Place Learning In Rats Research Articles

Effects of dorsal hippocampus catecholamine depletion on paired-associates learning and place learning in rats

Growing evidence suggests that the catecholamine (CA) neurotransmitters dopamine and noradrenaline support hippocampus-mediated learning and memory. However, little is known to date about which forms of hippocampus-mediated spatial learning are modulated by CA signaling in the hippocampus. Therefore, in the current study we examined the effects of 6‐hydroxydopamine-induced CA depletion in the dorsal hippocampus on two prominent forms of hippocampus-based spatial learning, that is learning of object-location associations (paired-associates learning) as well as learning and choosing actions based on a representation of the context (place learning). Results show that rats with CA depletion of the dorsal hippocampus were able to learn object-location associations in an automated touch screen paired-associates learning (PAL) task. One possibility to explain this negative result is that object-location learning as tested in the touchscreen PAL task seems to require relatively little hippocampal processing. Results further show that in rats with CA depletion of the dorsal hippocampus the use of a response strategy was facilitated in a T-maze spatial learning task. We suspect that impaired hippocampus CA signaling may attenuate hippocampus-based place learning and favor dorsolateral striatum-based response learning.

Profound retrograde but absence of anterograde amnesia for cued place learning in rats with hippocampal lesions

Previous studies in our lab have shown that slight modifications in the spatial reference memory procedure can overcome the deficit in spatial learning typically observed in rats with hippocampal damage. However, it is unknown if memory acquired under such training circumstances is spared after hippocampal lesions. With this aim a four-arm plus-shaped maze and a spatial reference memory paradigm were used, in which the goal arm was doubly marked: by an intramaze cue (a piece of sandpaper positioned on the floor of the arm) and by the extramaze constellation of stimuli around the maze. Experiment 1 replicated previous findings showing that hippocampally damaged rats can learn a place response just as well as the controls when the intramaze cue is present during the training, but they are unable to do so in the absence of the intramaze signal. When the learning procedure was doubly signaled, a transfer test performed 24h after the end of acquisition demonstrated that lesioned rats showed perfect memory for the goal arm when the intramaze cue was removed. Experiment 2 investigated the effect of hippocampal damage 1 day after the learning. Results showed that regardless of the training procedure employed (with or without the intramaze cue), hippocampal lesions produced a profound retrograde amnesia. Thus, although the absence of anterograde amnesia suggests that structures other that the hippocampus can take charge of the acquisition, the presence of retrograde amnesia indicates the critical role of the normal hippocampus in the long-term formation of allocentric information.

The Effects of Hippocampal Lesions on Response, Direction, and Place Learning in Rats.

Rats with hippocampal or sham lesions were trained to find food on a T maze located at 2 positions. Response rats were required to make a right or left turn. Direction rats were required to go in a consistent direction (east or west). Place rats were required to go to a consistent location, relative to room cues. One place group had distinguishable start points at the 2 maze positions, whereas another place group had start points facing the same side of the room. Controls took longer to solve a place problem than the response and direction problems when the start points were not distinguishable. Rats with hippocampal lesions were not different than controls on the response problem but were impaired on the direction and place problems.

Individual variation in the spatial reference and working memory assessed under allothetic and idiothetic orientation cues in rat

The present study was designed to examine which kind of memory: reference or working, better correlates with individual variation in rats' spatial learning abilities. To answer this question two groups of rats were trained to an arbitrary criterion in a partially baited 12-arm radial maze under two different experimental conditions: with or without allothetic cues. After 10 days break, rats were examined under the same conditions for memory retention. Within- and between-group variation in the length of training to criterion, and in the frequency of reference and working memory errors were analysed. The present experiment confirmed the facilitating effect of the presence of distal visual cues on place learning in rats. Task-dependent (between-group) differences in the rate of learning were attributed to differences in the frequency of reference memory errors. Conversely, within-group variation in the rate of task acquisition reflected individual variation in the frequency of working memory errors. These results were looked upon from an evolutionary perspective. Low correlation between reference and working memory errors confirms that these two types of memory have different mechanisms. The fact that differences in the rate of learning were not paralleled by the differences in the memory retention supports the notion that memory acquisition and memory retention are two independent processes.

Effects of a novel arginine-vasopressin derivative, NC-1900, on the spatial memory impairment of rats with transient forebrain ischemia

NC-1900, an arginine-vasopressin derivative, has been reported to enhance memory for avoidance behavior. Specifically, NC-1900 ameliorated cycloheximide-induced learning impairments in a passive avoidance test in rats. In the present study, we investigated that effects of NC-1900 on place learning in rats with selective lesions in the CA1 subfield of the hippocampal formation produced by transient forebrain ischemia. NC-1900 was administered daily (1 μg/kg, p.o.) 1 h before the place learning task. A rat was required to alternate between 2 small circular areas located diametrically opposite each other on the circumference of an open field in order to obtain intracranial electrical stimulation reward (the spatial navigation task). Rats with hippocampal lesions showed severe place learning impairments both in task performance (indicated by number of rewards obtained per a session) and in navigation performance (forming efficient trails) over the 30-day test period. Treatment with NC-1900 ameliorated deficits in the place learning exhibited by rats with the same hippocampal lesions, such that their performance reached normal levels. There were no significant differences in the ischemic hippocampal lesions, spontaneous locomotor activity, and stimulation current intensity between the treated and untreated rats. The results demonstrated that NC-1900 reduced place learning impairments produced by hippocampal lesions.

