OCTOPAMINERGIC MODULATION OF THE FEMORAL CHORDOTONAL ORGAN IN THE STICK INSECT

The modulatory action of DL-octopamine on the multicellular femoral ch ordotonal organ (fCO) of the stick insect Cuniculina impigra was exami ned using extracellular recordings from the fCO nerve and intracellula r recordings from single sensory neurons. To determine the octopaminer gic effect on position, velocity and/or acceleration sensitivity of me chanoreceptors direct mechanical stimulations with defined parameters were applied to the fCO apodeme. The spontaneous activity in the fCO n erve was enhanced in a dose-dependent manner by octopamine (threshold 5 x 10(-7) M). This was based on enhanced activity or position sensiti ve neurons as the fCO activity for all position stimuli was shifted to higher values. Intracellular recordings of single sensory cells showe d that velocity-sensitivity of single sensory cells was not altered by octopamine. Similarly, the response of fCO afferents to ramp-and-hold stimuli revealed that acceleration sensitivity was unaffected by octo pamine. The observed alterations in the fCO activity indicate that res ponses to static stimuli are enhanced while responses to motion stimul i are not affected by octopamine. These findings suggest that the octo paminergic modulation of the fCO may affect the animals' posture and t hose leg movements that rely on position information.