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PubMed2005

Pontine-wave generator activation-dependent memory processing of avoidance learning involves the dorsal hippocampus in the rat.

The aim of this study was to test the hypothesis that the dorsal hippocampus plays a critical role in pontine-wave (P-wave) generator activation-dependent memory processing of two-way active avoidance (TWAA) learning. To achieve this objective, rats were given small bilateral lesions in the CA1, dentate gyrus (DG), or CA3 region of the dorsal hippocampus by microinjecting ibotenic acid. After recovery, lesioned and sham-lesioned rats were trained on a TWAA learning paradigm, allowed a 6-hr period of undisturbed sleep, and then were tested on the same TWAA paradigm. It was found that lesions in the CA3 region impaired retention of avoidance learning. Conversely, lesions in the CA1 and DG regions had no effect on TWAA learning retention. None of the groups showed any changes in the baseline sleep-wake cycle or in the acquisition of TWAA learning. All rats showed increased rapid eye movement (REM) sleep and increased REM sleep P-wave density during the subsequent 6-hr recording period. Impaired retention in the CA3 group occurred despite an increase in REM sleep and P-wave density, suggesting that during REM sleep, the P-wave generator interacts with the CA3 region of the dorsal hippocampus to aid in consolidation of TWAA learning. The results of the present study thus demonstrate that P-wave generator activation-dependent consolidation of memory requires an intact CA3 subfield of the dorsal hippocampus. The results also provide evidence that under mnemonic pressure, the dorsal hippocampus may not be involved directly in regulating the sleep-wake cycle.

Animals↗
PubMed1994

The effects of archistriatal lesions on one-trial passive avoidance learning in the chick.

The avian archistriatum, part of which may be homologous with the mammalian amygdala, has been implicated in fear and avoidance behaviour. There is also evidence to suggest its involvement in learning. One-trial passive avoidance learning (PAL) has been used extensively to study memory formation in the chick. Young chicks will peck spontaneously at a small, visually conspicuous bead. If the bead has been coated with an aversive substance, the chicks show a disgust response and learn in a single trial not to peck a similar bead on subsequent presentation. Successful acquisition of this one-trial PAL task involves the formation of a learned association between the bead and a noxious taste, followed by the expression of an avoidance response. In view of the possible involvement of the archistriatum in avoidance and learning behaviour, its role in one-trial PAL was investigated by ablation. Bilateral electrolytic lesions of the entire archistriatum prevented the acquisition of the one-trial PAL task. Neither bilateral lesions of the lateral cerebral area nor sham operation affected learning. The impairment of one-trial PAL caused by archistriatal lesions was not due to effects on the visual or motor components of pecking behaviour. The archistriatum could therefore be directly involved in memory formation. It could also be involved in the organization of avoidance behaviour associated with the task, or it could form part of a circuit linking two other forebrain regions previously implicated in one-trial PAL, the intermediate part of the medial hyperstriatum ventrale and the lobus parolfactorius.

Amygdala↗
PubMed1994

Flumazenil antagonizes the effect of diazepam on negative contrast in one-way avoidance learning.

The main aim of the present work was to study whether the effect of diazepam upon successive negative contrast in one-way avoidance learning-induced by shifting rats from a large reward (30s spent in the safe compartment) to a small reward (1s)-is mediated by the action of this drug on the benzodiazepine (BZ) receptor. Therefore, we studied the influence of flumazenil (FL), a BZ antagonist, on the effect of diazepam (DZ) on negative contrast. The i.p. administration of 5 and 12mg/kg, but not of 2mg/kg of FL, reliably antagonized the abolition by DZ (1mg/kg) on successive negative contrast. Moreover, FL (12mg/kg) did not affect either the avoidance response or the contrast effect. These results suggest that the GABA system is involved in the successive negative contrast effect in one-way avoidance learning, and that this experimental procedure may be useful in studies of anti-anxiety agents.

Journal Article↗
PubMed1997

Daily fluoxetine administration impairs avoidance learning in the rat without altering sensory thresholds.

