Beta adrenergic binding sites in the human eye: an autoradiographic study.

Beta adrenergic binding sites were localized and characterized in the human eye by means of "in vitro" autoradiography, using [125I] (-) iodocyanopindolol (125ICYP) as radioligand. Binding sites were visualized by apposition of isotope sensitive film to slide mounted eye sections. Receptor sites were present in the extraocular muscles, in the conjunctiva, in the epithelium and endothelium of the cornea, in the trabeculum and in the ciliary muscle. They were also present in the lens epithelium and in the retina. The pigmented ocular structures were heavily labelled but the binding was nonspecific. Characterization of these binding sites was achieved by testing the ability of selective adrenergic compounds to displace 125ICYP binding. These studies suggested that the majority of adrenergic binding sites in nonpigmented structures of human eye were of a beta2 type.

Different intrafusal fiber composition of spindles in sheep and pig extraocular muscles.

Histochemical profiles of intrafusal fibers have been examined in muscle spindles of extraocular muscles of sheep and pig. Results show that in the sheep the intrafusal content presents, in addition to chain fibers, at least one bag1 and one bag2 fiber, whereas in the pig almost all the spindles are one-bag-fiber [corrected] spindles.

Contractile properties and histochemistry of extraocular muscle in the pigmented and the albino guinea pig.

The inferior oblique muscles of pigmented and albino guinea pigs were compared with respect to contractile and histochemical properties. No differences were found between the 2 kinds of animal in twitch and tetanic response or in fatigue properties. They also had the same fiber composition and fiber and capillary densities of their inferior obliques. These findings indicate that differences in eye muscle previously demonstrated and Siamese (albino) cats are related to the state of binocular vision and not to genetic variations between pigmented and albino animals.

Co-expression of multiple myosin heavy chain genes, in addition to a tissue-specific one, in extraocular musculature.

We have investigated the developmental transitions of myosin heavy chain (MHC) gene expression in the rat extraocular musculature (EOM) at the mRNA level using S1-nuclease mapping techniques and at the protein level by polypeptide mapping and immunochemistry. We have isolated a genomic clone, designated lambda 10B3, corresponding to an MHC gene which is expressed in the EOM fibers (recti and oblique muscles) of the adult rat but not in hind limb muscles. Using cDNA and genomic probes for MHC genes expressed in skeletal (embryonic, neonatal, fast oxidative, fast glycolytic, and slow/cardiac beta-MHC), cardiac (alpha-MHC), and EOM (lambda 10B3) muscles, we demonstrate the concomitant expression at the mRNA level of at least six different MHC genes in adult EOM. Protein and immunochemical analyses confirm the presence of at least four different MHC types in EOM. Immunocytochemistry demonstrates that different myosin isozymes tend to segregate into individual myofibers, although some fibers seem to contain more than one MHC type. The results also show that the EOM fibers exhibit multiple patterns of MHC gene regulation. One set of fibers undergoes a sequence of isoform transitions similar to the one described for limb skeletal muscles, whereas other EOM myofiber populations arrest the MHC transition at the embryonic, neonatal/adult, or adult EOM-specific stage. Thus, the MHC gene family is not under the control of a strict developmental clock, but the individual genes can modify their expression by tissue-specific and/or environmental factors.

Rat extraocular muscle. 2. Histochemical fibre types.

A battery of histochemical stains was used to differentiate the component fibre populations in rat superior oblique muscle. Seven histochemical fibre types were identified and found to be comparable to those observed in a prior light and electron microscopic study of the muscle. The global region of the muscle contained three singly innervated fibre populations (pale, intermediate and red) and one of multiply innervated fibres. THe global singly innervated fibre populations produced a spectrum of fibre types with trichrome, succinate dehydrogenase and Sudan black. The overlying orbital surface layer contained two populations of singly innervated fibres and an additional population of multiply innervated fibres. All the singly innervated fibres (both global and orbital) exhibited a high mATPase activity at pH 10.4 and a low mATPase activity at pH 4.6. The global multiply innervated fibres had low mATPase activity at pH 10.4 and high mATPase activity at pH 4.6. The multiply innervated fibres of the orbital surface layer exhibited high mATPase activity at pH 10.4 and at pH 4.6. The global multiply innervated fibres are similar to the tonic fibres found in amphibian muscle, both histochemically and ultrastructurally. Based upon their histochemical reactivities with the various stains, the multiply innervated fibres of the orbital surface layer appear to be faster acting than the global multiply innervated fibres. Furthermore, it is postulated that the former have polyneuronal innervation and are capable of dual mATPase synthesis.

