Aerodynamics of hovering flight in the long-eared bat Plecotus auritus.
(1/1577)
Steady-state aerodynamic and momentum theories were used for calculations of the lift and drag coefficients of Plecotus auritus in hovering flight. The lift coefficient obtained varies between 3-1 and 6-4, and the drag coefficient between --5-0 and 10-5, for the possible assumptions regarding the effective angles of attack during the upstroke. This demonstrates that hovering flight in Plecotus auritus can not be explained by quasi-steady-state aerodynamics. Thus, non-steady-state aerodynamics must prevail. (+info)
Corticofugal amplification of facilitative auditory responses of subcortical combination-sensitive neurons in the mustached bat.
(2/1577)
Recent studies on the bat's auditory system indicate that the corticofugal system mediates a highly focused positive feedback to physiologically "matched" subcortical neurons, and widespread lateral inhibition to physiologically "unmatched" subcortical neurons, to adjust and improve information processing. These findings have solved the controversy in physiological data, accumulated since 1962, of corticofugal effects on subcortical auditory neurons: inhibitory, excitatory, or both (an inhibitory effect is much more frequent than an excitatory effect). In the mustached bat, Pteronotus parnellii parnellii, the inferior colliculus, medial geniculate body, and auditory cortex each have "FM-FM" neurons, which are "combination-sensitive" and are tuned to specific time delays (echo delays) of echo FM components from the FM components of an emitted biosonar pulse. FM-FM neurons are more complex in response properties than cortical neurons which primarily respond to single tones. In the present study, we found that inactivation of the entire FM-FM area in the cortex, including neurons both physiologically matched and unmatched with subcortical FM-FM neurons, on the average reduced the facilitative responses to paired FM sounds by 82% for thalamic FM-FM neurons and by 66% for collicular FM-FM neurons. The corticofugal influence on the facilitative responses of subcortical combination-sensitive neurons is much larger than that on the excitatory responses of subcortical neurons primarily responding to single tones. Therefore we propose the hypothesis that, in general, the processing of complex sounds by combination-sensitive neurons more heavily depends on the corticofugal system than that by single-tone sensitive neurons. (+info)
Co-expression of cytokeratins and vimentin by highly invasive trophoblast in the white-winged vampire bat, Diaemus youngi, and the black mastiff bat, Molossus ater, with observations on intermediate filament proteins in the decidua and intraplacental trophoblast.
(3/1577)
Histological and immunocytochemical studies of gravid reproductive tracts obtained from the white-winged vampire bat (Diaemus youngi) and the black mastiff bat (Molossus ater) have established that both species develop unusually invasive trophoblast. This is released by the developing discoidal haemochorial placenta, expresses both cytokeratins and vimentin, and invades the myometrium and adjacent tissues (including the ovaries) via interstitial migration within the walls of maternal blood vessels. Hence, this trophoblast is noteworthy for the extent to which it undergoes an epithelial-mesenchymal transformation. In Molossus, it originates from the cytotrophoblastic shell running along the base of the placenta, is mononuclear, and preferentially invades maternal arterial vessels serving the discoidal placenta. This trophoblast may have a role in dilatation of these vessels when the discoidal placenta becomes functional. In Diaemus, the highly invasive trophoblast appears to originate instead from a layer of syncytiotrophoblast on the periphery of the placenta is multinucleated, and vigorously invades both arterial and venous vessels. During late pregnancy, it becomes extensively branched and sends attenuated processes around many of the myometrial smooth muscle fibres. In view of its distribution, this trophoblast could have important influences upon myometrial contractility and the function of blood vessels serving the gravid tract. Other aspects of intermediate filament expression in the uteri and placentae of these bats are also noteworthy. Many of the decidual giant cells in Molossus co-express cytokeratins and vimentin, while the syncytiotrophoblast lining the placental labyrinth in Diaemus late in pregnancy expresses little cytokeratin. (+info)
Vectors of Chikungunya virus in Senegal: current data and transmission cycles.
(4/1577)
Chikungunya fever is a viral disease transmitted to human beings by Aedes genus mosquitoes. From 1972 to 1986 in Kedougou, Senegal, 178 Chikungunya virus strains were isolated from gallery forest mosquitoes, with most of them isolated from Ae. furcifer-taylori (129 strains), Ae. luteocephalus (27 strains), and Ae. dalzieli (12 strains). The characteristics of the sylvatic transmission cycle are a circulation periodicity with silent intervals that last approximately three years. Few epidemics of this disease have been reported in Senegal. The most recent one occurred in 1996 in Kaffrine where two Chikungunya virus strains were isolated from Ae. aegypti. The retrospective analysis of viral isolates from mosquitoes, wild vertebrates, and humans allowed to us to characterize Chikungunya virus transmission cycles in Senegal and to compare them with those of yellow fever virus. (+info)
Human rabies--Virginia, 1998.
