 0.9) and progesterone concentration (30.9 ± 5.4 vs 18.6±3.5 ng/mL) were greater (P < 0.05) in the DFR group than in the control group, respectively. The numbers of total ova (7.7 ±1.3 vs 3.9 ±1.0) and transferable embryos (4.6 ± 0.9 vs 2.3 ± 0.8) were also greater (P < 0.05) in the DFR group than in the control group, respectively. It is concluded that the removal of the dominant follicle 48 h before superstimulation promoted follicular growth, and increased ovulation and embryo production in Holstein cows.

Aspects of reproduction in the eastern rufous mouse lemur (Microcebus rufus) and their implications for captive management

AbstractThe eastern rufous mouse lemur is one of the smallest primate species. It inhabits the eastern rain forest of Madagascar. Its reproductive biology has not been examined because of its rarity in laboratories. We present the first data on reproduction and variation in reproductive success from a breeding colony of wild‐caught Microcebus rufus. The eastern rufous mouse lemur shows a seasonal change in testicular size and in the occurrence of estrus. Females had 2.5 cycles (range, one to four) per season. The estrous cycle length was 59 days (range, 51–66), the duration of vaginal opening during estrus was 7.5 days (range, 5–8), receptivity occurred on the third day of estrus, gestation length was 56.5 days (range, 56–57), litter size was two neonates (range, one to three). The frequency and duration of mating behavior varied widely among the pairs. Copulation seemed to occur on a single day per estrus within the first to fourth hour after light change to red light. In four cases (three pairs), copulation lasted between 15 and 240 seconds. Breeding success can be increased by choosing mates carefully. Microcebus rufus seems to be a seasonal breeder like its sibling species Microcebus murinus. In wild‐caught animals, males seemed to adapt quickly (first season) to the conditions of captivity, whereas in the females, individual variation (first to third season) in reproductive activity was observed. Air humidity of &gt;60% seems to facilitate the breeding success in wild‐caught pairs. First pregnancy and successful rearing of offspring occurred in the second and fourth year of captivity in two of three females. Wild‐caught eastern rufous mouse lemurs seemed to demonstrate variation in adapting to the conditions of captivity with regard to sex and individuality. Zoo Biol 20:157–167, 2001. © 2001 Wiley‐Liss, Inc.

The Fate of Corpora Lutea in the Cyclic Golden Hamster

Structural luteolysis shows striking interspecies differences. Morphological changes in the corpus luteum (CL) of the cyclic hamster have been studied alongside the potential involvement of known luteolytic hormones. Ovaries from intact Syrian golden hamsters killed at 1100 h on days 1 and 2 and at 1100 and 1700 h on days 3 and 4 of the estrous cycle were dissected for histological study. The day of ovulation, the day of estrus, was arbitrarily designated day 1 of the estrous cycle. Steroidogenic cells in the CL were scarcely luteinized on day 1 and reached full luteinization on day 2. On the morning of day 3, initial regressive changes (accumulation of lipid droplets, invasion by neutrophils, and accumulation of phagocytic cells) were observed. These regressive changes increased progressively and apoptotic cells as well as phagocytic cells containing phagocytized apoptotic cells were abundant on the evening of day 3. On the morning of day 4, apoptotic cells/bodies and phagocytic cells containing phagocytized material were extremely abundant throughout the CL. However, steroidogenic cells with intact nuclei and well-preserved blood vessels were also found. Surviving cells in the CL showed progressive morphological changes. These cells showed morphological features intermediate between luteal and interstitial cells in the evening of day 4 and were virtually indistinguishable from interstitial cells on day 1 of the following cycle. Additional animals were injected at 1100 h on day 2 with: (a) the dopaminergic agonist CB154 (0.4 mg) to block prolactin secretion, (b) the anti-estrogen LY117018 (1.6 mg) or the anti-androgen Flutamide (3 mg) to block estrogen or androgen receptors, respectively, and (c) progesterone (2 mg) to prevent the fall in serum progesterone concentrations. Ovaries from these animals were collected at 1700 h on day 3 and at 1000 h on day 4. The luteolytic process was not affected by any treatment. These data indicate that, in contrast to its close relatives (e.g., the rat), structural luteolysis in the hamster is independent of the apoptotic inducing luteolytic hormones. In addition, differences in the cellular mechanisms responsible for CL elimination were also present. In the hamster, part of the luteal cells do not undergo apoptosis and seemed to progress through another developmental path giving rise to interstitial-like cells.

