SAS CARE 2 - a randomized study of CPAP in patients with obstructive sleep disordered breathing following ischemic stroke or transient ischemic attack

Objective/background

The benefit of Continuous Positive Airway Pressure (CPAP) treatment following ischemic stroke in patients with obstructive sleep-disordered breathing (SDB) is unclear. We set out to investigate this open question in a randomized controlled trial as part of the SAS-CARE study.

Patients/methods.

Non-sleepy patients (ESS < 10) with ischemic stroke or transient ischemic attack (TIA) and obstructive SDB (AHI ≥ 20) 3 months post-stroke were randomized 1:1 to CPAP treatment (CPAP+) or standard care. Primary outcome was the occurrence of vascular events (TIA/stroke, myocardial infarction/revascularization, hospitalization for heart failure or unstable angina) or death within 24 months post-stroke. Secondary outcomes included Modified Rankin Scale (mRS) and Barthel Index.

Results

Among 238 SAS-CARE patients 41 (17%) non-sleepy obstructive SDB patients were randomized to CPAP (n = 19) or standard care (n = 22). Most patients (80%) had stroke and were males (78%), mean age was 64 ± 7 years and mean NIHSS score 0.6 ± 1.0 (range: 0–5). The primary endpoint was met by one patient in the standard care arm (a new stroke). In an intent-to treat analysis disregarding adherence, this corresponds to an absolute risk difference of 4.5% or an NNT = 22. mRS and Barthel Index were stable and similar between arms. CPAP adherence was sufficient in 60% of evaluable patients at month 24.

Conclusion

No benefit of CPAP started three months post-stroke was found in terms of new cardio- and cerebrovascular events over 2 years. This may be related to the small size of this study, the mild stoke severity, the exclusion of sleepy patients, the delayed start of treatment, and the overall low event rate.

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No benefit of CPAP started 3 months post-stroke was found.

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A sufficient CPAP compliance was observed over 2 years in 60% of patients.

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Studies of CPAP in mild stroke need to be large and include long-term outcomes.

Malpighamoeba infection compromises fluid secretion and P-glycoprotein detoxification in Malpighian tubules

Malpighian tubules, analogous to vertebrate nephrons, play a key role in insect osmoregulation and detoxification. Tubules can become infected with a protozoan, Malpighamoeba, which damages their epithelial cells, potentially compromising their function. Here we used a modified Ramsay assay to quantify the impact of Malpighamoeba infection on fluid secretion and P-glycoprotein-dependent detoxification by desert locust Malpighian tubules. Infected tubules have a greater surface area and a higher fluid secretion rate than uninfected tubules. Infection also impairs P-glycoprotein-dependent detoxification by reducing the net rhodamine extrusion per surface area. However, due to the increased surface area and fluid secretion rate, infected tubules have similar total net extrusion per tubule to uninfected tubules. Increased fluid secretion rate of infected tubules likely exposes locusts to greater water stress and increased energy costs. Coupled with reduced efficiency of P-glycoprotein detoxification per surface area, Malpighamoeba infection is likely to reduce insect survival in natural environments.

First draft genome assembly of the desert locust, Schistocerca gregaria

Background: At the time of publication, the most devastating desert locust crisis in decades is affecting East Africa, the Arabian Peninsula and South-West Asia. The situation is extremely alarming in East Africa, where Kenya, Ethiopia and Somalia face an unprecedented threat to food security and livelihoods. Most of the time, however, locusts do not occur in swarms, but live as relatively harmless solitary insects. The phenotypically distinct solitarious and gregarious locust phases differ markedly in many aspects of behaviour, physiology and morphology, making them an excellent model to study how environmental factors shape behaviour and development. A better understanding of the extreme phenotypic plasticity in desert locusts will offer new, more environmentally sustainable ways of fighting devastating swarms. Methods: High molecular weight DNA derived from two adult males was used for Mate Pair and Paired End Illumina sequencing and PacBio sequencing. A reliable reference genome of Schistocerca gregaria was assembled using the ABySS pipeline, scaffolding was improved using LINKS. Results: In total, 1,316 Gb Illumina reads and 112 Gb PacBio reads were produced and assembled. The resulting draft genome consists of 8,817,834,205 bp organised in 955,015 scaffolds with an N50 of 157,705 bp, making the desert locust genome the largest insect genome sequenced and assembled to date. In total, 18,815 protein-encoding genes are predicted in the desert locust genome, of which 13,646 (72.53%) obtained at least one functional assignment based on similarity to known proteins. Conclusions: The desert locust genome data will contribute greatly to studies of phenotypic plasticity, physiology, neurobiology, molecular ecology, evolutionary genetics and comparative genomics, and will promote the desert locust's use as a model system. The data will also facilitate the development of novel, more sustainable strategies for preventing or combating swarms of these infamous insects.

First draft genome assembly of the desert locust, Schistocerca gregaria

Background: At the time of publication, the most devastating desert locust crisis in decades is affecting East Africa, the Arabian Peninsula and South-West Asia. The situation is extremely alarming in East Africa, where Kenya, Ethiopia and Somalia face an unprecedented threat to food security and livelihoods. Most of the time, however, locusts do not occur in swarms, but live as relatively harmless solitary insects. The phenotypically distinct solitarious and gregarious locust phases differ markedly in many aspects of behaviour, physiology and morphology, making them an excellent model to study how environmental factors shape behaviour and development. A better understanding of the extreme phenotypic plasticity in desert locusts will offer new, more environmentally sustainable ways of fighting devastating swarms. Methods: High molecular weight DNA derived from two adult males was used for Mate Pair and Paired End Illumina sequencing and PacBio sequencing. A reliable reference genome of Schistocerca gregaria was assembled using the ABySS pipeline, scaffolding was improved using LINKS. Results: In total, 1,316 Gb Illumina reads and 112 Gb PacBio reads were produced and assembled. The resulting draft genome consists of 8,817,834,205 bp organised in 955,015 scaffolds with an N50 of 157,705 bp, making the desert locust genome the largest insect genome sequenced and assembled to date. In total, 18,815 protein-encoding genes are predicted in the desert locust genome, of which 13,646 (72.53%) obtained at least one functional assignment based on similarity to known proteins. Conclusions: The desert locust genome data will contribute greatly to studies of phenotypic plasticity, physiology, neurobiology, molecular ecology, evolutionary genetics and comparative genomics, and will promote the desert locust's use as a model system. The data will also facilitate the development of novel, more sustainable strategies for preventing or combating swarms of these infamous insects.

