Neural responses from the wind-sensitive interneuron population in four cockroach species

Abstract

The wind-sensitive insect cercal sensory system is involved in important behaviors including predator detection and initiating terrestrial escape responses as well as flight maintenance. However, not all insects possessing a cercal system exhibit these behaviors. In cockroaches, wind evokes strong terrestrial escape responses in Periplaneta americana and Blattella germanica, but only weak escape responses in Blaberus craniifer and no escape responses in Gromphadorhina portentosa. Both P. americana and Blab. craniifer possesses pink flight muscles correlated with flight ability while Blat. germanica possesses white flight muscles that cannot support flight and G. portentosa lacks wings. These different behavioral combinations could correlate with differences in sensory processing of wind information by the cercal system. In this study, we focused on the wind-sensitive interneurons (WSIs) since they provide input to the premotor/motor neurons that influence terrestrial escape and flight behavior. Using extracellular recordings, we characterized the responses from the WSI population by generating stimulus-response (S-R) curves and examining spike firing rates. Using cluster analysis, we also examined the activity of individual units (four per species, though not necessarily homologous) comprising the population response in each species. Our main results were: 1) all four species possessed ascending WSIs in the abdominal connectives; 2) wind elicited the weakest WSI responses (lowest spike counts and spike rates) in G. portentosa; 3) wind elicited WSI responses in Blab. craniifer that were greater than P. americana or Blat. germanica; 4) the activity of four individual units comprising the WSI population response in each species was similar across species.

Neural responses from the filiform receptor neuron afferents of the wind-sensitive cercal system in three cockroach species

“…We quantified the filiform afferent response by rectifying and integrating the signal averaged neural response elicited by different wind velocities (See Methods for more detail). McGorry et al (2014) found that the WSI responses in these same three species were not consistent throughout the 250 ms duration of the wind stimulus. Compared to the Second 150 ms of the response, the First 100 ms of the response: 1) contained more overall spikes; 2) contained more large amplitude spikes; and 3) had a faster spiking rate for the WSI population (Fig.…”

“…Therefore, the First 100 ms and Second 150 ms of the responses were analyzed separately. To directly relate the filiform afferent responses to the WSI responses from McGorry et al (2014), we analyzed the filiform afferent responses in the same manner by analyzing the responses during the First 100 ms and Second 150 ms of the stimulus separately.…”

“…5B). Previously, we defined the dynamic encoding range for the WSI population as the wind velocity that elicited 0.75 proportion of the maximum response (McGorry et al, 2014). A lower wind velocity indicated a narrower range of encoding wind velocity.…”

“…In a previous study, McGorry et al (2014) found differences in the response properties of the population of the WSIs in P. americana, B. craniifer, and G. portentosa . Wind evoked the least number of action potentials with the lowest spiking rates from the WSI population in G. portentosa .…”

“…Since the recording setup and system to generate wind stimuli was the same as used to measure WSI responses (McGorry et al, 2014), we compared the filiform afferent and WSI responses to examine the transfer of information at the first synapse of the cercal sensory system neural circuit, which may reveal additional information about sensory processing in these three species. We also measured morphological features of the cerci, including the number of filiform hairs, to relate to the physiological responses.…”