[The formation of the microcirculatory bed of the neuromuscular systems of the tongue in human prenatal ontogeny]. / Formirovanie mikrotsirkuliatornogo rusla nervno-myshechnykh sistem iazyka v prenatal'nom ontogeneze cheloveka.

A complex of adequate neurohistological and injection methods with use of mathematical analysis of the data obtained has been performed to study prenatal and early postnatal periods of ontogenesis of the microcirculatory bed of the human tongue neuromuscular systems. Certain changes of the degree in organization and structural-functional integration have been revealed; they demonstrate periodicity of the morphological changes of the vasculo-neural complex of the extra- and intrafusal part of the muscular tissue. In the neuromuscular spindles the microvascular network of capillaries is formed, their volumetric part changes in the process of development in greater degree than the microvascular bed of the extrafusal muscular fibers. In formation of the microcirculatory vascular bed of the neuromuscular spindles not only capillaries, getting into them together with nervous fibers, but also microvessels of the surrounding muscle tissue participate. This determines a higher level of the vascularization degree of the intrafusal muscle fibers.

Regeneration and recovery of cat muscle spindles after devascularization.

1. We have assessed the sensory reinnervation and recovery of regenerated muscle spindles in extensor digitorum longus (EDL) 6, 8 and 13 weeks after the muscle, with its nerve left intact, had been devascularized. Recordings were made from the dorsal roots of the responses of single afferent fibres to ramp-and-hold stretch of the regenerated spindles whose sensory reinnervation was subsequently examined in teased, silver preparations. 2. The spindle population in four normal EDL muscles ranged from 53 to 83 (mean 69); analysis of the afferent innervation of 166 normal b1b2c spindles showed that 23% had primary endings supplied by two Ia afferents. Regenerated spindles were identified as belonging to one of four groups in which afferents establish sensory endings on intrafusal muscle fibres in groups 1-3, but not in group 4. Sensory reinnervation was complete after 6 weeks recovery and similar proportions of group 1-3 spindles occurred after each recovery period, i.e. 58% after 6 weeks, 65% after 8 weeks and 62% after 13 weeks. We estimate that about half the original spindle population was lost owing to persistent ischaemic necrosis; that 30% regenerated and acquired functional afferent connections (group 1-3 spindles); and that the total loss of spindle afferents was over 60%. 3. The conduction velocities of the regenerated spindle afferents were very similar to those of normal EDL spindle afferents. The proportions that responded normally to ramp-and-hold stretch at the end of each recovery period increased from 58% after 6 weeks to 61% after 8 and 88% after 13. Other responsive spindle afferents were either predominantly phasic or only responded to supramaximal stretch. The proportions of these decreased as recovery progressed reducing from 19% after 6 weeks to 9% after 13 weeks in the case of those giving predominantly phasic responses and from 23% after 6 weeks to 3% after 13 weeks in the case of those unresponsive to physiological stretch. 4. The mean peak and held firing rates of regenerated spindle afferents responsive to 10 mms-1 ramp-and-hold stretches were all significantly lower than normal. There was no marked trend towards higher firing rates after longer periods of recovery through, considered separately, the mean peak firing rates of the normally responding afferents did show a distinct improvement. The mean dynamic and velocity indexes were not significantly different from normal. 5. The ratio of Ia:spindle II afferents, as identified by their responses to stretch, was 1:1.22 in the control animals and 1:1.26 in the experimental series.(ABSTRACT TRUNCATED AT 400 WORDS)

The effects of temporary ischaemia on rat muscle spindles.

