Bioinspired Zwitterionic Surface Coatings with Robust Photostability and Fouling Resistance

Great care has been paid to the biointerface between a bulk material and the biological environment, which plays a key role in the optimized performance of medical devices. In this work, we report a new superhydrophilic adsorbate, called L-cysteine betaine (Cys-b), having branched zwitterionic groups that give rise to surfaces and nanoparticles with enhanced chemical stability, biofouling resistance, and inertness to environmental changes. Cys-b was synthesized from the amphoteric sulfur-containing amino acid, L-cysteine (Cys), by quaternization of its amino group. Gold surfaces modified with Cys-b exhibited prominent repellence against the nonspecific adsorption of proteins, bacteria, and fibroblast cells. In addition, Cys-b existed in zwitterionic form over a wide pH range (i.e., pH 3.4 to 10.8), and showed excellent suppression in photoinduced oxidation on gold substrates. Furthermore, the modification of hollow Ag@Au nanoshells with Cys-b gave rise to nanoparticles with excellent colloidal stability and resistance to coordinative interaction with Cu(2+). Taken together, the unique features of Cys-b offer a new nanoscale coating for use in a wide spectrum of applications.

Influenza A plasma and serum virus antibody detection comparison in dogs using blocking enzyme-linked immunosorbent assay

Background and Aim:

The influenza A virus (IAV) is an important zoonotic pathogen with infections also reported in dogs. IAV infections can be detected through the presence of antibodies using the enzyme-linked immunosorbent assay (ELISA). Serum is the only standard sample source; however, there is no information on the availability of other sample sources for IAV antibody detection in dogs. Compared with serum, plasma is more widely employed in most animal hospitals. The object of this study is to investigate whether plasma collected in ethylenediaminetetraacetic acid (EDTA) tubes (EDTA plasma) or heparin tubes (heparin plasma) could be used in the ELISA protocol instead of serum for IAV antibody detection in dogs.

Materials and Methods:

Totally, 82 matched EDTA plasma and serum sample pairs and 79 matched heparin plasma and serum sample pairs were employed using blocking enzyme-linked immunosorbent assay (bELISA). The agreement and correlation between the plasma (EDTA or heparin plasma) and serum were assessed using the agreement index kappa (kD) calculation and Pearson correlation coefficient, respectively.

Results:

The agreement index kD of EDTA plasma and serum was 1.0, and that of heparin plasma and serum was 0.85. The Pearson correlation coefficient of EDTA plasma and serum was 0.87 (p<0.01), and that of heparin plasma and serum was 0.82 (p<0.01).

Conclusion:

The results proved that plasma, especially EDTA plasma, could be substituted for serum in the bELISA test. This might greatly expand the clinical applicability of IAV antibody detection in dogs.

Developing antifouling biointerfaces based on bioinspired zwitterionic dopamine through pH-modulated assembly

The use of synthetic biomaterials as implantable devices typically is accompanied by considerable nonspecific adsorption of proteins, cells, and bacteria. These may eventually induce adverse pathogenic problems in clinical practice, such as thrombosis and biomaterial-associated infection. Thus, an effective surface coating for medical devices has been pursued to repel nonspecific adsorption from surfaces. In this study, we employ an adhesive dopamine molecule conjugated with zwitterionic sulfobetaine moiety (SB-DA), developed based on natural mussels, as a surface ligand for the modification of TiO2. The electrochemical study shows that the SB-DA exhibits fully reversible reduction-oxidation behavior at pH 3, but it is irreversible at pH 8. A contact angle goniometer and X-ray photoelectron spectroscopy were utilized to explore the surface hydration, chemical states, and bonding mechanism of SB-DA. The results indicate that the binding between hydroxyl groups of SB-DA and TiO2 converts from hydrogen bonds to bidentate binding upon the pH transition from pH 3 to 8. In order to examine the antifouling properties of SB-DA thin films, the modified substrates were brought into contact with bovine serum albumin and bacteria solutions. The fouling levels were monitored using a quartz crystal microbalance with dissipation sensor and fluorescence optical microscope. Tests showed that the sample prepared via the pH transition approach provides the best resistance to nonspecific adsorption due to the high coverage and stability of the SB-DA films. These findings support the mechanism of the pH-modulated assembly of SB-DA molecules, and for the first time we demonstrate the antifouling properties of the SB-DA to be comparable with traditional thiol-based zwitterionic self-assemblies. The success of modification with SB-DA opens an avenue for developing a biologically inspired surface chemistry and can have applications over a wide spectrum of bioapplications. The strategy of the pH transition can also be applied to other functional dopamine derivatives.

