Small Laboratory Mammals Research Articles

Comparative Neuroanatomical Characterization of Ventral Midbrain Grey Matter of Some Small Laboratory Mammals

Empirical assessments of the similarities and variations of neurobiological structures in animals are the basis of comparative neuroanatomy. Animal models including small laboratory mammals are indispensable tools for neuroanatomical research. The mammalian midbrain has been described with grey matter structures including red nucleus (RN), and substantia nigra (SN) involved in important brain functions like regulation of motor and related activities. This study comparatively characterized the neuroanatomical features of the ventral midbrain grey matter (RN and SN) of three small laboratory mammals: Wistar rat, guinea pig (Cavia porcellus) and rabbit (Oryctolagus cuniculus). The laboratory mammals (n=3/species) were obtained and weighed. The brains of species were harvested and measured, and sections of RN and SN were processed for histologic and histometric assessments. Data obtained were compared among species using statistical (IBM SPSS v21) and imaging (MPP, AmScope, and ImageJ, US) software. Results revealed higher (p<0.05) values for body and brain weights with rabbits. Histologic examinations of the RN and SN pars compacta (SNc) revealed similarities and some variations in the species; RN and SNc presented with a variety of cell morphologies. The histometric characteristics (pyramidal cell soma area and perimeter) of the RN showed no significant difference between the species. However, SNc histometric characteristics were different (p<0.05) with lower mean values for guinea pigs. In conclusion, the assessed small laboratory mammalian species demonstrated similarities and variations in neuroanatomical characteristics of the ventral midbrain grey matter (SN and RN). Similarities of cytoarchitectural characteristics could be attributed to the commonality of the species’ ancestry as mammals.

Electrophysiological characterisation of atrial volume receptors using ex vivo models of isolated rat cardiac atria.

What is the central question of this study? What ex vivo preparation of the rat's cavoatrial junction is efficient for characterising atrial mechanoreceptors? What is the main finding and its importance? Of four different ex vivo preparations, static pressure, flow, open and euthermic, the optimal preparation was the euthermic one and involved direct recording from the right cardiac vagal branch with a Langendorff style perfusion at 37°C. Type A receptors were most common, and appeared insensitive to stretch and sensitive to atrial contraction. Type B and intermediate receptors were not isolated at 20°C but were observed closer to 37°C. The findings may suggest that type A and B receptors utilise different molecular transduction mechanisms. Atrial volume receptors are a family of afferent neurons whose mechanically sensitive endings terminate in the atria, particularly at the cavoatrial junctions. These mechanosensors form the afferent limb of an atrial volume receptor reflex that regulates plasma volume. The prevailing functional classification of atrial receptors arose as a result of in vivo recordings in the cat and dog and were classified as type A, B or intermediate according to the timing of peak discharge during the cardiac cycle. In contrast, there have been far fewer studies of the common small laboratory mammals such as the rat. Using several ex vivo rat cavoatrial preparations, a total of 30 successful single cavoatrial mechanosensory recordings were obtained. These experiments show that the rat possesses type A, B and intermediate atrial mechanoreceptors as described for larger mammals. Recording these cavoatrial receptors proved challenging from the main vagus, but direct recording from the cardiac vagal branch greatly increased the yield of mechanically sensitive single units. In contrast to type A units, type B atrial mechanoreceptor activity was never observed at room temperature but required elevation of temperature to a more physiological range in order to be detected. The adequate stimulus for these receptors remains unclear; however, type A atrial receptors appear insensitive to direct atrial stretch when applied using a programmable positioner. The findings may suggest that type A and type B atrial receptors utilise different molecular transduction mechanisms.

Anesthesia and Monitoring in Small Laboratory Mammals Used in Anesthesiology, Respiratory and Critical Care Research: A Systematic Review on the Current Reporting in Top-10 Impact Factor Ranked Journals.

