The modulatory effects of serotonin and octopamine in the visual system of the honey bee (Apis mellifera L.)

Abstract

1. Honeybees respond to a stripe pattern moving up- and downward with direction specific antennal responses. The reflex can be evoked for one antenna by stimulating the ipsilateral compound eye. The direction specific antennal response (DAR) was measured with an optoelectronic device. The effects of local injection of serotonin and octopamine into different neuropils of the visual system were determined by observing changes in the direction-specific antennal response. 2. Serotonin application (approximately 500 pl at a concentration of 10−5M) into the ipsilateral lobula leads to an immediate and long lasting (at least 30 min) decrease of the DAR when the ipsilateral compound eye is stimulated. The response to stimulation of the contralateral eye is also reduced. 3. Octopamine application (approximately 500 pl at a concentration of 10−6M) into the ipsilateral lobula leads to a small enhancement of the DAR. The effect is similar when the ipsi- or contralateral eye is stimulated. 4. The modulation of the direction-specific antennal response is dose-dependent for serotonin. The two amines act in a functionally antagonistic way. 5. Serotonin injection (approximately 500 pl, 10−5M) into the medulla or lamina leads to lasting reductions of the ipsilateral DAR whereas octopamine has no effect. 6. The experiments suggest that octopamine and serotonin are functionally antagonistic in their modulation of motion-sensitive neurons in the lobula and that serotonin can modulate visual neurons also in other optic neuropils.