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Competition between memory systems: acetylcholine release in the hippocampus correlates negatively with good performance on an amygdala-dependent task.

Lesions of the amygdala impair acquisition of a food conditioned place preference (CPP) task. In contrast, lesions of the fornix facilitate acquisition on this task, showing that an intact hippocampal system can interfere with learning an amygdala-dependent task. Our recent findings indicate that acetylcholine (ACh) release in the hippocampus increases while rats perform a hippocampus-dependent spontaneous alternation task. To the extent that ACh output in the hippocampus reflects activation of that brain area in learning and memory, the results obtained with fornix lesions suggest that ACh release in the hippocampus might be negatively correlated with learning on a CPP task. Using in vivo microdialysis, release of ACh was measured in the hippocampus while rats learned and were tested on an amygdala-dependent CPP task and a hippocampus-dependent spontaneous alternation task. Release of ACh in the hippocampus increased when rats were tested on either task. The magnitude of the increase in release of hippocampal ACh was negatively correlated with good performance on the amygdala-dependent CPP task. These findings suggest that ACh release may reflect activation and participation of the hippocampus in learning and memory, but in a manner that can be detrimental to performance on a task dependent on another brain area.

Acetylcholine↗

Visual and spatial trials paired in a new behavioral procedure: effects of benactyzine.

A paired discrimination (PD) task in which visual and spatial discrimination trials were combined is offered as a method for the evaluation of drug effects on various behavioral parameters. Acquisition of the PD task is characterized by six different parameters simultaneously recorded each session. Analysis of memory requirements suggest that intact reference memory is involved in the performance of both types of trials while working memory is involved only in the performance of the spatial trial. Benactyzine (1-4 mg/kg), an anticholinergic drug, was tested for its effects on visual and spatial tasks presented either separately or in the PD combination. Benactyzine-induced mydriasis was also determined for its possible role in photophobic-induced errors. Benactyzine was found to differentially increase the number of errors performed during the spatial but not during the visual trials. The data are in accord with earlier finding of specific cholinergic involvement in working memory processes. Thus, low doses of benactyzine, and the PD task, can prove useful in the cognitive analysis of cholinergic hypofunction and its reversal by memory-enhancing drugs.

Animals↗

The effect of intrahippocampal injections of ritanserin (5HT2A/2C antagonist) and granisetron (5HT3 antagonist) on learning as assessed in the spatial version of the water maze.

5HT(2A/2C) and 5HT(3) receptors have an important role in cognitive behavior specially in spatial learning and memory but the literature concerning the role of these receptors in hippocampus in cognition remains controversial. In the present study a 5HT(2A/2C) antagonist ritanserin (0, 2, 4, 8 microg/0.5 microl) and a 5HT(3) antagonist granisetron (0.0, 0.05, 0.25, 0.5 microg/0.5 microl) were injected bilaterally into the CA1 region of rat hippocampus, 20 min before each training session in Morris Water Maze (MWM) task. Compare with control group, ritanserin (4 microg/0.5 microl) significantly reduced the escape latency and traveled distance of swimming to platform, but granisetron (0.25 microg/0.5 microl) significantly increased those parameters. Both drugs had no effect on escape latency and traveled distance of a non-spatial visual discrimination task. These results suggest a differential role of 5HT(2A/2C) and 5HT(3) receptors during spatial learning that ritanserin improves rat performance in spatial discrimination task whereas granisetron impairs it.

Analysis of Variance↗

Proposed neural circuitry for spatial memory in the primate brain.

The possible cerebral cortical circuitry for spatial memory in primates is discussed in light of a conceptual model and clinical as well as animal behavioral data. It is proposed that spatial memory formation begins with the arrival of sensory information in primary sensory areas and involves progressive elaboration through parasensory and higher-order association cortices. The connectivity between the association areas and the paralimbic and limbic regions is viewed as critical to the consolidation process. Finally, the execution of spatial behavior is presumed to involve the post-Rolandic and paralimbic projections to the frontal lobe. It is hoped that this conceptualization may provide a framework for further studies dealing with spatial memory.

Animals↗

A theory of behavioral generality and specificity during mild stress.

