Force detection in cockroach walking reconsidered: discharges of proximal tibial campaniform sensilla when body load is altered

Abstract

We examined the mechanisms underlying force feedback in cockroach walking by recording sensory and motor activities in freely moving animals under varied load conditions. Tibial campaniform sensilla monitor forces in the leg via strains in the exoskeleton. A subgroup (proximal receptors) discharge in the stance phase of walking. This activity has been thought to result from leg loading derived from body mass. We compared sensory activities when animals walked freely in an arena or on an oiled glass plate with their body weight supported. The plate was oriented either horizontally (70-75% of body weight supported) or vertically (with the gravitational vector parallel to the substrate). Proximal sensilla discharged following the onset of stance in all load conditions. In addition, activity was decreased in the middle third of the stance phase when the effect of body weight was reduced. Our results suggest that sensory discharges early in stance result from forces generated by contractions of muscles that press the leg as a lever against the substrate. These forces can unload legs already in stance and assure the smooth transition of support among the limbs. Force feedback later in stance may adjust motor output to changes in leg loading.

Proprioceptors involved in stinging response of the honeybee, Apis mellifera

“…In the cockroach, for example, sensilla responding to an increase or decrease in the force of the legs contribute to the onset of swing and reinforce leg coordination during walking (Keller et al, 2007;Ridgel et al, 1999;Noah et al, 2001Noah et al, , 2004Zill et al, 2009). In our experiments, the pinching stimulus to the campaniform sensilla situated on the sting evoked the stinging response, and the stinging movement was sustained for as long as the sting was pinched.…”

Effects of aging on behavior and leg kinematics during locomotion in two species of cockroach

“…Therefore, alterations of posture and gait are often required to move an animal forward (Carlson-Kuhta et al, 1998;Pelletier and Caissie, 2001). In insects, force receptors on the legs would be important in the detection of changing gravitational forces during inclined walking (Duysens et al, 2000;Noah et al, 2001).…”

Load compensation in targeted limb movements of an insect

“…Those on the coxal and trochanteral segments near the base of the leg are key elements in load-compensating reactions during walking, when the leg is in contact with the ground (e.g. Zill et al, 1999;Noah et al, 2001). These campaniform sensilla are generally inactive when the leg is off the ground (as during scratching).…”

“…In insects, load compensation has been studied in the context of posture or gait control (e.g. Pearson, 1972;Bässler, 1977;Cruse, 1990;Dean, 1991;Noah et al, 2001), but not in the context of aimed limb movements where load sharing and other coordinating mechanisms between legs can be excluded. The goal of this paper is to determine whether such aimed movements in an insect are compensated against altered loading.…”