Selection of light or darkness, locomotor, and stridulatory activities in the cricket, Gryllus bimaculatus Degeer (Orthoptera: Gryllidae)

Male crickets, Gryllus bimaculatus Degeer, turned lights on or off in a chamber by a seesaw device: (1) during a 12 h, and (2) during a 24 h day. The crickets in (1) and the last-instar nymph in (2) turned the lights on and off at irregular intervals and duration. The selection rate for darkness was greater than that for light by an average exceeding 80%. The locomotor activity of the nymph in (1) was arrhythmic. In (1) the adults stridulated and were active in continuous darkness during the 12 h, while, in contrast in (2) they turned on the light and stridulated without switching the light off. The locomotor and stridulatory activities of the adult crickets in (2) were free-running. These activities resulted in a free-running rhythm of selection for light or darkness in (2). Under the conditions of the present experiments, the circadian pacemaker functioned in the same way in light and dark cycles as in constant light conditions.     

Estimating Location without External Cues

The ability to determine one''s location is fundamental to spatial navigation. Here, it is shown that localization is theoretically possible without the use of external cues, and without knowledge of initial position or orientation. With only error-prone self-motion estimates as input, a fully disoriented agent can, in principle, determine its location in familiar spaces with 1-fold rotational symmetry. Surprisingly, localization does not require the sensing of any external cue, including the boundary. The combination of self-motion estimates and an internal map of the arena provide enough information for localization. This stands in conflict with the supposition that 2D arenas are analogous to open fields. Using a rodent error model, it is shown that the localization performance which can be achieved is enough to initiate and maintain stable firing patterns like those of grid cells, starting from full disorientation. Successful localization was achieved when the rotational asymmetry was due to the external boundary, an interior barrier or a void space within an arena. Optimal localization performance was found to depend on arena shape, arena size, local and global rotational asymmetry, and the structure of the path taken during localization. Since allothetic cues including visual and boundary contact cues were not present, localization necessarily relied on the fusion of idiothetic self-motion cues and memory of the boundary. Implications for spatial navigation mechanisms are discussed, including possible relationships with place field overdispersion and hippocampal reverse replay. Based on these results, experiments are suggested to identify if and where information fusion occurs in the mammalian spatial memory system.     

Key Features of Human Episodic Recollection in the Cross-Episode Retrieval of Rat Hippocampus Representations of Space

Neurophysiological studies focus on memory retrieval as a reproduction of what was experienced and have established that neural discharge is replayed to express memory. However, cognitive psychology has established that recollection is not a verbatim replay of stored information. Recollection is constructive, the product of memory retrieval cues, the information stored in memory, and the subject''s state of mind. We discovered key features of constructive recollection embedded in the rat CA1 ensemble discharge during an active avoidance task. Rats learned two task variants, one with the arena stable, the other with it rotating; each variant defined a distinct behavioral episode. During the rotating episode, the ensemble discharge of CA1 principal neurons was dynamically organized to concurrently represent space in two distinct codes. The code for spatial reference frame switched rapidly between representing the rat''s current location in either the stationary spatial frame of the room or the rotating frame of the arena. The code for task variant switched less frequently between a representation of the current rotating episode and the stable episode from the rat''s past. The characteristics and interplay of these two hippocampal codes revealed three key properties of constructive recollection. (1) Although the ensemble representations of the stable and rotating episodes were distinct, ensemble discharge during rotation occasionally resembled the stable condition, demonstrating cross-episode retrieval of the representation of the remote, stable episode. (2) This cross-episode retrieval at the level of the code for task variant was more likely when the rotating arena was about to match its orientation in the stable episode. (3) The likelihood of cross-episode retrieval was influenced by preretrieval information that was signaled at the level of the code for spatial reference frame. Thus key features of episodic recollection manifest in rat hippocampal representations of space.     

