Localization of short-term memory in the brain of the bee, Apis mellifera

ABSTRACT. Fixed honey-bees were conditioned to a scent in a one-trial learning paradigm. In contrast to free-flying colour-conditioned bees, fixed scent-conditioned bees do not show a biphasic time dependence of the conditioned response. Small metal probes were used to cool localized areas of the antennal lobes, alpha-lobes, and calyces of the mushroom bodies of the brain at various times after conditioning. Localized cooling impaired the formation of memory in all three structures. The susceptibility to impairment after conditioning lasted approximately 3 min in the antennal lobes, 7 min in the alpha-lobes, and 10 min in the calyx area. It was possible to determine the influence of the contralateral hemisphere (relative to the learning antenna) by conditioning bees with only one antenna. No contralateral impairment was found in the antennal lobes; there were minor effects in the alphalobes; contralateral cooling led to reductions of the conditioned response only in the calyx area. The temperature dependence of memory impairment was different for the antennal lobes and the mushroom bodies (alpha-lobes and calyces). The latter were most sensitive to cooling at 5°C. No correlation between cooling duration and impairment of memory was found in the antennal lobes, but there was a linear relation between impairment and cooling duration in the alpha-lobes. Brief cooling (5 or 10 s) resulted in significant impairment of memory formation only in the calyx area. A series of control experiments proved that the impairment of memory is due to a reversible block of neural activity. It was possible to show that the impairment is specific for the three neural structures analysed, by cooling the lobula of the optic system at various times after conditioning. Lesions of the brain or application of KCl also resulted in time-dependent reductions of the conditioned response. Cooling the entire animal at various times after conditioning led to similar memory impairment to that resulting from localized cooling of the alphalobes.     

Hypophysiotropic Centers in the Brain of Amphibians and Fish

The subject is the localization of three different hypophysiotropiccenters in the brain of amphibians and fish. The thyrotropic hormone-releasing hormone (TRH) in Xenapus mayoriginate from the dorsal magno-cellular neurons of the preopticnucleus. This hypothesis is based on correlative changes betweenthese cells and alterations in thyroid activity during metamorphosis.Experimental data are in support of a functional relationshipbetween certain preoptic neurons and the thyrotropic activityof the pituitary. The MSH inhibiting activity of the hypothalamus is effectedby means of an aminergic innervation of the pars intermediain amphibians, teleosts and elasmobranchs. In amphibians theaminergic fibers originate from the caudal part of the paraventricularorgan (PVO); in elasmobranchs probably from the nucleus mediushypothalamicus(NMI); in teleosts the origin still has to beinvestigated. Two centers producing gonadotropic hormone-releasing hormone(GRH) have been demonstrated. Lesion experiments lead to thehypothesis that GRH is produced in the caudal hypothalamus,i.e., in the nucleus infundibularis ventralis of amphibiansand in the nucleus lateralis tuberis of fishes. ImmunoHuorescencestudies indicate in both groups the presence of neurons, infront of the preoptic area in the telencephalon, and these neuronsare immuno-reactive with anti-mammalian LH-RH.     

Nitrosubstituted Aromatic Compounds as Nitrogen Source for Bacteria

Bacteria which utilized nitroaromatic compounds (0.5 mM) as sole source of nitrogen were isolated from soil. With 2,6-dinitrophenol and succinate as carbon source, a Pseudomonas strain was isolated which liberated and assimilated nitrite. Approximately 2 mol of NO₂⁻ per mol of 2,6-dinitrophenol was released by resting cells. The xenobiotic compound was totally degraded, although specific growth yields were low even with succinate as a carbon source.     

Genetic improvement of acidophilic bacteria for biohydrometallurgical applications

Abstract

Recent success in introducing foreign genetic information into Acidiphilium and Thiobacillus ferrooxidans have opened the possibility of the improvement of the bioleaching properties of acidophilic bacteria through genetic means. The use of electroporation to transform acidophilic bacteria, while effective for diverse genera of bacteria, is potentially limited by observed strain dependence within a given species. Bacterial mating or conjugation may prove more widely applicable, but has not yet been demonstrated in T. ferrooxidans. An arsenic‐resistant, broad‐host‐range plasmid has been constructed and introduced by conjugation into Acidiphilium. This recombinant organism is being examined to assess whether it might lead to improved arsenopyrite leaching rates in mixed cultures with chemolithotrophs such as T. ferrooxidans and Leptospirillum ferrooxidans.     

