An n-3 fatty acid deficiency impairs rat spatial learning in the Barnes maze.

In this study, the authors demonstrate that rats with n-3 fatty acid deficiency display spatial learning deficits in the Barnes circular maze. Dams were deprived of n-3 fatty acids during pregnancy and lactation, and their offspring were weaned to the same deficient diet. There was a 58% loss of brain docosahexaenoic acid (DHA) in the n-3 fatty acid-deficient rats in comparison to n-3 fatty acid-adequate rats. At 8 weeks of age, deficient rats demonstrated moderate impairment in Barnes maze performance compared with the n-3 fatty acid-adequate rats during the initial training. In the reversal learning task, the n-3 fatty acid-deficient rats showed a profound deficit in performance: They required more time to find a new position of the escape tunnel, which was accompanied by a higher number of errors and perseverations. The n-3 fatty acid-deficient rats had reduced tissue levels of dopamine in the ventral striatum and enhanced levels of the metabolite 3,4-dihydroxyphenylacetic acid in frontal cortex and hypothalamus. In summary, this study demonstrates that rats with low brain DHA have a deficit in spatial reversal learning that could be related to changes in dopamine transmission in critical brain circuits. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dopaminergic modulation of olfactory bulb processing affects odor discrimination learning in rats.

Olfactory behavioral studies have shown that, when modulated through systemic injections, D1 and D2 receptors have opposing effects on odor discrimination learning. In the present study, cannulated male Sprague–Dawley rats were used to investigate how the modulation of these 2 types of dopaminergic receptors through direct infusion of D1/D2 agonists and antagonists into the olfactory bulb affect olfactory perception. Dopaminergic modulation was locally altered by manipulations of D1 (agonist SKF 82958: 14.6, 43.8, & 143.6 mM; antagonist SCH-23390: 13.4, 40.1, & 60.1 mM) and D2 (agonists quinpirole: 78.2, 117.3, & 156.4 mM; antagonist sulpiride: 0.3, 0.9, & 2.9 mM) receptors during a simultaneous odor discrimination task. The authors found that modulation of D2, but not D1, receptors significantly affected rats’ odor discrimination performance. A significant positive correlation between blockade of D2 receptors and discrimination performance, as well as a significant negative correlation between D2 receptor activation and discrimination performance, was observed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Modulation of memory consolidation for olfactory learning by reversible inactivation of the basolateral amygdala.

The role of the basolateral amygdala (BLA) in the consolidation of an association between an olfactory stimulus and footshock was investigated with a reversible lesion technique of posttraining infra-BLA infusions of tetrodotoxin. Rats receiving tetrodotoxin infusions following paired odor-shock presentations spent more time near the odor, and reacted differently on contact with the odor when tested 24 hr after training, than did rats receiving paired presentations and saline infusions, but they did not differ from rats receiving unpaired presentations and saline infusions. The results indicate that the BLA plays a similar role in influencing consolidation of olfactory-based memory as it does for memory based on other modalities. Thus, these findings strengthen the view that the BLA plays a general role in modulation of memory storage for emotionally arousing events. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Remembrance of places you passed: Social spatial working memory in rats.

Pairs of rats were tested in a radial-arm maze to determine whether the spatial choices made by one rat affect the subsequent spatial choices of the other rat. In a free-choice procedure, rats showed an increased tendency to choose the location that had most recently been chosen by a foraging partner but a decreased tendency to visit locations that the foraging partner had visited earlier. Forced-choice procedures were used to better control the social stimulus and the interactions between the rats. Under some conditions, locations were chosen later in the choice sequence of a subject rat if another rat had been observed choosing that location. Odor and other physical traces of the other rat's visits were ruled out as explanations for this effect. The results demonstrate the existence of working memory for locations visited by a familiar conspecific. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A comparison of discrimination and reversal learning for olfactory and visual stimuli in aged rats.