Regressions Fit for Purpose: Models of Locust Phase State Must Not Conflate Morphology With Behavior

Phenotypic plasticity often entails coordinated changes in multiple traits. The effects of two alternative environments on multiple phenotypic traits can be analyzed by multivariable binary logistic regression (LR). Locusts are grasshopper species (family Acrididae) with a capacity to transform between two distinct integrated phenotypes or "phases" in response to changes in population density: a solitarious phase, which occurs when densities are low, and a gregarious phase, which arises as a consequence of crowding and can form very large and economically damaging swarms. The two phases differ in behavior, physiology and morphology. A large body of work on the mechanistic basis of behavioral phase transitions has relied on LR models to estimate the probability of behavioral gregariousness from multiple behavioral variables. Mart́ın-Blázquez and Bakkali (2017; [10.1111/eea.12564]10.1111/eea.12564) have recently proposed standardized LR models for estimating an overall "gregariousness level" from a combination of behavioral and, unusually, morphometric variables. Here I develop a detailed argument to demonstrate that the premise of such an overall "gregariousness level" is fundamentally flawed, since locust phase transformations entail a decoupling of behavior and morphology. LR models that combine phenotypic traits with markedly different response times to environmental change are of very limited value for analyses of phase change in locusts, and of environmentally induced phenotypic transitions in general. I furthermore show why behavioral variables should not be adjusted by measures of body size that themselves differ between the two phases. I discuss the models fitted by Mart́ın-Blázquez and Bakkali (2017) to highlight potential pitfalls in statistical methodology that must be avoided when analysing associations between complex phenotypes and alternative environments. Finally, I reject the idea that "standardized models" provide a valid shortcut to estimating phase state across different developmental stages, strains or species. The points addressed here are pertinent to any research on transitions between complex phenotypes and behavioral syndromes.

Acute and chronic gregarisation are associated with distinct DNA methylation fingerprints in desert locusts

Desert locusts (Schistocerca gregaria) show a dramatic form of socially induced phenotypic plasticity known as phase polyphenism. In the absence of conspecifics, locusts occur in a shy and cryptic solitarious phase. Crowding with conspecifics drives a behavioural transformation towards gregariousness that occurs within hours and is followed by changes in physiology, colouration and morphology, resulting in the full gregarious phase syndrome. We analysed methylation-sensitive amplified fragment length polymorphisms (MS-AFLP) to compare the effect of acute and chronic crowding on DNA methylation in the central nervous system. We find that crowd-reared and solitary-reared locusts show markedly different neural MS-AFLP fingerprints. However, crowding for a day resulted in neural MS-AFLP fingerprints that were clearly distinct from both crowd-reared and uncrowded solitary-reared locusts. Our results indicate that changes in DNA methylation associated with behavioural gregarisation proceed through intermediate states that are not simply partial realisations of the endpoint states.

Environmental Adaptation, Phenotypic Plasticity, and Associative Learning in Insects: The Desert Locust as a Case Study

The ability to learn and store information should be adapted to the environment in which animals operate to confer a selective advantage. Yet the relationship between learning, memory, and the environment is poorly understood, and further complicated by phenotypic plasticity caused by the very environment in which learning and memory need to operate. Many insect species show polyphenism, an extreme form of phenotypic plasticity, allowing them to occupy distinct environments by producing two or more alternative phenotypes. Yet how the learning and memories capabilities of these alternative phenotypes are adapted to their specific environments remains unknown for most polyphenic insect species. The desert locust can exist as one of two extreme phenotypes or phases, solitarious and gregarious. Recent studies of associative food-odor learning in this locust have shown that aversive but not appetitive learning differs between phases. Furthermore, switching from the solitarious to the gregarious phase (gregarization) prevents locusts acquiring new learned aversions, enabling them to convert an aversive memory formed in the solitarious phase to an appetitive one in the gregarious phase. This conversion provides a neuroecological mechanism that matches key changes in the behavioral environments of the two phases. These findings emphasize the importance of understanding the neural mechanisms that generate ecologically relevant behaviors and the interactions between different forms of behavioral plasticity.

Pollen feeding proteomics: Salivary proteins of the passion flower butterfly, Heliconius melpomene

While most adult Lepidoptera use flower nectar as their primary food source, butterflies in the genus Heliconius have evolved the novel ability to acquire amino acids from consuming pollen. Heliconius butterflies collect pollen on their proboscis, moisten the pollen with saliva, and use a combination of mechanical disruption and chemical degradation to release free amino acids that are subsequently re-ingested in the saliva. Little is known about the molecular mechanisms of this complex pollen feeding adaptation. Here we report an initial shotgun proteomic analysis of saliva from Heliconius melpomene. Results from liquid-chromatography tandem mass-spectrometry confidently identified 31 salivary proteins, most of which contained predicted signal peptides, consistent with extracellular secretion. Further bioinformatic annotation of these salivary proteins indicated the presence of four distinct functional classes: proteolysis (10 proteins), carbohydrate hydrolysis (5), immunity (6), and "housekeeping" (4). Additionally, six proteins could not be functionally annotated beyond containing a predicted signal sequence. The presence of several salivary proteases is consistent with previous demonstrations that Heliconius saliva has proteolytic capacity. It is likely that these proteins play a key role in generating free amino acids during pollen digestion. The identification of proteins functioning in carbohydrate hydrolysis is consistent with Heliconius butterflies consuming nectar, like other lepidopterans, as well as pollen. Immune-related proteins in saliva are also expected, given that ingestion of pathogens is a likely route to infection. The few "housekeeping" proteins are likely not true salivary proteins and reflect a modest level of contamination that occurred during saliva collection. Among the unannotated proteins were two sets of paralogs, each seemingly the result of a relatively recent tandem duplication. These results offer a first glimpse into the molecular foundation of Heliconius pollen feeding and provide a substantial advance towards comprehensively understanding this striking evolutionary novelty.

Brain composition in Godyris zavaleta, a diurnal butterfly, Reflects an increased reliance on olfactory information

Interspecific comparisons of brain structure can inform our functional understanding of brain regions, identify adaptations to species-specific ecologies, and explore what constrains adaptive changes in brain structure, and coevolution between functionally related structures. The value of such comparisons is enhanced when the species considered have known ecological differences. The Lepidoptera have long been a favored model in evolutionary biology, but to date descriptions of brain anatomy have largely focused on a few commonly used neurobiological model species. We describe the brain of Godyris zavaleta (Ithomiinae), a member of a subfamily of Neotropical butterflies with enhanced reliance on olfactory information. We demonstrate for the first time the presence of sexually dimorphic glomeruli within a distinct macroglomerular complex (MGC) in the antennal lobe of a diurnal butterfly. This presents a striking convergence with the well-known moth MGC, prompting a discussion of the potential mechanisms behind the independent evolution of specialized glomeruli. Interspecific analyses across four Lepidoptera further show that the relative size of sensory neuropils closely mirror interspecific variation in sensory ecology, with G. zavaleta displaying levels of sensory investment intermediate between the diurnal monarch butterfly (Danaus plexippus), which invests heavily in visual neuropil, and night-flying moths, which invest more in olfactory neuropil. We identify several traits that distinguish butterflies from moths, and several that distinguish D. plexippus and G. zavaleta. Our results illustrate that ecological selection pressures mold the structure of invertebrate brains, and exemplify how comparative analyses across ecologically divergent species can illuminate the functional significance of variation in brain structure.

