Search Results

You are looking at 1 - 8 of 8 items for

  • Author: T. M. Lee x
  • Refine by Access: All content x
Clear All Modify Search
Free access

T. M. Lee and M. K. McClintock

Summary. Female laboratory rats housed in controlled environments of two separate laboratories displayed seasonal variation in fecundity. Fecundity peaked between May and August and reached a trough between December and February, as measured by oestrous cycle length, variability and regularity, as well as number of animals mating and the percentage of litters reared to weaning. The percentage of mated animals giving birth remained constant throughout the year. Seasonal variations in the laboratory coincided with the seasonal cycle reported for wild rats in natural conditions. Several environmental variables, e.g. food, water, humidity and airborne factors, were evaluated as putative cues for seasonal variation.

Free access

L. R. Meek and T. M. Lee

Mating behaviour and litter production of female meadow voles (Microtus pennsylvanicus) housed in long (14 h light:10 h dark; long day; LD) or short (10 h light:14 h dark; short day; SD) photoperiods were monitored to determine whether the reduced birthrate of SD females resulted from a lack of copulation. All females mated, but fewer SD females gave birth. LD and SD females fell into three distinct groups based on mating latency. The rapid onset group (RO) mated between 7 min and 9 h after pairing, the intermediate onset group (IO) mated between 16–44 h and the late onset group (LO) mated after 58–262 h of male contact. Sixty-seven per cent of LD females were assigned to group RO, 27% to IO, and 6% to LO. In contrast, 30% of SD females were assigned to group RO, 35% to IO and 35% to LO. Fertility was predicted by mating latency. Sixty-nine per cent of RO, 93% of IO and 33% of LO animals gave birth. In a further experiment, a small-mouthed cup was added to the environment to serve as an escape for females wishing to avoid mating. Although females did not use the cup to escape male approaches, mating occurred in only 66% of SD females, but was observed in all LD females. In a final experiment, mating latency and litter production were recorded in primiparous LD and SD females initially observed in the first experiment. Group LO was eliminated in parous females; all primiparous LD and SD females mated within 48 h. Birthrates of LD (82%) and SD (73%) parous females were increased compared with birthrates of nulliparous females (LD = 65%; SD = 55%). These observations suggest that long day-length and parity increase spontaneous oestrus in meadow voles (50% of nulliparous and 80% of primiparous RO animals mated in less than 1.5 h). Females in the IO and LO groups are probably induced into oestrus, as normally described for arvicoline rodents, by direct male contact. Rapid mating (<48 h) predicts greater fertility for both LD and SD females, while delayed mating (>58 h) predicts low fertility. Parity decreases mating latency and increases litter production. Short day females produce fewer litters than LD females in equivalent groups.

Free access

T. M. Lee, L. Smale, I. Zucker, and J. Dark

Summary. Meadow voles born to dams kept in short days (SD) beginning 5 or 11 weeks before parturition (SD-5, SD-11) had less developed testes, gained weight more slowly and built larger nests than did young gestated and maintained in long days (LD). Pelage development was greater in SD than in LD young at 21 and 45 days of age. At weaning, SD-5 young had less dense fur and shorter guard hairs than did SD-11 young, indicating that the photoperiodic history of dams before insemination affects the post-natal pelage development of their progeny. Short daylengths experienced by dams before mating may facilitate winter preparedness of their offspring.

Free access

T. M. Lee, L. Smale, I. Zucker, and J. Dark

Summary. The influence of daylength on body mass and food intake of pregnant and lactating voles was tested by comparing animals housed in long versus short day-lengths. Pregnancy rates were approximately 50% in long-day females and in voles kept in short days beginning 2 weeks before mating, but were significantly lower in voles preadapted to short days for 8 weeks before mating. Body mass and food intake increased substantially during pregnancy and lactation and the magnitude of the increase was unaffected by daylength; by contrast, body weight was significantly reduced in non-impregnated voles kept in short as compared to long days. The suppressive effects of short photoperiods on body weight were completely counteracted during pregnancy and lactation. Voles that breed during the short days of winter face extreme energetic challenges but the advantages of early breeding appear to justify the costs.

Free access

T. Jung, J. Fulka Jr, C. Lee, and R. M. Moor

In vitro maturation of cumulus enclosed and denuded pig oocytes was reversibly inhibited by the protein kinase inhibitor genistein. The half-maximal effect on maturation was observed at 40 μg ml−1. Genistein inhibited total protein phosphorylation and synthesis with the same does–response relationship (ED50: 40 pg ml−1). Protein phosphorylation and synthesis patterns were changed by effective concentrations of genistein. Pig oocytes were sensitive to genistein during the first 12 h of in vitro maturation. This genistein sensitive period corresponds closely with the period of sensitivity to the protein synthesis inhibitor cycloheximide. Whereas the inhibition of protein synthesis affects only nuclear membrane breakdown and not chromatin condensation, genistein inhibits both events. The results of these experiments suggest that protein phosphorylation and synthesis play major roles during pig oocyte maturation in vitro. It is concluded that genistein inhibited protein phosphorylation is a regulator of chromatin condensation, whereas both new protein synthesis and phosphorylation appear to be required for nuclear membrane disassembly. Caution about this second conclusion is, however, necessary because of the dual action of genistein on both protein phosphorylation and indirectly on protein synthesis.

