Manganese speeds up honey bees | The Source | Washington University in St. Louis
Negative impact of manganese on honeybee foraging
“We’ve known for a long time that high doses of manganese kill neurons that produce dopamine, causing a Parkinsonian-like disease in people,” said Ben-Shahar, an assistant professor of biology in Arts & Sciences. “In insects, as well, high levels of manganese kill dopaminergic neurons, reducing levels of dopamine in the brain.
“But in this study we were looking at low-level exposure and we saw the opposite effect. Instead of reducing dopamine levels, manganese increased them. Increases in dopamine and related neurotransmitters probably explain some of the abnormal behavior,” Ben-Shahar said.
Negative impact of manganese on honeybee foraging
Our studies support a model in which Mn2+ treatment leads to an early transition to foraging by increasing brain aminergic signalling, which is in agreement with previous studies of biogenic amines in honeybees [19]. However, our findings are also in contrast to previous studies in mammals [18] and Drosophila [21], which indicated that Mn2+ exposure leads to dopaminergic neuronal loss, and overall reduced levels of dopamine in the brain. We do not yet understand the main reason for the differences between our current findings and previous reports. Noteworthy, the Mn2+ doses we have used in our studies were far below previously reported neurotoxic levels [21]. As a result, these previously published data together with our current findings suggest that the interaction of Mn2+ with biogenic amine signalling and behaviour comprises two phases: exposure to low Mn2+ levels leads to an increase in biogenic amine synthesis but, once above the neurotoxic threshold, it leads to a reduction in biogenic amine levels.
As in the honeybee, we found that ingestion of 5 mM Mn2+ by Drosophila caused an increase in brain levels of octopamine and dopamine, but not serotonin.