Differential activation of serotonergic neurons during short- and long-term gregarization of desert locusts

Serotonin is a neurochemical with evolutionarily conserved roles in orchestrating nervous system function and behavioural plasticity. A dramatic example is the rapid transformation of desert locusts from cryptic asocial animals into gregarious crop pests that occurs when drought forces them to accumulate on dwindling resources, triggering a profound alteration of behaviour within just a few hours. The onset of crowding induces a surge in serotonin within their thoracic ganglia that is sufficient and necessary to induce the switch from solitarious to gregarious behaviour. To identify the neurons responsible, we have analysed how acute exposure to three gregarizing stimuli--crowding, touching the hind legs or seeing and smelling other locusts--and prolonged group living affect the expression of serotonin in individual neurons in the thoracic ganglia. Quantitative analysis of cell body immunofluorescence revealed three classes of neurons with distinct expressional responses. All ganglia contained neurons that responded to multiple gregarizing stimuli with increased expression. A second class showed increased expression only in response to intense visual and olfactory stimuli from conspecifics. Prolonged group living affected a third and entirely different set of neurons, revealing a two-tiered role of the serotonergic system as both initiator and substrate of socially induced plasticity. This demonstrates the critical importance of ontogenetic time for understanding the function of serotonin in the reorganization of behaviour.

Rapid behavioural gregarization in the desert locust, Schistocerca gregaria entails synchronous changes in both activity and attraction to conspecifics

Desert Locusts can change reversibly between solitarious and gregarious phases, which differ considerably in behaviour, morphology and physiology. The two phases show many behavioural differences including both overall levels of activity and the degree to which they are attracted or repulsed by conspecifics. Solitarious locusts perform infrequent bouts of locomotion characterised by a slow walking pace, groom infrequently and actively avoid other locusts. Gregarious locusts are highly active with a rapid walking pace, groom frequently and are attracted to conspecifics forming cohesive migratory bands as nymphs and/or flying swarms as adults. The sole factor driving the onset of gregarization is the presence of conspecifics. In several previous studies concerned with the mechanism underlying this transformation we have used an aggregate measure of behavioural phase state, Pgreg, derived from logistic regression analysis, which combines and weights several behavioural variables to characterise solitarious and gregarious behaviour. Using this approach we have analysed the time course of behavioural change, the stimuli that induce gregarization and the key role of serotonin in mediating the transformation. Following a recent critique that suggested that using Pgreg may confound changes in general activity with genuine gregarization we have performed a meta-analysis examining the time course of change in the individual behaviours that we use to generate Pgreg. We show that the forced crowding of solitarious locusts, tactile stimulation of the hind femora, and the short-term application of serotonin each induce concerted changes in not only locomotion-related variables but also grooming frequency and attraction to other locusts towards those characteristic of long-term gregarious locusts. This extensive meta-analysis supports and extends our previous conclusions that solitarious locusts undergo a rapid behavioural gregarization upon receiving appropriate stimulation for a few hours that is mediated by serotonin, at the end of which their behaviour is largely indistinguishable from locusts that have been in the gregarious phase their entire lives.

Phenotypic transformation affects associative learning in the desert locust

In desert locusts, increased population densities drive phenotypic transformation from the solitarious to the gregarious phase within a generation [1–4]. Here we show that when presented with odor-food associations, the two extreme phases differ in aversive but not appetitive associative learning, with solitarious locusts showing a conditioned aversion more quickly than gregarious locusts. The acquisition of new learned aversions was blocked entirely in acutely crowded solitarious (transiens) locusts, whereas appetitive learning and prior learned associations were unaffected. These differences in aversive learning support phase-specific feeding strategies. Associative training with hyoscyamine, a plant alkaloid found in the locusts’ habitat [5, 6], elicits a phase-dependent odor preference: solitarious locusts avoid an odor associated with hyoscyamine, whereas gregarious locusts do not. Remarkably, when solitarious locusts are crowded and then reconditioned with the odor-hyoscyamine pairing as transiens, the specific blockade of aversive acquisition enables them to override their prior aversive memory with an appetitive one. Under fierce food competition, as occurs during crowding in the field, this provides a neuroecological mechanism enabling locusts to reassign an appetitive value to an odor that they learned previously to avoid.

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Associative aversive learning is phase dependent, whereas appetitive learning is not

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Gregarization blocks the formation of new aversive memories

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Retention of previously acquired associative memories is unaffected by gregarization

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A behavioral feedback loop promotes override of a previously acquired aversive memory

A long-latency aversive learning mechanism enables locusts to avoid odours associated with the consequences of ingesting toxic food

Avoiding food that contains toxins is crucial for the survival of many animals, particularly herbivores, because many plants defend themselves with toxins. Some animals can learn to avoid food containing toxins not through its taste but by the toxins' effects following ingestion, though how they do so remains unclear. We studied how desert locusts (Schistocerca gregaria), which are generalist herbivores, form post-ingestive aversive memories and use them to make appropriate olfactory-based decisions in a Y-maze. Locusts form an aversion gradually to an odour paired with food containing the toxin nicotine hydrogen tartrate (NHT), suggesting the involvement of a long-latency associative mechanism. Pairing of odour and toxin-free food accompanied by NHT injections at different latencies showed that locusts could form an association between an odour and toxic malaise, which could be separated by up to 30 min. Tasting but not swallowing the food, or the temporal separation of odour and food, prevents the formation of these long-latency associations, showing that they are post-ingestive. A second associative mechanism not contingent upon feeding operates only when odour presentation is simultaneous with NHT injection. Post-ingestive memory formation is not disrupted by exposure to a novel odour alone but can be if the odour is accompanied by simultaneous NHT injection. Thus, the timing with which food, odour and toxin are encountered whilst foraging is likely to influence memory formation and subsequent foraging decisions. Therefore, locusts can form specific long-lasting aversive olfactory associations that they can use to avoid toxin-containing foods whilst foraging.

