Distribution and characteristics of poststimulus effects in proximal and distal forelimb muscles from red nucleus in the monkey

We used stimulus-triggered averaging (StTA) of electromyographic (EMG) activity to investigate two major questions concerning the functional organization of the magnocellular red nucleus (RNm) for reaching movements in the macaque monkey. The first is whether the clear preference toward facilitation of extensor muscles we have reported in previous studies for distal (wrist and digit) forelimb muscles also exists for proximal muscles (shoulder and elbow). The second question is whether distal and proximal muscles may be cofacilitated from RNm suggesting the representation of functional muscle synergies for coordinated reaching movements. Two monkeys were trained to perform a prehension task requiring multijoint coordination of the forelimb. EMG activity was recorded from 24 forelimb muscles including 5 shoulder, 7 elbow, 5 wrist, 5 digit, and 2 intrinsic hand muscles. Microstimulation (20 microA at 20 Hz) was delivered throughout the movement task. From 137 microstimulation sites in the RNm, a total of 977 poststimulus effects was obtained including 733 poststimulus facilitation effects (PStF) and 244 poststimulus suppression effects (PStS). Of the PStF effects, 58% were obtained from distal muscles; 42% from proximal muscles. Digit muscles were more frequently facilitated (35%) than the wrist, elbow, or shoulder muscles (20, 24, and 18%, respectively). The intrinsic hand muscles were infrequently facilitated (3%). At all joints tested, PStF was more common in extensor muscles than flexor muscles. This extensor preference was very strong for shoulder (85%), wrist (85%), and digit muscles (94%) and weaker for elbow muscles (60%). Of the PStS effects, 65% were in distal muscles and 35% in proximal muscles. Interestingly, the flexor muscles were more frequently inhibited from RNm than extensor muscles. At 72% of stimulation sites, at least two muscles were facilitated. The majority of these sites (61%) cofacilitated both proximal and distal muscles. At the remaining sites (39%), PStF was observed in either the proximal (17%) or distal muscles (22%). Facilitation most often involved combinations of shoulder, elbow, and distal muscles (30%) or shoulder and distal muscles (26%). Only rarely were intrinsic hand muscles part of the total muscle synergy. Our results show that the RNm 1) controls both proximal and distal muscles but the strength of influence is biased toward distal muscles, 2) preferentially controls extensor muscles not only at distal forelimb joints but also at proximal joints, and 3) output zones cofacilitate synergies of proximal and distal muscles involved in the control of forelimb reaching movements.     

Muscle injury in repetitive motion disorders

Documentation of causality between repetitive motions and musculoskeletal disorders calls for detailed understanding of the exposure variables and the corresponding physiologic responses in the biologic tissues. Quantification of the kinetics in some jobs characterized by repetitive motions is summarized with the physiologic responses in the muscles. Muscle activity pattern was studied in different shoulder muscles or muscle parts, and in elbow and wrist flexor muscles. Activity pattern was dependent on the kinetics of the work requirements. This holds true for the compound electromyographic signal and for single motor units. Low threshold motor units have been identified that are recruited continuously, the so called Cinderella fibers. The physiologic consequences of prolonged muscle fiber activity are reviewed, revealing mechanisms for the development of necrotic changes in the muscle, which support the likelihood of work relatedness for musculoskeletal disorders.     

Metabolic and phenotypic adaptations of diaphragm muscle fibers with inactivation

We hypothesized that metabolic adaptations to muscle inactivity are most pronounced when neurotrophic influence is disrupted. In rat diaphragm muscle (Dia(m)), 2 wk of unilateral denervation or tetrodotoxin nerve blockade resulted in a reduction in succinate dehydrogenase (SDH) activity of type I, IIa, and IIx fibers (approximately 50, 70, and 24%, respectively) and a decrease in SDH variability among fibers (approximately 63%). In contrast, inactivity induced by spinal cord hemisection at C2 (ST) resulted in much less change in SDH activity of type I and IIa fibers (approximately 27 and 24%, respectively) and only an approximately 30% reduction in SDH variability among fibers. Actomyosin adenosinetriphosphatase (ATPase) activities of type I, IIx, and IIb fibers in denervated and tetrodotoxin-treated Dia(m) were reduced by approximately 20, 45, and 60%, respectively, and actomyosin ATPase variability among fibers was approximately 60% lower. In contrast, only actomyosin ATPase activity of type IIb fibers was reduced (approximately 20%) in ST Dia(m). These results suggest that disruption of neurotrophic influence has a greater impact on muscle fiber metabolic properties than inactivity per se.     

