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Calf muscles of five adolescents aged 12 to 15 years (three males, two females) with spastic diplegia were massaged for 14 minutes twice a week for 5 weeks in a controlled sequence, stretching the muscles transversely rather than longitudinally, without eliciting pain. Slow, passive test stretches were applied before and after massage. After massage, the range of movement was not consistently increased but, on average, greater force was needed to stretch the muscle than before massage. However, after massage the resting ankle angle sometimes changed so that the calf muscles were either shorter or longer. We suggest that these phenomena could be explained if massage resets sarcomere lengths which corrects for thixotropic effects (i.e. previous use modifies a muscle's mechanical behaviour). A redistribution on sarcomere lengths within muscles could also have reset proprioceptive feedback. The incidence of abnormal stretch reflexes during test stretches fell from 40 to 22%, comparing the first five sessions with the last five sessions. The amplitude of voluntary alternating ankle rotation increased in three participants. Motor skills were assessed with the Gross Motor Function Measure-66 (GMFM-66) 1 week before the test period, during the 5th week, and 12 weeks later. Our participants in Gross Motor Function Classification System (GMFCS) Levels I and II made sustained improvements in GMFM-66 scores (6.4% at 5 weeks falling to 5.5% at 17 weeks), one increase being significant. One participant in GMFCS Level III improved significantly only after massage of all leg muscles for 30 weeks.

Ideas about the functions of static gamma-motoneurones are based on the responses of primary and secondary endings to electrical stimulation of single static gamma-axons, usually at high frequencies. We compared these effects with the actions of spontaneously active gamma-motoneurones. In anaesthetised cats, afferents and efferents were recorded in intramuscular nerve branches to single muscle spindles. The occurrence of gamma-spikes, identified by a spike shape recognition system, was linked to video-taped contractions of type-identified intrafusal fibres in the dissected muscle spindles. When some static gamma-motoneurones were active at low frequency (15 Hz) they coupled the firing of group Ia and II afferents. Activity of other static gamma-motoneurones which tensed the intrafusal fibres appeared to enhance this effect. Under these conditions the secondary ending responded at shorter latency than the primary ending. In another series of experiments on decerebrate cats, responses of primary and secondary endings of single muscle spindles to activation of gamma-motoneurones by natural stimuli were compared with their responses to electrical stimulation of single gamma-axons supplying the same spindle. Electrical stimulation mimicked the natural actions of gamma-motoneurones on either the primary or the secondary ending, but not on both together. However, gamma-activity evoked by natural stimuli coupled the firing of afferents with the muscle at constant length, and also when it was stretched. Analysis showed that the timing and tightness of this coupling determined the degree of summation of excitatory postsynaptic potentials (EPSPs) evoked by each afferent in alpha-motoneurones and interneurones contacted by terminals of both endings, and thus the degree of facilitation of reflex actions of group II afferents.

Noradrenaline is known to suppress transmission from group II muscle afferents when locally applied to gamma-motoneurones, and serotonin (5-HT) facilitates the transmission. The purpose of this investigation was to search for evidence of monoaminergic innervation of gamma-motoneurones. Eight gamma-motoneurones were labelled with rhodamine-dextran, and 50 micrometer thick sagittal sections of the spinal cord containing them were exposed to antibodies against dopamine beta-hydroxylase (DBH) and 5-HT. All the cells were directly and/or indirectly excited by muscle group II afferents from the muscle they innervated and/or other muscles. Appositions between monoaminergic fibres and the labelled somata and dendrites were located with three-colour confocal laser scanning microscopy by examining series of optical sections at 1 or 0.5 micrometer intervals. DBH and 5-HT varicosities formed appositions with the somata and dendrites of all the gamma-motoneurones. The mean packing densities for 5-HT (1.12 +/- 0.11 appositions per 100 micrometer(2) for somata and 0.91 +/- 0.07 per 100 micrometer(2) for dendrites) were similar to the densities of contacts reported for alpha-motoneurones. Monoaminergic varicosities in apposition to dendrites greatly outnumbered those on the somata. The density of DBH appositions was consistently lower - corresponding means were 53% and 62% of those for 5-HT on the somata and dendrites, respectively. It is concluded from an analysis of the distribution and density of varicosities in apposition to the gamma-motoneurones compared with the density in the immediate surround of the dendrites that there is indeed both a serotoninergic and noradrenergic innervation of gamma-motoneurones.

