Non-motor, efferent electrical activity in the antenna of the water-striderGerris paludum (Hemiptera, Insecta)

Summary

• 1. In the antenna ofGerris two forms of bipolar, extracellular single action potentials have been recorded: negative-positive (NP potentials) and positive-negative (PN potentials).

• 2. The main source of the afferent NP potentials is the distal half of the pedicellus, as shown by amputation and coagulation experiments (Fig. 13).

• 3. There is a reciprocal relationship between spontaneous sensory activity and efferent PN activity.

• 4. The reaction of PN units is comparable to the response of off-neurones to optical stimulation of the eye. The effects depend on light intensity (Fig. 9). It was also possible to record light-activated NP units, with phasic on-responses (Fig. 10).

• 5. Each antenna has at least three PN-units of its own. Temporal correlation of PN activity patterns exists between the two antennae; these activity patterns usually alternate (Fig. 8).

• 6. PN units are inhibited by: touching the body, air puffs, vibration of tarsi and bending of joints of legs and antennae (Figs. 13, 14). Because of this inhibition, PN units are silent during escape and antennal movements (Fig. 6). Therefore PN impulses cannot be action potentials of antennal muscles.

• 7. Because PN impulses have a conductive delay to the distal half of the pedicellus (Fig. 3), and passive electrical spread of potentials in the antenna is instantaneous (see test impulse Figs. 4, 5, 11c), it is concluded that efferent PN axons extend into the pedicellus. Two other facts support the suggested active conduction of PN impulses.

• 8. Because of the absence of muscles in the pedicellus and flagellum, one must conclude that PN impulses are not motor, but probably innervate sensory cells. The significance of such an innervation is discussed.