Glycogen depletion of bag1 fibers elicited by stimulation of static gamma axons in cat peroneus brevis muscle spindles.

Abstract

1. The distribution of static fusimotor axons to intrafusal muscle fibres in cat peroneus brevis spindles has been studied with the glycogen depletion method. 2. In each of six experiments three to seven static axons were stimulated. The muscle was subsequently quick-frozen and cut in serial transverse sections that were stained for glycogen. In each muscle, nearly all the spindles were examined for depletion. 3. Intrafusal muscle fibres displaying zones of complete glycogen depletion were observed in fifty-two whole spindles and seven half-spindles. Chain fibres were depleted in forty-eight (92%) of the whole spindles, bag2 fibres in thirty-five spindles (67%) and bag1 fibres in nineteen spindles (36%). 4. Seven other experiments were performed to test whether small amplitude sinusoidal stretching (30--100 Hz) of the muscle might produce glycogen depletion in bag1 fibres. Two hundred and seven spindles were examined. In nearly all of them the glycogen content of the intrafusal muscle fibres was normal. Two muscles had limited atrophic portions within which a few depleted spindles were found. 5. These experiments show that the intrafusal distribution of static gamma axons is not restricted to chain and bag2 fibres but that in a significant number of spindles the bag1 fibres are also supplied by static gamma axons.

Evolving views on the internal operation and functional role of the muscle spindle.

“…The activated muscle fibres then stand out from the rest by virtue of having been depleted of their normal glycogen stores. On applying this technique to the spindle it has been repeatedly shown that stimulation of static axons may deplete bag fibres as well as chain fibres, whereas on activation of dynamic axons the depletion is restricted to bag fibres (Brown & Butler, 1973, 1975 Emonet-Denand, Harker, Jami & Laporte, 1976;Emonet-Denand, Jami, Laporte & Tankov, 1980). (c) Intracellular recording.…”

Glycogen depletion elicited in tenuissimus intrafusal muscle fibres by stimulation of static gamma‐axons in the cat.

“…In conclusion, the view based on glycogen depletion observations Emonet-Denand et al 1980;Jami et al 1980) that static y-axons substantially participate in bag, innervation should now be abandoned since our present work strongly suggests that in 'fatigued' spindles (i.e. spindles in which the sensory ending responses to y stimulation have become very weak) non-neural depletion of bag, fibres occurs.…”

“…The non-neural factor is unlikely to be the stretch-induced contraction of bag1 fibres described by Poppele & Quick (1981), as proposed by Barker & Banks (1984), for two reasons: first, because in experiments A and B the chain and bag2 fibres that were activated for 5 and 9 h, respectively, had been given ample opportunity (if bag, stretching really occurs) to stretch neighbouring bag, fibres; however, only one bag, pole out of nineteen was depleted; secondly, because it is known that small amplitude vibrations applied to muscles in order to mimic possible stretch of bag, fibres by the contraction-relaxation of other intrafusal muscle fibres does not change the glycogen content of bag1 fibres (Emonet-Denand et al 1980). However, there is current evidence that large stretches can change the Ia responses to subsequent dynamic y stimulation (Emonet-Denand, Hunt & Laporte, 1983) and also elicit extensive glycogen depletion in bag1 fibres (L. Decorte, F. Emonet-Denand & Y.…”

“…They reported that in cat tenuissimus and peroneus longus spindles both bag and chain fibres were depleted after stimulation of static y-axons and that in tenuissimus spindles the depletion often affected all the bag fibres present in a given spindle pole. In a series of studies in which morphological criteria were used to distinguish the two types of bag fibre, known today as 'dynamic bag,' fibres and 'static bag2' fibres (see Boyd, 1981 a), it was found that a large proportion of bag1 fibres were depleted after stimulation of static y-axons in cat tenuissimus and peroneus brevis spindles (Barker, Emonet-Denand, Harker, Jami & Laporte, 1976;Emonet-Denand, Jami, Laporte & Tankov, 1980;Jami, Lan-Couton & Petit, 1980). These observations were interpreted as showing a substantial participation of static y-axons in the innervation of bag1 fibres, known to be the effectors of dynamic action (see reviews by Laporte, 1978;Boyd, 1981 b; Matthews, 1981 andBanks, 1984).…”

A study of motor nerve terminals on cat nuclear bag1 intrafusal muscle fibers using the ChE staining technique

“…More recently, a controversy has arisen as to whether motor axons which have a static action on spindle afferent discharge may ever terminate on the bag, fiber. On this subject, discrepancy exists between observations made with the glycogen-depletion method (Brown and Butler, 1973;Barker et al, 197613;Emonet-Denand et al, 1980) and cinematographical studies of living muscle spindles (Bessou and Pages, 1975;Boyd, 1976a;Boyd et al, 1977Boyd et al, , 1979. None of these studies has dealt with quantitative aspects of bag, fiber motor innervation.…”