Local inhibition of hippocampal nitric oxide synthase does not impair place learning in the Morris water escape task in rats.

Recent studies have provided evidence that nitric oxide (NO) has a role in certain forms of memory formation. Spatial learning is one of the cognitive abilities that has been found to be impaired after systemic administration of an NO-synthase inhibitor. As the hippocampus has a pivotal role in spatial orientation, the present study examined the role of hippocampal NO in spatial learning and reversal learning in a Morris task in adult rats. It was found that N omega-nitro-L-arginine infusions into the dorsal hippocampus affected the manner in which the rats were searching the submerged platform during training, but did not affect the efficiency to find the spatial location of the escape platform. Hippocampal NO-synthase inhibition did not affect the learning of a new platform position in the same water tank (i.e. reversal learning). Moreover, no treatment effects were observed in the probe trials (i.e. after acquisition and after reversal learning), indicating that the rats treated with N omega-nitro-L-arginine had learned the spatial location of the platform. These findings were obtained under conditions where the NO synthesis in the dorsal hippocampus was completely inhibited. On the basis of the present data it was concluded that hippocampal NO is not critically involved in place learning in rats.

Molecular, Cellular, and Neuroanatomical Substrates of Place Learning

Learning and remembering the location of food resources, predators, escape routes, and immediate kin is perhaps the most essential form of higher cognitive processing in mammals. Two of the most frequently studied forms of place learning are spatial learning and contextual conditioning. Spatial learning refers to an animal's capacity to learn the location of a reward, such as the escape platform in a water maze, while contextual conditioning taps into an animal's ability to associate specific places with aversive stimuli, such as an electric shock. Recently, transgenic and gene targeting techniques have been introduced to the study of place learning. In contrast with the abundant literature on the neuroanatomical substrates of place learning in rats, very little has been done in mice. Thus, in the first part of this article, we will review our studies on the involvement of the hippocampus in both spatial learning and contextual conditioning. Having demonstrated the importance of the hippocampus to place learning, we will then focus attention on the molecular and cellular substrates of place learning. We will show that just as in rats, mouse hippocampal pyramidal cells can show place specific firing. Then, we will review our evidence that hippocampal-dependent place learning involves a number of interacting physiological mechanisms with distinct functions. We will show that in addition to long-term potentiation, the hippocampus uses a number of other mechanisms, such as short-term-plasticity and changes in spiking, to process, store, and recall information. Much of the focus of this article is on genetic studies of learning and memory (L&M). However, there is no single experiment that can unambiguously connect any cellular or molecular mechanism with L&M. Instead, several different types of studies are required to determine whether any one mechanism is involved in L&M, including (i) the development of biologically based learning models that explain the involvement of a given mechanism in L&M, (ii) lesion experiments (genetics and pharmacology), (iii) direct observations during learning, and (iv) experiments where learning is triggered by turning on the candidate mechanism. We will show how genetic techniques will be key to unraveling the molecular and cellular basis of place learning.

Effects of dose-rate on Morris maze cued and place learning in rats treated with d-methamphetamine (MA) on postnatal (Pl days 11–20.

Effects of dose-rate on Morris maze cued and place learning in rats treated with d-methamphetamine (MA) on postnatal (Pl days 11–20.

Influence of local environmental olfactory cues on place learning in rats

The aim of the present study was to assess the influence of local environmental olfactory cues on place learning in rats. We developed a new experimental design allowing the comparison of the use of local olfactory and visual cues in spatial and discrimination learning. We compared the effect of both types of cues on the discrimination of a single food source in an open-field arena. The goal was either in a fixed or in a variable location, and could be indicated by local olfactory and/or visual cues. The local cues enhanced the discrimination of the goal dish, whether it was in a fixed or in a variable location. However, we did not observe any overshadowing of the spatial information by the local olfactory or visual cue. Rats relied primarily on distant visuospatial information to locate the goal, neglecting local information when it was in conflict with the spatial information.

Hippocampal and nonhippocampal contributions to place learning in rats.

Hippocampal and nonhippocampal contributions to place learning in rats.

Hippocampal and nonhippocampal contributions to place learning in rats.

Brain structures thought to be critical for learning and memory were lesioned, and the effects on rats' ability to locate food on a radial maze in situations that provided different types of information was used to suggest general principles of information processing by hypothesized neural systems that include each of the lesioned structures. When animals were confined to food-containing and empty arms on different training trials, the learned discrimination between the arms was amygdala based. More training trials were required for ambiguous (adjacent arms) than for unambiguous (widely separated arms) discriminations. When rats moved around and entered both food and no-food arms on the same trial, the unambiguous discrimination was learned by both dorsal striatum- and hippocampus-based systems; however, the ambiguous discrimination was learned only by the hippocampus system.