Implication of polymorphisms in DNA repair genes with an increased risk of hepatocellular carcinoma

We explored the association between 4 XRCC1 (Arg194Trp and Arg399Gln) and XPD (Asp312Asn and Lys751Gln) polymorphisms with the development and prognosis of hepatocellular carcinoma (HCC). A total of 218 cases with HCC and 277 healthy controls were included in the study. Genotyping of the XRCC1 (Arg194Trp and Arg399Gln) and XPD (Asp312Asn and Lys751Gln) polymorphisms was performed in a 384-well plate format on the Sequenom MassARRAY platform. We found that individuals with the XRCC1 399AA genotype had a higher risk of HCC compared with the GG genotype (odds ratio, OR = 1.85, 95% confidence interval, CI = 1.03-3.23). Similarly, individuals carrying the XPD 751GG genotype showed a greatly increased risk of HCC (OR = 2.97, 95%CI = 126- 7.38). Cox regression analysis showed that individuals carrying XPD 751Gln/Gln genotypes had a 0.30-fold increased risk of death from HCC. These results suggest that polymorphisms in XRCC1 and XPD may have functional significance in HCC.

Effects of clinoptilolite and modified clinoptilolite on the growth performance, intestinal microflora, and gut parameters of broilers

The purpose of this study was to evaluate the effect of natural clinoptilolite (NCLI) and modified clinoptilolite (MCLI) on broiler performance, gut morphology, and its relation to gut circumstances. A total of two hundred forty 1-d-old male chicks were randomly assigned to 3 treatments, each of which comprised 8 pens of 10 chicks per pen. Birds in the control group were fed the basal diet, whereas those in the experimental groups were fed diets supplemented with NCLI at 2% (NCLI group) or MCLI at 2% (MCLI group) for 42 d. The results showed that compared with the control, supplementation with NCLI or MCLI had no significant (P > 0.05) effects on productive parameters from d 1 to 42. Supplementation with MCLI and NCLI was associated with greater (P < 0.05) villus height in the jejunal and ileal mucosa compared with those areas in the controls from d 1 to 42. However, supplementation with NCLI and MCLI had no significant (P > 0.05) influence on the crypt depth in the jejunal and ileal mucosa compared with those in the controls. Total viable counts of Escherichia coli were significantly (P < 0.05) decreased by MCLI and NCLI from d 1 to 21. The NCLI and MCLI significantly increased the total viable counts of Lactobacillus acidophilus from d 22 to 42. Small intestine and cecal pH values in the MCLI group were found to be lower (P < 0.05) than those in other groups. Total volatile fatty acid concentrations were significantly (P < 0.05) decreased in both experimental groups from d 22 to 42. This study showed that NCLI or MCLI, as feed additives for broilers, had a positive effect on gut parameters by acting on microbial populations of the digestive tract.

