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R Menzel

Publications and source records attributed to R Menzel.

At least 37 records · Page 2Linked to original sources
PubMed2001

Colour thresholds and receptor noise: behaviour and physiology compared.

Photoreceptor noise sets an absolute limit for the accuracy of colour discrimination. We compared colour thresholds in the honeybee (Apis mellifera) with this limit. Bees were trained to discriminate an achromatic stimulus from monochromatic lights of various wavelengths as a function of their intensity. Signal-to-noise ratios were measured by intracellular recordings in the three spectral types of photoreceptor cells. To model thresholds we assumed that discrimination was mediated by opponent mechanisms whose performance was limited by receptor noise. Most of the behavioural thresholds were close to those predicted from receptor signal-to-noise ratios, suggesting that colour discrimination in honeybees is affected by photoreceptor noise. Some of the thresholds were lower than this theoretical limit, which indicates summation of photoreceptor cell signals.

Animals↗
PubMed2001

Cloning of a catalytic subunit of cAMP-dependent protein kinase from the honeybee (Apis mellifera) and its localization in the brain.

In the honeybee the cAMP-dependent signal transduction cascade has been implicated in processes underlying learning and memory. The cAMP-dependent protein kinase (PKA) is the major mediator of cAMP action. To characterize the PKA system in the honeybee brain we cloned a homologue of a PKA catalytic subunit from the honeybee. The deduced amino acid sequence shows 80-94% identity with catalytic subunits of PKA from Drosophila melanogaster, Aplysia californica and mammals. The corresponding gene is predominantly expressed in the mushroom bodies, a structure that is involved in learning and memory processes. However, expression can also be found in the antennal and optic lobes. The level of expression varies within all three neuropiles.

Amino Acid Sequence↗
PubMed2000

Odour representation in honeybee olfactory glomeruli shows slow temporal dynamics: an optical recording study using a voltage-sensitive dye.

Stimulation with odours has been shown to elicit characteristic patterns of activated glomeruli in the antennal lobe (AL) of honeybees. In this study we show that these patterns are dynamic in a time window of 2-3 s after stimulus onset. We measured changes in the averaged membrane potential of all cells in the glomerular neuropil by optical imaging of the voltage-sensitive dye RH795 using a slow scan CCD camera (3 frames/s). The four substances 1-hexanol, hexanal, citral and clove-oil as well as the binary mixtures hexanol+hexanal and hexanol+citral were used as stimuli (2 s stimulus duration). We found that: (1) every odour elicited an odour-specific activity pattern, and conversely every glomerulus had a characteristic odour response profile; (2) some glomeruli had a tonic, some a phasic-tonic, and some a slow phasic response pattern; (3) the difference between the glomerular response patterns increased within 2 s of stimulus presentation, which suggests that odour representations became more characteristic over stimulus time; and (4) the responses to odorant mixtures were complex and glomerulus-dependent: some responses correspond to the sum of the compounds' responses, some to the response of one of the components.

Journal Article↗
PubMed2000

Two spatial memories for honeybee navigation.

Insect navigation is thought to be based on an egocentric reference system which relates vector information derived from path integration to views of landmarks experienced en route and at the goal. Here we show that honeybees also possess an allocentric form of spatial memory which allows localization of multiple places relative to the intended goal, the hive. The egocentric route memory, which is called the specialized route memory (SRM) here, initially dominates navigation when an animal is first trained to a feeding site and then released at an unexpected site and this is why it is the only reference system detected so far in experiments with bees. However, the SRM can be replaced by an allocentric spatial memory called the general landscape memory (GLM). The GLM is directly accessible to the honeybee (and to the experimenter) if no SRM exists, for example, if bees were not trained along a route before testing. Under these conditions bees return to the hive from all directions around the hive at a speed comparable to that of an equally long flight along a trained route. The flexible use of the GLM indicates that bees may store relational information on places, connections between landmarks and the hive and/or views of landmarks from different directions and, thus, the GLM may have a graph structure, at least with respect to one goal, i.e. the hive.