Changes in distribution of androgen receptor during maturation of rat ovarian follicles.

Sequential changes in androgen receptor (AR) distribution were investigated in rat ovarian follicles during their physiological development. Mature female Wistar rats, exhibiting a regular 4-day oestrous cycle, were killed in succession on the day of oestrus, metoestrus, dioestrus, and pro-oestrus. Excised ovaries were submitted to immunohistochemical procedure in which polyclonal androgen receptor antibody, avidin-biotin-peroxidase complex, and DAB were used. Strong AR immunostaining was located predominantly in the nuclei of the granulosa layer of preantral and very early antral follicles, present in the ovaries at all stages of the oestrous cycle. At early oestrus a decline in AR was noted in the mural granulosa cells of presumably recruited early antral follicles. The decline involved the area of appearing pseudostratification. During metoestrus and dioestrus AR decline proceeded towards the antrum, but the antral regions connected with COC by strings of granulosa cells or lying in close proximity to COC were always strongly AR-positive. It was only on the day of pro-oestrus that AR was confined to COCs and a few antral cells bordering the antrum. These findings indicate that during the oestrous cycle AR decline starts in the mural granulosa cells of oestrous antral follicles beginning to differentiate and is completed at pro-oestrus, but even before ovulation it does not extend to COC. The persistence of AR immunostaining in the latter region suggests that androgens can play here a paracrine role especially before ovulation. Atretic follicles showed a different pattern of AR distribution, dependent on their stage of development and the advancement of this process.

GH and IGF-I binding sites in adipose tissue, liver, skeletal muscle and ovaries of feed-restricted gilts.

The influence of feed restriction on GH and IGF-I binding was examined in the cyclic gilt. IGF-1, IGFBPs, insulin and leptin levels in plasma were also measured. Twenty-four gilts whose oestrous cycle was synchronised were used. From day 3 to day 12, (with day 0 being the first day of oestrus) feed allowance was 240% and 80% of the energy requirements for maintenance for well-fed (H) and restricted gilts (L) respectively. Six gilts in each group were treated with an antagonist of GnRH but the treatment had no effect on any reported measurements. Blood and tissue samples were collected on days 12 and 13 respectively. L gilts lost live weight whereas H gilts gained weight. Plasma IGF-I, insulin and leptin concentrations were lower in L than in H gilts whereas plasma IGFBP levels were not affected by feed restriction. The specific binding of 125I-bGH to adipose tissue, liver, skeletal muscle and ovary membranes did not differ significantly between H and L gilts. Specific binding of 125I-IGF-I to hepatic membranes was higher in L than in H gilts whereas it did not differ between the two groups in the other tissue membranes.

Epidermal growth factor (EGF) in the goat uterus: immunohistochemical localization of egf and egf receptor and effect of egf on uterine activity in vivo

This study examined the distribution of immunoreactive epidermal growth factor (EGF) and EGF receptor (EGF-R) in the uterus and the effects of EGF on uterine activity in goats. Immunohistochemistry of EGF and EGF-R in the uteri showed distinct staining in the luminal and glandular epithelium and slight to moderate staining in the stromal and myometrial cells. To examine possible roles of the EGF system in the regulation of uterine activity, pressure changes in the intrauterine balloon were determined after intraluminal infusion of EGF into the uterine horn. Either at estrus or diestrus (9 to 14 days after the first day of estrus), treatment with 1 or 5 μg of EGF gradually reduced uterine activity, whereas infusion of the vehicle alone had no effect. The maximum reduction in uterine activity was seen 4 h after the treatment with 1 μg of EGF (40% to 45% reduction in the area surrounded by the contraction curve and its baseline), and the activity slowly returned thereafter. These results suggest that EGF in the uterus may play a role in regulating uterine activity in goats.

