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J W Rudy

Publications and source records attributed to J W Rudy.

At least 19 recordsLinked to original sources
PubMed1992

Brief exposure to an enriched environment improves performance on the Morris water task and increases hippocampal cytosolic protein kinase C activity in young rats.

This study was designed to determine whether brief exposure to an enriched environment around the time of weaning would affect learning and memory processes in young rats. In addition, this study sought to determine if experience in an enriched environment would alter hippocampal protein kinase C (PKC) which is thought to be a possible neural substrate that underlies learning and memory processes. Animals were either reared in an enriched environment or standard laboratory cages starting at 15 days old. After 6 (21 days old) or 12 (27 days old) days subjects were either tested in the Morris water task, or had the hippocampus removed for biochemical analysis of PKC activity. Morris water task results showed that compared to laboratory reared controls, the performance of subjects reared in the enriched environment for 12 days, but not 6 days, was improved. In addition, 12 days of exposure to the enriched environment, but not 6 days, produced more cytosolic hippocampal PKC activity. The particulate fraction appeared not to be affected by rearing in the enriched environment. Brief exposure to an enriched environment around weaning, therefore, both improved Morris water task performance and increased hippocampal PKC activity. These outcomes suggest that performance in the Morris water task and hippocampal PKC may be functionally related.

Animals↗
PubMed1992

Some properties of configural learning: an investigation of the transverse-patterning problem.

Little is known about the conditions that encourage animals to learn to use configural associations to guide their behavior or the consequences of such learning for transfer. This study provided some information about these issues by examining how rats solve the transverse-patterning problem, which requires a configural solution (Spence, 1952). Animals had to concurrently solve 3 simultaneous visual discriminations, represented abstractly as A+ versus B-, B+ versus C-, and C+ versus A-. Experiment 1 indicated that rats use a configural solution even when the problems have an elemental solution, provided that the significance of 1 element (e.g., B) shared by 2 problems is ambiguous (e.g., A+/B-; and B+/C-). Experiments 2 and 3 suggested that, when stimulated to use a configural solution by solving the A+/B- and B+/C- problems, rats transfer the configural solution to problems that have no ambiguous elements.

Animals↗
PubMed1991

Acute phorbol ester treatment improves spatial learning performance in rats.

Recent findings have lead researchers to speculate that hippocampal protein kinase C (PKC) in rodents is involved in spatial learning and memory. The purpose of this study was to determine if treating rats with a compound known to increase PKC activity would improve performance in a task that requires spatial learning processes. Rats were treated with a single intracerebroventricular injection of a phorbol ester, phorbol 12,13-dibutyrate (PDBu) that is known to increase PKC activity and then tested on the hidden-platform version of the Morris water taks. Results showed that PDBu-treated subjects' ability to learn to locate the escape platform was better than controls. In addition, PDBu-treated subjects showed signs of having remembered the location of the platform better than controls when tested 24 h later. These results support a role of brain PKC in processes required to learn the Morris water task.

Animals↗
PubMed1991

Multiple functions of context during conditioning: a developmental analysis.

Contextual stimuli may influence conditioned behavior in at least two ways (e.g. Bouton & Bolles, 1985). By becoming associated with the unconditioned stimulus (US), context cues can acquire excitatory strength that facilitates responding to a phasic conditioned stimulus (CS). The context also can function to clarify the meaning of an ambiguous CS. Data obtained with an appetitive Pavlovian conditioning paradigm suggest that the processes mediating these two influences of context are dissociated during development. Evidence of context-US associations was observed in rats that began training on Postnatal Day 17, but no evidence for a disambiguation function was found until pups were 20- to 23-days-old. Evidence for a context-US association was obtained by demonstrating that US alone presentations in the training context restored conditioned responding to an extinguished CS. Evidence for a disambiguation function was obtained by demonstrating that a context shift, concurrent with extinction of responding to a phasic CS, preserved responding to the CS when the subjects were subsequently tested in the training context. These findings were discussed in relation to (a) the development of the rat's ability to use relational representations, and (b) Nadel and Zola-Morgan's (1984) hypothesis linking hippocampal maturation to the role of context during development.

Aging↗
PubMed1990

Cholinergic receptor blockade can impair the rat's performance on both the place learning and cued versions of the Morris water task: the role of age and pool wall brightness.

It is known that the administration of a cholinergic receptor blocker impairs the rat's performance on the place learning version of the Morris water task. We confirm this finding but in addition report that animals receiving the cholinergic antagonist, scopolamine hydrobromide, are significantly impaired on the cued platform version of the Morris water task. This latter result, however, is dependent on both the age of the subject and the training context. Weanling animals were more impaired on the cued platform task than were adult animals, and the magnitude of the impairment was much larger when animals were trained in a pool with a gray interior wall than when the pool wall was white. Our findings suggest that the influence of cholinergic systems on performance in the Morris task extend beyond their contribution to place learning and memory processes. We suggest that functional central cholinergic systems also contribute to the processes that enable the animal to inhibit behaviors that are incompatible with the requirements of the task.