Variety of muscle responses to tactile stimuli

Influences exerted by tactile stimuli on the muscle activity were investigated with two methods: (1) analysis of kinematics and electromyographic (EMG) activity of eight forelimb muscles during contact placing (CP) reactions elicited by tactile stimuli applied to the dorsal, medial or lateral sides of the paw in cats, and (2) the Hoffmann (H)-reflex technique to quantify the effects of the tactile stimuli on the excitability of the alpha motoneurones of the soleus muscle in awake rats. The first group of the data showed that the tactile stimuli applied to dorsal, medial or lateral aspects of the paw led to different strategies of the forelimb movements during CP reactions. These differences arose from various patterns of activation of the elbow flexor and extensor muscles at the beginning of CP reactions and a various involvement of the medio-lateral components of movements, depending on the site of the tactile stimulus application. With the H-reflex technique it was found that the tactile stimulus diminished the excitability of alpha motoneurones of the soleus muscle when applied to the skin overlying the lateral side of the ankle joint. This effect was in line with the observation that the tactile stimulus applied to the lateral side of the paw activated the elbow flexor muscles but not their antagonists to initiate CP reaction.     

Functional reorganization of the rat motor cortex following motor skill learning

Functional reorganization of the rat motor cortex following motor skill learning. J. Neurophysiol. 80: 3321-3325, 1998. Adult rats were allocated to either a skilled or unskilled reaching condition (SRC and URC, respectively). SRC animals were trained for 10 days on a skilled reaching task while URC animals were trained on a simple bar pressing task. After training, microelectrode stimulation was used to derive high resolution maps of the forelimb and hindlimb representations within the motor cortex. In comparison with URC animals, SRC animals exhibited a significant increase in mean area of the wrist and digit representations but a decrease in elbow/shoulder representation within the caudal forelimb area. No between-group differences in areal representation were found in either the hindlimb or rostral forelimb areas. These results demonstrate that motor skill learning is associated with a reorganization of movement representations within the rodent motor cortex.     

Distribution of muscle weakness of central and peripheral origin

According to the established clinical tradition about the distribution of weakness, the ratios of flexor/extensor strength of patients with upper motor neuron lesions are expected to be relatively high for the elbow and wrist and low for the knee. To assess the diagnostic value of these patterns of weakness, muscle strength of 70 patients with limb weakness of central or peripheral origin was measured with a hand held dynamometer. The ratios of flexor/extensor strength at the knee, elbow, and wrist did not differ significantly between patients with central or peripheral origin of muscle weakness. The examination of tendon jerks proved to be of more value as a localising feature. The traditional notion about the distribution of weakness in upper motor neuron lesions may be explained by an intrinsically greater strength in antigravity muscles, together with the effects of hypertonia.     

Comparison of motor endings of the cat's muscle spindle stained for NADH-tetrazolium reductase and cholinesterase

Cat muscle spindles were examined histochemically in serial transverse sections of tenuissimus muscles stained for ATPase, NADH-TR and ChE alternating sequentially. Motor nerve terminals on nuclear bag1, bag2 and nuclear chain intrafusal muscle fibers were identified in periodic sections stained for ChE. Intrafusal fiber regions that carried ChE-active areas were then examined in staining for NADH-TR. The motor endings on the three types of intrafusal fiber differed in their apparent histochemical content of both ChE and NADH-TR. The observations suggest that functional differences may exist among motor nerve terminals on the various intrafusal fiber types.     

Contribution on substitution of lost elbow flexion in atypical post-partum paresis of the plexus brachialis

In a ten-year-old boy with an atypical partial post-partum paresis of the dextrolateral plexus brachialis the function of the shoulder was affected substantially and the flexion of the elbow completely. The musculature of the forearm and hand was preserved completely from the anatomical and functional aspect. In compliance with the parents wish, the possibility of replacement with a muscle from a remote site by microsurgical transfer was abandoned and the authors used the well known method of transposition of the insertion of the m. pectoralis major and new retrograde transposition of the tendon of the m. flexor carpi radialis into this muscle to restore the function of the m. biceps brachii. Through postoperative rehabilitation, 90 degrees flexion of the elbow in a supine position was achieved.     