A feedforward model for the formation of a grid field where spatial information is provided solely from place cells

Grid cells (GCs) in the medial entorhinal cortex (mEC) have the property of having their firing activity spatially tuned to a regular triangular lattice. Several theoretical models for grid field formation have been proposed, but most assume that place cells (PCs) are a product of the grid cell system. There is, however, an alternative possibility that is supported by various strands of experimental data. Here we present a novel model for the emergence of gridlike firing patterns that stands on two key hypotheses: (1) spatial information in GCs is provided from PC activity and (2) grid fields result from a combined synaptic plasticity mechanism involving inhibitory and excitatory neurons mediating the connections between PCs and GCs. Depending on the spatial location, each PC can contribute with excitatory or inhibitory inputs to GC activity. The nature and magnitude of the PC input is a function of the distance to the place field center, which is inferred from rate decoding. A biologically plausible learning rule drives the evolution of the connection strengths from PCs to a GC. In this model, PCs compete for GC activation, and the plasticity rule favors efficient packing of the space representation. This leads to gridlike firing patterns. In a new environment, GCs continuously recruit new PCs to cover the entire space. The model described here makes important predictions and can represent the feedforward connections from hippocampus CA1 to deeper mEC layers.     

Role of light and temperature in relation to seed germination and seedling growth ofAsteracantha longifolia Nees

Summary The seeds ofAsteracantha longifolia prefer germinating in light. Germination was also favoured in blue and red lights, whereas total darkness delayed this process. The optimum temperature for germination of seeds was 29° C in continuous white light. The seeds did germinate in total darkness as well, but the percentage of germination remained poor, and with high temperatures beyond 30° C, the pace of germination became slow. Higher temperatures suppressed the seedling growth both in continuous white light and total darkness. Blue and red lights promoted hypocotyl growth, whereas radicle was inhibited.     

Spatial cognition and neuro-mimetic navigation: a model of hippocampal place cell activity

 A computational model of hippocampal activity during spatial cognition and navigation tasks is presented. The spatial representation in our model of the rat hippocampus is built on-line during exploration via two processing streams. An allothetic vision-based representation is built by unsupervised Hebbian learning extracting spatio-temporal properties of the environment from visual input. An idiothetic representation is learned based on internal movement-related information provided by path integration. On the level of the hippocampus, allothetic and idiothetic representations are integrated to yield a stable representation of the environment by a population of localized overlapping CA3-CA1 place fields. The hippocampal spatial representation is used as a basis for goal-oriented spatial behavior. We focus on the neural pathway connecting the hippocampus to the nucleus accumbens. Place cells drive a population of locomotor action neurons in the nucleus accumbens. Reward-based learning is applied to map place cell activity into action cell activity. The ensemble action cell activity provides navigational maps to support spatial behavior. We present experimental results obtained with a mobile Khepera robot. Received: 02 July 1999 / Accepted in revised form: 20 March 2000     

Spectral preferences of Lycorma delicatula (Hemiptera: Fulgoridae)

Many insects prefer lights with certain spectral properties, and such preferences may be associated with behavioral contexts such as mating, host finding or dispersal. Lycorma delicatula (Hemiptera: Fulgoridae) is a newly invasive species in Korea and is spreading rapidly. It is diurnal and may rely on visual cues for orientation. We conducted a series of three phototaxis experiments to understand spectral preferences in L. delicatula: light/dark choice, UV/white light choice, and color preference experiments. Nymphs of the third and final stages as well as adults were used for these experiments. In the light/dark choice, the orientation of L. delicatula was bimodal between the white light and darkness, for all stages and both sexes. In a choice of UV (395–410 nm wavelengths) vs. white light, L. delicatula of both sexes and all stages preferred the UV light. In the color preference experiment where insects had a choice of four colors in a circular arena, L. delicatula stayed significantly longer in the blue light than in white, yellow or green lights. Overall, nymphs and adults of L. delicatula oriented toward lights with shorter wavelengths, and this orientation was consistent throughout all stages, regardless of sex. It is necessary to investigate the behavioral contexts under which L. delicatula prefers the UV and blue lights.     

