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Results for “Avoidance Learning”

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PubMed2003

Combined restraint and cold stress in rats: effects on memory processing in passive avoidance task and on plasma levels of ACTH and corticosterone.

The effect of restraint stress combined with water immersion (IMO+C), applied at various intervals before and after the acquisition of a passive avoidance task, was studied in rats. The procedure started with two pre-training trials. On the single training trial the rats received a footshock (0.3 mA, 3s) after they entered the preferred dark compartment. The exposure to IMO+C lasting 1 h terminated 4 or 1 h before application of the footshock or started immediately or 3 h after this aversive stimulus. Retention tests were performed 1 and 2 days after the acquisition trial. In an attempt to relate the behavioural responses to the stressor with plasma levels of two stress hormones we measured ACTH and corticosterone under similar conditions as were used in the behavioural experiments. IMO+C exposure terminating 1 h before the training resulted in very short avoidance latencies during retention testing. A similar impairment of retention test performance was found in animals exposed to the stressor immediately after training. When IMO+C exposure terminated 4 h before training the stressed rats exhibited comparably long avoidance latencies as shown by the controls. IMO+C presented 3 h after acquisition trial also did not influence retention of avoidance learning. The hormones were estimated 1 and 4 h after IMO+C, both in the absence and presence of footshock. Both ACTH and corticosterone were significantly increased 1 h after IMO+C termination, and their plasma levels returned to control values within 4 h. Footshock alone increased plasma corticosterone, however, the hormone levels were significantly lower than those estimated after IMO+C terminating 1 h before blood collection. Footshock substantially increased ACTH levels in rats exposed to IMO+C 1 h before footshock, but not in stressed rats with already high levels of corticosterone. In conclusion, IMO+C represents a strong stress stimulus exerting amnesic effect when applied shortly before or after the acquisition trial. Further, the findings indicate the restraint and cold stressor to interfere with consolidation of passive avoidance response. We suggest that the moderate circulating levels of corticosterone found after footshock may be positively related to the memory consolidation, while the exceedingly high levels have an opposite effect.

Adaptation, Physiological↗

PubMed1987

Cysteamine-induced depletion of central somatostatin-like immunoactivity: effects on behavior, learning, memory and brain neurochemistry.

The effects of a wide range of doses of systemically administered cysteamine were studied on locomotor behavior, passive avoidance memory, cortical and cerebrospinal fluid somatostatin-like immunoactivity and cortical levels of dopamine and norepinephrine. High doses of cysteamine (200 and 250 mg/kg s.c.) led to sustained locomotor activation. Doses of 150 mg/kg and above resulted in head and neck tremor and increased defecation. When cysteamine was administered immediately following the acquisition of a passive avoidance response, doses of 50 mg/kg and above resulted in significant attenuation of passive avoidance retention test performance. Cysteamine in doses of 50 mg/kg and above depleted cortical somatostatin-like immunoactivity by approximately 50%. The depletion of cortical somatostatin-like immunoactivity was accompanied by a rapid rise in somatostatin-like immunoactivity in cerebrospinal fluid. In addition to the depletion of somatostatin-like immunoactivity, high doses of cysteamine (150 mg/kg and above) produced changes in cortical levels of norepinephrine and dopamine, reminiscent of dopamine-beta-hydroxylase inhibition. The results of this series of experiments suggest that somatostatin, in addition to its effects on hormonal regulation, may play an important role in behavior and passive avoidance learning and memory. It is possible that the amnesia produced by cysteamine may have been due to the release of somatostatin into CSF from tissue stores, rather than somatostatin depletion per se. It is also possible that the catecholaminergic effects of high doses of cysteamine contribute to the behavioral deficits observed.

Animals↗

PubMedDate not supplied

[Retention of a memory trace of learning induced by a new and extinctive stimulus in C57BL/6J and BALB/c mice].

Influence of preliminary habituation to the experimental box on passive avoidance learning was studied in mice of C57BL/6J and BALB/c strains. The 20-fold preexposure of mice to the environmental stimulus inhibited the acquisition and consequent retention of a memory trace in BALB/c mice and did not affect the acquisition in C57BL/6J mice. Subsequent retention in this strain was facilitated. The interstrain differences are discussed with respect to detected genetically determined types of behavior and exstinctive inhibition at the habituation stage.

Animals↗

PubMed2005

Learning twice is different from learning once and from learning more.

The rat hippocampus plays a crucial role in the consolidation of a variety of memories, including that for a one trial inhibitory avoidance learning task in which stepping down from a platform is associated with a footshock. Here we show that this is the case regardless of the intensity of the footshock used and hence, of the strength of the learned response. However, additional learning produced by a second training session in this task does not involve the hippocampus but, instead, the striatum. Memory consolidation of the second trial requires glutamate alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate, N-methyl-D-aspartate and metabotropic receptors, activation of signaling pathways, gene expression and protein synthesis in the striatum, as are required in the hippocampus during memory consolidation of the first trial.

