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PubMed1996

Scanning electron microscopic study of the postnatal development of the rabbit cochlea, with an emphasis on innervation.

The development of nerve fiber arrangements of the organ of Corti was studied in rabbits 1, 3, 5, 7 and 12-days-old using thick sections from celloidin-embedded cochleas which were examined under a scanning electron microscope. The arrangements of nerve fibers varied with developmental age. The tunnel spiral bundle was thick and loosely collected in the immature cochlea. The outer spiral fibers were recognized even in the narrow space of Nuel in the one-day-old cochlea. As Nuel's space is extending, the fibers course along the medial side of Deiters' cells. The arrangement of the outer spiral fibers was irregular and sparse in the five-day-old cochlea, in contrast to the regular parallel pattern of the adult cochlea. Adult-like parallel arrangement of the outer spiral fibers was seen in the twelve-day-old cochlea. In the three-day-old cochlea, irregularly running nerve fibers were seen along the outer spiral fibers. They may be efferent axons which develop afterwards. Club-like immature nerve endings were recognized at the base of the outer hair cells in the seven-day-old cochlea. Some fibers climbed high up along the medial wall of the outer hair cells. A nearly mature pattern was seen in the twelve-day-old cochlea. This study confirms previous reports on the development of cochlear innervation.

Animals↗
PubMed1990

The relationship between ATPase activity, isometric force, and myosin light-chain phosphorylation and thiophosphorylation in skinned smooth muscle fiber bundles from chicken gizzard.

Isometric force developed by skinned gizzard muscle fiber bundles and levels of phosphorylation and thiophosphorylation of the 20,000-dalton myosin light chain were determined. These data showed a highly non-linear relationship between isometric force and myosin light-chain phosphorylation. Maximum force was developed at approximately 0.2 mol of phosphate/mol of light chain as reported previously (Hoar, P. E., Kerrick, W. G. L., and Cassidy, P. S. (1979) Science 204, 503-506). In contrast, the relationship between isometric force and myosin light-chain thiophosphorylation was linear, with maximum force occurring at 1.0 mol of thiophosphate/mol of myosin light chain. These observations are consistent with the latch-bridge hypothesis for conditions of varying myosin light-chain phosphatase/myosin light-chain kinase activity ratios as discussed by Hai and Murphy [1988) Am. J. Physiol. 254, C99-C106). To further test the latch-bridge hypothesis, ATPase activity was also measured during isometric force development in these fiber bundles. The relationship between isometric force and ATPase activity was linear whether the myosin light chains were phosphorylated or thiophosphorylated. Thus the number of cycling myosin cross-bridges, as measured by ATPase activity, was directly proportional to the force the muscle developed, not to the level of myosin light-chain phosphorylation. This finding that high levels of tension generated at low levels of light-chain phosphorylation are associated with high levels of ATPase activity is inconsistent with the latch-bridge model (Hai and Murphy, 1988).

Adenosine Triphosphatases↗
PubMed1980

[Intracellular recordings of the multiple innervation of Purkinje cells by climbing fibers in the cerebellum of the developing rat].

Intracellular recordings of postsynaptic potentials evoked in cerebellar Purkinje cells (PCs) by activation of the climbing fibers (CFs) have been obtained from 3 to 15 day-old Rats. The data presented confirm the multiple innervation of PCs by CFs on postnatal days 8-9, and demonstrate its existence at earlier stage (from day 3). The evolution of the precentage of multinnervated PCs and of the mean number of CFs collaterals per PC was followed until the monoinnervation was established on day 15.

Aging↗
PubMed1988

Morphology of chorda tympani fiber receptive fields and proposed neural rearrangements during development.

