Mastication in the musk shrew,Suncus murinus (mammalia,Soricidae)

High-speed cinematography shows that Suncus murinus (Crocidurinae) masticates fast (mean 5.5, 5–10 masticatory cycles per sec). Their grasping behavior is not stereotyped. The unilateral mandibular movements combine vertical, anteroposterior, and lateral displacements; and any masticatory sequence may include crushing, repositioning, shearing, and grinding components. Size and consistency of food influence the duration of individual chewing cycles. As food is transferred to the new working side, the chewing direction reverses, either near maximum closure or near maximum opening. An unfused mandibular symphysis permits tilting movements of the two halves of the mandible. Food may be squeezed between the lower incisors. The working side tilts outward during closing; this may improve shearing or grinding action. The closing phase is posteriorly directed. Thus, the masticatory movements of these shrews differ from those that have been described in many other mammals.     

Planned reproduction of the house musk shrew (Suncus murinus)

To investigate methods for the planned reproduction of the house musk shrew (Suncus murinus), increased reproduction was attempted from May through August, 1980 using 13 females and 13 males obtained from the breeding colony in the Laboratory of Animal Genetics, Faculty of Agriculture, Nagoya University. As a result, a reproduction colony consisting of 128 females and 60 males was formed in September, 1981. This was followed by repeated selective culling until a planned reproduction system with monthly production of over 100 pups was established in December, 1981. The production results for one year, 1982, showed that among the 994 females mated, there was a gestation rate of 74.1%, a parturition rate of 89.8%, average litter size of 3.5, a weaning rate of 77.2%, and a productive index of 1.8. A total of 1,780 weanlings was obtained and stable production throughout the year was achieved.     

Cloning of putative uncoupling protein 1 cDNA in a cold-intolerant mammal, the house musk shrew (Suncus murinus)

The house musk shrew (Suncus murinus), or suncus, is a unique experimental animal. We recently showed that this mammal is cold intolerant and hypothesized that its sensitivity to cold is caused by low thermogenic activity in brown adipose tissue (BAT). Thermogenesis in BAT is performed by a unique mitochondrial protein, uncoupling protein 1 (UCP1). Interestingly, only eutherians possess UCP1, and some traits in the suncus resemble those in the Ucp1-ablated mouse, including cold intolerance, histology of BAT, and obesity resistance. In a previous study, we hypothesized that UCP1 may not be present in BAT of the suncus or may be dysfunctional. Therefore, we performed cDNA cloning of suncus Ucp1 and compared it to homologs from other species. The deduced amino acid sequence showed high similarity to other mammalian UCP1. Northern blot analysis revealed mRNA in BAT, as in other mammals. However, a difference in an amino acid residue was observed in an important residue for thermogenesis. Genomic sequence analysis showed that this difference existed in our two genetically distant laboratory colonies. These results suggest that cold intolerance in the suncus is derived from low thermogenic activity of UCP1 and may exist in wild house musk shrews.     

Sebum-storing flank gland hairs of the musk shrew, Suncus murinus viridescens

Lipid droplets discharged from the disintegrating holocrine cells of the flank gland of the Indian musk shrew, Suncus murinus viridescens (Blyth) are stored in the lumen of the sebaceous acini and eliminated to the exterior through the glandular ducts. Specialized hairs developed on the surface of the flank gland of the shrew are deep rooted. The osmetrichia of the flank gland of both sexes of the shrew have flattened and thickly packed culicular scales. These scales are morphologically different from the largeconical-shaped scales of the dorsal body hairs. The surface of osmetrichia is soaked with the oily secretory materials of the flank gland. The medulla of osmetrichia is developed into Special chambers which are filled with the glandular secretory droplets.     

Patterns of sexual receptivity in the female musk shrew (Suncus murinus)

Female musk shrews (Suncus murinus) were tested daily to examine patterns of sexual receptivity. When only mounting was used as a criterion (to avoid pregnancy), nonpregnant females remained sexually receptive to males every day for 14 consecutive days. When insemination was allowed, most females continued to copulate for the first 5 days of pregnancy. Receptivity declined markedly around Day 10 of gestation, but a few females were receptive even into late pregnancy. Lactating females copulated with males 5 and 10 days after parturition. In general, unlike most mammals studied in the laboratory, the nonpregnant female musk shrew has no behavioral estrous cycle. Musk shrews are ready to mate anytime except in mild to late pregnancy, and even then occasionally mating is found.     

