Temporary amnesia induced by cold anesthesia and hypoxia in Drosophila

A cold and quiet brain: mechanisms of insect CNS arrest at low temperatures

Exposure to cold causes insects to enter a chill coma at species-specific temperatures and such temperature sensitivity contributes to geographic distribution and phenology. Coma results from abrupt spreading depolarization (SD) of neural tissue in the integrative centers of the CNS. SD abolishes neuronal signaling and the operation of neural circuits, like an off switch for the CNS. Turning off the CNS by allowing ion gradients to collapse will conserve energy and may offset negative consequences of temporary immobility. SD is modified by prior experience via rapid cold hardening (RCH) or cold acclimation which alter properties of K_v channels, Na⁺/K⁺-ATPase and Na⁺/K⁺/2Cl^- cotransporter. The stress hormone octopamine mediates RCH. Future progress depends on developing a more complete understanding of ion homeostasis in and of the insect CNS.

Color is necessary for face discrimination in the Northern paper wasp, Polistes fuscatus

Visual individual recognition requires animals to distinguish among conspecifics based on appearance. Though visual individual recognition has been reported in a range of taxa including primates, birds, and insects, the features that animals require to discriminate between individuals are not well understood. Northern paper wasp females, Polistes fuscatus, possess individually distinctive color patterns on their faces, which mediate individual recognition. However, it is currently unclear what role color plays in the facial recognition system of this species. Thus, we sought to test two possible roles of color in wasp facial recognition. On one hand, color may be important simply because it creates a pattern. If this is the case, then wasps should perform similarly when discriminating color or grayscale images of the same faces. Alternatively, color itself may be important for recognition of an image as a "face", which would predict poorer performance on grayscale discrimination relative to color images. We found wasps performed significantly better when discriminating between color faces compared to grayscale versions of the same faces. In fact, wasps trained on grayscale faces did not perform better than chance, indicating that color is necessary for the recognition of an image as a face by the wasp visual system.

Cold-induced anesthesia impairs path integration memory in dung beetles

Path integration is a general mechanism used by many animals to maintain an updated record of their position in relation to a set reference point.^1-11 To do this, they continually integrate direction and distance information into a memorized home vector. What remains unclear is how this vector is stored, maintained, and utilized for successful navigation. A recent computational model based on the neuronal circuitry of the insect central complex suggests that home vector memories are encoded across a set of putative memory neurons and maintained through ongoing recurrent neural activity.¹² To better understand the nature of the home vector memory and experimentally assess underlying mechanisms for maintaining it, we performed a series of experiments on the path integrating dung beetle Scarabaeus galenus.¹³ We found that, while the directional component of the home vector was maintained for up to 1 h, the distance component of the vector memory decreased gradually over time. Using cold-induced anesthesia, we disrupted the neural activity of beetles that had stored a home vector of known length and direction. This treatment diminished both components of the home vector memory, but by different amounts-the homing beetles lost their distance memory before their directional memory. Together, these findings present new insights into the functional properties of home vector memories and provide the first empirical evidence that a biological process that can be disrupted by cold-induced anesthesia is essential to support homing by path integration.

Anesthesia disrupts distance, but not direction, of path integration memory

Solitary foraging insects, such as ants, maintain an estimate of the direction and distance to their starting location as they move away from it, in a process known as path integration. This estimate, commonly known as the "home vector," is updated continuously as the ant moves^1-4 and is reset as soon as it enters its nest,⁵ yet ants prevented from returning to their nest can still use their home vector when released several hours later.^6,7 This conjunction of fast update and long persistence of the home vector memory does not directly map to existing accounts of short-, mid-, and long-term memory;^2,8-12 hence, the substrate of this memory remains unknown. Chill-coma anesthesia^13-15 has previously been shown to affect associative memory retention in fruit flies^14,16 and honeybees.^9,17,18 We investigate the nature of path integration memory by anesthetizing ants after they have accumulated home vector information and testing if the memory persists on recovery. We show that after anesthesia the memory of the distance ants have traveled is degraded, but the memory of the direction is retained. We also show that this is consistent with models of path integration that maintain the memory in a redundant Cartesian coordinate system and with the hypothesis that chill-coma produces a proportional reduction of the memory, rather than a subtractive reduction or increase of noise. The observed effect is not compatible with a memory based on recurrent circuit activity and points toward an activity-dependent molecular process as the basis of path integration memory.

