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At least 703 records · Page 39Linked to original sources
PubMed1986

Cholinergic suppression: a postsynaptic mechanism of long-term associative learning.

Food avoidance learning in the mollusc Pleurobranchaea entails reduction in the responsiveness of key brain interneurons in the feeding neural circuitry, the paracerebral feeding command interneurons (PCNs), to the neurotransmitter acetylcholine (AcCho). Food stimuli applied to the oral veil of an untrained animal depolarize the PCNs and induce the feeding motor program (FMP). Atropine (a muscarinic cholinergic antagonist) reversibly blocks the food-induced depolarization of the PCNs, implicating AcCho as the neurotransmitter mediating food detection. AcCho applied directly to PCN somata depolarizes them, indicating that the PCN soma membrane contains AcCho receptors and induces the FMP in the isolated central nervous system preparation. The AcCho response of the PCNs is mediated by muscarinic-like receptors, since comparable depolarization is induced by muscarinic agonists (acetyl-beta-methylcholine, oxotremorine, pilocarpine), but not nicotine, and blocked by muscarinic antagonists (atropine, trifluoperazine). The nicotinic antagonist hexamethonium, however, blocked the AcCho response in four of six cases. When specimens are trained to suppress feeding behavior using a conventional food-avoidance learning paradigm (conditionally paired food and shock), AcCho applied to PCNs in the same concentration as in untrained animals causes little or no depolarization and does not initiate the FMP. Increasing the concentration of AcCho 10-100 times, however, induces weak PCN depolarization in trained specimens, indicating that learning diminishes but does not fully abolish AcCho responsiveness of the PCNs. This study proposes a cellular mechanism of long-term associative learning--namely, postsynaptic modulation of neurotransmitter responsiveness in central neurons that could apply also to mammalian species.

Acetylcholine↗
PubMedDate not supplied

Comparative effects of long-term ethanol consumption and forebrain lesions on maze learning and active avoidance behavior in rats.

Male rats consumed a liquid diet containing 10.7% ethanol as their only source of food and fluid for 6.5 months, beginning at 2 months of age. During withdrawal, there were no differences between the alcohol group and their pair-fed or free-fed controls on EEG, body temperature, irritability and tremor measures. In behavioral tests begun 4-5 weeks after withdrawal, the rats that had consumed alcohol acquired accurate spatial behavior in a cross maze task more slowly than controls, but were unimpaired in shuttle-avoidance learning. In concurrent studies with groups of rats that had sustained lesions of the dorsal hippocampus, the mamillary bodies (MMB), or the mediodorsal thalamus, the pattern of behavioral deficits after MMB lesions was found to be qualitatively similar to that observed after the cessation of long-term alcohol consumption. These findings provide renewed hope that a useful rodent model for studying the neuropsychology of cognitive deficits associated with human alcoholism can be developed.

Alcoholism↗
PubMed1986

Reversal learning of an avoidance response in detelencephalated rats.

Avoidance learning followed by reversal learning was tested in rats after removal of all telencephalic brain structures. In phase I, 24 h after ablation of the telencephalon, rats were given a learning trial in the up-hill avoidance task and tested for retention 2 h later. The animals receiving a tail-shock contingent on the up-hill response showed significant increases in step-up latencies in comparison with control animals that had received noncontingent shock. In phase II, rats of the "reversal learning" group received a tail-shock if they did not perform the up-hill response within 5 s. Control animals received either another up-hill contingent shock or no shock. Two hours later the "reversal" group animals showed a decrement in step-up latencies in comparison with control animals, suggesting that reversal learning of the up-hill avoidance task is possible in rats devoid of the telencephalon.

Animals↗
PubMed2001

Predator experience on cryptic prey affects the survival of conspicuous aposematic prey.

Initially, aposematism, which is an unprofitable trait, e.g. noxiousness conspicuously advertised to predators, appears to be a paradox since conspicuousness should increase predation by naive predators. However, reluctance of predators for eating novel prey (e.g. neophobia) might balance the initial predation caused by inexperienced predators. We tested the novelty effects on initial predation and avoidance learning in two separate conspicuousness levels of aposematic prey by using a 'novel world' method. Half of the wild great tits (Parus major) were trained to eat cryptic prey prior to the introduction of an aposematic prey, which potentially creates a bias against the aposematic morph. Both prey types were equally novel for control birds and they should not have shown any biased reluctance for eating an aposematic prey. Knowledge of cryptic prey reduced the expected initial mortality of the conspicuous morph to a random level whereas control birds initially ate the conspicuous morph according to the visibility risk. Birds learned to avoid conspicuous prey in both treatments but knowledge of cryptic prey did not increase the rate of avoidance learning. Predators' knowledge of cryptic prey did not reduce the predation of the less conspicuous aposematic prey and additionally predators did not learn to avoid the less conspicuous prey. These results indicate that predator psychology, which was shown as reluctance for attacking novel conspicuous prey, might have been important in the evolution of aposematism.

Animals↗
PubMed2006

The role of the amygdala and rostral anterior cingulate in encoding expected outcomes during learning.

