Correlation between estrus and reduced light avoidance in mice

Female CD-1 mice showed reduced light avoidance at estrus compared to nonestrus in two experiments designed to control for possible effects of changes in general activity. Estrous mice were quicker to enter a light chamber from a dark chamber and slower to enter a dark chamber from a light chamber, than nonestrous mice. Also, estrous mice reared up on their hind legs more frequently than nonestrous mice in the light chamber, and there was no difference between estrous and nonestrous mice in motor activity in the dark chamber. These findings, along with previous findings of reduced shock avoidance at estrus, suggest a general decrement in avoidance motivation which may be adaptive to the process of mating and which does not appear to be secondary to a change in activity level.     

Relationship of declines in grain consumption and milk yield to estrus in dairy cattle

A retrospective study was done to determine if a reduction in daily grain consumption or decline in daily milk yield were accurate indicators of estrus in 25 Holstein cows. A computer automatically identified all cows that left more than 10% of their daily grain allocation in the feed stall or that gave less than 85% of their most current 7-d daily average milk yeild. By retrospectively analyzing breeding records, grain refusal and milk declines were identified as either occurring in conjunction with estrus or nonestrus. Declines in grain consumption and milk yield were frequently associated with estrus, but many cows in estrus did not exhibit such declines. While such declines hold promise as estrous detection aids, it was concluded that refusals of daily grain allocation or declines in daily milk yield were not sufficiently accurate to supplant other methods of estrous detection in dairy cattle.     

Cannulation of the equine oviduct and chemical analysis of oviduct fluid

Siliconized rubber tubes were used to cannulate one oviduct in 7 mares, and secretions were collected in a polycarbonate container located externally, in the region of the left paralumbar fossa. Secretion rates were recorded daily during the estrous cycle. Concentrations of calcium, magnesium, sodium, potassium, inorganic phosphorus and glucose were determined in the oviduct fluids secreted throughout the estrous cycle. Secretion rates were greatest during estrus (days 1-9), with a significant decrease (P<.01) noted during nonestrus (days 10-21). Concentrations of all constitutents measured were low during estrus, with a marked elevation in concentration during the nonestrus period. Histologic examination of oviducts following long-term cannulation demonstrated infiltration of lymphocytes, plasma cells, and small areas of degenerated epithelium.     

Identification and content of insulin-like growth factors in porcine oviductal fluid.

Oviductal fluid (OvF) was collected from gilts by indwelling catheters during the estrous cycle and analyzed for content of insulin-like growth factors (IGF-I, IGF-II). Group 1, composed of 9 gilts in a summer environment near a boar, yielded mean daily fluid volumes of 1.18 +/- 0.16 ml during estrus and 0.69 +/- 0.03 ml post-estrus. Group 2, composed of 7 gilts in a moderate-temperature, light-regulated room, yielded 1.20 +/- 0.18 ml during estrus and then OvF flow essentially stopped. Serum samples were also collected 2 times daily during the cycle and analyzed along with the OvF for IGF-I and IGF-II. Serum was also analyzed for estradiol-17 beta (E2). For group 1, OvF content (concentration x fluid volume) of IGF-I and IGF-II was greater (p less than 0.05) at estrus than pre- and post-estrus. Daily mean content values (ng/day) for IGF-I and IGF-II during peri-estrus were 30.9 +/- 6.3 and 62.2 +/- 12.3, respectively. During nonestrus, values were 6.8 +/- 6.3 and 11.7 +/- 12.3, respectively. For group 2, OvF content of IGF-I and IGF-II during estrus was similar to that of group 1. Whereas IGF content differed between estrus and nonestrus periods, IGF concentrations were similar (p greater than 0.05), a finding that results from the difference in OvF produced. Compared with OvF concentrations of IGF for a given pig, blood plasma concentrations of IGF-I and IGF-II were 2- to 5-fold higher in the plasma sample collected the same day.(ABSTRACT TRUNCATED AT 250 WORDS)     

