The efficiency of embryo banking for rat and mouse models of human disease and normal biological processes depends on the ease of obtaining embryos. Authors report on the effect of genotype on embryo production and rederivation. In an effort to establish banks of cryopreserved embryos, they provide two databases for comparing banking efficiency: one that contains the embryo collection results from approximately 11,000 rat embryo donors (111 models) and another that contains the embryo collection results from 4,023 mouse embryo donors (57 induced mutant models). The genotype of donor females affected the efficiency of embryo collection in two ways. First, the proportion of females yielding embryos varied markedly among genotypes (rats: 16–100%, mean=71%; mice: 24–95%, mean=65%). Second, the mean number of embryos recovered from females yielding embryos varied considerably (rats: 4–10.6, mean=7.8; mice 5.3–32.2, mean=13.7). Genotype also affected the efficiency of rederivation of banked rat and mouse embryos models by embryo transfer. For rats, thawed embryos ( n =684) from 33 genotypes were transferred into 66 recipient females (pregnancy rate: 76%). The average rate of developing live newborns for individual rat genotypes was 30% with a range of 10 to 58%. For mice, thawed embryos ( n =2,064) from 59 genotypes were transferred into 119 pseudopregnant females (pregnancy rate: 78%). The average rate of development of individual mouse genotypes was 33% with a range of 11 to 53%. This analysis demonstrates that genotype is an important consideration when planning embryo banking programs.
We have used a computer-based mathematical model of alpha-motoneurons and of group Ia synaptic input to them, based on anatomical and electrophysiological data from the cat spinal cord, in order to examine the effects of variations in neuron size and input resistance and of conductance magnitude and duration on the generation of excitatory postsynaptic potentials (EPSPs). The first set of calculations were designed to test the possible role of nonlinear EPSP summation in producing a differential distribution of posttetanic potentiation of group Ia EPSPs, described in the preceding paper (25; see also Refs. 26, 27). The results suggest that the negative correlations observed between the degree of posttetanic potentiation of Ia EPSPs and initial (pretetanic) EPSP amplitude as well as with the input resistance of the postsynaptic motoneurons can be explained in part by the inherent non-linearity between conductance change and the resultant potential change at chemical synapses. In a second set of calculations, we used the same model system to evaluate the effects produced by variations in neuronal membrane area, input resistance, and specific membrane resistivity, as well as of the density of excitatory synaptic input on the peak amplitude of EPSPs. With parameters constrained to match the properties of alpha-motoneurons and group Ia synaptic input, EPSP amplitudes were most sensitive to changes in synaptic density and were much less sensitive to alterations in neuron input resistance and specific membrane resistivity when synaptic density was constant.
