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Titolo:
REGULATION OF SOLEUS MUSCLE-SPINDLE SENSITIVITY IN DECEREBRATE AND SPINAL CATS DURING POSTURAL AND LOCOMOTOR ACTIVITIES
Autore:
BENNETT DJ; DESERRES SJ; STEIN RB;
Indirizzi:
UNIV ALBERTA,DIV NEUROSCI,DEPT PHYSIOL,513 HERITAGE MED RES CTR EDMONTON AB T6G 2S2 CANADA UNIV ALBERTA,DIV NEUROSCI,DEPT PHYSIOL EDMONTON AB T6G 2S2 CANADA
Titolo Testata:
Journal of physiology
fascicolo: 3, volume: 495, anno: 1996,
pagine: 835 - 850
SICI:
0022-3751(1996)495:3<835:ROSMSI>2.0.ZU;2-G
Fonte:
ISI
Lingua:
ENG
Soggetto:
PREMAMMILLARY CATS; GAMMA-MOTONEURONS; IMPULSE RATES; CORD INJURY; MODULATION; AFFERENTS; REFLEX; DISCHARGE; CLONIDINE; STRETCH;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Science Citation Index Expanded
Citazioni:
39
Recensione:
Indirizzi per estratti:
Citazione:
D.J. Bennett et al., "REGULATION OF SOLEUS MUSCLE-SPINDLE SENSITIVITY IN DECEREBRATE AND SPINAL CATS DURING POSTURAL AND LOCOMOTOR ACTIVITIES", Journal of physiology, 495(3), 1996, pp. 835-850

Abstract

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-beta-3,4-dihydroxyphenylalanine (L-DOPA). The soleus muscle was oscillated sinusoidally (0.25 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 gamma-motoneurones (dynamic gamma-drive) when associated with an increase in modulation to stretching, and in static gamma-motoneurones (static gamma-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 gamma-drive. Clonidine decreased and even eliminated this presumed resting gamma-drive in many afferents, both in the decerebrate (7 of 8) and the spinal (6 of 18) state. This effect on gamma-drive may account, at least in part, for its suppressive effect on spasticity in humans. 3. Whenlocomotion 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 gamma-drive (possibly accompanied by a small decrease in dynamic gamma-drive). Thesehigh 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 alpha-activity can occur without significant gamma-drive. 4. During locomotion in L-DOPA-treated spinal cats the inferred static gamma-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 thanbefore locomotion, suggesting a lack of effective gamma-drive. 5. Crossed extensor reflexes in decerebrate cats also produced a substantialincrease in primary afferent firing rate (+187 %) and decrease in sensitivity (-37 %), again suggesting increased static gamma-drive (n = 18). This gamma-drive was largely independent of EMG IG activity and often occurred without alpha-activity. The mean firing rate of secondarymuscle spindle afferents increased significantly during locomotion (with L-DOPA) and crossed extensor reflexes, again indicating increased static gamma-drive. Clonidine reduced or eliminated the gamma-drive inseven of eight afferents during crossed extensor reflexes. 6. In conclusion, although there are some common features, such as a predominantstatic gamma-drive in all walking preparations, the pattern of staticand dynamic gamma-drive is not closely linked to alpha-activity underthe conditions studied. As well as gamma-drive without alpha-activity, we have shown for the first time that alpha-motoneurones can be activated without significant gamma-drive to many spindles during behavioural tasks.

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Documento generato il 28/09/20 alle ore 18:40:31