Quantum Brayton cycle with coupled systems as working substance

We explore the quantum version of the Brayton cycle with a composite system as the working substance. The actual Brayton cycle consists of two adiabatic and two isobaric processes. Two pressures can be defined in our isobaric process; one corresponds to the external magnetic field (characterized by F(x)) exerted on the system, while the other corresponds to the coupling constant between the subsystems (characterized by F(y)). As a consequence, we can define two types of quantum Brayton cycle for the composite system. We find that the subsystem experiences a quantum Brayton cycle in one quantum Brayton cycle (characterized by F(x)), whereas the subsystem's cycle is quantum Otto cycle in another Brayton cycle (characterized by F(y)). The efficiency for the composite system equals to that for the subsystem in both cases, but the work done by the total system is usually larger than the sum of the work done by the two subsystems. The other interesting finding is that for the cycle characterized by F(y), the subsystem can be a refrigerator, while the total system is a heat engine. The result in this paper can be generalized to a quantum Brayton cycle with a general coupled system as the working substance.

A bio-inspired two-layer multiple-walled carbon nanotube-polymer composite sensor array and a bio-inspired fast-adaptive readout circuit for a portable electronic nose

We report a fully integrated, portable, battery-operated electronic nose system comprising a bio-inspired two-layer multiple-walled carbon nanotube (MWNT)-polymer composite sensor array, a bio-inspired fast-adaptive readout circuit, and a microprocessor embedded with a pattern recognition algorithm. The two-layer MWNT-polymer composite sensor is simple to operate, and the membrane quality can be easily controlled. These two-layer membranes have improved sensitivity and stability. The fast-adaptive readout circuit responds to the sensor response, while tuning out the long-term constant background humidity, temperature, and odors. This portable electronic nose system successfully classified four complex alcohol samples 40 times for each sample; these samples were sake, sorghum liquor, medical liquor, and whisky.

Numb regulates meiotic spindle organisation in mouse oocytes

Numb is an adaptor protein that controls the fate of cells in different species through asymmetrical inheritance by sibling cells during division. It has been investigated extensively in mitosis, mostly in neural progenitor cells, but its function in meiosis remains unknown. The present study was designed to investigate the expression, subcellular localisation and functional roles of Numb during mouse oocyte meiotic maturation. Using real-time polymerase chain reaction and western blotting, we found that the expression of Numb increased from the germinal vesicle (GV) to MII stages. Immunofluorescent staining revealed that Numb was mainly concentrated in the GV before meiosis resumption, aggregated in the vicinity of the chromosomes after GV breakdown and then localised to the spindle poles from prometaphase I to MII. Nocodazole treatment resulted in spindle destruction and Numb diffusion into the cytoplasm. However, Numb appeared at the spindle poles again once the spindles had formed when nocodazole-treated oocytes were washed and cultured for spindle recovery. Depletion of Numb by RNA interference resulted in chromosome misalignment, spindle deformation and even doubled spindle formation. Our results suggest that Numb is critical for spindle organisation during mouse oocytes meiosis. The present study provides evidence of a new function for Numb in addition to its action as a cell fate-determining factor.

Osteoclastogenic activity during mandibular distraction osteogenesis

Mandibular distraction osteogenesis is a well-developed clinical modality for the treatment of craniofacial deformities and dental arch discrepancies, in combination with orthodontic treatment. However, in our previous study, orthodontic tooth movement into the distraction gap caused severe root resorption. The present study aimed to clarify the osteoclastogenic activity of cells in the distraction gap. We hypothesized that the gene expression of osteoclastogenic- and osteoclast-supporting molecules in osteoblasts and stromal cells would increase at distraction sites during the consolidation period. An animal model experiment involving rabbits was designed for mandibular distraction osteogenesis and subjected to in situ hybridization analysis. The number of osteoclasts was larger in the distraction gap during the early consolidation period than in normal controls, due to an increase of gene expression for osteoclastogenic cytokines in osteoblasts. It was concluded that osteoclastogenic and osteoclastic activities are stimulated at distraction sites during the early consolidation period.