(5/1577)
On December 31, 1998, a 29-year-old man in Richmond, Virginia, died from rabies encephalitis caused by a rabies virus variant associated with insectivorous bats. This report summarizes the clinical and epidemiologic investigations by the Virginia Department of Health and CDC. (+info)
Single cortical neurons serve both echolocation and passive sound localization.
(6/1577)
The pallid bat uses passive listening at low frequencies to detect and locate terrestrial prey and reserves its high-frequency echolocation for general orientation. While hunting, this bat must attend to both streams of information. These streams are processed through two parallel, functionally specialized pathways that are segregated at the level of the inferior colliculus. This report describes functionally bimodal neurons in auditory cortex that receive converging input from these two pathways. Each brain stem pathway imposes its own suite of response properties on these cortical neurons. Consequently, the neurons are bimodally tuned to low and high frequencies, and respond selectively to both noise transients used in prey detection, and downward frequency modulation (FM) sweeps used in echolocation. A novel finding is that the monaural and binaural response properties of these neurons can change as a function of the sound presented. The majority of neurons appeared binaurally inhibited when presented with noise but monaural or binaurally facilitated when presented with the echolocation pulse. Consequently, their spatial sensitivity will change, depending on whether the bat is engaged in echolocation or passive listening. These results demonstrate that the response properties of single cortical neurons can change with behavioral context and suggest that they are capable of supporting more than one behavior. (+info)
Comparative anatomy of the vomeronasal organ complex in bats.
(7/1577)
The morphology of the vomeronasal organ complex was histologically described in eight out of fourteen chiropteran species investigated. Of the six families examined, all except the family Pteropodidae (suborder Megachiroptera) were found to have at least one member possessing the organ. The organ is best developed in phyllostomatids. It is absent in vespertilionids (including a Myotis embryo) except in Miniopterus. An accessory olfactory bulb is reported for the first time in the latter. The organ is described for the first time in Rhinopoma, Megaderma, and Hipposideros. The organ in Rhinolophus is also described. Homologous anterior nasal cartilages and patent nasopalatine ducts are present in all species. The organ occupies the anterior ventral nasal septum region. In Megaderma and Hipposideros it is level with the nasal cavity floor. Areas of epithelium similar to olfactory epithelium have been observed in some organs. Epithelia, vascular sinuses, vomeronasal nerves, paravomeronasal ganglia, accessory olfactory bulbs, and vomeronasal glands have been investigated. In bats with regressed or rudimentary organs (Megaderma, Rhinopoma, Rhinolophus, Hipposideros) accessory olfactory bulbs could not be identified. Thus, presence of the organ does not necessarily indicate presence of the accessory olfactory bulb. Septal pockets located superior to the organ complex and lined with pseudostratified columnar epithelium are described in Hipposideros and may play a part in nasophonation. A unique role is proposed for the organ in the feeding behaviour of Desmodus. The desirability of extending the useful terms 'diosmatic' and 'monosmatic' to all vertebrates in reference to their respective possession or lack of the vomeronasal organ is suggested. (+info)
On the homology of the alisphenoid.
(8/1577)
The relationships of the elements of the cavum epiptericum in a hypothetical primitive mammalian precursor are reconstructed, and these are analysed in relation to the development of recent mammals, especially the fruit bat Nyctinomus johorensis. The alisphenoid in mammals is part cartilage bone, part membrane bone. The mammalian homologue of the primitive reptilian processus ascendens appears to be internal to the maxillary nerve. If so, then the 'lamina ascendens', that portion of the alisphenoid of mammals which lies between maxillary and mandibular nerves, cannot be a true processus ascendens but must be neomorphic. It is suggested that the mammalian lamina ascendens arose from an upgrowth of the root of the quadrate ramus of the epipterygoid in cynodonts, separating foramen rotundum from foramen ovale. In Ditremata the alisphenoid is completed by an element of membrane bone; this, it is suggested here, originated as the anterior lamina of the periotic in cynodonts, which is retained in monotremes. It is suggested that the alicochlear commissure of mammals originated as the later flange of the periotic in cynodonts. (+info)