RationaleThis study aimed to investigate the quality of reporting of anesthesia and euthanasia in experimental studies in small laboratory mammals published in the top ten impact factor journals.MethodsA descriptive systematic review was conducted and data was abstracted from the ten highest ranked journals with respect to impact factor in the categories ‘Anesthesiology’, ‘Critical Care Medicine’ and ‘Respiratory System’ as defined by the 2012 Journal Citation Reports. Inclusion criteria according to PICOS criteria were as follows: 1) population: small laboratory mammals; 2) intervention: any form of anesthesia and/or euthanasia; 3) comparison: not specified; 4) primary outcome: type of anesthesia, anesthetic agents and type of euthanasia; secondary outcome: animal characteristics, monitoring, mechanical ventilation, fluid management, postoperative pain therapy, animal care approval, sample size calculation and performed interventions; 5) study: experimental studies. Anesthesia, euthanasia, and monitoring were analyzed per performed intervention in each article.ResultsThe search yielded 845 articles with 1,041 interventions of interest. Throughout the manuscripts we found poor quality and frequency of reporting with respect to completeness of data on animal characteristics as well as euthanasia, while anesthesia (732/1041, 70.3%) and interventions without survival (970/1041, 93.2%) per se were frequently reported. Premedication and neuromuscular blocking agents were reported in 169/732 (23.1%) and 38/732 (5.2%) interventions, respectively. Frequency of reporting of analgesia during (117/610, 19.1%) and after painful procedures (38/364, 10.4%) was low. Euthanasia practice was reported as anesthesia (348/501, 69%), transcardial perfusion (37/501, 8%), carbon dioxide (26/501, 6%), decapitation (22/501, 5%), exsanguination (23/501, 5%), other (25/501, 5%) and not specified (20/501, 4%, respectively.ConclusionsThe present systematic review revealed insufficient reporting of anesthesia and euthanasia methods throughout experimental studies in small laboratory mammals. Specific guidelines for anesthesia and euthanasia regimens should be considered to achieve comparability, quality of animal experiments and animal welfare. These measures are of special interest when translating experimental findings to future clinical applications.

The modified hole board--measuring behavior, cognition and social interaction in mice and rats.

This protocol describes the modified hole board (mHB), which combines features from a traditional hole board and open field and is designed to measure multiple dimensions of unconditioned behavior in small laboratory mammals (e.g., mice, rats, tree shrews and small primates). This paradigm is a valuable alternative for the use of a behavioral test battery, since a broad behavioral spectrum of an animal’s behavioral profile can be investigated in one single test.The apparatus consists of a box, representing the ‘protected’ area, separated from a group compartment. A board, on which small cylinders are staggered in three lines, is placed in the center of the box, representing the ‘unprotected’ area of the set-up. The cognitive abilities of the animals can be measured by baiting some cylinders on the board and measuring the working and reference memory. Other unconditioned behavior, such as activity-related-, anxiety-related- and social behavior, can be observed using this paradigm. Behavioral flexibility and the ability to habituate to a novel environment can additionally be observed by subjecting the animals to multiple trials in the mHB, revealing insight into the animals’ adaptive capacities.Due to testing order effects in a behavioral test battery, naïve animals should be used for each individual experiment. By testing multiple behavioral dimensions in a single paradigm and thereby circumventing this issue, the number of experimental animals used is reduced. Furthermore, by avoiding social isolation during testing and without the need to food deprive the animals, the mHB represents a behavioral test system, inducing if any, very low amount of stress.

The Modified Hole Board - Measuring Behavior, Cognition and Social Interaction in Mice and Rats

This protocol describes the modified hole board (mHB), which combines features from a traditional hole board and open field and is designed to measure multiple dimensions of unconditioned behavior in small laboratory mammals (e.g., mice, rats, tree shrews and small primates). This paradigm is a valuable alternative for the use of a behavioral test battery, since a broad behavioral spectrum of an animal’s behavioral profile can be investigated in one single test. The apparatus consists of a box, representing the ‘protected’ area, separated from a group compartment. A board, on which small cylinders are staggered in three lines, is placed in the center of the box, representing the ‘unprotected’ area of the set-up. The cognitive abilities of the animals can be measured by baiting some cylinders on the board and measuring the working and reference memory. Other unconditioned behavior, such as activity-related-, anxiety-related- and social behavior, can be observed using this paradigm. Behavioral flexibility and the ability to habituate to a novel environment can additionally be observed by subjecting the animals to multiple trials in the mHB, revealing insight into the animals’ adaptive capacities. Due to testing order effects in a behavioral test battery, naïve animals should be used for each individual experiment. By testing multiple behavioral dimensions in a single paradigm and thereby circumventing this issue, the number of experimental animals used is reduced. Furthermore, by avoiding social isolation during testing and without the need to food deprive the animals, the mHB represents a behavioral test system, inducing if any, very low amount of stress.