Effects of photoperiod and social variables on reproduction and growth in the male musk shrew (Suncus murinus)

In Exp. 1, the time course for the photoperiodic response in juvenile male musk shrews was examined by exposing animals to short (10L:14D) or long (14L:10D or 18L:6D) daylengths for 10, 20, 40 or 56 days. When compared with the response of animals maintained in long days, those exposed to short days showed an inhibition of reproductive maturation by 40 days of treatment. In Exp. 2, the combined effects of photoperiod and social cues were investigated in juvenile males that were either housed in short days (with or without a female) or in long days (with or without a female) for 40 days. The short photoperiod was generally inhibitory to sexual maturation, while the presence of an adult female was generally stimulatory, i.e. animals living with a female in long days had the greatest level of sexual maturity, while those living alone in short days had the lowest level of maturity. Animals that received opposing signals, i.e. short days in the presence of a female, had an intermediate response which was equivalent to the response seen in males living alone in long days. These results suggest that the presence of a female can partly reverse inhibitory effects of short days. In Exp. 3, the effects of photoperiod and social cues on the reproductive physiology of the adult male (same design as in Exp. 2) were investigated. The results show that the adult male musk shrew is responsive to both photoperiodic and social cues, in a manner similar to that of juvenile animals.(ABSTRACT TRUNCATED AT 250 WORDS)     

Unusual features of sperm ultrastructure in the musk shrew Suncus murinus

The spermatozoon of the Musk shrew Suncus murinus displays unusual fine anatomical features. In the head, the equatorial segment of the acrosome is recessed within a waist in the sperm nucleus in a way that could afford some protection for this fusogenic region, perhaps during penetration of the egg vestments. The perinuclear material has distinctive inner and outer regions, the latter being arranged as a series of coxcomblike spikes. These structures in Suncus could serve to anchor its characteristically giant acrosome to the sperm nucleus. In the tail, small aggregations of electron dense material appear against some centriolar triplets and also, proximally, against some axonemal doublets. In the midpiece, prominent satellite material aggregates proximally over the inner border of the dense fibers. More distally, the material maintains a close relationship with and primarily lies between the corresponding axonemal doublets and dense fibers 5 and 6, the latter being positioned asymmetrically in relation to the remaining dense fibers.     

Ultrastructure of secretory ameloblasts in the house musk shrew, Suncus murinus, Insectivora

Tooth germs from neonatal house musk shrews, Suncus murinus, were used for the study. The tooth morphogenesis was compared electron microscopically to that of Primates. In the tooth germ at the bell stage, the ameloblast was 3 x 50 microns in size, columnar in shape and had several tubular-type Golgi apparatus which were at the distal end of the cell. Most mitochondria were noted at the proximal end of ameloblasts. Tomes' processes were 1 micron in width, protruded 10 microns from the ameloblast and had many dense bodies and two kinds of vesicles. They were morphologically different from human ameloblasts and enamel rods.     

Histochemical study on the external ear of Suncus murinus (Indian musk shrew)

The histochemical study of the Ear of female Suncus murinus (Indian musk shrew) was studied by the use of the cholinesterase technique. Good and sharp results were obtained while studing the AChE activity in the hair, hair follicle, hair papillae, muscle spindle, and nerve endings. The investigations were performed under constant pH, temperatures 37 degrees C to 40 degrees C, and incubation times, from 16 hours to 18 hours. The hair follicle and hair shafts showed strong positive reaction; hair papillae also showed strong positive reaction of AChE activity, while hair showed the banded appearance and the muscle spindles showed mild reaction of the AChE activity.     

Growth and sexual maturation of the male house musk shrew (Suncus murinus)

The sexual maturation in the male house musk shrew, Suncus murinus, was investigated by weighing gonads, accessory sexual organs and various other organs, and measuring testosterone concentrations in the plasma from birth to 50 days of age. The histological and histochemical studies of the testis were also carried out. Testicular weight increased markedly from 10 days of age. On 15 days of age, the activity of delta 5-3 beta-Hydroxysteroid dehydrogenase (HSD) was detected in Leydig cells. In accordance with an increase of HSD activity, the concentrations of plasma testosterone raised rapidly from 15 days of age and reached a peak on Day 30. Growth of prostate glands and seminal vesicles showed a sigmoidal pattern and their significant growth began from Day 25. Sperms were detected first in the seminiferous tubules on Day 28, and most tubules were filled with many sperms on Day 33. From these results, the beginning of sexual maturation, i.e. puberty, of the male shrew is considered to be around Day 25. The weight gain of testes, accessory sexual organs and the body became slower on Day 40. The male animal of Day 40 could mate and impregnate the female. Therefore, the male shrew seems to attain to the sexual maturity between days 35 and 40.     

Mating stimulates estradiol production by ovaries of the musk shrew (Suncus murinus).