The average number of fungiform papillae in receptive fields of single chorda tympani nerve fibers decreases during development in sheep, and a greater proportion of small receptive fields that are highly responsive to NaCl, compared with NH4Cl, is acquired. To learn whether there also are developmental differences in the number of taste buds within the papillae in mapped receptive fields, we studied the morphology of receptive fields and fungiform papillae, and also counted fibers in the chorda tympani nerve, in fetal, perinatal, and postnatal sheep. Whether defined as the number of fungiform papillae or as the number of taste buds within papillae, receptive fields of chorda fibers decrease developmentally. Initially, however, there is an increase, and subsequently a decrease, in the number of taste buds per field. The differences in field size cannot be attributed to developmental alterations in numbers of fungiform papillae because the total number of papillae on the tongue remains constant. The average number of taste buds per papilla, however, also increases and then decreases, and the increase in perinatal animals is accompanied by the appearance of large, multipored taste buds. Because there is a significant relation between fungiform papilla size and number of taste buds in the papilla, papilla size could be one regulating factor for taste bud number. Furthermore, the number of chorda tympani nerve fibers apparently increases up to perinatal stages and then decreases postnatally, providing another potential regulating factor for the number of taste buds.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2006

Absence of alpha3 (Cx46) and alpha8 (Cx50) connexins leads to cataracts by affecting lens inner fiber cells.

Lens development and transparency have been hypothesized to depend on intercellular gap junction channels, consisting of alpha3 (Cx46) and alpha8 (Cx50) connexin subunits, to transport metabolites, secondary messages and ions between lens cells. To evaluate this hypothesis, we have generated alpha3(-/-) alpha8(-/-) double knockout mice and characterized their lens phenotypes. Without gap junctions between lens fiber cells, alpha3(-/-) alpha8(-/-) lenses displayed severe cataracts resulting from cell swelling and degeneration of inner fibers while normal peripheral fiber cells continued to form throughout life. Neither an increase of degraded crystallins nor an increase of water-insoluble crystallins was found in alpha3(-/-) alpha8(-/-) lenses. However, a substantial reduction of gamma-crystallin proteins, but not alpha- and beta-crystallins, was detected. These results suggest that gap junction communication is important for maintaining lens homeostasis of inner fiber cells and that a loss of gap junctions leads to cataract formation as well as reductions of gamma-crystallin proteins and transcripts.

Animals↗
PubMed2003

In situ orientations of protein domains: troponin C in skeletal muscle fibers.

A recently developed approach for mapping protein-domain orientations in the cellular environment was used to investigate the Ca(2+)-dependent structural changes in the tropomyosin/troponin complex on the actin filament that regulate muscle contraction. Polarized fluorescence from bifunctional rhodamine probes attached along four alpha helices of troponin C (TnC) was measured in permeabilized skeletal muscle fibers. In relaxed muscle, the N-terminal lobe of TnC is less closed than in crystal structures of the Ca(2+)-free domain, and its D helix is approximately perpendicular to the actin filament. In contrast to crystal structures of isolated TnC, the D and E helices are not collinear. On muscle activation, the N lobe orientation becomes more disordered and the average angle between the C helix and the filament changes by 32 degrees +/- 5 degrees. These results illustrate the potential of in situ measurements of helix and domain orientations for elucidating structure-function relations in native macromolecular complexes.

Actins↗
PubMed1976

Developmental aspects of the innervation of skeletal muscle fibers in the chick embryo.

The M. complexus in the chick, commonly called the hatching muscle, undergoes conspicuous growth during the latter stages of embryonic development. Myogenesis of this muscle was compared to that of M. biceps femoris with regard to development of types of muscle fiber and their innervation. In both muscles beta fibers are of relatively uniform size and show little growth in diameter between 12 days of development and hatching; alpha fibers develop continuously and display a wide range of diameters at all stages. Initial thickenings on the sarcolemma of beta fibers where axons are closely approximate were first observed at 10 days of development in both muscles. In both muscles beta fibers are innervated prior to alpha fibers. Terminal axon networks bridge intercellular spaces and contact beta fibers in different myogenic clusters. alpha fibers that develop on the surface membrane of beta fibers exhibit focal thickenings of the membrane and some cell projections that are directed toward axon-beta fiber contacts. These changes occurred only in alpha fibers of M. complexus. At 14 days of embryogenesis, the processes of synaptogenesis and of myelin formation are less advanced in M. biceps femoris than in M. complexus. At this stage alpha fibers were observed to be innervated in M. complexus, but not yet in M. biceps femoris. Each beta fiber was observed to be encircled by several preterminal axons. It is concluded that the earlier development of M. complexus is correlated with an equally early development of nerve-muscle interactions.