April 2015: This Month in JoVE - Studying Locomotion in Drunken Worms, Preserving Human Liver for Transplantation, and Visualizing Bacterial Swarms

Here's a look at what's coming up in the April 2015 issue of JoVE: The Journal of Visualized Experiments. In JoVE Neuroscience, it is clear that alcohol has profound effects on the brain. But why do different individuals respond so differently to alcohol, and why are some more prone to abuse? Some of the answers lie in our genes. In the nematode worm C. elegans, genes are easy to manipulate, and the neurobiology is simple. So it's an excellent model to study the effects of alcohol on behavior. Davies et al. use copper rings to corral worms with different genotypes on agar plates containing alcohol. They take videos of the worms at set time points and measure the locomotion of each genotype using object recognition software With this procedure, C. elegans can help unravel the molecular basis of alcohol sensitivity and tolerance, as well as the risk of abuse. In JoVE Medicine, alcohol doesn't just affect the brain; it also affects the liver, and for many patients with alcoholic liver disease, liver transplantation is the only hope. But there is a severe shortage of livers available for transplants. Therefore, Bruinsma et al. present an alternative way to preserve donor livers, which are traditionally stored statically on ice. In this new method, the donor liver is kept alive by a perfusion machine and perfused at 21°C-warmer than ice, but lower than normal body temperatures, which allows the liver to be assessed for function and transplantability. This technique may greatly expand the pool of donor livers available to patients in need of transplants. In JoVE Biology, one of the most commonly studied modes of bacterial motility is called swarming. However, the reproducibility of swarm plate assays can be difficult to achieve, so Morales-Soto et al. present a method that standardizes parameters (such as moisture content of plates) that affect swarming motility. By using bacterial strains expressing different fluorescent proteins, they can observe swarming competition dynamics between different species in a fluorescent time-lapsed video. This method can help elucidate various aspects of bacterial growth, such as how bacteria colonize different types of surfaces. In JoVE Behavior, Labots et al. demonstrate the modified hole board. This behavioral testing apparatus consists of a protected box and a board containing small cylinders. In one type of experiment, the board can be baited with tasty food rewards. In some cylinders, the treat is locked under a grid, and in differently colored cylinders, the treat is accessible. Small laboratory mammals (such as rats) are conditioned to the food reward and tested for behaviors such as object recognition or food intake inhibition. This test can help measure unconditioned behavior of small laboratory mammals and analyze their cognitive abilities. You've just had a sneak peek of the April 2015 issue of JoVE. Visit the website to see the full-length articles, plus many more, in JoVE: The Journal of Visualized Experiments.

An attempt to describe the ultrastructure and ultrahistochemistry of ciliary processes in mammals.

The aim of the present paper was to reexamine fine structural characteristics and glycogen topochemistry of ciliary processes in small laboratory mammals (hamsters, guinea-pigs and mice). A two-layered epithelium continuously covered all ciliary processes. The epithelium consisted of inner nonpigmented and outer pigmented cells whose apices faced each other. They were linked by desmosomes and tight junctions. Basal cell aspects showed extensively interdigitating processes adjacent to the inner (rarely also outer) basal lamina. The ciliary process core was made up of reticular fibers, few fibrocytes, and capillaries with or without fenestrations. No glycogen particles were found in the ciliary epithelium using the PA-TSC-SP procedure.

The osteoinductive potential of demineralized freeze-dried bone allograft in human non-orthotopic sites: a pilot study.

The use of demineralized freeze-dried bone allograft (DFDBA) in periodontal therapy is widely accepted. In addition to histologic studies demonstrating its role in regenerating the attachment apparatus, its recognized ability to exhibit osteoinduction in small laboratory mammals has prompted many clinicians to regard it as osteoinductive when utilized in periodontal therapy. Despite such a theoretical deduction, evaluating and establishing the osteoinductive potential of DFDBA in humans has been problematic. The purpose of this study was to investigate, through the use of a novel implantation/recovery model, the potential of DFDBA to induce new bone formation at sites not normally considered capable of de novo osteogenic activity. Seven patients scheduled to undergo periodontal therapy utilizing non-absorbable membranes agreed to have sterile polypropylene mesh capsules placed adjacent to the primary surgical site for the purpose of this investigation. One capsule was left empty while the second capsule contained DFDBA. At the appropriate time interval for removal of the therapeutic membrane, the capsules were removed and submitted for histologic analysis. Five of the subjects had procedures directed at regenerating bone within molar furcations (guided tissue regeneration) and had the membranes and associated capsules removed between 6 and 8 weeks. The 2 remaining patients had procedures directed toward ridge augmentation (guided bone regeneration) and had the membranes removed either at 8 or 9 months, respectively. In addition, one of the 2 long-term membrane patients had liberal cortical penetration performed directly beneath the implanted capsule. Histologic analysis of all recovered capsules by 2 independent oral and maxillofacial pathologists could not confirm the presence of either osteoblastic or osteoclastic activity associated with the DFDBA particles, although the 2 longer-term specimens clearly exhibited trace amounts of vital bone non-contiguous with the implanted material. The results of this pilot study do not support the osteoinductive potential of DFDBA when utilized in quantities normally associated with periodontal bone grafting, although they do support the use of this implantation/recovery model to study other preparations and mechanisms of bone formation.

