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At least 559 records · Page 31Linked to original sources
PubMed2003

Effects of nitric oxide inhibition on avoidance learning in the chick are lateralized and localized.

Bilateral administration of nitric oxide synthase inhibitors into the intermediate medial hyperstriatal (IMHV) region of the chick brain impairs memory formation for an avoidance task. The aim of the current study was to determine whether this effect was restricted to a particular location in the brain, and whether inhibition was equally effective in both hemispheres. White Leghorn x black Australorp chicks were administered 0.5 mM N(omega)-Nitro-L-arginine methyl ester bilaterally into the lobus parolfactorius (LPO), or unilaterally into the IMHV. Injections into the LPO between 5 min pre-training and 40 min post-training had no effect on retention. In contrast, unilateral injections into the IMHV impaired retention and memory loss occurred from 40 min post-training. The effective administration time was hemisphere-dependent, requiring left hemisphere administration around the time of training and right hemisphere administration between 15 and 25 min post-training. These data suggest that localized nitric oxide activity in each hemisphere of the chick brain is necessary for the consolidation of memory for this task.

Animals↗
PubMed1999

Reversible inactivation of the median raphe nucleus enhances consolidation and retrieval but not acquisition of passive avoidance learning in rats.

Involvement of median raphe nucleus (MRN) in acquisition, consolidation and retrieval of passive avoidance (PA) was investigated with functional suppression of this area by lidocaine. Rats carrying a chronically implanted cannula aimed at the MRN were trained on a step-through passive avoidance task and received intra-MRN injection of lidocaine or saline 5 min before training or 5, 90 and 360 min after acquisition trial or 5 min before the retrieval test. Lidocaine MRN inactivation had no effect on PA learning. Lidocaine injected 5 and 90 min after the acquisition trial significantly enhanced avoidance of the dark compartment in comparison with the control group injected with saline. But PA retention was not affected by lidocaine injected 360 min after acquisition or 5 min before training. Retention latency significantly increased, when lidocaine injected 5 min before retrieval test. Step-through latency of naive rats was not affected by MRN blockade. Furthermore, reversible inactivation of MRN did not have a significant effect on locomotor activity. Our results indicate that the MRN contributes to PA consolidation at least until 90 min after acquisition and involves in PA retrieval. It is concluded that functional ablation of the MRN may disrupt the inhibitory actions of MRN projections to sub-cortical circuits participating in PA memorization and retrieval.

Analysis of Variance↗
PubMed1978

6-Hydroxydopamine induced catecholamine depletion and passive avoidance learning in rats.

Rats were injected with 6-hydroxydopamine either intracisternally, intraperitoneally, or both, in order to examine the effects of central vs. peripheral catecholamine depletion on a step-down passive avoidance task. All rats acquired the response at the end of the five asquisition trials but the rates of acquisition of the drug-treated groups were siginificantly different from the control group. No significant difference in the performance results were observed between groups during the extinction period. These findings failed to confirm the hypothesis that an intact central and/or peripheral catecholaminergic systems may be necessary for the acquisition and extinction of a step-down passive avoidance response. In addition, this study also showed that plasma corticosterone levels in the rats depleted of central or peripheral catecholamine did not differ significantly from each other after passive avoidance training.

Animals↗
PubMed1990

Effects of a new TRH analogue, YM-14673, on disturbance of passive avoidance learning in senescence-accelerated mice.

Effects of a new TRH analogue, YM-14673 (N alpha-[[(S)-4-oxo-2-azetidinyl]carbonyl]-L-histidyl-L-prolinamide dihydrate), on disturbance of passive avoidance behavior were observed in senescence-accelerated mice (SAM). Latency of step-through in SAM-P/8/Ta (SAM-P/8, senescence-prone substrain) was significantly shorter than that in SAM-R/1/Ta (SAM-R/1, senescence-resistant substrain). Successive oral administration of YM-14673 (1 and 10 mg/kg) and TRH (10 mg/kg) for 3 weeks prolonged the shortened latency of step-through. These results suggest that YM-14673 is more potent than TRH in antiamnesic activities.