Animals↗

PubMed1993

Feeding behavior of grazing ruminants experiencing stress.

The mechanisms underlying diet selection of ruminants are less studied than those for monogastrics. However, recent studies have shown that these mechanisms may be more similar in ruminants and monogastrics than previously believed. Food aversion learning is observed in both monogastrics and ruminants, and the hypothalamic-pituitary-adrenal axis appears to be involved in avoidance learning. Using leafy spurge (Euphorbia esula), an introduced weed whose expansion has costly ecological and economic implications in western North America, as a model for underconsumed plant species, we hypothesized that sheep experience increased cortisol levels when they first consume leafy spurge and that this may be related to their reluctance to graze it. We also hypothesized that preexposure to leafy spurge would attenuate the development of a spurge-based aversion. Correspondingly, we hypothesized that preexposed sheep would not experience increased blood cortisol levels with leafy spurge gavage during an aversion trial. None of our hypotheses were disproved by the experiments. Our results lend support to the hypothesis that stress is required for the development of conditioned taste aversions and extend it to ruminants. We suggest that activity of the hypothalamic-pituitary-adrenal axis is integral to food aversion learning in ruminants.

Animals↗

PubMed1980

Learning in surgical and functional hemidecorticate rats: a preliminary study of compensation.

A case is made for the conjoint use of surgical and functional hemidecorticate preparations in the investigation of compensation. Direct comparison of the effects of surgical and functional hemidecortication in rats in an active runway avoidance learning situation is reported. Trials to successively higher avoidance criteria, total avoidance responses, longest runs of consecutive avoidance responses, response latencies and running times are compared. None of these measures reveal differences between the two types of hemidecorticate preparation, although compared with a normal group both hemidecorticate groups show a deficit. The implications of this finding in terms of the compensation issue are discussed.

Animals↗

PubMed1976

Behavioral effects of 5, 7-dihydroxytryptamine lesions of ascending 5-hydroxytryptamine pathways.

In protriptyline (25 mg/kg) pretreated rats stereotactic 5,7-dihydroxytryptamine (5,7-DHT) lesions of the medial plus laternal 5-hydroxytryptamine (5-HE) bundles in the mesencephalon increased the 5-HT fluorescence in these bundles, and reduced the in vitro uptake of [3H] 5-HT in the hypothalamus to 16% of control values after 2 mug 5,7-DHT/4mul and 12% after 4 mug 5,7-DHT/4mul, and in the cortex cerebri to 35 and 34% of control values, respectively. Selective lesion of the medial 5-HT bundle reduced [3H] 5-HT uptake both in hypothalamus and in cortex cerebri to 45-48% of control values, while selective lesion of the lateral 5-HT bundles significantly reduced [3H] 5-HT uptake only in cortex (to 73-75%). No significant change was observed in [3H] noradreanaline uptake after any injection, or in [3H] 5-HT uptake after vehicle injections. Locomotor activity in an open field 3-10 days postoperatively was significantly reduced by lesions of the medial plus lateral 5-HT bundles. 5-Hdroxytryptophan (50 mg/kg) and a peripheral decarboxylase inhibitor (MK 486, 75 mg/kg) 17 days postoperatively induced a pronounced behavioral "5-HT syndrome" in these rats with medial plus lateral lesions but not in controls. Pain sensitivity, as measured by the hot plate test, was not changed by any lesion, even when tryptophan hydroxylase was partly inhibited with alpha-propyldopacetamide (100 mg/kg). Morphine analgesia and acquisition of a one-way avoidance response also were unchanged. Apomorphine (2 mg/kg)-induced locomotor activity and stereotyped behavior, as measured in an Animex activity meter, were not significantly different from control values in the 5,7-DHT groups. It was concluded that the medial 5-JT BUNDLE INNERVATES BOTH THE HYPOTHALAMUS AND THE CORTEX CEREBRI AND THE LATERAL 5-HT bundle mainly the cortex. These ascending 5-HT neurons are involved in maintaining open field ambulation. No wupport was obtained for the view that they are involved in pain mechanisms, in morphine-induced analgesia, in apomorphine-induced motor behavior, or in one-way avoidance learning.

Afferent Pathways↗

PubMed1985

Passive avoidance deficits in mice following ethylcholine aziridinium chloride treatment.