GABA levels within the medial preoptic area: effects of chronic administration of sodium valproic acid.

Sodium valproic acid (VPA) is a widely prescribed anticonvulsant medication that has been shown to interfere with pubertal maturation of the reproductive system, and induce endocrine abnormalities in adults, within a subset of the clinical population. While VPA's mechanism of action is still poorly understood, it may exert its anti-reproductive effects by enhancing GABAergic inhibition of the GnRH neuronal population within the medial preoptic area (mPOA). The purpose of this study was to determine if chronic administration of VPA alters GABA levels within the mPOA region. In Experiment 1, the mPOA, caudate, and arcuate nucleus regions were harvested from VPA-treated and control mice. Analysis of whole tissue content of GABA revealed that levels were lower in the caudate and arcuate nucleus regions of VPA-treated animals, whereas there were no group differences for the mPOA region. Collapsing across drug group, there was also a trend for males having overall higher levels of GABA as compared to females. In Experiments 2 and 3, mice were implanted with microdialysis probes within the mPOA region and sampled for extracellular GABA levels. Females (Exp. 3) were sampled either on diestrous, proestrous, or estrous. Results from males (Exp. 2) revealed that VPA enhanced extracellular GABA levels in the mPOA region compared with controls. However, GABA levels for both groups remained stable across the sampling period. Conversely, in Exp. 3, females showed cyclical release of GABA across the sampling period. For control females, GABA levels increased during the afternoon on all cycle days, but the rise on proestrus was smaller than on other cycle days. VPA-treated animals showed an overall reduction in GABA levels compared with controls. Furthermore, while GABA increased over sampling time on estrus and diestrus days of the cycle, there was not a significant rise in GABA on proestrus. These data indicate: (1) regional specificity in VPA effects upon GABA levels, (2) a sex difference in the effects of VPA on GABA levels within the mPOA, and (3) GABA levels increase on the afternoon of all days of the estrous cycle with VPA attenuating the rise seen on the afternoon of proestrus. These results provide evidence that VPA effects upon the reproductive axis may involve changes in GABA release, and that males and females show different patterns of neurochemical response to the drug.

Mating Season Aggression and Fecal Testosterone Levels in Male Ring-Tailed Lemurs (Lemur catta)

The challenge hypothesis (J. C. Wingfield, R. E. Hegner, B. G. Ball, and A. M. Duffy, 1990, Am. Nat. 136, 829–846) proposes that in birds, reptiles, and fish, “the frequency or intensity of reproductive aggression as an effect of T[estosterone] is strongest in situations of social instability, such as during the formation of dominance relationships, the establishment of territorial boundaries, or challenges by a conspecific male for a territory or access to mates” (p. 833). To determine the extension of this hypothesis to mammalian species, we tested predictions of the hypothesis in a nonpaternal, seasonal breeding, prosimian primate (ring-tailed lemurs, Lemur catta). Semi-free-ranging males were studied during periods of social stability (premating period) and instability (mating period). The annual mating season consists of several days during which males fight for access to promiscuous group females as each individually becomes sexually receptive for 1 day. Male rates of aggression were compared to fecal testosterone levels within premating and mating periods. In the premating period male rate of aggression was not significantly correlated with testosterone level. By contrast, during the mating season testosterone and aggression levels were positively and significantly correlated. However, on days just preceding estrus, male rate of aggression was not significantly correlated with testosterone, but on days of estrus, when aggressive challenges peaked sharply, testosterone and aggression were highly positively correlated. These results suggest that the challenge hypothesis applies to mammals as well as to birds, reptiles, and fish. In addition, elevations in testosterone were tightly circumscribed around days of estrus, suggesting a compromise between costs and benefits of elevated testosterone levels.

Effectiveness of lipopolysaccharide as an intrauterine immunomodulator in curing bacterial endometritis in repeat breeding cross-bred cows.