Visually targeted reaching in horse-head grasshoppers

Visually targeted reaching to a specific object is a demanding neuronal task requiring the translation of the location of the object from a two-dimensionsal set of retinotopic coordinates to a motor pattern that guides a limb to that point in three-dimensional space. This sensorimotor transformation has been intensively studied in mammals, but was not previously thought to occur in animals with smaller nervous systems such as insects. We studied horse-head grasshoppers (Orthoptera: Proscopididae) crossing gaps and found that visual inputs are sufficient for them to target their forelimbs to a foothold on the opposite side of the gap. High-speed video analysis showed that these reaches were targeted accurately and directly to footholds at different locations within the visual field through changes in forelimb trajectory and body position, and did not involve stereotyped searching movements. The proscopids estimated distant locations using peering to generate motion parallax, a monocular distance cue, but appeared to use binocular visual cues to estimate the distance of nearby footholds. Following occlusion of regions of binocular overlap, the proscopids resorted to peering to target reaches even to nearby locations. Monocular cues were sufficient for accurate targeting of the ipsilateral but not the contralateral forelimb. Thus, proscopids are capable not only of the sensorimotor transformations necessary for visually targeted reaching with their forelimbs but also of flexibly using different visual cues to target reaches.

Microarray-based transcriptomic analysis of differences between long-term gregarious and solitarious desert locusts

Desert locusts (Schistocerca gregaria) show an extreme form of phenotypic plasticity and can transform between a cryptic solitarious phase and a swarming gregarious phase. The two phases differ extensively in behavior, morphology and physiology but very little is known about the molecular basis of these differences. We used our recently generated Expressed Sequence Tag (EST) database derived from S. gregaria central nervous system (CNS) to design oligonucleotide microarrays and compare the expression of thousands of genes in the CNS of long-term gregarious and solitarious adult desert locusts. This identified 214 differentially expressed genes, of which 40% have been annotated to date. These include genes encoding proteins that are associated with CNS development and modeling, sensory perception, stress response and resistance, and fundamental cellular processes. Our microarray analysis has identified genes whose altered expression may enable locusts of either phase to deal with the different challenges they face. Genes for heat shock proteins and proteins which confer protection from infection were upregulated in gregarious locusts, which may allow them to respond to acute physiological challenges. By contrast the longer-lived solitarious locusts appear to be more strongly protected from the slowly accumulating effects of ageing by an upregulation of genes related to anti-oxidant systems, detoxification and anabolic renewal. Gregarious locusts also had a greater abundance of transcripts for proteins involved in sensory processing and in nervous system development and plasticity. Gregarious locusts live in a more complex sensory environment than solitarious locusts and may require a greater turnover of proteins involved in sensory transduction, and possibly greater neuronal plasticity.

Associative olfactory learning in the desert locust, Schistocerca gregaria

Locusts can learn associations between olfactory stimuli and food rewards, and use the acquired memories to choose between foods according to their nutrient requirements. They are a model system for both the study of olfactory coding and insect nutritional regulation. Previous studies have used operant paradigms for conditioning freely moving locusts, restricting the study of the neural mechanisms underlying the acquisition of olfactory memories, which requires restrained preparations for electrophysiological recordings. Here we present two complementary paradigms for the classical conditioning of olfactory memories in restrained desert locusts (Schistocerca gregaria). These paradigms allow precise experimental control over the parameters influencing learning. The first paradigm is based on classical (Pavlovian) appetitive conditioning. We show that opening of the maxillary palps can be used as a measure of memory acquisition. Maxillary palp opening in response to odour presentation is significantly higher in locusts trained with paired presentation of an odour and a food reward than in locusts trained either with unpaired presentation of food and odour or the odour alone. The memory formed by this conditioning paradigm lasts for at least 24 h. In the second paradigm, we show that classical conditioning of an odour memory in restrained locusts influences their decisions in a subsequent operant task. When locusts that have been trained to associate an odour with a food reward are placed in a Y-maze, they choose the arm containing that odour significantly more often than naïve locusts. A single conditioning trial is sufficient to induce a significant bias for that odour for up to 4 h. Multiple- and block-trial training induce a significant bias that lasts at least 24 h. Thus, locusts are capable of forming appetitive olfactory memories in classical conditioning paradigms and can use these memories to modify their decisions.

Treatment failure in pneumonia: impact of antibiotic treatment and cost analysis

The aim of this study was to investigate treatment failure (TF) in hospitalised community-acquired pneumonia (CAP) patients with regard to initial antibiotic treatment and economic impact. CAP patients were included in two open, prospective multicentre studies assessing the direct costs for in-patient treatment. Patients received treatment either with moxifloxacin (MFX) or a nonstandardised antibiotic therapy. Any change in antibiotic therapy after >72 h of treatment to a broadened antibiotic spectrum was considered as TF. Overall, 1,236 patients (mean ± SD age 69.6 ± 16.8 yrs, 691 (55.9%) male) were included. TF occurred in 197 (15.9%) subjects and led to longer hospital stay (15.4 ± 7.3 days versus 9.8 ± 4.2 days; p < 0.001) and increased median treatment costs (€2,206 versus €1,284; p<0.001). 596 (48.2%) patients received MFX and witnessed less TF (10.9% versus 20.6%; p < 0.001). After controlling for confounders in multivariate analysis, adjusted risk of TF was clearly reduced in MFX as compared with β-lactam monotherapy (adjusted OR for MFX 0.43, 95% CI 0.27-0.68) and was more comparable with a β-lactam plus macrolide combination (BLM) (OR 0.68, 95% CI 0.38-1.21). In hospitalised CAP, TF is frequent and leads to prolonged hospital stay and increased treatment costs. Initial treatment with MFX or BLM is a possible strategy to prevent TF, and may thus reduce treatment costs.

Epigenetic remodelling of brain, body and behaviour during phase change in locusts

The environment has a central role in shaping developmental trajectories and determining the phenotype so that animals are adapted to the specific conditions they encounter. Epigenetic mechanisms can have many effects, with changes in the nervous and musculoskeletal systems occurring at different rates. How is the function of an animal maintained whilst these transitions happen? Phenotypic plasticity can change the ways in which animals respond to the environment and even how they sense it, particularly in the context of social interactions between members of their own species. In the present article, we review the mechanisms and consequences of phenotypic plasticity by drawing upon the desert locust as an unparalleled model system. Locusts change reversibly between solitarious and gregarious phases that differ dramatically in appearance, general physiology, brain function and structure, and behaviour. Solitarious locusts actively avoid contact with other locusts, but gregarious locusts may live in vast, migrating swarms dominated by competition for scarce resources and interactions with other locusts. Different phase traits change at different rates: some behaviours take just a few hours, colouration takes a lifetime and the muscles and skeleton take several generations. The behavioural demands of group living are reflected in gregarious locusts having substantially larger brains with increased space devoted to higher processing. Phase differences are also apparent in the functioning of identified neurons and circuits. The whole transformation process of phase change pivots on the initial and rapid behavioural decision of whether or not to join with other locusts. The resulting positive feedback loops from the presence or absence of other locusts drives the process to completion. Phase change is accompanied by dramatic changes in neurochemistry, but only serotonin shows a substantial increase during the critical one- to four-hour window during which gregarious behaviour is established. Blocking the action of serotonin or its synthesis prevents the establishment of gregarious behaviour. Applying serotonin or its agonists promotes the acquisition of gregarious behaviour even in a locust that has never encountered another locust. The analysis of phase change in locusts provides insights into a feedback circuit between the environment and epigenetic mechanisms and more generally into the neurobiology of social interaction.

