VISUAL AND TACTUAL EXPLORATION IN RATS REARED IN DIFFERENT DEGREES OF VISUAL AND TACTUAL STIMULATION

NIELSEN, T. C. Visual and tactual exploration in rats reared in different degrees of visual and tactual stimulation. Scand. J. Psychol. , 1971, 12, 53–61. – Four groups of eight rats each were reared in the four possible combinations of high and low visual and high and low tactual stimulation. Early tactual enrichment increased later tactual exploration regardless of visual stimulation. Visual enrichment did not influence exploration in the tactual enrichment groups, but in the tactual deprivation groups it seemed to produce more visual and less tactual exploration. The most deprived group exhibited a high locomotor activity which could not be explained in terms of an increased tendency to explore.     

The spontaneously hypertensive rat as an animal model of attention-deficit hyperactivity disorder: effects of methylphenidate on exploratory behavior

Spontaneously hypertensive rats (SHR) show a pervasive hyperactivity in several paradigms. Thus, these rats may be used as an animal model of childhood hyperactivity also called Attention-Deficit Hyperactivity Disorder. This disorder is frequently treated with psychomotor stimulant drugs, but little is known about the effects of such drugs on behavior. The present study investigated the behavioral effects of 1-24 mg/kg methylphenidate (Ritalin) on the exploratory behavior of male SHR and Wistar-Kyoto control rats (WKY) in a two-compartment free-exploration open field. Except following very high doses. SHR spent most of the session time in the field while WKY stayed in the home cage. Low and medium doses were followed by increased activity in the field for SHR and increased activity in the cage for WKY. The response-stimulatory effects of low to medium doses of methylphenidate are less in SHR than in WKY. Starting at medium doses, activity decreased and stereotyped behavior increased progressively by increasing dose. Locomotor activity in the field decreased following lower doses than locomotor activity in the cage, and vertical activity (rearing) was reduced by lower doses than horizontal activity (crossing). The following conclusions were drawn. (i) There is no "paradoxical" inhibition of SHR hyperactivity following methylphenidate. On the contrary, SHR activity is in fact stimulated, albeit to a lesser degree than that of WKY. (ii) The stimulatory effects of low to medium doses are, in general, most pronounced for the kind of exploratory behavior most frequently used by the rat during baseline conditions. (iii) Rearing might be more susceptible to adverse effects of methylphenidate than ambulation.     

The behavioral effects of depletions of brain serotonin induced by 5,7-dihydroxytryptamine vary with time after administration

Ether-anesthetized Sprague-Dawley rats were depleted of brain serotonin (5HT) by intraventricular injections of 50 micrograms 5,7-dihydroxtryptamine (57DHT). Oral pretreatment with 25 mg/kg desmethylimipramine was used to protect brain noradrenergic neurons from 57DHT. Liquid chromatographic assays revealed that this treatment did not significantly alter catecholamine levels but depleted hippocampal 5HT by 92% and striatal 5HT by 45%. Three or eleven days after lesioning, locomotor and exploratory behavior was characterized in separate groups of animals with a behavioral pattern monitor (BPM). On Days 4 and 12, the animals were retested following saline or 1.0 mg/kg amphetamine. Three days after depletion, lesioned rats exhibited a decrease rate of habituation of locomotor activity relative to controls. When challenged with amphetamine (1.0 mg/kg), 5HT-depleted rats exhibited increased corner and decreased center activity, as well as stereotyped patterns of locomotion. Eleven days following lesion, 5HT-depleted rats exhibited habituation rates greater than controls; amphetamine challenge yielded patterns of activity similar to those of control animals. These results show that central serotonergic pathways play an important role in modulating both spontaneous and amphetamine-elicited activity in rats, and that compensatory mechanisms operate over time to alter the behavioral effects of 57DHT-induced depletions of brain 5HT.     

The behavioral effects of enriched housing are not altered by serotonin depletion but enrichment alters hippocampal neurochemistry

To assess a possible role for serotonin in the mediation of the behavioral changes induced by enriched housing conditions (EC), adult female Long-Evans rats sustaining a serotonin depletion (150 microg of 5,7-dihydroxytryptamine, icv) and sham-operated rats were housed postoperatively for 30 days in enriched (12 rats/large cage containing various objects) or standard housing conditions (2 rats/standard laboratory cage). Thereafter, anxiety responses (elevated plus-maze), locomotor activity (in the home-cage), sensori-motor capabilities (beam-walking task), and spatial memory (eight-arm radial maze) were assessed. Monoamine levels were subsequently measured in the frontoparietal cortex and the hippocampus. Overall, EC reduced anxiety-related responses, enhanced sensori-motor performance and improved the memory span in the initial stage of the spatial memory task. Despite a substantial reduction of serotonergic markers in the hippocampus (82%) and the cortex (74%), these positive effects of EC were not altered by the lesion. EC reduced the serotonin levels in the ventral hippocampus (particularly in unlesioned rats: -23%), increased serotonin turnover in the entire hippocampus (particularly in lesioned rats: +36%) and augmented the norepinephrine levels in the dorsal hippocampus (+68% in unlesioned and +49% in lesioned rats); no such alterations were found in the frontoparietal cortex. Our data suggest that an intact serotonergic system is not a prerequisite for the induction of positive behavioral effects by EC. The neurochemical changes found in the hippocampus of EC rats, however, show that the monoaminergic innervation of the hippocampus is a target of EC.     