Contractile properties of rat, rhesus monkey, and human type I muscle fibers.

It is well known that skeletal muscle intrinsic maximal shortening velocity is inversely related to species body mass. However, there is uncertainty regarding the relationship between the contractile properties of muscle fibers obtained from commonly studied laboratory animals and those obtained from humans. In this study we determined the contractile properties of single chemically skinned fibers prepared from rat, rhesus monkey, and human soleus and gastrocnemius muscle samples under identical experimental conditions. All fibers used for analysis expressed type I myosin heavy chain as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Allometric coefficients for type I fibers from each muscle indicated that there was little change in peak tension (force/fiber cross-sectional area) across species. In contrast, both soleus and gastrocnemius type I fiber maximal unloaded shortening velocity (Vo), the y-intercept of the force-velocity relationship (Vmax), peak power per unit fiber length, and peak power normalized for fiber length and cross-sectional area were all inversely related to species body mass. The present allometric coefficients for soleus fiber Vo (-0.18) and Vmax (-0.11) are in good agreement with published values for soleus fibers obtained from common laboratory and domesticated mammals. Taken together, these observations suggest that the Vo of slow fibers from quadrupeds and humans scale similarly and can be described by the same quantitative relationships. These findings have implications in the design and interpretation of experiments, especially those that use small laboratory mammals as a model of human muscle function.

Toxicity of 2‐Bromopropane on Spermatogonia and Spermatocyte

Journal of Occupational HealthVolume 39, Issue 1 p. 1-2 Rapid CommunicationFree Access Toxicity of 2-Bromopropane on Spermatogonia and Spermatocyte Minoru Omura, Minoru Omura Department of Hygiene, Kyushu UniversitySearch for more papers by this authorMangen Zhao, Mangen Zhao Department of Hygiene, Kyushu UniversitySearch for more papers by this authorYesid Romero, Yesid Romero Department of Hygiene, Kyushu UniversitySearch for more papers by this authorNaohide Inoue, Naohide Inoue Department of Hygiene, Kyushu UniversitySearch for more papers by this author Minoru Omura, Minoru Omura Department of Hygiene, Kyushu UniversitySearch for more papers by this authorMangen Zhao, Mangen Zhao Department of Hygiene, Kyushu UniversitySearch for more papers by this authorYesid Romero, Yesid Romero Department of Hygiene, Kyushu UniversitySearch for more papers by this authorNaohide Inoue, Naohide Inoue Department of Hygiene, Kyushu UniversitySearch for more papers by this author First published: 07 April 2006 https://doi.org/10.1539/joh.39.1Citations: 15 Correspondence to :M. Omura, Department of Hygiene, Kyushu University, Fukuoka 812-82, Japan. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. References 1Park JS, Kim YH, Park DW, et al. Epidemiological survey on the outbreak of intoxication due to submerging solution including 2-bromopropane, Korea. Presented at 25th International Congress on Occupational Health 1996, Stockholm, Sweden. 2Ichihara G, Asaeda N, Kumazawa T, et al. Testicular toxicity of 2-bromopropane. J Occup Health 1996; 38: 205– 206. 3Manderly JL, Tesarek JE, Sifford LJ, et al. Respiratory measurements of unsedated small laboratory mammals using nonbreathing valves. Lab Anim Sci 1979; 29: 323– 329. 4Clermont Y, Harvey SC. Duration of the cycle of the seminiferous epithelium of normal, hypophysectomized and hypophysectomized-hormone treated albino rats. Endocrinol 1965; 76: 80– 89. 5Clermont Y, Perey B. The stages of the cycle of the seminiferous epithelium of the rat: Practical definitions in PA-Schiff-hematoxylin and hematoxylin-eosin stained sections. Rev Canad Biol 1957; 16: 451– 462. Citing Literature Volume39, Issue1January 1997Pages 1-2 ReferencesRelatedInformation

Toxic-induced hypothermia and hypometabolism: Do they increase uncertainty in the extrapolation of toxicological data from experimental animals to humans?

