Discrimination Learning In Rats Research Articles

P-157 - Ameliorating effects of TDN-345, a novel stimulator of NGF production, on impaired sound-light discrimination learning in rats with intraventricular injection of AF64A.

P-157 - Ameliorating effects of TDN-345, a novel stimulator of NGF production, on impaired sound-light discrimination learning in rats with intraventricular injection of AF64A.

Facilitation of olfactory learning by a modulator of AMPA receptors

The effects of a benzoyl-piperidine drug (BDP) that facilitates AMPA receptor-mediated synaptic responses were tested on the acquisition and retention of long-term memory at dosages that had no detectable effects on a variety of performance measures. BDP-12 produced a dose-dependent suppression of exploratory activity in rats with statistically reliable effects occurring at 50 mg/kg (i.p.). The drug had no effects on balance beam performance at 30 mg/kg but at 45 mg/kg reduced the number of crossings made within a session; it did not, however, affect the time required to perform a traversal. The performance of well-trained rats presented with a familiar pair of odors (correct and incorrect) was not not detectably altered by BDP-12 at 30 mg/kg; however, the number of correct responses made in a five-trial test was reduced at 45 mg/kg. These results indicate that the AMPA receptor modulator at 30 mg/kg has little influence on arousal, motivation, sensori-motor processing, and attention; higher dosages cause a depression of learned and unlearned prepotent responses. The effects of the lower concentration were tested on two-odor discrimination learning in rats that had extensive training on the task. The animals (n = 20) were given three or five acquisition trials with novel odor pairs immediately after an injection of drug or vehicle and then tested 1-3 d later for retention in five unrewarded probe trials. Retention performance was not significantly better than chance 52.6 +/- 4.5% correct) for odors learned on vehicle injection days but was well above chance for odors learned on drug injection days (70.6 +/- 4.2% correct). Within-subject comparisons confirmed the memory enhancing effect of BDP-12 (p < 0.01). Analyses of performance during five training trials indicated that the rats made more correct responses on days on which they were given the drug than on days on which they were injected with vehicle (p < 0.02). Within-subject differences in acquisition were correlated with differences in retention (r = 0.70). There were no evident effects of the drug on response latencies during acquisition. These results suggest that AMPA receptor modulators reduce the amount of training needed for the formation of long-term memory and do so at dosages which have little effect on variables that secondarily influence acquisition. Possible reasons for this selectivity are discussed.

Relation between septo-hippocampal cholinergic system and the discrimination learning in rats: A microdialysis study

Relation between septo-hippocampal cholinergic system and the discrimination learning in rats: A microdialysis study

High-fat diets impair conditional discrimination learning in rats

At the age of 1 month, four separate groups of Long-Evans rats were placed on diets varying in the amount and composition of dietary fat. High-saturated-fat diets (lard based) were either 20% or 10% (w/w) of the diet. High-polyunsaturated-fat diets (soybean oil based) were either 20% or 5% (w/w) of the diet. A fifth group of rats consumed standard laboratory chow (4.5% w/w fat). After 3 months, all the rats were tested on a conditional discrimination learning task in which they were required to associate different stimuli with different responses. Independent of the source of dietary fat, the animals fed high-fat diets (20% w/w) were impaired on the task. Performance of the animals fed the 10% lard diet was indistinguishable from that of the animals fed the 20% fat diets. In contrast, the rats fed 5% soybean oil (SBO) or chow diets displayed superior performance in comparison with all other groups. These data demonstrate that high-fat diets can have adverse effects on learning and memory and provide suggestive evidence that saturated fatty acids may be associated with the adverse effect.

Spatial discrimination learning in rats as an animal model of cognitive ageing

Spatial discrimination learning and memory in the rat seems to be a valid animal model for age differences in human cognitive functioning. Inherent to these models are problems concerning the validity of the task and the possible confounding effect of the measures by age differences in non-mnemonic factors such as motor performance, motivation and problem-solving strategies. We have used different tasks such as the holeboard, the conefield and the Morris water-escape task to evaluate spatial discrimination learning in rats of different ages. In the conefield task, we unexpectedly found that old Lewis rats performed better than young Lewis rats on the measure spatial reference memory. In contrast, the performance of old Lewis rats was markedly impaired in the Morris water- escape task compared to that of young Lewis rats. We suggest that the difference in outcome of these two studies is related to confounding variables which have distinct effects in young and old rats. The consequences of these findings for the use of spatial discrimination tasks as an animal model of cognitive ageing are discussed.

Neonatal glutamate can destroy the hippocampal CA1 structure and impair discrimination learning in rats

Neonatal Wistar rats were subcutaneously injected with 0.1, 1, or 2 mg/g b.wt. of monosodium glutamate (MSG) at 1, 3, 5, 7, and 9 days after birth. The animals were observed for degeneration of pyramidal cells in the hippocampus. The histological change disappeared when the animals were concurrently injected with glutamate diethyl ester (GDEE), an antagonist of the glutamate receptor. When ligh-dark discrimination learning was carried out at 10 weeks old, the correct response in the acquisition period was impaired in the animals given 1 and 2 mg/g of neonatal MSG. Their retention scores were also impaired in comparison with the control animal. The behavioral impairment recovered with pre-treatment with GDEE. No significant changes were observed in the concentrations of transmitter substances, including amino acids and monoamines. These results suggest that neonatal MSG destroys the hippocampus and impairs acquisition and retention of discrimination learning through the mechanism of glutamate receptors.

