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PubMed1979

Neonatal suprachiasmatic nucleus lesions: effects on the development of circadian rhythms in the rat.

Previous studies of the effects of suprachiasmatic nucleus (SCN) destruction and visual pathway transections in adult rodents have revealed the primary significance of the SCN and the retinohypothalamic (RH) projection in the generation and entrainment of circadian rhythms. In the present study we found that complete ablation of the SCN in 2-day-old rats, prior to its innervation by the RH projection, permanently eliminates circadian rhythms in spontaneous locomotor activity and drinking; activity and drinking appear randomly distributed over the light-dark cycle. In addition, females exhibit long periods of constant vaginal cornification and an absence of normal estrous cycles. These effects are independent of the animal's visual status; that is, they occur in blinded as well as sighted animals. Incomplete SCN lesions results in partial disruption of rhythmic functions such as damping of circadian rhythms in activity and/or drinking, irregular estrous cycling, and/or complete disruption of only one or two of these measures of rhythmicity. The absence of spared functions after early SCN destruction is consistent with the high degree of specificity for the SCN exhibited by developing RH fibers and further emphasizes the significance of the SCN in circadian rhythm generation. Neither morphological nor functional plasticity has been found following neonatal ablation of the SCN in the rat.

Animals↗
PubMed1990

Pharmacologic evidence for NMDA, APB and kainate/quisqualate retinotectal transmission in the isolated whole tectum of goldfish.

The optic tectum of goldfish with intact optic and toral marginal fiber tracts was isolated in a perfusion chamber where the effectiveness of antagonists was tested on synaptic field potential responses to stimulation of each afferent system. There were 3 main conclusions about excitatory synapses. First, monosynaptic activation of retinotectal synapses was not detectably antagonized by D-tubocurarine, implying there is no nicotinic cholinergic component to optic transmission nor strong cholinergic gating of optic terminals. Second, a significant component of retinotectal transmission was shown to be mediated by kainate and quisqualate receptors since 6,7-dinitroquinoxaline-2,3-dione and kynurenate strongly suppressed the optic field potential. In addition, activation of these synapses involves two previously undescribed N-methyl-D-aspartate (NMDA) and APB receptor subtypes since optic field potentials were partially suppressed by 2-amino-5-phosphonovalerate (APV), 2-amino-4-phosphonobutyrate (APB) and MK-801. This is the first evidence that APB receptors exist in the visual system central to the retina. Together, these results are consistent with the possibility that retinal ganglion cells use multiple glutamate receptor subtypes. Third, the optic tectum contains a population of intrinsic glutaminergic synapses activated by a non-optic input, the marginal fibers, which can be suppressed by both APV and kynurenate. The existence of tectal NMDA receptors which are not at primary optic synapses implies that APV used to interfere with rearrangement of optic fibers during development may act not only at afferent synapses but also at a more central component of the circuit.

Afferent Pathways↗
PubMed1985

Enhanced reappearance of fast fibers in regenerating crayfish claw closer muscles.

In the pristine claws of adult crayfish the muscle fibers of the closer are all of slow type as judged by sarcomere lengths of greater than 6 micron, and a uniform degree of myofibrillar ATPase activity. In regenerating claws of mature and immature crayfish, the muscle has a central band of fast type fibers as characterized by shorter sarcomeres (less than 6 micron) and a higher degree of ATPase activity than the surrounding slow fibers. During primary development, the closer muscle has a fiber composition similar to that of the regenerating muscle except for a smaller proportion of fast fibers. Thus the reappearance of fast fibers during regeneration recapitulates ontogeny while their enhanced proportions may reflect epigenetic influences such as restriction of nerve-mediated muscle activity in the limb bud.

Adenosine Triphosphatases↗
PubMed1986

Molecular structure of the axolemma of developing axons following altered gliogenesis in rat optic nerve.

