Biometrical and histochemical comparison between extra- and intra-fusal muscle fibres in denervated and re-innervated rat muscle

Effect of muscle electrostimulation on afferent activities from tibialis anterior muscle after nerve repair by self-anastomosis

Numerous previous studies were devoted to the regeneration of motoneurons toward a denervated muscle after nerve repair by self-anastomosis but, to date, few investigations have evaluated the regeneration of sensory muscle endings. In a previous electrophysiological study (Decherchi et al., 2001) we showed that the functional characteristics of tibialis anterior muscle afferents are affected after self-anastomosis of the peroneal nerve even when the neuromuscular preparation was not chronically stimulated. The present study examines the regeneration of groups I-II (mechanosensitive) and groups III-IV (metabosensitive) muscle afferents by evaluating the recovery of their response to different test agents after self-anastomosis combined or not with chronic muscle stimulation for a 10-weeks period. We compared five groups of rats: C, control; L, nerve lesion without suture; LS, nerve lesion with suture; LSE(m): nerve lesion plus chronic muscle stimulation with a monophasic rectangular current; and LSE(b): nerve lesion plus chronic stimulation with a biphasic current with modulations of pulse duration and frequency, eliciting a pattern of activity resembling that delivered by the nerve to the muscle. Compared to the control group, (1) muscle kept only its original weight in the LSE(b) group, (2) in the LS group the response curve to tendon vibration was shifted toward the highest mechanical frequencies and the response of groups III-IV afferents after fatiguing muscle stimulation lowered, (3) in the LSE(m) group, the pattern of activation of mechanoreceptors by tendon vibrations was altered as in the LS group, and the response of metabosensitive afferents to KCl injections was markedly reduced, (4) in the LSE(b) group, the response to tendon vibration was not modified and the activation of metabosensitive units by increased extracellular potassium chloride concentration was conserved. Both LSE(b) and LSE(m) conditions were ineffective to maintain the post muscle stimulation activation of metabosensitive units as well as their activation by injected lactic acid solutions. Our data indicate that chronic muscle electrostimulation partially favors the recovery of mechano- and metabosensitivity in a denervated muscle and that biphasic modulated currents seem to provide better results.

The fine structure of denervated and reinnervated muscle spindles: morphometric study of intrafusal muscle fibers

The fine structure of normal, denervated, and reinnervated muscle spindles in lower lumbrical muscles of rats was studied morphometrically at time intervals ranging from 3-14 months. In control spindles, the mean transverse area of mitochondria was estimated to be more than twice as large in nuclear chain than in typical nuclear bag fibers. Following denervation, there was a severe decrease of the mean number and transverse area of mitochondria, and a moderate, but statistically significant decrease of the mean transverse area of intrafusal muscle fibers (IMFs) despite an increase of the number of IMFs. At 12-14 months of reinnervation, changes of the transverse areas of IMFs were statistically insignificant, but the mean values for the mitochondria were incompletely restored. At 4 x 3 months, after fourfold repeated crush injuries to the nerve, most of the values estimated (transverse area of mitochondria; number, shape, and transverse area of IMFs and nuclei) tended to approach those in denervated rather than in reinnervated IMFs. The differences of the reactions of intra- and extrafusal muscle fibers following complete motor and sensory denervation appeared to be in accordance with their normal dimensional dissimilarities.

Ultrastructure of the muscle spindle in dystrophia myotonica. II. The sensory and motor nerve terminals

The normal pattern of innervation was lost in the four dystrophia myotonica muscle spindles examined. There had been a proliferation of both sensory and motor nerve terminals, and many endings showed varying degrees of structural abnormality. The changes seen in the sensory nerve endings were an incomplete contact relationship between the terminal and the muscle fibre, the association of Schwann cell processes with the nerve ending, abnormal shape of the terminal, multiple sensory endings, and changes in the ultrastructural organization of the terminal axoplasm. Remnants of degenerated sensory terminals, and isolated sensory endings were also seen. Motor nerve terminals varied in size and shape. In general, they contained a normal complement of vesicles and mitochondria. Junctional folding was often absent or simplified, and sarcoplasmic specialization was, at the most, rudimentary. The relationship between these changes and intrafusal muscle fibre fragmentation is discussed.

Target-targetoid phenomenon of the human muscle fibers. A histological, histochemical and ultrastructural study

Target and targetoid fibers in a muscle biopsy from a patient with paralysis of the deltoid and supraspinatus muscles were studied by light and electron microscopy. The probable cause of the neuropathy was tumor compression. Target and targetoid change was exclusively confined to hypertrophic or normal-sized fibers. Morphometric evaluation of the target and targetoid fibers showed no significant difference between them. With the electron microscope, up to 4 structural zones were seen in the typical target fiber but many were devoid of either zone 2(halo) or zone 3, or both. It was conceivable that focal irregularity and streaming of Z-bands were the primary alterations in the process of target-targetoid fiber formation, and that this phenomenon was induced both by partial residual innervation as well as re-innervation.

The target phenomenon in rat muscle following tenotomy and neurotomy. A comparative light microscopic and histochemical study

Target fibers were checked at regular intervals in two groups of rat gastrocnemius muscle namely after tenotomy and neurotomy. The highest amount of target fibres was observed during the first week following tenotomy and around the seventh week, when the muscle became again functional by spontaneous union of the tendon. The target phenomenon was restricted to the type II fibres. It appeared also in the early stage of re-innervation, 5 weeks following neurotomy and remained present subsequently in a transitional zone between denervated and re-innervated muscle fibres and was restricted to the type I muscle fibres. The target phenomenon was not the only histochemical alteration observed following tenotomy and neurotomy. This experimental study allowed to determinate more precisely the causal factors of the target phenomenon.

The target phenomenon in human muscle: a comparative light microscopic histochemical and electron microscopic study

A large number of target fibres is observed in a muscle biopsy from a patient with an acute flaccid paraplegia of the lower limbs due to a polyneuroradiculopathy of unknown origin. With the electron microscope up to 4 structural zones are seen in the target fibers. The histochemical and ultrastructural observations in this case, suggest that the "target fiber" phenomenon is due to a disturbed trophic influence of the nervous system.

Intrafusal fibre types in rat limb muscle spindles: morphological and histochemical characteristics

Morphological, histochemical and ultrastructural characteristics of intrafusal fibre types were studied in rat muscle spindles. The existence of three intrafusal fibre types, namely the typical bag, the intermediate bag and the chain fibres was confirmed. Intrafusal fibres differ in diameter, length and number of nuclei in the equatorial zone. Histochemically, typical bag fibres exhibit both alkali- and acid-stable ATPase activity and low SDH activity. Intermediate bag fibres possess low alkali-stable ATPase activity; after acid-preincubation, however, they have low activity only in the juxtaequatorial region, whereas in the polar zones they exhibit high acid-stable ATPase activity. The SDH activity varies from moderate to high. The chain fibres exhibit high alkali-stable and low acid-stable ATPase and high SDH activity in the extensor digitorum longus muscle, whereas in the soleus muscle the acid-stable ATPase activity varies from a low one to a high one, either among individual chain fibres in one spindle, and/or repeatedly along the fibre length. Since there are regional differences in morphological characteristics and in staining properties of intrafusal fibres, a reliable identification of intrafusal fibre types can only be achieved by an analysis of serial sections.