AbstractsBiology & Animal Science

High specific activity tritiated thymidine (40-60 Ci/mM) and autoradiographic techniques were used to study cell renewal systems in the freshwater mussel, Margaritifera margaritifera. Groups of mussels were injected with tritiated thymidine (1.0 [?? Ci/g) and then serially sacrificed. Tissues from selected areas of the body were routinely processed, and slides were made and coated with Ilford K5 emulsion. After exposure, slides were developed to obtain autoradiographs and stained. High specific activity tritiated thymidine ( ??H-TdR) may have significant potential for application in cell renewal studies in mollusks and other organisms in which the time of DNA synthesis may be long with respect to the time of ??H-TdR availability. It was necessary to expose slides for only 2-3 days as compared to exposure times of 15 days to 6 months in previous studies. No clear radiobiological affects or cytoplasmic labelling due to labelled by-products were observed. Labelling was observed in aLl tissues studied  – stomach, intestine, rectum, mantle epithelium, gills, some blood cell types and connective tissues in most areas of the body. The cell renewal systems in the gills of M. margaritifera can be considered to consist of a stem-type population in the gill furrow, a maturing, dividing transient population on the proximal gill ridge side, and a functional, simple transient population on the distal gill ridge side and gill ridge tip. The minimum transit time from the dividing transient population to the functional population may be no more than 24 hours.