Biomedical subjects

Birgit Greiner

Publications and source records attributed to Birgit Greiner.

12 recordsLinked to original sources

PubMed2006

Celestial polarization patterns during twilight.

Scattering of sunlight produces patterns of partially linearly polarized light in the sky throughout the day, and similar patterns appear at night when the Moon is bright. We studied celestial polarization patterns during the period of twilight, when the Sun is below the horizon, determining the degree and orientation of the polarized-light field and its changes before sunrise and after sunset. During twilight, celestial polarized light occurs in a wide band stretching perpendicular to the location of the hidden Sun and reaching typical degrees of polarization near 80% at wavelengths >600 nm. In the tropics, this pattern appears approximately 1 h before local sunrise or disappears approximately 1 h after local sunset (within 10 min. after the onset of astronomical twilight at dawn, or before its end at dusk) and extends with little change through the entire twilight period.

Journal Article↗

PubMed2006

Visual adaptations in the night-active wasp Apoica pallens.

The apposition compound eye of the nocturnal polistine wasp Apoica pallens shows, in comparison to the closely related diurnal wasp Polistes occidentalis, specific adaptations to vision at low light intensities. When considering recent work on nocturnal and diurnal bees, general principles for dim-light vision in hymenopterans become evident: The rhabdom diameters in nocturnal bees and wasps are 4 times wider compared to their diurnal relatives, leading to wide receptive fields, which in turn account for a 25-fold higher optical sensitivity. Interestingly, the rhabdom diameters in both nocturnal bees and wasps measure 8 mum, which may represent the maximum width for nocturnal hymenopteran apposition eyes. A ratio of 1.8 times larger eyes is present in the nocturnal bees and wasps, which in A. pallens is achieved by increasing the facet number, instead of enlarging the facets, as in nocturnal bees. Although this initially indicates spatial resolution to be important for the nocturnal wasp, the wide receptive fields of the rhabdoms will reduce its potentially high acuity. As the optical sensitivity alone cannot account for the 8 log units intensity difference between day and night, a possible role of neural summation within the first optic ganglion (lamina) of nocturnal hymenopterans is discussed.

Animals↗

PubMed2006

Visual summation in night-flying sweat bees: a theoretical study.

Bees are predominantly diurnal; only a few groups fly at night. An evolutionary limitation that bees must overcome to inhabit dim environments is their eye type: bees possess apposition compound eyes, which are poorly suited to vision in dim light. Here, we theoretically examine how nocturnal bees Megalopta genalis fly at light levels usually reserved for insects bearing more sensitive superposition eyes. We find that neural summation should greatly increase M. genalis's visual reliability. Predicted spatial summation closely matches the morphology of laminal neurons believed to mediate such summation. Improved reliability costs acuity, but dark adapted bees already suffer optical blurring, and summation further degrades vision only slightly.

Animals↗

PubMed2006

Adaptations for nocturnal vision in insect apposition eyes.

Due to our own preference for bright light, we tend to forget that many insects are active in very dim light. Nocturnal insects possess in general superposition compound eyes. This eye design is truly optimized for dim light as photons can be gathered through large apertures comprised of hundreds of lenses. In apposition eyes, on the other hand, the aperture consists of a single lens resulting in a poor photon catch and unreliable vision in dim light. Apposition eyes are therefore typically found in day-active insects. Some nocturnal insects have nevertheless managed the transition to a strictly nocturnal lifestyle while retaining their highly unsuitable apposition eye design. Large lenses and wide photoreceptors enhance the sensitivity of nocturnal apposition eyes. However, as the gain of these optical adaptations is limited and not sufficient for vision in dim light, additional neural adaptations in the form of spatial and temporal summation are necessary.

Adaptation, Biological↗

PubMed2005

A neural network to improve dim-light vision? Dendritic fields of first-order interneurons in the nocturnal bee Megalopta genalis.

Using the combined Golgi-electron microscopy technique, we have determined the three-dimensional dendritic fields of the short visual fibres (svf 1-3) and first-order interneurons or L-fibres (L1-4) within the first optic ganglion (lamina) of the nocturnal bee Megalopta genalis. Serial cross sections have revealed that the svf type 2 branches into one adjacent neural unit (cartridge) in layer A, the most distal of the three lamina layers A, B and C. All L-fibres, except L1-a, exhibit wide lateral branching into several neighbouring cartridges. L1-b shows a dendritic field of seven cartridges in layers A and C, dendrites of L2 target 13 cartridges in layer A, L3 branches over a total of 12 cartridges in layer A and three in layer C and L4 has the largest dendritic field size of 18 cartridges in layer C. The number of cartridges reached by the respective L-fibres is distinctly greater in the nocturnal bee than in the worker honeybee and is larger than could be estimated from our previous Golgi-light microscopy study. The extreme dorso-ventrally oriented dendritic field of L4 in M. genalis may, in addition to its potential role in spatial summation, be involved in edge detection. Thus, we have shown that the amount of lateral spreading present in the lamina provides the anatomical basis for the required spatial summation. Theoretical and future physiological work should further elucidate the roles that this lateral spreading plays to improve dim-light vision in nocturnal insects.