Lesions of the Basal Forebrain Cholinergic System in Mice Disrupt Idiothetic Navigation

Loss of integrity of the basal forebrain cholinergic neurons is a consistent feature of Alzheimer’s disease, and measurement of basal forebrain degeneration by magnetic resonance imaging is emerging as a sensitive diagnostic marker for prodromal disease. It is also known that Alzheimer’s disease patients perform poorly on both real space and computerized cued (allothetic) or uncued (idiothetic) recall navigation tasks. Although the hippocampus is required for allothetic navigation, lesions of this region only mildly affect idiothetic navigation. Here we tested the hypothesis that the cholinergic medial septo-hippocampal circuit is important for idiothetic navigation. Basal forebrain cholinergic neurons were selectively lesioned in mice using the toxin saporin conjugated to a basal forebrain cholinergic neuronal marker, the p75 neurotrophin receptor. Control animals were able to learn and remember spatial information when tested on a modified version of the passive place avoidance test where all extramaze cues were removed, and animals had to rely on idiothetic signals. However, the exploratory behaviour of mice with cholinergic basal forebrain lesions was highly disorganized during this test. By contrast, the lesioned animals performed no differently from controls in tasks involving contextual fear conditioning and spatial working memory (Y maze), and displayed no deficits in potentially confounding behaviours such as motor performance, anxiety, or disturbed sleep/wake cycles. These data suggest that the basal forebrain cholinergic system plays a specific role in idiothetic navigation, a modality that is impaired early in Alzheimer’s disease.     

Spectral preference and temporal modulation of photic orientation by Colorado potato beetle on a servosphere

The Colorado potato beetle (CPB), Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae), is a diurnal insect that strongly relies on visual cues to guide its walk. In the present study, we investigated the orientation behavior of non‐diapausing walking CPB in response to emissive colors produced by light emitting diodes (LEDs) in a dual choice arena adapted to a servosphere, where the only illumination available came from the photo‐stimuli. Our results demonstrate that CPB show positive phototactic behavior when stimulated with different wavelengths of light; they preferred to orient towards white (420–775 nm), ultraviolet (UV) (351 nm), blue (472 nm), green (570 nm), yellow (585 nm), orange (590 nm), and red (660 nm) over darkness when both alternatives were offered, but no orientation responses were elicited by infrared (940 nm). Both males and females preferred yellow and green over other colors, but did not show any particular preference between them, thus correlating with their preference for wavelengths reflected by vegetation. Sexual differences were noted in that male CPB preferred white over either red or UV, whereas female CPB did not show any preferences when offered these colors. Female CPB preferred UV and blue over red, whereas males showed no preferences when these colors were offered. Colorado potato beetles turned at higher angles and performed more tortuous walks in complete darkness and when infrared vs. darkness were offered compared with the rest of the colored lights. Both sexes preferred continuous over pulsed yellow light. Colorado potato beetles subjected to pulsed yellow light showed a temporal alteration of their walking performance by walking less, slower, and turning at a higher rate. The results are discussed with regard to the role of color in the CPB attraction to host plants and conspecifics as well as the role of intermittent photic stimuli in their orientation behavior. The information provided here provides a basis for the improvement of trapping devices for detection and survey of incipient or invasive CPB, and development of alternate control strategies for this important pest of potatoes and other solanaceous crops.     

Orientation by the Bat Phyllostomus discolor (Phyllostomidae) on the Return Flight to its Resting Place

Bats have a well-developed spatial memory, which enables them to navigate even when the conditions are extremely unfavourable for orientation. However, if they were to adhere too strictly to a flight path planned from memory and independent of exteroceptive control, they would be in danger of colliding with unexpected obstacles. In the experiments described here, Phyllostomus discolor that had familiarized themselves with an octagonal flight arena developed a clear preference for certain resting sites and were able to fly to these sites without recourse to external orientational cues. Proximal and distal cues were ruled out separately, by rotating the direction in which the bats started out within the arena or by rotating the entire arena in the room. Furthermore, by marking the preferred site with a visible identifier it was shown that even when additional aids to orientation are available, the bats do not make use of them. On the other hand, all the bats tested responded immediately to a reduction of the landing area, demonstrating that they are capable of incorporating exteroceptive information into the orientation process in certain circumstances.     