Adenosine Triphosphatases↗
PubMed1956

Electron microscopic and histochemical observations of muscle degeneration after tourniquet.

As an experimental model for the different forms of muscle degeneration, injury caused by 2 hours' ischemia has been studied from 20 minutes to 16 hours after release of the tourniquet. Discoid degeneration developed in stretched fibers by dissolution of the I bands (Z substances and actin). The discs represented the Q bands (A-H-A). In fibers which passively maintained contraction lengths during degeneration, the Z substances were dissolved, but the continuity of the fibrils was preserved, since the filaments are continuous over all sarcomeres under these conditions. Mitochondria and the tubules of the endoplasmic reticulum swelled, ruptured, and disintegrated. Granular degeneration developed in fibers where mitochondria were abundant. Unstretched degenerating fibers with few mitochondria gave a homogeneous or hyaline appearance. The different forms of degeneration therefore were dependent on the status of stretch and the fiber type. The extent of degeneration was not a function of time after ischemia, there being both nearly normal and severely damaged fibers at 20 minutes and 16 hours after the release of tourniquets. When degeneration occurred, however, the basic alterations were the same in all fibers; there was mitochondrial and reticular swelling, dissolution of the Z substances, and finally disintegration of the contractile material. Some damage developed in the sarcolemmas and capillaries. The mitochondrial disintegration was not linked with inactivation of the succinic dehydrogenase system.

Animals↗
PubMed1951

Loss and recovery of excitability by normal and by degenerating nerves deprived of sodium.

A study has been made of the loss of excitability in a sodium-free medium and of the recovery of excitability in Ringer's solution by A fibers of normal frog nerves and of nerves in advanced stages of Wallerian degeneration. With normal nerves that are being kept in a sodium-free medium the number of conducting fibers does not undergo a readily detectable decrease in less than 1 to 2 hours; inexcitability of all the A fibers does not develop in less than 7 to 8 hours. During the development of inexcitability the speed of conduction of the still conducting fibers undergoes a progressive decrease; in advanced stages the speed of conduction is not more than one-fifth of the normal speed. The nerve fibers lose the ability to conduct rhythmic trains of impulses earlier than the ability to conduct single impulses. The recovery of excitability in Ringer's solution duplicates in a reverse order the sequence of changes that have been previously observed during the development of inexcitability. The rate of the recovery of excitability in Ringer's solution is higher than the rate of the loss of excitability in the sodium-free medium. With degenerating nerves the effect of the lack of sodium develops qualitatively in the same manner in which it develops with normal nerves. Degenerating nerve fibers, however, become inexcitable in a sodium-free medium earlier than normal fibers. The recovery of the excitability in Ringer's solution takes place in much the same manner in normal and in degenerating nerve fibers. The loss of excitability during Wallerian degeneration is a process that develops simultaneously, or practically so, throughout the entire length of the fibers. The nerve fibers retain a great deal of functional ability throughout the several days which precede the onset of inexcitability and then suddenly become inexcitable.

Sodium↗
PubMed1982

Differentiation of muscle fiber types in the teleost Brachydanio rerio, the zebrafish. Posthatching development.

