[Image by Thomas Shahan via Creative Commons]
If you watched the Sapolsky video below, you know that he touched on something that we forget about: pheromones. I think people like to think that pheromones are limited to those baser animals, or insects, and that our behavior is more controlled. The idea that smells are influencing our choices all the time is not something most people realize. So here’s some neuroscience research on one of my favorite things – social insects.
We’re going to be talking about bees today, and about how bees use a pheromone known as queen mandibular pheromone (QMP) that controls their social behavior. This pheromone is a complex blend of chemicals designed to entice workers to feed and groom the queen. As the attendant bees exchange food with nest mates, they spread it throughout the colony. However, not all bees attend the queen – it is mainly young bees, with the older ones being the colony’s foragers. It’s interesting then, that reactions to QMP are age-dependent: very young bees find it attractive, while the older foragers try to stay away from it. What’s going on here?
Well, one component of QMP is homovanyllil alcohol (HVA). This chemical interferes with dopamine signaling, a neurotransmitter responsible for learning (in particular, learning aversive memories). But each bee is a little different; some like QMP more, some less. Why? Well, when you examine transcription levels of various neurotransmitter receptors, there’s no correlation between behavior and transcription levels in the brain – but there is in the antennae. In particular, Amoa1 and Amdop3 were significantly higher in bees attracted to QMP, which are an octopamine receptor and D2-like dopamine receptor activated by HVA, respectively. Futhermore, activation of AmDOP3 inhibits accumulation of a molecule known as cAMP; one effect of this lack of accumulation is that signaling of D1-type receptors are inhibited (Amdop1/2).
Here’s what you do next: stuff a bunch of QMP in the face of bees from emergence and see what changes. One effect is that Amdop1 transcription levels in the antennae fall significantly (though not Amdop2). Another effect is that bees exposed to the QMP are much more attracted to it, in every age group tested. What’s happening here? The theory is that octopamine enhances sensitivity to pheromone cues and to positive appetitive stimuli, while dopamine reinforces aversive stimuli. QMP activates AmDOP3 receptors, which in turn downregulates AmDOP1 receptors; this interference with dopamine inhibits the unattractive parts of QMP. Since Amdop3 levels correlate highly with QMP attractiveness, and since Amdop3 decreases with age, it is likely that this is a primary reason for the switch from caring to foraging behavior. After proffering that explanation, however, Amoa1 is forgotten because no developmental effect is seen.
So there you have it. Queen pheromone affects dopamine signaling behavior not just in the brain, but also at the level of primary sensory neurons. Apparently, this shift between avoidance and approach behavior among mammalian mothers and offspring is also due to dopamine signaling… Oh, and for the record, I know the picture above is a yellow jacket and not a bee, but it looks pretty sweet, doesn’t it?
Vergoz V, McQuillan HJ, Geddes LH, Pullar K, Nicholson BJ, Paulin MG, and Mercer AR. Peripheral modulation of worker bee responses to queen mandibular pheromone. PNAS 2009 106:20930-20935; doi:10.1073/pnas.0907563106