Lymnaea stagnalis as model for translational neuroscience research: From pond to bench

The purpose of this review is to illustrate how a reductionistic, but sophisticated, approach based on the use of a simple model system such as the pond snail Lymnaea stagnalis (L. stagnalis), might be useful to address fundamental questions in learning and memory. L. stagnalis, as a model, provides an interesting platform to investigate the dialog between the synapse and the nucleus and vice versa during memory and learning. More importantly, the "molecular actors" of the memory dialogue are well-conserved both across phylogenetic groups and learning paradigms, involving single- or multi-trials, aversion or reward, operant or classical conditioning. At the same time, this model could help to study how, where and when the memory dialog is impaired in stressful conditions and during aging and neurodegeneration in humans and thus offers new insights and targets in order to develop innovative therapies and technology for the treatment of a range of neurological and neurodegenerative disorders.

Testing the habituation assumption underlying models of parasitoid foraging behavior

BACKGROUND

Habituation, a form of non-associative learning, has several well-defined characteristics that apply to a wide range of physiological and behavioral responses in many organisms. In classic patch time allocation models, habituation is considered to be a major mechanistic component of parasitoid behavioral strategies. However, parasitoid behavioral responses to host cues have not previously been tested for the known, specific characteristics of habituation.

METHODS

In the laboratory, we tested whether the foraging behavior of the egg parasitoid Trissolcus basalis shows specific characteristics of habituation in response to consecutive encounters with patches of host (Nezara viridula) chemical contact cues (footprints), in particular: (i) a training interval-dependent decline in response intensity, and (ii) a training interval-dependent recovery of the response.

RESULTS

As would be expected of a habituated response, wasps trained at higher frequencies decreased their behavioral response to host footprints more quickly and to a greater degree than those trained at low frequencies, and subsequently showed a more rapid, although partial, recovery of their behavioral response to host footprints. This putative habituation learning could not be blocked by cold anesthesia, ingestion of an ATPase inhibitor, or ingestion of a protein synthesis inhibitor.

DISCUSSION

Our study provides support for the assumption that diminishing responses of parasitoids to chemical indicators of host presence constitutes habituation as opposed to sensory fatigue, and provides a preliminary basis for exploring the underlying mechanisms.

Natural variation in long-term memory formation among Nasonia parasitic wasp species

Closely related species of parasitic wasps can differ substantially in memory dynamics. In this study we demonstrate differences in the number of conditioning trials required to form long-term memory between the closely related parasitic wasp species Nasonia vitripennis and Nasonia giraulti (Hymenoptera: Pteromalidae). A single conditioning trial, in which a female wasp associates an odour with the reward of finding a host, results in the formation of transcription-dependent long-term memory in N. vitripennis, whereas N. giraulti requires spaced training to do so. Memory formation does not depend on the type of reward: oviposition, which was hypothesized to be a 'larger' reward results in similar memory retention as host feeding in both Nasonia species. There are several genetic and genomic tools available for Nasonia species to identify genetic mechanisms that underlie the observed variation in the number of trials required to form long-term memory.

Critical period of memory enhancement during taste avoidance conditioning in Lymnaea stagnalis

The present study investigated the optimal training procedure leading to long-lasting taste avoidance behavior in Lymnaea. A training procedure comprising 5 repeated pairings of a conditional stimulus (CS, sucrose), with an unconditional stimulus (US, a tactile stimulation to the animal's head), over a 4-day period resulted in an enhanced memory formation than 10 CS-US repeated pairings over a 2-day period or 20 CS-US repeated pairings on a single day. Backward conditioning (US-CS) pairings did not result in conditioning. Thus, this taste avoidance conditioning was CS-US pairing specific. Food avoidance behavior was not observed following training, however, if snails were immediately subjected to a cold-block (4°C for 10 min). It was critical that the cold-block be applied within 10 min to block long-term memory (LTM) formation. Further, exposure to the cold-block 180 min after training also blocked both STM and LTM formation. The effects of the cold-block on subsequent learning and memory formation were also examined. We found no long lasting effects of the cold-block on subsequent memory formation. If protein kinase C was activated before the conditioning paradigm, snails could still acquire STM despite exposure to the cold-block.

