Adult Shrews Research Articles

Effects of Brain Size on Adult Neurogenesis in Shrews.

Shrews are small animals found in many different habitats. Like other mammals, adult neurogenesis occurs in the subventricular zone of the lateral ventricle (SVZ) and the dentate gyrus (DG) of the hippocampal formation. We asked whether the number of new generated cells in shrews depends on their brain size. We examined Crocidura russula and Neomys fodiens, weighing 10–22 g, and Crocidura olivieri and Suncus murinus that weigh three times more. We found that the density of proliferated cells in the SVZ was approximately at the same level in all species. These cells migrated from the SVZ through the rostral migratory stream to the olfactory bulb (OB). In this pathway, a low level of neurogenesis occurred in C. olivieri compared to three other species of shrews. In the DG, the rate of adult neurogenesis was regulated differently. Specifically, the lowest density of newly generated neurons was observed in C. russula, which had a substantial number of new neurons in the OB compared with C. olivieri. We suggest that the number of newly generated neurons in an adult shrew’s brain is independent of the brain size, and molecular mechanisms of neurogenesis appeared to be different in two neurogenic structures.

New collection locality of Cryptotis tropicalis (Merriam, 1895) (Eulipotyphla: Soricidae) in the south lowlands of Guatemala, Central America

In January 2013, we carried out a mammal inventory in the south lowlands of Guatemala (elevation below 500 m), in the south slope of the Tecuamburro Volcano, in Taxisco, Santa Rosa. The area is immersed in Subtropical Very Wet Forest (Castañeda 2008). We captured a male adult shrew in a pitfall container located within a riparian forest, following the river bank locally known as El Pajal, at 410 msnm (14,119N, -90,505W). The specimen was collected, and prepared as dried skin and skull following the protocols of The Animal Care and Use Committee (Gannon et al. 2007). As a collaboration agreement, it was housed as voucher in the Mammals Collection of El Colegio de la Frontera Sur, San Cristóbal de Las Casas, Mexico

Tactile experience shapes prey-capture behavior in Etruscan shrews

A crucial role of tactile experience for the maturation of neural response properties in the somatosensory system is well established, but little is known about the role of tactile experience in the development of tactile behaviors. Here we study how tactile experience affects prey capture behavior in Etruscan shrews, Suncus etruscus. Prey capture in adult shrews is a high-speed behavior that relies on precise attacks guided by tactile Gestalt cues. We studied the role of tactile experience by three different approaches. First, we analyzed the hunting skills of young shrews' right after weaning. We found that prey capture in young animals in most, but not all, aspects is similar to that of adults. Second, we performed whisker trimming for 3–4 weeks after birth. Such deprivation resulted in a lasting disruption of prey capture even after whisker re-growth: attacks lacked precise targeting and had a lower success rate. Third, we presented adult shrews with an entirely novel prey species, the giant cockroach. The shape of this roach is very different from the shrew's normal (cricket) prey and the thorax—the preferred point of attack in crickets—is protected by a heavy cuticle. Initially shrews attacked giant roaches the same way they attack crickets and targeted the thoracic region. With progressive experience, however, shrews adopted a new attack strategy targeting legs and underside of the roaches while avoiding other body parts. Speed and efficiency of attacks improved. These data suggest that tactile experience shapes prey capture behavior.

Chemoarchitecture of Layer 4 Isocortex in the American Water Shrew (Sorex palustris)

We examined the chemoarchitecture of layer 4 isocortex and the number of myelinated nerve fibers of selected cranial nerves in the American water shrew (Sorex palustris). This study took advantage of the opportunity to examine juvenile brain tissue, which often reveals the most distinctive cortical modules related to different sensory representations. Flattened cortical sections were processed for the metabolic enzyme cytochrome oxidase, revealing a number of modules and septa. Subdivisions related to sensory representations were tentatively identified by performing microelectrode recordings in a single adult shrew in this study, combined with microelectrode recordings and anatomical findings from a previous investigation. Taken together, these results suggest that characteristic chemoarchitectonic borders in the shrew neocortex can be used to delineate and quantify cortical areas. The most obvious subdivisions in the water shrew include a relatively small primary visual cortex which responded to visual stimuli, a larger representation of vibrissae in the primary somatosensory cortex, and a prominent representation of oral structures apparent in the more rostral-lateral cortex. A presumptive auditory area was located in the far caudal cortex. These findings for the cortex are consistent with counts from optic, auditory and trigeminal nerves, suggesting that somatosensory inputs dominate the shrew’s senses whereas visual and auditory inputs play a small role in navigation and in finding prey. More generally, we find that shrews share unusual features of cortical organization with moles, supporting their close taxonomic relationship.

