Al-Izki, S.; (2007) Actions of the rubrospinal tract in the cervical spinal cord of the rat. Doctoral thesis , University of London.

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Abstract

This thesis describes the electrophysiological and anatomical distribution of the projections from the rubrospinal tract (RST) in the cervical spinal cord of the rat, in control animals and animals with a dorsal column lesion. It also describes the behavioural changes following the lesion. The RST originates from the magnocellular region of the red nucleus (RNm), from where its axons project to the contralateral spinal cord, mostly in the dorsolateral funiculus (DLF). Previous work has shown that the RST is implicated in precise limb movements. It has also been demonstrated that where the corticospinal tract (CST) is impaired, the RST is capable of motor control and will compensate for the damage to the CST. In terminal experiments, electrical stimulation of the RNm elicited two orthodromic descending volleys recorded from the contralateral DLF. The latency of the early one indicated that it is produced by direct activation of fibres in or close to the RNm. Temporal facilitation demonstrated that the second volley is elicited by synaptic excitation of RNm neurons. Postsynaptic responses related to the second volley were seen only in the intermediate zone of the contralateral spinal cord. In animals with a dorsal column lesion, the distribution of RST actions is similar to that of the controls. Functional recovery in lesioned animals was assessed using three behavioural tests: pellet retrieval, cylinder, and the sticker removal test. The cylinder and sticker removal tests have both shown to be ineffective in providing important information on the recovery. However, the pellet retrieval test, which requires skilled motor control, has enabled correlation of recovery to size of lesion. The results obtained demonstrate that lesion to dorsal columns alone has little effect on the success rate. The anatomical and electrophysiological experiments provide information on the distribution of RST actions, which will be correlated in the thesis with the behavioural results. Evidence for plasticity will be discussed.

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