A definitional system is given for the concepts of generality and specificity for behavioral variables, relating to signs and sizes of their intercorrelations. In particular, a mapping sentence is provided for defining the universe of observations for emotional behavior of mice under mild stress. Its three content facets are: (a) the temporal features of frequency, latency, and duration, (b) type of control, autonomic or voluntary, and (c) the experimental situation, the apparatus. Data from three studies published previously by other authors are analyzed by Smallest Space Analysis (SSA-I). In each case, the smallest space is found to be partitioned into contiguous regions corresponding to the elements of the three facets.

Animals↗

Effects of repetitive motor training on movement representations in adult squirrel monkeys: role of use versus learning.

Current evidence indicates that repetitive motor behavior during motor learning paradigms can produce changes in representational organization in motor cortex. In a previous study, we trained adult squirrel monkeys on a repetitive motor task that required the retrieval of food pellets from a small-diameter well. It was found that training produced consistent task-related changes in movement representations in primary motor cortex (M1) in conjunction with the acquisition of a new motor skill. In the present study, we trained adult squirrel monkeys on a similar motor task that required pellet retrievals from a much larger diameter well. This large-well retrieval task was designed to produce repetitive use of a limited set of distal forelimb movements in the absence of motor skill acquisition. Motor activity levels, estimated by the total number of finger flexions performed during training, were matched between the two training groups. This experiment was intended to evaluate whether simple, repetitive motor activity alone is sufficient to produce representational plasticity in cortical motor maps. Detailed analysis of the motor behavior of the monkeys indicates that their retrieval behavior was highly successful and stereotypical throughout the training period, suggesting that no new motor skills were learned during the performance of the large-well retrieval task. Comparisons between pretraining and posttraining maps of M1 movement representations revealed no task-related changes in the cortical area devoted to individual distal forelimb movement representations. We conclude that repetitive motor activity alone does not produce functional reorganization of cortical maps. Instead, we propose that motor skill acquisition, or motor learning, is a prerequisite factor in driving representational plasticity in M1.

Animals↗

Memory-dependent novelty-related location preferences: sex-related attenuation of forgetting by D-glucose and tacrine.

Following confinement to one chamber of a two-chamber exploration box (acquisition trial), male and female rats were intraperitoneally injected with saline, glucose (50, 100 mg/kg) or tacrine (1, 3 mg/kg). Twenty-four hours later they were given free access to this chamber and an identical novel one (retention trial). Tendencies to occupy the novel chamber (novelty-related location preferences) were increased by both doses of glucose for females and by the higher dose for males. While neither dose of tacrine affected this response for females, increased preferences occurred for males following the higher dose. However, when the higher doses of both agents were administered 2 h after acquisition, there were no significant effects for either sex. In view of the rats' lack of significant preferences for the novel chamber when treated with saline both immediately and 2 h after acquisition, the results were interpreted as sex-dependent attenuation of forgetting by post-acquisition treatment with both agents.

Animals↗

Room novelty, sex, scopolamine and their interactions as determinants of general activity and rearing, and light-dark preferences in rats.

Male and female rats were assessed for effects of scopolamine on general activity, rearing and light-dark preferences when tested in either a familiar or a novel room. Males but not females reared more often when tested in the familiar rather than novel room, and the response was increased by scopolamine for all rats combined. Whereas scopolamine increased general activity for females (but not males) in the familiar room, it decreased the response for males (but not females) in the novel room. Females crossed more often between the dark and light sides of a light-dark box and, when treated with saline but not drug, spent more time in the light side than males. Scopolamine reduced the amount of time spent in the light side for females only. While the results were discussed mainly in terms of sex differences in fearfulness, their principal value was in demonstrating the effectiveness of room novelty and sex in determining levels of the behaviors recorded, and drug responsiveness.

Animals↗

Generalization in place learning across geometrically different environments is impaired by hippocampal lesions in rats.