Soleus muscle of adult rat is revascularized 5-8 days after sectioning the supplying blood vessels. The temporary ischaemia thus produced results in the rapid concomitant degeneration of extra- and intrafusal muscle fibres along with their nerve terminals and supplying axons. The basal lamina of all muscle fibres usually remains intact throughout the degenerative phase. Necrotic sarcoplasm is removed by phagocytic cells. Satellite cells survive the temporary ischaemia and give rise to presumptive myoblasts which fill the basal-lamina tubes. These myoblasts fuse to form myotubes which, by the 14th day after devascularization, are maturing into muscle fibres in the absence of any innervation. Within the spindle, nuclear-bag fibres degenerate more rapidly than nuclear-chain fibres. Regeneration proceeds more rapidly within the basal-lamina tubes of the original bag fibres than within those of the chain fibres. Reinnervation of regenerating extra- and intrafusal fibres begins 21 days after devascularization and is completed some 7 days later, during which time further equatorial differentiation of some reinnervated intrafusal fibres may occur. Regenerated spindles vary considerably with respect to their innervation and equatorial nucleation. Most contain short, thin, additional muscle fibres as well as those that have regenerated within the basal-lamina tubes of the original fibres.

Ultrastructural study of a blood-muscle spindle barrier after systemic administration of horseradish peroxidase.

The permeability of the normal muscle spindle capsule to the entrance of an exogenous protein tracer was assessed by the use of horseradish peroxidase (HRP). Adult mice were injected intravenously with a solution of HRP (MW 40,000). After varying intervals, ranging from two to 240 minutes, animals were perfused aortically with fixative, and anterior tibialis muscles were removed, processed, and examined. The results were evaluated by electron microscopic cytochemical techniques, and attention was directed to the movement of tracer and its relationship to the outer and inner capsule of the muscle spindle. HRP was first demonstrated in cytoplasmic vesicles crossing the continuous capillary endothelium supplying the muscle spindle, and was then detected in the interstitial space surrounding the outer capsule. In polar regions, HRP had entered the periaxial space by two minutes, and it was seen in cytoplasmic vesicles of the attenuated outer capsule. Later, HRP abutted the sarcolemma of intrafusal fibers, and by 12.5 minutes there was evidence of tracer in T-tubules of these muscle cells. Whereas at no time was tracer observed traversing any of the numerous intracellular junctions of the capsule, it appeared that polar regions were leaky and open-ended at their distal portions. The sensory equatorial zone was considerably less permeable to the entrance of tracer. Whereas HRP was visible intially in cytoplasmic vesicles of the subjacent capillary endothelium, it was not until 12.5 minutes that racer could be demonstrated within some vesicles of equatorial outer capsule cells. At later times, a small amount of HRP was observed in the equatorial periaxial space, where it was phagocytosed and finally sequestered by cells of the inner capsule as membrane-bound lysosomal deposits. Consequently, at no time was tracer incorported into either intrafusal fibers or their sensory nerve terminals. Thus, in contract to polar regions, the muscle spindle capsule in the equatorial zone appears to be effective in preventing the indiscriminate penetration of HRP from the bloodstream. This suggests dissimilar paths of tracer movement from the microvasculature into sensory and non-sensory regions of the muscle spindle.

The blood supply of duck muscle spindles.

The blood supply of duck muscle spindles from the extensor pollicis and the extensor digitorum comminis wing muscles has been studied by light and electron microscopy. Capillaries usually accompany the nerve bundle that innervates the spindle, approaching at an oblique angle around the midequatorial region. Capillaries may run for some distance along the surface of the outer capsule, or penetrate partially into the outer capsule and lie between layers of the capsule cell processes. Some capillaries also penetrate the outer capsule, running into the periaxial space and continuing further towards the polar region. They have been shown to be in close contact with intrafusal muscle fibres, from the juxta-equatorial to the polar region, but have not been encountered among sensory terminals in the mid-equatorial region.

The blood supply of muscle spindles in some mammals and the pigeon.

