Retinofugal projections in the house musk shrew, Suncus murinus.

Retinofugal projections in the house musk shrew (Suncus murinus) were studied with the WGA-HRP method. After WGA-HRP injection into the vitreous cavity of one eye, terminal labeling was seen in the suprachiasmatic nucleus, dorsal and ventral lateral geniculate nuclei, pretectum and superficial layer of the superior colliculus. The terminal labeling in the suprachiasmatic nucleus was more marked on the side ipsilateral to the injection than on the contralateral side, whereas that in other regions was seen mainly on the contralateral side. A retino-intergeniculate leaflet projection was observed. No unequivocal terminal labeling was found in the lateroposterior thalamic nucleus.     

Immunohistochemical study of adenohypophysial gonadotropes in the musk shrew, Suncus murinus L. (Insectivora)

Most gonadotropes in the pituitary of male Suncus murinus L. are immunostained with both LH beta and FSH antisera, whereas only a few gonadotropes are positive only for LH beta. The former gonadotropes consist of polygonal or polyhedral cells of medium size, and can be identified by the presence of two types of secretory granules of low density: smaller ones (about 150-250 nm in diameter) which are spherical in shape, and larger ones of irregular form with a maximum diameter of about 1,500 nm. The endoplasmic reticulum is not prominent, while the Golgi apparatus is distinct. Mitochondria are found throughout the cytoplasm but are often concentrated in and around the region of the Golgi apparatus. These fine structural features are somewhat similar to those of the classical Barnes "FSH cells" and Kurosumi-Oota "FSH cells".     

Potential energetic implications of emesis in the house musk shrew (Suncus murinus)

During the course of studies investigating novel anti-emetic therapies we serendipitously observed a previously unreported behaviour related to emesis in the house musk shrew. This behaviour consisted of spontaneous ingestion of vomit in about half of the animals (males and females) in which emesis was induced by either nicotine (4 mg kg-1 sc.) or horizontal motion (1 Hz, 4 cm, 10 min). Analysis of vomit samples and gastric contents revealed that in a "typical" individual the gastric contents would be voided by as few as 3 vomits. Energetic calculations of the metabolisable energy of food, gastric contents, vomit and field metabolic rate (FMR) predict that a male weighing 60 g would lose 17.3% of its hourly energy requirement for FMR if it vomited once. A 40 g female, however, would experience an hourly energy loss of approximately 22.8%. The possible energetic consequences and resulting ecological implications of this unusual behaviour are discussed.     

Osteology of the musk shrew (Suncus murinus)

In the present study using 29 adult musk shrew of both sexes, most findings were identified to be similar to those by Sharma (1958) on the osteology , and there was no remarkable difference between skeletal structure of wild musk shrew in India and that of breeding species in Japan except the number of the vertebra lumbalis and existance of the dens caninus . However, it was elucidated that the os articulare coccygis like H-letter in shape is characteristic for this animal, and shows 17 components as many between interspace ventral to the adjacent os coccygis , and that there exists the proc. spinosus appendicularis nominated newly over the vertebra thoracica II, which plays significant role to head and neck as origin or insertion for strong m. serratus dorsalis, m. splenius, and m. semispinalis .     

Retinal cysts in the eye of the Asian musk shrew, Suncus murinus, (Mammalia, Insectivora)

The development of retinal cysts in the eye primordia of Suncus murinus embryos was studied. Retinal infoldings were first identified in the 17.5-day-old embryo (crown rump length--CRL = 6.3 mm). At this time, the apex of the developing retinal fold could be identified attached to the lens. The pigmented epithelium did not take part in the formation of the cyst. The retinal fold closed, to form a cyst, by day 23 of embryonic development (CRL = 14.0 mm). The newly formed retinal cyst remained continuous with the retina and extended toward the lens where it attached to the lens epithelium. Retinal cysts had an oval, bilaterally symmetrical shape and a narrow lumen, which, lined by the internal limiting membrane, occasionally contained cellular debris. The dimensions of the cysts were usually 100 to 150 microns (diameter) by 200 to 250 microns (length). Retinal cysts appeared in 45 per cent of the embryos examined.     

