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- Harrison, P. J., et al.
(författare)
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Further evidence for synaptic actions of muscle spindle secondaries in the middle lumbar segments of the cat spinal cord.
- 1988
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Ingår i: The Journal of Physiology. - : Wiley. - 0022-3751 .- 1469-7793. ; 402, s. 671-686
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Tidskriftsartikel (refereegranskat)abstract
- 1. The aim of this study has been to investigate the receptor origin of postsynaptic actions evoked by group II muscle afferents in mid‐lumbar segments of the cat spinal cord. The experiments tested the hypothesis that the afferents involved were the secondary endings of muscle spindles. 2. Spindle afferents were activated by contractions of intrafusal muscle fibres which were induced by electrical stimulation of fusimotor axons in the distal parts of transected ventral roots by one to three stimuli at 150‐500 stimuli/s. A separate series of experiments has shown that such stimuli are effective in activating a considerable proportion of muscle spindle secondaries when contractions of extrafusal muscle fibres are eliminated by differential fatigue of these fibres, provided that several fusimotor axons are stimulated simultaneously. 3. Extracellular field potentials were recorded in the dorsal horn, at such locations where synaptic actions were evoked by electrical stimulation of group II but not group Ia muscle spindle or group Ib tendon organ afferents of pretibial flexors. Effects of activation of spindle afferents following stimulation of fusimotor axons were then compared with effects evoked by electrical stimulation of group II afferents of anterior tibial or extensor digitorum longus nerves and by small stretches of these muscles. 4. Distinct field potentials were evoked by stimulation of ventral root fibres at all locations at which field potentials were obtained from group II afferents stimulated electrically. The latencies of these field potentials were in both cases shorter in the dorsal horn than in the ventral horn. 5. The appearance of these field potentials was not related to contractions of extrafusal muscle fibres and was also observed when these contractions were practically eliminated. Furthermore, their threshold and similar dependence on a potentiating effect of two to three stimuli, as found for single secondaries, allow them to be attributed to secondary endings of muscle spindles. © 1988 The Physiological Society
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| 2. |
- Harrison, P. J., et al.
(författare)
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Lamina VIII interneurones interposed in crossed reflex pathways in the cat.
- 1986
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Ingår i: The Journal of Physiology. - : Wiley. - 0022-3751 .- 1469-7793. ; 371, s. 147-166
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Tidskriftsartikel (refereegranskat)abstract
- The location of a group of interneurones projecting to contralateral motor nuclei has been established using retrograde transneuronal transport of horseradish peroxidase conjugated with wheat germ agglutinin (WGA‐HRP). After labelling the motoneurones of semitendinosus, medial gastrocnemius or quadriceps muscles, interneurones which were secondarily labelled were found in lamina VIII and in the neighbouring narrow strip of lamina VII. They were found to be distributed from the 4th lumbar to the 1st sacral segments, with the highest concentration in the 6th and 7th lumbar segments and at the border between the 4th and 5th lumbar segments. The electrophysiological properties of lamina VIII interneurones of the 6th lumbar segment have been investigated using both extracellular and intracellular recording. Many of these interneurones could be antidromically activated following weak stimuli applied in contralateral motor nuclei. Post‐synaptic potentials were evoked from a variety of primary afferents including group I muscle afferents. However, when present, the post‐synaptic potentials (p.s.p.s) of group I origin were of considerably smaller amplitudes than p.s.p.s. evoked from higher threshold muscle or cutaneous afferents and smaller than p.s.p.s. which followed stimulation of the spinal cord at the thoracic level. P.s.p.s. from the latter two sources appear to constitute the main input to lamina VIII interneurones. Group I input has been found in forty lamina VIII interneurones. These were usually affected by either ipsilateral or contralateral group I afferents and only exceptionally by both. Excitatory post‐synaptic potentials (e.p.s.p.s) from ipsilateral afferents were evoked in about twice as many neurones as e.p.s.p.s from the contralateral afferents. E.p.s.p.s were often accompanied by inhibitory post‐synaptic potentials (i.p.s.p.s). Group Ia afferents appeared to contribute to both e.p.s.p.s and i.p.s.p.s, whether these were evoked from ipsilateral or from contralateral afferents. In several cases Ia afferents were as effective as all group I afferents while in other cases Ib afferents appeared to be an important or even the exclusive source of the p.s.p.s. The latencies of e.p.s.p.s indicated that they were evoked mono‐, di‐ or trisynaptically from ipsilateral group I afferents and di‐ or trisynaptically from contralateral afferents, I.p.s.p.s appeared to be evoked via pathways with only one additional interneurone. About one‐third of all the intracellularly investigated lamina VIII interneurones were both affected by group I afferents and antidromically activated from the contralateral motor nuclei.(ABSTRACT TRUNCATED AT 400 WORDS) © 1986 The Physiological Society
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| 3. |
- Harrison, P. J., et al.
(författare)
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Organization of input to the interneurones mediating group I non‐reciprocal inhibition of motoneurones in the cat.