Composition and Function of Haemolymphatic Tissues in the European Common Shrew

BackgroundStudies of wild animals responding to their native parasites are essential if we are to understand how the immune system functions in the natural environment. While immune defence may bring increased survival, this may come at a resource cost to other physiological traits, including reproduction. Here, we tested the hypothesis that wild common shrews (Sorex araneus), which produce large numbers of offspring during the one breeding season of their short life span, forgo investment in immunity and immune system maintenance, as increased longevity is unlikely to bring further opportunities for mating. In particular, we predicted that adult shrews, with shorter expected lifespans, would not respond as effectively as young animals to infection.Methodology/Principal FindingsWe examined haemolymphatic tissues from wild-caught common shrews using light and transmission electron microscopy, applied in conjunction with immunohistology. We compared composition and function of these tissues in shrews of different ages, and the extent and type of inflammatory reactions observed in response to natural parasitic infections. All ages seemed able to mount systemic, specific immune responses, but adult shrews showed some signs of lymphatic tissue exhaustion: lymphatic follicles in adults (n = 21) were both smaller than those in sub-adults (n = 18; Wald = 11.1, p<0.05) and exhibited greater levels of depletion (Wald = 13.3, p<0.05).Conclusions/SignificanceContrary to our expectations, shrews respond effectively to their natural parasites, and show little indication of immunosenescence as adults. The pancreas of Aselli, a unique lymphoid organ, may aid in providing efficient immune responses through the storage of large numbers of plasma cells. This may allow older animals to react effectively to previously encountered parasites, but infection by novel agents, and eventual depletion of plasma cell reserves, could both still be factors in the near-synchronous mortality of adult shrews observed shortly after breeding.

Generation recruitment and death of brain cells throughout the life cycle ofSorexshrews (Lipotyphla)

Young shrews of the genus Sorex that are born in early summer reduce their body size before wintering, including a reduction of brain weight of 10-30%. In the spring they mature sexually, double their body weight and regain about half of the loss in brain weight. To investigate the mechanisms of brain weight oscillations we studied the rate of cell death and generation in the brain during the whole life cycle of the common shrew (Sorex araneus) and pygmy shrew (S. minutus). After weaning, shrews generate new brain cells in only two mammalian neurogenic zones and approximately 80% of these develop into neurones. The increase of the shrew brain weight in the spring did not depend on recruitment of new cells. Moreover, adult Sorex shrews did not generate new cells in the dentate gyri. Injections of 5-HT1A receptor agonists in the adult shrews induced neurogenesis in their dentate gyri, showing the presence of dormant progenitor cells. Generation of new neurones in the subventricular zone of the lateral ventricles and their recruitment to olfactory bulbs continued throughout life. TUNEL labelling showed that the rate of cell death in all brain structures, including the proliferation zones and olfactory bulb, was very low throughout life. We conclude that neither cell death nor recruitment significantly contributes to seasonal oscillations and the net loss of brain weight in the Sorex shrews. With the exception of dentate gyrus and olfactory bulb, cellular populations of brain structures are stable throughout the life cycle of these shrews.

Metal bioaccumulation in the greater white-toothed shrew, Crocidura russula, inhabiting an abandoned pyrite mine site

Hepatic and renal concentrations of iron, magnesium, zinc, lead, copper, manganese, mercury, cadmium, molybdenum, chromium, and nickel were quantified in shrews ( Crocidura russula) inhabiting a pyrite mine site in Portugal. Several morphological parameters (body weight, residual index, and relative weights) were also examined to clarify the physiological effects of pollution. Shrews from the mine showed increased bioavailability of Fe, Pb, Hg, Cd, Mo, and Ni in comparison with reference specimens. Adult shrews had the highest Cd levels while Cr and Ni concentrations diminished. Intersexual differences were found for Mo and Ni. As a consequence of metal pollution, the relative hepatic weight was higher in shrews from the mine site when compared with reference specimens. These data indicate that C. russula is a good bioindicator of metal pollution. We also evaluated the toxic effects of Pb, Hg, Cd, and Ni, because several shrews from the polluted site showed high concentrations of these metals. To approximate at the real biological impact of abandoned mines, after this first step it is necessary to associate the bioaccumulation levels and morphological effects with other physiological, ecological and genetical biomarkers.

The evolution of the thyroid hormone distributor protein transthyretin in the order insectivora, class mammalia.

