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Biomedical subjects

J C Mira

Publications and source records attributed to J C Mira.

At least 37 records · Page 2Linked to original sources
PubMed1994

Brachial plexus repair by peripheral nerve grafts directly into the spinal cord in rats. Behavioral and anatomical evidence of functional recovery.

Over the years, peripheral nerve grafts, a favorable environment for the support of axonal elongation, have attracted interest as a possible means of promoting spinal cord repair. In the experiments described here, rats underwent an avulsion injury of the brachial plexus, and the musculocutaneous nerve was repaired by direct insertion of peripheral nerve grafts into the spinal cord. After varying postoperative periods, the rats were submitted to a series of behavioral tests to evaluate forelimb and hindlimb function. They also underwent retrograde double-labeling studies. Nerve grafts were harvested and processed for electronic microscopy. The biceps muscle was removed and weighed and its histology studied. After surgery, central axons effectively regenerated about 65 mm along the peripheral nerve grafts, restoring normal active elbow flexion. Forelimb movements were well coordinated in both voluntary and automatic activities. Clinical investigations showed that there were no side effects in the ipsilateral forepaw, contralateral forelimb, or either hindlimb. Regenerating axons stemmed from original motoneurons, foreign motoneurons, and even antagonist motoneurons, but this did not impair function. Ganglionic neurons from adjacent roots also sent processes to the peripheral nerve grafts.

Animals↗
PubMed1993

Opposite regulations by androgenic and thyroid hormones of V1 myosin expression in the two types of rabbit striated muscle: skeletal and cardiac.

The finding that V1 cardiac myosin is expressed in masticatory skeletal muscles of the rabbit provided a unique opportunity for comparing the hormonal regulation of V1 in skeletal and cardiac muscles. Thyroid hormones had no significant effect on the postnatal expression of V1 in masticatory muscles, but increased this expression in cardiac ventricles. In contrast, androgenic hormones reduced V1 expression in masticatory muscles, but did not affect it significantly in cardiac ventricles. Modulation of V1 gene transcription in striated muscle is thus shown here to depend both on the target muscle and on the hormone.

Androgens↗
PubMed1993

Nerve repair using freezing and fibrin glue: immediate histologic improvement of axonal coaptation.

Despite the fine microsurgical techniques available, injuries to peripheral nerves are still a surgical problem. Sutures placed in the epineurium or perineurium cause compression, brushing, and misdirection of endoneural tissue. A technique of nerve repair using freezing to trim the nerve and fibrin glue to coat it before thawing is described. The entire surgical repair procedure is carried out with the nerve stumps frozen. The observed axonal alignment with this technique was much better than that obtained by microsuture alone.

Anastomosis, Surgical↗
PubMed1993

Behavioral evaluating methods in the objective clinical assessment of motor function after experimental brachial plexus reconstruction in the rat.

Unfortunately, the results of brachial plexus surgery have not fulfilled expectations. Although the components of the rat brachial plexus are similar to those of the human plexus, experimental work in this field is limited. No functional test to assess experimental brachial plexus reconstruction has so far been published. We worked out a method of evaluating brachial plexus impairment in rats in the laboratory. It consists of a simple test in which a bowl of water is projected over the animal's head, eliciting grooming movements of the forepaws towards the head. This test is therefore called the 'grooming test'. A system of scoring the animals' performance is suggested. Rats were also submitted to walking tracks analysis, but this was of limited value in assessing brachial plexus impairment.

Animals↗
PubMed1993

[Longitudinal excursion of the sciatic nerve: an experimental study in the adult rat].

Every nerve must have the capacity to adapt to different positions by passive movement relative to the surrounding tissue. This capacity is called longitudinal excursion (LE). The LE of the sciatic nerve has been studied in 40 Wistar rats. The LE was measured, the nerve was cut, sutured, a metallic body was put into the anastomotic site for later radiographic controls (at the 8th week) and then the anastomosis was protected with different kinds of tissue. After 16 weeks the sciatic nerve was exposed, the LE was measured again and the nerve was dissected out for light microscopy. The LE is produced by two mechanisms: 1) rectification of the undulating course of the nerve and 2) elasticity of the neural connective tissue sheaths. The paraneurim provides a gliding tissue. During flexion movements, it acts as an external support and keeps the nerve under a longitudinal compression force. The normal LE is the release of this compression. These properties enable the nerve to glide without changing its diameter. The gag after nerve section is approximately 75% of LE. After repairing the nerve the new LE is 55% of the original value. In peripheral nerve surgery, to create a new nerve-bed or to protect the anastomoses, a muscle flap should be avoided. On the other hand, no difference could be found between other tissue flaps. When transposing a nerve, the submuscular position is preferable to the intramuscular position.