Sera from children with active Henoch-Schönlein purpura can enhance the production of interleukin 8 by human umbilical venous endothelial cells

OBJECTIVE

To investigate the ability of sera from children with active Henoch-Schonlein purpura (HSP) to enhance endothelial interleukin (IL) 8 production and intercellular adhesion molecule (ICAM)-1 expression.

METHODS

Nine children with active HSP and nine normal healthy children were enrolled. IL8 serum levels of patients and controls at different stages were analysed. Production of IL8 and expression of ICAM-1 by human umbilical venous endothelial cells were detected (ELISA for IL8, flow cytometry for ICAM-1) and compared under various stimuli, including sera of patients at different stages, sera of controls, and medium alone.

RESULTS

Serum levels of IL8 were increased at the acute stage. Levels of IL8 in supernatants from human umbilical venous endothelial cells (HUVEC) co-cultured with sera from children with active HSP were significantly higher than those from HUVEC without any treatment (p = 0.001), HUVEC treated with inactive sera (p = 0.004), and HUVEC treated with sera from healthy controls (p = 0.004). Sera from patients and from controls did not enhance the expression of ICAM-1 on HUVEC.

CONCLUSIONS

Some factors may be present in sera from children with active HSP that could activate endothelial cells to produce IL8. This process may account, in part, for the mechanisms of perivascular neutrophil infiltration and leucocytosis in HSP.

Berry phase in a composite system

The Berry phase in a composite system with one driven subsystem has been studied in this Letter. We choose two coupled spin-1 / 2 systems as the composite system; one of the subsystems is driven by a time-dependent magnetic field. We show how the Berry phases depend on the coupling between the two subsystems, and the relation between the Berry phases of the composite system and those of its subsystems.

Activity-dependent dynamics of coexisting brain-derived neurotrophic factor, pro-opiomelanocortin and alpha-melanophore-stimulating hormone in melanotrope cells of Xenopus laevis

Brain-derived neurotrophic factor (BDNF) is involved as an autocrine factor in the regulation of the secretory activity of the neuroendocrine pituitary melanotrope cells of Xenopus laevis. We studied the subcellular distribution of BDNF in Xenopus melanotropes using a combination of high-pressure freezing, cryosubstitution and immunoelectron microscopy. Presence of BDNF, pro-opiomelanocortin (POMC) and alpha-melanophore-stimulating hormone (alphaMSH) within melanotrope secretory granules was studied by triple-labelling immunoelectron microscopy. In addition, intracellular processing of BDNF was investigated by quantifying the number of immunogold particles in different stages of secretory granule maturation, in animals adapted to black or white background light conditions. The high-pressure freezing technique provides excellent preservation of both cellular ultrastructure and antigenicity. BDNF coexists with POMC and alphaMSH within secretory granules. BDNF-immunoreactivity increases along the secretory granule maturation axis (i.e. from electron-dense, via moderately electron-dense, to electron-lucent secretory granules). Immature, low immunoreactive, electron-dense secretory granules are assumed to contain mainly or even exclusively proBDNF. Strongly immunoreactive electron-lucent secretory granules represent the mature granule stage in which proBDNF has been processed to mature BDNF. Furthermore, in moderately electron-dense secretory granules, immunoreactivity is markedly (+79%) higher in black-adapted than in white-adapted animals, indicating that stimulation of melanotrope cell activity by the black background condition speeds up processing of BDNF from its precursor in this granule stage. It is concluded that, in the Xenopus melanotrope, BDNF biosynthesis and processing occur along the secretory granule maturation axis, together with that of POMC-derived alphaMSH, and that the environmental light condition not only controls the biosynthesis and secretion of BDNF and of POMC end-products, but also regulates the rate of their intragranular processing.