The distribution of membrane-glycogen complexes in the orbital surface layer of rabbit superior rectus.

The distribution of membrane--glycogen complexes along the length of individual muscle fibers was compared among three fiber populations in the orbital surface layer of rabbit superior rectus. These three populations were (a) 61 singly innervated fibers (SIFs), (b) 10 multiply innervated fibers of relatively constant 10 micrometer diameter (10 micrometer MIFs), and (c) 22 multiply innervated fibers which are of about 5 micrometer diameter toward the middle of their length and of about 15 micrometer diameter toward their proximal and distal segments (5--15 micrometer MIFs). The orbital surface layer was sampled by electron microscopy at 68 sequential locations. Membrane--glycogen complexes were not seen in any of the 1738 samples of the SIFs. In the MIFs, such complexes were observed in 14% of the 1541 samples. However, both the 10 micrometer MIFs and 5--15 micrometer MIFs displayed a preferential concentration of membrane--glycogen complexes toward their distal fiber portions, and such complexes were seen in about 50% of the MIF samples near the beginning of the muscle's distal third. In the distal portion of 5--15 micrometer MIFs, there was a direct relationship between their increasing fiber diameter and their increasing frequency of occurrence of membrane--glycogen complexes.

Contractile and histochemical properties of the inferior oblique muscle in the rat and in the cat.

Mechanical and histochemical properties of inferior oblique muscles(IO) were compared in adult albino rat and pigmented cat. The twitch contraction times and the fusion frequencies were about the same in both species indicating similar contractile properties of the fast contracting fibers. Rat IO seemed to contain fewer slowly contracting fibers than cat IO; half-decay time of the twitch was shorter in rat than in cat muscles and fusion started at higher stimulus frequencies. Fatique resistance was lower in rat than in rat than in cat. Post-tetanic potentiation occurred in the cat but not in the rat IO. Almost all fibers of rat IO were rich in myofibrillar ATPase. In cat IO most fibers showed high myofibrillar ATPase activity, but some fibers in the global layer had moderate to small amounts of this enzyme. This correlates well with the physiological differencies between cat and rat IO.

Extraocular muscles: light microscopy and ultrastructural features.

Thirty extraocular muscles (EOM) from 20 patients were evaluated by light microscopy (LM), electron microscopy (EM), and enzyme histochemistry (EZH). Twenty-one EOM were obtained from 13 patients with strabismus, 9 EOM from 4 patients undergoing eye surgery for other reasons and from 3 autopsy cases. One mum thick sections revealed marked variation in muscle fibre shape and size and in myofibrillar structure; also noted were small, hypertrophied, whorled, and ringbinden fibres. Dense and granular material in the central portion of some fibres and sarcomere disruption in 2--3 mum sections was observed. EZH revealed the absence of the classical mosaic pattern usually found in skeletal muscles. ATPase studies were inconsistent and did not correlate with the expected reciprocal activity of NAD-H diaphorase, particularly on the large fibres. Ultrastructural features consisted of vacuoles within myofilament bundles, "smearing" of Z bands, and "nemaline rods". Occasional myelin figures and lipid-like droplets were observed in subsarcolemmal spaces, associated with scattered clusters of glycogen granules. Abnormal mitochondria and subsarcolemmal inclusions of dense and granular material were conspicuous. "Leptomeric" profiles, "Zebra bodies", or "striated bodies" were noted in 8 EOM's, and an Hirano body was found in 1. The intramuscular nerves contained structures resembling "Luse bodies" in 7 cases. These observations suggest that EOM from individuals with and without strabismus possess unique structural characteristics suggestive of developmental and morphological disarrangement of contractile elements. Some of these changes might play a role in the pathogenesis of strabismus and in the development of clinical symptoms. These features are significantly different from striated skeletal muscle. Therefore the criteria used in the pathological evaluation and diagnosis of skeletal muscle disorders cannot be unequivocally applied to EOM investigations. These data establish the necessity to determine histological norms, ultrastructural patterns, and develop new enzyme histochemistry criteria for the evaluation of EOM. Only then can an acceptable comparison of EOM and skeletal muscle be made.