Asian musk shrews (Suncus murinus) are induced ovulators, but exhibit no cyclic changes in reproductive structures or in sexual behavior. Mating behavior is induced by contact with a male. To determine if mating induces changes in ovarian steroidogenesis, ovaries removed from unmated animals and at 3, 10, 15, and 36 h after mating were cultured for 4 h in the presence or absence of gonadotropins (LH + FSH, 1 microgram/ml). Histological analysis revealed no obvious changes in follicular size or appearance at the end of culture in ovaries cultured at 3 and 10 h post-mating, as compared with ovaries from unmated shrews, and mating did not stimulate any discernable changes in steroid secretion in these two groups. However, at the end of the culture period, ovulation had occurred or was occurring in ovaries from 35% of the animals ovariectomized at 15 h after mating, and corpora lutea (CLs) were present in 39% of ovarian pairs obtained 36 h after mating. At 15 h post-mating, ovaries with ovulations secreted three times more estradiol than did ovaries that showed no evidence of stimulation by mating, but there were no differences in testosterone or progesterone production. In contrast, ovaries isolated 36 h post-mating with CLs secreted dramatically more of all three steroids than ovaries without CLs (23, 13, and 52 times more estradiol, testosterone, and progesterone, respectively). These data are consistent with plasma concentrations of estradiol at the time of ovariectomy, which were twice as high at both 15 and 36 h after mating, in animals whose ovaries showed evidence of ovarian stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Response to opioids of isolated small intestine in the house musk shrew, Suncus murinus.

1. Response to the opioids of isolated small intestine of Suncus murinus, an insectivore, was examined and compared with that of guinea-pig ileum. 2. The mechanical response to morphine and U50,488H, preferential mu- and kappa-agonist respectively, was relaxation which was antagonized by tetrodotoxin and naloxone in the Suncus small intestine. 3. Methionine5-enkephalin and D-alanine2, D-leucine5-enkephalin, both preferential delta-agonists, elicited contraction or relaxation in the Suncus small intestine, while enkephalins elicited sustained contraction in the tetrodotoxin-pretreated intestine. 4. In the guinea-pig ileum, the response to morphine and enkephalins was consistently relaxation which was antagonized by tetrodotoxin and naloxone. 5. Morphine, D-alanine2,D-leucine5-enkephalin and U50,488H inhibited electrically-evoked twitch responses of intestine in a concentration-dependent manner in both animals. 6. The relative potencies calculated from IC50 values of opioids for twitches followed the order, D-alanine2,D-leucine5-enkephalin greater than U50,488H greater than morphine in the Suncus small intestine, whereas U50,488 greater than D-alanine2,D-leucine5-enkephalin greater than morphine in the guinea-pig ileum. 7. Suncus small intestine has unique features such that D-alanine2,D-leucine5-enkephalin was most potent in inhibiting electrically-evoked twitches and that enkephalins induced contraction following tetrodotoxin pretreatment.     

Kinky coat, a new autosomal recessive mutation in the musk shrew, Suncus murinus.

A kinky-coat mutant was discovered at the fifth generation of the BAN strain originating from wild musk shrews (Suncus murinus) in Bangladesh. Mating experiments indicated that the kinky-coat character is controlled by a single autosomal recessive gene designated kc (kinky coat), which is not allelic to the gene ch (curly hair) previously reported in the Tr strain derived from wild musk shrews on Taramajima Island, Japan. Because the kc/kc homozygotes were fully fertile and viable, the kc gene should be useful as a genetic marker in linkage studies. In external appearance, homozygotes were characterized by curly vibrissae, somewhat unkept coat hair, and wavy long hair on the tail. Both the length and width of coat hair did not differ significantly between homozygous and normal shrews. Light microscopic observations showed that shafts of the kc coat hair are wavy and often have small swellings with disorganization of the medullary structure. Scanning electron microscopic examinations further revealed that the shafts of the vibrissae, coat hair, and tail hair have abnormalities such as longitudinal fissures, twists, and hollows. It is clear that these modifications caused waviness or curling of the shafts of the three kinds of hairs observed.     

The force driving mating behavior in the house musk shrew (Suncus murinus)

The mating behavior of the domesticated house musk shrew was observed in detail under laboratory conditions. The observations revealed that the house musk shrew has a series of behaviors before copulation. Tactile, auditory and chemical senses appear to function as flags for the recognition of conspecifics and to promote the development of an interaction between the sexes. The tactile senses and the use of the snout were particularly important in the mating sequence, and mutual contact appeared to give rise to driving the sequence to completion. The two sexes contacted each other 'politely', came to mounting by continuous following, and the male finished with a series of post-ejaculatory offensive behaviors and scent markings. The variation in the contact reduced once the female commenced tail-wagging. The ratio of the time spent in front-and-behind contact to that spent in multi-lateral contact increased when both sexes commenced following formation. This ratio was maintained until the male's post-ejaculatory offensive behavior finished. The series of mating behavior was completed by the continuous touching of both sexes and by changes in the manner of contact.     