Gregarious desert locusts have substantially larger brains with altered proportions compared with the solitarious phase

The behavioural demands of group living and foraging have been implicated in both evolutionary and plastic changes in brain size. Desert locusts show extreme phenotypic plasticity, allowing brain morphology to be related to very different lifestyles in one species. At low population densities, locusts occur in a solitarious phase that avoids other locusts and is cryptic in appearance and behaviour. Crowding triggers the transformation into the highly active gregarious phase, which aggregates into dense migratory swarms. We found that the brains of gregarious locusts have very different proportions and are also 30 per cent larger overall than in solitarious locusts. To address whether brain proportions change with size through nonlinear scaling (allometry), we conducted the first comprehensive major axis regression analysis of scaling relations in an insect brain. This revealed that phase differences in brain proportions arise from a combination of allometric effects and deviations from the allometric expectation (grade shifts). In consequence, gregarious locusts had a larger midbrainoptic lobe ratio, a larger central complex and a 50 per cent larger ratio of the olfactory primary calyx to the first olfactory neuropile. Solitarious locusts invest more in low-level sensory processing, having disproportionally larger primary visual and olfactory neuropiles, possibly to gain sensitivity. The larger brains of gregarious locusts prioritize higher integration, which may support the behavioural demands of generalist foraging and living in dense and highly mobile swarms dominated by intense intraspecific competition.

Motor neurone responses during a postural reflex in solitarious and gregarious desert locusts

Desert locusts show extreme phenotypic plasticity and can change reversibly between two phases that differ radically in morphology, physiology and behaviour. Solitarious locusts are cryptic in appearance and behaviour, walking slowly with the body held close to the ground. Gregarious locusts are conspicuous in appearance and much more active, walking rapidly with the body held well above the ground. During walking, the excursion of the femoro-tibial (F-T) joint of the hind leg is smaller in solitarious locusts, and the joint is kept more flexed throughout an entire step. Under open loop conditions, the slow extensor tibiae (SETi) motor neurone of solitarious locusts shows strong tonic activity that increases at more extended F-T angles. SETi of gregarious locusts by contrast showed little tonic activity. Simulated flexion of the F-T joint elicits resistance reflexes in SETi in both phases, but regardless of the initial and final position of the leg, the spiking rate of SETi during these reflexes was twice as great in solitarious compared to gregarious locusts. This increased sensory-motor gain in the neuronal networks controlling postural reflexes in solitarious locusts may be linked to the occurrence of pronounced behavioural catalepsy in this phase similar to other cryptic insects such as stick insects.

[The impact of viruses in lower respiratory tract infections of the adult. Part III: therapy and prevention]

In industrialized countries respiratory tract infections are one of the most common reasons for medical consultations. It is assumed that almost one third of these infections include the lower respiratory tract (LRTI), e. g. acute bronchitis, acute exacerbation of chronic obstructive pulmonary disease (COPD), community- or hospital-acquired pneumonia and influenza. Due to a lack of sufficient and valid investigations to prove the presence of respiratory viruses their impact in the pathogenesis of lower respiratory tract infection has probably been underestimated for a long time. Therefore, there might have been many cases of unnecessary antibiotic treatment, especially in cases of acute bronchitis or acute exacerbations of COPD, because of an assumed bacteriological cause. With the introduction of more sensitive investigational procedures, such as polymerase chain reaction, it is possible to sufficiently prove respiratory viruses and therefore illuminate their role in the pathogenesis of lower respiratory tract infections of the adult. We have reviewed the current literature on the impact of viruses in lower respiratory tract infections to elucidate the role of viruses in the pathogenesis of lower respiratory tract infections. The preceding parts of this series provided an introduction to the frequently found viruses, pathogenesis, and diagnostic procedures (part I) as well as common viral infections of the lower respiratory tract (part II). The present 3 (rd) part deals with therapy for and prevention of viral LRTI.

[The impact of viruses in lower respiratory tract infections of the adult. Part II: acute bronchitis, acute exacerbated COPD, pneumonia, and influenza]

In industrialized countries respiratory tract infections are one of the most common reasons for medical consultations. It is assumed that almost one third of these infections affect the lower respiratory tract (LRTI), e. g. acute bronchitis, acute exacerbation of chronic obstructive pulmonary disease (COPD), community- or hospital-acquired pneumonia and influenza. Due to a lack of sufficient and valid investigations on the epidemiology of respiratory viruses, their impact on the pathogenesis of LRTI has probably been underestimated for a long time. Therefore, there might have been many cases of needless antibiotic treatment, particularly in cases of acute bronchitis or acute exacerbations of COPD, because of an assumed bacteriological aetiology. Following the introduction of diagnostic procedures with increased sensitivity, such as polymerase chain reaction, it is possible to reliably detect respiratory viruses and to illuminate their role in the pathogenesis of LRTI of the adult. We have reviewed the current literature to elucidate the role of viruses in the pathogenesis of LRTI. The first part of this series described frequent viral pathogens, pathogenesis of viral LRTI, and diagnostic procedures. In this 2 (nd) part the aetiological role of viruses in the most frequent forms of LRTI will be highlighted, and the third and last part will provide an overview of therapeutic and preventive options.

[The impact of viruses in lower respiratory tract infections of the adult. Part I: Pathogenesis, viruses, and diagnostics]

In industrialised countries respiratory tract infections are one of the most common reasons for medical consultations. It is assumed that almost one third of these infections include the lower respiratory tract (LRTI), e. g. acute bronchitis, acute exacerbation of chronic obstructive pulmonary disease (COPD), community- or hospital-acquired pneumonia and influenza. Due to a lack of sufficient and valid investigations on the epidemiology of respiratory viruses, their impact on the pathogenesis of LRTI has probably been underestimated for a long time. Therefore, there might have been many cases of needless antibiotic treatment, particularly in cases of acute bronchitis or acute exacerbations of COPD, because of an assumed bacteriological aetiology. Following the introduction of diagnostic procedures with increased sensitivity, such as polymerase chain reaction, it is possible to reliably detect respiratory viruses and to illuminate their role in the pathogenesis of LRTI of the adult. We have reviewed the current literature to elucidate the role of viruses in the pathogenesis of LRTI. The first part of this series deals with the relevant pathogens, pathogenesis, and diagnostic procedures. In the subsequent 2 parts of this series a review will be given on the most common variants of viral LRTI (part II), and therapeutic and preventive options (part III).