Organization of single motor units in feline sartorius

1. We depleted single motor units in feline sartorius muscles of glycogen by stimulating their motoneurons intracellularly. We mapped the intramuscular distribution of depleted fibers by inspecting histological cross-sections throughout the length of sartorius. 2. We selected ten depleted motor units for detailed study and quantitative analysis. Nine motor units were located in the anterior head of sartorius. One was located in a muscle whose distal half appeared to have been damaged some time before the acute experiment. A single motor unit was located in the medial head of sartorius. 3. Five motor units were composed of fast-twitch glycolytic (FG) muscle fibers, two of fast-twitch oxidative glycolytic (FOG) muscle fibers, and three of slow-twitch oxidative (SO) muscle fibers. Estimates of the numbers of depleted fibers in motor units of anterior sartorius indicated that FG motor units were larger (mean 566 fibers) than FOG and SO motor units (SO mean 190, FOG mean 156 fibers). The SO motor unit in the damaged muscle had 550 fibers. One motor unit depleted in the medial head of sartorius had 270 fibers with FG profiles. 4. Muscle fibers belonging to each anterior motor unit were never distributed throughout the whole cross-section of anterior sartorius at any proximodistal level. Furthermore, fibers were distributed nonuniformly along the proximodistal axis of the muscle. In most muscles at least a few depleted fibers were found at all proximodistal levels. However, in one normal muscle and the damaged muscle, depleted fibers were confined to the proximal end. 5. The fibers in the medial motor unit were confined to a strip that did not extend across the whole cross-section of the muscle head. Fibers within this strip were scattered quite evenly from origin to insertion. This medial FG motor unit occupied a smaller territory and contained fewer fibers than anterior motor units of the same histochemical type. 6. These results show that sartorius motor units are not distributed uniformly in the mediolateral plane; those in anterior sartorius were distributed asymmetrically in the proximodistal axis as well. This finding has important functional implications for the way in which we model force development and transmission in sartorius and other long muscles.     

Nitric oxide synthase in the heterogeneous population of intramural striated muscle fibres of the human membranous urethral sphincter

PURPOSE: Nitric oxide (NO) is known to relax urethral smooth muscle. The role of NO in the control of urethral striated muscle remains unknown. We have investigated the distribution of nitric oxide synthase (NOS) immunoreactivity and its possible relationship with subtypes of intramural striated muscle fibers in the human male membranous urethra. MATERIALS AND METHODS: Whole transverse cryostat sections from seven membranous urethrae were studied using NOS immunohistochemistry and NADPH diaphorase histochemistry. Striated fiber subtypes were demonstrated using immunohistochemistry for troponin T and histochemistry for myofibrillary adenosine triphosphatase (ATPase). Consecutive sections were used to assess the correlation between the distribution of NOS immunoreactivity and the type of striated fibers. RESULTS: NOS immunoreactivity and NADPH diaphorase activity were detected in the sarcolemma of 48.5% of the intramural striated muscle fibers. NOS immunoreactive nerve trunks and fine nerve fibers, a few of which appeared to end on muscle fibers, were present in the striated sphincter. Fast twitch fibers were detected by ATPase staining, and also exhibited positive immunoreactivity for troponin T, constituting 34.6% of the total number of striated fibers. Two populations of slow twitch fibers were identified; one with small diameter (mean: 15.7 microns) and another of larger diameter (mean: 21.7 microns) comparable to that of fast twitch fibers. 86% of the fast twitch fibers and 29% of slow twitch fibers (most of which had larger diameters) exhibited NOS immunoreactivity and NADPH diaphorase activity in the sarcolemma. CONCLUSIONS: The presence of nitrergic nerve fibers in the striated urethral sphincter suggests an involvement in the innervation of urethral striated muscle. Furthermore, the presence of NOS immunoreactivity in the sarcolemma may indicate a role for NO in the regulation of urethral striated muscle metabolism and contraction.     

Effects of surface electrostimulation on the structure and metabolic properties in monkey skeletal muscle

