Intra- and intersegmental pathways active during walking in the locust

Abstract

Electrical stimulation of femoral chordotonal organs, trochanteral campaniform sensilla, trochanteral hairplates and tibial muscles was used to reveal neuronal pathways active in the standing and walking locust. Responses evoked by campaniform sensilla stimulation were recorded intracellularly from flexor motoneurons in fixed animals. The trochanteral campaniform sensilla have a direct short-latency connection to tibial extensor motoneurons and more labile, longer-latency, excitatory and inhibitory connections to the tibial flexors of the same leg. Trains of stimuli to the trochanteral campaniform sensilla initiated an early swing only if the stimulation was timed to occur during late stance. Stimulation of the femoral chordotonal organ revealed short latency, exictatory pathways to both extensor and flexor motoneurons of the same leg. Stimulation of the posterior trochanteral hairplates often evoked a swing but the latency could be several hundred milliseconds. Deafferentation showed that sensory input is critical for interganglionic coordination. There are labile polysynaptic excitatory and inhibitory pathways from the trochanteral companiform senilla to the flexor motoneurons of the adjacent leg. Stimulation of the chordotonal organ revealed fast-conducting stable pathways to the flexors and extensors of all the ipsilateral legs. Load afference is necessary for the effectiveness of the intersegmental chordotonal input to the walking-pattern generator. [Stimulation of the trochanteral hairplate revealed no intersegmental pathway.] The intra- and intersegmental pathways are summarized diagrammatically. An important function of load afference is to modulate the flow of proprioceptive and motor information within the walking-pattern generator.