(averaged)-60-401 c 2 m V
m V 2 m s 2 m s fle xio n fle xio n extension extension difference (f-e) rest
rest co rd dorsum 2 m V E D B 2t LG S 2t E D L 1.4t
dis yna ptic m onosyn aptic
科学
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C E
D L 2t
E D L 2t E DL intracell.LG S eng S art eng Group I disynaptic excitation in flexor and bifunctional motoneurons during locomotion.Jorge Quevedo, Brent Fedirchuk, Simon Gosgnach and David McCrea. Dept. Physiology U.Manitoba, Winnipeg, Canada. Annals of the New York Academy of Sciences, 860: 499-501(1998).扁鹊治病教学设计
In the abnce of locomotion, activation of extensor muscle spindle (Ia) and tendon organ (Ib) afferents
evokes a widespread pattern of interneuronally mediated inhibition and excitation through the non-reciprocal reflex systems (1). During the extension pha of fictive locomotion,however, the same afferents evoke a disynaptic excitation of extensor motoneurons (2). Recently it has been reported that stimulation of flexor group I afferents also evokes a locomotor-dependent excitation of ankle flexor motoneurons (3). The prent study further examined the distribution of locomotor-dependent group I excitation of flexor motoneurons and extended the analysis to motoneurons showing complex patterns of depolarization during locomotion, i.e. motoneurons innervating bifunctional muscles. Intracellular recordings of antidromically identified motoneurons were made (using glass microelectrodes filled with QX-314 to block action potentials) in decerebrate cats in which fictive locomotion was elicited by brainstem stimulation following neuromuscular blockade (e reference 2).
We found a wide distribution of locomotion-dependent group I disynaptic excitation in motoneurons innervating flexor and bifunctional muscles. Fig. 1 illustrates an extensor digitorum longus (EDL) motoneuron depolarized during the flexor pha of the step cycle. Stimulation of the homonymous nerve produced monosynaptic excitation followed by a disynaptic EPSP (Fig.1B; Fig 1C, black and white arrowheads respectively) that was larger during flexion. Extensor digitorum brevis (EDB) nerve 沟通协调能力
stimulation produced disynaptic EPSPs that again were largest during flexion (Fig. 1C). Most (38/43) flexor motoneurons (mainly EDL, tibialis anterior,sartorius and peroneus longus) showed disynaptic EPSPs during locomotion with latencies (1.3-
2.2 ms, 32/38 < 1.9ms) suggesting a single interneuron interpod between flexor group I afferents and motoneurons. Disynaptic EPSPs were evoked by the electrical stimulation of flexor nerves, recruiting both Ia and Ib afferents as well as by lective activation of Ia muscle spindle afferents produced by small (30 µm) stretches of the EDL muscle. In all cas disynaptic EPSPs were largest during flexion, very small or abnt during extension and rarely prent at rest.Stimulation of extensor nerves produced no respons in flexor motoneurons (e. g. LGS stimulation in Fig. 1C).
Figure 1. Disynaptic excitation in an EDL
motoneuron evoked by homonymous and heteronymous group I afferents is largest during flexion. (A ) from left to right, integrated rectified
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extensor (LGS) and flexor (Sart) neurograms (ENGs)
and low (vertical trace ) and high gain (horizontal
traces ) intracellular recordings. The horizontal high-gain intracellular records show the effects of EDL
nerve stimulation (twice threshold, 2t intensity)during flexion (dots ) and extension (dashes ). (B )from top to bottom, averaged traces (76 step cycles)
of the high gain intracellular recordings calculated during flexion and extension, the difference between flexion and extension, the effects before locomotion (rest, dotted trace ) and the cord dorsum recording.The disynaptic component (white arrowhead ) is small during extension and abnt at rest.
鲁滨逊漂流记目录Monosynaptic EPSPs (black arrowhead ) are larger during extension. (C ) averages of the PSPs produced by the stimulation of extensor digitorum brevis (EDB), lateral gastrocnemius-soleus (LGS) and EDL nerves. EDB stimulation produced disynaptic EPSPs that were largest during flexion and without a monosynaptic component.
LGS eng m V -70-60
intracell.1 c A B
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ED L eng 2 m s 2 m V 0.5 mV MG 2t PerT+B 1.8t Late flexion (Lf)L f early extension (ee)
ee e x t e n s i o n f l e x i o n Late extension (Le)rest rest r e s t e e L L Stimulation of EDL with a strength 1.4t produced mono- and disynaptic EPSPs and LGS stimulation was without effect.
