AsianScientist (Jul. 3, 2015) – Although sexual desire tends to fall as males grow older, a study in flies suggests that dopamine might be able to boost flagging libidos. The study, published in Nature Communications, showed that enhanced levels of dopamine in specific neurons could restore sexual responses in aged (40 day old) flies.
The neurotransmitter dopamine is known to regulate a wide range of human behaviors including reward-seeking and motivation. A lack of dopamine has been implicated in conditions such as Parkinson’s disease and attention deficit hyperactivity disorder.
Interestingly, there have been cases where Parkinson’s patients treated to increase their levels of dopamine experienced hypersexuality as a side effect, suggesting that dopamine can regulate sexual behaviors in humans. However, the exact neurons responsible and the underlying mechanism remains unknown.
In the present study, a team of Taiwanese researchers led by Assistant Professor Fu Tsai-Feng from the National Chi Nan University used genetically engineered fruit flies (Drosophila melanogaster) to tease out the specific neurons involved in regulating male sexual behavior.
They showed that overexpressing tyrosine hydroxylase (TH)—the enzyme responsible for producing dopamine—was sufficient to increase courtship behaviors in 40 day old flies. To rule out the effect of male-female interactions, the researchers also used decapitated female flies and found that old male flies with elevated dopamine levels increased courtship behaviors to the immobilized female flies as well.
A similar effect was seen when the flies were fed L-DOPA, the precursor of dopamine. In contrast, when dopamine levels were lowered by either inhibition of TH or by inhibiting vesicle transport with reserpine, male flies showed a marked reduction in courtship behavior.
Using flies engineered to express TH and green fluorescent protein in a subset of neurons, the researchers were able to identify PPL2ab neurons as the source of dopamine regulating male courtship behavior. Unlike global reduction of dopamine which causes motor dysfunction, modifying the levels of dopamine in only PPL2ab neurons had no effect on motor and sensory activity or the lifespan of flies.
Although this study sheds light on the role of dopamine in sexual behavior, it also raises further questions such as which are the effector neurons downstream of PPL2ab dopamine signalling. The authors intend to investigate sexually dimorphic neurons in future studies, particulaly those expressing the fruitless (fru) genes.
The article can be found at: Kuo et al. (2015) PPL2ab Neurons Restore Sexual Responses in Aged Drosophila Males through Dopamine.
Copyright: Asian Scientist Magazine; Photo: Radu Privantu/Flickr/CC.
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