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The intelligibility of particular words in sentences was studied in a paradigm where subjects were asked a wh— question before or after they heard a statement masked by white noise. The answer to the question was always a single word from the accompanying statement. The statements and questions used each contained two noun phrases, whose position, emphasis, function, and redundancy were varied. The results obtained suggest that both syntactic and semantic factors influenced intelligibility of the nouns in these phrases.

DNA from Chinese hamster ovary (CHO) cells which had been irradiated with 1 krad of x rays was sedimented in alkaline sucrose gradients with the single strands of DNA and large DNA-containing species which can be released from mammalian cells. It was found that the CHO DNA profile is suited for use as a marker in such circumstances because it has both a characteristic shape and principal component (~165S) which are substantially independent of DNA concentration, EDTA concentration, and lytic storage time. The sedimentation rate of the principal component varied with rotor speed and radius as predicted by Zimm for single-stranded DNA molecules with a molecular weight of approximately 5 x 10/sup 8/ daltons. The irradiated CHO cells can be frozen and stored without changing the sedimentation characteristics of the marker DNA. (auth)

The in vivo DNA repair kinetics of rat cerebellar neurons and intracerebral 9L tumor cells were simultaneously assessed in the same rat after a single 5000-rad dose of X rays using an alkaline sucrose gradient sedimentation technique in slow reorienting zonal rotors. An X-ray dose of 5000 rad produced the same amount of DNA damage in both 9L tumor cells and cerebellar neurons. However, at every repair time studied up to 24 hr, the tumor cell DNA was always repaired to a greater extent than the neuronal DNA. Restoration of the chromosomal DNA structure to its unirradiated state in intracerebral 9L tumor cells and in cerebellar neurons required 24 and 38 hr, respectively. Thus, nondividing neurons appear to repair their radiation-induced DNA damage to the same extent as the dividing tumor cells, but they do so at a slower rate.

The rejoining of the strand breaks formed by X- and -y-irradiation of the DNA in the internal granular layer neurons of the canine cerebellum was followed in vivo at the level of the 165S chromosomal subunit. Single-strand breaks were produced with an efficiency of 58 + 5 eV in the DNA of differentiated neurons, a value similar to that found for cultured dividingcell lines, e.g., Chinese hamster ovary cells and murine leukemic lymphoblasts. The expression of the strand-break rejoining in neuronal DNA in vivo differed from that observed in dividing cells in vitro because reconstituted 165S subunits were degraded into smaller molecules during the early repair period. Large molecular weight species similar to those observed in unirradiated neurons did not appear in significant quantities until 10 hr after irradiation. The exact mechanistic relationships of these events are not known at this time.

Increasing doses of γ-radiation to the rabbit retina result in the sudden loss of the b-wave of the electroretinogram at a dose of 4300 ± 300 rads. In this same dose range, the photoreceptor cells of the retina appear to undergo an equally rapid impairment of a specific DNA repair mechanism. This impairment could result from damage to the repair mechanism itself, an accumulation of irreparable damage in the DNA, or the onset of a degradation process which overwhelms the repair mechanism. None of these alternatives can be eliminated at this time.