Axonal and axolemmal development of fibers from rat optic nerves in which gliogenesis was severely delayed by systemic injection of 5-azacytidine (5-AZ) was examined by freeze-fracture electron microscopy. In neonatal (0-2 days) rat optic nerves, all fibers lack myelin, whereas in the adult, virtually all axons are myelinated. The axolemma of neonatal premyelinated fibers is relatively undifferentiated. The P-fracture face (P-face) displays a moderate (approximately 550/micron 2) density of intramembranous particles (IMPs), whereas the E-fracture face (E-face) has few IMPs (approximately 125/micron 2) present. By 14 days of age, approximately 25% of the axons within control optic nerves are ensheathed or myelinated, with the remaining axons premyelinated. The ensheathed and myelinated fibers display increased axonal diameter compared to premyelinated axons, and these larger caliber fibers exhibit marked axonal membrane differentiation. Notably, the P-face IMP density of ensheathed and myelinated fibers is substantially increased compared to premyelinated axolemma, and, at nodes of Ranvier, the density of E-face particles is moderately high (approximately 1300/micron 2), in comparison to internodal or premyelinated E-face axolemma. In optic nerves from 14-day-old 5-AZ-treated rats, few oligodendrocytes are present, and the percentage of myelinated fibers is markedly reduced. Despite delayed gliogenesis, some unensheathed axons within 5-AZ-treated optic nerves display an increased axonal diameter compared to premyelinated fibers. Most of these large caliber fibers also exhibit a substantial increase in P-face IMP density. Small (less than 0.4 micron) diameter unensheathed axons within treated optic nerves maintain a P-face IMP density similar to that of control premyelinated fibers. Regions of increased E-face particle density were not observed. The results demonstrate that some aspects of axolemma differentiation continue despite delayed gliogenesis and the absence of glial ensheathment, and suggest that axolemmal ultrastructure is, at least in part, independent of glial cell association.

Animals↗
PubMed1986

Metabolic properties of human acetylcholine receptors can be characterized on cultured human muscle.

Experiments examining acetylcholine receptor (AChR) metabolism in tissue culture have hitherto been limited to animal systems. For many studies, the human AChR on human skeletal muscle provides a more physiologic target. However, previous studies suggested that the levels of AChR produced on cultured human muscle were inadequate for metabolic studies. We demonstrate here that the metabolism of human acetylcholine receptors can be analysed on pure human muscle fibers that develop in tissue culture. Degradation of AChR follows first-order kinetics and is inhibited 85% by leupeptin, demonstrating that proteolysis of human AChR occurs in the lysosome. New AChR continue to appear on the cell surface for 3 h in the presence of cycloheximide, indicating the existence of a pool of intracellular AChR destined for the cell membrane. This pool is equivalent to approximately one-third of the AChR present on the surface of the cell. At any given time, the rate of AChR accumulation on the cell surface can be quantitatively accounted for by the rates of synthesis and degradation. Our results demonstrate that studies on the effects of hormones, neurotoxins or antibodies from patients with autoimmune neuromuscular diseases are now possible with human AChR which develop on intact human muscle myotubes formed in tissue culture.

Cell Differentiation↗
PubMed1989

Clonal selection by fluorescence redistribution after photobleaching (FRAP)--a "fast" lateral mobility fibroblast mutant (E7G1).

Fluorescence redistribution after photobleaching (FRAP) was utilized to select a "fast" lateral mobility clone from Kirsten murine sarcoma virus-transformed 3T3 (KMSV-3T3) fibroblasts. The clone, E7G1, demonstrated a lateral mobility for membrane wheat germ agglutinin (WGA) and succinylated concanavalin A (sCon A) receptors of (2.1 +/- 1.6) X 10(-9) cm2/s and (2.7 +/- 2.3) X 10(-9) cm2/s, respectively. These mobilities were approximately equivalent to phospholipid mobility (2.8 +/- 1.9 X 10(-9) cm2/s). The fast mobility phenotype is observed when the cells are unattached and spherical. Upon attachment, the mobility decreases to (0.19 +/- 0.19) X 10(-9) cm2/s. In addition, the ability of Con A to initiate global modulation was completely lost in spread as well as spherical cells in the E7G1 fast mobility clone. A comparison of F-actin patterns between untransformed Balb/c fibroblasts and the E7G1-transformed line suggests a correlation between well-developed stress fiber assemblies and the ability to induce global modulation. The fast mobility clone was stable for at least 23 passages.

Actins↗
PubMed1992

Is there capacity for anatomical and functional repair in the adult somatosensory thalamus?