Animals↗

PubMed2005

Legislation for smoke-free workplaces and health of bar workers in Ireland: before and after study.

OBJECTIVES: To compare exposure to secondhand smoke and respiratory health in bar staff in the Republic of Ireland and Northern Ireland before and after the introduction of legislation for smoke-free workplaces in the Republic. DESIGN: Comparisons before and after the legislation in intervention and control regions. SETTING: Public houses in three areas in the Republic (intervention) and one area in Northern Ireland (control). PARTICIPANTS: 329 bar staff enrolled in baseline survey; 249 (76%) followed up one year later. Of these, 158 were non-smokers both at baseline and follow-up. MAIN OUTCOME MEASURES: Salivary cotinine concentration, self reported exposure to secondhand smoke, and respiratory and sensory irritation symptoms. RESULTS: In bar staff in the Republic who did not themselves smoke, salivary cotinine concentrations dropped by 80% after the smoke-free law (from median 29.0 nmol/l (95% confidence interval 18.2 to 43.2 nmol/l)) to 5.1 nmol/l (2.8 to 13.1 nmol/l) in contrast with a 20% decline in Northern Ireland over the same period (from median 25.3 nmol/l (10.4 to 59.2 nmol/l) to 20.4 nmol/l (13.2 to 33.8 nmol/l)). Changes in self reported exposure to secondhand smoke were consistent with the changes in cotinine concentrations. Reporting any respiratory symptom declined significantly in the Republic (down 16.7%, -26.1% to -7.3%) but not in Northern Ireland (0% difference, -32.7% to 32.7%). After adjustment for confounding, respiratory symptoms declined significantly more in the Republic than in Northern Ireland and the decline in cotinine concentration was twice as great. CONCLUSION: The smoke-free law in the Republic of Ireland protects non-smoking bar workers from exposure to secondhand smoke.

Cotinine↗

PubMed2004

Neural organisation in the first optic ganglion of the nocturnal bee Megalopta genalis.

Each neural unit (cartridge) in the first optic ganglion (lamina) of the nocturnal bee Megalopta genalis contains nine receptor cell axons (6 short and 3 long visual fibres), and four different types of first-order interneurons, also known as L-fibres (L1 to L4) or lamina monopolar cells. The short visual fibres terminate within the lamina as three different types (svf 1, 2, 3). The three long visual fibres pass through the lamina without forming characteristic branching patterns and terminate in the second optic ganglion, the medulla. The lateral branching pattern of svf 2 into adjacent cartridges is unique for hymenopterans. In addition, all four types of L-fibres show dorso-ventrally arranged, wide, lateral branching in this nocturnal bee. This is in contrast to the diurnal bees Apis mellifera and Lasioglossum leucozonium, where only two out of four L-fibre types (L2 and L4) reach neighbouring cartridges. In M. genalis, L1 forms two sub-types, viz. L1-a and L1-b; L1-b in particular has the potential to contact several neighbouring cartridges. L2 and L4 in the nocturnal bee are similar to L2 and L4 in the diurnal bees but have dorso-ventral arborisations that are twice as wide. A new type of laterally spreading L3 has been discovered in the nocturnal bee. The extensive neural branching pattern of L-fibres in M. genalis indicates a potential role for these neurons in the spatial summation of photons from large groups of ommatidia. This specific adaptation in the nocturnal bee could significantly improve reliability of vision in dim light.

Animals↗

PubMed2004

Nocturnal vision and landmark orientation in a tropical halictid bee.

BACKGROUND: Some bees and wasps have evolved nocturnal behavior, presumably to exploit night-flowering plants or avoid predators. Like their day-active relatives, they have apposition compound eyes, a design usually found in diurnal insects. The insensitive optics of apposition eyes are not well suited for nocturnal vision. How well then do nocturnal bees and wasps see? What optical and neural adaptations have they evolved for nocturnal vision? RESULTS: We studied female tropical nocturnal sweat bees (Megalopta genalis) and discovered that they are able to learn landmarks around their nest entrance prior to nocturnal foraging trips and to use them to locate the nest upon return. The morphology and optics of the eye, and the physiological properties of the photoreceptors, have evolved to give Megalopta's eyes almost 30 times greater sensitivity to light than the eyes of diurnal worker honeybees, but this alone does not explain their nocturnal visual behavior. This implies that sensitivity is improved by a strategy of photon summation in time and in space, the latter of which requires the presence of specialized cells that laterally connect ommatidia into groups. First-order interneurons, with significantly wider lateral branching than those found in diurnal bees, have been identified in the first optic ganglion (the lamina ganglionaris) of Megalopta's optic lobe. We believe that these cells have the potential to mediate spatial summation. CONCLUSIONS: Despite the scarcity of photons, Megalopta is able to visually orient to landmarks at night in a dark forest understory, an ability permitted by unusually sensitive apposition eyes and neural photon summation.