Pregnancy rates and sexual behavior under pasture breeding conditions in mares

Pony mares (n=480) and 16 stallions were assigned to four herds of 60 mares and one stallion (large herds) and to 12 herds of 20 mares and one stallion (small herds). The stallions remained with the herds continuously for all of the large herds and seven of the small herds. In the five remaining small herds the stallion was put into a herd for three hours every two days for 12 observation periods. Pregnancy rates and day of ovulation were estimated by size of embryonal enlargements. Mean pregnancy rates of 51% and 54% were obtained in the small herds and 42% in the large herds during a 48-day period (equivalent to two estrous cycles). Pregnancy rates for herds with the stallion present continuously were higher (P<0.01) for the small herds than for the large herds for days 1-24 (42% versus 19%). There was no effect of herd size on number of mares becoming pregnant per herd on days 1-24, but more mares (P<0.01) became pregnant during days 25-48 in the large herds (13.2 mares per herd versus 1.8). In the herds in which the stallion was present intermittently, the number of times that the stallion rebred the same mare when more than one mare was in estrus was greater (P<0.01) than what would be expected to occur by chance (observed, 21%; expected, 11%). Repeated breeding of the same mare seemed related to the availability or activity of the mare, since such mares more frequently followed and positioned themselves in the vicinity of the stallion. Most of the interferences by a mare which involved keeping the stallion and another mare apart were directed at the mare, whereas most of the interferences during mounting were directed at the stallion (P<0.01). Mares were more likely (P<0.01) to interfere when in estrus than when in nonestrus. When interfering mares were in nonestrus, their hostility was usually directed at the stallion (92%), whereas when in estrus their interference was more frequently directed at a mare (73%, P<0.01).     

Prenatal stress alters reproductive responses of rats in behavioral estrus and paced mating of hormone-primed rats

Adult female offspring of dams exposed to gestational stress (prenatal stress, PNS) may show altered reproductive behavior, exploration in novel environments, and/or social interactions than do their non-PNS counterparts. These behavioral differences may be more readily observed in a seminatural, paced mating paradigm, in which females have greater control of their sexual contacts, than in a standard mating situation. Adult offspring of dams exposed to restraint and lights for 45 min on Gestational Days 14-20 (PNS) were compared with those not subjected to stress (non-PNS, control condition). The motor, reproductive, and sociosexual behaviors of hormone-primed (Experiment 1) or cycling adult offspring in behavioral estrus (Experiment 2) were examined following 20 min of restraint stress under bright lights (postnatal stress). Hormone-primed PNS rats displayed less motor behavior in a novel arena than did non-PNS rats. In a standard mating test, hormone-primed PNS females tended to be more aggressive toward the male than were non-PNS rats. In a seminatural mating situation, hormone-primed PNS females showed increased avoidance behavior, such as longer latencies to the initial intromission, greater return latencies following mounts and intromissions, and more exiting subsequent to mounts and intromissions, than did non-PNS rats. PNS rats in behavioral estrus had decreased incidence and intensity of lordosis, and fewer solicitation behaviors, in both standard or paced mating situations, in which latency to and number of mounts were also increased. Thus, hormone-primed PNS rats exposed to restraint showed more avoidance behaviors in paced mating situations, while cycling PNS rats in behavioral estrus had greater disruption of reproductive responses in standard or paced mating paradigms than did non-PNS control rats.     

Identification of putative pheromones in bovine (Bos taurus) faeces in relation to estrus detection

Ten different volatile compounds were detected in bovine faeces using three chromatograms. The chemical profiles of estrus faeces were distinguished significantly from other phases by the presence of three specific substances, viz. acetic acid and propionic acid and 1-iodo undecane. The estrus specific synthetic compounds were rubbed onto the genital region of nonestrus animals (dummy cows), and the bulls were allowed to sniff the genital region and observed sexual behaviours. The statistical significance was higher (P<0.001) in bulls exhibiting repeated flehmen and mounting behaviours towards the mixture of acetic acid, propionic acid and 1-iodo undecane. The bioassay revealed that the fatty acids viz., acetic acid; propionic acid and 1-iodo undecane produced in faeces during estrus appear to be estrus specific. The results suggest that these compounds may be used as estrus indicator in cow, probably involved in bovine biocommunication.     

