Responses of giant interneurons of the cockroachPeriplaneta americana to wind puffs of different directions and velocities
Controlled wind puffs of different directions and velocities were delivered to the cerci of cockroaches (Periplaneta americana), while the responses of individually identifiable giant interneurons (GI's) were recorded intracellularly.
All fourteen histologically identified GI's (seven bilateral pairs) respond with a burst of action potentials to wind from some or all directions. The directional sensitivity of a given GI is consistent from animal to animal (Fig. 7).
Varying the angle of delivery of wind puffs revealed that, in each side of the nerve cord, two GI's (2, 4) show little or no directional selectivity, two GI's (1, 7) have a greater response to wind from the ipsilateral side, two GI's (3, 6) respond primarily to wind from in front of the animal, and one GI (5) responds primarily to wind from the ipsilateral rear quadrant (Fig. 7). These directional properties are independent of wind velocity up to at least 2.6 m/s (Fig. 8).
Varying the peak velocity of the wind stimuli (delivered from each GI's maximal response angle) showed that the number of action potentials evoked increases with wind velocity up to at least 2.6 m/s for some GI's (1, 5, 6, 7), while the number does not increase with velocity beyond 0.5 m/s for others (2, 3, 4) (Fig. 9).
Covering or removing the cercus contralateral to a given GI reduced the response of each GI without appreciably altering its directional selectivity (Fig. 11 A). Eliminating the ipsilateral cercus also moderately reduced the responses of some GI's (4, 5, 7), but nearly or completely abolished responses in others (GI's 1, 2, 3, 6) (Fig. 11B).
The spike frequencies of the GI's in response to “standard wind puffs” (peak velocity 0.6 m/s or 2.6 m/s) are high, with maintained frequencies often over 300 spikes per s (Table 1), and instantaneous frequencies some times over 900 per s (Fig. 10).
The directional selectivity, high spike frequency, and rapid conduction velocity of the GI's may be adaptations for mediating the short latency, directional evasive behavior of the cockroach. The results are discussed in terms of the presumed role of the GI's in this behavior and implications for sensory integration.
KeywordsWind Velocity Peak Velocity Instantaneous Frequency Nerve Cord Sensory Integration
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