Animals↗

PubMed2004

Three-dimensional antennal lobe atlas of the male moth, Agrotis ipsilon: a tool to study structure-function correlation.

The glomerular structure of the primary olfactory neuropil has long been thought to play an important role in odour coding. In insects, the number of glomeruli in the antennal lobe is limited in most species to fewer than 100 compared with more than 1,000 in vertebrates, making it possible to identify individual glomeruli. A complete three-dimensional atlas of the glomeruli within the antennal lobe of the male noctuid moth Agrotis ipsilon was constructed. All 66 glomeruli were singly identifiable in both antennal lobes of the three brains investigated. Further, six antennal lobes containing intracellularly stained projection neurones were reconstructed. By using the atlas, the respective target glomerulus of each projection neurone could be identified. The importance of the glomerular atlas as a tool to study central olfactory processing and its plasticity is discussed.

Action Potentials↗

PubMed2004

Retinal and optical adaptations for nocturnal vision in the halictid bee Megalopta genalis.

The apposition compound eye of a nocturnal bee, the halictid Megalopta genalis, is described for the first time. Compared to the compound eye of the worker honeybee Apis mellifera and the diurnal halictid bee Lasioglossum leucozonium, the eye of M. genalis shows specific retinal and optical adaptations for vision in dim light. The major anatomical adaptations within the eye of the nocturnal bee are (1) nearly twofold larger ommatidial facets and (2) a 4-5 times wider rhabdom diameter than found in the diurnal bees studied. Optically, the apposition eye of M. genalis is 27 times more sensitive to light than the eyes of the diurnal bees. This increased optical sensitivity represents a clear optical adaptation to low light intensities. Although this unique nocturnal apposition eye has a greatly improved ability to catch light, a 27-fold increase in sensitivity alone cannot account for nocturnal vision at light intensities that are 8 log units dimmer than during daytime. New evidence suggests that additional neuronal spatial summation within the first optic ganglion, the lamina, is involved.

Animals↗

PubMed2002

Central processing of plant volatiles in Agrotis ipsilon males is age-independent in contrast to sex pheromone processing.

Male moths rely on female sex pheromones to find their mating partner and on plant volatiles for the detection of food sources. In the noctuid moth, Agrotis ipsilon, plasticity of central sex pheromone processing has been shown previously in the antennal lobe. The sensitivity of antennal lobe interneurons increases with age and juvenile hormone level. Here we investigated whether age affects not only central sex pheromone processing, but also central processing of plant volatiles in A. ipsilon males. Intracellular recordings of antennal lobe interneurons were made in males of different ages after stimulation of the antennae with seven different plant volatiles. The sensitivity and specificity of the antennal lobe interneurons for any of the plant volatiles tested did not change with age. From these results we conclude that the sensitivity of the antennal lobe interneurons involved in central plant volatile processing is age-independent and that the action of juvenile hormone is specific for central sex pheromone processing in A. ipsilon males.

Age Factors↗

PubMed2002

Job stress, unwinding and drinking in transit operators.

OBJECTIVE: This study tests the spillover model of the effects of work stress on after-work drinking, using the variable "length of time to unwind" as a mediator. METHOD: A total of 1,974 transit operators were contacted and 1,553 (79%) of them participated in a personal interview. Complete data on the variables in this analysis were available for 1,208 respondents (84% men). Using latent variable structural equation modeling, a model was tested that predicted that daily job problems, skipped meals and less social support from supervisor would increase alcohol consumption through the mediator, length of time to unwind and relax after work. Increased alcohol consumption was, in turn, hypothesized to increase drinking problems. RESULTS: As predicted, skipped meals and daily job problems increased length of time to unwind and had an indirect positive relationship with overall drinking, even when controlling for drinking norms and demographic variables. Overall drinking was positively associated with drinking problems. Supervisor support at work, however, did not significantly influence length of time to unwind. Difficulty unwinding (longer time to unwind) did not have direct effects on drinking problems; however, indirect effects through overall drinking were observed. CONCLUSIONS: These results provide preliminary support for the mediating role of length of time to unwind and relax after work in a spillover model of the stress-drinking relationship. This research introduces a new mediator and empirical links between job problems, length of time to unwind, drinking and drinking problems, which ground more substantively the domains of work stress and alcohol consumption.

Alcohol Drinking↗