The blood supply of muscle spindles was studied in serial cross sections in macaque, cat, rabbit, guinea pig, mouse and pigeon muscles which had been incubated in a medium containing 3,3' diaminobenzidine. Lumina of blood vessels were recognized by the reaction product that was localized within erythrocytes. The outer capsule was well vascularized, but few or no capillaries were seen in the periaxial space. The inner spindle capsule, which closely invests the axial bundle, was rarely contacted by periaxial capillaries at the equator and juxtequator. Capillaries occurred more frequently adjacent to intrafusal fibers at the polar region and beyond the end of the outer capsule. Shorter diffusion distances and, usually, higher capillary densities were found at the polar region than at the spindle midsection. This suggests that transcapillary exchange at the polar segment is nearer to conditions prevalent in extrafusal muscle than elsewhere in the spindle, provided the inner and outer capsules are not less permeable at the poles than at the midsection. Differences in blood supply among mammalian species appear to be related to receptor size.

Morphometric comparison of capillaries in muscle spindles, nerve, and muscle.

Morphometric study was performed on transverse sections of microdissected muscle spindles from rabbit tenuissimus muscles. It showed a statistically significant difference in size and structure between the intrafusal capillaries and those of extrafusal muscle. The former are larger in diameter, circumference, and area due to a proportionate increase in the number of endothelial cells. Vesicles within spindle endothelial cells are fewer, mitochondrial counts are greater, but in proportion to the increased number of endothelial cells, intercellular junctions are tight and pericyte coverage is greater. The basement membrane around endothelial cells and pericytes is thicker and more often multilayered. The endoneurial capillaries of tenuissimus intramuscular nerve are morphologically identical to intrafusal capillaries. The similarity of the capillaries of spindles to those in brain suggests that a blood-nervous system barrier extends from brain into the peripheral nerves and muscle spindles.

[Formation of the circulatory bed of the neuromuscular spindles in forearm and hand muscles]. / Formirovanie gemotsirkuliatornogo rusla nervno-myshechnykh vereten v myshtsakh predplech'ia i kisti.

The data are presented on the formation and main constitutional principles in the blood supply of the neuromuscular spindles in the human forearm and hand during embryogenesis and early postnatal life. It has been stated that the neuromuscular spindles posses their own microcirculatory bed which is formed by the vessels of the surrounding muscular tissue, tends to separate in the course of development and subdivides into two parts: extracapsular and intracapsular. The vessels of the extracapsular part form dense capillary nets on the external surface of the capsule and follow extracapsular parts of the intrafusal muscular fibres. The intracapsular vessels either cover the internal surface of the capsule, or adjoin the intrafusal muscular fibres, or else run in the free subcapsular space.

Microvasculature of rabbit muscle spindles.

The microvasculature of the muscle spindle and its relationship to the microcirculation of teniussimus extrafusal muscle is described. Muscle spindles lie in close proximity and parallel to the central artery, vein, and nerve. The arterioles to spindle capillaries are third to fourth order branches of the central artery, whereas most arterioles to extrafusal capillaries are sixth to eighth order. Two or three capillaries enter each spindle. At least one entry consistently was encountered in the equatorial area near the sensory endings. Branches of intrafusal capillaries run longitudinally, anastomose with each other, and cradle the sensory zone in a longitudinal capillary loop. Capillaries in muscle spindles are larger than those in extrafusal muscle. These characteristic features are presumed to enhance the capability of these capillaries to provide sufficient circulation to the spindle, particularly to the region of the sensory endings.

Permeability of muscle spindle capillaries and capsule.

The permeability of capillaries in rabbit muscle spindles, intramuscular nerves, and extrafusal muscle to intraaortically infused horseradish peroxidase (HRP) was studied. The permeability of the capsule cells of the muscle spindles was also examined. Immediately following the infusion of HRP, most extrafusal capillaries contained a dense accumulation of HRP reaction product, which began to escape into the surrounding extracellular space within 2-3 min. In contrast, the concentration of HRP in the intrafusal and endoneurial capillaries was much lower than that in extrafusal capillaries, and HRP was never found outside the former vessels. In addition, HRP never completely penetrated through the spindle capsule from the extracellular into the periaxial space, although it was regularly found between the outer two or three layers of capsule cells. The results indicate that the permeability characteristics of the muscle spindle capillaries and capsule to the tracer protein HRP are very similar to those of capillaries in peripheral nerve.