Comparison of controlled internal drug release device and melengesterol acetate as progestin sources in an estrous synchronization protocol for beef heifers

The objectives of this experiment were to compare estrous synchronization responses and AI pregnancy rates of beef heifers using protocols that included either CIDR or MGA as the progestin source. The hypotheses tested were that: (1) estrous synchronization responses after (a) progestin removal, and (b) PGF(2alpha); and, (2) AI pregnancy rates, do not differ between heifers synchronized with either progestin source. At the start of the experiment (Day 0) in both years, heifers were assigned randomly to receive, MGA supplement for 14 days (MGA-treated; n=79) or CIDR for 14 days (CIDR-treated; n=77). On Day 14 progestin was removed and heifers were observed for estrus up to and after PGF(2alpha) on Days 31 and 33 for CIDR-treated and MGA-treated heifers, respectively. Heifers that exhibited estrus within 60h after PGF(2alpha) were inseminated by AI 12h later; the remaining heifers were inseminated at 72h after PGF(2alpha) and given GnRH (100mug). More (P<0.05) CIDR-treated heifers exhibited estrus within 120h after progestin removal than MGA-treated heifers. Intervals to estrus after progestin removal were shorter (P<0.05) for CIDR-treated heifers than MGA-treated heifers. More (P<0.05) CIDR-treated heifers exhibited estrus and were inseminated within 60h after PGF(2alpha) than MGA-treated heifers. Pregnancy rates did not differ (P>0.10) between MGA-treated (66%) and CIDR-treated (62%) heifers. In conclusion, the use of CIDR as a progestin source in a 14-day progestin, PGF(2alpha), and timed AI and GnRH estrous synchronization protocol was as effective as the use of MGA to synchronize estrus and generate AI pregnancies in beef heifers.     

Effects of early malnutrition on Swiss white mice: avoidance learning after rearing in large litters

Mice were undernourished by rearing in litters of 20 pups per mother, weaned onto stock diet and their shuttle-box avoidance performance measured at 2 months of age. The mice from these large litters learned the avoidance response more slowly than controls (mice reared in litters of 5). In a second experiment, avoidance performance was measured after nutritional rehabilitation until 2, 4 or 6 months old. No significant improvement was observed in the previously malnourished mice. In the controls, performance was high at 2 and 4 months but by 6 months had fallen almost to the same level as the test group.     

The ACTH/MSH (4-9) analog Org2766 improves retrieval of information after a fimbria fornix transection

The fimbria fornix of male Wistar rats was transected unilaterally after they had been successfully trained in the Morris maze and the passive avoidance task. Sham-operated and lesioned animals were treated either with Org2766 or saline for two weeks. Subsequently, the performance of all groups was tested again starting two days after the last treatment. The lesioned animals showed a deficit in performance in both tasks, indicating interference of the lesion with retrieval of information. Org2766 improved the poor performance of the lesioned animals in the Morris maze, but not in the passive avoidance task.     

Infusion of methylphenidate into the basolateral nucleus of amygdala or anterior cingulate cortex enhances fear memory consolidation in rats

The psychostimulant methylphenidate (MPD; also called Ritalin) is a blocker of dopamine and norepi-nephrine transporter. It has been clinically used for treatment of Attention Deficit and Hyperactivity Disorder (ADHD). There have been inconsistent reports regarding the effects of systemically adminis-tered MPD on learning and memory, either in animals or humans. In the present study, we investigated the effect of direct infusion of MPD into the basolateral nucleus of amygdala (BLA) or the anterior cin-gulate cortex (ACC) on conditioned fear memory. Rats were trained on a one-trial step-through inhibi-tory avoidance task. MPD was infused bilaterally into the BLA or the ACC, either at ‘0’ or 6 h post-training. Saline was administered as control. Memory retention was tested 48 h post-training. In-tra-BLA or intra-ACC infusion of MPD ‘0’ h but not 6 h post-training significantly improved 48-h memory retention: the MPD-treated rats had significant longer step-through latency than controls. The present results indicate that action of MPD in the BLA or the ACC produces a beneficial effect on the consoli-dation of inhibitory avoidance memory.     