1. The aim of this investigation was to identify static gamma-axons which do not drive any Ia afferents at any stimulus frequency in any spindle which they supply, and to determine their occurrence in various hindlimb muscles (peroneus tertius, brevis, longus and tenuissimus). 2. Ia responses to static gamma stimulation were classified as 'non-driven' when the discharge did not follow the stimulation frequency, or its subharmonics, at any time during a linear increase in stimulus frequency up to 150 Hz lasting 2-3 s, and when tested at two muscle lengths--except in the tenuissimus muscle. In almost all experiments, cross-correlograms were used in addition to evaluate the percentage of these 'non-driven' responses in which a time-locking of discharge to stimulus pulses was obscured by irregularity of the Ia discharge. 3. In 104 spindles, out of 347 responses to stimulation of single static gamma-axons 332 (93%) could be characterized, and of these, 57% (183) were of the non-driven type. The mean number of static gamma effects characterized per spindle was 4.1 (fourteen experiments). In the large majority of spindles (79%, 82 out of 104) at least one response was of the non-driven type. 4. Of the static gamma-axons studied 16% were called 'non driving' ('ndr' gamma s-axons) because they elicited non-driven effects, and since they had the same qualitative effect consistently in all spindles whose discharge was modulated by stimulating them they were called specific 'ndr' axons. If axons with non-driven effects, but acting on one spindle were included in the 'non-driving' category the proportion was 23%. Of spindles tested 63% were innervated by at least one 'ndr' axon. 5. Absence of Ia driving during ramp frequency stimulation of gamma s-axons has been equated with selective bag2 contraction. All the non-driven responses identified in this study cannot be attributed to exclusive bag2 involvement because the total number of 'ndr' responses was too high. In fact, in the isolated spindle preparation bag2 and chain co-contraction were shown to elicit non-driven responses, so chain contraction is not detected reliably in all experimental conditions. Possibly chain fibre contraction is sometimes too weak to dominate the response, or can be of a non-driving character.(ABSTRACT TRUNCATED AT 400 WORDS)

1. Extra- or intracellular recordings were made from seventy-six gamma-motoneurones of hindlimb muscles in chloralose anaesthetized cats to re-assess the coupling between secondary muscle spindle afferents (group II muscle afferents) and these neurones. The latencies of a number of responses evoked by group II muscle afferents in gamma-motoneurones were shorter than minimal latencies of responses induced disynaptically in other spinal neurones. These latencies are therefore compatible with monosynaptic coupling between muscle spindle secondaries and gamma-motoneurones. 2. Responses fulfilling criteria for monosynaptically evoked responses were seen in about one third of gamma-motoneurones with input from the group II muscle afferents tested (in 6 of 18 motoneurones recorded intracellularly and in 26 of 74 motoneurones recorded extracellularly). They were usually evoked from only one of the stimulated nerves, stimulation of group II afferents of other nerves being followed by responses at longer latencies. 3. Most gamma-motoneurones were excited by group II afferents from several muscles, both flexors and extensors. However, a comparison of group II input to gamma-motoneurones innervating medial gastrocnemius and four other hindlimb muscles revealed differences in both incidence and sources. 4. This study extends results of previous studies by providing evidence that some synaptic actions of group II afferents, including afferents from the same muscle, are evoked monosynaptically, and may assist in sustaining the activation of gamma-motoneurones by positive feedback.