Environmental light-darkness conditions induce changes in brain and peripheral pyroglutamyl-peptidase I activity

To evaluate the influence of light and darkness on brain pyroglutamyl-peptidase I (pGluPI) activity, four experimental groups of rats were compared at the same time-point (10.00 h). Two groups were designed with a standard 12-12 h light-dark cycle: In group A, the lights were on from 7.00 h to 19.00 h, and the experiment was done under light conditions; in group B, the lights were on from 19.00 h to 7.00 h, and the experiment was done under darkness conditions. Two additional groups were designed with nonstandard light-dark conditions: In group C, the animals were subjected to constant light, and the experiment was done under light conditions. In group D, animals were subjected to constant darkness, and the experiment was done under darkness conditions. Light (vs darkness) and standard (vs nonstandard) conditions produced significant changes on pGluPI activity in specific structures; the data suggested that endogenous substrates of pGluPI such as thyrotropin-releasing hormone and gonadotropin-releasing hormone, might be modified in parallel. There was left predominance in the retina under light conditions on a standard schedule (group A). The regional pattern of distribution of activity was similar in groups on a standard schedule (A vs B) and in groups tested under constant light-dark conditions (C vs D). However, this pattern differed between groups subjected to standard vs constant light-dark conditions (A and B vs C and D). These results support an influence of environmental light and darkness on pGluPI activity, which may reflect concomitant changes in its susceptible substrates and consequently in their functions.     

Mutations in the Reelin pathway are associated with abnormal expression of microglial IgG FC receptors in the cerebellar cortex

Microglia are the immune cells of the central nervous system involved in a variety of developmental processes, such as regulation of cell death and survival, spatial patterning, and contribute to the development of Purkinje cells (PCs) during migration. Microglia express immunoglobulin G Fc receptors (FcgRs). In this report, we describe microglial FcgR expression and its relation to abnormal PC migration in the cerebellum during development. To detect microglial FcgR, the direct anti-IgG (secondary antisera) and high concentrations of Triton X-100 were applied as a method for labeling microglial cells without the use of any specific primary antiserum. By using Acp2^?/? mice, which show an excessive PC migration into the molecular layer (ml), and 3 different types of mice with a null to alter the Reelin pathway (Reeler-, Dab1 (SCM)-, and Apoer mutant mice), we studied the location of PCs and the expression of FcgRs. Wild type littermates were used as controls in all studies. We show that the expression of microglial FcgRs was absent and PCs were ectopically located in the white matter in the cerebella of all mutant mice, except for the Acp2^?/? mice (PCs were located in the ml). These results suggest a role for FcgRs in the Reelin signaling pathway, not in regulating PC migration, but rather in the adaptation to an environment with a relatively large number of ectopically located PCs. However, the exact correlation between the ectopic location of PCs and lack of FcgRs in Reeler, SCM, and Apoer^?/? mice and the presence of FcgRs and directed PC location in the ml in Acp2^?/? mice are yet to be determined.

     

Illumination preferences of pigs

The illumination preferences of pigs have been examined by placing individual animals in light-proof chambers in which they could turn the lights on or off by interrupting an infrared beam switch with their snouts. The pigs were tested, on separate occasions, at two light intensities; bright (110 lux) and dim (10 lux). During 24-h periods, pigs spent an average of 54% of the time with the lights on when they were in bright light. When tested in dim light they spent an average of 63% of each 24 h with the lights on. Their motivation to obtain light was investigated using operant tests in which pigs, in darkness, obtained 40 s of light for interrupting an infrared beam. They obtained 1.5–2 h of light per 24 h. By contrast, pigs in continuous light would not operate the beam switch to obtain 40-s periods of darkness.     