The Role of the δ GABA(A) Receptor in Ovarian Cycle-Linked Changes in Hippocampus-Dependent Learning and Memory

The δ subunit of the GABA_AR is highly expressed in the dentate gyrus of the hippocampus where it mediates a tonic extrasynaptic inhibitory current that is sensitive to neurosteroids. In female mice, the expression level of the δ subunit within the dentate gyrus is elevated in the diestrous relative to estrous phase of the estrous cycle. Previous work in our lab found that female δ-GABA_AR KO mice showed enhanced hippocampus-dependent trace but normal hippocampus-independent delay fear conditioning. Wild-type females in this study showed a wide range of freezing levels, whereas δ-GABA_AR KO mice expressed only high levels of fear. We hypothesized that the variability in the wild-type mice may have been due to estrous cycle-mediated changes in the expression of the δ-GABA_AR, with low levels of freezing in mice that were in the diestrous phase when dentate gyrus tonic inhibition is high. In the present study we tested this hypothesis by utilizing contextual, delay, and trace fear conditioning protocols in mice that were trained and tested in either the diestrous or estrous phases. Consistent with our hypothesis, we found a significant impairment of hippocampus-dependent learning and memory during diestrus relative to estrus in wild-type mice and this impairment was absent in δ-GABA_AR mice. These findings argue that the δ-GABA_AR plays an important role in estrous cycle-mediated fluctuations in hippocampus-dependent learning and memory.     

Reproductive performance of ewe lambs from ewes from different selection practices with or without induced estrus

Three groups of ewe lambs born in May (experiment 1; n=211) or April (experiment 2; n=174) were used to evaluate the effects of selection line and induction of estrus on pregnancy rate. Experiment 1 was a single factor experiment with induction of estrus as the main effect. In early December, May-born Targhee (n=82) and Rambouillet x Targhee (n=129) ewes were randomly assigned within body weight to one of two treatment groups: control or induction of estrus. Experiment 2 was designed in a 2x2 factorial array with the main effects of induction of estrus or selection line. In early November, April-born Targhee lambs (n=174) from two distinct selection lines were either treated as controls or received an estrus induction treatment. The two lines included an unselected control line of randomly bred ewes and a line that had been selected since 1976, based on the weight of lamb weaned. Ewes from each line were randomly assigned within body weight to one of the treatment groups. In experiments 1 and 2, estrus was induced using MAP pessaries. Pessaries were inserted for 12 days. At the time of pessary removal, ewe lambs received 400 IU eCG i.m. All ewe lambs were bred in multi-sire pens. Pregnancy rate and fetal numbers were determined either by lambing data or real-time ultrasound. Body weight, lambing date and fetal numbers were analyzed by GLM, and remaining variables were analyzed by CATMOD. For experiment 1, estrus induction increased (P<0.01) pregnancy rates (61 versus 31%) and number of fetuses estimated by real-time ultrasound (79 versus 35%) compared to control ewe lambs. Pregnancy rate and fetal number were increased (P<0.01) for the 1st year compared to the 2nd year. For experiment 2, estrus induction tended to increase (P<0.07) pregnancy rate, and pregnancy rate differed (P<0.01) between selection lines. Estrus induction increased (P<0.05) fetal numbers (0.96) compared to controls (0.77). Fetal numbers were greater (P<0.01) for the selected line (1.06) compared to random bred controls (0.67). Average date of lambing was earlier in both experiments for the estrus-induced ewe lambs compared to controls. These results indicate that induction of estrus can be recommended if increased reproduction is desired for ewe lambs.     

MHC-mediated fetal odourtypes expressed by pregnant females influence male associative behaviour

Mice can recognize one another by individually characteristic phenotypic body odours (odourtypes) that reflect their genetic constitution at the highly polymorphic major histocompatibility complex (MHC) of genes on chromosome 17. We have shown previously that MHC-determined odours are produced by fetuses: house mice, Mus domesticus, can be trained to discriminate between genetically identical pregnant females carrying 9-18-day-old fetuses of differing MHC type. Theoretically, it should be possible for a mouse to determine the MHC type of the sire based on the odourtype of the pregnant female. In the current study we investigated whether untrained male mice show spontaneous discrimination between such pregnant mice. In experiment 1, sexually inexperienced male mice spent more time near pregnant females that carried fetuses most genetically different from the males themselves. Experiment 2, designed to evaluate possible experiential effects on this preference, tested males that were cohabiting and had impregnated a female that was either genetically identical to the test male (excepting X and Y chromosomes) or differed from him only at the MHC. Males in the former case performed virtually identically to those tested in experiment 1. In contrast males in the latter group did not display this preference. These studies reveal that among untrained male mice, fetal MHC type influences choice behaviour presumably via fetal odourtypes expressed in maternal secretions/excretions and that previous housing and/or mating experience modulates male choice. Copyright 2000 The Association for the Study of Animal Behaviour.     