Long-term effects of fertilization on soil organic carbon changes in continuous corn of northeast China: RothC model simulations

Soil organic C (SOC) content can increase by managing land use practices in which the rates of organic C input exceed those of organic C mineralization. Understanding the changes in SOC content of Black soils (mainly Typic Halpudoll) in northeast China is necessary for sustainable using of soil resources there. We used the RothC model to estimate SOC levels of Black soils under monoculture cropping corn in a long-term fertilization trial at Gongzhuling, Jilin Province, China. The model outputs for the changes in SOC were compared with measured data in this long-term fertilization/manure trial. The sound performance of model in simulating SOC changes suggests that RothC is feasible with Black soils in the temperate climatic region of northeast China. The modeled and measured results indicated that the treatment without fertilizer/farmyard manure (FYM) addition led to a continuous decline in SOC during the study period and N and NPK fertilization were inadequate to maintain the SOC levels in the plow layer (upper 20 cm) unless FYM was added under the current conventional management associated with no above-ground crop residues returning into the soil. Soil organic carbon could follow the same path of decline if the same management practices are maintained. Model results indicate that returning above-ground crop residues to the soil from 2002 to 2022 would increase SOC by 26% for the treatment without fertilization addition, 40% for N treatment, 45% for NPK treatment, and 38% and 46% for N and NPK treatments with FYM addition, compared to the levels in the corresponding treatments in 2002. The simulation results suggest that the RothC model is a feasible tool to assess SOC trend under different management practices, and returning above-ground crop residues into the soil would lead to a remarkable increase in SOC of Black soils in the region.

Recovery of type I fiber regionalization in gastrocnemius medialis of the rat after reinnervation along original and foreign paths, with and without muscle rotation

After reinnervation following transection of the sciatic nerve, normal patterns of regional type I fiber distribution are known to return in rat hindlimb muscles. Here we investigate how this recovery is influenced by experimental conditions. In an initial operation, the nerve of gastrocnemius medialis (GM) of adult rats was cut close to the muscle and reinserted either (i) close to the original nerve entry, or (ii) at a more medial 'foreign' site. In other groups of animals, these nerve operations were combined with a rotation of the GM muscle around its longitudinal axis, trying to ascertain whether the position of the muscle within the limb was of importance for the reinnervation processes. In a control group the muscle was rotated but innervation remained intact. After 21 weeks, the GM muscles were removed from both hindlimbs. Cross-sections were cut at seven different levels along each muscle, and 'slow' type I fibers were identified after staining for myofibrillar ATPase. The topographical positions were mapped out for all type I fibers. In all reinnervated muscles, an extensive type I fiber grouping was seen, indicating a widespread respecification of muscle fiber properties by ingrowing 'slow' axons. Normal topographical directions of type I fiber regionalization were about equally well restored in groups with the nerve inserted at the original or at the foreign site. In rotated muscles, the direction of type I fiber regionalization was significantly less rotated than the muscle as a whole. The results suggest that ingrowing 'slow' motor axons are guided toward their normal 'slow' regions by clues which are largely independent of the i.m. path of regeneration (original vs. foreign nerve entry site) but partly dependent on the position of the target muscle within the limb (rotated vs. non-rotated cases).

Fibre type regionalisation in lower hindlimb muscles of rabbit, rat and mouse: a comparative study

The topographical distribution of different fibre types in muscles of the lower hindlimb in rabbits and mice was quantitatively determined. The results were compared to those previously obtained, using the same new quantification methods, in homologous muscles of the rat. Type I fibres ('slow') were identified using myofibrillar ATPase histochemistry and mapped out at the mid proximo-distal level for 11 'fast' muscles in the rabbit and 7 'fast' muscles in the mouse. For the slow soleus muscle the procedure was undertaken for the type II fibres. Furthermore, for 5 of the 'fast' muscles from each animal species (extensor digitorum longus; flexor digitorum and hallucis longus; gastrocnemius medialis; peroneus longus; tibialis anterior), several more proximal and distal cross-sectional levels were also analysed. All the investigated 'fast' muscles showed a significant degree of topographical eccentricity in the midlevel distribution of type I fibres. For most muscles, the direction of this 'vector regionalisation' of type I fibres was similar between the three animal species. For homologous muscles, the degree of vector regionalisation was significantly different: mouse > rat > rabbit. The relative area of the region containing the type I fibres, inversely related to the degree of 'area regionalisation', was also significantly different: mouse < rat < rabbit. Also within each animal species, muscles with a marked degree of vector regionalisation tended to show a marked area regionalisation. Proximo-distal differences in type I fibre density were observed in all the three species of animals; also these patterns showed marked inter-species differences. The findings demonstrate the general occurrence of, and systematic relationships between, different aspects of type I fibre regionalisation. The observed interspecies differences suggest that the expression of this phenomenon is adapted to differing functional needs.

