Mechanisms of adaptation in a mechanoreceptor : A study of mechanical and ionic factors in the crayfish stretch receptors

- The stretch receptor organ of the crayfish, an analog to the human muscle spindle, is a unique preparation for the study of mechanotransduction. The organ consists of a rapidly and a slowly adapting receptor each composed of a receptor muscle fibre into which inserts the dendrites of a multipolar sensory neuron. The present work explored various aspects of the mechanotranduction process with regard to the differences in adaptive properties between the rapidly and the slowly adapting receptors. The rapidly adapting receptor muscle fibre is statically less stiff, and the transient tensiol response more pronounced, as shown by a greater ratio of the peak to steady-state tension, compared to that of the slowly adapting receptor muscle fibre. These facts show that the visco-elastic properties do contribute to receptor adaptation. The presence of the initial stiffness could be considered as an increase in dynamic sensitivity of the receptor at small extension levels. Mechanosensitive (MS) ion channels generate a receptor current in the rapidly and the slowly adapting neuron. In the rapidly adapting neuron the receptor current was larger, decayed faster and llad a steeper slope of the stimulus-response relationship than in the slowly adapting neuron. It is concluded that the adaptive properties of the rapidly adapting receptor neuron depend on the viscoelastic properties of the muscle fibre but that the MS channels also contribute. Gadolinium (Gd3+) blocked the receptor current in the receptor neurons. Decreasing extracellular calcium concentration increased the affinity of Gd3+. However, the Gd3+effect was not selective, sodium and potassium channels were also blocked. The potential-dependent outward current, carried by potassium ions, is present in the rapidly and the slowly adapting receptor neurons. However, some electrical properties of the K+ currents differed between the receptors. Analysis of the dose-response relationship for TEA block indicates the presence of two different K+ channel populations with different relative densities in the two neurons. The action potential was shown to be generated by a potential-dependent inward current carried by sodium ions both in the rapidly and the slowly adapting receptor neurons. However, it was demonstrated that in the rapidly adapting neuron the inactivation kinetics and the current-voltage relationship of the sodium current as well as the changes induced by crude scorpion venom from Leiurus quinquestriatus were different from those observed in the slowly adapting neuron. The action potentials were different in the two neurons in agreement with the differences the sodium current. It is concluded that in the slowly adapting neuron the sodium current may consist of two components located in the axon and soma, whereas one of these current components is either absent or very small in the rapidly adapting neuron. The impulse response adaptation is thus a product of the properties of the receptor muscle fibre, the mechano-gated channels in the neuronal dendrites, the voltage-gated sodium and potassium channels and the ion-pumping mechanisms which all seem to have evolved to favor either the slow or the rapid adaptation seen in the two receptor organs. Keywords: Crayfish, stretch receptor, adaptation, visco-elastic properties, mechanosensitive channels, potassium channels, sodium channels, gadolinium, tetraethylammonium chloride, 4-amino pyridine, scorpion venom Leiurus quinquestrialus ~) Nuhan Purali, 1997 Printed in Sweden by Repro Print AB, Stockholm lSBN 91-628-2386-

Evaluation Of Dentinal Tubule Penetration Depth And Push-Out Bond Strength Of Ah 26, Bioroot Rcs, And Mta Plus Root Canal Sealers In Presence Or Absence Of Smear Layer

Background. This study compared the effect of smear layer on the penetration depth and push-out bond strength of various root canal sealers. , Methods. A total of 90 extracted human mandibular premolars were assigned into 2 groups: smear layer preserved and smear layer removed. Then the roots were further divided into 3 subgroups according to the sealer tested: AH 26, BioRoot RCS and MTA Plus. Obturation was performed with gutta-percha and the relevant sealer was mixed with 0.1% rhodamine B. Three 1-mm-thick slices were obtained from the mid-third area of each root. Two slices were selected for the push-out test and the remaining slice was used to calculate the dentinal tubule penetration depth and percentage. , Results. The retention of MTA Plus and BioRoot RCS was higher than that of AH 26 when the smear layer was preserved (P<0.05). BioRoot RCS showed the lowest penetration depth when the smear layer was removed (P<0.05). , Conclusion. Dentinal tubule penetration of root canal sealers had a limited effect on their adhesion to root canal wall.PubMe

Push-Out Bond Strength And Dentinal Tubule Penetration Of Different Root Canal Sealers Used With Coated Core Materials