Slight influence of the estrous cycle stage on the mucosal and systemic specific antibody response induced after vaginal and intraperitoneal immunization with protoxin Cry1Ac from Bacillus thuringiensis in mice

Since the immune response appears to be variable according to the hormonal stage of the mammalian female, the aim of this study was to determine whether estrous cycle stage modifies the mucosal and systemic immune responses induced by intraperitoneal and vaginal immunization of mice with protoxin Cry1Ac. We tested the influence of three immunizations on the specific antibody response elicited at estrus and diestrus, that were the same estrous cycle stages at which the antigen was applied. Both intraperitoneal and vaginal immunization of mice with Cry1Ac either at estrus or diestrus induces specific antibody responses at serum, vagina and large intestine. The stage of the estrous cycle have little or non influence in the magnitude of the response induced, since only at serum the IgM was slightly higher at estrus than at diestrus by both routes. At the large intestine only the IgA response elicited via the intraperitoneal route changed, being higher at diestrus, whereas at the vagina IgA response induced did not change significantly due to the cycle stage. Present results suggest that Cry1Ac may be used as an antigen carrier as it can elicit antibody responses at systemic level and at several mucosal sites including the vagina that are not modified significantly throughout the reproductive cycle.     

Sexual cycle period and resistance of mice to acute experimental hypoxia]

Variations of survival to an acute hypoxia (nitrogen) were studied, in 200 females, OF1, SPF mice, 72 days old, in groups of 10, at different periods of their estrus cycle, which were evidenced by vaginal smears. In mice which were in diestrus since 3-4 following days, the hypoxic survival (27.27%) was statistically less than in mice which were in estrus (58.00 %) or at the beginning of the diestrus (53.85 %).     

Gut T1R3 sweet taste receptors do not mediate sucrose-conditioned flavor preferences in mice

Most mammals prefer the sweet taste of sugars, which is mediated by the heterodimeric T1R2+T1R3 taste receptor. Sugar appetite is also enhanced by the post-oral reinforcing actions of the nutrient in the gut. Here, we examined the contribution of gut T1R3 (either alone or as part of the T1R3+T1R3 receptor) to post-oral sugar reinforcement using a flavor-conditioning paradigm. We trained mice to associate consumption of a flavored solution (CS+) with intragastric (IG) infusions of a sweetener, and a different flavored solution (CS-) with IG infusions of water (23 h/day); then, we measured preference in a CS+ vs. CS- choice test. In experiment 1, we predicted that if activation of gut T1R3 mediates sugar reinforcement, then IG infusions of a nutritive (sucrose) or nonnutritive (sucralose) ligand for this receptor should condition a preference for the CS+ in B6 wild-type (WT) mice. While the mice that received IG sucrose infusions developed a strong preference for the CS+, those that received IG sucralose infusions developed a weak avoidance of the CS+. In experiment 2, we used T1R3 knockout (KO) mice to examine the necessity of gut T1R2+T1R3 receptors for conditioned flavor preferences. If intact gut T1R3 (or T1R2+T1R3) receptors are necessary for flavor-sugar conditioning, then T1R3 KO mice should not develop a sugar-conditioned flavor preference. We found that T1R3 KO mice, like WT mice, acquired a strong preference for the CS+ paired with IG sucrose infusions. The KO mice were also like WT mice in avoiding a CS+ flavor paired with IG sucralose infusions These findings provide clear evidence that gut T1R3 receptors are not necessary for sugar-conditioned flavor preferences or sucralose-induced flavor avoidance in mice.     

