Relative distribution of mature erythrocytes, polychromatic erythrocytes (PE) and micronucleated PE on mouse bone-marrow smears: control observations.

Maps are presented showing the distribution of normal erythrocytes (NE), polychromatic erythrocytes (PE) and micronucleated PE (MPE) on 3 mouse bone-marrow smears. Adjacent areas of each slide were assessed along their whole length, and it was found that both the incidence of MPE and the ratio of PE:NE varied between different regions of the slide. These two variables were essentially independent of each other. The maps give the impression of clusters or islands of MPE on the slide, but these become less significant when the number of erythrocytes in those areas is taken into account. The present data confirm our previous conclusion that the resolving power of the bone-marrow micronucleus assay is related to the number of PE assessed for MPE per slide. Our data also illustrate that in instances where small departures from control values are observed, clarification/confirmation of the result can be obtained by extending the assessment of slides for MPE. It is proposed that the present recognition of the inherent sensitivity contained within this assay necessitates careful examination of the criteria for a positive response. The selection of PE suitable for assessment is discussed, and our recent 24-h oral corn oil control data are analysed.