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The mechanical properties of anisotropic polymers: progress report no. 5
A report of work carried out during the period
1st October, 1967, to 31st March, 1963
The mechanical properties of anisotropic polymers: progress report no. 7
Part I
General Developments
The major part of the period under review was devoted to a study of
the tensile creep properties of isotropic and uniaxially oriented Perspex
sheets (standard grade) using the three heavy-duty creep rigs mentioned in
the previous Progress Report (No. 6. September, 1968). Measurements of
lateral contraction were made simultaneously with the tensile strain
measurements during most of the creep tests. The creep rupture behaviour
and optical anisotropy of the oriented sheets were also studied in an
attempt to present a more complete picture of the behaviour of the material.
Some of the early results of this work have already been published and
copies sent to the Ministry. (Darlington and Saunders; 1969). Details
of the complete work will be found in part II of this report.
The two types of contraction extensometer described in Progress Report
No. 5 were used during the Perspex studies and reasonable agreement was
obtained between the results. The techniques required with the contraction
devices were considerably improved during the period under review and the
absolute validity of the contraction measurements is now more certain.
Some comments on the general performance of the apparatus are given in
section 2.8.4
The mechanical properties of anisotropic polymers: Progress report no. 6
Part 1
General Developments
The basic development work on the tensile creep apparatus was
completed by March, 1968. A description of the latest 'heavy-duty' creep
rig and two types of contraction extensometer, together with the relevant
creep trials, was given in Progress Report No. 5. Since then two further
'heavy-duty' creep rigs have been assembled and tested and are now ready
for use with rigid plastics. In addition, further trials of the double
transducer contraction extensometer described in Report No. 5 have been
carried out. These trials are described in part 2 of this report The
trials were considered reasonably satisfactory and each of the three heavy-duty
creep rigs has now been fitted with a device of this type in addition
to the normal tensile extensometer. The polythene creep rig described in
Progress Report No. 3 has been working satisfactorily for over a year and
no further modifications have been made in the period under review. At
the conclusion of the above-mentioned trials it was considered that the
creep apparatus was unlikely to require any further major changes. A
detailed report of all the apparatus has therefore been prepared with the
intention of submitting it for publication to the Journal of Scientific
Instruments. It is at present being examined at the Ministry of Technology.
(CoA Memo. No. 158)
Creep studies on oriented thermoplastics
The enhancement of many of the mechanical properties of thermoplastics
which may be achieved by orienting the molecules has been known for some
time. It has been exploited in the production of textile fibres end
oriented films. Molecular orientation also occurs during processes such
as extrusion, moulding or forming. Here, unless carefully controlled, it
may well cause a deterioration in the properties of the finished article.
In view of this a systematic study on the anisotropy of the mechanical
properties of thermoplastics, resulting from molecular orientation, is
being carried out at present in these laboratories … [cont.]
An apparatus for the measurement of tensile creep and contraction ratios in small non-rigid specimens
An apparatus is described for precise measurement of
creep properties in specimens with gauge lengths down to 1.2
cm. An extensometer has been developed which is supported
independently of the specimen and exerts a load on the specimen
of less than 5 grams. It can thus be used with small non-rigid
specimens. The extensometer will detect strains down to
2 x 10-6. The stability is excellent. An adaptation of the
system which allows simultaneous measurement of tensile strain
and lateral strain during creep is also described. The apparatus
was designed for the measurement of anisotropy of creep
properties in oriented thermoplastics and reference to such
measurements is given. It is however entirely suitable for
general application to small specimens
Dependence receptor involvement in subtilisin-induced long-term depression and in long-term potentiation