Thyroid hormones are involved in the regulation of growth and metabolism in all vertebrates. Transthyretin is one of the extracellular proteins with high affinity for thyroid hormones which determine the partitioning of these hormones between extracellular compartments and intracellular lipids. During vertebrate evolution, both the tissue pattern of expression and the structure of the gene for transthyretin underwent characteristic changes. The purpose of this study was to characterize the position of Insectivora in the evolution of transthyretin in eutherians, a subclass of Mammalia. Transthyretin was identified by thyroxine binding and Western analysis in the blood of adult shrews, hedgehogs, and moles. Transthyretin is synthesized in the liver and secreted into the bloodstream, similar to the situation for other adult eutherians, birds, and diprotodont marsupials, but different from that for adult fish, amphibians, reptiles, monotremes, and Australian polyprotodont marsupials. For the characterization of the structure of the gene and the processing of mRNA for transthyretin, cDNA libraries were prepared from RNA from hedgehog and shrew livers, and full-length cDNA clones were isolated and sequenced. Sections of genomic DNA in the regions coding for the splice sites between exons 1 and 2 were synthesized by polymerase chain reaction and sequenced. The location of splicing was deduced from comparison of genomic with cDNA nucleotide sequences. Changes in the nucleotide sequence of the transthyretin gene during evolution are most pronounced in the region coding for the N-terminal region of the protein. Both the derived overall amino sequences and the N-terminal regions of the transthyretins in Insectivora were found to be very similar to those in other eutherians but differed from those found in marsupials, birds, reptiles, amphibians, and fish. Also, the pattern of transthyretin precursor mRNA splicing in Insectivora was more similar to that in other eutherians than to that in marsupials, reptiles, and birds. Thus, in contrast to the marsupials, with a different pattern of transthyretin gene expression in the evolutionarily "older" polyprotodonts compared with the evolutionarily "younger" diprotodonts, no separate lineages of transthyretin evolution could be identified in eutherians. We conclude that transthyretin gene expression in the liver of adult eutherians probably appeared before the branching of the lineages leading to modern eutherian species.

Delayed development of reflexes and hyperactive locomotion in the spontaneous mutant "waltzing" of the musk shrew, Suncus murinus.

The autosomal recessive mutation waltzing (wz), displaying abnormal circling and head-shaking behavior, has previously been reported in the musk shrew (Suncus murinus). Postnatal development of reflexes and locomotor patterns in an open arena were examined in wz/wz mutant shrews. The wz/wz shrews showed extreme developmental delays in surface-righting reflex and negative geotaxis until 10-16 days after birth, but both reflexes eventually recovered to the levels of +/wz normal. Nevertheless, the wz/wz adults exhibited bi-directional circling behavior 59 times, head-tossing behavior 22 times and horizontal head-shaking behavior 6 times more frequent than in the +/wz controls. Although the wz/wz adult shrews were extremely hyperactive with daily spontaneous locomotor activity exceeding 4-7 times control shrew activity, they appeared to have a normal circadian rhythm. This shrew mutant may therefore be useful as a model for hyperactivity syndromes in humans.

Magnificent expression of asialo GM1 on thymus cells and spleen T cells of the musk shrew, Suncus murinus

The expression of asialo GM1 (GA1) was observed on almost all thymocytes from young musk shrew, at the age of 4 weeks by flow cytometric analysis. In adult shrew aged 10 months, the ratio of GA1-negative thymocytes was increased. Among several anti-glycolipid antibodies used, anti-GM1 and anti-Forssman also reacted with the thymocytes. Protein fraction of the thymocytes was analyzed by SDS-PAGE followed by immunoblotting. Anti-GA1 and anti-GM1 showed two bands and one band, respectively, however, their mobilities were different from each other. Anti-Forssman did not stain any protein. The GA1-positive population in spleen T cell fraction was not detected in young shrew but most of the T cells were changed to GA1-positive cells in adult shrew. When mixed lymphocyte culture was performed, the GA1-negative spleen T cells in young shrew were changed to express GA1 marker on their cell surface by differentiation. Abbreviations used were as follows: GA1, Galβ 1-3GalNAcβ1-4Galβ1-4Glc-Cer; GM1, Galβ1-3GalNAcβ1-4(NeuAcα2-3)Galβ 1-4Glc-Cer; Forssman, GalNAcα1-3GalNAcβ1-3Galα1-4Galβ1-4Glc-Cer.