Fig. 2 illustrates a Peroneus tertius or brevis motoneuron displaying a complex pattern of depolarization during the transition from flexion to extension and from extension to flexion (lower trace in Fig. 2A). Stimulation of the homonymous nerve (PerT+B) produced disynaptic EPSPs (latency 1.5 ms, 2B) following the monosynaptic EPSP that were largest during late flexion and abnt at rest and during late extension. Ankle extensor nerve (medial gastrocnemius, MG)stimulation produced disynaptic EPSPs (latency 1.3 ms; Fig. 2B) that were largest during early extension and produced IPSPs during late flexion (Fig. 2B). Most (21/30) motoneurons biphasically depolarized during flexion and extension (mainly Quadriceps, Rectus Femoris and Per-tert/brevis) received disynaptic EPSPs from homonymous and heteronymous flexor nerves.Although the modulation of disynaptic EPSPs in bifunctional motoneurons is complex, disynaptic EPSPs were generally largest when the target motoneuron is depolarized.
Figure 2. Differential modulation of
disynaptic EPSPs produced by two different nerves in a Peroneus brevis or tertius motoneuron. (A ) integrated and rectified LGS and EDL ENGs and the low gain intracellular record. The step cycle was divided in four gments (early flexion, late flexion, early extension and late extension) as indicated in order to construct the averages in (B ). Stimulation of the PerT+B nerve produced a disynaptic EPSP (white arrowhead ) following the monosynaptic EPSP (black arrowhead ).
The largest disynaptic EPSP occurred during late flexion and not when the motoneuron was most depolarized. The right panel in (B ) shows that the EPSPs produced by MG nerve stimulation were largest during early extension; i. e.in a different pha that the PerT+B evoked EPSPs.The differential phasic modulation of disynaptic EPSPs in extensor (2), flexor (3, and prent results) and bifunctional (prent results) motoneurons indicates the cyclic modulation during locomotion of veral excitatory interneuron populations projecting directly to motoneurons. Some motoneurons receive disynaptic excitation from at least two populations of excitatory interneurons (e. g. the PerT+B and MG effects illustrated in Fig. 2B). The abnce of group I disynaptic EPSPs at rest suggests that the involved interneurons are tonically inhibited during non-locomoting conditions. Candidate interneurons located in the intermediate nucleus likely to mediate disynaptic excitation of extensors have been described recently (4). Disynaptic excitation may be one of the mechanisms by
which muscle spindle and tendon organ feedback can reinforce the ongoing step cycle (2,5). Since a short-latency group I excitatory component can also be expresd during human locomotion (6), understanding the control of disynaptic excitatory pathways may be important for an appreciation of reflex dysfunction (i.e. spasticity) following stroke or spinal injuries. Supported by the Canadian MRC and Rick Hann Legacy Fund.
REFERENCES
1. Jami, L. 199
掉睫毛2. Golgi tendon organs in mammalian skeletal muscle: Functional properties and
central actions. Physiol. Rev. 72: 623-666
2. Angel, M.J., P. Guertin, I. Jiménez & D.A. McCrea. 1996. Group I extensor afferents evoke
disynaptic EPSPs in cat hindlimb extensor motorneurones during fictive locomotion. J.渣男星座排名
Physiol. 494: 851-861.
3. Degtyarenko, A.M., E.S. Simon, T. Norden-Krichmar, & R.E. Burke. 1998. Modulation of
oligosynaptic cutaneous and muscle afferent reflex pathways during fictive locomotion and scratching in the cat. J. Neurophysiol.79: 447-463.
4. Angel, M. J., E. Jankowska & D.A. McCrea (in preparation). Fictive locomotor activity of
candidate interneurones mediating group I disynaptic EPSPs in extensor motoneurones in the cat. To be submitted to J. Physiol.
5. McCrea, D.A., S.J. Shefchyk, M.J. Stephens & K.G. Pearson. 1995. Disynaptic group I
excitation of synergist ankle extensor motoneurones during fictive locomotion in the cat.
J. Physiol.487: 527-539.
6. Stephens, M. J. & J.F. Yang. 1996. Short latency, non-reciprocal group I inhibition is reduced
during walking in humans. Brain Res.743: 24-31.
