<h2>Serotonin and dopamine levels</h2>

<p>Researchers have succeeded in disentangling the neuro-molecular mechanism underlying defensive behaviour in bees when they are exposed to the sting alarm pheromone that they release in response to a threat.</p>

<p>The research team led by Professor Martin Giurfa of the University of Toulouse (France) discovered that the odour of isoamyl acetate, the main component of the alarm pheromone, increases serotonin and dopamine levels in the bees’ brains. This, in turn, enhances stinging behaviour and thereby helps to repel a threat. The alarm pheromone itself does not act as a stimulus, but increases the probability that guard bees will repel a threat by stinging.</p>

<p>Bees collected from four hives that were involved in colony defence were used in the study. When exposed to isoamyl acetate in the laboratory, guard bees collected from two colonies showed a greater propensity to sting than bees from the other two colonies.</p>

<p>While dopamine levels did not show any significant differences between brain regions in bees from all four colonies, serotonin levels were significantly higher in the central brain (where olfactory processing takes place) in bees that exhibited a greater propensity to sting. This provided the first indication of a role for serotonin in defensive behaviour.</p>

<p>The link between serotonin and threat responsiveness was verified in individual bees displaying defensive and passive behaviour by measuring the amounts of serotonin and dopamine in the brain. Both serotonin and dopamine were significantly elevated in the central brain after exposure to isoamyl acetate. Serotonin levels were even higher in the optic lobes and the suboesophageal zone of bees that showed stronger defensive behaviour.</p>

<h2>Link with aggression</h2>

<p>“This study established a link between higher serotonin levels after exposure to isoamyl acetate and stinging behaviour,” explains Dr Souvik Mandal, who holds a PhD from the Indian Institute of Science (IISc) in Bengaluru. He was a visiting researcher at the University of Toulouse to conduct behavioural experiments on bees and is one of the authors of an article published in Proceedings of the Royal Society B.</p>

<p>“We confirmed the bees’ stinging behaviour by topically introducing different concentrations of serotonin and dopamine into the thorax. Compared with controls, aggressive behaviour was markedly increased when the highest concentration of serotonin and dopamine was applied topically,” explains Dr Mandal.</p>

<p>The researchers introduced serotonin and dopamine antagonists to reconfirm their role in stinging behaviour. “Aggressive behaviour decreased significantly when we introduced the antagonists,” he explains.</p>

<p>This confirmed that variations in serotonin or dopamine content directly affect the stinging behaviour of bees.</p>

<p>Bees were more likely to sting as a result of an increase in serotonin in the central brain and, to a “lesser extent”, dopamine.</p>

<p>See also:</p>

<p>►&nbsp;<a href="https://www.2imanagement.ch/fr/divers/liens/wwwapisavoirch/la-vitellogenine">Vitellogenin</a></p>

<p>►&nbsp;<a href="https://www.2imanagement.ch/fr/divers/liens/wwwapisavoirch/introduction-a-la-genetique-des-abeilles">Introduction to bee genetics</a></p>

<p>►&nbsp;<a href="https://www.2imanagement.ch/fr/divers/liens/wwwapisavoirch/danse-des-abeilles">Bee dance</a></p>

<p>&nbsp;</p>

<p><em>Source (see original article in the appendix):</em></p>

<p><em>Nouvian M, Mandal S, Jamme C, Claudianos C, d’Ettorre P, Reinhard J, Barron AB, Giurfa M. 2018. Cooperative defence operates by social modulation of biogenic amine levels in the honey bee brain. Proc. R. Soc. B 285: 20172653. http://dx.doi.org/10.1098/rspb.2017.2653</em></p>

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