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- Jankowska, Elzbieta, et al.
(författare)
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Effects of 4-aminopyridine on synaptic transmission in the cat spinal cord
- 1982
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Ingår i: Brain Research. - : Elsevier BV. - 0006-8993. ; 240, s. 117-129
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Tidskriftsartikel (refereegranskat)abstract
- An analysis was made of effects of 0.1-1.0 mg/kg 4-aminopyridine (4-AP) i.v. on excitatory and inhibitory spinal reflex pathways in lightly anaesthetized or decerebrated cats. The effects appeared within the first minutes of the injection, reached maximum after about 10-15 min and remained stable during at least several hours. 4-AP enhanced the following synaptic actions on motoneurones: monosynaptic excitation from Ia afferents and descending tracts, disynaptic and polysynaptic excitation from group Ib, group II, cutaneous and high threshold muscle afferents, disynaptic inhibition from Ia and Ib afferents and recurrent and polysynaptic inhibition from different afferents. 4-AP also increased primary afferent depolarization and excitation of ascending tract cells by peripheral stimuli. In the case of the disynaptic inhibitory pathways it has been shown that 4-AP may enhance the excitation of the interposed interneurones but it also increases the actionof these interneurones on the motoneurones; monosynaptic inhibition evoked in motoneurons by electrical stimulation of the axons of the inhibitory interneurones was used as a test response in these experiments. No indications were found of direct effects of 4-AP on excitability of afferent fibres or motoneurones to electrical stimuli. No systematic changes were either found in the membrane potential of motoneurones or in the duration of action potentials of these neurones or of primary afferents. It is therefore concluded that small doses of 4-AP enhance synaptic transmission in the spinal cord by an action at a presynaptic level. © 1982.
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- Jankowska, Elzbieta, et al.
(författare)
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Observations on neuronal pathways subserving primary afferent depolarization
- 1981
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Ingår i: Journal of Neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 46, s. 506-516
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Tidskriftsartikel (refereegranskat)abstract
- Latencies of presynaptic depolarization of group I muscle afferents and cutaneous afferents have been reinvestigated in an attempt to define the minimal number of interneurons interposed in the pathways of the presynaptic depolarization. Intra-axonal records from individual afferents, records of dorsal root potentials, and measurements of changes in excitability of individual afferents were used for this purpose. Some of the animals were treated with 4-aminopyridine to facilitate transmission via neuronal pathways. The minimal segmental latencies were measured relative to afferent volleys evoked by single electrical stimuli applied to peripheral nerves and to the second of a pair of stimuli. Due to subthreshold facilitatory effects of the first stimulus, the responses to the second stimulus appeared at a reduced latency. The minimal latencies of primary afferent depolarization found in this way were 1.7-2.0 ms. They were similar for group I and cutaneous afferents and in both cases compatible with a trisynaptic pathway (two interposed interneurons). Primary afferent depolarization was also evoked by local intraspinal stimuli applied in the dorsal horn, in the intermediate zone, and in the ventral horn to define the location of the last-order interneurons mediating depolarization group I and cutaneous afferents. Lowest threshold responses appearing with the shortest latencies (about 0.8 ms) and attributed to activation of the last-order interneurons were found when stimulating fairly restricted areas: within laminae V-VI for group I afferents and within laminae III-IV for cutaneous afferents. Both areas corresponded to the regions where the largest monosynaptic field potentials were evoked by fibers receiving the presynaptic depolarization. It is thus proposed that both the first- and last-order interneurons of the pathways may be located within these areas.
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