Successful passive avoidance learning is thought to require the use of learned stimulus-reinforcement associations to guide decision making [Baxter, M.G., Murray, E.A., 2002. The amygdala and reward. Nature Reviews. Neuroscience 3, 563-573]. The current experiment investigated the neural correlates of successful passive avoidance learning in 19 healthy adults. Behaviorally, subjects showed a distinct pattern of performance: early indiscriminate responding to stimuli (pre-criterion performance), followed by relatively rapid learning before a plateau of successful performance (post-criterion performance). Neural responses to post-criterion correct responses were compared with neural responses to both incorrect responses and pre-criterion correct responses. Post-criterion correct responding was associated with increased activation in regions including rostral anterior cingulate, insula, caudate, hippocampal regions, and the amygdala.

Adult↗
PubMed2004

The effect of alternative prey on the dynamics of imperfect Batesian and Müllerian mimicries.

Both Batesian and Müllerian mimicries are considered classical evidence of natural selection where predation pressure has, at times, created a striking similarity between unrelated prey species. Batesian mimicry, in which palatable mimics resemble unpalatable aposematic species, is parasitic and only beneficial to the mimics. By contrast, in classical Müllerian mimicry the cost of predators' avoidance learning is shared between similar unpalatable co-mimics, and therefore mimicry benefits all parties. Recent studies using mathematical modeling have questioned the dynamics of Müllerian mimicry, suggesting that fitness benefits should be calculated in a way similar to Batesian mimicry; that is, according to the relative unpalatability difference between co-mimics. Batesian mimicry is very sensitive to the availability of alternative prey, but the effects of alternative prey for Müllerian dynamics are not known and experiments are rare. We designed two experiments to test the effect of alternative prey on imperfect Batesian and Müllerian mimicry complexes. When alternative prey were scarce, imperfect Batesian mimics were selected out from the population, but abundantly available alternative prey relaxed selection against imperfect mimics. Birds learned to avoid both Müllerian models and mimics irrespective of the availability of alternative prey. However, the rate of avoidance learning of models increased when alternative prey were abundant. This experiment suggests that the availability of alternative prey affects the dynamics of both Müllerian and Batesian mimicry, but in different ways.

Animals↗
PubMed1985

Interaction between consecutive learnings: inhibitory avoidance and habituation.

Rats were submitted to step-down inhibitory avoidance training and to habituation of a rearing response to a tone with a 2-h interval between the two tasks, and were tested for retention of both tasks on the next day. When animals were trained first in inhibitory avoidance and then in habituation, retention of the avoidance behavior was impaired. When the animals were trained first in the habituation task and then in the avoidance task, retention of the two tasks was normal. The same results were obtained regardless of the order in which the two tasks were presented on the day of testing. This asymmetrical influence of habituation training on inhibitory avoidance retention could be due either to cognitive or, more likely, to task-specific neurochemical interactions.

Animals↗
PubMed1986

Effects of learned flavor avoidance on grooming behavior in rats.

In Experiment 1, rats were conditioned to avoid saccharin in tapwater by pairing it with LiCl in carboxymethylcellulose (CMC) applied to the fur. Conditioned flavor avoidance (CFA) of saccharin was then assessed in drinking and grooming tests. In Experiment 2, rats were given saccharin CMC on their fur and NaCl in water (or vice-versa) as conditioned stimuli in a CFA paradigm. Two-choice tests (saccharin vs. NaCl) followed in drinking and grooming contexts. In Experiment 3, rats were given saccharin CMC on one flank and vehicle (CMC only) on the other. After grooming, animals were injected with LiCl and then given 2-choice tests, first between saccharin and water, then between saccharin-CMC and plain-CMC, and finally, between saccharin and water. Strong CFA was exhibited in drinking tests in all 3 experiments. This was not the case in grooming tests. Rats continued to groom when tastant was applied to only one flank (Experiment 1), and exhibited only weak CFA when a different tastant was applied to each flank (Experiments 2 and 3). We conclude that grooming can be directed to minimize the ingestion of noxious substances, but that such ingestion is not sufficiently reduced to affect the efficacy of grooming as a delivery method for unpalatable substances (e.g., rodenticides, chemosterilants). We speculate that grooming represents a weakness in rodents' defenses against dietary poisoning, and that it might be used to deliver toxicants as part of crop protection schemes that make use of CFA.

Animals↗
PubMed2003

Discriminative taste aversion learning: a learning task for older chickens.

The study of learning and memory using the chicken model has relied on three learning paradigms, passive avoidance learning, imprinting and the pebble floor task. Passive avoidance learning and imprinting have been used predominantly in very young chickens and cannot be used to access learning and memory in older chickens. We have established a new behavioural learning paradigm, Discriminative Taste Aversion Learning (DTAL), that can be used with both young and older animals. The task requires chickens to discriminate between food crumbs dyed either red or yellow with one colour being associated with the aversive tasting substance, methylanthranilate. Learning can be tested at various times after the training session by presenting chickens with the coloured food crumbs without an aversive taste. Both chickens tested at 5 and 15 days post-hatch learned to avoid the aversive crumbs. Furthermore, the protein synthesis inhibitor anisomycin (30 mM; 10 microl per hemisphere) injected into the intermediate medial hyperstriatum ventrale 15 min pre-training or 45 min post-training blocked long-term memory for the DTAL task when tested 24 h later. Memory for the task was unaffected by anisomycin injection 120 min post-training or in control animals injected with saline at similar times. The timing of the cellular processes of protein synthesis needed for consolidation of the DTAL appears to be similar to those described for the other behavioural paradigms in young chickens.

