Decreased response or alternative defensive strategies in escape: two different types of long-term memory in the crab Chasmagnathus

An opaque screen moving overhead elicits an escape response in the crab Chasmagnathus that after a few presentations habituates for a long period (long-term habituation). Two types of long-term habituation were previously described: the (context-signal)-long-term habituation yielded by spaced training – context dependent, cycloheximide sensitive and long lasting; and the (signal)-long-term habituation yielded by massed training – context independent, cycloheximide insensitive and shorter lasting. Present research is focused on the defensive strategies crabs display during acquisition of both long-term habituations, using video analysis as the main method of study. Aside from the escape response, Chasmagnathus shows a rigid motionless display, an alternative defensive response we term freezing response. The escape response is predominantly exhibited at night and in summer months, while freezing occurs during day light hours and in winter months. During acquisition of (signal)-long-term habituation, the escape response vanishes without being replaced by freezing. During acquisition of (context-signal)-long-term habituation, the escape response vanishes and is replaced by a strong freezing that finally becomes the only defensive strategy. The former, but not the latter, meets the current concept of habituation. Accepted: 1 December 1998     

Age-related deficits of long-term memory in the crab Chasmagnathus

Short and long-term memory in adult crabs Chasmagnathus granulatus of different age are evaluated in two learning paradigms: habituation to a visual danger stimulus and appetitive conditioning. No difference between young, middle-aged and aged animals is found in short-term habituation with 15 training trials. A good level of retention of the habituated response at 24 h is exhibited by young and middle-aged crabs but a poor one by aged crabs. When the training-to-testing interval is lengthened to 48 h or the training session reduced to 7 trials, young and middle-aged crabs continue to show long-term habituation but aged individuals exhibit no retention at all. As regards appetitive conditioning, young, middle-aged and aged crabs present similar short-term memory with 5 training trials and similar long-term memory when tested at 24 h, but an age-related deficit in long-term retention is exhibited when the intersession interval is lengthened to 48 h or the training reduced to 3 trials. Thus, a reduction of long-term memory related to age is demonstrated in the crab Chasmagnathus. Since it is shown in two different learning paradigms, the possibility of explaining the deficit in terms of a failure in memory mechanisms due to aging rather than as a consequence of ontogenetic shift in the crab's behavior is discussed.     

Habituation and associative learning during exploratory behavior of the crab Chasmagnathus

Summary Chasmagnathus crabs placed in a choice-chamber device (a dark compartment, DC, and a light one, LC, of identical size separated by a central partition with a sliding door) display an exploratory activity that declines over time (training session). Such decrement persists at the testing session, 24 h later, and meets the criterion of stimulus specificity, so that it is accounted for in terms of a long-term habituation. Alternative explanations involving far-reaching effects of handling, change of context or isolation during the training session, are excluded. If animals are allowed to find food in LC during training, no decrease in the exploratory activity is shown and the enhanced effect on exploring is retained for at least 24 h. This result is interpreted as an instance of associative learning, appetitively motivated. Performances are analysed measuring the latencies to pass from DC to LC, so that crabs given food in training show in testing shorter latencies than controls. In addition, unlike controls, trained crabs often display at testing a feeding behavior despite the absence of food or odor of food in the choice-chamber. The possible use of both exploratory habituation and appetitive learning in studies on memory modulation is discussed.     

Failure of interocular transfer in two types of learning in the crab Chasmagnathus

Crabs (Chasmagnathus granulatus) were trained monocularly and then tested after 24 h, in order to study interocular transfer (IOT) in two habituation paradigms. 1) Habituation of the escape response to an iterated visual danger stimuli. Monocular crabs exhibited retention after 24 h when trained and tested with the same uncovered eye, but not with different uncovered eyes. 2) Habituation of the exploratory activity to a novel environment. This long term habituation of the exploratory activity is exhibited after 24 h in monocular animals trained and tested with the same uncovered eye but not with different uncovered eyes. An explanation of this failure of IOT will be discussed in terms of retrieval impairment due to a) a different perception of training and testing stimuli, b) lateralization of memory storage, or c) the existence of two symmetrical, independent and redundant lateral storage sites.     