Serotonin mediates behavioral gregarization underlying swarm formation in desert locusts

Desert locusts, Schistocerca gregaria, show extreme phenotypic plasticity, transforming between a little-seen solitarious phase and the notorious swarming gregarious phase depending on population density. An essential tipping point in the process of swarm formation is the initial switch from strong mutual aversion in solitarious locusts to coherent group formation and greater activity in gregarious locusts. We show here that serotonin, an evolutionarily conserved mediator of neuronal plasticity, is responsible for this behavioral transformation, being both necessary if behavioral gregarization is to occur and sufficient to induce it. Our data demonstrate a neurochemical mechanism linking interactions between individuals to large-scale changes in population structure and the onset of mass migration.

Enhanced fidelity of diffusive nitric oxide signalling by the spatial segregation of source and target neurones in the memory centre of an insect brain

The messenger molecule nitric oxide (NO) is a key mediator of memory formation that can diffuse in the brain over tens of micrometres. It would seem therefore that NO derived from many individual neurones may merge into a volume signal that is inevitably ambiguous, relatively unspecific and thus unreliable. Here we report on the neuronal architecture that supports the NO-cyclic GMP signalling pathway in the mushroom body of an insect brain, the key centre for associative learning. We show that, in the locust (Schistocerca gregaria), parallel axons of intrinsic neurones (Kenyon cells) form tubular NO-producing zones surrounding central cores of NO-receptive Kenyon cell axons, which do not produce NO. This segregated architecture requires NO to spread at physiological concentrations up to 60 microm from the tube walls into the central NO-receptive cores. By modelling NO diffusion we show that a segregated architecture, which requires NO to act at a distance, affords significant advantages over a system where the same sources and targets intermingle. Segregation enhances the precision of NO volume signals by reducing noise and ambiguity, achieving a reliable integration of the activity of thousands of NO-source neurones. In a neural structure that forms NO-dependent associations, these properties of the segregated architecture may reduce the likelihood of forming spurious memories.

Nitric oxide synthase in crayfish walking leg ganglia: Segmental differences in chemo-tactile centers argue against a generic role in sensory integration

Nitric oxide (NO) is a diffusible signaling molecule with evolutionarily conserved roles in neural plasticity. Prominent expression of NO synthase (NOS) in the primary olfactory centers of mammals and insects lead to the notion of a special role for NO in olfaction. In insects, however, NOS is also strongly expressed in non-olfactory chemo-tactile centers of the thoracic nerve cord. The functional significance of this apparent association with various sensory centers is unclear, as is the extent to which it occurs in other arthropods. We therefore investigated the expression of NOS in the pereopod ganglia of crayfish (Pacifastacus lenisculus and Procambarus clarkii). Conventional NADPH diaphorase (NADPHd) staining after formaldehyde fixation gave poor anatomic detail, whereas fixation in methanol/formalin (MF-NADPHd) resulted in Golgi-like staining, which was supported by immunohistochemistry using NOS antibodies that recognize a 135-kDa protein in crayfish. MF-NADPHd revealed an exceedingly dense innervation of the chemo-tactile centers. As in insects, this innervation was provided by a system of prominent intersegmental neurons. Superimposed on a putatively conserved architecture, however, were pronounced segmental differences. Strong expression occurred only in the anterior three pereopod ganglia, correlating with the presence of claws on pereopods one to three. These clawed pereopods, in addition to their role in locomotion, are crucially involved in feeding, where they serve both sensory and motor functions. Our findings indicate that strong expression of NOS is not a universal feature of primary sensory centers but instead may subserve a specific requirement for sensory plasticity that arises only in particular behavioral contexts.

[Diagnosis and therapy of aspiration pneumonia]

Aspiration pneumonia is an important and frequent complication following aspiration of infectious material from the oropharynx or stomach. Therefore the microbiological flora generally comprises a mixed spectrum of microbes including aerobic, microaerobic and anaerobic mircoorganisms. There are a number of risk factors for aspiration such as compromised consciousness or esophageal diseases. Aspiration pneumonia presents as a subacute or chronic disease. An endoscopic inspection of the bronchial system and a bacteriological evaluation should be performed in all patients. The principal therapeutic strategy for aspiration pneumonia is an antibiotic therapy. In uncomplicated cases a treatment for 7-10 days should be sufficient, but in case of complications like necrotizing pneumonia or lung abscess a prolonged administration (14-21 days, up to weeks or months) will be necessary. Recommended antibiotic regimens include clindamycin +/- cephalosporin, ampicillin/sulbactam and moxifloxacin.

Modeling cooperative volume signaling in a plexus of nitric-oxide-synthase-expressing neurons

In vertebrate and invertebrate brains, nitric oxide (NO) synthase (NOS) is frequently expressed in extensive meshworks (plexuses) of exceedingly fine fibers. In this paper, we investigate the functional implications of this morphology by modeling NO diffusion in fiber systems of varying fineness and dispersal. Because size severely limits the signaling ability of an NO-producing fiber, the predominance of fine fibers seems paradoxical. Our modeling reveals, however, that cooperation between many fibers of low individual efficacy can generate an extensive and strong volume signal. Importantly, the signal produced by such a system of cooperating dispersed fibers is significantly more homogeneous in both space and time than that produced by fewer larger sources. Signals generated by plexuses of fine fibers are also better centered on the active region and less dependent on their particular branching morphology. We conclude that an ultrafine plexus is configured to target a volume of the brain with a homogeneous volume signal. Moreover, by translating only persistent regional activity into an effective NO volume signal, dispersed sources integrate neural activity over both space and time. In the mammalian cerebral cortex, for example, the NOS plexus would preferentially translate persistent regional increases in neural activity into a signal that targets blood vessels residing in the same region of the cortex, resulting in an increased regional blood flow. We propose that the fineness-dependent properties of volume signals may in part account for the presence of similar NOS plexus morphologies in distantly related animals.