Fine structure of the atrial cardiocytes in the house musk shrew (Suncus murinus).

The atrial and ventricular cardiocytes of the house musk shrew were examined by immunohistochemistry, and the right atrium containing the auricle was studied by transmission electron microscopy. The atrial natriuretic peptide (ANP)-granules of the cardiocytes in the auricle and the rest of the atrium were also analyzed by ultrastructural morphometry. On immunohistochemistry, ANP immunoreactivity was detected in the atria, with the most intensely reacting cardiocytes being localized in the right auricular part of the atrium. ANP immunoreactivity was not detected in the ventricular muscles. On ultrastructure, in most of the atrial cardiocytes including the auricle, ANP-granules, well-developed Golgi apparatus and rough endoplasmic reticulum were observed, and the nuclei were characteristically situated in the periphery of the cardiocytes, being different from many other mammalian hearts. The ANP-granules were classified into two types (A and B), with most of these granules being located in the paranuclear region in association with the Golgi apparatus, and a few ANP granules being observed throughout the sarcoplasmic layers intervening between the myofibrilar bundles. On ultrastructural morphometry, the total number of granules in the right auricular cardiocytes was significantly greater than those in the atrial cardiocytes, and the diameter of the A-granules was significantly greater than that of the B-granules in both the atrial and auricular cardiocytes.     

Histochemistry of glycoconjugates in ovarian follicles of the adult house musk shrew, Suncus murinus

In ovarian follicles of the adult house musk shrew, Suncus murinus, glycoconjugates have been studied by means of light- and electron-microscopic histochemistry. The results obtained are that: (1) glycoconjugates of the zona pellucida of oocytes are provided with vicinal diol and acidic groupings, and sialic acid-galactose dimer, alpha-D-mannose, alpha-D-glucose, beta-D-galactose, N-acetyl-D-glucosamine and alpha-L-fucose residues; (2) glycoconjugates of the intercellular matrix of the granulosa and theca folliculi are comparable in histochemical properties to those of the zona pellucida, except for the relatively smaller amount of vicinal diol and acidic groupings, and (3) the zona pellucida can be divided into outer and inner layers by the binding degrees of the lectins used. The possible histophysiological significances of all these glycoconjugates are discussed with special reference to the particular ovarian follicular structures.     

Comparative FISH mapping of human cDNA clones to chromosomes of the musk shrew (Suncus murinus, Insectivora)

Forty-one cDNA clones of human functional genes were newly mapped to chromosomes of the musk shrew (Suncus murinus, Insectivora) by fluorescence in situ hybridization, and a comparative cytogenetic map of 51 genes, including 10 genes reported in our previous study, was constructed between human (HSA) and musk shrew (SMU) chromosomes. In this comparative map, the 51 genes localized to human autosomes, except HSA 8, 16, and 20, were mapped to 15 shrew autosomes, except SMU 4, 16, 17 and 18. Twelve conserved segments were identified between human and shrew chromosomes, and six segments among the musk shrew, human, and mouse. Our results defined the presence of at least one inversion and several interchromosomal rearrangements that occurred during evolution after the two species diverged from a common ancestor. Localization of three major histocompatibility complex (MHC) genes to shrew chromosome 3 suggested that the MHC genes of the musk shrew are located in a cluster on chromosome 3. The cytogenetic map constructed in this study is the first cytogenetic map with many functional genes in insectivore species. This approach provides clues for clarifying the chromosomal evolution in this order.     

Expression and localization of aquaporins in the kidney of the musk shrew (Suncus murinus).

Expression and localization of members of the aquaporin (AQP) family (AQP1, 2, 3, 4, and 5) in the kidney of the musk shrew (Suncus murinus) was examined by immunohistochemistry. AQP1 was expressed in the proximal tubules and in the thin limb of the loops of Henle. AQP1 was the only water channel expressed in the proximal nephron examined, indicating that AQP1 may be an independent water transporter in the proximal nephron. AQP2 and AQP5 were localized to the apical cytoplasm of the cortical to medullary collecting duct (CD) cells and AQP3 and AQP4 were localized to the basal aspect of the cortical to medullary CD cells. AQP3 expression was weaker in the cortical cells compared with the medullary cells, whereas AQP4 was strongly positive throughout the CD. These indicate that the CD is the main water reabsorption segment of the nephron and is regulated by AQPs. Indeed, apical water transport of CD cells of the musk shrew may be controlled by both AQP2 and AQP5. The characteristic expression pattern of the AQPs in this animal provides a novel animal model for elucidating the regulation of water reabsorption by AQPs in the mammalian kidney.