ISSN:
1432-2013
Keywords:
Frog
;
Inhibition
;
Presynaptic
;
Postsynaptic
;
Recurrent
;
Frosch
;
Hemmung
;
Präsynaptisch
;
Postsynaptisch
;
Rekurente Hemmung
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Summary Three mechanisms of inhibition in the spinal cord of frogs (Xenopus laevis) were investigated. Motoneuron excitability was assessed by the method of monosynaptic testing. The study revealed that orthodromic as well as antidromic volleys initiate central inhibitory phenomena. 1. Orthodromic volleys result in two different inhibitory processes. (i) Postsynaptic inhibition of motoneurons. The latency and time course of this inhibition is compatible with the view that the inhibitory pathway contains at least on inhibitory interneuron and is therefore comparable to the simplest inhibitory pathway of the mammalian spinal cord. (ii) Presynaptic inhibition of polysynaptic excitatory pathways. The time course of this mode of inhibition is identical with the time course of orthodromically elicited dorsal root potentials. Both postsynaptic and presynaptic inhibition by dorsal root volleys are similar to the corresponding processes in mammals. This presynaptic inhibition, however, does not affect monosynaptic reflex arcs. The demonstration of their existence is complicated in the frog by the occurrence of a powerful facilitatory component in a dorsal root volley. 2. Antidromic or recurrent volleys inhibit monosynaptic reflexes according to the same time course as antidromically elicited dorsal root potentials. The presynaptic location of the inhibition in the frog is confirmed by: (i) the finding that testing from descending motor pathways failed to show the inhibition and (ii) its subsistance under the influence of strychnine. The time course of recurrent inhibition and probably integrative value are comparable in frogs and in mammals. The mechanism underlying this inhibition in the frog, however, is very different from the postsynaptic Renshaw mechanism of the mammalian spinal cord. These observations show that the same result (recurrent inhibition) is obtained by different means in the two classes of vertebrates.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00596387
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