Structure of the palate and pharynx in the house musk shrew (Suncus murinus)

Anatomical features of the palates and pharynges in Suncus murinus were examined through a dissecting microscope. The palatopharyngei (PP) on both sides join at the caudal, median line of the palatine velum and converge in an area immediately caudal to a mucosal notch, the pharyngeal torus before radiating into the dorsal wall of the esophagus. Some muscle bundles of the PP are attached to the veli palatini cartilage. The nasopharyngeal cartilage is situated rostral to curved mucosal plicae of the palatine velum. The pharyngeal torus interlocks with the rostrally lying corniculate tubercles. The structural relationships of the corniculate tubercles, pharyngeal torus and PP suggest that muscular tension of the PP sustains the epiglottis and retains it in the nasopharynx, i.e. the PP acts as a circumscribed sphincter around the epiglottis and establishes a short, secure air passageway to the larynx. The nasopharyngeal and veli palatini cartilages could keep the passageway in shape.     

Scent marking in the musk shrew (Suncus murinus)

The hormonal regulation of scent marking was examined in male and female musk shrews. In males castration depressed flank, perineal, and throat marking frequencies, and a physiological dose of testosterone restored perineal and throat marking to intact levels. Females exhibited high levels of marking whether tested in a non-pregnant state, late in gestation, or when post-partum. Moreover, ovariectomy had no influence on marking behavior. Adrenalectomy, in addition to ovariectomy, caused a significant decline in two of the three marking behaviors examined, flank and perineal marking. These results demonstrate that these sexually monomorphic scent marking behaviors are under gonadal control in male musk shrews, but not in females. Furthermore, two of the three different types of scent marking examined in female musk shrews appear to require adrenal hormones. Throat marking in the female musk shrew apparently is not regulated by steroidal hormones.     

Unique structure of the esophago-gastric junction of the house musk shrew (Suncus murinus)

The house musk shrew (Suncus murinus) belongs to the Order Insectivora, and has been used for the research in comparative anatomy as one of the most primitive placental mammals. Another feature of this shrew is its ability to easily vomit which mimics the human emesis or motion sickness response. The house musk shrew has thus been utilized as a rare small experimental animal for studies on the neurophysiological mechanism of vomiting. However, there is no report investigating the morphological background of vomiting in this species. The purpose of this study is to provide detailed morphological and histological features of the house musk shrew stomach as they possibly correlate to vomiting. The stomachs of ten female house musk shrews were used. Six of them were the wild type (Jic: SUN), two were the high-emesis strain (Jic: SUN-Her) and the rest of them were the low-emesis strain (Jic: Sun-Ler). In addition to the macroscopic anatomy, the region of esophago-gastric (EG) junction and the gastric groove were observed using the light and transmission electron microscopy. Although evident differences in structure of stomach were not found among the three strains, some interesting findings in comparative anatomy were noted. The circular valve-like thick fold was seen at the cardiac portion, which protruded into the esophageal lumen forming a deep groove between its frilled edge and the esophagus. The second frilled ridge was often found as inner ridge of this valve-like thick fold. The esophago-gastric junction between the stratified squamous and the simple columnar epithelium was found at the edge of the second frilled ridge. The lamina propria of the frilled edge was occupied by loose connective tissue and many large lumens of lymphatic vessels. The lamina muscularis mucosae, which developed in the esophageal region, was not in the main frilled edge. A well-developed inner muscle layer was found around the base of the fold, which seemed to correspond to the human lower esophageal sphincter. Cardiac glands occupied most of the thick cardiac wall, forming complicated crypts lined by simple columnar epithelium, and ducts of cardiac gland opened to these crypts. Since the house musk shrew has no esophageal gland, these cardiac glands may actively protect the lower part of the esophagus. In the cardiac wall, the inner circular and outer longitudinal muscle layer largely crossed each other obliquely as same as other reports. The transition area from the striated to the smooth muscle was observed in the sphincter surrounding the distal end of the cardiac wall. The gastric groove, lined by simple columnar epithelium in the lesser curvature, which has been reported to play a role as a shortcut from the cardia to the pylorus in other species including rodents, was also confirmed in the house musk shrew. The mucosal fold in the boundary between the esophageal and the gastric epithelium of house musk shrew may correspond to the structure called the limiting ridge (in mouse, rat and hamster), the teeth-like fimbria or Grenzfalten (in vole), and the gastric teeth (in crustacean and mollusk). The valve-like mucosal fold protruding into the esophageal cavity, the well developed huge cardiac glands, and the cardiac sphincter localized distally to the cardiac gland appear to facilitate the regurgitation of the stomach content, that is, vomiting. These findings suggest that this structure might have developed to support the feeding habit of house musk shrew, and that the differences of strains in vomiting may be determined by neurophysiological mechanisms.     