Antibiotics are usually used to combat microbial infections of the uterus, responsible for hindering establishment of pregnancy in cross-bred cows. The major disadvantages of antibiotics are: development of bacterial resistance, high costs and diminishing uterine defense mechanisms (UDM). As an alternative therapy, intrauterine application of Escherichia coli Lipopolysaccharide (E. coli LPS) as a uterine defense stimulator was used in this study in confirmed clinical cases of repeat breeding associated with bacterial endometritis. In the treated group (n=12), on the day of estrus, 100 microg of E. coli LPS dissolved in 30-ml sterile phosphate buffer saline (PBS) was infused intrauterine; while in the control group (n=12), only 30 ml of PBS was infused. Six-hour post-treatment, in the treatment group uterine washings showed a 100-fold increase in the total leucocytic count (TLC). Out of the cellular contents, more than 80% of the cells were recognised as neutrophils; above 60% were alive and their phagocytic activity was five bacteria/neutrophil. Such a cellular response was maintained until 72-h post-treatment. At the subsequent estrus period, the cervicovaginal mucus (CVM) became clear in 9 out of 12 cows (75%) and showed no bacterial growth. In the control group, similar micro-organisms were present in CVM of all the 12 cows before and after the PBS infusions. During the subsequent estrus, all nine cows with sterile CVM in the treatment group conceived while only one cow conceived from the control group. It was concluded that, administration of intrauterine E. coli LPS as single infusion in cows with bacterial endometritis stimulated UDM and cleared the infection within one estrous cycle, and thereby restoring fertility.

Effects of Prostaglandin F2α Treatment on the Behavior of Pseudopregnant Pigs in an Extensive Environment

In seminatural environments, prepartum sows leave the herd and construct a maternal nest (a dug out hollow lined with vegetation) prior to the birth of their piglets. The endocrine drives motivating this behavior are not understood, but may involve prostaglandin (PG) F2α. This study examined the effect of PGF2α treatment on the behavior of pseudopregnant gilts housed in a large enclosure. Pseudopregnancy was induced using 5 mg/ml estradiol valerate/day im from days 11 to 15 of the estrous cycle (first day of estrus = day 0). The gilts' behavior was recorded on a control day, during which no treatment was given, and a test day (= 45.9 ± 0.42 days of pseudopregnancy) when gilts received either 15 mg PGF2α (dinoprost: Lutalyse, Upjohn, Crawley, UK, n = 11) or 0.9% saline (n = 10) im at 11.00 h. PGF2α-treated gilts traveled further and were more frequently >10 m from the nearest pig than saline-treated animals. In the hour following injection, PGF2α-treated animals also showed increased frequencies of rooting and pawing the ground and stood for longer than saline-treated animals. However, gathering and carrying nest materials were not increased. These results suggest that PGF2α, given as a single dose to extensively housed gilts, initiated many, but not all, of the behaviors characteristic of prepartum nest building. The dose and duration of PGF2α treatment may have limited the observed behaviors. In addition, environmental feedback is likely to affect the degree to which some nest building behaviors are expressed.

Thyroid hormone deficiency before the onset of hearing causes irreversible damage to peripheral and central auditory systems.

Both a genetic or acquired neonatal thyroid hormone (TH) deficiency may result in a profound mental disability that is often accompanied by deafness. The existence of various TH-sensitive periods during inner ear development and general success of delayed, corrective TH treatment was investigated by treating pregnant and lactating rats with the goitrogen methimazole (MMI). We observed that for the establishment of normal hearing ability, maternal TH, before fetal thyroid gland function on estrus days 17-18, is obviously not required. Within a crucial time between the onset of fetal thyroid gland function and the onset of hearing at postnatal day 12 (P12), any postponement in the rise of TH-plasma levels, as can be brought about by treating lactating mothers with MMI, leads to permanent hearing defects of the adult offspring. The severity of hearing defects that were measured in 3- to 9-mo-old offspring could be increased with each additional day of TH deficiency during this critical period. Unexpectedly, the active cochlear process, assayed by distortion product otoacoustic emissions (DPOAE) measurements, and speed of auditory brain stem responses, which both until now were not thought to be controlled by TH, proved to be TH-dependent processes that were damaged by a delay of TH supply within this critical time. In contrast, no significant differences in the gross morphology and innervation of the organ of Corti or myelin gene expression in the auditory system, detected as myelin basic protein (MBP) and proteolipid protein (PLP) mRNA using Northern blot approach, were observed when TH supply was delayed for few days. These classical TH-dependent processes, however, were damaged when TH supply was delayed for several weeks. These surprising results may suggest the existence of different TH-dependent processes in the auditory system: those that respond to corrective TH supply (e.g., innervation and morphogenesis of the organ of Corti) and those that do not, but require T3 activity during a very tight time window (e.g. , active cochlear process, central processes).