Effect of taurine on toxicity of cadmium in rats

A study was undertaken to investigate the effect of taurine on the toxicity of cadmium in male Wistar rats. The rats were divided into six groups and fed different diets with or without supplement of 5% taurine and 150-300 ppm cadmium for 2 months. It was found that the body weight of rats, the ratios of liver and kidney weight to body weight, and the level of glutathione in the liver were decreased with increasing the dose of cadmium. The levels of cadmium in the liver and kidney, the levels of thiobarbituric acid-relative substances (TBARS) in the plasma and liver, the activities of aspartate transaminase (AST) and alanine transaminase (ALT) in the plasma, and the levels of blood urea nitrogen (BUN) and creatinine in the plasma of rats were increased with the increasing dose of cadmium. Hence, symptoms of cadmium toxicity in rats included loss of body weight, hepatotoxicity and nephrotoxicity. However, these toxic effects of cadmium were significantly reduced when the rats fed diet with supplement of taurine. Furthermore, the level of cadmium in the feces of rats treated with taurine and cadmium was higher than that of rats treated with cadmium alone. It indicated that taurine might play a role in reducing the toxic effect of cadmium in rats.

Effect of ginseng saponins on beta-amyloid-suppressed acetylcholine release from rat hippocampal slices

In view of the facts that ginseng has been shown to improve age-related memory deficits and beta-amyloid-related peptides have been suggested to play a significant role in memory degeneration in the elderly, the present study was carried out to examine the effect of various ginsenosides on beta-amyloid peptides-modulated acetylcholine (ACh) release, a key neurotransmitter in memory processing, from the hippocampal slices. Addition of beta-amyloid fragment(25 - 35) (0.01 - 1 microM) in the superfusion medium suppressed the K(+)-evoked [(3)H]-ACh release from the rat hippocampal slices in a concentration-related manner and about 40 % reduction in ACh outflow was observed when incubating with the highest concentration of an amyloid fragment (1 microM). Inclusion of the ginsenoside components Rb(1) (0.1 microM), but not Rg(1), caused a rightward shift of the concentration-response curve of beta-amyloid. The reversal of the beta-amyloid-inhibited ACh release by Rb(1) was not blocked by tetrodotoxin (1 microM) indicating that an interaction occurs at the cholinergic synapse. These results suggest that Rb(1) may elicit its anti-amnesic effect by minimizing the inhibitory effect of beta-amyloid peptides.

The uptake inhibitors cocaine and benztropine differentially alter the conformation of the human dopamine transporter