Age-associated and Cell-type Specific Changes in NGF Requirement for Neurite Regeneration From Trigeminal Ganglion Cells of the Shrew (Suncus murinus)

Low density (20-50 cells/cm2), dissociated cultures of trigeminal ganglion (TRG) cells of the shrew, were made in a serum-free medium, and neurite growth was compared across ages of the animal and between NGF-free and NGF-rich conditions. TRG cells from newborn shrew (0-3 days old), which grew long neurites in an NGF-rich medium, failed to grow any neurites in an NGF-free medium. In contrast, TRG cells from aged shrew (16-19 months), which grew neurites without NGF, exhibited no further increment in neurite length when NGF (50-200 ng/ml) was added to the culture medium. TRG cells from adult shrew (4-5 months) were revealed to be a mixture of NGF-dependent and NGF-independent cells. The NGF-dependent cells (20% of the population) had large-sized somata of 24-32 microns diameter (L-type cells) and 2-7 long neurites enriched with arborizations. The remaining NGF-independent cells (80%) had small-sized somata (15-25 microns, S-type cells), and grew 1-3 neurites with a small number of arborizations. These findings suggest that the primary sensory neuron of the shrew has a cell-type specific critical period in the aging process with respect to the requirement of NGF for neurite promotion.

Isolation and characterization of shrew ( Suncus murinus) liver alcohol dehydrogenases

1. 1. Starch gel electrophoresis of adult shrew ( Suncus murinus) liver extracts revealed five forms of alcohol dehydrogenase (ADH 1–5) and four of them were purified. 2. 2. ADH-4 and ADH-5 resemble human class I ADH in terms of electrophoretic mobility, substrate specificity and sensitivity to pyrazole inhibition. 3. 3. ADH-2 does not belong to any of the three classes of human ADHs but rather with catalytic properties similar to those of the class B ADH found in guinea pig liver. 4. 4. ADH-1 prefers secondary alcohol over primary alcohol substrates and between the enantiomers tested, the enzyme favors the S isomers.

Development of a laboratory line (SRI line) derived from the wild house musk shrew, Suncus murinus, indigenous to Sri Lanka.

Five male and 9 female house musk shrews (Suncus murinus) captured in Koralawella, Sri Lanka were acquired by our laboratory. One male and 3 females alone contributed to the development of a new laboratory line (SRI line). The SRI line has been maintained as a closed breeding colony consisting of more than 40 shrews. Gestation period and litter size at birth averaged 31.2 days (43 cases) and 2.4 (43 litters), respectively. The SRI line shrews were uniformly covered with light gray fur. The body weight and total length of adult shrews averaged 72.9 g and 23.9 cm in males, and 49.6 g and 21.0 cm in females. These data indicate a body size intermediate between BAN line shrews originating from Bangladesh and Nag or OKI line shrews from Japan. The SRI shrews are also characterized by having 30 chromosomes in diploid, being the smallest number in the entire species, whereas the otherlines (Nag, OKI and BAN) all have 40 chromosomes.

Studies on shrew (Suncus murinus) epidermal growth factor.

The shrew SMG contains a very high level of EGF. By heterologous radioreceptor assay, the EGF content was determined to be about 300 pmol/mg wet weight in the male. The content is sex dependent; in the female gland, it is only 4% of the male gland level. EGF level and EGF receptor content in other tissues showed a reciprocal distribution pattern with the parotid gland containing the second highest level of EGF and the liver containing the largest amount of EGF receptor. Shrew EGF is heat stable. It could induce early eyelid opening and incisor eruption in neonatal rat pups at a very low dose level. There is apparently no high molecular weight form of EGF in shrew tissues and body fluids. However, gel chromatography revealed that the foetus contained multiple forms of EGF. The contribution of a high EGF level to the active life in adult shrews and the exceptionally high growth rate in shrew pups are discussed.

The oxidation-reduction activity of organs in Sorex araneus Linnaeus, 1758

1. 1. Examination was made of variations in the oxidation-reduction activity of organs of the common shrew, identified by the chemiluminescence method, from the seasonal and age aspect. 2. 2. Differences were found in the level of investigated activity depending on the given function in the organism, and four types of organs were distinguished, differing in respect of length of the period during which the given organ was highly active. 3. 3. The investigated activity of all the organs examined in young adult shrews abruptly increased in autumn. 4. 4. No correlation was found between the weights of organs and their investigated activity. 5. 5. Variations in oxidation-reduction activity were compared with the variations, previously examined. in the activity of metabolically active substances in the organs of shrews in relation to seasonal and age variations in the metabolism of animals of this species.

On Growth, Form, and Function—A Fantasia on the Design of a Mammal

The development of a system’s biology, as a common construct for both physiologist and engineer, requires both a theory of structures (form) and a theory of dynamics (function). A dynamic organizing principle—“homeokinesis”—for the living system was proposed earlier. Based on thermodynamic reasoning, homeokinesis attempts to capture the physical essence of homeostasis. Now, a primitive foundation is proposed from which a large family of design characteristics might emerge, by self-organization, in complex biological organisms. This foundation is directed at the emergence of major form parameters of the entire class of mammalia, from 3 gm adult shrews to 100,000 kg whales.