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Author  |
Alvarez, J.; Fadic, R. |
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Title |
Assembly and disassembly of axonal microtubules of the toad Xenopus laevis under the effect of temperature |
Type |
Journal Article |
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Year |
1992 |
Publication |
The Journal of Experimental Zoology |
Abbreviated Journal |
J Exp Zool |
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Volume |
264 |
Issue |
3 |
Pages |
261-266 |
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Keywords |
Animals; Axons/*physiology; Cytoplasm/metabolism; Kinetics; Microtubules/*physiology; Seasons; *Temperature; Tubulin/metabolism; Xenopus laevis |
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Abstract |
In toads Xenopus laevis living at 11 degrees (winter), the microtubular density of 4-microns myelinated axons of lumbosacral nerves was assessed with the electron microscope. In controls, the density was 11.2 microtubules/microns2. In nerves incubated at 0 degrees, microtubules decreased following a simple exponential curve with a half time of 4.7 min (k = 0.149 min-1); residual microtubules were 4.5%. After rewarming, the full complement of microtubules reappeared within 60 min. In steady state, the microtubular density exhibited a linear relationship with temperature (range: 0-22 degrees; slope 0.94 microtubules/microns 2 per degree; r, 0.96). After heating the nerve by 11 degrees above the physiological temperature, microtubules increased by 83%, whereby the pool of unpolymerized tubulin was at least 2.7 mg/ml of axoplasm. A seasonal variation of the microtubular density was observed which accorded with the environmental temperature. The macroscopic kinetics of microtubule disassembly in the axoplasm is similar to that reported for purified tubulin but that of assembly is slower. Microtubules of peripheral axons of Xenopus are cold-labile and vary during the annual cycle. |
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Call Number |
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Serial |
1174 |
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Author |
Crider, M.E.; Cooper, R.L. |
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Title |
Importance of stimulation paradigm in determining facilitation and effects of neuromodulation |
Type |
Journal Article |
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Year |
1999 |
Publication |
Brain Research |
Abbreviated Journal |
Brain Res |
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Volume |
842 |
Issue |
2 |
Pages |
324-331 |
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Keywords |
Animals; Astacoidea; Axons/*physiology; Electric Stimulation; Electromyography; Evoked Potentials; In Vitro Techniques; Membrane Potentials; Muscle, Skeletal/innervation/physiology; Nerve Endings/physiology; Neuromuscular Junction/*physiology; Synaptic Transmission/physiology |
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Abstract |
Evoked synaptic activity within the CNS and at the neuromuscular junction in most in vivo preparations studied occurs not with single isolated stimuli, but with trains, or bursts, of stimuli. Although for ease in studying the mechanisms of vesicular synaptic transmission one often uses single discrete stimuli, the true mechanisms in the animal may be far more complex. When repetitive stimuli are present at a nerve terminal, often a heightened (i.e., facilitated) postsynaptic potential can be as a result. Facilitation is commonly used as an index of synaptic function and plasticity induced by chronic stimulation or by neuromodulation. The mechanisms that give rise to facilitation are thought to be the same that may underlie short-term learning and memory [C.H. Bailey, E.R. Kandel, Structural changes accompanying memory storage. Annu. Rev. Physiol. 55 (1993) 397-426.]. Differences in short term facilitation (STF) are seen depending on the conventional stimulation paradigm (twin pulse, train, or continuous) used to induce facilitation. Thus, a battery of paradigms should be used to characterize synaptic function to obtain a closer understanding of the possible in vivo conditions. |
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Call Number |
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Serial |
1593 |
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