Pairs of Ia and II afferent fibres supplying primary and secondary endings lying in the same tenuissimus spindles were prepared in barbiturate anaesthetized cats in order to compare the variability in the rhythm of discharge of the two endings during responses elicited by the contraction of different intrafusal muscle fibres, especially by chain fibres. In these spindles, the intrafusal muscle fibres supplied by single static gamma-axons were identified with a recently developed technique based on the types of primary ending activation observed during gamma stimulation at 30 and 100 stimuli/s. The responses of the secondary endings to contraction of chain fibres either alone or with bag2 fibres were smaller and much more regular than the responses of the primary endings lying in the same spindles. This difference is probably related to the position of secondary endings along the intrafusal muscle fibres and to the mechanical properties of the muscle fibre regions on which the terminals lie. The dynamic properties of the encoding site of primary afferent impulses probably contribute to the difference. The different degrees of variability observed among secondary ending responses elicited either by chain fibres alone or by chain and bag2 fibres are not related to the type of activated intrafusal muscle fibres.

The terminations of static gamma-axons on chain fibres may be associated with a muscle surface contour thrown into complex folds at one extreme, ranging through lesser degrees of folding to being apparently uninfluenced by the presence of the terminals. The folding is not necessarily confined to the postsynaptic membrane. As a quantitative indicator of the degree of folding seen in cross-sections, the perimeters of the two halves of the intrafusal fibre with, and without the ending were compared. Both complexity of endplate structure and an undifferentiated appearance could co-exist within individual endings (of six static gamma-axons on thirteen chain fibres), associated with axons that supplied only chain fibres in the spindle isolated. (It should be noted, however, that the type of intrafusal fibres innervated by a particular axon was definitively identified only for the spindle isolated.) Endings of three other static gamma-axons on six chain fibres had a more homogeneous and less complex endplate structure; these supplied bag2 fibres in addition to the chain fibres and their endplates on the bag2 fibres were less folded than those of three axons which supplied bag2 fibres only. A sensory inhibitory influence on folding was not apparent because complexly folded endplates on chain fibres lay close (less than 500 microns) to sensory endings. All the endings studied were functional. In our experimental conditions all nine static gamma-axons which innervated chain fibres, alone, or together with a bag2 fibre, drove the Ia afferent at some stimulus frequencies; none of the three static gamma-axons innervating bag2 fibres alone caused driving at any frequency. These findings are discussed in relation to the concept of a dynamic remodelling of ending structure during life, to the relationship between the motor axon and the intrafusal fibre it innervates, and to the possibility that subgroups of static gamma-motoneurones might exist which could release different amounts of the trophic substances responsible for moulding the endplate structure.

1. Six muscle spindle poles, five from experiments in which foci of sarcomere convergence had been observed during stimulation of fusimotor axons, were serially sectioned for light and electron microscopy. Every somatic motor terminal was studied in ultrathin sections at several levels.2. In all six poles static gamma axons, or presumed static gamma axons, supplying the static bag(2) fibre and/or chain fibres had no terminations on the dynamic bag(1) fibre. In five poles, the dynamic bag(1) fibre was selectively innervated by dynamic gamma or beta axons save in one case where a dynamic gamma axon also innervated one chain fibre.3. Seventy-seven motor endings were of four distinct ultrastructural types: ;m(a) plates' lay superficially on the surface of static bag(2) or chain fibres; ;m(b) plates' were deeply indented into dynamic bag(1) fibres; in ;m(c) plates', found on chain fibres only, the muscle surface was thrown into projecting fingers between which the axon terminals were embedded; one type ;m(d) plate' was found, fully indented into a long chain fibre. A few plates of intermediate form (m(ab)) were variants of m(a) and m(b) plates.4. The muscle membrane beneath both m(a) and m(b) plates was smooth, or had a few wide, shallow folds; m(c) plates usually had wide, shallow subjunctional folds; numerous deep, narrow folds were characteristic of the m(d) plate. The length of unmyelinated pre-terminal axon or the number of sole plate nuclei were not useful diagnostic features.5. Obvious foci of sarcomere convergence in the capsular sleeve region of dynamic bag(1) and static bag(2) fibres coincided with the location of motor plates. Additional contraction foci were observed in the extracapsular region of dynamic bag(1) fibres where there was no motor innervation; contraction occurs principally in the outer half of these fibres. No foci of contraction or motor plates were observed in the extracapsular region of static bag(2) fibres; contraction in these fibres is typically mid-polar.6. In some poles local contraction of chain fibres centred on the location of m(c) plates. In others, very localized contraction occurred distal to the sites of m(a) plates. Both m(a) and m(c) plates were never found on the same pole of a chain fibre.7. Dynamic gamma or beta axons end in m(b) plates, probably equivalent to p(2) plates. The concept of distinctly different p(1) and p(2) plates on dynamic bag(1) fibres, supplied by dynamic beta and gamma axons, respectively, is not supported by ultrastructural evidence.8. Some static gamma axons end in multiple m(a) plates which correspond with ;trail endings', or in single large m(a) plates, on static bag(2) or chain fibres. The m(c) plates are the terminations of other static gamma, or occasionally dynamic gamma, axons on chain fibres. Static beta axons probably end in m(d) plates on long chain fibres which may correspond with p(1) plates.9. It is proposed that there are two types of static gamma motoneurone, one terminating in m(a) plates and the other in m(c) plates, possibly directed preferentially towards static bag(2) fibres and chain fibres, respectively.

