Live analysis of free centrosomes in normal and aphidicolin-treated Drosophila embryos

In a number of embryonic systems, centrosomes that have lost their association with the nuclear envelope and spindle maintain their ability to duplicate and induce astral microtubules. To identify additional activities of free centrosomes, we monitored astral microtubule dynamics by injecting living syncytial Drosophila embryos with fluorescently labeled tubulin. Our recordings follow multiple rounds of free centrosome duplication and separation during the cortical division. The rate and distance of free sister centrosome separation corresponds well with the initial phase of associated centrosome separation. However, the later phase of separation observed for centrosomes associated with a spindle (anaphase B) does not occur. Free centrosome separation regularly occurs on a plane parallel to the plasma membrane. While previous work demonstrated that centrosomes influence cytoskeletal dynamics, this observation suggests that the cortical cytoskeleton regulates the orientation of centrosome separation. Although free centrosomes do not form spindles, they display relatively normal cell cycle-dependent modulations of their astral microtubules. In addition, free centrosome duplication, separation, and modulation of microtubule dynamics often occur in synchrony with neighboring associated centrosomes. These observations suggest that free centrosomes respond normally to local nuclear division signals. Disruption of the cortical nuclear divisions with aphidicolin supports this conclusion; large numbers of abnormal nuclei recede into the interior while their centrosomes remain on the cortex. Following individual free centrosomes through multiple focal planes for 45 min after the injection of aphidicolin reveals that they do not undergo normal modulation of their astral dynamics nor do they undergo multiple rounds of duplication and separation. We conclude that in the absence of normally dividing cortical nuclei many centrosome activities are disrupted and centrosome duplication is extensively delayed. This indicates the presence of a feedback mechanism that creates a dependency relationship between the cortical nuclear cycles and the centrosome cycles.     

Teratogenicity and toxicity of coniine in cows, ewes, and mares

Cows, ewes, and mares varied considerably in susceptibility to toxicoses from the oral administration of the piperidine alkaloid, coniine. Cows were most susceptible and ewes least. Only calves had teratogenic effects from maternal administration of coniine during gestation; lambs and foals were apparently resistant. Results suggest that the marked differences between cattle and sheep are probably not due to variation in gut absorption or rumen metabolism.     

Cerebral tissue response to electrode implantation

Tissue response to platinum electrodes was assessed after an eight-day implantation period. The regions of study included the cortical areas at the opercular gyri and at the sulcus parieto-occipitalis externus, as well as the sub-cortical white matter in these cases. Perivascular and intraparenchymal hemorrhagic lesions as well as edematous changes characterized both by extensive intra and extracellular swelling were noted. Numerous phagocytic elements and degenerative strucutres were present at the electrode/parenchymal interface. Tissue alterations were asymmetrical as observed both around and at the tip of the implanted electrode. The parenchymal alterations extended from 0.2mm to 3.5mm distance from the electrode path/parenchymal interface. Greater tissue involvement was found in the subcortical white matter as compared to the adjacent cortical gray matter.