Effects of cold immobilization and recovery period on honeybee learning, memory, and responsiveness to sucrose

In addition to human error and variation in laboratory conditions, there are numerous factors that can complicate comparisons among studies. Furthermore, differences in how experimental methods are executed can make it difficult to distinguish between effects of focal versus extraneous variables. Insect neural function is commonly evaluated using Pavlovian conditioning techniques; learning and memory in many species can be assessed using the proboscis extension reflex (PER). However, there are significant inconsistencies in methods used to immobilize insects prior to PER tests. We compared responses of honeybees immobilized in a refrigerator, on ice, and in a freezer, and evaluated influence of recovery interval before testing. Ice-chilling weakly decreased learning (response to an originally neutral odor) more so than refrigeration or freezing, but not 24-h recall of odor. We found no significant differences in responsiveness to sucrose relative to cooling method, but responsiveness was significantly lower among honeybees left to recover for only 0.75h versus 1.5 or 3h. Finally, we observed increased responsiveness to sucrose and geraniol between June and August. Our results suggest that inconsistencies in cold immobilization methods could confound interpretation and comparison of results from a large body of work on honeybee learning and memory.

Natural variation in learning rate and memory dynamics in parasitoid wasps: opportunities for converging ecology and neuroscience

Although the neural and genetic pathways underlying learning and memory formation seem strikingly similar among species of distant animal phyla, several more subtle inter- and intraspecific differences become evident from studies on model organisms. The true significance of such variation can only be understood when integrating this with information on the ecological relevance. Here, we argue that parasitoid wasps provide an excellent opportunity for multi-disciplinary studies that integrate ultimate and proximate approaches. These insects display interspecific variation in learning rate and memory dynamics that reflects natural variation in a daunting foraging task that largely determines their fitness: finding the inconspicuous hosts to which they will assign their offspring to develop. We review bioassays used for oviposition learning, the ecological factors that are considered to underlie the observed differences in learning rate and memory dynamics, and the opportunities for convergence of ecology and neuroscience that are offered by using parasitoid wasps as model species. We advocate that variation in learning and memory traits has evolved to suit an insect's lifestyle within its ecological niche.

Early activation of extracellular signal-regulated kinase signaling pathway in the hippocampus is required for short-term memory formation of a fear-motivated learning

1. According to its duration there are, at least, two major forms of memory in mammals: short term memory (STM) which develops in a few seconds and lasts several hours and long-term memory (LTM) lasting days, weeks and even a lifetime. In contrast to LTM, very little is known about the neural, cellular and molecular requirements for mammalian STM formation. 2. Here we show that early activation of extracellular signal-regulated kinases 1/2 (ERK1/2) in the hippocampus is required for the establishment of STM for a one-trial inhibitory avoidance task in the rat. Immediate posttraining infusion of U0126 (a selective inhibitor of ERK kinase) into the CA1 region of the dorsal hippocampus blocked STM formation. 3. Reversible inactivation of the entorhinal cortex through muscimol infusion produced deficits in STM and a selective and rapid decrease in hippocampal ERK2 activation.4. Together with our previous findings showing a rapid decrease in ERK2 activation and impaired STM after blocking BDNF function, the present results strongly suggest that ERK2 signaling in the hippocampus is a critical step in STM processing.