The trunk musculature of adult zebrafishes contains three major fiber types: adult red, intermediate, and white; and two minor populations: red muscle rim and scattered intermediate fibers. In this paper, the post hatching development of these muscle fiber types was studied by means of immunohistochemistry, using anti-myosin sera. Just hatched larvae contain two muscle fiber populations: embryonic red and white, which give rise to the red muscle rim and the intermediate fibers respectively. Adult red fibers arise post hatching as a new separate population with distinct myosin properties. The differentiation of these fiber types occurs within the first four weeks after fertilization, when the adult pattern of peripheral axon bundles has become established. Differences in the muscle fiber type composition between the midbody and the tail myotomes become apparent in two month old fries. The number of scattered intermediate fibers increases from rostral to caudal, the opposite holds for the red muscle rim fibers. The red and intermediate area is triangular in the midbody; in the tail part it is stretched out along the lateral surface of the myotomes. These changes are considered as adaptations to improve the efficiency of the swimming performance.

Animals↗
PubMed1996

Dietary fat and fiber differentially alter intracellular second messengers during tumor development in rat colon.

The effect of fat, fiber and carcinogen on colonic epithelial intracellular second messengers 1,2-diacyl-sn-glycerol (DAG), ceramide, and the steady-state level of phospholipase C (PLC-gamma1) was determined in 160 male Sprague-Dawley rats (10 rats per group). The study was a 2 x 2 x 2 x 2 factorial design with two types of fat (corn oil or fish oil), two types of fiber (cellulose or pectin), two injected subgroups (with or without azoxymethane (AOM), and two time points (15 and 37 weeks). At the final time point (37 weeks) there were an additional 20 rats per diet in each of the carcinogen-treated groups for tumor analyses only (n = 80), for a total of 240 animals in the entire study. At each time point (15 and 37 weeks), 80 rats were killed and colonic mucosa obtained for DAG, ceramide and PLC-gamma1 assays. At the first time point (15 weeks), there was no microscopic evidence of tumors. At the final time point (37 weeks), fish oil resulted in a lower proportion of animals with adenocarcinomas relative to corn oil feeding (56.1 % versus 69.6 %, P < 0.05). There was no significant main effect of fiber on the percentage of animals with tumors. At 15 weeks post-injection, AOM injected animals fed corn oil-containing diets had a significantly (P < 0.001) higher DAG mass and steady-state levels of PLC-gamma1 compared with AOM-injected animals fed fish oil and saline injected rats on all diets. Animals fed corn oil diets also had a significantly (P < 0.01) elevated mucosal ceramide mass compared with fish oil fed animals. Moreover, rats injected with AOM had a significantly (P < 0.02) elevated colonic mucosal DAG/ceramide ratio versus saline injected animals. In contrast, dietary fiber had no effect on any of the parameters measured at 15 weeks. However, at 37 weeks post-injection, dietary fiber significantly altered DAG (P < 0.02), and PLC-gamma1 expression (P < 0.05) in the absence of an effect on tumor incidence. These data demonstrate that the ability of dietary fish oil to reduce experimental colon carcinogenesis may be mediated by changes in colonic intracellular mediators during the initial stages of tumorigenesis.

Adenocarcinoma↗
PubMed2002

Molecular dynamics simulation of site-directed spin labeling: experimental validation in muscle fibers.

We have developed a computational molecular dynamics technique to simulate the motions of spin labels bound to the regulatory domain of scallop myosin. These calculations were then directly compared with site-directed spin labeling experimental results obtained by preparing seven single-cysteine mutants of the smooth muscle (chicken gizzard) myosin regulatory light chain and performing electron paramagnetic resonance experiments on these spin-labeled regulatory light chains in functional scallop muscle fibers. We determined molecular dynamics simulation conditions necessary for obtaining a convergent orientational trajectory of the spin label, and from these trajectories we then calculated correlation times, orientational distributions, and order parameters. Simulated order parameters closely match those determined experimentally, validating our molecular dynamics modeling technique, and demonstrating our ability to predict preferred sites for labeling by computer simulation. In several cases, more than one rotational mode was observed within the 14-ns trajectory, suggesting that the spin label samples several local energy minima. This study uses molecular dynamics simulations of an experimental system to explore and enhance the site-directed spin labeling technique.

Animals↗
PubMed1982

Distribution and properties of myosin isozymes in developing avian and mammalian skeletal muscle fibers.