Drug discrimination learning in rats with excitotoxic lesions of nucleus basalis and ventral globus pallidus

Rats can readily acquire conditional discriminations in which mixtures of drugs serve as compound internal discriminative stimuli. Excitotoxic lesions in the region of the nucleus basalis have been shown to impair the acquisition of conditional discriminations based upon external visual stimuli, but nothing was known about their effects on discrimination of internal stimuli. A baseline of undiscriminated bar-pressing for food reinforcers was established prior to surgery. Lesions were made by infusing either ibotenic or quisqualic acid bilaterally into the basal forebrain (the ibotenate-induced lesions had been shown previously to impair cortical cholinergic function and to produce non-specific damage). After surgery, rats were trained to discriminate effects of drug mixtures using a standard, two-bar operant conditioning procedure. The ibotenate, but not the quisqualate, lesion impaired the acquisition of a discrimination of a mixture of (+)-amphetamine plus pentobarbitone, while neither lesion impaired acquisition with a mixture of (-)-nicotine plus midazolam. The ibotenate lesions also reduced overall rates of responding in both experiments. Thus, the deficit in the acquisition of drug discrimination in rats with ibotenate lesions had some pharmacological specificity, but could not be related easily to disturbances in neocortical cholinergic function. In comparisons with other published data, the results suggest a possible dichotomy in the processing of interoceptive and external information in the basal forebrain, a major target of ventral striatal overflow.

CS memory after trace conditioning

Two experiments investigated successive discrimination learning in rats. Of central interest was the influence of the interval between the reinforced stimulus (S+) and the reinforcer (shock) on discriminative performance. Experiment 1 demonstrated that when shock immediately followed the S+ the discrimination was formed rapidly—subjects quickly came to show conditioned responding exclusively during the S+. However, when there was a 30-s trace interval between the S+ and shock the discrimination was only poorly formed, and conditioned responding occurred on both S+ and nonreinforced (S−) trials. In Experiment 2 subjects received concurrent training on a visual and an auditory discrimination. For one discrimination the S+ was immediately followed by shock and for the second discrimination there was a trace interval between the reinforced cue and shock. The former discrimination was acquired more readily than the latter. Implications of these results for contemporary theories of discrimination learning are explored and parallels between these results and the phenomena of contrast and of “marking” are examined.

Neonatal glutamate destroyed CA1 neurons and impaired discrimination learning in rats

Neonatal glutamate destroyed CA1 neurons and impaired discrimination learning in rats

Enhanced spatial discrimination learning in rats following 5,7-DHT-induced serotonergic deafferentation of the hippocampus

Learning in rats trained in the Stone 14-unit T-maze, a complex, positively reinforced spatial discrimination task was assessed following cytotoxic (5,7-dihydroxytryptamine; 5,7-DHT) deafferentation of the serotonergic inputs to the hippocampus. Serotonergic deafferentation was accomplished by infusing the cytotoxin in to the fornix-fimbria/cingulum bundle. Lesioned rats reached criterion (i.e. learned) in significantly fewer trials and made significantly fewer errors throughout training than either vehicle-injected or sham-operated controls. This represents the first time that the effects of selective chronic destruction of serotonergic inputs to the hippocampus have been investigated. The present results provide, therefore, evidence in support of a neuromodulatory role for serotonin (5-HT) within the rat hippocampus in the mediation of the processes underlying learning and memory for this task. Other studies are, therefore, warranted in order to determine whether hippocampal 5-HT also plays a role in the mediation of the processes underlying learning and memory in other types of tasks.

Corpus callosum section disrupts motor behaviour strategies during visual discrimination learning in rat

Monocularly patched rats were trained on a series of visual tilt discriminations ordered from simple to difficult to measure the angular difference threshold of each eye. The stereotyped running pattern which the animal made was also recorded. Callosal section disrupted a preoperatively established running pattern and produced an ocular neglect; the animal's performance dropped to chance when it used the eye ipsilateral to the preferred side of approach.

Effects of uncontrollable shock on subsequent appetitive discrimination learning in rats

Effects of uncontrollable shock on subsequent appetitive discrimination learning in rats

The effects of anteromedial cortex lesions on pattern discrimination learning in rat

The visual angular difference threshold of rats with unilateral anteromedial cortex lesions was measured. The stereotyped running pattern and preoperatively preferred side of approach in a two-choice visual discrimination apparatus was recorded for each animal. Lesions in the hemisphere ipsilateral to the preferred approach side did not affect either the running pattern or the angular difference threshold. However, there was a general reduction in the detection of the positive stimulus throughout the scale. Lesions in the contralateral hemisphere produced a transient reversal of the side preference with an overall loss of S + detection in the field contralateral to the side approached.