A recent study (Tommasi & Thinus-Blanc, 2004) found that when rats trained to search for food hidden in the center of a square-shaped enclosure were tested in the absence of food, they searched precisely in the center of the enclosure. Transfer tests carried out in enclosures differing in shape or size (rectangular-, large square-, and equilateral triangle-shaped) showed that rats searched in the geometric center of the novel environments. In the present work, half of those rats were lesioned bilaterally to the hippocampus and were then re-trained and re-tested in the same task, to be compared to sham rats that received the same retraining/re-test protocol. Results show that lesioned rats, although unimpaired in relearning to localize the center of the square-shaped enclosure, performed considerably worse than sham rats in the transfer tests in the enclosures differing in shape, suggesting a relevant role of the hippocampus in geometry-driven place generalization.

Animals↗

The testosterone metabolite and neurosteroid 3alpha-androstanediol may mediate the effects of testosterone on conditioned place preference.

The abuse of androgens may be related to their ability to produce positive, hedonic interoceptive effects. Conditioned Place Preference (CPP) has been used in many experiments to examine hedonic effects of drugs. This review is focused on studies from our laboratory that utilized CPP to examine potential positive hedonic effects of testosterone (T), and its androgenic metabolite dihydrotestosterone (DHT), and its metabolite 3alpha-androstanediol (3alpha-diol). We hypothesized that administration of a high concentration of 3alpha-diol would produce a CPP, pharmacological concentrations of plasma androgens, and alter androgen receptors (AR) and the function of GABA(A)/benzodiazepine receptor complexes (GBR). In our studies, we observed that systemic 3alpha-diol (1.0 mg/kg) prior to exposure to the non-preferred side of a CPP chamber significantly increased preference for the non-preferred side of the chamber compared to baseline preference and homecage controls. Furthermore, administration of T, DHT, or 3alpha-diol increased levels of these androgens, decreased ARs (decreased seminal vesicle weight and intrahypothalamic AR) and GBR function (decreased GABA-stimulated chloride influx in cortical synaptoneurosomes, and muscimol binding in the hippocampus compared to control groups). With systemic administration of 3alpha-diol that enhanced CPP, concentrations of 3alpha-diol were increased in the nucleus accumbens (NA). Central implants of T, DHT, or 3alpha-diol to the NA also produced a CPP compared to baseline preference and vehicle controls. These data indicate that systemic 3alpha-diol is more effective at enhancing CPP and increasing circulating 3alpha-diol levels than is T or DHT and that central administration of 3alpha-diol to the NA can condition a place preference. These findings indicate that 3alpha-diol produces positive hedonic effects and suggest that T's variable effects on CPP may be due in part to T's metabolism to 3alpha-diol.

Androstane-3,17-diol↗

Positive geotaxis in infant rats (Rattus norvegicus): a natural behavior and a historical correction.

Infant rats (Rattus norvegicus) placed on a shallow incline (2 degrees, 4 degrees, or 8 degrees) oriented and moved downhill within 1 min; that is, they displayed positive geotaxis. Their downhill translocation increased with angle of inclination. A variety of possible behavioral elements (e.g., initial orientation, rotational movements, ambulatory velocities) were eliminated as explanations of the geotaxis. Wall contact was recognized as a determinative event: Pups on the inclines showed no orientation with respect to the geogravitational stimulus before contacting a wall. The event of wall contact, however, evoked reliable downhill orientation and more linear movements. Positive geotaxis was created by pups' orientation against walls and an associated increase in movement velocity. This is a distinct perspective on a behavioral response that replaces a traditionally misinterpreted phenomenon. The authors discuss the ecological validity and historical context of these findings.

Animals↗

Do dogs (Canis familiaris) understand invisible displacement?

Domestic dogs (Canis familiaris) perform above chance on invisible displacement tasks despite showing few other signs of possessing the necessary representational abilities. Four experiments investigated how dogs find an object that has been hidden in 1 of 3 opaque boxes. Dogs passed the task under a variety of control conditions, but only if the device used to displace the object ended up adjacent to the target box after the displacement. These results suggest that the search behavior of dogs was guided by simple associative rules rather than mental representation of the object's past trajectory. In contrast, Experiment 5 found that on the same task, 18- and 24-month-old children showed no disparity between trials in which the displacement device was adjacent or nonadjacent to the target box.

Animals↗