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Title: Behavioural and physiological differences in the motor systems of solitarious and gregarious locusts
Author: Blackburn, L.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2006
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There are differences in the walking behaviour of solitarious and gregarious locusts. Gregarious locusts walk 2.5 times faster; steps are longer and higher; the excursion of the femoro-tibial angle of the hind leg is larger; the body is held up and at an angle off the floor and the antennae are held up. Solitarious locusts hold the thorax and abdomen close to and parallel with the ground and hold the antennae down. There are also differences in the firing rate of the slow extensor tibiae motor neuron (SETi) in response to simulated flexion and extension of the leg, achieved by the controlled movement of the apodeme of the femoral chordotonal organ, a proprioceptor that monitors the movement of the leg around the femoro-tibial joint. At all simulated leg angles, the firing rate of SETi is higher in solitarious locusts than in gregarious. Muscle forces of the extensor tibiae (ETi) muscle of the hind leg were measured in response to extracellular stimulation of SETi and the fast extensor tibiae motor neuron (FETi) of the muscle. When SETi is stimulated at 1 Hz, the ETi of gregarious locusts produces twitches that are 3 times the amplitude, and that contract and relax faster than in solitarious. From 7 Hz to 50 Hz there no difference in the amplitude of contradictions produced. Solitarious locusts maintain greater catch tension in the presence of the neuromodulator octopamine, which otherwise potentiates twitch tension and increases the rate of contraction and relaxation of muscle contractions in both phases. When FETi is stimulated at 50 Hz for 10 seconds, there is a decline in tetanus of 32% over the stimulation period in solitarious locusts but 66% in gregarious. Spikes in FETi elicit excitatory post synaptic potentials (EPSPs) in F1Ti motor neurons (Hoyle and Burrows, 1973). The relationship between FETi and FlTi motor neurons was examined using double intracellular recording. At stimulation of 0.5-2 Hz, antidromically induced FETi spikes in solitarious locusts cause a greater degree of depression of flexor EPSPs than in gregarious. At 5-20 Hz there is no difference in EPSP depression, for example 20 Hz depression reaches 20% original amplitude in both phases after a stimulus train of 10 pulses. At all frequencies EPSP amplitude recovers less well in solitarious locusts. When a single stimulus pulse is given 10 seconds after the stimulus train at 20 Hz, EPSP amplitude in gregarious locusts recovers to 76% original height, but only to 63% in solitarious. Firing patterns recorded in FETi and flexors during kicking in solitarious show some similarities and some differences to those previously obtained in gregarious locusts.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available