When fruit flies lack a receptor for the inhibitory neurotransmitter gamma aminobutyric acid (GABA), their ability to learn or remember is enhanced, the first time scientists have been able to induce this effect in the insects, said Baylor College of Medicine researchers in a report that appears in the journal Neuron.
"We now know that the neurotransmitter GABA is a neurotransmitter that inhibits learning," said Xu Liu, a graduate student in the laboratory of Dr. Ronald Davis, professor of molecular and cellular biology at BCM. Liu is first author of the report and Davis is senior author.
"One of the exciting things about this is that normal learning might occur by inhibiting the inhibition of GABA," said Davis.
In this study, Liu, Davis and their colleagues studied the effects of the GABA receptor called Resistance to dieldrin (Rdl), which is expressed or activated in the mushroom bodies of Drosophila melanogaster or the fruit fly most commonly studied in the laboratory. Mushroom bodies are key to learning and memory related to odors in the fruit fly.
When Liu overexpressed or caused too much of the receptor to be present in the mushroom body, the flies had a learning defect. But when he reduced the expression of the receptor, the flies learned better than normal.
Using a special temperature-sensitive "switch" developed by a former student in Davis' lab, Liu raised fruit flies in which the overexpression of the receptor occurred only at higher temperatures. The flies were raised in cooler temperatures, but when they were adults, he moved them into higher temperatures for days at a time.
The flies learned less quickly in the higher temperature, when the overexpression was turned on. When they were moved back to lower temperatures, their learning ability returned to normal.
"It looks as though this affects only memory acquisition but not memory stability," said Liu. "Flies that overexpress the receptor can't learn as fast, but once they learn, they remember it as well as those who do not have the overexpression."
Dr. William C. Krause of BCM also took part in this study.
Funding for this study came from the National Institutes of Health, the G. Harold and Leila Y. Mathers Charitable Foundation and the R. P. Doherty-Welch Chair in Science at the Baylor College of Medicine.
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