Isozymes of myosin have been localized with respect to individual fibers in differentiating skeletal muscles of the rat and chicken using immunocytochemistry. The myosin light chain pattern has been analyzed in the same muscles by two-dimensional PAGE. In the muscles of both species, the response to antibodies against fast and slow adult myosin is consistent with the speed of contraction of the muscle. During early development, when speed of contraction is slow in future fast and slow muscles, all the fibers react strongly with anti-slow as well as with anti-fast myosin. As adult contractile properties are acquired, the fibers react with antibodies specific for either fast or slow myosin, but few fibers react with both antibodies. The myosin light chain pattern slow shows a change with development: the initial light chains (LC) are principally of the fast type, LC1(f), and LC2(f), independent of whether the embryonic muscle is destined to become a fast or a slow muscle in the adult. The LC3(f), light chain does not appear in significant amounts until after birth, in agreement with earlier reports. The predominance of fast light chains during early stages of development is especially evident in the rat soleus and chicken ALD, both slow muscles, in which LC1(f), is gradually replaced by the slow light chain, LC1(s), as development proceeds. Other features of the light chain pattern include an "embryonic" light chain in fetal and neonatal muscles of the rat, as originally demonstrated by R.G. Whalen, G.S. Butler- Browne, and F. Gros. (1978. J. Mol. Biol. 126:415-431.); and the presence of approximately 10 percent slow light chains in embryonic pectoralis, a fast white muscle in the adult chicken. The response of differentiating muscle fibers to anti-slow myosin antibody cannot, however, be ascribed solely to the presence of slow light chains, since antibody specific for the slow heavy chain continues to react with all the fibers. We conclude that during early development, the myosin consists of a population of molecules in which the heavy chain can be associated with a fast, slow, or embryonic light chain. Biochemical analysis has shown that this embryonic heavy chain (or chains) is distinct from adult fast or slow myosin (R.G. Whalen, K. Schwartz, P. Bouveret, S.M. Sell, and F. Gros. 1979. Proc. Natl. Acad. Sci. U.S.A. 76:5197-5201. J.I. Rushbrook, and A. Stracher. 1979. Proc Natl. Acad. Sci. U.S.A. 76:4331-4334. P.A. Benfield, S. Lowey, and D.D. LeBlanc. 1981. Biophys. J. 33(2, Pt. 2):243a[Abstr.]). Embryonic myosin, therefore, constitutes a unique class of molecules, whose synthesis ceases before the muscle differentiates into an adult pattern of fiber types.

Animals↗
PubMed1980

Mechanisms of septal lamination in the developing hippocampus revealed by outgrowth of fibers from septal implants. I. Positional and temporal factors.

Pieces of embryonic septal tissue were implanted into a cavity within the entorhinal or occipital cortices of neonatal rat hosts (2-3 days old). The initial outgrowth of fibers originating from the grafts and their pattern of termination within the host hippocampal formation was examined using a histochemical stain for acetylcholinesterase (AChjE). Fimbrial transections were performed in conjunction with the implant surgery to eliminate native septohippocampal fibers. When placed in the occipital cortex, septal implants innervate specific laminar zones within the host hippocampus and dentate gyrus; these are the same laminar zones that receive septal efferents in the normal animal. Septal implants placed in the entorhinal cortex also produce a pattern of AChE staining in the host hippocampus which is similar to that seen in the normal hippocampus. In the dentate gyrus ipsilateral to the implant, however, the unstained commissural/association (C/A) zone is expanded. Temporal characteristics of the outgrowth of fibers from the implant were studied in animals sacrificed 6, 8, 10 and 12 days after the implant surgery. AChE activity indicative of innervation from the implant is present in 50% of the animals sacrificed 10 days post-implant; by 12 days post-implant all but one animal displayed AChE reaction product in the dentate molecular layer. AChE-positive processes emanating from cells in the implant were oriented toward the hippocampus throughout the developmental period. The position of the afferent source and the time of arrival of the afferent fibers in the target area do not seem to be critical to the mechanisms underlying the development of specific connection patterns in the septohippocampal system. We have proposed that contact between a 'critical afferent' (C/A system in this case) and the target cell might initiate the events underlying the development of appropriate patterns of connectivity.

