The locomotor discharge characteristics of ankle flexor gamma‐motoneurones in the decerebrate cat.

Murphy, Peter R.; Hammond, Geoffrey R.

doi:10.1113/jphysiol.1993.sp019543

Cited by 14 publications

(14 citation statements)

References 26 publications

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“…It is also evident from this discussion that the central drive to the y-motoneurones is not reciprocally organized between flexors and extensors, as for a-motoneurones. In the decerebrate cat, for example, the static y-drive in extensors is strongly activated throughout the step cycle (Murphy et al 1984;Bessou et al 1986), even though there is also strong static y-drive in the flexors (Cabelguen, 1981;Murphy & Hammond, 1993). Similar conclusions probably hold for clonidine-treated spinal cats (Fig.…”

Section: Discussionsupporting

confidence: 67%

Regulation of soleus muscle spindle sensitivity in decerebrate and spinal cats during postural and locomotor activities.

Bennett

Serres

1996

The Journal of Physiology

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1. In order to study fusimotor control in reduced preparations, soleus muscle spindle afferents were recorded in premammillary decerebrate cats (n = 15) during crossed extensor reflexes and, after spinalization, during locomotion produced by either clonidine or L-l-3,4-dihydroxyphenylalanine (L-DOPA). The soleus muscle was oscillated sinusoidally (025 mm, 4 Hz) and the afferent mean firing rate and modulation were calculated. An increase in firing rate was assumed to arise from activity in dynamic y-motoneurones (dynamic y-drive) when associated with an increase in modulation to stretching, and in static y-motoneurones (static y-drive) when modulation decreased. 2. At rest in all preparations the firing rate and modulation in primary muscle spindle afferents were generally much higher than after de-efferentation (ventral root section), suggesting a predominant dynamic y-drive. Clonidine decreased and even eliminated this presumed resting y-drive in many afferents, both in the decerebrate (7 of 8) and the spinal (6 of 18) state. This effect on y-drive may account, at least in part, for its suppressive effect on spasticity in humans. 3. When locomotion commenced in clonidine-treated spinal cats, primary afferents generally fired with much higher mean rates (+121 %) and lower sensitivities (-32 %), suggesting a large increase in static y-drive (possibly accompanied by a small decrease in dynamic y-drive). These high rates were usually maintained tonically throughout the step cycle. However, a third of the afferents were silenced during locomotor contractions, and de-efferentation had no significant effect on their firing rates. Thus, for some spindles a-activity can occur without significant y-drive. 4. During locomotion in L-DOPA-treated spinal cats the inferred static y-drive only occurred phasically, coactivated with the EMG, though it could precede the EMG by 100-500 ms. In the flexion phase both the afferent rate and modulation were lower than before locomotion, suggesting a lack of effective y-drive. 5. Crossed extensor reflexes in decerebrate cats also produced a substantial increase in primary afferent firing rate (+187 %) and decrease in sensitivity (-37 %), again suggesting increased static y-drive (n = 18). This y-drive was largely independent of EMG activity and often occurred without a-activity. The mean firing rate of secondary muscle spindle afferents increased significantly during locomotion (with L-DOPA) and crossed extensor reflexes, again indicating increased static y-drive. Clonidine reduced or eliminated the y-drive in seven of eight afferents during crossed extensor reflexes. 6. In conclusion, although there are some common features, such as a predominant static y-drive in all walking preparations, the pattern of static and dynamic y-drive is not closely linked to a-activity under the conditions studied. As well as y-drive without a-activity, we have shown for the first time that a-motoneurones can be activated without significant y-drive to many spindles during behavioural tasks.

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Section: Discussionsupporting

confidence: 67%

Regulation of soleus muscle spindle sensitivity in decerebrate and spinal cats during postural and locomotor activities.