Induction of emetic response to staphylococcal enterotoxins in the house musk shrew (Suncus murinus)

The emetic responses induced by staphylococcal enterotoxin A (SEA), SEB, SEC2, SED, SEE, SEG, SEH, and SEI in the house musk shrew (Suncus murinus) were investigated. SEA, SEE, and SEI showed higher emetic activity in the house musk shrew than the other SEs. SEB, SEC2, SED, SEG, and SEH also induced emetic responses in this animal model but relatively high doses were required. The house musk shrew appears to be a valuable model for studying the mechanisms of emetic reactions caused by SEs.     

Scanning electron microscopy of the ovary in the house musk shrew, Suncus murinus

The structure of the house musk shrew (Suncus murinus) ovary, prepared by the Osmium-DMSO-Osmium method, was examined with a scanning electron microscope. Many ovarian follicles in various stages of development can be seen in the musk shrew ovary, but fully matured follicles (Graafian follicles) are never observed. In the inner layer of zona granulosa of the preantral follicles, the follicular cells containing a large amount of glycogen deposition in the cytoplasm are observed. Folded and collapsed zona pellucida surrounding the remnant of the degenerated oocyte, which is thought to be a residual form of atretic follicle, is observed in a small, crypt-like depression on the surface of the ovary where it has been split by cracking.     

Lower axial skeleton of the musk shrew (Suncus murinus)

Macroscopic structure as well as pre- and postnatal development of the lumbar, sacral, and caudal vertebrae of the musk shrew (Suncus murinus, Insectivora) were observed. The lumbar vertebrae possess two pairs of unusual processes, hyperapophyses and hypapophyses. The hyperapophyses are located on the dorsal surface of the caudal articular processes of all the lumbar vertebrae, whereas the hypapophyses are found on the caudal part of the ventral surface of the bodies in the first few lumbar vertebrae. The former gives attachment to the Mm. rotatores lumborum and the latter to the Mm. psoas major and minor. The articular processes of the lumbar vertebrae are oriented more horizontally compared with those in other mammals. The sacrum is very narrow transversely due to poor development of the ventrolateral wing. The auricular surface includes cranial parts of the wing and of the fused vertebral arches as well as the cranial articular process of the first sacral vertebra. In the caudal vertebrae, chevron bones are H-shaped when viewed ventrally, and give attachment to tendons of the caudal muscles. This report describes the relationships between the structural peculiarities of the lower axial skeleton and the locomotive habits of the musk shrew.     

Gross anatomical study of the sympathetic cardiac nerves in the house musk shrew (Suncus murinus)

The sympathetic cardiac nerves originating from the cervical and upper thoracic sympathetic ganglia in the house musk shrew (Suncus murinus) were examined using macroscopic and whole‐mount immunohistochemical methods. Based on the results, the nerves were macroscopically classified into the following three groups: nerves innervating the cervical sympathetic ganglia mainly to the arterial porta of the heart; nerves supplying the stellate and thoracic sympathetic ganglia at the level of T2–T5 or T6 for both the arterial and venous portae of the heart; and nerves innervating the thoracic sympathetic ganglia at the level of T4–T9 to the esophagus and lung and then the heart via the blood vessels within the mediastinal pleura. These findings in the house musk shrew suggest a possible primitive morphological pattern of the cervical and thoracic sympathetic nervous system that may be related to those in other mammals, including humans. Anat Rec, 2007. © 2007 Wiley‐Liss, Inc.     

Structure of the middle ear and auditory tube in the house musk shrew, Suncus murinus

Anatomical features of the middle ear and auditory tube (AT) in the house musk shrew, Suncus murinus, were examined by dissection and light microscopy. The tensor veli palatini (TVP) and tensor tympani (TT) have no connections with the wall or cartilage of the AT although they are connected by the intermediate tendon. None of the levator veli palatini (LVP) muscle bundles are attached to the AT. The salpingopharyngeus (SA) alone has its origin on the caudal edge of the tubal cartilage. The origin extends to the pharyngeal two thirds of the cartilage. The SA originates perpendicular to the AT and runs caudomedialward. Some SA muscle bundles intermingle with those of the palatopharyngeus to end on the dorsal wall of the pharynx. The observations provide no evidence that the TVP, LVP and TT have any role in AT function. The only muscle affecting the AT function in S. murinus is the SA, and it would be the AT dilator.     