Animals↗
PubMed2000

Risk-indifferent foraging behaviour in honeybees.

We studied the influence of variance in reward volume on choice behaviour of honeybees, Apis mellifera carnica, by training bees to collect sucrose solution from four newly developed artificial feeders. The feeders were electromechanical devices, each controlled by a microprocessor, which monitored the experiments, controlled reward delivery and stored the data. The parameters that varied between the feeders were the amount and variance of reward. The four feeders were arranged in two pairs, with the two feeders in each pair set to the same reward parameters. Constant feeders offered a fixed amount of sucrose solution at each bee visit; variable feeders offered a normally distributed reward with a standard deviation equal to the mean. We tested three reward combinations under two variance conditions. The bees matched their choice frequencies to the mean amount of reward. This applied both to the constant and the variable feeders. Thus the bees were able to discriminate feeders by the amount of reward and were able to estimate the mean reward for the variable flowers. The proportion of immediate returns to the same feeder increased with the amount of sucrose solution imbibed at each visit, indicating that bees were able to perceive the amount of reward at each visit. However, there was no influence of variance on the choice behaviour of the bees, ruling out the possibility that bees are risk sensitive under these conditions. We discuss risk indifference in choice behaviour of bees in the context of several models of risk sensitivity. Copyright 2000 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed2000

Odour perception in honeybees: coding information in glomerular patterns.

Major advances have been made during the past two years in understanding how honeybees process olfactory input at the level of their first brain structure dealing with odours, the antennal lobe (the insect analogue of the mammalian olfactory bulb). It is now possible to map physiological responses to morphologically identified olfactory glomeruli, allowing for the creation of a functional atlas of the antennal lobe. Furthermore, the measurement of odour-evoked activity patterns has now been combined with studies of appetitive odour learning. The results show that both genetically determined components and learning-related plasticity shape olfactory processing in the antennal lobe.

Animals↗
PubMed2000

Sensory preconditioning in honeybees.

Sensory preconditioning means that reinforcement of stimulus A after unreinforced exposure to a compound AB also leads to responses to stimulus B. Here, we describe and analyze sensory preconditioning in an insect, the honeybee Apis mellifera. Using two-element odorant compounds in classical conditioning of the proboscis extension reflex, we found (i) that sensory preconditioning is not due to stimulus generalization, (ii) that paired, but not unpaired, presentation of elements supports sensory preconditioning, (iii) that simultaneous, but not sequential, exposure to the elements of the compound supports sensory preconditioning and (iv) that a single presentation of the compound yields maximal sensory preconditioning. The results are discussed with respect to configural and chain-like associative explanations for sensory preconditioning. We suggest an experience-dependent step of compound processing, establishing configural units, as an additional explanation for sensory preconditioning.

Animals↗
PubMed1999

Differential impact of substitution of amino acids 9-13 and 91-101 of human CD14 on soluble CD14-dependent activation of cells by lipopolysaccharide.

The soluble form of the endotoxin receptor CD14 is required for the LPS-induced activation of cells lacking membrane-bound CD14. It has been shown that a deletion mutant of human CD14 consisting of the N-terminal 152 amino acids has the capacity to mediate the stimulation of different cell types by LPS. To identify the structural domains of the molecule related to this functional property, we screened a set of alanine substitution mutants using CD14-negative U373 astrocytoma cells. We show that 3 of 18 soluble mutants of human CD14 failed to mediate the LPS-induced IL-6 production in U373 cells. These mutants were located in two regions of the molecule (aa 9-13 and 91-101) that are not essential for LPS binding. In addition, the mutants had a reduced capacity to mediate LPS-stimulated IL-6 production in human vascular endothelial and SMC. In contrast, the potential of sCD14(91-94,96)A, and sCD14(97-101)A to signal LPS-induced activation of human PBMC was not significantly reduced. These results show that the regions 9-13 and 91-101 are involved in the sCD14-dependent stimulation of cells by LPS but that the mechanisms by which different cell types are activated may not be identical.