Age Factors↗
PubMed1990

Undernutrition during the brain growth period of the rat significantly delays the development of processes mediating Pavlovian trace conditioning.

Pavlovian trace conditioning procedures allow one to assess the ability of animals to associate events that are temporally separated because the conditioned stimulus terminates prior to the occurrence of the unconditioned stimulus. We report that undernutrition during Postnatal Days 2-18 significantly delays the development of trace conditioning to a visual stimulus. Previously undernourished 20-day-old rats conditioned when no temporal interval separated the termination of the CS and US onset (0-s trace interval). However, it was not until the undernourished pups were 30 days old that they conditioned when the trace interval was 10 or 30 s. In contrast, control pups only 20 days old were able to condition when a 10-s trace interval separated the CS and US events, and 25-day-old control pups conditioned when the interval was either 10 or 30 s. These results suggest that undernutrition delays the development of processes that enable the rat to sustain a representation of a visual CS during the trace interval.

Animals↗
PubMed1990

The cholinergic agent physostigmine enhances short-term-memory-based performance in the developing rat.

There are age-related differences in the rat's short-term memory processes. Rats 24-25 days old are 90% correct when the delay interval separating the forced run and choice run of a trial is either 10 or 30 s, but they perform at chance when the delay interval is 60 s. In contrast, the choice performance of 30-day-old rats remains constant across all delay intervals. It is reported that the cholinergic agent physostigmine dramatically improved the short-term-memory-based performance of rats 24-25 days old such that they displayed no loss in choice accuracy even when the delay interval was 60 s. No such enhanced performance was seen in rats treated with neostigmine, a peripherally acting anticholinesterase. The results support the hypothesis that postnatal maturational differences in central cholinergic systems may contribute to age-related differences in short-term memory.

Age Factors↗
PubMed1989

The hippocampal formation is necessary for rats to learn and remember configural discriminations.

A negative patterning discrimination problem was arranged by reinforcing rats for bar pressing when either a light or tone was presented (L+/T+) but not reinforcing the response when the compound stimulus, light and tone, was presented (LT-). To solve this problem, the animal must be able to construct a unique configural representation of the compound that can be distinguished from the representations of the individual elements. We have proposed that the hippocampal formation is essential for the acquisition and retention of associations involving configural representations. Thus, our theory predicts that animals with hippocampal formation damage will not learn the negative patterning problem and that animals who learned this problem before receiving hippocampal formation damage will not retain the solution. These predictions were confirmed by the results of two experiments. The animals with hippocampal formation damage were unable to solve the negative patterning problem. These animals were able to solve a simple discrimination in which responding in the presence of a light was rewarded but responding in the presence of a tone was not rewarded. These results are discussed in relation to several other theories of hippocampal formation function.

Animals↗
PubMed1989

Early-life undernutrition impairs the development of the learning and short-term memory processes mediating performance in a conditional-spatial discrimination task.

Previously undernourished and well-nourished control rats 23, 30, 40, and 90 days old were compared in a win-shift version of a conditional-spatial discrimination task. Control animals at each age were able to reach criterion on this problem. In contrast, the underfed rats were unable to solve this problem until they were at least 40 days old. The short-term memory of the 40- and 90-day-olds was further evaluated by increasing the interval between the forced run and choice run to 30, 60, and 180 s. Control animals could bridge all intervals; however, the undernourished animals' performance fell to chance when the interval was only 60 s. Thus, early-life undernutrition severely impaired the development of the ability of animals to solve spatial-conditional discrimination tasks and permanently impaired their short-term memory capacity. A simple threshold model relating undernutrition, brain development, and behavior is proposed to account for these data.

Animals↗
PubMed1989

Early-life malnutrition impairs the performance of both young and adult rats on visual discrimination learning tasks.

Previously malnourished young (20-40-day-old) and mature (70-77-day-old) rats were compared on position, brightness, and pattern discrimination problems using an aquatic version of the Lashley jump stand. Malnutrition did not affect performance on the position discrimination. In contrast, previously malnourished 24-34-day-olds failed to solve the brightness discrimination, 40-day-olds were impaired on the brightness problem, and 40-77-day olds were impaired on the pattern problem. The impaired performance of the 40-day-olds on the brightness problem was eliminated by prior training on the pattern discriminations, and the impaired performance of the 70-day-olds on the pattern discrimination could be eliminated if they were first trained on the brightness problem. These impairments were attributed to the effects of early-life malnutrition on the maturation of attention processes that enable the rat to suppress responding to irrelevant cues. The relevance of a contextual-organismic perspective for understanding the effects of early-life malnutrition was discussed.

Age Factors↗
PubMed1989

Damage to the hippocampal formation in rats selectively impairs the ability to learn cue relationships.

