Five experiments concerned with feeding were performed. Experiment 1 was exploratory in nature, and using time-lapse cinematography, we found that the approach to food (seaweed) involved an initial arousal and then a slow movement toward the food with considerable pausing and head waving. In Experiment 2 a T-maze apparatus was used to show that Aplysia will consistently turn toward the highest concentration of food chemical. Experiment 3 showed that food-aroused animals proceeded upstream against a slow current, while those unaroused proceeded up or down stream. Experiments 4 and 5 showed that chemical stimulation of the rhinophores, anterior tentacles, and dorsal head area resulted in feeding responses; and tactile stimulus-response relationships varied markedly with the state of arousal.This report describes one of a series of studies of the behavior of the sea hare, Aplysia californica, which is a marine mollusk found off the shores of California. This species is well known for its usefulness in neurophysiological research (see, e.g., Kandel & Spencer, 1968) and recently has been used in important studies of brain-behavior relationships (see Bruner & Tauc, 1966;Kupfermann, Castellucci, Pinsker, & Kandel, 1970;Peretz, 1970). Our general purpose is to provide more insight into the behavior of Aplysia to facilitate the latter type of study.Comparatively little is known about Aplysia behavior. The few studies which have been done include investigations of habituation (
Telomeres in most species consist of repeat units of a small number of nucleotides that together with secondary structures and associated proteins stabilize the linear chromosomal DNA molecule. Chromosomes lose a small amount of telomeric DNA after each cell replication. It has been proposed that when telomeres shorten below a critical length, a DNA damage response pathway is activated and induces cell cycle arrest. In cells such as stem cells that maintain a proliferative capacity, telomere length is maintained by the reverse transcriptase, telomerase. In addition, telomerase activity is present in 90% of primary human tumors, suggesting a role for telomerase in providing a proliferative capacity to cells, which is a requirement in progression to malignancy. Telomerase activity can be involved in chromosome healing, although telomerase-independent processes also appear to be capable of capping broken chromosome ends. This review describes the structure and maintenance of telomeres, the importance of a critical telomere length to cell proliferation and the telomeric status of broken chromosome ends produced during development or by spontaneous or induced DNA damages.
Presumptive evidence for functional germ cell chimerism in the marmoset was evaluated by calculating the offspring sex ratio of young derived from animals in which the blood chimerism status was known. In the four possible mating combinations involving chimeric and non-chimeric marmosets, there was no apparent deviation from the anticipated 1:1 sex ratio. Analysis of 2,500 primary spermatocytes from ten known blood chimeras failed to reveal a single cell in which an unequivocal XX bivalent could be identified. The combined breeding and cytogenetic data offer presumptive evidence against functional germ cell chimerism in the marmoset.
Cytogenetic assays are an integral component of the battery of short-term assays that are used for the hazard identification component of a cancer risk assessment. The protocol for the conduct of such assays for maximal sensitivity for detecting clastogenicity has to be attendant to the mechanism of induction of the endpoint being assessed and the fact that several aberration types are cell lethal necessitates that analysis be for cells at their first posttreatment metaphase. Cytogenetic assays for human populating monitoring have been used for predicting potential for carcinogenicity in humans. However, the assays as typically conducted are not appropriate for chronic exposures because nontransmissible alterations are assessed. The use of fluorescent in situ hybridization (FISH) techniques for the assessment of transmissible changes such as reciprocal translocations are required to make population monitoring studies interpretable, and for removing some of the concern over the influence of confounders on outcome. The database for the cytogenetic effects of ethylene oxide in vitro and in vivo, with an emphasis on human population monitoring, has been critically reviewed. Based on the endpoints studied, the size of the study groups, the information on exposure, the nature of any exposure response data, and the possible influence of confounders (i.e., control matching), it is concluded that acute, high exposures to ethylene oxide with sampling shortly (a few days) after exposure can be detected by increases in chromosome aberrations or SCE in peripheral lymphocytes. Such increases are indicators of exposure to a genotoxic chemical and not predictors of subsequent adverse health effects to individuals. The effect of chronic and/or low level (less than about 25 ppm) exposures cannot be reliably evaluated using current methods. The use of FISH, for example, for assessing reciprocal translocation frequencies (as a measure of transmissible events) will greatly improve the ability to detect chronic exposures to clastogenic chemicals.
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