Commonly used experimental mammals, such as the rat and mouse, exhibit hypothermia and hypometabolism when exposed acutely to many drugs and other chemical substances. This toxic-induced hypothermic/hypometabolic state may be an inherently protective response that can reduce the lethality of a toxic insult. However, as body mass increases, the ability to lower body temperature in response to toxic insult is diminished. Hence, the presence of a protective hypothermic/hypometabolic response in small laboratory mammals and apparent lack thereof in larger species, such as humans, may represent an additional physiological dissimilarity which may underestimate the risk assessment of acute toxicological data. It is proposed that acute toxicological studies in rodents be performed at relatively warm ambient temperatures (ca. 28 to 32 degrees C) to prevent toxic-induced hypothermia. This would assure a more uniform internal thermal environment between species, thus reducing a major physiological variable in species-to-species extrapolation.

Nuclear transplantation in sheep embryos.

Nuclear transplantation and cell fusion techniques have proved valuable for embryological studies in several non-mammalian animal species. More recently these procedures have been used successfully in small laboratory mammals, notably the mouse, to investigate the ability of nuclei and cytoplasm from various sources to produce viable embryos when combined. The use of a similar approach to study the developmental biology of large domestic animals presents a number of technical and practical difficulties, and so far there has been no report of attempts to perform nuclear transplantation in sheep embryos. Here I describe such a procedure and its use to investigate the development of embryos in which whole blastomeres from 8- and 16-cell embryos were combined with enucleated or nucleated halves of unfertilized eggs. The procedure involves bisection of single-cell eggs in a medium containing cytochalasin; fusion of egg halves with single blastomeres, induced using Sendai virus or an electrofusion apparatus; and embedding in agar, followed by culture of the reconstituted embryos in the ligated oviducts of ewes in dioestrus. I show that fully viable embryos may be obtained by this procedure.

Pulmonary function testing in small laboratory mammals.

The lung is the primary organ likely to be exposed by inhalation studies and, therefore, measurement of changes in lung function are of particular interest to the pulmonary physiologist and toxicologist. Tests of pulmonary function have been developed which can be used with small animals to measure spirometry (lung volumes), mechanics, distribution of ventilation, gas exchange or control of ventilation. These tests were designed on the basis of similar tests which are used in humans to diagnose and manage patients with lung disease. A major difference is that many of the measurements are performed in anesthetized animals, while human pulmonary function is usually measured in awake cooperating individuals. In addition, the measurement of respiratory events in small animals requires sensitive and rapidly responding equipment, because signals may be small and events can occur quickly. In general, the measurements described provide information on the change in normal lung function which results primarily from structural changes. These tests of pulmonary function can be repetitively and routinely accomplished and the results appear to be highly reproducible. Although some are quite sophisticated, many can be undertaken with relatively inexpensive equipment and provide useful information for toxicological testing.

Pulmonary Function Testing in Small Laboratory Mammals

The lung is the primary organ likely to be exposed by inhalation studies and, therefore, measurement of changes in lung function are of particular interest to the pulmonary physiologist and toxicologist. Tests of pulmonary function have been developed which can be used with small animals to measure spirometry (lung volumes), mechanics, distribution of ventilation, gas exchange or control of ventilation. These tests were designed on the basis of similar tests which are used in humans to diagnose and manage patients with lung disease. A major difference is that many of the measurements are performed in anesthetized animals, while human pulmonary function is usually measured in awake cooperating individuals. In addition, the measurement of respiratory events in small animals requires sensitive and rapidly responding equipment, because signals may be small and events can occur quickly. In general, the measurements described provide information on the change in normal lung function which results primarily from structural changes. These tests of pulmonary function can be repetitively and routinely accomplished and the results appear to be highly reproducible. Although some are quite sophisticated, many can be undertaken with relatively inexpensive equipment and provide useful information for toxicological testing.