Modulation of the truncated GAD25 by estrogen in the olfactory bulb of adult rats.

The aim of our study was to investigate the influence of gonadal steroids on the expression of different GAD isoforms. Here we show that, in addition to the adult GAD forms, the two embryonic splice variants of GAD67 mRNA and the truncated GAD25 are present in the adult rat olfactory bulb, a brain region with high synaptic plasticity, which has preserved some features of the developing brain. By Western blot analysis, we could demonstrate that the expression of the embryonic GAD25 is cyclic in females: its quantity is higher on estrus day. Furthermore, in ovariectomized animals 17-beta-estradiol treatment induced an increase of GAD25 within 3 h, reaching a maximum at 9-12 h. Our data are compatible with the interpretation that the embryonic GAD isoforms may play a role in the neuroplastic changes induced by sexual steroids.

Plasma insulin-like growth factor-I concentrations increase during the estrous phase in goats

The objective of this study was to characterize plasma insulin-like growth factor-I (IGF-I) profiles during the estrous cycle in goats. Frequent blood samples were drawn during the day of estrus and during the luteal phase on Day 10 after estrus, and plasma growth hormone (GH) and IGF-I profiles were examined. Then, daily blood samples were drawn throughout the estrous cycle or during induction of estrus by prostaglandin F 2α (PGF 2α) to further clarify the IGF-I profiles. GH was secreted in an episodic manner in the estrous and luteal phases in goats. There were no significant differences in the mean concentrations, pulse amplitude and pulse frequency of GH between the estrous and luteal phases. IGF-I concentrations during estrous phase were higher than those in the luteal phase (P < 0.05). Plasma IGF-I increased approximately two days before behavioral estrus, and the IGF-I peak was observed in accordance with the appearance of estrus. The elevated IGF-I levels then declined to basal values 4 to 5 days after estrus. When estrus was induced by PGF 2α, plasma IGF-I concentrations increased after treatment, and the concentration 2 days after treatment (day of appearance of behavioral estrus) was significantly higher than concentrations before treatment (P < 0.05). The elevated IGF-I levels then declined during the 3 days after treatment. These results indicate that plasma IGF-I concentrations increase during estrus in goats.

Induction of superovulation by inhibin vaccine in cyclic guinea-pigs

Experiments were conducted to determine whether neutralizing endogenous inhibin affects follicular development and ovulation rate in guinea-pigs. Eighteen female guinea-pigs bearing 4 week progesterone implants were divided into three groups. At 1 week after removal of the progesterone implants, the animals were given a s.c. injection of 1 ml placebo (saline in oil emulsion; control), or 25 or 50 micrograms inhibin vaccine three times at 4 week intervals. Blood samples were collected once a week throughout the experiment for measuring inhibin antibody titres. After the third injection of inhibin vaccine, blood samples and ovaries were collected on the morning of day 8 after the day of oestrus. Inhibin vaccine increased the ovulation rate in a dose-dependent manner (placebo: 4.2 +/- 0.4; 25 micrograms inhibin vaccine: 6.2 +/- 0.9; 50 micrograms inhibin vaccine: 9.8 +/- 0.9) without any effects on the duration of the oestrous cycle. The results also showed that active immunization against inhibin increased the number of atretic follicles of 300-399 microns in diameter on day 8 after ovulation. The present study is the first to show that the active immunization against inhibin may be a useful method for inducing multiple ovulation in guinea-pigs.