Muscle fibre types and muscle spindles in the jaw musculature of the rat.

The fibre composition and occurrence of muscle spindles was studied in the masticatory, the suprahyoid and the infrahyoid muscles of the rat. Muscle fibres were typed as fast-white, fast-intermediate, fast-red and slow-red according to their ATPase and SDH activity. Fibre type appeared to be closely related to fibre diameter. In most of the muscles, all four fibre types were found. Slow-red fibres were absent in the superficial masseter, the transverse mandibular and the omohyoid muscles; fast-white fibres were absent in the mylohyoid muscle. The masticatory muscles were mainly composed of the three fast-fibre types; the jaw-opener muscles (the anterior digastric, the posterior digastric, the posterior digastric, the stylohyoid and the lateral pterygoid muscle) showed more slow-red fibres. In the masticatory and most of the suprahyoid muscles, the slow-red fibres were restricted to an area with high SDH activity. In the infrahyoid muscles, the fibre types were evenly distributed. Many muscle spindles, often clustered, were found in the masticatory muscles, except in the lateral pterygoid. In most of the suprahyoid muscles, these sensory structures were absent. In the infrahyoid muscles, solitary muscle spindles were found.

Histochemical properties of intrafusal fibers in the soleus muscle of the aged rat.

ATPase reaction profiles of intrafusal fibers in the muscle spindle of the soleus muscle of 135-week-old rats were examined. Nuclear bag1 fibers contained an acid- and alkaline-labile form of the enzyme or an acid-labile and alkaline-stabile form, nuclear bag2 fibers contained an acid- and alkaline-stabile form, and nuclear chain fibers contained an acid-labile and alkaline-stabile form. These results indicate that the enzyme histochemical heterogeneity of intrafusal fibers is well-preserved during ageing.

An investigation into the site of termination of static gamma fibres within muscle spindles of the cat peroneus longus muscle.

1. The distribution of static fusimotor fibres to intrafusal muscle fibres of cat peroneus longus muscle spindles was investigated using the glycogen-depletion technique of Edström & Kugelberg (1968). Single static gamma fibres were stimulation intermittently at high rates for 3 hr with the blood supply occluded for some of this time. Subsequently the portion of muscle containing the activated spindles was fixed, sectioned and stained for glycogen with the periodic acid-Schiff (PAS) method. 2. Ten static axons caused depletion in eleven spindles. In five of these the only glycogen-depleted fibres were nuclear chain fibres. In the other six spindles one nuclear bag fibre was depleted in addition to chain fibres and this was always the larger of the two within the spindle. 3. These results on a medium-sized hind limb muscle are compared with findings concerning the distribution of static gamma fibre axons previously investigated only in very small muscles. The results agree in showing that nearly all static gamma fibres innervate nuclear chain fibres but that in 50-75% of the times in which static gamma fibres innervate spindles the distribution is to bag fibres as well as to chain fibres. The interpretation to be put upon this is uncertain. One possibility with which the results from peroneus longus are consistent is that the bag fibres which are usually innervated by static axons are the 'intermediate' bag fibres whose ultrastructure has recently been shown to resemble that of chain fibres.

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

Muscle spindles were traced in serial transverse sections of cat tenuissimus muscles. Histochemical staining for "myofibrillar" adenosine 5'-triphosphatase was employed to identify nuclear bag1 intrafusal muscle fibers. Staining for cholinesterases (ChE) was used to demonstrate the termination sites of motor axons along the fibers. Several types of ChE deposits could be distinguished along the bag1 fibers based on intensity of staining and morphological characteristics. Most ChE deposits could be classified as either the "pale" or the "nonpale" plates. Some ChE active areas fitted neither of these two categories. Among 328 ChE "plates" encountered on 192 bag, fiber poles, 197 (60%) were of the "pale" and 27 (8%) of the "nonpale" type with 104 (32%) remaining unclassified. These histochemical observations are discussed with regard to the current structural and functional concepts of motor innervation of the nuclear bag1 fiber. It is suggested that the histochemical (ChE staining intensity) and morphological (length and form) characteristics of bag1 fiber motor endings are not determined solely by the nature of the corresponding motor axons.

Histochemical heterogeneity of intrafusal muscle fibres in slow and fast skeletal muscles of the rat.