The capacity for structural and functional remodeling in damaged adult CNS sensory systems can be studied by replacement of neurons in damaged structures by fetal cells from these anatomical origins. For integration to take place, the replacement paradigm assumes that (a) reconnection of adult host afferent fibers onto developing neurons is possible and (b) that the correct molecular signals exist also in the adult brain for fetal neurons to extend axons and pattern synaptic contacts. We have tried to answer some of these fundamental questions by using neuronal depletion models followed by neuronal replacement in the adult rat CNS (Isacson et al. 1984. Nature (London) 311: 458-460; Isacson et al. 1988. Prog. Brain Res. 78: 13-27; Nothias et al. 1988. Brain Res. 461: 349-354; Peschanski and Isacson. 1988. J. Comp. Neurol. 274: 449-463; Sofroniew et al. 1990. Prog. Brain Res. 82: 313-320). In one such model, kainic acid infusions deplete the ventrobasal complex (VB) of all neurons projecting to the somatosensory cortex, while afferent axons from the lemniscal and monoaminergic systems remain in the area. Direct implantation of fetal neurons (gestation age 15-16) of ventrobasal destination allows reconnection of circuitry to take place at the thalamic level, as studied by anatomical tracers, electron microscopy, and functional 2-deoxyglucose studies, while fetal thalamic VB neurons appear less likely to grow through the internal capsule toward the cortical level.

Aging↗
PubMed1992

Development of myelinated and unmyelinated fibers of human vagus nerve during the first year of life.

As an important component of cardiorespiratory control, the vagus nerve and its maturation were evaluated in normal infants in order to provide standards of comparison with infants with dysfunctional neural control mechanisms. Myelinated and unmyelinated fibers in the cervical vagus nerve were examined in 27 term infants. Number of fibers, axon diameters, and myelin thickness were compared among four age groups. The histograms of axon size exhibited a skewed distribution that persisted during the age range examined for both myelinated and unmyelinated vagus fibers. Fiber size distributions of myelinated fibers, however, already showed an incipient multimodal distribution after 3 months. No major increase was observed in the average axon size of myelinated and unmyelinated fibers. A significant increase was observed, however, in the average content of myelin in myelinated fibers expressed as myelin thickness, number of lamellae or g ratio (internal/external diameter). These results suggest an active myelination during the first 9 months of life without a major change in the axonal characteristics of the fibers. A marginal increase in the density of myelinated fibers with age, both in terms of total number and the relation to unmyelinated fibers, suggests a slow transition from unmyelinated to myelinated fibers during the first year of life, particularly during the first 3 months. The present morphometric parameters indicate an active deposition of myelin before the maturation of cross-axonal dimensions. The distribution of g ratios also suggests that optimal conduction velocity is compromised only in a fraction of all vagal myelinated fibers.

Aging↗
PubMed1996

Competitive exclusion between axons dependent on a single trophic substance: a mathematical analysis.

A mathematical model is presented of competition between axons for a trophic substance, such as is believed to occur particularly during development. The model is biologically realistic. The growth-stimulating activity of the trophic molecules is assumed to result from their binding to high-affinity receptors on neurons and their axons, but the model also incorporates uptake by nonneuronal cells possessing only lower affinity receptors. Plausible and fairly general assumptions are made concerning the kinetics of binding and internalization and the effects on axonal growth. The model takes into account the possibility that trophic factor production may be regulated by the afferent axons or autoregulated. The variables specified are the "axonal vigor" of each axon, representing the ability of each axon to take up trophic molecules, and the concentration of trophic molecules in the extracellular space of the axonal target region. Of the several parameters introduced, the most important turns out to be the "zero vigor-growth parameter," which is defined as the concentration of trophic molecules that gives zero growth of the vigor of a given axon. By means of a Lyapunov function, it is shown that the system will approach asymptotically to a stable equilibrium characterized by the survival of only the axon whose zero-growth parameter is lowest. Or, if several axons share the same lowest zero-growth parameter, these will all survive. The model may be particularly relevant to the elimination of polyneuronal innervation from developing muscle fibers and from autonomic ganglion cells.

Animals↗
PubMed1977

Long-term results after intentional tooth reimplantation in monkeys.

The purpose of this study was to evaluate histologically the long-term response to intentional tooth reimplantation in six rhesus monkeys. The study revealed that cervical and apical root resorption is a universal complication after tooth reimplantation and that arrested areas of resorption will show repair by deposition of cementum. A highly cellular periodontal membrane usually will develop. Periodontal fibers will reattach to reparative bone and cementum but seldom regain functional orientation. Partial or complete ankylosis may result. A further complication is progressive undermining resorption of the ankylosed teeth. Long-term studies are mandatory to evaluate the response to intentional tooth reimplantation.

Alveolar Process↗
PubMed1980

Variation in cytoskeletal assembly during spreading of progressively subcultivated human embryo fibroblasts (IMR-90).

