Longitudinal coordination of motor output during swimming in Xenopus embryos.
Little is known about the neural mechanisms that control the phenomenon of rostro-caudal delay. In Xenopus embryos there is a constant rostro-caudal delay of 2-5 ms mm-1 during fictive swimming. Rostro-caudal delay is not significantly correlated with cycle period. When NMDA is applied to the caudal spinal cord there is a decrease and in some cases a reversal in rostro-caudal delay. Conversely applying excitatory antagonists to the caudal spinal cord leads to an increase in delay. When caudal mid-cycle inhibition is reduced either pharmacologically using strychnine or surgically through hemisection of the spinal cord, there is an increase in rostro-caudal delay. Rostro-caudal delays are too small to be explainable on the basis of axonal conduction velocities and synaptic delays. This suggests that the central pattern generator of Xenopus behaves as a series of coupled oscillators and that the nature of the coupling, together with a longitudinal gradient in excitability associated with the oscillators, contributes to the observed rostro-caudal delay.
Tunstall
M J
MJ
Department of Zoology, Bristol University, U.K.
Roberts
A
A
D000818:Animals; D004625:Embryo, Nonmammalian; D009046:Motor Neurons / Q000187:drug effects / Q000502:physiology*; D016202:N-Methylaspartate / Q000494:pharmacology; D005082:Physical Exertion / Q000502:physiology*; D013116:Spinal Cord / Q000187:drug effects / Q000502:physiology; D013550:Swimming; D014982:Xenopus laevis
D016202:N-Methylaspartate