Biomedical subjects
Publications and source records attributed to C E Adams.
Observations made during these investigations agree with the findings of various authors concerning atresia and follicular growth. In addition the results demonstrate that it is possible to induce the resumption of meiosis in rabbit oocytes without ovulation. This will be a useful tool for further investigations of changes in the chromosomal events during preovulatory ageing.
Standard autoradiographic tracing methods which employed intracortical injections of 3H-leucine were used to describe the time course of development in those components of the corticopontine system which originate in sensorimotor (SM) or visual (VIS) cortices. These studies were performed using male or female pigmented rats ranging in age from 1 to 24 days (birth = day 0). Labeled axons could easily be recognized within the cerebral peduncle at the level of the basilar pons on postnatal day 1 following either an SM or a VIS cortical injection. Labeling over the basilar pontine neuropil suggestive of axonal ingrowth could also be seen on day 1 following SM injections but not until day 3 in cases with VIS injections. During the latter part of the first postnatal week, both SM and VIS axon terminal fields were established in the pontine neuropil in locations generally similar to those described in the adult. However, at this time they occupied a larger area and appeared more diffusely organized than in the adult. Subsequently during the second postnatal week, both SM and VIS projection fields gradually became more focused and circumscribed until by day 16 in the case of the SM system, and day 18 for the VIS projection, an adultlike configuration was attained. At no time during development was there any evidence of a more substantial contralateral projection than that described for the adult. Correlation of these events with previous Golgi observations and ongoing electron microscopic studies on pontine synaptogenesis suggest that the focusing or constriction of corticopontine axon terminal fields might be the result of a selective degeneration process in which the presynaptic (corticopontine axon) and postsynaptic (basilar pontine neurons) elements both play an active role. Furthermore, the absence of a stage in development characterized by an increase in the density of the contralateral component of the projection confirms the interpretation of earlier studies which suggested that the aberrant contralateral corticopontine projections observed following neonatal cortical lesions were the result of sprouting from the intact corticopontine system and not due to failure of retraction in one component of a system which in fact distributes bilaterally for a time during development.
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The effectiveness of 200 micrograms oestradiol benzoate (ODB) given at various times following ovulation, to overcome a 3-4-day difference in ovulation times between donor and recipient was examined. In approximately half of the recipients in which the interval from the administration of human chorionic gonadotrophin (hCG) to ODB was 2 days, some of the eggs implanted. With a 4-day interval, however, neither implantations nor degenerate blastocysts were found at autopsy on days 11 or 12 in recipients of either tubal or uterine eggs.
Following injections of tritiated leucine restricted to occipital (visual) regions of cerebral cortex during the first postnatal week (days 3--6), labeled corticofugal axons were followed caudally through the pons, medullary pyramid, pyramidal decussation and into the cervical spinal cord. However, when similar injections were made into visual cortex during the second postnatal week, labeled corticofugal axons could not be traced beyond mid-pontine levels where abundant axon terminal labeling was evident in the basilar pontine nuclei. Since axonal labeling did not subsequently appear at levels caudal to the pons during later stages of development or in the adult, it is suggested that the contribution to the corticospinal system made by visual cortical axons in the first postnatal week is a transient connection which is eventually lost either by a process of selective axon collateral elimination or cell death.
The growth and reproductive performance of rabbits reared on diet 18 and transferred to diet R14 (low protein/energy ratio) for (a) 3-4 weeks prior to mating or (b) 4 weeks prior to mating and throughout pregnancy were examined. Observations are presented on bodyweights, size and colour of the vulva and mating behaviour, pregnancy rate, and neonatal mortality. No significant differences were noted in comparison with 'controls' receiving Diet 18.
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Rabbits, 5-29 days pregnant, were placed for 2 h either in or near a machine designed to simulate transport, which exposed them to vibration stress and sound. There was no apparent effect on the maintenance of pregnancy, gestation length, litter size, perinatal mortality or condition of the young at birth compared with control rabbits. However, respiration rate, normally 65/min, was increased to 120/min by moving the animals from their cages and to 160/min in the machine; noise alone produced an intermediate response. Respiration returned to normal values after 20 min to 4 h, depending upon the initial level of response.
The lifetime reproductive performance of Mongolian gerbils from which an ovary had been removed 7 days before pairing at 100 days of age was only slightly inferior to that of normal females. A general decline in fertility was evident only in the oldest females. The mean number of litters, young born and age at last parturition were 7.6 +/- 3.8, 37 +/- 20 and 462 +/- 196 days (2 ovaries) compared with 6.9 +/- 3.5, 30 +/- 16 and 417 +/- 142 days (1 ovary) respectively.
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In mink, restricting the duration of copulation (<or=6 min) results in reduced fertility, either due to too few spermatozoa being ejaculated or defective sperm transport (4). The objective of the present work was to determine the effect on fertility of prolonging mating using a sterile male. When copulation was restricted to 5 min, only 3/14 mink whelped, and in 2 of the 3 cases the litter size was well below normal. The use of a vasectomized male, either before or after the intact male, caused a significant increase both in whelp rate (21/24) and litter size. The beneficial effect of the vasectomized male was still present after 4 hr. It is concluded that in short matings, defective sperm transport is the major factor limiting fertility and that the duration of coitus affects the efficiency of sperm transport.
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Up to 26 ejaculations were obtained from male rabbits within a period of 8 hours. During the next 20 days, further ejaculates were collected to establish the pattern of restoration of normal values. Repeated ejaculation resulted in a marked and progressive decline in the 3 semen characters examined; sperm density returned only slowly (3 weeks) to the initial level whereas fructose and volume, in particular, responded much faster. No significant effect of ejaculate order on fertility, litter size or sex ratio was demonstrated.
In gerbils mated post partum gestation was prolonged when 3 or more young were nursed. A well-defined linear, positive relationship existed between the length of gestation and number of young nursed, with an increase of 1.9 days per individual young. No evidence was found for the existence of implantation periods approximating in length to a normal oestrous cycle.