The present study investigated age-related differences in discrimination and reversal learning for olfactory and visual stimuli in 6-month and 24-month-old rats. Rats were trained to discriminate between two pseudo-randomly selected odors or objects. Once each animal reached a criterion on discrimination trials, the reward contingencies were reversed. Young and aged rats acquired the olfactory and visual discrimination tasks at similar rates. However, on reversal trials, aged rats required significantly more trials to reach the learning criterion on both the olfactory and visual reversal tasks than young rats. The deficit in reversal learning was comparable for odors and objects. Furthermore, the results showed that rats acquired the olfactory task more readily than the visual task. The present study represents the first examination of age-related differences in reversal learning using the same paradigm for odors and objects to facilitate cross-modal comparisons. The results may have important implications for the selection of memory paradigms for future research studies on aging. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Adolescent cocaine residually impairs working memory and enhances fear memory in rats.

The residual effects of cocaine during adolescence on memory in male young adult rats were studied. Animals were injected with 20 mg/kg cocaine on postnatal Days 28 through 35, whereas lab-chow (LC) and pair-fed (PF) control subjects received saline. Assessment of spatial working and long-term memory in the Morris water maze, and 72-h retention of an inhibitory avoidance task was conducted at about 5 and 9 weeks postcocaine, respectively. Relative to PF control subjects, cocaine-treated subjects showed impairments in the water maze when required to swim to the hidden platform placed in a quadrant diagonal from the location of its original location (i.e., on reversal learning). These same drug-treated animals, however, exhibited enhanced inhibitory avoidance retention relative to both control groups. These seemingly disparate findings are seen as being consistent with previous data showing that cocaine during adolescence residually impairs spatial memory and leads to enhanced fear responses. Moreover, when taken with previous findings from our laboratory, the present water maze data indicate that the deleterious effects of cocaine, when administered during adolescence, is delayed until 5 weeks after initiation of abstinence. It is speculated that alterations to limbic circuitry, especially those associated with the amygdala, account for the behavioral results observed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Olfactory learning and memory impairments following lesions to the hippocampus and perirhinal-entorhinal cortex.

The role of the hippocampus and perirhinal-entorhinal cortex was examined in an olfactory discrimination paradigm. Small neurotoxic lesions of the hippocampus (21% tissue damage) yielded relatively unimpaired olfactory retention across brief (30 s), intermediate (approximately 5 min), and 24-hr delays, whereas impairments were noted at 5-day retention intervals. Larger hippocampal lesions (63% tissue damage) spared memory at intermediate delays, with no impact at 8-day retention intervals. Aspiration lesions directed at the perirhinal-entorhinal cortex produced a variable performance pattern, with impairments noted at intermediate, 24-hr, and 5-day delays. Results suggest the hippocampus is not specifically involved in retaining olfactory information, with additional consideration given to the relationship between lesion size and memory impairment. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Behavioral effects of intracerebroventricular microinfusion of agmatine in adult rats.

The present study investigated the behavioral effects of intracerebroventricular microinfusion of agmatine. Rats with low dose (10 μg), but not high dose (100 μg), of agmatine spent significantly less time in the enclosed arm and more time in the open arm in the elevated plus maze. In the water maze task, the high dose group displayed a transient impairment in searching for a hidden platform, whereas the low dose group had reduced latency in the first probe test. In the object recognition task, all groups could detect the novel object, but the low dose group spent significantly more time exploring displaced objects. Furthermore, the low dose group made significantly fewer errors in the working, but not the reference, memory version of the radial arm maze task. These results suggest that the behavioral effects of agmatine are task- and dose-dependent, and agmatine may be an anxiolytic and memory modulator. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Enrichment to odors improves olfactory discrimination in adult rats.

The authors tested how prior odor enrichment affects the spontaneous discrimination of both preexposed and novel odors. Experimental rats were exposed to single odors or to pairs of similar or dissimilar odors for 1-hr periods twice daily over 20 days. Spontaneous discriminations between pairs of similar odors were tested before and after the odor exposure period using an olfactory habituation task. The authors found that (a) experimental rats did not spontaneously discriminate similar odor pairs before the exposure period, whereas they spontaneously discriminated them after the enrichment period, and (b) the improvement of performance was not selective for the odors used during enrichment. These results show that odor experience changes perception in the manner predicted based on other groups' electrophysiological experiments. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Chronic neonatal nicotine increases anxiety but does not impair cognition in adult rats.