Objectives The aim of this study was to compare the push-out bond strength and dentinal tubule penetration of root canal sealers used with coated core materials and conventional gutta-percha. Materials and Methods A total of 72 single-rooted human mandibular incisors were instrumented with NiTi rotary files with irrigation of 2.5% NaOCl. The smear layer was removed with 17% ethylenediaminetetraacetic acid (EDTA). Specimens were assigned into four groups according to the obturation system: Group 1, EndoRez (Ultradent Product Inc.); Group 2, Activ GP (Brasseler); Group 3, SmartSeal (DFRP Ltd. Villa Farm); Group 4, AH 26 (Dentsply de Trey)/gutta-percha (GP). For push-out bond strength measurement, two horizontal slices were obtained from each specimen (n = 20). To compare dentinal tubule penetration, remaining 32 roots assigned to 4 groups as above were obturated with 0.1% Rhodamine B labeled sealers. One horizontal slice was obtained from the middle third of each specimen (n = 8) and scanned under confocal laser scanning electron microscope. Tubule penetration area, depth, and percentage were measured. Kruskall-Wallis test was used for statistical analysis. Results EndoRez showed significantly lower push-out bond strength than the others (p < 0.05). No significant difference was found amongst the groups in terms of percentage of sealer penetration. SmartSeal showed the least penetration than the others (p < 0.05). Conclusions The bond strength and sealer penetration of resin-and glass ionomer-based sealers used with coated core was not superior to resin-based sealer used with conventional GP. Dentinal tubule penetration has limited effect on bond strength. The use of conventional GP with sealer seems to be sufficient in terms of push-out bond strength.PubMe

Interaction of MC3T3-E1 cells with titanium implants

Objective

Osteogenic differentiation of MC3T3-E1 cells on different titanium surfaces

mRNA expressions related to osteogenic differentiation of MC3T3-E1 cells on electro-polished smooth (S), sandblasted small-grit (SSG) and sandblasted large-grit (SLG) surfaces of titanium alloys were investigated in vitro. Gene expression profiles of cells were evaluated using the RT2 Profiler PCR microarray on day 7. Mineralizing tissue-associated proteins, differentiation factors and extracellular matrix enzymes mRNA expressions were measured using Q-PCR. SLG surface upregulated 23 genes over twofolds and downregulated 3 genes when compared to the S surface. In comparison to the SSG surface, at least a twofold increase in 25 genes was observed in the SLG surface. BSP, OCN, OPN, COL I and ALP mRNA expressions increased in the SLG group when compared to the S and the SSG groups. BMP-2, BMP-6 and TGF-beta mRNA expressions increased in both the SSG and the SLG surfaces. MMP-2 and MMP-9 mRNA expressions increased as the surface roughness increased. This study demonstrated that surface roughness of titanium implants has a significant effect on cellular behavior and SLG surface apparently increased gene expressions related to osteogenesis when compared to the S and the SSG surfaces

Effect of mesenchymal stem cells therapy in experimental kaolin induced syringomyelia model

Background: Syringomyelia is a pathological cavitation of the spinal cord. In this study, we examined whether a syrinx cavity would limit itself with axonal regeneration and stem cell activity in the cavity, and we evaluated subjects on a functional basis.Methods: Groups were designated as kaolin, trauma, kaolin-trauma, and saline groups. Also divided out of the syringomyelia treated groups were those given human mesenchymal stem cells (hMSCs). All groups were evaluated with immunohistochemistry, electron microscopy, confocal microscopy and functionally.Results: The kaolin-trauma group had a significant correction of BBB score with hMSCs therapy. The syrinx cavity measurements showed significant improvement in groups treated with hMSCs. The tissue surrounding the syrinx cavity, however, appeared to be better organized in groups treated with hMSCs. The process of repair and regeneration of damaged axons in the lesion were more improved in groups treated with hMSCs. Using confocal microscopy, fluorescence of hMSCs was observed in the central canal, in the ependymal tissue, and around the lesion.Conclusions: It was concluded that axonal repair accelerated in groups receiving stem cells, and thus, stem cells may be effective in recovery of neural tissue and myelin damage in syringomyelia

Periodontal ligament cell behavior on different titanium surfaces

Aim. The purpose of this study was to investigate proliferation, morphology, mineralization and mRNA expressions of mineralized tissue associated proteins of PDL cells on smooth (S), sandblasted small-grit (SSG), sandblasted large-grit (SLG) and sodium titanate (NaTi) coated titanium alloys, in vitro. Methods and materials: PDL cells were cultured with DMEM media containing 10% FBS on the S, SSG, SLG and NaTi titanium surfaces. PDL cell proliferation, mineralization and immunohistochemistry experiments for Bone Sialoprotein (BSP) were performed. The morphology of the PDL cells was examined using confocal and scanning electron microscopy (SEM). Gene expression profiles of cells were evaluated using a quantitative-polymerase chain reaction (Q-PCR) for type I collagen (COL I), Osteocalcin (OCN), osteopontin (OPN) and Runt-related transcription factor-2 (Runx2) on days 7 and 14. Results. Proliferation results on days 6 and 10 were similar in groups, while those of day 13 revealed a decrease in the NaTi group when compared to the S group. NaTi surface induced BSP mRNA expression which was correlated with mineralization tests and BSP immunostaining results. Increased Runx2 mRNA expression was also noted in the NaTi surface when compared to other surfaces. Conclusions. This study considers the NaTi surface as a potential alternative to SSG and SLG surfaces. This surface might provide a promising environment for PDL ligament-anchored implants