Three-dimensional distribution patterns of PRL,GH and ACTH cells in the house musk shrew ( Suncus murinus)

Despite a multitude of reports on the classification and distribution of anterior pituitary cells, no previous study has attempted to obtain the three-dimensional (3D) and computer-graphic distribution pattern of each cell type in the whole pituitary. Therefore, we mapped the anterior pituitary cells of the house musk shrew ( Suncus murinus) and found a distinct cellular distribution pattern. Serial horizontal sections of whole shrew pituitaries were stained immunohistochemically for prolactin (PRL), growth hormone (GH), and adrenocorticotropic hormone (ACTH) cells. The contours of positive cells and the anterior, intermediate, and posterior lobes in each section were digitized for 3D visualization by a volume rendering method. The reconstructed images and virtual frontal and sagittal slices were examined in detail. On the 3D reconstructed images, the PRL and GH cells had similar distribution patterns, although the former were concentrated in the dorsolateral and ventrocentral portions, and the latter in the dorsocentral portions of the anterior lobe. On both sides of the pituitary stalk, there lay portions that were conspicuous by scarcity of PRL and GH cells. ACTH cells were widely scattered throughout the whole anterior lobe, but they were very few in the above portions and the dorsocentral portions where GH cells were concentrated. No sex difference in the distribution patterns of each cell type was observed. However, PRL cells in females were more numerous than in males, whereas the opposite was true for GH and ACTH cells. We discuss the relationship between the formation of the spatial distribution patterns and anterior pituitary ontogeny.     

Differential activity of drugs to induce emesis and pica behavior in Suncus murinus (house musk shrew) and rats

We have previously reported that emetic stimuli induce kaolin ingestion behavior (pica behavior) in rats and mice (i.e., species that do not have the emetic reflex) and that the behavior may be analogous to gastrointestinal discomfort, such as nausea and emesis. We hypothesized that pica behavior may also occur in species capable of vomiting and that it may serve as an additional index of discomfort relevant to antiemetic drug development. The present experiments were conduced using Suncus murinus and rats and kaolin consumption was measured at 24 h after the administration of nicotine (1.25-5 mg/kg, s.c.), copper sulfate (10-120 mg/kg, p.o.), lithium chloride (50-200 mg/kg, i.p.) and cisplatin (1-30 mg/kg, i.p.). In S. murinus, all treatments, excepting lithium chloride, were emetic but none induce kaolin consumption. Conversely, all treatments induced kaolin consumption in rats without inducing emesis. The results indicate that pica behavior is not likely to be useful to assess gastrointestinal discomfort in S. murinus.     

Effect of daily linear acceleration training on the hypergravity-induced vomiting response in house musk shrew (Suncus murinus)

The effects of repeated linear acceleration training and the antimotion sickness drug, promethazine, on hypergravity-induced motion sickness were examined in musk shrew (Suncus murinus), which is known to show a vomiting response to motion stimulation. Animals were assigned into five groups: vestibular intact, untreated animals (Sham), vestibular lesioned (VL) animals, vestibular intact animals with promethazine hydrochloride administered as daily drinking water (Prom), vestibular intact animals who underwent horizontal linear accelerator motion training (Train), and vestibular intact animals treated with both promethazine hydrochloride and linear acceleration training (Prom + Train). In Sham animals, the number of vomiting episodes was 14 ± 2 during 2 G exposure for 10 min, and was accompanied by intense Fos expression in the medial vestibular nucleus (MVe), the nucleus of the solitary tract (NTS), the area postrema (AP), and the paraventricular hypothalamic nucleus (PVN). The vomiting response and Fos expression were completely abolished in VL animals, indicating that these responses are mediated via the vestibular system. Although Train and Prom animals experienced a significantly reduced number of hypergravity-induced vomiting episodes compared with Sham animals, the effect was significantly greater in Train animals than in Prom animals. Fos expression in the NTS, AP, and PVN were significantly more reduced in Train animals than in Prom animals. Higher dose of bolus injection of promethazine (50 mg/kg, i.p.) completely abolished the vomiting episodes, although the animals were drowsy and sedated due to side effects. In conclusion, daily linear acceleration training and promethazine could prevent the hypergravity-induced vomiting episodes.