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The neuronal basis of the excitation received by motoneurones during swimming in curarized Xenopus embryos has been investigated further. Extracellular stimulation of axons in the fibre tracts of the spinal cord has been used to evoke unitary excitatory post-synaptic potentials (p.s.p.s) in motoneurones. The p.s.p.s. had a rise time of 3-5 ms and a long(More)
The spinal neurons in the embryos and young larvae of two amphibians (Xenopus and Triturus) and two fish (Oryzias and Brachydanio) are described and compared. They can be placed into a limited number of common neuron classes: Rohon-Beard sensory, dorsolateral and dorsolateral commissural sensory interneurons, inhibitory ascending interneurons, two classes(More)
Competitive athletes completed two studies of 2-h steady-state (SS) cycling at 70% peak O(2) uptake followed by 7 kJ/kg time trial (TT) with carbohydrate (CHO) intake before (2 g/kg) and during (6% CHO drink) exercise. In Study A, 12 subjects received either 6 mg/kg caffeine 1 h preexercise (Precaf), 6 x 1 mg/kg caffeine every 20 min throughout SS (Durcaf),(More)
We have used computer simulations as one way to test the hypothesis that locomotor rhythm production for swimming in frog embryo spinal cord depends on rebound from inhibition and is sustained by mutual re-excitation among spinal excitatory interneurons. All simulations were based on physiological and anatomical data on the neurons and circuitry of Xenopus(More)
Bath application of N-methyl-D-aspartate (NMDA), kainate or quisqualate to Xenopus embryos depolarized spinal cord motoneurones and reduced their input resistance in both normal salines and salines containing 20 mM-Mn2+ and 0.5 mM-Ca2+, or 2 X 10(-6) M-tetrodotoxin. This suggests that motoneurones possess all three types of excitatory amino acid receptor.(More)
Rohon-Beard neurones show substance P-like immunoactivity in their somas and in their centrally projecting axons. Peripherally, the morphology of their free nerve endings within the trunk skin has been shown using horseradish peroxidase staining. The excitation of Rohon-Beard neurones by natural and electrical stimulation of the skin has been examined using(More)
The young Xenopus tadpole is a very simple vertebrate that can swim. We have examined its behavior and neuroanatomy, and used immobilized tadpoles to study the initiation, production, coordination, and termination of the swimming motor pattern. We will outline the sensory pathways that control swimming behavior and the mainly spinal circuits that produce(More)
Understanding the neuronal networks in the mammal spinal cord is hampered by the diversity of neurons and their connections. The simpler networks in developing lower vertebrates may offer insights into basic organization. To investigate the function of spinal inhibitory interneurons in Xenopus tadpoles, paired whole-cell recordings were used. We show(More)
We have used an antibody to glutaraldehyde fixation complexes of gamma-amino butyric acid (GABA) to stain the developing central nervous system of Xenopus laevis embryos. Neuronal somata, growth cones, axons, and dendrites were found with GABA-like immunoreactivity. Transmission electron microscope (TEM) observations were made of axons and synapses. By(More)