The serine protease subtilisin induces a form of long-term depression (LTD) which is accompanied by a reduced expression of the axo-dendritic guidance molecule Unco-ordinated-5C (Unc-5C). One objective of the present work was to determine whether a loss of Unc-5C function contributed to subtilisin-induced LTD by using Unc-5C antibodies in combination with the pore-forming agents Triton X-100 (0.005%) or streptolysin O in rat hippocampal slices. In addition we have assessed the effect of subtilisin on the related dependence receptor Deleted in Colorectal Cancer (DCC) and used antibodies to this protein for functional studies. Field excitatory postsynaptic potentials (fEPSPs) were analysed in rat hippocampal slices and protein extracts were used for Western blotting. Subtilisin produced a greater loss of DCC than of Unc-5C, but the antibodies had no effect on resting excitability or fEPSPs and did not modify subtilisin-induced LTD. However, antibodies to DCC but not Unc-5C did reduce the amplitude of theta-burst long-term potentiation (LTP). In addition, two inhibitors of endocytosis – dynasore and tat-gluR2(3Y) – were tested and, although the former compound had no effect on neurophysiological responses, tat-gluR2(3Y) did reduce the amplitude of subtilisin-induced LTD without affecting the expression of DCC or Unc-5C but with some loss of PostSynaptic Density Protein-95. The results support the view that the dependence receptor DCC may be involved in LTP and suggest that the endocytotic removal of a membrane protein or proteins may contribute to subtilisin-induced LTD, although it appears that neither Unc-5C nor DCC are involved in this process. (220)
Prenatal inhibition of the tryptophan–kynurenine pathway alters synaptic plasticity and protein expression in the rat hippocampus
Glutamate receptors sensitive to N-methyl-d-aspartate (NMDA) are important in early brain development, influencing cell proliferation and migration, neuritogenesis, axon guidance and synapse formation. The kynurenine pathway of tryptophan metabolism includes an agonist (quinolinic acid) and an antagonist (kynurenic acid) at these receptors. Rats were treated in late gestation with 3,4-dimethoxy-N-[4-(3-nitrophenyl)thiazol-2-yl]-benzene-sulphonamide (Ro61-8048), an inhibitor of kynurenine-3-monoxygenase which diverts kynurenine metabolism to kynurenic acid. Within 5Â h of drug administration, there was a significant decrease in GluN2A expression and increased GluN2B in the embryo brains, with changes in sonic hedgehog at 24Â h. When injected dams were allowed to litter normally, the brains of offspring were removed at postnatal day 21 (P21). Recordings of hippocampal field excitatory synaptic potentials (fEPSPs) showed that prenatal exposure to Ro61-8048 increased neuronal excitability and paired-pulse facilitation. Long-term potentiation was also increased, with no change in long-term depression. At this time, levels of GluN2A, GluN2B and postsynaptic density protein PSD-95 were all increased. Among several neurodevelopmental proteins, the expression of sonic hedgehog was increased, but DISC1 and dependence receptors were unaffected, while raised levels of doublecortin and Proliferating Cell Nuclear Antigen (PCNA) suggested increased neurogenesis. The results reveal that inhibiting the kynurenine pathway in utero leads to molecular and functional synaptic changes in the embryos and offspring, indicating that the pathway is active during gestation and plays a significant role in the normal early development of the embryonic and neonatal nervous system
Selective depletion of tumour suppressors Deleted in Colorectal Cancer (DCC) and neogenin by environmental and endogenous serine proteases: linking diet, obesity and cancer
Background:
The related tumour suppressor proteins Deleted in Colorectal Cancer (DCC) and neogenin are absent or weakly expressed in many cancers, whereas their insertion into cells suppresses oncogenic behaviour. Serine proteases influence the initiation and progression of cancers although the mechanisms are unknown.
Methods:
The effects of environmental (bacterial subtilisin) and endogenous mammalian (chymotrypsin) serine proteases were examined on protein expression in fresh, normal tissue and human neuroblastoma and mammary adenocarcinoma lines. Cell proliferation and migration assays (chemoattraction and wound closure) were used to examine cell function. Cells lacking DCC were transfected with an ectopic dcc plasmid.
Results:
Subtilisin and chymotrypsin selectively depleted DCC and neogenin from cells at nanomolar concentrations without affecting related proteins. Cells showed reduced adherence and increased migration, but after washing they re-attached within 24Â h, with recovery of protein expression. These effects are induced by chymotryptic activity as they are prevented by chymostatin and the soybean Bowman-Birk inhibitor typical of many plant protease inhibitors.
Conclusions:
Bacillus subtilis, which secretes subtilisin is widely present in soil, the environment and the intestinal contents, while subtilisin itself is used in meat processing, animal feed probiotics and many household cleaning agents. With chymotrypsin present in chyme, blood and tissues, these proteases may contribute to cancer development by depleting DCC and neogenin. Blocking their activity by Bowman-Birk inhibitors may explain the protective effects of a plant diet. Our findings identify a potential non-genetic contribution to cancer cell behaviour which may explain both the association of processed meats and other factors with cancer incidence and the protection afforded by plant-rich diets, with significant implications for cancer prevention
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