Adaptative changes in skeletal muscle following surface electrical stimulation (SES) were investigated in rhesus monkeys. SES was performed on the triceps brachialis muscle (TB) according to an intermittent pattern. The procedure was carried out for 3 wk, using a current with a medium frequency of 60 Hz normally observed in fast motor axons. The histochemical assays performed on biopsies taken from proximal and distal parts of the TB muscle, before and after the SES program, showed that the distribution of fibers typed by ATPase was unaffected. On the other hand, SES led to an overall increase in the mean fiber cross-sectional area (FCSA); P < 0.01 (+13.7%, NS, in proximal portion, vs +31%, P < 0.01 in distal portion). This increase in size occurred in all fiber types. SES was shown to induce an overall increase in capillary to fiber ratio (C/F; +11.06%, NS, in proximal portion, vs +25.93%, P < 0.05 in distal portion). The number of capillaries surrounding fiber Type II (CAFII) was significantly increased by SES (P < 0.05): +3.21%, NS, in proximal portion, versus +21.47%, P < 0.05 in distal portion. Moreover, the number of capillaries surrounding fiber Type I (CAFI) was statistically unaffected by SES. These results suggest that a stimulation of capillary growth may occur following SES-training. Citrate synthase activity was significantly increased after SES. This enhancement in oxidative potential was shown to occur in all fiber types (NADH-diaphorase staining).(ABSTRACT TRUNCATED AT 250 WORDS)     

Lipid and lipoprotein distributions in children by ethnic group, gender, and geographic location--preliminary findings of the Child and Adolescent Trial for Cardiovascular Health (CATCH)

Male and female isometric strength curves for elbow fixation, shoulder flexion, and wrist supination-pronation are obtained during systematic variation in arm configuration. The shape of a given moment-angle curve is found to be a function of the orientations of joints kinematically coupled to the primary joint. It is also found that female elbow strength curves are shifted toward flexion with respect to male elbow-strength curves, suggesting that the in situ rest length of upper-limb muscles relative to joint angle may be longer for males than for females. Experimental results were contrasted with simulation results obtained using a three-dimensional musculoskeletal model which estimates the relationships between initial joint orientations, muscle tension-length behavior, and joint moments. In most of the cases, simulation results complimented experimental data and provided insights into likely in situ muscle rest lengths and moments arms, especially for the multiarticular biceps brachii muscle. Where inconsistencies exist between simulated and experimental data, subtle biomechanical complexities within the forearm and the shoulder girdle complex are identified that require future investigation.     

Self-reinnervated cat medial gastrocnemius muscles. II. analysis of the mechanisms and significance of fiber type grouping in reinnervated muscles

1. The technique of glycogen depletion was used to determine whether regenerating motor axons reestablish the normal regionalization of motor units (MUs) in the cat medial gastrocnemius (MG) muscle, 2) whether the extent of clumping between MU fibers and/or type grouping of muscle fibers progressively increases with a decrease in reinnervated MU numbers, and 3) whether the pattern of innervation can explain why MUs fail to increase significantly in size when the cut nerve is sutured directly to the muscle, even when few axons make functional connections. 2. Distributions of MU fibers were analyzed in 5 normal and 14 reinnervated cat MG muscles 4.5-16 mo after sectioning of its nerve and suturing of the proximal end to the distal nerve sheaths (N-N suture) or directly to the muscle fascia (N-M suture). Muscle unit distributions were quantified according to location, territory size, density, and extent of clumping between fibers from the same MU. 3. Normal MU fibers were regionalized within five regions along the muscle's longitudinal and transverse axes. Reinnervated MUs were located within similar regions, indicating that regenerating axons follow the major proximal nerve branches to restore normal compartmentalization. 4. Muscle unit fibers were diffusely scattered within discrete MU territories in normal muscles. Territory size tended to increase with MU size, whereas density of muscle unit fibers within the territory decreased. 5. Territories increased with MU size after N-N suture but were smaller and showed little size variation after N-M suture. The extent of muscle unit fiber clumping was inversely related to the number of reinnervated MUs. On average, the extent of clumping was substantially higher in muscles reinnervated after N-M suture. These results indicate that distal nerve sheaths facilitate proximal axon branching, which establishes MU territory size. Once the territory is established, motor axons branch distally to increase MU size, which in turn compensates for reduced MU numbers. 6. Muscles reinnervated by < 80% of the MUs exhibited fiber type grouping of type I fibers, and on average the extent of clumping was substantially higher in muscles reinnervated after N-M suture. With less innervation, type grouping increased inversely with the number of reinnervated MUs. However, for a similar number of MUs, type I fiber type grouping was substantially higher in muscle reinnervated after N-M suture. Type grouping therefore reflects muscle unit fiber clumping under conditions where MU size increased (N-N suture) or MU territory size decreased (N-M suture).     