High-affinity choline uptake (HACU) appears to be the rate-limiting step in the synthesis of the neurotransmitter acetylcholine. The present experiment was designed to examine the effects of irreversible inhibition of HACU by ethylcholine aziridinium chloride (ECA) on passive avoidance retention in mice. Animals were injected intracerebroventricularly, and one-trial passive avoidance retention evaluated 21 days later. A significant retention deficit was observed in ECA-treated animals upon retest 24 hours after training. ECA-induced changes in retention were accompanied by significant reductions in choline acetyltransferase (CAT) activity in only two of seven brain regions tested, hippocampus (48% of control) and cerebellum (76% of control). The results support the involvement of hippocampal cholinergic activity in mediation of passive avoidance learning.

Animals↗

PubMed1967

Amnesic effects of small bilateral brain puncture in the mouse.

A small acute brain puncture produced retrograde amnesia in a passive avoidance learning situation in mice. If injury to the hippocampus was inflicted either immediately, 1 hour after the learning, or 1 hour before the learning, the animals showed a retention deficit; the degree of this deficit was related to the time interval. No effect of this injury was observed on retest performance when the animals were treated as long as 6 hours before or after the learning trial.

Amnesia↗

PubMed1975

Stimulus controllability and the latent inhibition effect.

The effects of stimulus controllability on latent inhibition was examined in instrumental and classical conditioning. Rats allowed control over stimulus termination prior to avoidance conditioning exhibited no retardation of avoidance learning whereas subjects yoked to these rats with respect to pattern and amount of stimulus exposure but given no control over stimulus termination were retarded. However, groups of rats differentiated only by control over stimulus termination, prior to classical conditioning, were equally and severely retarded in the acquisition of a classically conditioned response as indexed by the CER technique. The results were discussed in terms of a learning hypothesis of latent inhibition.

Animals↗

PubMed1976

Avoidance behavior and ileum motility post-cingulumotomy in monkey.

Two experiments were conducted utilizing rhesus monkeys to determine (i) the effects of cingulumotomy on conditioned-avoidance acquisition and extinction and (ii) the effects of avoidance learning on distal ileum motility in control- and cingulum-lesioned animals. Active (AAR) and passive (PAR) avoidance schedules singly or in combination were employed during short daily periods (less than 2 hr) of "shaping," training, acquisition, and extinction. The data indicated that the control-lesion and cingulum groups did not differ in the acquisition or extinction of an AAR. The cingulum group, however, showed a significant deficit in the acquisition of a PAR and a noticeably slower rate of lever pulling during avoidance trials in the combined avoidance training sessions. The results also suggested that ileum motility and avoidance behavior parallel on another, i.e., if either changed the other often changed in the same direction; that cingulum monkeys seemed to be less "reactive" than control-lesion monkeys; and that cingulum animals may been somewhat more regular in their percent daily motility patterns than the control animals.

Animals↗

PubMed1979

Avoidance acquisition in cats as a function of temporal and intensity factors.

Acquisition of an active bar-pressing avoidance response was investigated in a factorial design with 3, 5 or 9 s CS-US intervals and CSs of 70- or 50-dB of white noise. As the CS-US interval increased the required time to meet the avoidance criterion decreased. The shorter the CS-US interval and the more intense the CS, the shorter the median response latencies observed at the end of the training. The latency data were analyzed in Vincentized fifths of acquisition trials. At the beginning of training, when the highest proportion of responses occurred soon after the US onset, escape latencies were shorter in groups trained with shorter CS-US intervals and the more intense CS. During the 1st and 2nd fifths of training, avoidances occurred with the same probability in each part the CS-US interval. By the middle of the training, after a performance level of 50 percent avoidance responses was reached, a rapid increase in the number of short-latency avoidance was observed, which was more pronounced in groups trained with the 70 dB CS. While the general shape of the latency distributions was preserved during the remaining two fifths of the training, a further increase in the intensity effect was noted, which occurred along with a decrease in the CS-US interval effect. The data are in favour of Two-factor Theory of Avoidance learning and suggest that at various stages of training, different variables emerge for acquisition and consolidation of the avoidance reflex. Data supported the hypothesis that two different mechanisms are involved in performance of short- and long-latency avoidance responses.

Animals↗

PubMed1977

[The applied time interval as a learnable dimension].

The possibility of learning time intervals was examined. 7 male BDE-rats (70 days old at the beginning of the experiments) were trained (shock avoidance learning) in a modified test chamber to learn bar-pressing only in distinguished time periods (LD 12 : 12). In a second part of the experiment it was examined with 5 rats what effect an extension of the light phase has. The results show that there is a possibility of learning time intervals and of maintaining this behaviour under these specific conditions of training.

Animals↗

PubMed1979

PA-learning in young rats with dorsal hippocampal- and hippocampo-entorhinal atropine.