Developmental nicotine exposure has been implicated in the association between maternal smoking and adverse outcomes in offspring. The 3rd trimester of human pregnancy is equivalent to the 1st postnatal week in rodents; both are periods of active brain growth during which nicotinic acetylcholine receptors are transiently upregulated. Chronic neonatal nicotine (CNN; 6 mg/kg/day) from postnatal Days 1 to 7 was given orally to rat pups to evaluate long-term behavioral effects. Males and females were tested as adolescents or as young adults. CNN significantly decreased center time, ambulatory behavior, and rearing in the open-field test and decreased the number of entrances and time spent in the open arm of the elevated plus-maze in both sexes and ages. CNN did not change performance in the T maze or in the water maze in adult males or females. Motor coordination was not altered. In summary, CNN had long-term effects on anxiety-like behavior but did not affect spatial learning and memory functions. This finding is particularly important when evaluating the benefits of nicotine-replacement therapies during human pregnancies, which may improve smoking cessation rates but could result in long-term behavioral consequences. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Estrogen-induced changes in place and response learning in young adult female rats.

Many findings suggest that changes in circulating estrogen levels influence cognition, in some cases impairing performance and in others enhancing performance. One interpretation of these mixed effects is that estrogen biases the strategy used to solve a task. To test this idea, young adult female rats, ovariectomized for 21 days, were trained after acute hormone or control treatment in 2 very similar tasks with different cognitive requirements. One task required place learning and the other response learning. Rats given two 10-μg injections of estradiol 48 and 24 hr before training learned the place task significantly faster than did rats without estradiol. Conversely, rats without estradiol performed better on the response task than did rats with replacement. These data suggest that the cognitive actions of estrogen may be task-specific by modulating the relative contribution of different learning and memory systems. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Benzodiazepines impair the acquisition and reversal of olfactory go/no-go discriminations in rats.

The present study assessed whether benzodiazepines impair the acquisition, performance, and reversal of olfactory and auditory go/no-go discriminations in rats. Experiment 1 showed that midazolam (0.5-2 mg/kg sc) did not affect the performance of a well-learned two-odor olfactory discrimination and moderately facilitated performance of a go/no-go auditory discrimination. Experiment 2 found that midazolam (1 mg/kg) increased the number of errors made in the acquisition of a novel go/no-go olfactory discrimination task and in the reversal of a previously well-learned olfactory discrimination. However, midazolam did not affect the acquisition and reversal of an equivalent auditory discrimination task. Experiment 3 showed that diazepam (1 mg/kg) also impaired the acquisition and reversal of a novel olfactory discrimination task. Taken together, these results indicate that benzodiazepines cause a selective impairment of olfactory discrimination learning. This may reflect an effect of benzodiazepines in the glomerular circuitry of the olfactory bulb and at downstream olfactory processing sites such as the piriform cortex and orbitofrontal cortex. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Spatial pattern learning in rats: Control by an iterative pattern.

Rats searched in a matrix of vertical poles for food hidden on top of the poles. The only information available about the location of the food was the consistent spatial pattern of the baited poles, which was a checkerboard. This spatial pattern of hidden-food locations came to control the choices of poles made by the rats. The experiments ruled out the possibility that this control can be explained by the acquisition of simple response tendencies to move from pole to pole. Instead, this behavioral control of choices was attributed to the development of a representation of the checkerboard pattern of baited locations. Spatial pattern learning may have mechanisms in common with other forms of pattern learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cognitive performance in rats differing in their inborn anxiety.

There is profound evidence that cognitive processes and anxiety are interrelated. To learn more about this interaction, the authors tested rats bred for either high (HABs) or low (LABs) anxiety-related behavior in a modified hole board task. This task allows parallel investigation of various cognitive processes and possibly related behavioral dimensions, both under baseline conditions and during cognitively stressful situations. The authors provide evidence that the degree of anxiety is differentially associated with enhanced performance for distinct informational processes in rats. As HABs and LABs did not differ in their anxiety-related behavior after habituation, that is, in a familiar environment during appetitive learning, the authors conclude that anxiety behavior in naive HABs may be due to differential cognitive processing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Transmission of learned behavior between rats.

"Six rats were trained to follow leader rats in an elevated T maze to secure a reward of water. An incidental cue of two lights was then introduced such that the leaders responded consistently with respect to it. After 100 trials of following leaders who were responding to the incidental cue, Ss were given 20 trials alone. On 77% of these test trials Ss went to the arm marked by the cue to which the leader had been going. This finding was interpreted as a demonstration of transmission of learned behavior between animals, and it was explained on the basis of a continuity theory of discrimination learning." (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The CA3 subregion of the hippocampus is critical for episodic memory processing by means of relational encoding in rats.