Presynaptic function during muscle remodeling in insect metamorphosis

During metamorphosis the leg neuromuscular system of the moth Manduca sexta undergoes an extensive remodeling as the larval muscles degenerate and are replaced by new muscles in the adult. The terminal processes of persistent leg motoneurons undergo severe regression followed by regrowth (Consoulas et al., 1996), accompanied, as shown here, by the loss and re-establishment of functional presynaptic specializations. Before and shortly after the degeneration of the larval muscle, immunoreactivity for the vesicular protein synaptotagmin was localized to the presynaptic varicosities of the motoneurons. Similarly localized were distinct sites of Ca2+-dependent uptake of the fluorescent dye FM1-43. During myoblast migration and accumulation about the re-expanding motor axons, synaptotagmin immunoreactivity was widely distributed in axons, and specific FM1-43 staining revealed vesicle exocytosis in distal axon branches. During myoblast proliferation and fusion, and myotube formation, synaptotagmin staining remained widely distributed in nerve branches, whereas FM1-43 staining was more localized to subdomains of these nerve branches. These initial presynaptic active sites were transient and were replaced by new sites in more distal nerve processes as the muscle anlage increased in size and additional myotubes formed. After myotube separation, synaptotagmin staining disappeared from primary branches but remained distributed within secondary and high-order nerve branches. FM1-43 staining was detected in high-order branches only. During muscle fiber striation, growth, and maturation, both FM1-43 staining and synaptotagmin immunoreactivity became localized to terminal varicosities. Thus, presynaptic function can persist after the loss of the target and occurs transiently in axon shafts before becoming restricted to terminal domains as the underlying muscle fibers mature.     

Specificity and development of innervation pattern of Xenopus pectoralis muscle

Multielectrode recordings were used to identify and measure the axonal inputs to each end plate on contiguous surface fibers covering about 25% of the Xenopus pectoralis muscle in mature and developing animals. The mature innervation pattern was remarkably precise. Individual axons tended to innervate fibers of similar input resistance (R(in)) in compact motor units restricted to only a portion of the region studied. Motor units comprising fibers of similar R(in) overlapped mainly near their borders. Most fibers had two end plates. In more than 80% of these fibers, both end plates received input from the same axon. In 57%, this was the only input to both end plates. This implies a powerful mechanism for excluding or eliminating inputs from other axons. About 16% of the mature junctions showed focal polyneuronal innervation, with the weaker end plate potential component often less than 1 mV in noncurarized preparation. However, we have no evidence that the weaker inputs were being eliminated. During development, motor units became more compact, which was associated with synapse elimination; but from the earliest times studied, soon after metamorphosis when many fibers were adding second end plates, a majority of those that had two end plates were innervated at both sites by the same axon.     

Effects of muscle length on the response to unloading

Muscle mass, distribution of fiber types, fiber cross-sectional areas (CSA) and selected enzyme activities were determined in rats hindlimb-suspended free of immobilization (Susp-Free), suspended with the ankle dorsiflexed (Susp-DF, soleus stretched) or plantarflexed (Susp-PF, soleus shortened) for 10 days and compared to cage-control (Con) rats. Reduction of muscle weight associated with suspension was prevented in Susp-DF rats. The mean CSAs of slow fibers were Con = Susp-DF > Susp > PF > Susp-Free and of fast and intermediate fiber tended to be Susp-DF > Con > Susp-PF = Susp-Free. Mean activities of succinate dehydrogenase (SDH), alpha-glycerophosphate dehydrogenase (GPD) and myofibrillar adenosine triphosphatase (mATPase) in slow and fast fibers were similar in Con and Susp-Free rats. Mean SDH activity in slow fibers was higher in Susp-DF and Susp-PF than in Con and Susp-Free. No significant differences in SDH activities of fast fibers were observed among groups. GPD activity was higher in slow fibers of Susp-DF and Susp-PF compared to Con. The mATPase activity was higher in slow fibers of Susp-DF compared to Con and Susp-Free rats and lower in fast fibers of Susp-DF compared to Con rats. Thus, when compared to control, the patterns of adaptation were more similar in the Susp-DF and Susp-PF than in the Susp-Free. Although these results are consistent with previous studies demonstrating that the load placed on a muscle can affect protein metabolism, the direction and magnitude of the adaptive responses observed in the present study were closely associated with the chronically imposed changes in muscle length, i.e. fixed at either a shortened or a lengthened position.     