Twenty-one-day-old rats injected with atropine into dorsal hippocampus and trained on a white-black step-through passive avoidance task, did not perform differently from their controls in acquisition or extinction. In contrast, when atropine was administered into the ventral hippocampo-entorhinal area, the animals displayed a passive avoidance deficit. The results support the finding that the posteroventral but not the anterodorsal part of the hippocampal complex is implicated in passive avoidance learning and suggest a cholinergic mediation of this effect.

Animals↗

PubMed2005

Acute and chronic effects of MDMA on molecular mechanisms implicated in memory formation in rat hippocampus: surface expression of CaMKII and NMDA receptor subunits.

Acute 3,4-methylenedioxymethamphetamine (MDMA, "ecstasy") treatment induces learning deficits in different animal models. In a passive avoidance learning task in rats, previous studies suggested a role for Ca2+/calmodulin-dependent protein kinase II (CaMKII) and N-methyl-D-aspartate (NMDA) receptors in the acute learning impairment. As cognitive deficits by "ecstasy" in humans have been only reported in frequent recreational users, we examined whether a repeated MDMA treatment could induce in rats lasting molecular changes related to memory consolidation of passive avoidance. In rats with a pronounced 5-HT depletion by MDMA, the effect of another drug challenge was also examined. The surface expression in the hippocampus of NMDA receptor subunits, the scaffolding postsynaptic density protein PSD-95, phosphorylated CaMKII and protein phosphatase 1 (PP1) was measured. In rats repeatedly treated with MDMA (10 mg/kg) twice daily for 4 consecutive days, hippocampal 5-HT levels were markedly reduced 1 week later. At this time, neither learning performance was affected nor changes in membrane levels of NMDA receptor subunits, PSD-95, CaMKII and PP1 were found. In these rats, however, another drug challenge produced a rapid reduction in PSD-95 immunoreactivity and prevented the learning-specific increase in the NMDA receptor NR1 subunit and phosphorylated CaMKII. The results show no lasting change in learning-associated molecular events after a neurotoxic MDMA treatment. This drug only produces transient effects on early molecular events involved in memory consolidation, which do not appear to depend on endogenous 5-HT levels.

Animals↗

PubMedDate not supplied

Behavioral performance of rats following neonatal hypoxia-ischemia.

The behavioral performance of rats subjected in the neonatal period to hypoxia-ischemia at either 37 degrees C or 21 degrees C was compared to that of sham-ligated animals. Performance on complex motor tests was significantly delayed only in the hypoxic-ischemic 37 degrees C rats. However, cognitive testing disclosed significant delay of spatial learning in animals subjected to hypoxia-ischemia at 21 degrees C and those with gross infarction at 37 degrees C. There was enhanced avoidance learning in the animals with gross infarction in the hypoxia-ischemia 37 degrees C group. Hypoxic-ischemic damage in the neonatal rat at 37 degrees C results in transient delay of complex motor skills, but longer lasting cognitive changes. Hypoxia-ischemia during hypothermia produces no motor deficits, although there may be similar alterations in learning.

Animals↗

PubMed1977

Effect of corticosteroids in the hippocampus on passive avoidance behavior in the rat.

The site of action of corticosteroids in avoidance learning was investigated in 110 rats. Injection of cycloheximide, 30 min before one-trial training on a passive avoidance task suppressed corticosteroid secretion in response to footshock, and produced an avoidance deficit in a test 6 days later. However, an additional injection of hydrocortisone, either subcutaneously or intra-hippocampally within 5 min of training, restored the avoidance response in the test. Septal and hypothalamic injections of the hormone were ineffective in reversing the cycloheximide effect, whereas the effect of hormone injection into the amygdala was equivocal because of an increased level of activity. Corticosteroids secreted following an aversive experience appear to act upon the steroid-sensitive neurons in the hippocampus to influence the animal's later performance of passive avoidance response.

Adrenal Cortex Hormones↗

PubMed1998

Cognitive involvement by negative modulation of histamine H2 receptors in passive avoidance task in mice.

In this study, the intracerebroventricular administration of 4-methylhistamine (3 and 10 micrograms/head), a histamine H2 receptor agonist, shortened the step-through latency in the retention trial using a step-through passive avoidance task in mice. This deteriorating effect of 4-methylhistamine (3 micrograms/head) was clearly antagonized by pretreatment with zolantidine (10 mg/kg, i.p.), a histamine H2 receptor antagonist, 20 min before an acquisition trial. Zolantidine alone at the dose tested had no effect. Thus, it is likely that activation of histamine H2 receptors has a deteriorating effect on avoidance learning in mice. The present results indicate the cognitive involvement by negative modulation of histamine H2 receptors in passive avoidance task in mice.

Animals↗