Nonspiking local interneurons in insect leg motor control.
Bschges, Ansgar, and Harald Wolf.
Fachbereich Biologie, Universitt Kaiserslautern, Postfach 3049, 67663,
Kaiserslautern, Germany, Fakultt for Biologie, Universitt Konstanz, Postfach
5560-M627, 78434, Konstanz, Germany.
APStracts 2:0019N, 1995.
SUMMARY AND CONCLUSIONS
1. Locusts (Locusta migratoria) and stick insects (Carausius morosus)
exhibit different strategies for predator avoidance. Locusts rely primarily on
walking and jumping to evade predators, while stick insects become cataleptic,
catalepsy forming a major component of the twig mimesis exhibited by this
species. The neuronal networks which control postural leg movements in
locusts and stick insects are tuned differently to their specific behavioral
tasks. An important prerequisite for the production of catalepsy in the stick
insect is the marked velocity dependency of the control network, which appears
to be generated at the level of nonspiking local interneurons (Driesang and
Bschges 1993). We examined interneuronal pathways in the network controlling
the femur-tibia joint of the locust middle leg, and compared its properties
with those described for the stick insect middle leg. It was our aim to
identify possible neural correlates of the species-specific behavior with
regard to postural leg motor control. 2. We obtained evidence that the
neuronal networks which control the femur-tibia joints in the two species
consist of morphologically and physiologically similar - and thus probably
homologous - interneurons. Qualitatively, these interneurons receive the same
input from the femoral chordotonal organ receptors and they drive the same
pools of leg motoneurons in both species. 3. Pathways that contribute to the
control of the femur-tibia joint include interneurons that support both
"resisting" and "assisting" responses with respect to the
motoneuron activity which is actually elicited during reflex movements. Signal
processing via parallel, antagonistic pathways therefore appears to be a
common principle in insect leg motor control. 4. Differences between the two
insect species were found with regard to the processing of velocity
information provided by the femoral chordotonal organ. Interneuronal pathways
are sensitive to stimulus velocity in both species. However, in the locust
there is no marked velocity dependency of the interneuronal responses, while
in the same interneurons of the stick insect, it is pronounced (Bschges,
1990). This characteristic was maintained at the level of the motoneurons
controlling the femur-tibia joint. Pathways for postural leg motor control in
the locust thus lack an important prerequisite for the generation of
catalepsy, that is, a marked velocity dependency.
Received 23 June 1994; accepted in final form 4 January 1995.
APS Manuscript Number J375-4.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 3 April 1995.