The cytoskeletons of early and late passage IMR-90 human diploid fibroblasts have been directly imaged in replicas of Triton X-100 extracted cells during spreading following reseeding. All cells from both young and sensescent cultures exhibit a cytoskeletal network of actin microfilaments, intermediate (10 nm) filaments, microtubules, and interconnecting thin filaments (6-8 nm in diameter) which do not interact with heavy meromyosin. Early passage cells assemble linear aggregates of actin filaments within 1 h of spreading. By 4 h of incubation, these bundles establish a structural bond with the cell membrane which results in resistance by the plasmalemma to detergent extraction at these sites. Furthermore, these membrane regions are associated with developing stress fibers of well-spread cells. In contrast, late passage cells exhibit slower spreading which correlates with a retarded assembly of actin bundles. In addition, by 8 h of spreading, cells of older cultures do not exhibit the regions of membrane-actin interaction which impart detergent resistance to the plasmalemma. We conclude that the ability to reassemble actin-actin and actin-membrane association during cell spreading is reduced with increased serial subcultivation of cells.

Aging↗
PubMed1982

Cerebellar macroneurons in microexplant cell culture. Postsynaptic amino acid pharmacology.

Cerebellar neurons derived from 17- to 19-day-old fetal rats have been grown in a monolayer in microexplant cell culture, and intracellular recording coupled with iontophoresis of amino acid neurotransmitters has been employed to characterize their amino acid chemosensitivity. Although these cultures contain at least 3 different neuronal cell types, intracellular recordings were obtained from large neurons (diameter greater than 15 microns) with 1-5 dendritic shafts and fine dendritic arborizations and which could, on morphological grounds, be identified as Purkinje cells. All neurons with resting membrane potentials greater than 25 mV and with action potentials evoked by intracellular stimulation, responded to iontophoretically applied glutamate and GABA. There was essentially no chemosensitivity to glycine, beta-alanine or taurine. Aspartate application evoked only small responses at high iontophoretic currents. GABA reversibly increased membrane conductance and produced hyperpolarization at resting membrane potential with reversal potentials between -50 and -40 mV (5-10 mV more negative than resting membrane potential). Glutamate reversibly increased membrane conductance and produced depolarizing responses with extrapolated reversal potentials between 0 and -10 mV. Aspartate augmented glutamate responses at low iontophoretic currents which did not directly alter membrane potential or conductance. Thus Purkinje cells grown in the absence of parallel fiber and climbing fiber input develop autonomous neuropharmacologic specificity similar to that of Purkinje cells in vivo.

Amino Acids↗
PubMed1986

Postnatal differentiation and growth of cat entopeduncular neurons. A transient spiny period associated with branch elongation.

Qualitative and computer-assisted analyses were performed on Golgi-impregnated neurons which were serially reconstructed in 3 dimensions. Analysis of the temporal pattern of growth indicated that the initial outgrowth, formation of the adult number of dendrites and virtually all dendritic branching occurred in the prenatal period. About 40% of the total growth of the dendrites occurred in the postnatal period. Maturation was completed by 90-120 days. Analyses of the mode of dendritic growth and of the morphological changes associated with growth revealed two significant findings. First, the outward expansion of the dendritic tree was not due to the addition of new branches but resulted from the elongation of terminal and non-terminal branches. Thus, growth occurred between branch points as well as on terminal portions of dendrites. Second, a transient population of spines was found during the period of postnatal growth. These spines may play an integral role in synaptogenesis and dendritic branch elongation. We suggest that developing afferent fibers initially contact spines. As spines retract, axon terminals are brought to the shaft of the dendrites. Further, the dendrites elongated because membrane associated with spines is incorporated into the shafts of dendrites. Striopallidal projections and other afferents may provide an important trophic influence for the normal dendritic differentiation of pallidal neurons by inducing the elaboration or retraction of spines.

Aging↗
PubMed1993

Developmental profile of inositol 1,4,5-trisphosphate 3-kinase in rat cerebellar cortex: light and electron microscopic immunohistochemical studies.

Developmental expression and intracellular distribution of inositol 1,4,5-trisphosphate 3-kinase in the rat cerebellar cortex were studied immunohistochemically. Immunoreactivity appeared first at postnatal day 1 in the rostral region of the cerebellum and by day 15 had extended throughout the whole cerebellum, being localized in the Purkinje cell layer. Shortly after the expression of the enzyme in each Purkinje cell, the labelling showed a tendency to accumulate in the dendrites in a fine granular pattern. Electron microscopy revealed that immunoreactivity was present in the Purkinje dendritic trunks with accentuation in the distal segments during the early postnatal period, thereafter becoming concentrated in the dendritic spines at later developmental stages. Labelling was associated mainly with the plasmalemma, including the postsynaptic densities and open coated vesicles, and the subplasmalemmal vesicles of the smooth endoplasmic reticulum. Immunoreactivity was also evident in the perisomatic processes of immature Purkinje cells, which are transient projections synapsing with climbing fibers. In developing Purkinje axons, immunoreactivity was accentuated in the distal segments, associated with the plasmalemma and synaptic vesicles. These results suggest that inositol 1,4,5-trisphosphate 3-kinase is involved in the dendritic arborization and subsequent spine synaptogenesis of Purkinje cells, and that the developing presynaptic nerve endings of these cells are another functional site for the enzyme.