1. The behaviour of nuclear bag and nuclear chain intrafusal fibres in isolated cat muscle spindles with a blood supply, during stimulation of dynamic gamma axons, dynamic beta axons, or static gamma axons in ventral root filaments was observed and recorded on still and moving film. 2. Most spindles were controlled by one dynamic gamma axon (sometimes a beta axon) and three static gamma axons, one of which was often non-selective in distribution. A large majority of fusimotor axons controlled one pole of the spindle only. 3. Dynamic gamma and beta axons produced focal contraction in only one of the two nuclear bag fibres in any spindle and this fibre was never activated by static gamma axons. Maximal tetanic contraction was attained slowly and the primary sensory spiral on this fibre was stretched by a small amount only. This fibre has been named the 'dynamic nuclear bag fibre'. 4. Static gamma axons produced either: (a) focal contraction in the second of the two nuclear bag fibres only; (b) local contraction in the bundle of nuclear chain fibres only; or (c) contraction in one nuclear bag fibre and the nuclear chain fibres together. Maximum tetanic contraction of this nuclear bag fibre stretched its primary sensory spiral considerably and the time to plateau was relatively short. This fibre has been named the 'static nuclear bag fibre'. 5. 'Driving' of the Ia afferent discharge could always be produced by non-selective static gamma axons, frequently by static gamma axons controlling nuclear chain fibres alone, and was probably due to mechanical oscillation in nuclear chain fibres. It was never produced by dynamic gamma axons and on one occasion only by a static gamma axon controlling a nuclear bag fibre alone. 6. The conduction velocities of dynamic gamma and static gamma axons overlapped extensively, though dynamic gamma axons were absent from the lower end, and static gamma axons innervating nuclear chain fibres only were absent from the upper end, of the range of velocities. 7. The observations are correlated with spindle structure and histochemistry. Dynamic and static nuclear bag fibres are shown to correspond with 'bag1 fibres' and 'bag2 fibres', respectively (Ovalle & Smith, 1972). 8. The possible origin of the dynamic and static actions of fusimotor axons and the role of the dynamic and static intrafusal systems in motor control are discussed.

Six muscle spindles and three muscle spindle poles from four rat soleus muscles have been sectioned serially at 1 micron intervals to trace the motor innervation by light microscopy. Forty myelinated axons had 92 endings on the intrafusal muscle fibres. 67.5% of these axons supplied a single type of muscle fibre only, 22.5% to dynamic bag1 (Db1) fibres, 15% to static bag2 (Sb2) fibres and 30% to chain fibres. The rest supplied more than one fibre type, 5% supplying the Db1 and one chain fibre, 20% supplying the Sb2 and chain fibres, but 7.5% (three axons) supplied all the fibre types together. Apart from these three axons all the fusimotor axons would be expected to have a clear dynamic or static action on the Group Ia discharge. Whilst for the cat entirely non-specific distribution does not exist, or at least is very rare, since only a small proportion of the rat fusimotor axons were in this category we conclude that fusimotor distribution in rats and cats is essentially similar.