Figure 1.
Effect of lesions in the cockroach CNS on the wasp's stinging duration.
A. Left: A Jewel Wasp stinging a cockroach in the head. Right: Schematic lateral view of the cockroach head cavity (CNS is in yellow) and the wasp's stinger (St), shown as a scanning electron micrograph superimposed and drawn to scale, penetrating through the head cuticle to reach the cerebral ganglia (supra-esophageal ganglion, SupEG, and sub-esophageal ganglion, SEG). Locations of experimental CNS lesions are marked with scissors: In SEG-ablated cockroaches, the connectives rostral and caudal to the SEG were severed and the ganglion physically removed from the head cavity. In neck connectives-cut cockroaches, by contrast, only the neck connectives (NC) caudal to the SEG were severed, with the ganglion itself left intact. Es: esophagus. Ant: antenna. Scale bar: 0.5 mm. Modified from [17]. B. Wasp stinging behavior after specific experimental lesions of the cockroach's cerebral CNS. Cerebral lesions do not affect the duration of the first sting directed at the thorax (black bars). In contrast, physically removing the SEG from the cockroach head cavity prior to the sting (SEG ablated), but not cutting the cockroach neck connectives (NC-cut), significantly increases the duration of the second sting directed at the head (red bars). ***p<0.001, as compared with sham-operated and NC-cut cockroaches.
Figure 2.
Procaine-induced inhibition of SEG neural activity depresses cockroach locomotion.
A. Extracellular bipolar recording of spiking activity in the SEG of a non-stung cockroach. Transient (1 min, red bar) application of the sodium-channel blocker, procaine, completely and reversibly abolishes neuronal activity in the ganglion. B. Behavioral analysis of non-stung cockroaches injected with saline (black bars) or procaine into the SEG (red bars) or the SupEG (green bars). Spontaneous walking (top) and evoked escape responses (bottom) are reversibly suppressed by the inhibition of neuronal activity in the SEG but not of the SupEG. ***p<0.001, as compared with controls.
Figure 3.
Behavioral analysis of stung and non-stung cockroaches injected with crude milked venom into different regions of the cerebral ganglia.
Venom injected into the SEG, similar to a natural wasp sting, significantly depresses spontaneous walking (top) and escape responses (bottom). In contrast, venom injected into the SupEG has an opposite, albeit not significant effect. ***p<0.001 compared with the respective controls.
Figure 4.
Spontaneous neural activity in the SEG of control and stung cockroaches.
A, B. Extracellular bipolar microelectrode recordings of spontaneous spiking activity in the core of the SEG in one non-stung (‘control’) and one stung cockroach. The dashed region in A is enlarged in B. C. The spontaneous firing rate in the core of the SEG is significantly decreased in stung cockroaches. **p<0.05.
Figure 5.
Evoked neural activity in the SEG of control and stung cockroaches.
A. Extracellular bipolar microelectrode recordings of evoked activity in the core of the SEG in one non-stung (‘control’) and one stung cockroach (left: wind stimulus to the cerci; right: tactile stimulus to the antenna; arrows: stimulus onset). B. Peri-stimulus time histograms for wind (left) and tactile (right) stimuli. Each data point represents the mean (± SEM) number of spikes within a 20 ms time bin. The response to stimuli is decreased in stung cockroaches, especially during the first 200 ms after stimulus onset (represented by a bar above the histograms). C. The number of spikes during the first 200 ms immediately after the stimulus onset. Stung cockroaches show decreased responses to wind and tactile stimuli. **p<0.05. D. The latency between stimulus onset and maximal spiking response is similar in stung and control cockroaches.