A histochemical study of the neuro-muscular spindles in the tongue of some rodents.

An investigation was undertaken to study the Neuro-muscular spindles in the tongue (Rattus rattus rufescens and Suncus murinus) by cholinesterase technique, under maintained pH of 5.2, incubation period 20 h., and temperature 38 degrees C (Rattus) and 39 degrees C (Suncus). Neuro-muscular spindles were observed frequently distributed from anterior to posterior of the tongue and took a little darker stain than the ordinary muscle fibres (negatively stained) while the nerve fibres and ganglia took still darker stain. Nerve fibres (myelinated, non-myelinated and tortuous) were seen penetrating and embracing the muscle spindles and most of them ran parallel to the spindles. Ganglia of various shapes (oval, irregular, elongated and rounded) and sizes (large, Rattus and medium and small, Suncus) were AChE-positive. Ganglia small and medium in size, rounded and elongated in shape were arranged in chain-like fashion on the muscle spindles in Suncus (Fig. 9, 10). The blood vessels (artery, vein, and capillary) were recorded either in close association with the muscle spindles or lying parallel to it. In all cases they were closely related and deeply associate either with the nerve fibres of the plexus of the muscle spindles or with the nerve fibres of the neural network of vessel. Perivascular and perimuscular ganglia with pre- and postganglionic nerve fibres were closely related to each other. Nerve endings, dot-like (Rattus) and bulb-like (Suncus) were occasionally recorded. AChE activity was found randomly in the muscle spindles (Fig. 2, 5.) and in the form of dark brown patches in the ordinary muscle fibres.

Fine structure of the avian muscle spindle capsule.

The capsule of the muscle spindle from the anterior and posterior latissimus dorsi muscles of the adult domestic chicken has been studied with the electron microscope. As in other species, two distinct portions of the spindle capsule are distinguished: an outer capsule and an inner capsule. The outer capsule is structurally similar to and continuous with the perineural epithelium. Outer capsule cells are noted by the abundance of pinocytotic vesicles and a network of 6-7-nm microfilaments. The disposition of these microfilaments is circumferential with respect to the longitudinal axis of the spindle. It is proposed that they may provide a contractile mechanism for the capsule which may be related to the over-all functioning of the spindle during movements of the muscle. The inner capsule is composed of a contiguous network of cells possessing long cytoplasmic processes which envelop the intrafusal fibers and their nerve endings in sensory equatorial regions of the spindle. These cells may elaborate the fibrillar and amorphous extracellular material found in periaxial spindle space. They also possess modified cilia with a "9+0" microtubular pattern. It is suggested that these cilia may behave as sensory transducers, relating fluid changes in the periaxial space to the intrafusal fiber nerve endings. Capillaries of the non-fenestrated variety commonly traverse the outer and inner portions of the capsule and are usually completely surrounded by tenuous overlapping processes of inner capsule cells. These findings suggest that the spindle capsule plays a role as a metabolically-active diffusion barrier to the entrance of substances from the external milieu.

An ultrastructural study of neuromuscular spindles in normal mice: with reference to mice and man infected with Mycobacterium leprae.

Mycobacterium leprae have been found within muscle spindles in mice, using electron microscopy, and in man, using light microscopy. Their mode of entry clearly is important. It may be via capsular cells, capillaries or nerves. For this reason muscle spindles from normal mice were studied by electron microscopy with special reference to the capsule and the relationship of it with capillaries and nerves, as well as details of the intrafusal fibres and capsular space. A fenestrated capillary was found between the capsular cell layers and outside the capsule in one spindle and in another spindle both a fenestrated and a continuous type of a capillary were found between the capsular cells; this may be of interest for pharmacological studies. However, the muscle spindles of the mouse were in the main similar to muscle spindles studied by other workers in man and other mammals.