Age Factors↗
PubMed1996

Effects of feeding on conditioned avoidance responses in rats.

Possible effects of feeding on learning were studied by comparing learned avoidance rates among three groups of Wistar rats that were given a diet at 1 h (1-h pretest group) and 5 h (5-h pretest group) before and immediately after (post-test group) the conditioned avoidance test. Learned avoidance rates during eight test sessions were higher in the order of the 1-h pretest, post-test, and 5-h pretest groups. This suggests that both pre- and post-test (training) feeding facilitates acquisition of conditioned avoidance learning presumably based on neurohumoral processes influenced by available glucose concentrations.

Animals↗
PubMed1999

Effects of oral administration of the competitive N-methyl-D-aspartate antagonist, CGP 40116, on passive avoidance, spatial learning, and neuromotor abilities in mice.

The effects were investigated of the potent competitive N-methyl-D-aspartate (NMDA) receptor antagonist CGP 40116[D-(E)-2-amino-4-methyl-5-phosphono-3-pentenoic acid] on the performance of mice in water maze and passive avoidance tasks, and in wire suspension, rotarod, and cage activity tests. The drug was administered per os (p.o.) in its anticonvulsant dose range. CGP 40116 dose-dependently impaired passive avoidance learning when given before, but not when given after training. The antagonist (5, 10, and 20 mg/kg, administered 4 h before each training session) dose-dependently affected water maze acquisition, and impaired retention test performance in both hidden- and visible-platform water maze tasks. In addition, the drug dose-dependently decreased swimming speed during water maze acquisition. Repeated administration of CGP 40116 (20 mg/kg, p.o.) persistently decreased cage activity and wire suspension test performance, whereas motor coordination and equilibrium on the rotarod apparatus remained unimpaired. In our administration protocol, no tolerance was found to the effects of the drug on passive avoidance learning and neuromotor abilities. The parallel effects of CGP 40116 on memory and motor performance are discussed, and it was concluded that the antagonist impairs neuromotor abilities and also induces memory impairments which cannot be entirely reduced to motor interference.

2-Amino-5-phosphonovalerate↗
PubMed1997

Response of domestic chicks to methyl anthranilate odour

Methyl anthranilate is widely used to make ingestive stimuli taste aversive in studies of visually mediated passive-avoidance learning in domestic chicks, Gallus gallus domesticusHowever, since methyl anthranilate smells strongly to the human nose, its odour may be involved in the learning process. We sought (1) to determine whether chicks can use the odour of methyl anthranilate as a disciminative stimulus in passive-avoidance learning and (2) to evaluate the use of denatonium benzoate as an alternative odourless reinforcer. In experiments 1 and 2, chicks were presented with familiar- or novel-coloured food or water, with or without the odour of methyl anthranilate or denatonium benzoate, to see whether either odour would elicit neophobia. Methyl anthranilate odour increased chicks' latency to eat or drink when it was presented in conjunction with novel-coloured food or water, showing that chicks can detect it. Denatonium benzoate had no effect. In experiment 3, chicks learned to avoid food or water that was made unpalatable by means of denatonium benzoate and paired with the odour of methyl anthranilate, showing that chicks can use this odour as a discriminative stimulus in taste-avoidance learning. In experiment 4, chicks learned to avoid pecking at a pin-head coated with denatonium benzoate or paired with the odour of methyl anthranilate, showing that denatonium benzoate is a satisfactory reinforcer for one-trial passive avoidance learning and that the odour of methyl anthranilate is in itself a punishing stimulus. We conclude that methyl anthranilate odour does influence avian learning and that denatonium benzoate is a suitable odourless alternative for use as a punishing stimulus.

Journal Article↗
PubMed1989

Differences in open-field behavior and in learning tasks between two rat strains differing in their reactivity to stressors.

The study characterizes differences between inbred Wistar-Kyoto (WKYs) and Brown-Norway (BNs) rats in open-field behavior, and in discriminative learning and acquisition of an avoidance learning task. Hyper-reactivity of WKYs to novelty was demonstrated in an open-field test. Discriminative learning and retention thereof was slower in WKYs, but as efficient as in BNs. Acquisition of avoidance learning was also slower in WKYs, but their maximal avoidance score was much higher (approximately 85%) than in BNs. Also, recall of avoidance learning was slower for WKYs. We conclude: (1) hyper-reactivity of WKYs to novelty is expressed by their exceptional immobility and excess defecation in the open-field and is paralleled by their known hyper-reactivity to stressful stimuli, and (2) no strain differences exist in the ability to learn a discriminative task, but both acquisition and recall of an avoidance task are slower in WKYs. This may imply that the degree of reactivity to stressful environmental stimuli may play an important role in the acquisition of learning.

Animals↗