左炔诺孕酮炔雌醚片所致动情期同步的雌性小鼠的研制

目的　促使NIH雌性小鼠的动情期同步出现 ,同时避免其与雄性小鼠交配后受孕。方法　用左炔诺孕酮炔雌醚片灌胃 ,并以已烯雌酚作为对照药 ,比较雌性小鼠动情期同步出现的几率 ,寻找出制作同步动情期的雌性小鼠的最佳造模方法。结果　发现左炔诺孕酮炔雌醚片的灌胃剂量为人体的 2倍 ,且每 5天灌胃一次 ,雌性小鼠的动情期同步几率就可以达到 80 %或以上。结论　本研究为房室不节致肾虚证雄性小鼠模型所需同步动情期雌性小鼠的制作提供了较为简便的方法。     

Effectiveness of administration of gonadotropin-releasing hormone at Days 11, 14 or 15 after anticipated ovulation for increasing fertility of lactating dairy cows and non-lactating heifers

One strategy for improving fertility in cattle is mid-cycle administration of GnRH to increase progesterone secretion and delay luteolysis. This strategy might be especially useful during hot weather because heat stress increases uterine prostaglandin release and reduces development of the elongating embryo. A series of experiments was conducted to test the efficacy of GnRH for increasing fertility. There was no effect of administration of 100 microg GnRH at Day 11 after anticipated ovulation on pregnancy rates in virgin heifers subjected to timed artificial insemination (TAI) during the summer. Similarly, there was no beneficial effect of administration of GnRH at Day 11 after anticipated ovulation on pregnancy rates of lactating cows subjected to TAI in summer and winter. Three experiments tested effects of injection of GnRH at Days 14 or 15 after anticipated ovulation on pregnancy rates of lactating cows. The first experiment used 477 lactating cows subjected to TAI. Cows receiving GnRH at Day 14 had higher pregnancy rates in both summer and winter than cows receiving vehicle (20.3 versus 12.7%, P<0.02). When this experiment was repeated during summer with 137 cows, there was a negative effect of GnRH treatment at Day 14 on pregnancy rate. In the third experiment, lactating cows during summer were inseminated at detected estrus and cows were assigned to treatment with either GnRH or vehicle at Days 14 or 15 after insemination. Pregnancy rates were 25.6% (32/125) for cows receiving vehicle, 20.7% (19/92) for cows receiving GnRH at Day 14, and 20.3% (16/79) for cows receiving GnRH at Day 15. In conclusion, GnRH administration at Days 11-15 after anticipated ovulation or estrus did not consistently increase pregnancy rates in either cool or warm seasons.     

Effects of leptin on memory processing

Leptin is a peptide hormone secreted by adipose tissue. Studies have shown that leptin crosses the blood-brain barrier (BBB) by a saturable transport system where it acts within the hypothalamus to regulate food intake and energy expenditure. Leptin also acts in the hippocampus where it facilitates the induction of long-term potentiation and enhances NMDA receptor-mediated transmission. This suggests that leptin plays a role in learning and memory. Obese mice and rats, which have leptin receptor deficiency, have impaired spatial learning. In disease states such as diabetes, humans and animals develop leptin resistance at the BBB. This suggests that low leptin levels in the brain may be involved in cognitive deficits associated with diabetes. In the current study, the effects of leptin on post-training memory processing in CD-1 mice were examined. Mice were trained in T-maze footshock avoidance and step down inhibitory avoidance. Immediately after training, mice received bilateral injections of leptin into the hippocampus. Retention was tested 1 week later in the T-maze and 1 day later in step down inhibitory avoidance. Leptin administration improved retention of T-maze footshock avoidance and step down inhibitory avoidance. Leptin administered 24 h after T-maze training did not improve retention when tested 1 week after training. SAMP8 mice at 12 months of age have elevated amyloid-beta protein and impaired learning and memory. We examined the effect of leptin on memory processing in the hippocampus of 4 and 12 months old SAMP8 mice. Leptin improved retention in both 4 and 12 months old SAMP8 mice; 12 month SAMP8 mice required a lower dose to improve memory compared to 4 months SAMP8 mice. The current results indicate that leptin in the hippocampus is involved in memory processing and suggests that low levels of leptin may be involved in cognitive deficits seen in disease states where leptin transport into the CNS is compromised.