Acetylcholinesterase↗
PubMed1997

Fast synaptic signaling by nicotinic acetylcholine and serotonin 5-HT3 receptors in developing visual cortex.

Cholinergic and serotonergic fiber systems invade the developing visual cortex several weeks before eye opening; both transmitters have been implicated in plasticity of neocortical circuits. These transmitters have been presumed to act predominantly through second messenger-coupled receptors, because fast cholinergic or serotonergic neurotransmission has never been observed in neocortex. However, acetylcholine and serotonin also act on ligand-gated ion channels; the nicotinic acetylcholine receptor and the serotonin 5-HT3 receptor, respectively. Here, using whole-cell patch-clamp techniques in developing ferret visual cortex, we pharmacologically isolated fast, spontaneous, and evoked cholinergic and serotonergic synaptic events in pyramidal cells and interneurons of all cortical layers. The number of cells receiving such inputs increased with the ingrowth of thalamic afferents, and the frequencies of the spontaneous events increased at eye opening. Thus, both acetylcholine and serotonin can mediate fast synaptic transmission in the visual cortex; the early onset of these mechanisms suggests a role during initial stages of circuit formation and during subsequent experience-dependent remodeling of cortical connections.

Acetylcholine↗
PubMed1980

Canine gastric sling fibers: contractile properties.

The contractile properties of canine sling fibers and the longitudinal and circular muscles were characterized and compared. The longitudinal and circular muscles developed spontaneous contractions, but the sling fibers developed no spontaneous phasic contractions. The cholinergic receptors of all three muscles were excitatory. The alpha- and beta-adrenergic receptors of the longitudinal and circular muscles were inhibitory, but the sling fiber alpha-adrenergic receptors were excitatory and the beta receptors inhibitory. Large concentrations of atrophine induced contractions of all three muscles. Some of the contractile properties of the sling fibers are more similar to those of the distal esophageal circular muscle than to those of the gastric longitudinal and circular muscles. The sling fibers together with the esophageal circular muscle may play an important role in the gastroesophageal sphincter mechanism.

Acetylcholine↗
PubMed1996

Postnatal development and plasticity of specialized muscle fiber characteristics in the hindlimb.

Recent progress in defining molecular components of pathways controlling early stages of myogenesis has been substantial, but regulatory factors that govern the striking functional specialization of adult skeletal muscle fibers in vertebrate organisms have not yet been identified. A more detailed understanding of the temporal and spatial patterns by which specialized fiber characteristics arise may provide clues to the identity of the relevant regulatory factors. In this study, we used immunohistochemical, in situ hybridization, and Northern blot analyses to examine the time course and spatial characteristics of expression of myoglobin protein and mRNA during development of the distal hindlimb in the mouse. In adult animals, myoglobin is expressed selectively in oxidative, mitochondria-rich, fatigue-resistant myofibers, and it provides a convenient marker for this particular subset of specialized fibers. We observed only minimal expression of myoglobin in the hindlimb prior to the second day after birth, but a rapid and large (50-fold) induction of this gene in the ensuing neonatal period. Myoglobin expression was limited, however, to fibers located centrally within the limb which coexpress myosin isoforms characteristic of type I, IIA, and IIX fibers. This induction of myoglobin expression within the early postnatal period was accompanied by increased expression of nuclear genes encoding mitochondrial proteins, and exhibited a time course similar to the upregulation of myoglobin and mitochondrial proteins, and exhibited a time course similar to the upregulation of myoglobin and mitochondrial protein expression that can be induced in adult muscle fibers by continuous motor nerve stimulation. This comparison suggests that progressive locomotor activity of neonatal animals may provide signals which trigger the development of the specialized features of oxidative, fatigue-resistant skeletal muscle fibers.

Animals↗