Alanine↗
PubMed1999

Reversible downregulation of protein kinase A during olfactory learning using antisense technique impairs long-term memory formation in the honeybee, Apis mellifera.

In this study, we examined the role of cAMP-dependent protein kinase (PKA) in associative olfactory learning of the honeybee, Apis mellifera. In the bee, specific interference with molecules to clarify their role in a certain behavior is difficult, because genetic approaches, such as mutants or transgenic animals, are not feasible at the moment. As a new approach in insects in vivo, we report the use of short antisense oligonucleotides. We show that phosphorothioate-modified oligodeoxynucleotides complementary to the mRNA of a catalytic subunit of PKA directly injected into the bee brain cause a reversible and specific downregulation of both the amount of the catalytic subunit and of PKA activity by 10-15%. The amounts of the regulatory subunit of PKA, as well as PKC, are not affected. The slight "knockdown" of PKA activity during the training procedure, a classical olfactory conditioning of the proboscis extension reflex, neither affects acquisition nor memory retention 3 or 6 hr after training. However, it causes an impairment of long-term memory retention 24 hr after training. Downregulation of PKA 3 hr after training has no detectable effect on memory formation. We conclude that PKA contributes to the induction of a long-term memory 24 hr after training when activated during learning. Second, we demonstrate that the antisense technique is feasible in honeybees in vivo and provides a new and powerful tool for the study of the molecular basis of learning and memory formation in insects.

Animals↗
PubMed1999

Increased thermosensitivity associated with topoisomerase I deletion and promoter mutations in Escherichia coli.

An Escherichia coli mutant with three of the promoters for the topoisomerase I gene (topA) deleted, such that only the sigma 32-dependent promoter (P1) remained, had a decreased level of topoisomerase I at 30 degrees C and showed increased thermosensitivity at 52 degrees C. However, it could still develop thermotolerance and had a wild-type level of resistance to 52 degrees C treatment if exposed first to 42 degrees C. This indicated that newly synthesized topoisomerase I from transcription initiated at P1 was important for development of thermotolerance. Two other E. coli mutants lacking topA were > 100 times more sensitive to high temperature than their wild-type isogenic strains.

DNA Topoisomerases, Type I↗
PubMed1999

Nicotinic acetylcholine currents of cultured Kkenyon cells from the mushroom bodies of the honey bee Aapis mellifera.

1. Acetylcholine-induced currents of mushroom body Kenyon cells from the honey bee Apis mellifera were studied using the whole-cell configuration of the patch clamp technique. Pressure application of 1 mM acetylcholine (ACh) induced inward currents with amplitudes between -5 and -500 pA. 2. The cholinergic agonists ACh and carbamylcholine had almost equal potencies of current activation at concentrations between 0.01 and 1 mM; nicotine was less potent. The muscarinic agonist oxotremorine did not elicit any currents. 3. Approximately 80 % of the ACh-induced current was irreversibly blocked by 1 microM alpha-bungarotoxin. Atropine (1 mM) did not block the ACh-induced current. 4. Upon prolonged ACh application the current desensitized with a time course that could be approximated by the sum of two exponentials (tau1 = 276 +/- 45 ms (mean +/- s.e.m. ) for the fast component and tau2 = 2.4 +/- 0.7 s for the slow component). 5. Noise analyses of whole-cell currents yielded elementary conductances of 19.5 +/- 2.4 pS for ACh and 23.7 +/- 5.0 pS for nicotine. The channel lifetimes, calculated from the frequency spectra, were tauo = 1.8 ms for ACh and tauo = 2.5 ms for nicotine. 6. Raising the external calcium concentration from 5 to 50 mM shifted the reversal potential of the ACh-induced current from +4. 6 +/- 0.9 to +37.3 +/- 1.3 mV. The calcium-to-sodium permeability ratio (PCa : PNa) was 6.4. 7. In high external calcium solution (50 mM) the ACh-induced current rectified in an outward direction at positive membrane potentials. 8. We conclude that Kenyon cells express nicotinic ACh receptors with functional profiles reminiscent of the vertebrate neuronal nicotinic ACh receptor subtype.