Effect of Photoperiod on Stomatal Opening in Vicia faba

Stomatal apertures in darkness and subsequent average opening rates in light were measured in Vicia faba leaf discs throughout the nyctoperiods for plants grown on three light:dark cycles (8:16, 12:12, and 16:8). The time course of opening in darkness depended on the specific light:dark cycle with the maximum aperture always occurring at the time the lights normally went on. The light-induced opening rate was also maximum at the end of the nyctoperiod.     

Combination and competition between path integration and landmark navigation in the estimation of heading direction

Successful navigation requires the ability to compute one’s location and heading from incoming multisensory information. Previous work has shown that this multisensory input comes in two forms: body-based idiothetic cues, from one’s own rotations and translations, and visual allothetic cues, from the environment (usually visual landmarks). However, exactly how these two streams of information are integrated is unclear, with some models suggesting the body-based idiothetic and visual allothetic cues are combined, while others suggest they compete. In this paper we investigated the integration of body-based idiothetic and visual allothetic cues in the computation of heading using virtual reality. In our experiment, participants performed a series of body turns of up to 360 degrees in the dark with only a brief flash (300ms) of visual feedback en route. Because the environment was virtual, we had full control over the visual feedback and were able to vary the offset between this feedback and the true heading angle. By measuring the effect of the feedback offset on the angle participants turned, we were able to determine the extent to which they incorporated visual feedback as a function of the offset error. By further modeling this behavior we were able to quantify the computations people used. While there were considerable individual differences in performance on our task, with some participants mostly ignoring the visual feedback and others relying on it almost entirely, our modeling results suggest that almost all participants used the same strategy in which idiothetic and allothetic cues are combined when the mismatch between them is small, but compete when the mismatch is large. These findings suggest that participants update their estimate of heading using a hybrid strategy that mixes the combination and competition of cues.     

Isolation and characterization of a mouse protein C cDNA.

Protein C (PC) is a vitamin K-dependent serine protease, a deficiency of which results in thrombus. There is no spontaneously occurring mouse model of the disease. Attempts to create such a model in mice by using anti-sense gene technology requires isolation of a normal mouse PC cDNA. When a mouse liver (BALB/c) cDNA library was screened using a human PC cDNA as a probe, nine overlapping cDNA clones were isolated and sequenced. The cloned mouse PC cDNA comprised 1,512 nucleotides and the open reading frame of the cDNA encoded a polypeptide of 461 amino acids residues including a leader peptide composed of 41 amino acids. Mouse PC exhibited high homology to both human and bovine PCs. Mouse PC also had several structural features common in other PCs; locations of 23 Cys residues, location of putative beta-hydroxy Asp71, possible carbohydrate attachment sites involving Asp residues at amino acid positions 249, 314, and 330, and location of active sites such as His212, Asp258, and Ser361. Northern blot hybridization analysis identified a single species of mouse PC mRNA (2.0 kb in length) in mouse liver.     

Circadian Locomotor Activity Rhythm in the Freshwater Crab Pseudothelphusa americana (De Saussure, 1857): Effect of Eyestalk Ablation

The circadian rhythm of locomotor activity in the freshwater crab, Pseudothelphusa americana , was studied in aquaria using infrared crossing sensors. Individuals with ablated eyestalks were compared with intact individuals in constant darkness (DD) and in light-dark cycles (LD). Our results showed that intact animals in DD displayed bimodal rhythms. In LD conditions the two peaks were associated with lights on and lights off, respectively. A significant difference in the free running periods before and after LD was observed in all intact animals. After eyestalk ablation (ES-X), the circadian rhythm of locomotor activity disappeared immediately, but reappeared several days later. Diurnal activity was seen in some ES-X animals when exposed to LD. Our results indicate that locomotor activity rhythm in P. americana is driven primarily by oscillators located outside the eyestalks, and that extraretinal photoreceptors mediate either entrainment or masking effects.     