Characterisation of cAMP-dependent protein kinase isoforms in the brain of the crab Chasmagnathus

In the crab Chasmagnathus learning model, systemic administration of cAMP analogues that are specific activators or inhibitors of cAMP-dependent protein kinase (PKA) proved to respectively facilitate or impair long-term retention. The aims of the present work were to analyse PKA activity distribution in the crab brain and to characterise PKA isoforms. The neuropils from the eyestalk showed higher levels of induced PKA activity when compared with other neuropils of the central nervous system. Two PKA isoforms, homologous to mammalian PKA I and PKA II, were detected from central brain protein extracts using DEAE chromatography. Only PKA II was found in lateral protocerebrum extracts, suggesting a role of this isoform in the processing of visual inputs and in the integration of this information with other sensory inputs. PKA I was observed to be ten-fold more sensitive to cAMP than PKA II. cGMP induced a high activation of both PKA isoforms, similar to that obtained with cAMP. PKA I showed a two-fold greater sensitivity for cGMP than PKA II. An autophosphorylation assay was performed and a protein of 55 kDa, corresponding to phosphorylated R II regulatory subunit, was detected. The presence of a PKA I isoform with high sensitivity for cAMP in the central brain suggests a role of this subtype in long-term memory. Accepted: 29 August 2000     

A field model of learning: 2. Long-term memory in the crab Chasmagnathus granulatus

In the previous companion paper, the possibility of learning by Chasmagnathus in field conditions was demonstrated. Here, we study long-term memory inquiring to what extent an internal representation could be maintained in a complex environment. Two 45-min training sessions, each of 15 visual danger stimulus presentations with 3-min intertrials, were given at a 24-h interval. Throughout the first training session and during the first 22.5 min of re-training on day 2, crabs kept the same hiding response level but then, during the second phase of re-training, the re-emerging increased up to the point that 32% of surface crabs ignored the stimulus. Each session was followed by a 22.5-min testing without stimulation. At testing on day 2 after re-training, crabs showed a change in the usual exploring strategy. Results reveal long persistency in responding despite a rest interval of 24 h followed by a gradual decrease in response until it vanishes. The statistical analysis was performed by comparing performances at day 2 (Rescorla in Am Psychol 43:151–160, 1988) and then confirmed through comparisons between day 1 and day 2. However, it is not possible to identify separate and taxonomically well-defined learnings but rather a tangled collection of processes that influence each other blurring some of the diagnostic features of each learning.     

A field model of learning: 1. Short-term memory in the crab Chasmagnathus granulatus

Learning and memory studies have been performed for more than two decades using the crab Chasmagnathus in our laboratory. Here, our research was aimed at disclosing some instances of learning in field conditions. Three experiments were performed non-simultaneously, all with a 22.5-min pre-training preceding the first visual-danger-stimulus, an opaque rectangle passing overhead. In Experiment 1, crabs received a single stimulus followed by 22.5-min testing without stimulation, where the re-emerging latency was considered the basic latency response. In Experiment 2, training consisted of 15 stimulus 3-min apart, followed by 22.5-min testing without stimulation. Throughout training crabs were underground but re-emerged at testing with latencies longer than the basic latency response. Both at pre-training and testing the usual strategy of exploring was the short-near excursions. In Experiment 3, training included three stimulus 22.5-min apart, followed by 22.5-min testing. Crabs left their burrows before the end of each inter-trial, showing a mean latency like the basic latency response, but a sensitization to the stimulus and a preponderance of the fast-far excursions over the usual slow-near. In brief: through 15-3 training, crabs learn that the stimulus is iteratively presented; through 3-22.5 training, crabs acquire sensitization to the stimulus and a different strategy of exploration.     

Fractal rigidity by enhanced sympatho-vagal antagonism in heartbeat interval dynamics elicited by central application of corticotropin-releasing factor in mice

