Meanwhile, the research in the Spacelab module was proceeding well, including the controversial dissection of several mice in the General Purpose Work Station (GPWS) by Williams and Buckey on 18 April. Four adults were decapitated in order to recover tissue samples from their brains and inner ears, which were needed by members of Neurolab's 'neuronal plasticity' team, who were investigating how nerve cells 'rewire' themselves under the stress of a new and unfamiliar environment. It was hoped that this work could ultimately lead to new insights into neurological ailments on Earth.
''There are different kinds of neurologic assaults - stroke, Parkinson's disease, some kinds of balance disorders - that trigger the brain to reorganise in these ways,'' said researcher Gay Holstein. ''So we can use this microgravity experiment to gain some more insight into what's the best way to treat these neurologic patients.'' Jim Pawelczyk, who participated in several dissections, added that the surgery had to be conducted quickly to avoid the onset of degradation in certain nerve fibres. In response to questions of whether the poking-and-prodding medical experiments had spoiled his first day in space, he replied simply ''That's why we're here!''
Although it was not the first time that animal dissections had been conducted on the Shuttle - that had been pioneered by the SLS-2 crew in October 1993 - many scientists considered the previous work to be messy and time-consuming. Neurolab, on the other hand, demonstrated the ability of trained medical specialists to conduct incredibly intricate surgery in a weightless environment. ''We're thrilled!'' said Holstein, of the Mount Sinai School of Medicine. ''I can't wait to obtain the tissue
and start to do my experiments.'' Later, embryos were taken from euthanised pregnant mice as part of studies into gravity's role in their early development.
The results of such studies will prove crucial in determining whether or not humans or animals could someday be born in space, thus enabling colonies to be established and long-duration trips to the stars, which will undoubtedly take place over many generations. Before dissecting them, the astronauts injected the pregnant mice with cell 'markers' to label the brain cells in their embryos, track the development and migration of the cells and compare the results with data gathered from Earth-born mice. ''The dissections are proceeding real well,'' Pawelczyk said during the operation.
Typically, the pea-sized foetuses ranged between 10 and 14 days old and, after removal from their mothers, were preserved whole until the end of the mission. Other mice, with 'hyperdrive' units fitted to their heads connected to the hippocampus area of their brains, were placed in the GPWS on two different, maze-like 'racetracks' as part of the Escher Staircase Behaviour Testing experiment. The hippocampus helps develop spatial maps to help the mice to navigate from place to place and the investigation sought to explain the disorientation frequently experienced by Alzheimer's sufferers.
The hyperdrive units did not create unpleasant side-effects for the mice because their brains had no pain receptors. ''It's actually crucial to us that our animals are quite happy, not suffering in any way,'' said psychologist Bruce McNaughton of the University of Arizona, a memory and ageing expert. ''If they are, they won't perform the tasks we ask them to. So it's extremely important in our line of research [that] we make extremely good friends with our animals.''
Many healthy astronauts frequently report unpleasant sensations of disorientation when they first leave terrestrial gravity, giving them a temporary kinship with Alzheimer's patients. ''We're trying to reverse-engineer the most complex structure in the known Universe,'' said McNaughton. ''Having that knowledge is a critical prerequisite to any kind of intervention. This structure we're looking at is actually the highest level-of-association cortex in our brains and it's the first thing that goes wrong during the breakdown that begins to occur in early Alzheimer's disease. By understanding the basic biology of how this system works, it will give us the understanding we need to be able to tell what is going wrong in this system when it breaks down.''
The mice had been taught to use the racetracks - one dubbed the 'Escher staircase' because of its twisting, three-dimensional resemblance to a well-known lithograph by Dutch artist M.C. Escher, the other known as the 'magic carpet' because astronauts flipped and turned it once the mice were on board - before Columbia lifted off, receiving rewards of sweetened condensed milk after completing a certain number of right turns. In space, however, the rules were changed and investigators monitored neural activity as the mice struggled to recognise 'home base' after making fewer turns than they had been taught on the ground.
''In the future, obviously you would like to have some sort of family life on the Moon or Mars,'' said neuroscientist Kerry Walton of New York University Medical Center, and by studying critical periods of development in the mice, ''we would
know how long a child of a particular age could be in an environment other than Earth. This way, maybe people could grow up to be 'dual-adapted' so that they could switch from an Earth environment to low-gravity in the same way that children can switch between one language and another.''
Several of these mice exercised their 'space legs' for the first time on 22 April, using their forelimbs to scoot around a small jungle gym, but hardly using their hindlimbs, according to the crew. As they moved, the astronauts videotaped them and marked their joints with permanent black ink, so as to allow each motion to be meticulously analysed after Columbia's landing. ''We think it's really neat because these animals - their nervous systems - are going to develop and essentially they're going to think they were born in zero-gravity,'' said Walton, but added that she expected them to quickly readapt to terrestrial conditions.
''It's amazing to watch these animals behave in orbit,'' said Linnehan, who had worked with hippos, rhinos, giraffes and bears at Baltimore Zoo before joining the US Navy's marine mammals project and later becoming an astronaut. ''They act just we do. They learn very fast how to get around their cages and get to food and water. Just last night [24 April], we were checking on some of the young rats, watching them eat. It was kind of akin to the way we eat. We float around and hold our food to feed ourselves. One of the rats was holding onto a piece of food [with] his front paws, munching on it leisurely, letting [it] go and going over to drink some water, coming back and grabbing the food again.''
Later, on 30 April, the first survivable surgical procedure was conducted on six mice: Buckey and Williams anaesthetised and injected them with dye markers in a muscle-development study. Although the procedure itself was relatively straightforward, NASA's chief veterinarian Joe Bielitzky noted that it paved the way for more elaborate research on the space station.
''Everything went well; all six have recovered,'' Buckey reported jubilantly at the completion of the procedure.
Elsewhere, a minor problem cropped up with the four oyster toadfish on board Columbia. They possess gravity-sensing organs reminiscent of human inner ears, and although each had been fitted with a small transmitter before launch to monitor neuronal activity, the signals were found to be intermittent, possibly due to an electrical fault or problems with the oxygen-circulation pumps in their aquariums. Nonetheless, Stephen Highstein of the Washington University School of Medicine said, ''We think we can achieve 100% of our science goals even with intermittent data.''
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