The binding affinity of the cocaine analog [(3)H]2 beta-carbomethoxy-3beta-(4-fluorophenyl) tropane (WIN) for the dopamine transporter (DAT) is increased by the reaction of Cys-90, at the extracellular end of the first transmembrane segment, with methanethiosulfonate (MTS) reagents. Cocaine enhances the reaction of Cys-90 with the sulfhydryl reagents, thereby augmenting the increase in binding. In contrast, cocaine decreases the reaction of Cys-135 and Cys-342, endogenous cysteines in cytoplasmic loops, with MTS reagents. Because this reaction inhibits [(3)H]WIN binding, cocaine protects against the loss of binding caused by reaction of these cysteines. In the present work, we compare the abilities of DAT inhibitors and substrates to affect the reaction of Cys-90, Cys-135, and Cys-342 with MTS ethyltrimethylammonium (MTSET). The results indicate that the different abilities of compounds to protect against the MTSET-induced inhibition of binding are attributable to differences in their abilities to attenuate the inhibitory effects of modification of Cys-135 and Cys-342 as well as to enhance the reaction with Cys-90 and the resulting potentiation of binding. The inhibitor benztropine was unique in its inability to protect Cys-135. Moreover, whereas cocaine, WIN, mazindol, and dopamine enhanced the reaction of Cys-90 with MTSET, benztropine had no effect on this reaction. These two features combine to give benztropine its weak potency in protecting ligand binding to wild-type DAT from MTSET. These results indicate that different inhibitors of DAT, such as cocaine and benztropine, produce different conformational changes in the transporter. There are differences in the psychomotor stimulant-like effects of these compounds, and it is possible that the different behavioral effects of these DAT inhibitors stem from their different molecular actions on DAT.

Laboratory diagnosis of heparin-induced thrombocytopenia type II after clearance of platelet factor 4/heparin complex

Laboratory confirmation of heparin-induced thrombocytopenia (HIT) is limited by assay sensitivity. We investigated whether laboratory confirmation can be improved after antigen clearance by determining free antibody and combining the results of antigenic and biologic assays. Blood samples were collected over 5 to 6 weeks in 14 HIT patients. As an antigenic assay, the fluorescence-linked immunofiltration assay (FLIFA) was performed, and as a biologic assay, the carbon 14-labeled serotonin release assay was performed. At day 1 when heparin was stopped, 11 of 14 patients showed positive results in both assays; thus each assay had a sensitivity of 80%. The 3 patients with negative results seroconverted in one or both assays during the subsequent 7 days. Combining the positive results of the assays increased the sensitivity to 100% at day 7, regardless of whether the antigenic or the biologic assay was performed first. Both assays became negative in all patients within 5 to 6 weeks. The sensitivity of antigen and biologic assays in HIT patients increased to 100% after the time course of the heparin-induced antibody. We assume that in some HIT patients the free antibody can be detected after withdrawal of heparin and after clearance of the platelet-factor 4/heparin complex.

Proximo-distal organization and fibre type regionalization in rat hindlimb muscles

Five muscles of the rat's lower hindlimb were compared with regard to their histochemical fibre type distribution at seven different proximo-distal levels. The muscles were: extensor digitorum longus (ED), flexor digitorum and hallucis longus (FD), gastrocnemius medialis (GM), peroneus longus (PE) and tibialis anterior (TA). In all the five muscles, the relative density of the 'slow' type I fibres showed a striking and similar decrease from proximal toward more distal levels. In addition, the type I fibres were concentrated within smaller and more eccentrically placed regions at distal than at more proximal levels. As a background for the further analysis of these lengthwise aspects of type I fibre regionalization, architectural features of the muscles were determined. Pinnation angles and the position of major tendons and tendon sheets were assessed in fresh specimens. Muscle fibre lengths were measured for single fibres dissected from different regions of macerated muscles. In all cases, fibre length was much shorter than muscle length (mean fraction ranging from 21 to 55%), implying that the proximo-distal changes in histochemical fibre properties were indeed explainable as being due to gradual lengthwise changes in fibre type populations. The similarity of these lengthwise changes across the muscles was in contrast to their differences in other aspects of functional organization, such as the average density of type I fibres and architectural features determining their relative capacities for shortening and force generation. The possible functional role of the proximal accumulation of type I fibres was discussed in relation to circulation and thermal balance; besides, the proximo-distal regionalization of type I fibres might (partly) reflect processes that had been associated with early stages of muscle differentiation. Furthermore, the results underline that, when determining the fibre type composition of rat hindlimb muscles, identifying the proximo-distal level of sampling is a matter of great importance.