Biogenic amines are among the best known neuromodulators in both vertebrates and
invertebrates. They have been implicated in the control of numerous forms of
behavior
whose expression is influenced by changes in both environmental and physiological
conditions. Neuromodulators act by modifying the effects of hormones and
neurotransmitters to modulate nervous system responses to various stimuli. Their
broad distribution in the brain and other parts of the nervous system allow them to act
on many neurons.
The biogenic amines dopamine, serotonin, and octopamine are found in all parts of the
honey bee brain. In the antennal lobes, foragers have higher levels of all three
amines than do nurses, regardless of age. Differences are larger for octopamine than
for dopamine or serotonin. In the mushroom bodies, older bees have higher levels
of all three amines than younger bees, regardless of behavioral state. These
correlative results suggest that increases in octopamine in the antennal lobes may
be particularly important in the control of age-related division of labor in honey
bees.
Recent experiments have shown that oral treatments of octopamine, but not serotonin,
accelerate the rate at which young bees become foragers. This octopamine treatment
effect is both dose-dependent and time-dependent. Bees treated early in life
as pre-foragers and
then switched to being untreated do not become foragers at an earlier age, while
young bees treated around the time at which foraging becomes possible do show
accelerated behavioral development.
This supports the idea that octopamine acts as a neuromodulator of division of
labor, suggesting that high levels are necessary at a time when foraging is
possible to alter the responses of other neurons
to specific task-related stimuli.