The dynamics of heartbeat interval fluctuations were studied in awake unrestrained mice following intracerebroventricular application of the neuropeptide corticotropin-releasing factor (CRF). The cardiac time series derived from telemetric ECG monitoring were analyzed by non-parametric techniques of nonlinear signal processing: delay-vector variance (DVV) analysis, higher-order variability (HOV) analysis, empirical mode decomposition (EMD), multiscale embedding-space decomposition (MESD), multiexponent multifractal (MEMF) analysis. The analyses support the conjecture that cardiac dynamics of normal control mice has both deterministic and stochastic elements, is nonstationary, nonlinear, and exerts multifractal properties. Central application of CRF results in bradycardia and increased variability of the beat-to-beat fluctuations. The altered dynamical properties elicited by CRF reflect a significant loss of intrinsic structural complexity of cardiac control which is due to central neuroautonomic hyperexcitation, i.e., enhanced sympatho-vagal antagonism. The change in dynamical complexity is characterized by an effect referred to as fractal rigidity, leading to a significant impairment of adaptability to extrinsic challenges in a fluctuating environment. The impact of dynamical neurocardiopathy as a major precipiting factor for the propensity of cardiac arrhythmias or sudden cardiac death by unchecked central CRF release in significant acute life events in man is critically discussed.     

Physiological and behavioral effects of chemoreceptors located in different body parts of the swimming crab Callinectes danae

By perfusing their branchial chambers with filtered seawater, we have developed a preparation that allows us to maintain the swimming crab Callinectes danae outside water without any major effects on its cardiac activity. This in turn allowed us to selectively stimulate chemoreceptors located in different body parts, and specifically to discriminate between the receptors located in the branchial chambers and those located in the oral region (mainly in the mouthparts, antennules and antennae). We show that a taurine solution can evoke bradycardia when applied to the oral region or to a combination of the oral region and the branchial chambers. Although the precise localization of the oral region receptors involved remains to be determined, ablation experiments show that the olfactory organs (i.e., the antennules) are not involved. Finally, we show that although stimulating the pereiopods has no effect on the animals' cardiac activity it causes the animals to move, putatively to try to grasp a piece of food, a reaction not evoked by stimulating the gills or the oral regions. Our results lend support to the idea that chemoreceptors located in different parts of the body play different functional roles in decapod crustaceans.     

Effect of Isolation-Rearing on Conditioned Dopamine Release In Vivo in the Nucleus Accumbens of the Rat

Abstract: Intracerebral microdialysis in conjunction with HPLC coupled to electrochemical detection was used to investigate the effect of isolation-rearing in the rat on extracellular dopamine (DA) and its metabolites in vivo, in the shell region of the nucleus accumbens, in response to footshock and in relation to a conditioned emotional response. Male Lister hooded rats were reared from weaning for 6–8 weeks in either social isolation or groups of five. In the training phase, rats were exposed to a novel environment for 10 min where they experienced mild footshock. Footshock caused an immediate increase in basal extracellular DA levels in both rearing groups relative to control rats. However, the increase in extracellular DA was prolonged in the case of the isolation-reared rats and significantly greater than in group-reared rats. Exposure to the novel environment without shock (control groups) did not significantly alter basal extracellular DA in the nucleus accumbens shell; 140 min later rats were returned to the testing box (contextual stimulus) without receiving footshock. The contextual stimulus increased basal extracellular DA in the nucleus accumbens of both groups of rats with respect to controls; however, this increase was significantly greater and more prolonged in isolates. Extracellular levels of the metabolites 3,4-dihydroxyphenylacetic acid and homovanillic acid did not differ between isolation- and group-reared rats, and they were not significantly affected by either footshock or the contextual stimulus. These results suggest that exposure to footshock and a contextual stimulus are associated with increases in basal extracellular DA levels in the nucleus accumbens shell. The results also support evidence in favour of an isolation-induced enhancement in dopaminergic activity in the nucleus accumbens, which probably underlies aspects of the behavioural syndrome associated with isolation.     

Ultrastructure of the branchial epithelium of an amphibious brackish-water crab

The ultrastructure of the branchial epithelium of the amphibious brackish-water crab Uca mordax (Smith) was investigated in relation to adaptation to the salinity of the medium. No distinct differences were observed in the epithelial structure of animals adapted to either 100% sea water or to 1% sea water. Thus any interpretation of the significance of particular structures in relation to specific transport processes should be regarded with caution. Apart from strict epithelial cells, pillar cells and glycogen (presumed) storage cells were found. The epithelial cells showed very well-developed apical microvilli or lamellae and basal interdigitations with adjacent cells. Well-developed junctional complexes were seen (band desmosomes, septate desmosomes, gap junctions). The cells are extremely rich in mitochondria. Microtubules, peroxisome-like bodies, multivesicular bodies and near-nuclear Golgi complexes were present.     