1. Male rats given daily intraperitoneal injections of fluoxetine (10 mg/kg) were slower to escape foot shock by jumping a low barrier. 2. When switched to a shuttle task requiring two crosses to terminate shock, the FLU-treated animals failed to learn in 55 trials. 3. A second experiment found FLU-treated animals could learn a one-way avoidance response, but were significantly slower to learn than control animals. 4. FLU-treated animals were no different than controls on tests of sensory thresholds for foot shock or heat. 5. Tests of motor behaviors revealed no differences in latency to traverse a narrow beam to reach a goal box, however FLU-treated animals were less active in an open field. 6. Several hypotheses can account for these data, the most promising being that a central motivational system (fear) is less active in FLU-treated animals.

Analgesia↗
PubMed1992

Multitrial inhibitory avoidance learning in the crab Chasmagnathus.

Chasmagnathus crabs placed in the dark compartment (DC) of a double-chamber device and given electrical shocks whenever they entered or remained in the light compartment (LC), showed an LC-avoidance behavior when tested 24 h after a training session of three 30-min periods with 60-min intervals. The avoidance behavior depended neither on the shock number nor on the distribution at training but only on exposure to the LC-shock contingency, thus suggesting that crabs learn to associate the LC with an aversive situation. The learning outcome disclosed a higher degree of refraining from entering the LC rather than a faster escaping to the DC. Distributed practice proved more effective on crab avoidance learning than massive practice. Retention of the learned behavior occurred after a 24-h rest interval in an environment different from that of the training apparatus. Experimental devices previously used in avoidance learning studies with crabs were improved here by automating both the computation of latency values and the event recording.

Animals↗
PubMed2002

The effects of selective dopamine agonists on a passive avoidance learning task in the day-old chick.

Recent examination of the mixed dopamine agonist apomorphine suggests that dopamine inhibits both passive avoidance and response suppression learning. The present study investigated the effects of selective dopamine agonists on memory consolidation using a passive avoidance task in the day-old chick. The dopamine D1 agonist SKF 38393, the D2 agonist quinpirole, and the D4 agonist PD 168077 all failed to disrupt memory consolidation when injected immediately after training. However, chicks injected with 6.0 mg/kg of the D3 agonist (+)-7-hydroxy-N,N-di-n-propyl-2-aminotetralin (7-OH-DPAT) displayed memory impairment 180 min after aversive training. A study of the time course of this effect of 7-OH-DPAT showed that it first appeared 90 min after aversive training. Pretreatment with the dopamine D3 antagonist U 99194 eliminated the disturbance of passive avoidance learning induced by 7-OH-DPAT. These results indicate that dopamine is involved in the later stages of the memory formation process and that the D3 receptor is crucially involved in this disruption.

Animals↗
PubMed1997

Effects of training procedure on memory formation using a weak passive avoidance learning paradigm.

One-day-old chicks will learn, in one trial, to avoid pecking a bead that tastes aversive. This procedure is used widely as a model for learning and memory, although a variety of training procedures and bead types are used in different laboratories. Here we report that the decay of memory following training on a weak (10% methylanthranilate) avoidance task is dependent on the training procedure rather than the characteristics of the beads or the strain of chick used. Chicks that have been presented with a bead in pretraining and a similar bead coated in MeA during training fail to avoid the bead when tested 2 h posttraining, whereas chicks presented with a bead of particular color and size for the first time at training demonstrate high levels of avoidance at 2 h posttraining. These results resolve the differences in the time course of memory formation for a weak passive avoidance task described by the groups at Monash University (Crowe, Ng, & Gibbs, 1989) and the Open University (Sandi & Rose, 1994).

Animals↗
PubMed1991

Avoidance learning during antidepressant withdrawal in mice.

Shuttle-box avoidance acquisition, locomotor activity and density of adrenoreceptors in the cerebral cortex have been evaluated, in CD-1 mice, during withdrawal from repeated treatment with desipramine or mianserin (5 or 14 daily injections of antidepressant drug, 10 mg kg-1). Withdrawal from mianserin did not produce any behavioural or neurochemical change. Mice withdrawn from desipramine exhibited avoidance facilitation, when training started 24 h (but not 72 or 120 h) after the last injection. Locomotor activity was not affected and no change was found in the density of beta-adrenoreceptors. An up-regulation of alpha 2- and, to a lesser extent, of alpha 1-adrenoreceptors, occurred 72 h following desipramine withdrawal. However, the assessment of the role played by these neurochemical changes in the avoidance facilitation observed during withdrawal from the antidepressant treatment requires further study.

Animals↗