We assessed the contribution of the hippocampal formation to performance in tasks that require rats to respond to a relationship between discriminative stimuli. The first experiment employed a nonmatching-to-sample procedure in a Y-maze. Three pairs of boxes were used which differed in brightness of the walls and in the odors that they contained. The rats were trained prior to receiving kainic acid and colchicine-induced damage to the hippocampal formation or electrolytic damage to the amygdala. After surgery all rats performed the nonmatching-to-sample task accurately if both brightness and odor cues were present in the sample and choice boxes or if the boxes contained either visual cues alone or odor cues alone. If the available cue modality was different in sample and choice boxes, then the amygdala-damaged, but not the hippocampal-damaged, rats performed accurately. In the second experiment control rats or rats with hippocampal formation damage were trained postoperatively in a conditional black/white discrimination task in a Y-maze. Only the control group successfully learned to select the white arm if the start box was illuminated and the black arm if the start box was dark. Subsequently, both groups learned a simple black/white discrimination. The same rats were tested in the hidden platform version of the Morris water task and only the control group learned to swim accurately to the goal. Both groups learned to swim accurately to a visible black platform. The results are consistent with the notion that the hippocampal formation is essential to learning that involves control exerted by a configural relationship among cues, independently of the spatial or conditional requirements of tasks.

Amygdala↗
PubMed1988

Changes in the categorization of appetitive and aversive events during postnatal development of the rat.

Environmental stimuli are not clearly categorized into appetitive and aversive classes during the first postnatal week. Three- and 6-day-old rats are highly activated by nominally appetitive (milk infusions) and aversive (foot shock) stimuli. Both evoked the same generalized behavioral responses (rolling, curling). By 12 days of age, these stimuli were responded to differently; mouthing and probing occurred in response to milk while flinching and escape responses were observed to shock. The affective properties of mild shock were found to be hedonically opposite for 6- and 12-day-old pups. Six-day-olds showed an acquired preference for an odor paired with shock which increased with intensity (.1-.5 mA) similar to that observed with milk infusions. An acquired odor aversion was displayed by 12 days old using these shock parameters. These results suggest that young rat pups may not differentiate many appetitive and aversive events behaviorally or affectively until the second postnatal week.

Affect↗
PubMed1987

Ontogenetic change in the analysis of sound frequency in the infant rat.

Previous research has shown that there is an ontogenetic shift in the spatial code of sound frequency in the cochlea and central auditory nuclei. During ontogenesis, a given area of the basilar membrane or central auditory nuclei is maximally stimulated by sounds of progressively higher frequencies. Here, a similar ontogenetic shift in the rat's "perception" of sound frequency is reported. Animals were trained with a tone (CS) paired with footshock (US) and generalization of their conditioned response (CR) to different frequencies was assessed either 0.5 or 72 hr later. When 15-day-old animals were trained with an 8-kHz tone and tested 0.5 hr later, greater suppression of activity (CR) was evoked by the 8-kHz tone than by either a 12-kHz or a 6-kHz tone. When tested 72 hr after training, however, greater suppression of activity was evoked by a 12-kHz tone than by the 8-kHz training stimulus or by a 24-kHz tone. This shift in the peak of the generalization gradient could not be accounted for by changes in unconditioned responses to the test stimuli. Additionally, the observed shift in the generalization gradient was age-dependent. It was not observed when pups were trained at 18 days old and tested 72 hr later. The implications of these data for studies of the ontogenesis of learning and memory are discussed.

Age Factors↗
PubMed1987

Ontogenesis of trace conditioning in young rats: dissociation of associative and memory processes.

Hooded rats from 15 to 30 days of age were trained with a Pavlovian trace fear conditioning procedure in order to study the development of their capacity to learn associations between events separated in time. For both the auditory and visual systems, the associative processes necessary to learn about temporally contiguous events emerged earlier during ontogenesis than the processes necessary to integrate events separated in time. Furthermore, the ability of the rats to integrate events separated by increasingly long intervals continued to improve as they got older. We suggest that the emergence of the capacity to integrate temporally separate events reflects the maturation of memory processes that retain representations of stimulus events over time, and that these processes continue to mature for a considerable period after the basic associative processes have become functional.

Acoustic Stimulation↗
PubMed1987

Early-life malnutrition selectively retards the development of distal- but not proximal-cue navigation.

The effects of early-life malnutrition on the distal-cue and proximal-cue versions of the Morris (1981) water maze were studied with different-aged rats. Consistent with the existing literature, malnutrition only mildly influenced the distal-cue navigation of relatively old pups (30 day olds). Pups 20-27 days old, however, displayed no evidence of distal-cue navigation if they had been malnourished previously. Malnutrition had no effect on proximal-cue based navigation by pups at any age. The effect of malnutrition on distal-cue performance could not be attributed to any general debilitating effects, sensory, motor, or motivational deficits. Instead, it appears to selectively influence the development of the neural system (perhaps the hippocampus and related structures) more directly involved in learning to utilize distal cues.

Aging↗
PubMed1987

Development of interocular equivalence in rats trained on a distal-cue navigation task.

What is learned about the visual world through one eye can be retrieved and used to guide behavior by the other eye. To study the development of this phenomenon, called interocular equivalence, we trained rats on a spatial learning task. Rats only 22 days old were able to learn this task with one eye, but they demonstrated no interocular equivalence. This capacity began to emerge when pups were 25 days old but was not robust until pups were 28 days old. That interocular equivalence emerges gradually during development suggests that the young rat, in some ways, may function as a split-brain animal.

Animals↗