Bennett

Serres

1996

The Journal of Physiology

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“…Another source of similar data was more strongly supportive of there being such modulated static fusimotor drive (Loeb, Hoffer & Pratt, 1985). Recently, further recordings from ã_motoneurones in decerebrates have been taken to favour a modulated static discharge in hindlimb flexors (Murphy & Hammond, 1993). It is possible that the differences between the various studies may reflect real differences in the strategy of use of the ã_motor system in different muscles groups and tasks.…”

Section: Discussionmentioning

confidence: 82%

Fusimotor Influence on Jaw Muscle Spindle Activity during Swallowing‐Related Movements in the Cat

Taylor

Hidaka

Durbaba

et al. 1997

The Journal of Physiology

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The activity patterns of muscle spindle afferents in jaw‐closer muscles were studied during reflex swallowing movements in anaesthetized cats. Simultaneous records were made of the electromyogram (EMG) in masseter and anterior digastric muscles and of the unloaded jaw movements. The underlying patterns of fusimotor activity were deduced by comparing afferent discharges occurring during active swallowing with those occurring when exactly the same movements were imposed passively. The interpretation of spindle behaviour was greatly facilitated by characterizing the afferents according to the evidence for their contact with the various intrafusal muscle fibres, derived from testing with succinylcholine. It was also valuable to have two different types of afferent recorded simultaneously. There was clear evidence of fusimotor activity occurring during active jaw closing so as to oppose the spindle silencing. This effect was most marked in b2c‐type afferents (probably secondaries) and was therefore attributed to a modulation of static fusimotor discharge approximately in parallel with α‐activity. Afferents with evidence of bag1 fibre contacts (primaries) showed much greater sensitivity to muscle lengthening during active movement than when the movement was imposed. This difference was exaggerated when anaesthesia was deepened for the passive movements. This was interpreted as evidence for a higher level of dynamic fusimotor activity maintained during active movements than at rest. The results support the view that for a variety of active jaw movements, static fusimotor neurone firing is modulated roughly in parallel with α‐activity but leading it so as to counteract spindle unloading. Dynamic fusimotor neurone firing appears to be set at a raised level during active movements. Anaesthesia appears to depress activity in the α‐motoneurones more than in γ‐motoneurones.

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“…By indirect means, an association was made between high resting rates, highly modulated discharge during locomotion and dynamic nature of gamma efferents, whereas low resting rates and non-modulated discharge during locomotion were ascribed to static efferents. When Murphy & Hammond (1993) recorded from gamma efferents supplying a denervated ankle flexor muscle, they Fig. 6 Identification of gamma axons by stimulation of the midbrain.…”

Section: Fusimotor Activity During Locomotionmentioning

confidence: 99%

Muscle spindle and fusimotor activity in locomotion

2015

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Mammals may exhibit different forms of locomotion even within a species. A particular form of locomotion (e.g. walk, run, bound) appears to be selected by supraspinal commands, but the precise pattern, i.e. phasing of limbs and muscles, is generated within the spinal cord by so-called central pattern generators. Peripheral sense organs, particularly the muscle spindle, play a crucial role in modulating the central pattern generator output. In turn, the feedback from muscle spindles is itself modulated by static and dynamic fusimotor (gamma) neurons. The activity of muscle spindle afferents and fusimotor neurons during locomotion in the cat is reviewed here. There is evidence for some alpha-gamma co-activation during locomotion involving static gamma motoneurons. However, both static and dynamic gamma motoneurons show patterns of modulation that are distinct from alpha motoneuron activity. It has been proposed that static gamma activity may drive muscle spindle secondary endings to signal the intended movement to the central nervous system. Dynamic gamma motoneuron drive appears to prime muscle spindle primary endings to signal transitions in phase of the locomotor cycle. These findings come largely from reduced animal preparations (decerebrate) and require confirmation in freely moving intact animals.

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The locomotor discharge characteristics of ankle flexor gamma‐motoneurones in the decerebrate cat.

Cited by 14 publications

References 26 publications

Regulation of soleus muscle spindle sensitivity in decerebrate and spinal cats during postural and locomotor activities.

Regulation of soleus muscle spindle sensitivity in decerebrate and spinal cats during postural and locomotor activities.

Fusimotor Influence on Jaw Muscle Spindle Activity during Swallowing‐Related Movements in the Cat

Muscle spindle and fusimotor activity in locomotion

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