Locomotor plasticity in the chick

• Main Author: Muir, Gillian D.
• Format: Others
• Language: English
• Published: 2009
• Online Access: http://hdl.handle.net/2429/4809

This thesis examines the behavioural plasticity of bipedal locomotion in the chick, both during normal development and after spinal cord injury. The locomotor characteristics of chicks were quantified as animals moved overground unrestrained. Kinematic data were recorded on videotape, while kinetic data were collected from a force platform built into the walkway. All measurements were made over a range of velocities and at regular intervals throughout the first 2 weeks posthatching. The results show that, although chicks can innately run as well as adults, they need to learn to walk in a mature manner over the first week posthatching. This disparity may arise from the distinct actions of the legs in these two behaviours, and the requirement for longer durations of single leg support during walking. In a separate group of animals, locomotor abilities were quantified as above prior to hemisection of the left thoracic spinal cord, and thereafter at regular intervals for 2 weeks. Chicks were also videotaped while they swam in a tank of water. In one group, phasic cutaneous stimulation was provided during swimming trials. Twenty-four to 48 hours after hemisection, chicks moved overground with a distinctly asymmetric gait. Range of joint motion of the left leg (ipsilateral to the hemisection) was reduced. Over the two week recovery period, left leg joint angles during walking recovered to normal pre-operative values, but did not return to pre-operative values during swimming trials. However, when chicks were provided with phasic cutaneous stimulation during swimming trials for 14 days, they showed improvements in leg motion which were retained even when the cutaneous stimulation was not provided. Possible neurophysiological mechanisms include reflexive activation of limb extensors in response to cutaneous stimulation, and subsequent strengthening of reflex pathways after repeated training with stimulation. It is proposed that, because the locomotor neural circuitry has completed development well before hatching in chicks, changes in locomotor behaviour posthatching or after spinal injury necessarily arise from plasticity of existing neural circuits rather than growth/regeneration of new projections. Chicks may therefore be a useful model for examination of neuroanatomical plasticity responsible for locomotor development and recovery after spinal injury. === Medicine, Faculty of === Graduate