- 1985
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Ingår i: The Journal of Physiology. - : Wiley. - 0022-3751 .- 1469-7793. ; 361, s. 403-418
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Tidskriftsartikel (refereegranskat)abstract
- Patterns of convergence of different presynaptic fibre types onto interneurones mediating non‐reciprocal inhibition of motoneurones have been studied in order to investigate to what extent the population of these interneurones is homogeneous or can be divided into subgroups on the basis of their input. In a sample of interneurones, all of which were interposed in pathways from the group I afferents of one group of muscles (triceps surae and plantaris), individual interneurones exhibited a wide variety of convergence patterns. Some interneurones were influenced by only a few types of afferent or descending fibre systems whereas others were influenced by many. Furthermore, various fibre systems excited and/or inhibited individual interneurones in different combinations. While there appeared to be too many patterns of convergence to allow any simple classification into a few distinct groups of interneurones, two possibilities were considered. One was that certain presynaptic fibre types influence individual interneurones in preferred combinations. The other was that they converge entirely at random. To investigate this, the frequencies of convergence of various pairs of fibre types were predicted assuming that each of them influences a proportion of the interneurones independently of other sources. Generally, there was close correspondence between such predicted and observed frequencies of occurrence of tested combinations of input. These findings are thus compatible with an organization whereby individual presynaptic fibres innervate a random sample of the population of interneurones. Deviations from the predicted incidence of convergence patterns were found primarily for synaptic actions mediated di‐ or oligosynaptically and are attributed to a consequence of convergence at the pre‐interneuronal level. A particular consequence of such an organization is that interneurones in pathways of non‐reciprocal inhibition are shared by afferents of different muscles in a continuum of combinations. The functional implications of this arrangement are discussed. © 1985 The Physiological Society
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| 4. |
- Harrison, P. J., et al.
(författare)
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Primary afferent depolarization of central terminals of group II muscle afferents in the cat spinal cord.
- 1989
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Ingår i: The Journal of Physiology. - : Wiley. - 0022-3751 .- 1469-7793. ; 411, s. 71-83
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Tidskriftsartikel (refereegranskat)abstract
- 1. The origin of primary afferent depolarization (PAD) of the central terminals of group II afferent fibres of tibialis anterior and extensor digitorum longus muscles has been investigated in the cat. Changes in the excitability of the terminals to intraspinal stimuli, upon application of conditioning stimuli to muscle nerves (quadriceps, sartorius, gracilis, posterior biceps‐semitendinosus, anterior biceps‐semimembranosus, gastrocnemius‐soleus, deep peroneal), cutaneous nerves (sural, superficial peroneal) and the posterior nerve to the knee joint, were used as a measure of PAD. 2. PAD was most readily evoked by conditioning stimuli which were maximal for group II muscle afferents. However, some PAD was also evoked from group I afferents and evidence is presented that group Ia afferents contributed. Afferents of posterior biceps‐semitendinosus and sartorius muscles appeared to be most effective. PAD was also evoked by stimulation of cutaneous and joint nerves, often in the same fibres which were affected by group Ia afferents. 3. It is concluded that there are several common sources of PAD of group II and group Ia afferent terminals on the one hand, and group Ib afferent terminals on the other. 4. The properties of PAD of group II afferents are discussed in relation to the problem of how PAD affects transmission from fibres with long terminal branches of small diameter. © 1989 The Physiological Society
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| 5. |
- Harrison, P. J., et al.
(författare)
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Sources of input to interneurones mediating group I non‐reciprocal inhibition of motoneurones in the cat.
- 1985
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Ingår i: The Journal of Physiology. - : Wiley. - 0022-3751 .- 1469-7793. ; 361, s. 379-401
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Tidskriftsartikel (refereegranskat)abstract
- Intracellular recordings have been made from laminae V‐VI interneurones interposed in pathways of non‐reciprocal inhibition of motoneurones from group I afferents of triceps surae and/or plantaris. A comparison of actions of brief stretches of triceps surae and plantaris with actions of electrical stimulation of nerves of these muscles revealed that I a afferents influenced about a half of the interneurones excited by I b afferents. Electrical stimulation of seven muscles nerves, three cutaneous nerves, posterior knee joint and interosseous nerves, the red nucleus and the pyramidal tract, evoked excitatory post‐synaptic potentials (e.p.s.p.s) in various proportions of interneurones. Most of the interneurones were excited monosynaptically, or both monosynaptically and disynaptically by group I afferents. This, together with a very small proportion of interneurones in which e.p.s.p.s were evoked only disynaptically, indicates that the same last‐order interneurones may subserve di‐ and trisynaptically evoked inhibition of motoneurones. Other fibre systems excited these interneurones monosynaptically (interosseal, rubro‐ and corticospinal), disynaptically (cutaneous, rubro‐ and corticospinal) and polysynaptically. The coupling of the earliest e.p.s.p.s from group II and joint afferents could not be established, but was consistent with their mediation by only one or two interposed interneurones. Inhibition was evoked from all fibre systems with excitatory input to the same or to other interneurones of the sample, except from group II afferents, the effects of which were found in a much smaller number of cells and may not be fully representative. © 1985 The Physiological Society
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