Timed and targeted differential regulation of nitric oxide synthase (NOS) and anti-NOS genes by reward conditioning leading to long-term memory formation

In a number of neuronal models of learning, signaling by the neurotransmitter nitric oxide (NO), synthesized by the enzyme neuronal NO synthase (nNOS), is essential for the formation of long-term memory (LTM). Using the molluscan model system Lymnaea, we investigate here whether LTM formation is associated with specific changes in the activity of members of the NOS gene family: Lym-nNOS1, Lym-nNOS2, and the antisense RNA-producing pseudogene (anti-NOS). We show that expression of the Lym-nNOS1 gene is transiently upregulated in cerebral ganglia after conditioning. The activation of the gene is precisely timed and occurs at the end of a critical period during which NO is required for memory consolidation. Moreover, we demonstrate that this induction of the Lym-nNOS1 gene is targeted to an identified modulatory neuron called the cerebral giant cell (CGC). This neuron gates the conditioned feeding response and is an essential part of the neural network involved in LTM formation. We also show that the expression of the anti-NOS gene, which functions as a negative regulator of nNOS expression, is downregulated in the CGC by training at 4 h after conditioning, during the critical period of NO requirement. This appears to be the first report of the timed and targeted differential regulation of the activity of a group of related genes involved in the production of a neurotransmitter that is necessary for learning, measured in an identified neuron of known function. We also provide the first example of the behavioral regulation of a pseudogene.

Localization of nitric oxide synthase in the central complex and surrounding midbrain neuropils of the locust Schistocerca gregaria

Nitric oxide (NO), generated enzymatically by NO synthase (NOS), acts as an important signaling molecule in the nervous systems of vertebrates and invertebrates. In insects, NO has been implicated in development and in various aspects of sensory processing. To understand better the contribution of NO signaling to higher level brain functions, we analyzed the distribution of NOS in the midbrain of a model insect species, the locust Schistocerca gregaria, by using NADPH diaphorase (NADPHd) histochemistry after methanol/formalin fixation; results were validated by NOS immunohistochemistry. NADPHd yielded much higher sensitivity and resolution, but otherwise the two techniques resulted in corresponding labeling patterns throughout the brain, except for intense immunostaining but only weak NADPHd staining in median neurosecretory cells. About 470 neuronal cell bodies in the locust midbrain were NADPHd-positive positive, and nearly all major neuropil centers contained dense, sharply stained arborizations. We report several novel types of NOS-expressing neurons, including small ocellar interneurons and antennal sensory neurons that bypass the antennal lobe. Highly prominent labeling occurred in the central complex, a brain area involved in sky-compass orientation, and was analyzed in detail. Innervation by NOS-expressing fibers was most notable in the central body upper and lower divisions, the lateral accessory lobes, and the noduli. About 170 NADPHd-positive neurons contributed to this innervation, including five classes of tangential neuron, two systems of pontine neuron, and a system of columnar neurons. The results provide new insights into the neurochemical architecture of the central complex and suggest a prominent role for NO signaling in this brain area.

An evolutionarily conserved mechanism for sensitization of soluble guanylyl cyclase reveals extensive nitric oxide-mediated upregulation of cyclic GMP in insect brain

Soluble guanylyl cyclase (SGC) is the main receptor for the gaseous signalling molecule nitric oxide (NO) in vertebrates and invertebrates. Recently, a novel class of drugs that regulate mammalian SGC by NO-independent allosteric mechanisms has been identified [e.g. 3-(5'-hydroxymethyl-2'-furyl)-1-benzyl indazole, YC-1]. To assess the evolutionary conservation and hence the potential physiological relevance of these mechanisms, we have tested YC-1 on the brains of two model insects, the cockroach Periplaneta americana and the locust Schistocerca gregaria. YC-1 strongly potentiated the NO-induced elevation of total cyclic 3',5'-guanosine monophosphate (cGMP) and amplified the intensity and consistency of NO-induced cGMP-immunoreactivity in the brain. Our data indicate that the effect of YC-1 was independent of phosphodiesterase inhibition and thus mediated by direct sensitization of SGC. Immunohistopharmacology and co-labelling with antibodies against the SGC alpha-subunit confirmed that cGMP induced by co-application of NO and YC-1 is predominantly attributable to SGC. The staggering number of NO-responsive neurons revealed by YC-1 suggests that previous studies may have considerably underestimated the number of cellular targets for NO in the insect brain. Moreover, a subset of these targets exhibited cGMP-immunoreactivity without application of exogenous NO, demonstrating that YC-1 can be exploited for visualization of physiological cGMP signals in response to endogenous NO production. In conclusion, our discovery that YC-1 is a potent sensitizer of insect SGC indicates that a NO-independent regulatory site is an evolutionarily conserved feature of SGC. Our findings add considerable momentum to the concept of an as yet unidentified endogenous ligand that regulates the gain of the NO-cGMP signalling pathway.

Serial hearing organs in the atympanate grasshopper Bullacris membracioides (Orthoptera, Pneumoridae)

In different insect taxa, ears can be found on virtually any part of the body. Comparative anatomy and similarities in the embryological development of ears in divergent taxa suggest that they have evolved multiple times from ubiquitous stretch or vibration receptors, but the homology of these structures has not yet been rigorously tested. Here we provide detailed analysis of a novel set of hearing organs in a relatively "primitive" atympanate bladder grasshopper (Bullacris membracioides) that is capable of signaling acoustically over 2 km. We use morphological, physiological, and behavioral experiments to demonstrate that this species has six pairs of serially repeated abdominal ears derived from proprioceptive pleural chordotonal organs (plCOs). We demonstrate continuity in auditory function from the five posterior pairs, which are simple forms comprising 11 sensilla and resembling plCOs in other grasshoppers, to the more complex anterior pair, which contains 2000 sensilla and is homologous to the single pair of tympanate ears found in "modern" grasshoppers. All 12 ears are morphologically differentiated, responsive to airborne sound at frequencies and intensities that are biologically significant (tuned to 1.5 and 4 kHz; 60-98 dB SPL), and capable of mediating behavioral responses of prospective mates. These data provide evidence for the transition in function and selective advantage that must occur during evolutionary development of relatively complex organs from simpler precursors. Our results suggest that ancestral insects with simple atympanate pleural receptors may have had hearing ranges that equal or exceed those of contemporary insects with complex tympanal ears. Moreover, auditory capability may be more prevalent among modern insect taxa than the presence of overt tympana indicates.

