Date:3/18/2013

mine. In previous studies, Bochum's biochemists already demonstrated that histamine is recycled via the glial cells surrounding the photoreceptors. There, the enzyme Ebony inactivates the neurotransmitter histamine by binding it to the amino acid -alanine, thus creating -alanyl-histamine. This molecule is transported from the glial cells back into the photoreceptors. Here, -alanine is split off again by the enzyme Tan, and histamine is produced. Previously, it was assumed that the enzyme Black is responsible for producing the -alanine, which is required for the inactivation of histamine. However, if a fly's eye has no functional Black, the visual process still runs normally. Hovemann's team therefore looked into the question of whether there is another supply route for -alanine. They also tested whether the fly eye can get around the recycling of histamine; this would be possible if the photoreceptors could directly reabsorb the released neurotransmitter, without it being inactivated in the glial cells.

No functioning sense of sight without histamine recycling

The researchers examined flies that were neither able to produce histamine themselves nor recycle it, because they lacked the enzyme for histamine synthesis and the enzyme Ebony. The team measured the flies' vision using so-termed electroretinography, which not only shows the excitation of the photoreceptor cells, but also the transmission of the signal to the brain. Even when the researchers added histamine from outside, the flies were blind. With this test, they showed for the first time that, for vision, Drosophila is dependent on the histamine recycling in the glial cells. Without recycling the enzyme Ebony, the cells in the insect eye cannot make any use of the neurotransmitter.

Flies can also see with disturbed -alanine production

Cells are not only able to produce -alanine with the aid of the enzyme Black, but also by converting the molecule uraci
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Contact: Bernhard Hovemann Bernhard.Hovemann@rub.de 49-234-322-4235 Ruhr-University Bochum Source:Eurekalert

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