ISSN:
1432-1351
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Medicine
Notes:
Summary 1. The physiological effects of two inhibitory axons supplying the stretcher muscles of three crabs (Hyas, Gecarcinus andGrapsus) were investigated, with a view to establishing the relative importance of pre- and postsynaptic inhibition. 2. InHyas, the specific inhibitory (SI) axon and the common inhibitory (CI) axon both exerted powerful presynaptic inhibition on the terminals of the excitatory axon. The effect of the SI axon was generally stronger, but some excitatory terminals were found in which CI axon stimulation was more effective. Thus, inhibition of the excitatory postsynaptic potential recorded intracellularly from the muscle fiber is the statistical result of variable inhibition at different excitatory terminals. 3. InHyas, postsynaptic inhibition was insignificant at low frequencies of stimulation, but increased at higher frequencies, for both SI and CI axons. The SI axon had a stronger postsynaptic effect than the CI axon. 4. InGecarcinus, the CI axon had a more powerful postsynaptic effect than the SI axon, whereas the SI axon was more effective at the presynaptic level. The two axons are specialized for different types of inhibition. 5. InGrapsus, the SI axon was more effective than the CI axon at both pre- and postsynaptic levels. Thus, considerable variation in pre- and postsynaptic connections of the two inhibitor axons occurs in different species of crabs. 6. In all species, the CI axon was least effective in muscle fibers with small, facilitating excitatory postsynaptic potentials. Sometimes the CI axon did not produce any effect at all in such fibers. 7. Presynaptic inhibition in crabs probably occurs mainly at narrow “bottlenecks” of the excitatory axon, where impulses are easily blocked by inhibitory synaptic action.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00613836
Permalink