Free access

T. M. Lee, L. Smale, I. Zucker, and J. Dark

Summary. Pregnancy and lactation inhibited moult into winter pelage in voles maintained in short daylengths; development of a winter pelage was, however, greatly accelerated once the short-day dams weaned their litters. The presumed elevation of prolactin titres during lactation appears to mask full development and expression of pelage changes induced by short daylengths. Nest-building behaviour, by contrast, was increased in response to short photoperiods and was further augmented during lactation and may thereby facilitate thermoregulation in short-day dams that do not develop a winter pelage.

Free access

L. J. Cummins, T. O'Shea, B. M. Bindon, V. W. K. Lee, and J. K. Findlay

Summary. The inhibin content of ovaries collected from highly fecund Booroola Merino ewes was only one third that of control Merino ewes. Ovariectomized ewes of both strains were treated with charcoal-treated ovine follicular fluid for 2 days. A dose-dependent effect on plasma FSH was observed: maximum FSH suppression was observed on the day after the last injection of follicular fluid. Ewes receiving the highest dose of follicular fluid (total dose 72 000 units of inhibin) had FSH levels depressed to only 8% of pre-treatment levels. Booroola ewes showed FSH suppression 1 day earlier than control ewes but otherwise the responses of the two strains to follicular fluid were similar. Plasma LH levels were only slightly depressed with the highest dose of follicular fluid. These results suggest that the feedback relationship of inhibin and FSH in Booroola ewes may be set differently from that in control ewes and this may contribute to the difference in ovulation rate between ewes of the two genotypes.

Free access

C. C. Miller, R. A. Fayrer-Hosken, T. M. Timmons, V. H. Lee, A. B. Caudle, and B. S. Dunbar

Summary. This study was designed to explore the composition of the equine zona pellucida (EZP) by one- and two-dimensional polyacrylamide gel electrophoresis (1D- and 2D-PAGE), silver staining and immunoblotting techniques. Antral follicles palpable on frozen–thawed equine ovaries were aspirated with a needle and syringe, and the resultant follicular fluid, cellular material and oocytes were pooled. Oocytes were placed in Petri dishes, moved by narrow-bore pipette to droplets of phosphate-buffered saline (PBS) and mechanically cleaned of cumulus cells. The EZP from these collected oocytes was solubilized, and then analysed by 1D- and 2D-PAGE. Silver stained 2D-PAGE of the EZP revealed the presence of three EZP glycoprotein families of apparent molecular mass ranges of 93–120 kDa, 73–90 kDa and 45–80 kDa. Immunoblot analysis of EZP glycoproteins resolved by 2D-PAGE using rabbit antisera against pig zonae pellucidae (RαHSPZ) confirmed the presence of three EZP glycoprotein families and established the existence of common epitopes between equine and porcine ZP glycoproteins. Further immunodetection using 2D-PAGE-separated glycoproteins illustrated that the 45–80 kDa family is recognized by the monoclonal antibody R5, developed against the porcine ZP glycoprotein of molecular mass 55–120 kDa. Guinea-pig antiserum against endo-β-galactosidase-treated rabbit ZP 55 kDa glycoprotein (R55K), which specifically recognizes the rabbit ZP glycoprotein with the lowest molecular mass, also recognized the EZP 45–80 kDa glycoprotein family. Guinea-pig polyclonal antisera developed against total heat-solubilized rabbit ZP (GPαHSRZ) recognized the 73–90 kDa EZP glycoprotein family exclusively. After heat solubilization and treatment of EZP with endo-β-galactosidase to remove polylactosaminoglycans, silver stained 1D-PAGE again demonstrated the presence of three glycoproteins with apparent molecular masses of 60, 75 and 90 kDa. The partially deglycosylated 60 kDa equine glycoprotein is recognized on immunoblot by the monoclonal antibody R5; the 75 kDa EZP glycoprotein is recognized by GPαHSRZ; and all three EZP glycoproteins separated by 1D-PAGE are recognized by RαHSPZ. These data add further support to the concept of cross-species zona pellucida glycoprotein antigenicity.

Keywords: horse; zona pellucida; polyacrylamide gel electrophoresis; antigenicity; glycoproteins