Portal de Periódicos da CAPES

Functional Specificity of Spinal Cord Segments in the Control of Limb Movements

1963; The Company of Biologists; Volume: 11; Issue: 2 Linguagem: Inglês

10.1242/dev.11.2.431

1477-9129

George Székely,

Assisted Reproductive Technology and Twin Pregnancy

ABSTRACT Spinal cord segments from limb levels (both brachial and lumbo-sacral) were homoplastically grafted into the place of previously removed thoracic segments in newt embryos. In other embryos the brachial segments were replaced by lumbo-sacral segments or vice versa. In early larval stages a pair of supernumerary limbs were transplanted at the level of the grafted segments in the thoracic region. The function of normal and supernumerary limbs inner-vated by heterotopic spinal cord segments was studied. When brachial segments were substituted for thoracic segments the super-numerary limbs yielded co-ordinated stepping movements, perfectly synchro-nized with the normal forelimbs. Apart from minor discrepancies arising from differences in gross anatomical structure, the same rhythm and co-ordination of stepping movements were found whether fore- or hindlimbs were transplanted. Brachial segments in lumbo-sacral positions were able to bring the normal hindlimbs into co-ordinated movement. Although there was no correlation in the movements between the four limbs, the hindlimbs showed a definite ten-dency to move in parallel with the forelimbs on the same side. Supernumerary limbs, innervated by heterotopic lumbo-sacral segments grafted into thoracic regions, showed co-ordinated movements which accom-panied the movements of the normal hindlimbs either synchronously or, in most cases, with some delay. Essentially the same movement patterns were given both by transplanted fore- and hindlimbs except that the motility of the elbow was poorer than that of a normal forelimb. This was regarded as a ‘hindlimb character’ in the movement of forelimbs innervated by lumbo-sacral segments. Orthotopic forelimbs innervated by heterotopic lumbo-sacral segments grafted into brachial regions also disclosed co-ordinated movements with a tendency to move in parallel with the hindlimbs on the same side. Well-defined ‘hindlimb character’ was verified in both the motility and the posture of such limbs. The following conclusions were drawn, (i) A special segmental apparatus, already determined in early embryonic stages, exists at limb levels of the spinal cord for controlling co-ordinated limb movements, (ii) The rhythm and character of limb movements executed by these apparatus corresponded always to the nature of the innervating segments irrespective of the nature of the innervated limbs, (iii) A secondary process of determination was assumed to provide the fore- or hindlimb character of the differentiation of these segmental apparatus. The incomplete establishment of this determination might explain the observed time lag and irregularities in function of heterotopic lumbo-sacral segments under certain experimental conditions.