Graduate Thesis Or Dissertation
 

Behavioral and electrophysiological evidence for the mechanisms involved in the detection of ionizing radiations by the crayfish Pacifastacus trowbridgii

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  • The light-adapted crayfish, Pacifastacus trowbridgii (Stimpson, 1957), displayed a behavioral response to exposure to 300 kV x-rays at exposure rates of 10 to 30 R/s. Within this range, the proportion of subjects that responded increased with an increase in exposure rate. The response latency was inversely proportional to the exposure rate. Ophthalmectomized animals exhibited a similar response with a significantly shorter latency than the intact animals at the same exposure rate (30 R/s). Partial body exposure of ophthalmectomized animals also elicited a behavioral response and indicated that a radiation-sensitive receptor was located in the abdomen. X-ray exposure of the dark-adapted compound eye evoked an electroretinogram (ERG) that was similar to the light evoked ERG. The x-ray evoked ERG amplitude was found to be dependent on total exposure for stimulus durations of 300 ms or less. With stimulus durations greater than 300 ms, the ERG amplitude increased in relation to the logarithm of the exposure rate. Similar responses with light, indicated that the mechanism of interaction may be the same for x-rays. The time course for maximal dark - adaptation, after a 500 ms exposure to 3.85 ft-c of light, was comparable for both x-ray and light exposure (9 min). Differences observed in ERG amplitude between the light and x-ray evoked responses during the initial recovery period can be attributed to absorption of light by migrating accessory pigments or by differential interaction of light with photosensitive pigments in the eye. X-ray exposure (10 to 35 R/s) of the medial branch of the antennule and the cheliped of the first walking leg did not yield any significant chemoreceptor responses as judged by electrophysiological tests. The presence of chemoreceptors was indicated by responses elicited after administration of glutamic acid, glycine, and fish extract. X-irradiation of the dark-adapted sixth abdominal ganglion in both isolated and in vivo preparations elicited similar increases in neural impulse frequency. Significant increases occurred after ten seconds of exposure with an exposure rate of 25 R/s. The response latency decreased to five seconds with 30 and 35 R/s. It was observed that the spike potentials evoked with x-rays were similar to those evoked by light (75-100 microvolts). There was, however, a supplemental increase in spike potentials of lower amplitude (40-50 microvolts) during x-irradiation that was not observed with light. This indicated that neural elements other than the photo sensitive neurons of the ganglion were activated. It appears likely that the behavioral response in crayfish, subjected to abdomen-only exposure may be instigated by x-ray excitation of the sixth ganglion.
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