Synaptic plasticity and learning: selective impairment of learning rats and blockade of long-term potentiation in vivo by the N-methyl-D- aspartate receptor antagonist AP5

This paper reports a series of 5 experiments concerned with a possible role for N-methyl-D-aspartate (NMDA) receptors in certain types of learning. The results show that chronic intraventricular infusion of the NMDA receptor antagonist D,L-2-amino-5-phosphonopentanoic acid (D,L-AP5) caused an impairment of spatial but not of visual discrimination learning in rats. Such selectivity of the learning impairment occurred despite widespread distribution of the drug throughout the CNS. AP5 sometimes caused a disturbance of sensorimotor function during learning, but one experiment addressing whether this disturbance could be responsible for the spatial learning impairment established that it was statistically independent. Another experiment showed that AP5 did not affect the retention of previously acquired spatial information. These behavioral effects were all obtained with a concentration of AP5 that, in a final study, was found to be sufficient to block hippocampal long-term potentiation (LTP) in vivo without affecting normal synaptic transmission. Taken together, these observations (1) implicate NMDA receptors in certain types of learning, and (2) extend recent work showing that saturation of LTP causes an anterograde spatial amnesia (McNaughton et al., 1986). A preliminary report of parts of this work has been published (Morris et al., 1986a).

Effects of two ACTH analogs on successive odor discrimination learning in rats

Olfactory discrimination learning has been shown to provide a powerful tool to investigate the mechanisms involved in the formation, storage and retrieval of information in rodent CNS. In the present study we tested the effects of two ACTH analogs, which were previously reported to influence the processes of learning and memory, on various olfactory learning tasks. The ACTH(4–9) analog HOE 427 produced an apparent increase in storage of olfactory information as shown by the difficulty experienced by the animals to rapidly reverse their behavioral responses to previously learned odors. Similarly, the ACTH (4–9) analog ORG 2766 appears to enhance the storage of olfactory information when administered either before or after the learning trials. These data are consistent with the notion that ACTH and related analogs facilitate performance in a variety of learning tasks. In addition, our results suggest possible mechanisms by which some neuroactive peptides might modulate learning and memory processes in the CNS.

Hippocampal system dysfunction and odor discrimination learning in rats: Impairment of facilitation depending on representational demands.

The performance of normal rats and that of rats with hippocampal system damage were compared on acquisition of different versions of the same two-odor discrimination task that placed different encoding and representational demands on memory. Rats with fornix lesions were impaired when explicit comparisons among multiple odor cues and differential response choices were encouraged. However, when odor-cue comparison was hindered and explicit cues for response choice were eliminated, rats with fornix lesions out performed normal animals. The results support an hypothesis that the hippocampal system is critical to a memory representation based on encoding relations among multiple percepts, and other brain systems support performance adaptations based on encodings of stimuli individually.

Olfaction and the "data" memory system in rats.

A set of studies was conducted to characterize the memory system involved in successive olfactory discrimination learning in rats. Two odors emanated from different arms of a radial maze; one of the arms contained a water reward. After training on four or five pairs of odors (20 trials per day), rats learned to discriminate the members of a new pair in 5-10 trials. Experiments in which either member of the pair was compared with a novel cue indicated that the rats learn both positive and negative odors, rather than simply ignoring the negative cue. The memories for the odors were apparently persistent, and no evidence for retroactive interference from subsequent training was obtained. Training on 30 pairs did not result in any slowing of subsequent learning, which suggest that the capacity of the memory system for odors is substantial. In a second group of experiments, we tested whether rats distinguish between odors by identifying unshared subcomponents or instead treat odors in a gestalt (i.e., unitary) fashion. Animals trained on three component odors with two in common did not recognize the elements that were unshared when these were presented by themselves. Even when one of the two shared components was combined with the differentiating component into a cue (i.e., two thirds of the original three-component odor), the new cue was treated as a novel odor. However, inclusion of a previously learned simple odor in a complex odor did affect the learning of that odor.(ABSTRACT TRUNCATED AT 250 WORDS)

Discrimination learning in rats following early-life undernutrition and stimuli pre-exposure

Discrimination learning in rats following early-life undernutrition and stimuli pre-exposure

Visuomotor strategies in pattern discrimination learning in rats

Normal rats were trained on a series of visual tilt discriminations ordered from simple to difficult to measure their angular difference thresholds. The stereotyped visuomotor running pattern which the animal made was recorded for all angular differences binocularly and whilst the animal was monocularly patched. The results show that the running pattern does not reflect visual guidance strategies and can produce a visual field bias for the field ipsilateral to the preferred approach side.

Role of mediodorsal thalamic nucleus in olfactory discrimination learning in rats.

Severe deficits in the acquisition of an olfactory learning-set task resulted from lesions of the central (olfactory) component of the mediodorsal thalamic nucleus but not from large lesions that destroyed olfactory projections to the amygdala. Complex olfactory learning may be mediated by the olfactory thalamocortical system and not by olfactory projections to the limbic system.