Adipose Tissue↗
PubMed1992

Reinnervation of denervated extensor digitorum longus of the rat by the nerve of the soleus does not induce the type I myosin synthesis directly but through a sequential transition of type II myosin isoforms.

The fast-contracting extensor digitorum longus (EDL) muscle of 1-month-old rats was denervated and reinnervated by the nerve innervating the slow-contracting soleus muscle. After variable periods of time, the myosin isoform content of the EDL was analyzed by sensitive electrophoretic techniques, which allowed to discriminate between the slow-type I and the three, IIA, (IID or IIX) and IIB, fast-type II myosin isoforms. Compared to the control EDL, which contains predominantly the IIB isoform, the operated muscles contained variable proportions of all the isoforms. Analysis of the results leads us to conclude that reinnervation of EDL induces a sequential transition of myosin isoforms: IIB----(IID or IIX)----IIA----I.

Animals↗
PubMed1991

The same myosin isoforms are found in the female and male sexually dimorphic levator ani muscle of the rat, but their postnatal transitions are not synchronous.

The levator ani of the female adult rat is greatly atrophied in comparison to the same muscle in males. In the present study, the female levator ani was, nevertheless, found to contain type IIb myosin isoforms similar to those contained in the male muscle. These adult type isoforms were, however, synthesized later in the female than in the male levator ani: the half-transition times of the myosin transition curve were 20 days postnatal in the male and 35 days postnatal in the female. The transition curves for castrated and uncastrated male rats were the same. Thus, the presence of male gonadal hormones apparently did not affect the myosin transition.

Animals↗
PubMed1991

[Effect of age on the number and size of myelinated nervous fibers. A qualitative and quantitative study in the rat].

The number and the average diameter of the myelinated fibers have been recorded in the both medial gastrocnemius nerves in the rat. The study concerned foetus at the end of the intra-uterine life as well as old rats (24 months). It seemed the absolute necessity to collect these data before studying the consequences of age on nervous regeneration. Electron microscopy was used in very small samples, photonic microscopy in bigger ones. The first myelinated fibers appear during the first day of life. Their number becomes steady around 2 months of live. But their diameter changes and increases until the end of the 6th month. In pubescent animals, the global variations between the two sides are negligible (average right number 260 +/- 8 fibers, average left 258 +/- 12, average right diameter 1.7 +/- 0.7 microns, average left diameter 7.1 +/- 0.6 microns).

Aging↗
PubMed1991

[Effect of age on the number and size of myelinated nerve fibers. A study after localized freezing on section-suture of the sciatic nerve in the pubescent rat].

The regeneration of the myelinated fibers has been studied after a localized congelation or a section followed by an immediate suture in the left sciatic nerve of rats aged of 1 1/2, 3, 6, 12, 18 and 24 months at the moment of the operation. The regenerated fibers has been observed in the left internal gastrocnemius nerve, the right nerve being considered as the sham. For each nerve, the number and the caliber of the myelinated nerves has been systematically registered at standard levels allowing to calculate the average diameter of the fibers, their repartition and to draw their histogram. The results seem to prove that the potential of regeneration is correlated to the age, the velocity and intensity of the axonal growth decreasing in the old age. This potential of regeneration remains during the whole life. The integrity of the schwannian membranes considerably facilitates the nervous fibers regeneration, their interruption is a major obstacle to the axonal regrowth.

Aging↗
PubMed1990

Muscle-specific response to thyroid hormone of myosin isoform transitions during rat postnatal development.