Bias in the Listeria monocytogenes enrichment procedure: lineage 2 strains outcompete lineage 1 strains in University of Vermont selective enrichments

Listeria monocytogenes can be isolated from a range of food products and may cause food-borne outbreaks or sporadic cases of listeriosis. L. monocytogenes is divided into three genetic lineages and 13 serotypes. Strains of three serotypes (1/2a, 1/2b, and 4b) are associated with most human cases of listeriosis. Of these, strains of serotypes 1/2b and 4b belong to lineage 1, whereas strains of serotype 1/2a and many other strains isolated from foods belong to lineage 2. L. monocytogenes is isolated from foods by selective enrichment procedures and from patients by nonselective methods. The aim of the present study was to investigate if the selective enrichment procedure results in a true representation of the subtypes of L. monocytogenes present in a sample. Eight L. monocytogenes strains (four lineage 1 strains and four lineage 2 strains) and one Listeria innocua strain grew with identical growth rates in the nonselective medium brain heart infusion (BHI), but differed in their growth rate in the selective medium University of Vermont medium I (UVM I). When coinoculated in UVM I, some strains completely outgrew other strains. This outcome was dependent on the lineage of L. monocytogenes rather than the individual growth rate of the strains. When inoculated at identical cell densities in UVM I, L. innocua outcompeted L. monocytogenes lineage 1 strains but not lineage 2 strains. In addition, lineage 2 L. monocytogenes strains outcompeted lineage 1 L. monocytogenes strains in all combinations tested, indicating a bias in strains selected by the enrichment procedures. Bias also occurred when coinoculating two lineage 2 or lineage 1 strains; however, it did not appear to correlate with origin (clinical versus food). Identical coinoculation experiments in BHI suggested that the selective compounds in UVM I and II influenced this bias. The results of the present study demonstrate that the selective procedures used for isolation of L. monocytogenes may not allow a true representation of the types present in foods. Our results could have a significant impact on epidemiological studies, as lineage 1 strains, which are often isolated from clinical cases of listeriosis, may be suppressed during enrichment by other L. monocytogenes lineages present in a food sample.     

Ethylene Production in Spinach Leaves during Floral Induction

Spinach plants were induced to flower by transferring them fromshort days to continuous light. Their leaf laminae releasedmore ethylene than those from vegetative plants. These leavesalso exhibited a greater capacity to convert exogenous ACC intoethylene. Cell wall preparations from the leaves of continuouslyilluminated plants also converted exogenous ACC into ethylenemore readily than extracts from short day plants. These effectsand also those previously reported for peroxidases appear verysimilar to these brought about by various environmental stressessuch as pollution and mechanical irritation. Key words: Ethylene, floral induction, stress, photoperiod, spinach     

Selenate reduction by bacteria from a selenium-rich environment

Samples collected from Kesterson Reservoir were screened for bacterial presence and selenate reduction capability. Selenate concentrations of 100 mg/liter were not toxic to indigenous bacteria. Of the 44 samples collected, 20 possessed microbial populations capable of reducing selenate. Reduction was observed in 4% of the water samples, 92% of the sediment samples, and 100% of the soil samples. Microbial reduction of 100 mg of selenate per liter was complete within 1 week of incubation. Up to 75 mg of selenate per liter was reduced beyond selenite to an insoluble red precipitate. Data collected indicate that indigenous bacteria have a significant role in the biogeochemical cycling of selenium.     

Stacking Capacity and Chlorophyll Forms of Thylakoids in Normal and Mutant Maize Chloroplasts of Different Granum Content

Stacking of chloroplast lamellae, isolated from normal and carotenoid mutant chloroplasts of maize (Zea mays L.), was determined after a high-salt treatment. Stacking of isolated lamellae under favourable ionic conditions was almost identical with that occurring in intact chloroplasts; thus, differences in granum content could be attributed to the architectural properties of lamellae. Gaussian analyses, performed on the red band of room temperature absorption spectra, have shown that chloroplasts with lamellae of high stacking capacity contain relatively more Chl a₆₆₂ than chloroplasts containing lamellae of low stacking capacity. The presence of Chl a_705–708 was characteristic of preparations containing considerable amounts of stroma lamellae.     

Multimodal signals in male European treefrog (Hyla arborea) and the influence of population isolation on signal expression

In nocturnal treefrogs, mate choice implies the use of acoustic and visual signals. Multimodality is suspected to have evolved for either information redundancy or information complementariness. It is essential to explore multimodality in a natural context to understand the selection pressures operating on the signals. In the present study, we investigated calling and coloration in relation to male biometry and condition in four populations of European treefrog (Hyla arborea) varying in size and genetic isolation. We compared the signal intensity between core and satellite populations to estimate the impact of genetic diversity on male secondary sexual traits. The results obtained show important regional variations in both traits, likely as a result of local adaptations. Call and coloration are weakly correlated within an individual, implying that these traits likely convey different information about the signaller's identity or quality, thus supporting the hypothesis of complementariness of multiple messages. By contrast to the experimental evidence, we find that call and coloration are not related to male condition (as estimated by the residual of mass over size), suggesting that the condition‐dependence of these traits may be mediated by complex mechanisms not accurately reflected by the chosen estimator. Finally, male call and colour phenotypes present no robust pattern of variation with isolation status, probably because of variation in local selective pressures and in history of population dynamics. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103 , 633–647.