Animals↗
PubMed1999

Microbial resistance: novel screens for a contemporary problem.

Historically, natural products have been the source of a large variety of antibacterial agents. In the 1980s, no additional useful antibacterial agents were discovered, leading to the belief that most useful chemotypes from natural product sources had already been discovered. At this time, advances in biotechnology made it feasible to produce sufficient enzyme to set up cell-free screens. Chemical compound libraries and combinatorial synthesis became the source of chemical diversity for the screens. In spite of these efforts, very few new antibacterial agents have been discovered in the last decade. At Small Molecule Therapeutics, Inc., we have developed phenotype-based screens that take advantage of the natural physiology and biochemistry of the target enzymes. We have developed a screen to identify bacterial DNA gyrase and topoisomerase IV poisons. The "hits" identified in this screen are being characterized further. A second screen has also been developed against bacterial topoisomerase 1 in which compounds that cause DNA damage through their interaction with bacterial topoisomerase 1 have been identified. Three of the compounds identified in the screen inhibit DNA relaxation mediated by bacterial topoisomerase 1, induce DNA cleavage, are noncytotoxic at >10 microM, and have MICs of 4.0 microg/mL against Staphylococcus aureus.

Animals↗
PubMed1999

Optical imaging of odor-evoked glomerular activity patterns in the antennal lobes of the ant camponotus rufipes

Ants have a well developed olfactory sense, which they need both for the perception of environmental chemicals, and for a highly sophisticated intraspecific communication system based on pheromones. The question arises therefore as to how different odors are coded in the antennal lobe, the first central neuropil to process olfactory information. We measured odor-evoked activity patterns using in vivo neuropil calcium recording in the antennal lobe of the ant Camponotus rufipes. We found that (a) odors elicit focal activity spots (diameter ca. 20 &mgr;m) which most probably represent the olfactory glomeruli; (b) different odors are coded in odor specific patterns of such activated spots, and a particular spot can participate in the pattern for different odors; (c) calcium increased in the activated spots within the 2-s stimulation period and slowly declined thereafter.

Journal Article↗
PubMed1999

Neuroethology, its roots and future.

Scholars in a particular scientific field should be familiar with its historical roots. Such knowledge will put their own research into a historical perspective, and, in addition, will allow them to assess current strengths and weaknesses in their particular area of research. To keep an exciting field like neuroethology alive and close to fast moving scientific frontiers, it is necessary to constantly adapt and broaden its approaches to newly emerging ideas from other fields, and to quickly incorporate new methodologies. The following article tries to expose some of the roots of neuroethology, and, in addition, will present some evidence as to why the authors think this field needs a broader definition than that formulated in the past. Doing so after the 5th International Congress of Neuroethology in San Diego in August 1998 seems to the authors the most appropriate time.

Animals↗
PubMed1999

A digital three-dimensional atlas of the honeybee antennal lobe based on optical sections acquired by confocal microscopy.

We present a digital atlas of the glomeruli in the antennal lobe of the honeybee, Apis mellifera, accessible to the scientific community via the Internet. The atlas allows the identification of glomeruli in preparations in which the glomeruli can be recognized, be it in sections or in whole-mounts. The high resolution of the anatomical data upon which the atlas is based and its electronic form should prove to be an important tool for anyone involved in the study of the honeybee antennal lobe. Its accessibility via the Internet is a step towards interactive and freely accessible databases of animal brains.

Animals↗