Inducible NO synthase II and neuronal NO synthase I are constitutively expressed in different structures of guinea pig skeletal muscle: implications for contractile function

The expression of NOS isoforms was studied in guinea pig skeletal muscle at the mRNA and protein level, and the effect of NO on contractile response was examined. Ribonuclease protection analyses demonstrated NOS I and NOS II mRNAs in diaphragm and gastrocnemius muscle. In Western blots, NOS I and NOS II immunoreactivities were found in the particulate but not the soluble fraction of skeletal muscle. NOS activity was found almost exclusively in the particulate fraction. About 50% of this activity was Ca2+ independent. In immunohistochemistry, the anti-NOS I antibody stained distinct membrane regions of muscle fibers. The most intense staining was seen in neuromuscular endplates identified by labeling with alpha-bungarotoxin. The anti-NOS II antibody labeled muscle fibers that contained alkali-labile myosin ATPase (type I fibers). NOS II was located to intracellular structures and was also seen in "specific pathogen-free" animals. Pretreatment of guinea pigs with bacterial lipopolysaccharide (LPS) markedly intensified NOS II staining. Significant NOS III immunoreactivity was detected only in vascular endothelium. In functional experiments, tetanic muscle contractions were induced in diaphragm and gastrocnemius muscle by electrical stimulation of the innervating nerves. Pretreatment of guinea pigs with LPS or addition of S-nitroso-N-acetyl-D,L-penicillamine to the organ bath markedly decreased tetanic contractions. N(G)-nitro-L-arginine, on the other hand, increased contractile force and reversed the effect of LPS. Our data indicate that NOS II and NOS I are expressed in different structures of skeletal muscle and are involved in the regulation of contractile response.     

Type II muscle fibers are stained by anti-Fas antibody

To examine whether apoptosis related proteins are present in skeletal muscles we studied biopsied muscles immunohistochemically and by Western blot analysis. Biopsied muscles from patients with several disorders were studied with anti-Fas antibody and anti-BCL2 antibody. Type II muscle fibers identified by ATPase staining were positively stained by anti-Fas antibody in both normal control and diseased muscles. Anti-BCL2 antibody did not stain any muscle fibers. Western blot analysis using anti-Fas antibody showed a single band at 45 kDa in both skeletal muscle and lymphocytes. Anti-Fas antibody has been reported to induce apoptosis in the cells. The presence of anti-Fas antibody reactive materials in type II muscle fibers might be related to type II fiber atrophy in muscular disorders.     

Corticomotoneuronal postspike effects in shoulder, elbow, wrist, digit, and intrinsic hand muscles during a reach and prehension task

We used spike-triggered averaging of rectified electromyographic activity to determine whether corticomotoneuronal (CM) cells produce postspike effects in muscles of both proximal and distal forelimb joints in monkeys performing a reach and prehension task. Two monkeys were trained to perform a self-paced task in which they reached forward from a starting position to retrieve a food reward from a small cylindrical well. We compiled spike-triggered averages from 22 to 24 separate forelimb muscles at both proximal (shoulder, elbow) and distal (wrist, digits, intrinsic hand) joints. Of 174 cells examined, 112 produced postspike effects in at least one of the target muscles. Of those cells, 45.5% produced postspike effects in both proximal and distal forelimb muscles. A nearly equal number (44.7%) produced postspike effects in distal muscles only, whereas a clear minority (9.8%) produced postspike effects in only proximal muscles. The majority of CM cells (71.4%) produced effects in two or more muscles, with an average muscle field of 3.1 +/- 2.1 (mean +/- SD) for facilitation plus suppression. Of 345 postspike effects identified, 70.7% were facilitation effects and 29.3% were suppression effects. The large majority of effects (72.2%) were in distal muscles. When averaged by joint, the latency and peak magnitude of postspike facilitation showed a stepwise increase from proximal to distal joints. The results of this study show that the majority of CM cells engaged in coordinated forelimb reaching movements facilitate and/or suppress muscles at multiple joints, including muscles at both proximal and distal joints. The results also show that CM cells make more frequent and more potent terminations in motoneuron pools of distal compared with proximal muscles.     

Polyneural innervation in the psoas muscle of the developing rat

Polyneural innervation was studied in the psoas muscle in developing rats from P4 till P25 and at adult age, with the combined silver-acetylcholinesterase technique. Nerve endings were counted, and end-plates were measured. These data were compared with such data in the human. The end of polyneural innervation in the rat (around P20) and in the human (around 12 weeks postterm age) in both cases coincides with a transformation in motor behavior and postural control. The rat's psoas muscle at early stages is less heavily innervated than this muscle in the human. Up to three axons per motor end-plate were counted at P4, but in the human up to five axons at 25 weeks of post menstrual age. This difference might be related to the lower percentage of type I muscle fibers in the rat.