Intrafusal muscle fibres of the slow soleus (Sol) and fast vastus lateralis (VL) muscles of the rat were studied histochemically. Serial transverse sections were incubated for the localization of succinate dehydrogenase (SDH), alpha glycerophosphate dehydrogenase (GPD) and adenosine triphosphatase (ATPase). The latter was examined further after preincubation in acidic solution held at either low or room temperature (RT). The bag2 intrafusal fibres in both muscles displayed high regular and acid stable ATPase, but low SHD and GPD activities. Bag1 intrafusal fibres showed low to moderate regular ATPase, a regional heterogeneity after RT acid preincubation (low activity in juxtaequatorial and high in polar zones), moderate SDH, but low GPD reactions. In both muscles the chain fibres usually exhibited high ATPase for both regular and cold acid preincubated reactions, but usually low activity after RT acid preincubation; they had high SDH but variable GPD activities. In Sol muscle, however, approximately 25% of spindles contained chain fibres that showed high acid-stable ATPase reaction after both cold and RT acid preincubation. In contrast, chain fibres in some VL spindles had a characteristically low ATPase reaction even after cold acid preincubation. This study, therefore, has delineated the existence of an inherent heterogeneity among chain fibres (with respect to their histochemical reactions) in muscle spindles located within slow and fast muscles and also between those found within populations of either Sol or VL muscle spindles.

One-bag-fiber muscle spindles in tenuissimus muscles of the cat.

Over 150 complete and 139 incomplete single muscle spindles were examined in serial transverse sections of cat tenuissimus muscles in search for spindles lacking one of the two types of nuclear bag intrafusal fiber. Several histochemical reactions were used to type the intrafusal muscle fibers and assess the spindle motor and sensory innervation. One complete spindle lacked a bag1 fiber, and another spindle lacked a bag2 fiber. Several incomplete spindles also lacked bag1 fibers. In addition, ten double tandem spindles contained one capsular unit each that lacked the bag1 fiber, and one triple tandem spindle had two such capsules. All one-bag-fiber spindles had primary sensory innervation, but none had secondary sensory innervation. Their motor innervation was similar to that of the usual two-bag-fiber spindles in the number and disposition of intrafusal motor endings. It is unclear whether the one-bag fiber spindles, either single or tandem-linked, are products of an aberrant spindle development or represent a true anatomical and functional subcategory of the cat muscle spindle.

Studies of capsule and capsular space of cat muscle spindles.

The presence of hyaluronate in the capsular space of the cat muscle spindle was demonstrated using alcian blue staining at various pHs, the critical electrolyte concentration technique and hyaluronidase treatment. In spindles with intact capsules an extracellular marker, the dye Ruthenium Red, gained access to the capsular space through the gap in the sleeve region, but for a limited distance. In muscle spindles with the capsule nicked, the marker diffused into the capsular space in the equatorial region, revealing a dense network in this space which consisted of globular structures interconnected by thin filaments. Based on their thickness, these filaments were inferred to be hyaluronic acid, and the globular structures were inferred to be protein molecules. Longitudinal diffusion of the dye into the capsular space through the nicked site was limited. The limited diffusion is probably due to electrostatic binding of the dye, which is a hexavalent cation, to negatively charged glycosaminoglycan hyaluronate that is present in the space. The transcapsular potential was measured by use of glass micropipettes filled with 3 M-KCl. The value was 15 mV +/- 4 (average +/- S.D., n = 12; range, 10-20 mV) inside negative. The input resistance and capacitance of the capsule, measured with two independent electrodes, varied widely (1.3-8.0 M omega and 0.5-1.3 nF, n = 4) and the capsule showed marked delayed rectification to outward current pulses. [K+] in the space measured with K+-sensitive resin-filled glass micropipettes was a few millimolar higher than that in the bathing solution. The effects of [K+] and [Ca2+] on impulse activities were examined in spindles with intact capsules or with partially resected capsules. In spindles with intact capsules the effects of [K+] and [Ca2+] were significantly less or negligible compared with those in spindles with the capsule opened. Hyaluronidase (approximately 10(-4) g/ml) added to the bathing solution around nicked capsules significantly reduced both resting and stretch-induced impulse activities in 40-50 min. By this time the capsular space was completely collapsed. An increase in [K+] of the bathing solution from 3.5 to 6 or 8 mM restored these impulse activities. A similar restoring effect was also observed when [Ca2+] in the bathing solution was reduced.(ABSTRACT TRUNCATED AT 400 WORDS)

Healthy and diseased striated muscle studied by analytical scanning electron microscopy with special reference to fibre type.

X-ray microanalytical investigations of striated muscles in the scanning electron microscope are reviewed. The main part of the studies was performed on cryosections cut with a conventional cryostat operating at -20 degrees C to -40 degrees C. The preparation procedure including different types of attachment of the sections to the specimen holder is described in detail. The elemental changes in muscle are related to the muscle fibre type as demonstrated by histochemical methods or to histochemically demonstrated inclusions in diseased muscles. This is of great importance, because muscle disorders are often characterised by selective involvement of different muscle fibre types. The preparation methods of muscle for analytical scanning electron microscopy and the obtained results are compared with studies performed on thin cryo and epoxy sections, analysed in the transmission and scanning-transmission electron microscope. It is evident that X-ray microanalysis performed on thick cryosections provide a quick survey of the elemental composition of whole cells, and should be followed in interesting cases by close examination on the organelle level studied in thin cryosections in the transmission and scanning-transmission electron microscope.