Aging↗
PubMed1987

Acute tabun toxicity; biochemical and histochemical consequences in brain and skeletal muscles of rat.

Male Sprague-Dawley rats injected s.c. with an acute non-lethal dose (200 micrograms/kg) of ethyl N,N-dimethylphosphoramidocyanidate (tabun) showed onset of hypercholinergic activity within 10-15 min. The maximal severity of toxicity signs was evident within 0.5-1 h and persisted for 6 h. Except for mild tremors no overt toxicity signs were evident after 24 h. Within 1 h a dramatic decline of acetylcholinesterase (AChE) activity occurred in all the brain structures (less than 3%) and skeletal muscles (less than 10% in soleus and hemi-diaphragm; and 32% in extensor digitorum longus (EDL)). No significant recovery was seen up to 48-72 h. Within 7 days rats became free of toxicity signs and AChE activity had recovered to about 40% in brain structures (except cortex, 14%) and 65-70% in skeletal muscles. Within 1 h the 16 S molecular form of AChE located at the neuromuscular junction was most severely inhibited in soleus, followed by hemi-diaphragm and least in the EDL, and had fully recovered in all the muscles when examined after day 7. Muscle fiber necrosis developed within 1-3 h in soleus and hemi-diaphragm and after a delay of 24 h in EDL. The highest number of necrotic lesions in all muscles was seen at 72 h with the hemi-diaphragm maximally affected and EDL the least. To determine detoxification of tabun by non-specific binding, the activity of butyrylcholinesterase (BuChE) and carboxylesterase (CarbE) was measured. The inhibition and recovery pattern of BuChE activity was quite similar to that of AChE, except that the rate of recovery was more rapid. Within 1 h the remaining activity of CarbE was 10% in plasma, about 30% in brain structures, and 79% in liver; recovery was complete within 7 days. The inhibition of BuChE and CarbE can serve as a protective mechanism against tabun toxicity by reducing the amount available for AChE inhibition. The prolonged AChE inhibition in muscle and brain may indicate storage of tabun and delayed release from non-enzymic sites. Since tabun is a cyanophosphorus compound, the toxic effects from the released cyanide (CN) could be another reason for the delayed recovery after tabun.

Acetylcholinesterase↗
PubMed2004

Distribution of RA175/TSLC1/SynCAM, a member of the immunoglobulin superfamily, in the developing nervous system.

RA175 is a new member of the immunoglobulin superfamily with trans interaction activity, and it plays a role as a tumor suppressor in lung carcinoma (TSLC1) and as a cell adhesion molecule promoting the formation of functional synapses (SynCAM). Little is known about the biological function of RA175/TSLC1/SynCAM neural network formation during neurogenesis. We examined the distribution and colocalization of the RA175/TSLC1/SynCAM protein with other members of the immunoglobulin superfamily such as NCAM, L1, and TAG-1 in the mouse developing nervous system. Consistent with the expression of RA175/TSLC1/SynCAM mRNA, the protein was localized in the brain neuroepithelium at embryonic day (E) 9.5, neural crest at E10.5, motor neurons at E10.5, and olfactory epithelium at E16.5. In contrast with its mRNA, the protein was intensely detected on the fasciculated axons in the floor plates, ventral root, and dorsal funiculus in the E10.5-11.5 spinal cord and colocalized with NCAM and L1 on the ventral root and dorsal funiculus and partly colocalized with TAG-1 on the commissural axons and dorsal funiculus. In the E13.5-15.5 brain, RA175/TSLC1/SynCAM colocalized with NCAM and L1 on the developing thalamocortical fibers from the internal capsule (IC) and partly colocalized with TAG-1 on the cortical efferent axons in the intermediate zone (IZ). RA175/TSLC1/SynCAM was localized on the axons of some of the cortical neurons cultured in vitro. Thus, in addition to cell adhesion activity in the neuroepithelium and the synapses, RA175/TSLC1/SynCAM may be involved in neuronal migration, axon growth, pathfinding, and fasciculation on the axons of differentiating neurons.

Animals↗