Skin and Dermal Appendages of Small Laboratory Mammals: I. Comparative Morphology of the Skin and Hair of the Mouse, Rat, Hamster, Guinea Pig and Rabbit

Skin and Dermal Appendages of Small Laboratory Mammals: I. Comparative Morphology of the Skin and Hair of the Mouse, Rat, Hamster, Guinea Pig and Rabbit

Activity of Commercial Fasciolicides in Small Laboratory Mammals

The activity is reported of 6 commerical fasciolicides and disophenol administered at doses of effective in sheep, against 6- and 12-week-old Fasciola hepatica in rats and rabbits and 6-week-old flukes in guinea pigs. Tests in rats and rabbits do not give a reliable indication of the activity of fasciolicides in sheep, but results with guinea pigs were closer to those in sheep. A comparison of the effective dose in rats and sheep indicates that tests in rats usually underestimate activity in sheep. The use of a simple egg count procedure in sheep to provide information on potential fasciolicides is described.

A survey of parasites in commercially available small laboratory mammals (author's transl)

A survey of parasites in commercially available small laboratory mammals (author's transl)

Observations on the ultimobranchial gland in small wild and laboratory mammals, with special reference to the histochemical localization of polysaccharides

AbstractThis is the last of a series of observations involved in a comparative histological study of the ultimobranchial body in vertebrates. Complete serial longitudinal or transverse paraffin sections were made of formol alcohol, Bouin's, and formalin‐fixed ultimobranchial and thyroid tissues that had been removed from adult specimens of the cat, cotton rat, ground squirrel, Guinea pig, kangaroo rat, bushytailed wood rat, rabbit, and raccoon. The alcian blue‐PAS, aldehyde fuchsin‐alcian blue, mucicarmine, alcian blue‐safranin, Best's carmine, and toluidine blue staining procedures show that the glandular mammalian ultimobranchial tissue is capable of producing considerable amounts of various mucosubstances, particularly the acid mucopolysaccharides, and other carbohydrate‐containing materials. The carbohydrate moiety has been histochemically identified as mucopolysaccharides possessing acidic groups, those having both carboxyl and ester sulfate groups; and as glycogen, muco‐and glycoproteins and other carbohydrate‐protein complexes. The differences in the intensity and localization of a given staining reaction reflect not only individual and species variations but also significant differences in the position of the ultimobranchial tissue in relation to the thyroid gland. An accessory thyroid lobule found near parathyroid IV and thymus IV in a bushy‐tailed wood rat may represent a cystic manifestation of the ultimobranchial body because its follicles varied greatly in size and were lined by a thick stratified squamous epithelium. The possible hormonal mechanisms (TSH, thyroxine) involved in the regulation of ultimobranchial activity are discussed in relation to the gland's production, storage, and release of mucopolysaccharides and other secretory substances.

Quantitative Studies on the Radiation Pathology of the Bone Marrow of Small Laboratory Mammals: I. The Film-Ratio Method: Absolute Counts from Films Prepared with Suspensions of Bone Marrow Cells

A film-ratio method was devised in which absolute counts of suspended bone marrow cells were acheived by means of a lasting film on a microscopic slide, prepared with a medium containing standard particles (spores) in a known concentration. The ratio of cells to spores was determined by microscopic examination of the film. The marrow cell count = R (cell-to-particle ratio in film) times N (number of standard particles in marrow suspension). Such films have the advantage of not requiring immediate counting. Their examination is no more laborious than the conventional method (chamber count plus differential count). Uniformity trials were carried out, sources of variance were explored, and results were compared with those obtained with the hemacytometer and with the electronic counter. The method was shown to be practical in a trial experiment dealing with changes in the marrow of irradiated mice. (auth)

Blood capillaries of the heart and other organs.

The article is a review of work recently carried out on blood capillaries by the author in collaboration with Drs. M. G. Farquhar, G. Majno, and S. L. Wissig. It reviews the morphology of these vessels at the electron-microscope level and confirms the existence of at least 3 distinct types of blood capillaries in small laboratory mammals. It shows that the capillary wall consists of 3 concentric layers (endothelium, basement membrane, and adventitia), and indicates that the basement membrane forms a continuous layer in all capillaries so far studied. Experiments in which colloidal gold particles were used as a tracer have shown that, in capillaries with a continuous endothelium (muscle capillaries), the particles are transported across it by "pinocytic" vesicles. At the end of this step they must still transverse the basement membrane. Experiments on glomerular capillaries, which typically have a discontinuous s endothelium, were carried out on normal and nephrotic rats using ferritin as a tracer. By its accumulation on the luminal side of the basement membrane, the ferritin has identified this layer as the main filtration barrier. A similar function of the basement membrane was demonstrated in muscle venules and venous capillaries by experiments in which the endothelium was rendered discontinuous by local treatment with histamine and serotonin.