Transitions from embryonic and neonatal to adult-type-II isomyosins are known to be related to the increase in the thyroid hormone plasma concentration during postnatal development. These transitions have been shown, however, to occur at different times, depending on the muscle, suggesting that each muscle responds differently to the thyroid hormone. We have investigated quantitatively the effects of experimental hypothyroidism and hyperthyroidism on isomyosin transitions from birth until the 45th postnatal day in eight rat muscles: diaphragm, intercostals, gastrocnemius medialis, soleus, plantar muscles of the foot, tongue muscle, levator ani and bulbocavernosus complex, and masseter. Hypothyroidism delayed the isomyosin transitions in all the muscles examined, particularly in the sexually dimorphic muscles (levator ani and bulbocavernosus complex and masseter). However, it did not eventually inhibit isomyosin transitions, indicating that the thyroid hormone was not an absolute requirement for these to occur. Hyperthyroidism had only a slight effect on isomyosin transition in the diaphragm, and accelerated such transitions in the other muscles. The transition curves of all the muscles investigated, except those of the sexually dimorphic muscles, became similar to that of the diaphragm, demonstrating that the various muscles did not display the same sensitivity to the thyroid hormone but were regulated by it in the same way. The isomyosin transitions in the sexually dimorphic muscles remained late in comparison to that in the diaphragm, which suggests a more complex regulation. The effect of hyperthyroidism was not permanent and could be reversed, by interruption of the treatment, to a greater or lesser extent depending on the muscle. In all muscles containing slow-type-I isomyosin, hypothyroidism had no effect on this isomyosin synthesis, whereas hyperthyroidism inhibited it. This inhibition ceased rapidly after the interruption of the treatment.

Age Factors↗
PubMed1989

Myosin isoform transitions in regeneration of fast and slow muscles during postnatal development of the rat.

Regeneration of rat fast (gastrocnemius medialis) and slow (soleus) muscles was examined after degeneration of myofibers had been achieved by injection of cardiotoxin into the hindleg during the first week after birth. Myogenesis in the regenerating muscles was compared to postnatal myogenesis in the contralateral and in control muscles. Synthesis of embryonic and neonatal myosin isoforms was initiated 3 days after injury. These forms were gradually replaced by the intermediate and fast adult isoforms (type II fiber myosins), whose synthesis followed the same curve in regenerating, contralateral, and control muscles. In contrast, synthesis of the slow myosin isoform (type I fiber myosin) was greatly delayed in injured muscles, but eventually became equal to its synthesis in contralateral and control muscles. It therefore appears that synthesis of type II fiber myosins is similarly regulated, probably by thyroid hormone, in developing regenerating and normal muscles, while synthesis of type I fiber myosin depends on other factor(s).

Animals↗
PubMed1989

Formation of functional endplates by spinal axons regenerating through a peripheral nerve graft. A study in the adult rat.

Peripheral nerve (PN) autografts were used in the adult rat to join the midcervical spinal cord to a nearby denervated skeletal muscle. Retrograde tracing, morphological and electrophysiological studies indicated the following: 1) a great number of neurons, located bilaterally, between C3 and C7 in most laminae of the grey matter, extended axons into the PN grafts, 2) a lesser number of neurons regenerated up to the reconnected muscle, but most of them were typical motoneurons, 3) neuromuscular junctions were formed in ectopic locations, around the tip of the grafted nerve, and at the sites of original endplates, 4) these junctions were functional and formed by axons that had regenerated into the PN bridges, as muscle contraction was obtained by electrical stimulation of the grafted nerves, 5) they were proved to be cholinergic since endplate potentials, evoked by stimulating the PN graft, were suppressed by curare. These results strongly suggest that spinal neurons, and especially motoneurons, are involved in the formation, through PN bridges, of new functional cholinergic connections with denervated skeletal muscles.

Action Potentials↗
PubMed1988

Regeneration after cardiotoxin injury of innervated and denervated slow and fast muscles of mammals. Myosin isoform analysis.

The regeneration of adult rat and mouse slow (soleus) and fast (sternomastoid) muscles was examined after the degeneration of myofibers had been achieved by a snake venom cardiotoxin, under experimental conditions devised to spare as far as possible the satellite cells, the nerves, and the blood vessels of the muscles. Three days after the injury, no myosin was detectable in selected portions of the muscles. New myosins of embryonic, neonatal, and adult types started to be synthesized during the following two days. Adult myosins thus appeared more precociously than in development, which implies that the synthesis of myosin isoforms during regeneration does not entirely 'recapitulate' the sequence of myosin transitions observed during normal development. Two weeks after the injury, the isomyosin electrophoretic pattern displayed by regenerated muscles was already the same as that of control muscles; the normal adult pattern was therefore expressed more rapidly in regenerating than in developing muscles. Except for the synthesis of the slow isoform which was generally inhibited in denervated muscles, the same types of myosins were expressed during the early stages of regeneration in denervated as in innervated muscles; long-term denervation prevented however the qualitative and quantitative recovery of the normal myosin pattern.

Animals↗