Localisation and origin of the bacteriochlorophyll-derived photosensitizer in the retina of the deep-sea dragon fish Malacosteus niger

Most deep-sea fish have a single visual pigment maximally sensitive at short wavelengths, approximately matching the spectrum of both downwelling sunlight and bioluminescence. However, Malcosteus niger produces far-red bioluminescence and its longwave retinal sensitivity is enhanced by red-shifted visual pigments, a longwave reflecting tapetum and, uniquely, a bacteriochlorophyllderived photosensitizer. The origin of the photosensitizer, however, remains unclear. We investigated whether the bacteriochlorophyll was produced by endosymbiotic bacteria within unusual structures adjacent to the photoreceptors that had previously been described in this species. However, microscopy, elemental analysis and SYTOX green staining provided no evidence for such localised retinal bacteria, instead the photosensitizer was shown to be distributed throughout the retina. Furthermore, comparison of mRNA from the retina of Malacosteus to that of the closely related Pachystomias microdon (which does not contain a bacterichlorophyll-derived photosensitzer) revealed no genes of bacterial origin that were specifically up-regulated in Malacosteus. Instead up-regulated Malacosteus genes were associated with photosensitivity and may relate to its unique visual ecology and the chlorophyll-based visual system. We also suggest that the unusual longwave-reflecting, astaxanthin-based, tapetum of Malacosteus may protect the retina from the potential cytotoxicity of such a system

On visual pigment templates and the spectral shape of invertebrate rhodopsins and metarhodopsins

The absorbance spectra of visual pigments can be approximated with mathematical expressions using as single parameter the absorbance peak wavelength. A comparison of the formulae of Stavenga et al. in Vision Res 33:1011–1017 (1993) and Govardovskii et al. in Vis Neurosci 17:509–528 (2000) applied to a number of invertebrate rhodopsins reveals that both templates well describe the normalized α-band of rhodopsins with peak wavelength > 400 nm; the template spectra are virtually indistinguishable in an absorbance range of about three log units. The template formulae of Govardovskii et al. in Vis Neurosci 17:509–528 (2000) describe the rhodopsin spectra better for absorbances below 10−3. The template predicted spectra deviate in the ultraviolet wavelength range from each other as well as from measured spectra, preventing a definite conclusion about the spectral shape in the wavelength range <400 nm. The metarhodopsin spectra of blowfly and fruitfly R1-6 photoreceptors derived from measured data appear to be virtually identical. The established templates describe the spectral shape of fly metarhodopsin reasonably well. However, the best fitting template spectrum slightly deviates from the experimental spectra near the peak and in the long-wavelength tail. Improved formulae for fitting the fly metarhodopsin spectra are proposed

Lateral spread of light adaptation in the rat retina

Recordings from the rat optic tract fibers were used to assess changes in sensitivity under various conditions of adaptation. An adapting background which excites only a small fraction of the rods can yet cause a several-fold change in sensitivity. A small adapting spot much more effectively decreases the cell's sensitivity to a superimposed test than to test spots in positions far from the adapting locus. Thus, adaptation spreads laterally but not uniformly throughout the ganglion cell center. Scattered light does not account for the spread, since a displaced adapting spot can be more effective than one superimposed on the test spot.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/23063/1/0000635.pd

Dark Activation of the Stationary Flight of the Fruitfly Drosophila

The fruitfly Drosophila and the housefly Musca develop, under conditions of stationary flight in still air, greater thrust in complete darkness than at constant illumination. This effect of “dark activation” has been demonstrated in earlier experiments with Musca by L. MAF-FEI. The present investigations establish similar reactions in Drosophila. The thrust reduction as a function of luminance resembles the transducer characteristics of light receptors. Dark activation can be elicited throughout the visual field. The effect is mainly mediated by the directly stimulated visual element of the compound eye, provided that the source luminance is low enough to prevent stray light effects in neighbouring elements. Covering the ocelli has little, if any, effect on the dark activation. An influence of position and distribution of the light stimulus on the dark activation is expected, respectively, from the discontinuities of the receptive fields and from possible lateral interactions between neighbouring visual elements. However, an estimate of the expected variations shows that a considerable experimental effort would be necessary to distinguish these variations from statistical fluctuations of the dark activation

The effects of rehabilitation on the muscles of the trunk following prolonged bed rest

Microgravity and inactivity due to prolonged bed rest have been shown to result in atrophy of spinal extensor muscles such as the multifidus, and either no atrophy or hypertrophy of flexor muscles such as the abdominal group and psoas muscle. These effects are long-lasting after bed rest and the potential effects of rehabilitation are unknown. This two-group intervention study aimed to investigate the effects of two rehabilitation programs on the recovery of lumbo-pelvic musculature following prolonged bed rest. 24 subjects underwent 60 days of head down tilt bed rest as part of the 2nd Berlin BedRest Study (BBR2-2). After bed rest, they underwent one of two exercise programs, trunk flexor and general strength (TFS) training or specific motor control (SMC) training. Magnetic resonance imaging of the lumbo-pelvic region was conducted at the start and end of bed rest and during the recovery period (14 and 90 days after re-ambulation). Cross-sectional areas (CSAs) of the multifidus, psoas, lumbar erector spinae and quadratus lumborum muscles were measured from L1 to L5. Morphological changes including disc volume, spinal length, lordosis angle and disc height were also measured. Both exercise programs restored the multifidus muscle to pre-bed-rest size, but further increases in psoas muscle size were seen in the TFS group up to 14 days after bed rest. There was no significant difference in the number of low back pain reports for the two rehabilitation groups (p = .59). The TFS program resulted in greater decreases in disc volume and anterior disc height. The SMC training program may be preferable to TFS training after bed rest as it restored the CSA of the multifidus muscle without generating potentially harmful compressive forces through the spine