Receptive fields and response properties of neurons in the star-nosed mole's somatosensory fovea.
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Star-nosed moles have an extraordinary mechanosensory system consisting of 22 densely innervated nasal appendages covered with thousands of sensitive touch domes. A single appendage acts as the fovea and the star is constantly shifted to touch this foveal appendage to objects of interest. Here we investigated the receptive fields on the star and the response properties of 144 neurons in the mole's primary somatosensory cortex (S1). Excitatory receptive fields were defined by recording multiunit activity from the S1 representations of the nasal appendages that form the star, while stimulating the touch domes on the skin surface with a small probe. Receptive fields were among the smallest reported for mammalian glabrous skin, averaging <1 mm(2). The smallest receptive fields were found for the fovea representation, corresponding to its greater cortical magnification. Single units were then isolated, primarily from the representation of the somatosensory fovea, and the skin surface was stimulated with a small probe attached to a piezoelectric wafer controlled by a computer interface. The response properties of neurons and the locations of inhibitory surrounds were evaluated with two complementary approaches. In the first set of experiments, single microelectrodes were used to isolate unit activity in S1, and data were collected for stimulation to different areas of the sensory star. In the second set of experiments, a multi-electrode array (4 electrodes spaced at 200 microm in a linear sequence) was used to simultaneously record from isolated units in different cortical areas representing different parts of the sensory periphery. These experiments revealed a short-latency excitatory discharge to stimulation of the fovea followed by a long-lasting suppression of spontaneous activity. Sixty-one percent of neurons responded with an excitatory OFF response at the end of the stimulus; the remaining 39% of cells did not respond or were inhibited at stimulus offset. Stimulation of areas surrounding the central receptive field often revealed inhibitory surrounds. Forty percent of the neurons that responded to mechanosensory stimulation of the receptive field center were inhibited by stimulation of surrounding areas of skin on the same appendage. In contrast to neurons in rodent barrels, few neurons within a stripe representing an appendage responded to stimulation of neighboring (nonprimary) appendages on the snout. The small receptive fields, short latencies, and inhibitory surrounds are consistent with the star's role in rapidly determining the locations and identities of objects in a complex tactile environment. (+info)
Fine structural changes in the epididymal epithelium of moles (Talpa europaea) throughout the year.
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The epididymis of the European mole (Talpa europaea) was studied by light and electron microscopy. In the sexually active animal, spermatozoa mature during their passage through the epididymis and the structure of the cells lining the duct suggests a clear regional division into initial, middle and terminal segments. Numerous intra-epithelial vesicles were present in the distal part of the middle segment of sexually active moles and the lining epithelium in the terminal segment appeared to be secretory. Variation in the sensitivity of different regions of the epididymis to androgens was apparent: the principal cells of the initial segment were morphologically active only during the peak of the breeding season in spring, while the cells of the terminal segment became active earlier and remained so for longer. During sexual regression, many autophagic vacuoles were found in the principal cells, and these became transformed into lipofuscin pigment granules. Cells heavily laden with these granules appeared concurrently in the lining epithelium. It is suggested that such cells may be involved in the regression of principal cells by means of heterophagic activity. A similar situation was also observed, but to a lesser extent, at the beginning of the breeding season. Outside the breeding season, the organelles of the principal cells were poorly developed throughout the epididymis, and lipofuscin pigment granules remained in the principal and basal cells of adults. Such granules were seldom seen in immature animals. (+info)
Ultrastructure of vascular capillary of lingual filiform papillae in the mole (Mogella wogura wogura).
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Detailed observation of the structure of filiform papillae (FP) and microvasculature of those papillae in Japanese Azuma mole were described. In the anterior and medial regions, FP was cylinder in shape with two processes. In the posterior region, it had a long, sharp conical shape. The microvascular casts showed two types of hairpin-shaped capillary loops on three regions of the tongue. In the anterior and medial regions, the end of the capillary loops were shaped like a spoon. In contrast, in the posterior region, it was knot-like end of capillary loop. Since the shape of capillary loop was more complex in the anterior and medial regions than that in the posterior region, it was speculated that the spoon-like end of capillary loops of the FP in the anterior and medial regions supply nutrients to the filiform papillary cells and may be related to the movement of the tongue during mastication in Japanese Azuma mole. (+info)
Abnormal sex-duct development in female moles: the role of anti-Mullerian hormone and testosterone.
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We have performed a morphological, hormonal and molecular study of the development of the sex ducts in the mole Talpa occidentalis. Females develop bilateral ovotestes with a functional ovarian portion and disgenic testicular tissue. The Mullerian ducts develop normally in females and their regression is very fast in males, suggesting a powerful action of the anti-Mullerian hormone in the mole. RT-PCR demonstrated that the gene governing this hormone begins to be expressed in males coinciding with testis differentiation, and expression continues until shortly after birth. Immunohistochemical studies showed that expression occurs in the Sertoli cells of testes. No expression was detected in females. Wolffian duct development was normal in males and degenerate in prenatal females, but developmental recovery after birth gave rise to the formation of rudimentary epididymides. This event coincides in time with increasing serum testosterone levels and Leydig cell differentiation in the female gonad, thus suggesting that testosterone produced by the ovotestes is responsible for masculinisation of female moles. During postnatal development, serum testosterone concentrations decreased in males but increased in females, thus approaching the levels that adult males and females have during the non-breeding season. (+info)
Variation in ovarian morphology in four species of New World moles with a peniform clitoris.
