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.     

Gonadal influences on sexual behavior in the male musk shrew (Suncus murinus)

In this series of experiments the hormonal bases for male copulatory behavior in the musk shrew (Suncus murinus) were examined. Male musk shrews failed to show copulatory behavior after castration. Testosterone replacement fully reinstated sexual behavior. Males castrated at birth, and tested as adults after receiving testosterone implants, did not show male-typical sexual behavior. It appears that the gonads are essential for the regulation of male sexual behavior in this primitive mammal.     

Effects of food restriction and social cues on sexual maturation and growth in male musk shrews (Suncus murinus)

In the first experiment, the effects of food availability on growth and reproduction were assessed by placing male musk shrews on 3 different feeding schedules, i.e. fed ad libitum, fed 50% of the amount eaten by the ad-libitum controls or fed 25% of the amount eaten by the ad-libitum controls. After 25 days, growth and sexual maturation were significantly retarded in both of the food-restricted groups compared to the control group. In the second experiment, the combined effects of food availability and social cues were investigated in juvenile males that were either fed ad libitum (during the day) or placed on a restricted diet known to inhibit growth and reproduction. Half of these males were either housed alone or with an adult female (separated from female during the day by a wire barrier, but in full contact at night). The ad-libitum-fed males living with a female ate more food, gained more body weight and were more sexually mature than ad-libitum-fed animals living alone. Furthermore, males in the two food-restricted groups had lower body weights and were sexually immature compared with males in both of the ad-libitum-fed groups. Finally, there were little or no differences in growth and reproduction between animals in the two food-restricted groups. These results suggest that food availability is an important environmental regulator of the timing of sexual maturation, and that stimulatory social cues cannot override the inhibitory effects of an inadequate diet.     

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.     

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.     

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)     

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.     

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.     

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.     

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.     

Role of the ovary and adrenal gland in the sexual behavior of the musk shrew, Suncus murinus

The contributions of the ovary and the adrenal gland to sexual behavior were examined in the female musk shrew (Suncus murinus). Ovariectomy eliminated sexual behavior, and treatment with estradiol or testosterone restored it in almost all shrews. Progesterone was ineffective in this regard. Adrenalectomy, likewise, blocked sexual behavior in most females with intact ovaries. Taken together, these results suggest that sexual behavior in this primitive eutherian mammal is normally modulated by secretions of both the ovary and the adrenal gland.     

Characterization of drug responses of the intestine of the house musk shrew (Suncus murinus)

• 1.1. To characterize the pharmacological properties of the intestine of Suncus murinus, an Insectivora, the effects of drugs on the mechanical activity of the isolated intestine were examined.
• 2.2. The drugs examined include: (1) autonomie drugs such as acetylcholine, nicotine, norepinephrine, epinephrine and isoproterenol; (2) autacoids such as histamine and 5-hydroxytryptamine; (3) peptides such as bradykinin, thyrotropin releasing hormone and methionine-enkephalin.
• 3.3. The present study shows that the pharmacological responses of the intestine of Suncus murinus, especially to isoproterenol, histamine and peptides, have some properties distinct from those of rodents.

     

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.     

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)     

Inter-male mating-like behavior in the domesticated house musk shrew, Suncus murinus

In the present study, inter-male interaction of the domesticated house musk shrew was observed in detail under laboratory conditions. In most cases, during inter-male interaction, male house musk shrews exhibited a sequence of behavior items including tail-wagging, following, mounting and thrusting. In the minority of cases, males did not progress beyond following. Offensive behavior was not sufficiently violent to cause injury. It appeared that role assignment was decided by contact manner and vocalization. One of fundamental characters of this animal made a start of following, in which one shrew followed another, who touched and then separated. Role assignment (i.e., which male led and which followed) was decided in status battle. Roles were often reversed during following. Following behavior was maintained by 'polite' mutual contact, and the interaction progressed to thrusting in the majority cases. After role assignment, the variation in contact manner decreased. The ratio of time spent in front-and-behind contact to that spent in multi-lateral contact increased when both males commenced following behavior simultaneously. This ratio was maintained until the following male snapped after he finished thrusting. Even if the following male did not reach thrusting, he mounted the preceding male. The pairs who did not reach thrusting repeated following behavior or mounting. In those cases, while one male concentrated on touching the other to maintain following, the other attempted to divert attention from the following behavior. Male shrews were able to reach thrusting irrespective of sex.     

The morphological and histological characters of the male external genitalia of the house musk shrew, Suncus murinus

External genitalia are the reproductive organs necessary for efficient copulation and internal fertilization in various mammalian species. Their morphogeneses display significant morphological and developmental differences among species. The house musk shrew, Suncus murinus (hereafter described as suncus) is a species of the order Insectivora, which has been considered as primitive and one of the earliest eutheria phylogenetically. Comparative anatomical analyses of phylogenetically different mammals will contribute to the better understanding of morphological diversity of external genitalia. This study performed various anatomical and histological analyses concerning the organization of the external genitalia of male suncus. It was shown that the external genitalia of suncus possessed a muscular structure, which we proposed as musculus ischiocavernosus dorsalis of suncus. The musculus ischiocavernosus dorsalis is originated from the inner surface of the tuber ischiadicum and was allocated adjacent to the corpus cavernosum penis. In addition, a pair of alpha-smooth muscle actin positive muscles was located bilaterally to the urethra. This unique morphology of the external genitalia of suncus males may provide a unique model system to investigate genital morphogenesis.     

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.