New techniques for whole-mount NADPH-diaphorase histochemistry demonstrated in insect ganglia

Fixation-resistant NADPH-diaphorase (NADPHd) activity is used widely as a marker for nitric oxide synthase (NOS). In frozen sections, NADPHd histochemistry yields high anatomic definition. In whole-mounts, however, poor penetration of the reagents, background staining, and tissue opacity severely limit its application. Here we report a combination of new methods that significantly improves whole-mount NADPHd staining. We demonstrate these methods in the thoracic ganglia of a large insect, the locust Schistocerca gregaria, in which NADPHd has been analyzed previously using both whole-mounts and serial section reconstructions. The penetration of the staining reagents was markedly improved after fixation in methanol/formalin compared to phosphate-buffered formaldehyde. Methanol/formalin also reduced nonspecific NADPHd and enhanced the selective staining. Penetration was further enhanced by incubation regimens that exploit the temperature- or pH-dependence of NADPHd. In combination with methanol/formalin fixation, this permitted staining to develop evenly throughout these comparatively large invertebrate ganglia. These improvements were complemented by a new clearing technique that preserves the NADPHd staining, gives excellent transparency, and avoids distortion of specimen morphology. The new methods revealed the three-dimensional architecture of NADPHd expression in locust ganglia in unprecedented detail and may similarly improve whole-mount detection of NADPHd in other invertebrate and vertebrate preparations.

GABA-like immunoreactivity in nonspiking interneurons of the locust metathoracic ganglion

Nonspiking interneurons are important components of the premotor circuitry in the thoracic ganglia of insects. Their action on postsynaptic neurons appears to be predominantly inhibitory, but it is not known which transmitter(s) they use. Here, we demonstrate that many but not all nonspiking local interneurons in the locust metathoracic ganglion are immunopositive for GABA (γ-aminobutyric acid). Interneurons were impaled with intracellular microelectrodes and were shown physiologically to be nonspiking. They were further characterized by defining their effects on known leg motor neurons when their membrane potential was manipulated by current injection. Lucifer Yellow was then injected into these interneurons to reveal their cell bodies and the morphology of their branches. Some could be recognised as individuals by comparison with previous detailed descriptions. Ganglia were then processed for GABA immunohistochemistry. Fifteen of the 17 nonspiking interneurons studied were immunopositive for GABA, but two were not. The results suggest that the majority of these interneurons might exert their well-characterized effects on other neurons through the release of GABA but that some appear to use a transmitter other than GABA. These nonspiking interneurons are therefore not an homogeneous population with regard to their putative transmitter.

Nitric oxide synthase histochemistry in insect nervous systems: Methanol/formalin fixation reveals the neuroarchitecture of formaldehyde-sensitive NADPH diaphorase in the cockroach Periplaneta americana

Formaldehyde-insensitive NADPH diaphorase (NADPHd) activity is used widely as a histochemical marker for neuronal nitric oxide synthase (NOS). However, in several insects including the cockroach Periplaneta americana, NOS is apparently formaldehyde-sensitive; NADPHd fails to reveal neuron morphology and results in faint generalized staining. Here we have used a novel fixative, methanol/ formalin (MF), to reveal for the first time the neuroarchitecture of NADPHd in the cockroach, with intense selective staining occurring in neurons throughout the brain and thoracic ganglia. Immunocytochemical and histochemical analysis of cockroach and locust nervous systems indicated that neuronal NADPHd after MF fixation can be attributed to NOS. However, NADPHd in locust glial and perineurial cells was histochemically different from that in neurons and may thus be due to enzymes other than NOS. Histochemical implications of species-specific enzyme properties and of the transcriptional complexity of the NOS gene are discussed. The present findings suggest that MF fixation is a valuable new tool for the comparative analysis of the neuroarchitecture of NO signaling in insects. The Golgi-like definition of the staining enabled analysis of the NADPHd architecture in the cockroach and comparison with that in the locust. NADPHd in the tactile neuropils of the thoracic ganglia showed a similar organization in the two species. The olfactory glomeruli of the antennal lobes were in both species densely innervated by NADPHd-positive local interneurons that correlated in number with the number of glomeruli. Thus, the NADPHd architectures appear highly conserved in primary sensory neuropils. In the cockroach mushroom bodies, particularly dense staining in the gamma-layer of the lobes was apparently derived from Kenyon cells, whereas extrinsic arborizations were organized in domains across the lobes, an architecture that contrasts with the previously described tubular compartmentalization of locust mushroom bodies. These divergent architectures may result in different spatiotemporal dynamics of NO diffusion and suggest species differences in the role of NO in the mushroom bodies.

Contralateral inhibition as a sensory bias: the neural basis for a female preference in a synchronously calling bushcricket, Mecopoda elongata

Imperfect synchrony between male calls occurs widely in acoustically courting crickets and bushcrickets. Males which are able to establish the temporal leadership usually attract more females in choice experiments but the proximate mechanism for this precedence effect is unknown. Here we show that contralateral inhibition, the neural basis for lateral contrast enhancement in the auditory pathways of insects and vertebrates, is also the probable proximate neural mechanism for this female preference. We recorded simultaneously from a pair of identified auditory interneurons in the synchronizing bushcricket Mecopoda elongata. When two identical acoustic stimuli are presented from opposite directions, one preceding the other by 120 ms, the neural representation within the receiver is far stronger for the leader signal. This results from a suppression of the neural response to the follower chirp by reciprocal contralateral inhibition. The advantage of the representation of the leader is 2-3-fold with time delays between 70 and 130 ms; the most clear-cut female preferences have also been found with such delays in previous behavioural experiments. In time-intensity trading experiments, a lead by 120 ms could only be compensated for by increasing the amplitude of the follower signal by 7-11 dB. We discuss contralateral inhibition in auditory systems as a sensory bias that results in female preference for leading signals, with important evolutionary consequences for male calling strategies.

Sensory afferents and motor neurons as targets for nitric oxide in the locust

In the adult locust, nitric oxide (NO) synthase is expressed in interneurons that innervate mechanosensory neuropils, indicating that NO may participate in mechanosensory processing. Here, we have identified potential neuronal targets of NO by localizing the expression and activity of soluble guanylyl cyclase (SGC), its principal molecular target in the nervous system. We used two complementary approaches, namely immunolocalization of SGC alpha-subunit (SGCalpha), and of cyclic GMP (cGMP) after exposure to an NO donor. The cell bodies, axons and central projections of thoracic exteroceptors, proprioceptors, auditory receptors, and chemoreceptors were strongly immunoreactive for SGCalpha. Strong SGCalpha immunoreactivity also occurred in all thoracic motor neurons, including their axon terminals. NO-donors induced a pattern of cGMP immunostaining that was similar to the distribution of SGCalpha, indicating that both sensory and motor neurons contain functional SGC. Therefore, NO may modulate both the input from these sensory neurons and the output of motor neurons. Although the expression of SGCalpha was highly consistent, NO donors did not always induce cGMP-staining in SGC-containing neurons, suggesting that SGC is coregulated by factors other than NO. Complementing previous reports in the visual and olfactory system, our results indicate a general role for NO-cGMP signaling in early sensory processing; diffusible signals may mediate a cross-adaptation or -sensitization within neural maps where similarly tuned neurons have adjacent projections, an anatomical arrangement shared by many sensory systems.