This experiment tested the theory that the CA3 subregion of the hippocampus mediates episodic learning of arbitrary associations. The authors developed 2 tasks based on the episodic flavor-place paired-associate task described by M. Day, R. Langston, and R. G. Morris (2003): an object-cued spatial location recall task and a spatial location-cued object recall task. After rats were trained to a criterion of 80% correct on 1 of the 2 tasks, they received either a dorsal CA3 lesion or a vehicle control lesion. Control animals continued performing well on both tasks. Rats with lesions to dorsal CA3 were impaired on both tasks and performed at chance but were able to perform a nonepisodic version of the task as a control. These data suggest that CA3 mediates episodic learning of arbitrary associations as tested in the 1-trial object-cued spatial location recall and spatial location-cued object recall tasks. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Gap detection deficits in rats with tinnitus: A potential novel screening tool.

The study describes a novel method for tinnitus screening in rats by use of gap detection reflex procedures. The authors hypothesized that if a background acoustic signal was qualitatively similar to the rat's tinnitus, poorer detection of a silent gap in the background would be expected. Rats with prior evidence of tinnitus at 10 kHz (n = 14) exhibited significantly worse gap detection than controls (n = 13) when the gap was embedded in a background similar to their tinnitus. No differences between tinnitus and control rats were found with 16 kHz or broadband noise backgrounds, which helped to rule out explanations related to hearing loss or general performance deficits. The results suggest that gap detection reflex procedures might be effective for rapid tinnitus screening in rats. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cognitive psychometrics: Assessing storage and retrieval deficits in special populations with multinomial processing tree models.

This article demonstrates how multinomial processing tree models can be used as assessment tools to measure cognitive deficits in clinical populations, This is illustrated with a model developed by W. H. Batchelder and D. M. Riefer (1980) that separately measures storage and retrieval processes in memory. The validity of the model is tested in 2 experiments, which show that presentation rate affects the storage of items (Experiment 1) and part-list cuing hurts item retrieval (Experiment 2). Experiments 3 and 4 examine 2 clinical populations: schizophrenics and alcoholics with organic brain damage. The model reveals that each group exhibits deficits in storage and retrieval, with the retrieval deficits being stronger and occurring more consistently over trials. Also, the alcoholics with organic brain damage show no improvement in retrieval over trials, although their storage improves at the same rate as a control group. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Examination of bilateral eyeblink conditioning in rats.

This experiment monitored eyelid responses bilaterally during delay eyeblink conditioning in rats. Rats were given paired or unpaired training with a tone or light conditioned stimulus (CS) and a unilateral periorbital shock unconditioned stimulus (US). Rats given paired training acquired high levels of conditioned responses (CRs), which occurred in both eyelids. However, acquisition was faster, and the overall percentage of CRs was greater in the eyelid that was ipsilateral to the US. CRs in the eyelid ipsilateral to the US also had shorter onset latencies and larger amplitudes than CRs in the contralateral eyelid. Both eyelids consistently showed high percentages of unconditioned responses (UR) to the US, and the UR amplitude decreased across training sessions in the paired group. The present study demonstrated that CRs occur robustly in both eyelids of rats given eyeblink conditioning, which is similar to previous findings in humans and monkeys. The results also showed that conditioning occurs more prominently in the eyelid that is ipsilateral to the US, which is similar to previous findings in humans, monkeys, dogs, and rabbits. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Odor tracking in rats with orbital frontal lesions.

Rats track self-, conspecific, and artificial odors to locate food. The orbital frontal cortex has been implicated in olfactory behavior, but whether it plays a role in a species-typical behavior, such as odor-guided navigation, has not been studied. Rats were trained to track 1 of 3 different odors deposited on a string. After rats were reliably tracking a scented string, they received a series of 2- and 3-odor discrimination tests. Next, all the rats received bilateral aspiration lesions of the orbital frontal cortex and experienced the same sequence of tasks. Rats learned to track and discriminate between different odors reliably. These results suggest that other areas of the brain mediate odor-guided navigation following damage to the orbital frontal cortex. (PsycINFO Database Record (c) 2010 APA, all rights reserved)