Fig. 8.

Putative model for effect of octopamine in the honey bee antennal lobe. a Our data and previously published data are consistent with the model shown (see text for details): Odor receptor neurons (ORN, black) are activated by the presence of an odor. Octopaminergic neurons (e.g., VUMmx1, red) make synaptic contacts with inhibitory local neurons (orange) which synapse onto other inhibitory local neurons (yellow) which synapse onto projection neurons (uPN, green, measured in this study). Synaptic strength (number of OA receptors, black bars in the Figure) differs in different glomeruli. Therefore, the effect of OA is quantitatively different from one glomerulus to the next, and not consistent across animals. When OA is present, the orange neuron is excited, thus the yellow neuron is inhibited, and as a consequence the projection neuron is disinhibited, i.e. its odor response is stronger. b A more complex model includes OA input onto local neurons that inhibit uPNs. With this addition, OA release (e.g. by VUMmx1 during appetitive training, or responding to a learned odor) will facilitate some glomeruli (via the circuit shown in a), and inhibit others (via the synapse onto the yellow neuron)