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Female moles of the Old World genus Talpa display a curious suite of reproductive features that include a peniform clitoris and ovaries with a discrete interstitial gland or testis-like region (so-called 'ovotestes'). The masculinization of the female external genitalia in Talpa has accordingly been linked with secretion of androgens from the interstitial gland region of the fetal gonad. Although their ovarian morphology has received less attention, some species of New World moles also have ovaries with a pronounced interstitial gland (for example star-nosed mole, Condylura cristata), whereas females of other species do not (for example eastern mole, Scalopus aquaticus). Although it is difficult to determine the sex of both Old and New World moles, published accounts describing the external genitalia of female moles are available only for Talpa. The hypothesis that masculinization of the female external genitalia in moles is associated with the presence of an ovarian interstitial gland (OIG) was tested in the present study by using a comparative approach to determine whether these features are ever found in isolation of one another. Three genera of North American moles (Scapanus, Condylura and Neurotrichus) were studied and a peniform clitoris was found in all three species, but OIG were found in only two of three genera. The ovaries of S. latimanus and S. orarius were unremarkable, with no evidence of a discrete interstitial gland or testis-like region. Mapping these results onto recent talpid phylogenies indicates that loss of the bipolar ovarian morphology is a derived trait in Scapanus, and conclusively demonstrates that masculinization of the external genitalia in female moles can develop in the presence or absence of 'ovotestes'. (+info)
Testis-like development of gonads in female moles. New insights on mammalian gonad organogenesis.
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Moles are unique among mammals because all females of several species of genus Talpa have bilateral ovotestes (gonads with both ovarian and testicular tissue). Based on the analysis of a large sample of embryos, foetuses and infants over a 13-year period, we have studied the development of the gonads in male and female moles of the species Talpa occidentalis. Several new field and laboratory procedures were developed specifically to obtain and manage this singular material. Our results reveal that gonads of female moles develop according to a testis-like pattern, which includes cord formation and mesonephric cell migration, and begins at the same time as testis differentiation in males. The first signs of sex differentiation do not appear in males but in females. Female (but not male) gonads are regionalised with a cortex (precursor of the ovarian tissue) and a medulla (precursor of the testicular tissue). Germ cells concentrate only in the cortex, so that the medulla soon becomes sterile. Testicular tissue development is transiently retarded in females for about a week before birth, and resumes afterwards. Development of the ovarian tissue in females is considerably delayed with respect to that of testicular tissue in both males and females. The molecular characterisation of peritubular myoid cells, which are exclusive of testes, evidences the presence of testicular tissue in the gonads of female moles, which also contain Leydig cells. However, the absence of fully differentiated Sertoli cells indicates that these cells are not responsible for triggering the differentiation of such a testicular tissue. Our results are also discussed regarding the definition of Sertoli cell morphology and function, and the possible role of germ cells in the sex-reversal process. Differences observed between XX and XY gonad development in moles suggest that the mammalian testis-determining gene, SRY, has an "anti-regionalisation" role during gonadal development, at least in those mammalian species in which regionalisation of the female gonad occurs. (+info)
Cross-species chromosome painting in the golden mole and elephant-shrew: support for the mammalian clades Afrotheria and Afroinsectiphillia but not Afroinsectivora.
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Cross-species painting (fluorescence in situ hybridization) with 23 (human Homo sapiens (HSA)) chromosome-specific painting probes (HSA 1-22 and the X) was used to delimit regions of homology on the chromosomes of the golden mole (Chrysochloris asiaticus) and elephant-shrew (Elephantulus rupestris). A cladistic interpretation of our data provides evidence of two unique associations, HSA 1/19p and 5/21/3, that support Afrotheria. The recognition of HSA 5/3/21 expands on the 3/21 synteny originally designated as an ancestral state for all eutherians. We have identified one adjacent segment combination (HSA2/8p/4) that is supportive of Afroinsectiphillia (aardvark, golden mole, elephant-shrew). Two segmental combinations (HSA 10q/17 and HSA 3/20) unite the aardvark and elephant-shrews as sister taxa. The finding that segmental syntenies in evolutionarily distant taxa can improve phylogenetic resolution suggests that they may be useful for testing sequence-based phylogenies of the early eutherian mammals. They may even suggest clades that sequence trees are not recovering with any consistency and thus encourage the search for additional rare genomic changes among afrotheres. (+info)
Evolution of sensory specializations in insectivores.
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Although insectivores have traditionally been thought of as primitive mammals with few specializations, recent studies have revealed great diversity in the sensory systems and brain organization of members of this mammalian order. The present article reviews some of these findings in three insectivore families that are thought to form a monophyletic group. These include hedgehogs (Erinaceidae), moles (Talpidae), and shrews (Soricidae). Members of each group live in unique ecological niches, have differently specialized senses, and exhibit different behaviors. Hedgehogs have well-developed visual, auditory, and somatosensory systems. Shrews make use of visual and auditory cues, but appear to depend most heavily on touch, particularly through prominent vibrissae. Moles are somatosensory specialists with small eyes and ears and unique epidermal mechanoreceptors called Eimer's organs used to identify prey and investigate their environment. In contrast to historical views of the insectivore order, members of this group have discrete and well-organized cortical sensory areas with sharp borders as determined from both electrophysiological mapping and analysis of cortical histology. Comparison of cortical organization across species reveals a number of specializations, including expansion of cortical representations of important sensory surfaces, the addition of cortical areas to some processing networks, and the subdivision of areas into separate cortical modules. In the case of the star-nosed mole, the somatosensory system has a tactile fovea and shares a number of features in common with the visual systems of sighted mammals. (+info)