Circadian Locomotor Activity Rhythm in the Freshwater Crab Pseudothelphusa americana (De Saussure, 1857): Effect of Eyestalk Ablation

The circadian rhythm of locomotor activity in the freshwater crab, Pseudothelphusa americana, was studied in aquaria using infrared crossing sensors. Individuals with ablated eyestalks were compared with intact individuals in constant darkness (DD) and in light-dark cycles (LD). Our results showed that intact animals in DD displayed bimodal rhythms. In LD conditions the two peaks were associated with lights on and lights off, respectively. A significant difference in the free running periods before and after LD was observed in all intact animals. After eyestalk ablation (ES-X), the circadian rhythm of locomotor activity disappeared immediately, but reappeared several days later. Diurnal activity was seen in some ES-X animals when exposed to LD. Our results indicate that locomotor activity rhythm in P. americana is driven primarily by oscillators located outside the eyestalks, and that extraretinal photoreceptors mediate either entrainment or masking effects.     

Dark-stimulated calcium ion fluxes in the chloroplast stroma and cytosol

Using transgenic Nicotiana plumbaginifolia seedlings in which the calcium reporter aequorin is targeted to the chloroplast stroma, we found that darkness stimulates a considerable flux of Ca(2+) into the stroma. This Ca(2+) flux did not occur immediately after the light-to-dark transition but began approximately 5 min after lights off and increased to a peak at approximately 20 to 30 min after the onset of darkness. Imaging of aequorin emission confirmed that the dark-stimulated luminescence emanated from chloroplast-containing tissues of the seedling. The magnitude of the Ca(2+) flux was proportional to the duration of light exposure (24 to 120 h) before lights off; the longer the duration of light exposure, the larger the dark-stimulated Ca(2+) flux. On the other hand, the magnitude of the dark-stimulated Ca(2+) flux did not appear to vary as a function of circadian time. When seedlings were maintained on a 24-h light/dark cycle, there was a stromal Ca(2+) burst after lights off every day. Moreover, the waveform of the Ca(2+) spike was different during long-day versus short-day light/dark cycles. The dark-stimulated Ca(2+) flux into the chloroplastidic stroma appeared to affect transient changes in cytosolic Ca(2+) levels. DCMU, an inhibitor of photosynthetic electron transport, caused a significant increase in stromal Ca(2+) levels in the light but did not affect the magnitude of the dark-stimulated Ca(2+) flux. This robust Ca(2+) flux likely plays regulatory roles in the sensing of both light/dark transitions and photoperiod.     

Dynamic Grouping of Hippocampal Neural Activity During Cognitive Control of Two Spatial Frames

Cognitive control is the ability to coordinate multiple streams of information to prevent confusion and select appropriate behavioral responses, especially when presented with competing alternatives. Despite its theoretical and clinical significance, the neural mechanisms of cognitive control are poorly understood. Using a two-frame place avoidance task and partial hippocampal inactivation, we confirmed that intact hippocampal function is necessary for coordinating two streams of spatial information. Rats were placed on a continuously rotating arena and trained to organize their behavior according to two concurrently relevant spatial frames: one stationary, the other rotating. We then studied how information about locations in these two spatial frames is organized in the action potential discharge of ensembles of hippocampal cells. Both streams of information were represented in neuronal discharge—place cell activity was organized according to both spatial frames, but almost all cells preferentially represented locations in one of the two spatial frames. At any given time, most coactive cells tended to represent locations in the same spatial frame, reducing the risk of interference between the two information streams. An ensemble''s preference to represent locations in one or the other spatial frame alternated within a session, but at each moment, location in the more behaviorally relevant spatial frame was more likely to be represented. This discharge organized into transient groups of coactive neurons that fired together within 25 ms to represent locations in the same spatial frame. These findings show that dynamic grouping, the transient coactivation of neural subpopulations that represent the same stream of information, can coordinate representations of concurrent information streams and avoid confusion, demonstrating neural-ensemble correlates of cognitive control in hippocampus.