Aging↗
PubMed2005

Inhibitory avoidance learning altered ensemble activity of amygdaloid neurons in rats.

In this study, we examined single-unit activity in the amygdala before and after a rat had acquired an inhibitory avoidance task. Long-Evans rats with microwires chronically implanted into the central nucleus (CeA) or basolateral complex (BLC) of the amygdala were acclimatized to the apparatus of a step-through inhibitory avoidance task for three sessions. On the fourth session, rats in the experimental group received an inescapable footshock (3 mA, 1 s) as they stepped from the lit side into the dark side of the task apparatus, whereas rats in the control group received the same amount of shock on a different apparatus. All rats were tested for retention in the task apparatus 1 day after shock training. The experimental rats showed better retention than the controls as they stayed longer in the lit side. Ensemble unit activities were recorded in the amygdala nuclei from the indwelling wire bundles during the acclimation and test sessions. The data collected from well-isolated amygdala units showed that neuronal discharge habituated from the first to the third acclimation session. In the test session, the experimental group, but not the control group, showed elevated firing rates in the CeA or BLC neurons located on either side of the brain. These findings provide the first piece of evidence showing that learning of an inhibitory avoidance task leads to an increase in amygdala neuronal discharges during a retention test.

Action Potentials↗
PubMed1991

Disturbance of brightness discrimination and active avoidance learning after lesions of nucleus reticularis tegmenti pontis (NRTP) of rats are related to impairment of goal-directed behaviour.

Long-Evans hooded rats were not able neither to reach criterion of active avoidance tasks in a Y-maze and in a jump test, nor in brightness discrimination after lesions of the NRTP without preoperative experience in these tests. After preoperative consolidation of active avoidance, the retention of Y-maze avoidance performance was zero and of jump test avoidance at 25%. The Y-maze avoidance was again relearned except in the task with 2:2 alternation of goals whereas retention of brightness discrimination was not affected. In the jump test, avoidance relearning was evidently retarded. Ambulatory and exploratory behaviour in the open field were significantly reduced after NRTP lesions. The NRTP is evidently involved in the establishment and control of goal-directed behaviour.

Animals↗
PubMed1979

Circadian variations in the effect of alpha-methyl-p-tyrosine on avoidance learning.

Circadian variations in alpha-methyl-p-tyrosine's (alpha MT) disruption of active avoidance acquisition were studied, alpha MT administered between 11.0 and 13.00 h, 17.00 and 19.00 h and 23.00 and 01.00 h impaired learning, but alpha MT administered between 05.00 and 07.00 h did not impair learning. The time of alpha MT ineffectiveness corresponds with the reported circadian peak in brain catecholamines, suggesting that the circadian susceptibility rhythm of alpha MT depends upon circadian fluctuations of brain catecholamines.

Animals↗
PubMed1993

A dissociation between the proactive ECS effects on inhibitory avoidance learning and on classical fear conditioning.

This study investigated if the nature of the task is a determinant factor of whether or not a series of electroconvulsive shock (ECS) will proactively affect learning in animals. Rats were administered one daily ECS for 7 days. A day after the last administration they were concomitantly trained on an inhibitory avoidance task and on classical conditioning of fear response to a brief tone. Twenty-four hours later they were exposed for 8 min to an open-field arena and the freezing reaction was measured both before and after tone presentation (classical fear conditioning test). On the subsequent day the step-through latency (without presentation of the tone) was measured on the avoidance apparatus (inhibitory avoidance test). Impairment of inhibitory avoidance was seen in ECS-administered animals in comparison to controls, but the freezing reaction to the tone was equally high in both groups. Additional groups of rats were trained in order to control for ECS alone-induced freezing and pseudoconditioning. Also, it was demonstrated that the differential ECS effects on the two tasks were not due to the order of testing since similar dissociation was obtained when inhibitory avoidance test was conducted before the open-field test.

Animals↗