大壁虎与嗅觉相关的学习记忆

壁虎科动物鼻腔较大,化学感觉系统发达,类似于对化学信息敏感的舌端游离的蜥蜴目动物（Malan,1946),并且嗅黏膜面积很大,感觉器神经元多,嗅神经系统十分完善（Gabe and Saint,1976).     

Characterization of microsatellite loci for the Chinese mitten crab,Eriocheir sinensis

The Chinese mitten crab, Eriocheir sinensis is an important human food source in Asia and causes considerable ecological and economical damage as a recent invader of North America and Europe. Here we report the isolation and characterization of 12 highly polymorphic microsatellite loci for E. sinensis. The number of observed alleles per locus ranged from 7 to 40 and the observed heterozygosity from 0.50 to 0.95. These markers should prove a useful tool to investigate the colonization process and its evolutionary implications.     

Circadian rhythm of pigment migration induced by chromatrophorotropins in melanophores of the crab Chasmagnathus granulata

The circadian rhythm of black pigment migration of melanophores of the crab Chasmagnathus granulata and the variation in responsiveness of these cells to pigment-dispersing hormone (beta-PDH), crustacean cardioactive peptide (CCAP), and red pigment-concentrating hormone (RPCH) were investigated. Melanophores of C. granulata possess an endogenous circadian rhythm of pigment migration, with black pigments staying more dispersed during the day period and more aggregated during the night period. This rhythm seems to be largely dependent on an endogenous release of neurohormones from eyestalks, and to a lesser extent on a primary response to illumination. beta-PDH was the most potent PDH isoform to induce pigment dispersion in both in vivo (EC50 = 0.4 pmol/animal) and in vitro (EC50 = 0.18 microM) assays. CCAP also induced pigment dispersion in vivo and in vitro assays (EC50 = 12 microM), but it was less potent than beta-PDH. In vivo, RPCH induced a low and nondose-dependent pigment aggregation, while in vitro, it had no effect on pigment migration. The responsiveness of melanophores of C. granulata to beta-PDH was significantly higher during the day period when compared to the night period in both assays, in vitro and in vivo. These results suggest that the endogenous circadian rhythm of black pigment migration is dependent on both endogenous circadian rhythm of beta-PDH synthesis and/or release from eyestalks and on an endogenous rhythm of responsiveness of melanophores to beta-PDH.     

Neurochemical changes associated with the action of acute administration of diazepam in reversing the behavioral paradigm conditioned emotional response (CER)

Neurotransmitter turnover of biogenic monoamines (dopamine, norepinephrine, and serotonin) and amino acids (glutamate, aspartate, and gamma-aminobutyric acid) was evaluated in rats exposed to the conditioned emotional response (CER) paradigm in the absence (total suppression) or presence of acute 5 mg/kg i.p. diazepam (which reversed suppression and restored normal responding). Based on previous studies of CER, with controls for shock and stimulus histories, the results with respect to the anxiolytic could be divided into several categories: changes in turnover which are associated only with the CER behavior; changes associated only with the drug, diazepam; changes which augmented the effects of the behavior; or changes which were the reverse of those associated with the behavior. Due to the multitude and complexity of the results, not all observations have clear explanations at this time. However, for the CER behavior per se, it is apparent that a combination of neurotransmitters, including some implications about acetylcholine, act in concert to bring about the behavioral suppression. The action of diazepam is more complex, involving the full spectrum of neurotransmitters to bring about its direct and indirect effects.In honor of Distinguished Professor Morris Herman Aprison     

The temporal pattern of responding in conditioned bar-press suppression: the role of the context switch and training mode

The present study examined the temporal pattern of responding in a conditioned bar-press suppression task in rats. Rats were exposed to either a 30-s or a 120-s conditioned stimulus (CS) followed by a footshock. Training took place either while the rats were lever-pressing for water (online), or with the lever removed from the box (offline). They were then exposed to the CS while they were lever-pressing for water, either in the training context or in a different context. Bar-press suppression during the CS was constant across the duration of the CS during training, but was restricted to the initial portion of the CS at the time of testing, especially when subjects were tested in a different context. Those results replicate the reactive (as opposed to anticipatory) pattern observed in a lick suppression procedure by Jozefowiez et al. (2011) and indicate that a change in context at the time of testing might be critical for its expression.