Different parameters support generalization and discrimination learning in Drosophila at the flight simulator

We have used a genetically tractable model system, the fruit fly Drosophila melanogaster to study the interdependence between sensory processing and associative processing on learning performance. We investigated the influence of variations in the physical and predictive properties of color stimuli in several different operant-conditioning procedures on the subsequent learning performance. These procedures included context and stimulus generalization as well as color, compound, and conditional discrimination (colors and patterns). A surprisingly complex dependence of the learning performance on the colors' physical and predictive properties emerged, which was clarified by taking into account the fly-subjective perception of the color stimuli. Based on estimates of the stimuli's color and brightness values, we propose that the different tasks are supported by different parameters of the color stimuli; generalization occurs only if the chromaticity is sufficiently similar, whereas discrimination learning relies on brightness differences.

Glutamate uptake is stimulated by extracellular S100B in hippocampal astrocytes

1.S100B is a calcium-binding protein expressed and secreted by astrocytes, which has been implicated in glial-neuronal communication. Extracellular S100B appears to protect hippocampal neurons against toxic concentrations of glutamate. Here we investigated a possible autocrine role of S100B in glutamate uptake activity. 2. Astrocyte cultures were prepared of hippocampi from neonate Wistar rats. [(3)H] Glutamate uptake was measured after addition of S100B protein, antibody anti-S100B or TRTK-12, a peptide that blocks S100B activity mediated by the C-terminal region. 3.Antibody anti-S100B addition decreased glutamate uptake measured 30 min after medium replacement, without affecting cell integrity or viability. Moreover, low levels of S100B (less than 0.1 ng/mL) stimulated glutamate uptake measured immediately after medium replacement. 4. This finding reinforces the importance of astrocytes in the glutamatergic transmission, particularly the role of S100B neuroprotection against excitotoxic damage.

Exposure to hypomagnetic field space for multiple generations causes amnesia in Drosophila melanogaster

This is the introduction of Drosophila into the study of learning and memory affected by removal of the geomagnetic field (GMF) for successive generations. Using the operant visual learning/memory paradigm at a flight simulator, the present study revealed that wild-type flies raised in a hypomagnetic field environment continuously for 10 successive generations were gradually impaired in visual conditioning learning and memory formation and finally the 10th generation flies became morphs of nonlearners and completely amnesiac. The control experiments show that the impairment could not be ascribed to any apparent sensorimotor problems in Drosophila. The reverse shift from hypomagnetic field (HMF) to natural GMF restored the GMF-free induced amnesia fully after six consecutive generations. Thus, our findings demonstrate conclusively that some serious, but reversible learning and memory impairment may occur for living organisms in a prolonged separation from GMF over many consecutive generations. And Drosophila has the potential to develop into a new model organism for the study of the neurobiology of magnetism for multiple generations.

Neural substrates of memory: from synapse to system

One of the fundamental challenges of modern neuroscience is to understand how memories are acquired, stored, and retrieved by the brain. In the broadest terms, attempts to dissect memory can be broken down into four experimental disciplines: (1) identification of molecular components, (2) ex vivo and in vivo cellular analysis of neuronal function, (3) theoretical modeling approaches of neural systems, and (4) organismal-level behavioral analyses. Our objective here is to offer a conceptually unifying perspective and to discuss this perspective in relation to an experiment analysis of memory in Drosophila.

The operant and the classical in conditioned orientation of Drosophila melanogaster at the flight simulator

Ever since learning and memory have been studied experimentally, the relationship between operant and classical conditioning has been controversial. Operant conditioning is any form of conditioning that essentially depends on the animal's behavior. It relies on operant behavior. A motor output is called operant if it controls a sensory variable. The Drosophila flight simulator, in which the relevant behavior is a single motor variable (yaw torque), fully separates the operant and classical components of a complex conditioning task. In this paradigm a tethered fly learns, operantly or classically, to prefer and avoid certain flight orientations in relation to the surrounding panorama. Yaw torque is recorded and, in the operant mode, controls the panorama. Using a yoked control, we show that classical pattern learning necessitates more extensive training than operant pattern learning. We compare in detail the microstructure of yaw torque after classical and operant training but find no evidence for acquired behavioral traits after operant conditioning that might explain this difference. We therefore conclude that the operant behavior has a facilitating effect on the classical training. In addition, we show that an operantly learned stimulus is successfully transferred from the behavior of the training to a different behavior. This result unequivocally demonstrates that during operant conditioning classical associations can be formed.