Suppression of the rat’s locomotor activity at low intensities of electric footshock

Over 50% of all just noticeably different footshock intensities lie below ,3 mA for rats. Unfortunately, the suppression of the rat’s locomotor activity by low-intensity footshock precludes the use of these shock intensities in active escape or avoidance training. This activity-suppression effect was demonstrated in an alley and in a tilt cage. One explanation of this effect is that rats remain relatively immobile in order to avoid painful peaks in current density that occur when the animals’ paws make or break contact with “hot” grids. If this explanation is correct, the activity-suppression effect should be more pronounced with higher impedance shock sources. Some evidence is reported that is consistent with this explanation.     

Isolation rearing effects on probabilistic learning and cognitive flexibility in rats

Isolation rearing is a neurodevelopmental manipulation that produces neurochemical, structural, and behavioral alterations in rodents that in many ways are consistent with schizophrenia. Symptoms induced by isolation rearing that mirror clinically relevant aspects of schizophrenia, such as cognitive deficits, open up the possibility of testing putative therapeutics in isolation-reared animals prior to clinical development. We investigated what effect isolation rearing would have on cognitive flexibility, a cognitive function characteristically disrupted in schizophrenia. For this purpose, we assessed cognitive flexibility using between- and within-session probabilistic reversal-learning tasks based on clinical tests. Isolation-reared rats required more sessions, though not more task trials, to acquire criterion performance in the reversal phase of the task, and were slower to adjust their task strategy after reward contingencies were switched. Isolation-reared rats also completed fewer trials and exhibited lower levels of overall activity in the probabilistic reversal-learning task than did the socially reared rats. This finding contrasted with the elevated levels of unconditioned investigatory activity and reduced levels of locomotor habituation that isolation-reared rats displayed in the behavioral pattern monitor. Finally, isolation-reared rats also exhibited sensorimotor gating deficits, reflected by decreased prepulse inhibition of the startle response, consistent with previous studies. We concluded that isolation rearing constitutes a valuable, noninvasive manipulation for modeling schizophrenia-like cognitive deficits and assessing putative therapeutics.     

The effects of naloxone and cage size on social play and activity in isolated young rats

The effects of large and small housing environments as well as naloxone on social play (as defined by pinning behavior) in isolated postweanling male rats were investigated. Animals housed in small cages played significantly more than those housed in larger cages. This effect was not observed when cage size was reversed. Administration of 0.5, 1.0, and 5.0 mg/kg of naloxone resulted in significant decreases in play behavior as compared to saline controls, both before housing environments were switched, and after. Animals in both isolation conditions were also compared to animals that were socially housed. Isolation was found to increase social play as well as the time spent in active social interaction, but had no effect on locomotor activity. While housing in a small cage increases play behavior, it had no effect on the amount of time spent in active social interaction or on activity. While administration of 0.5, 1.0, and 5.0 mg/kg naloxone to habituated animals differentially housed did not result in an overall decrease in activity, when compared with saline controls, only those animals housed in small cages and injected with the high dose of naloxone differed significantly from controls. In animals having no prior play experience, the activity of animals housed in the large and small cages differed significantly from each other only in the saline and 5.0 mg/kg naloxone conditions. Since naloxone's effect on play behavior was strong, but its effect on activity was not profound, our data suggest that naloxone primarily affects the affective component of play rather than altering activity levels.     

Conditioned increases in locomotor activity produced with morphine as an unconditioned stimulus, and the relation of conditioning to acute morphine effect and tolerance

Rats administered 5 mg/kg morphine SO4, through subcutaneously implanted catheters, during each of several daily sessions in an open field showed a progressive increase in locomotor activity measured in the open field prior to each morphine administration. Since the increases in activity were not observed in rats given morphine in a different environment (home cage) and saline in the open field, it is concluded that the increases were due to conditioning. In addition, the increases in activity were retained over a 7-day rest period; they were also produced when a second opiate (5 microgram/kg etorphine HCl) was substituted for morphine, were not seen when 2 mg/kg naloxone HCl (ip) was administered during treatment, and were present in rats showing tolerance to opiate-produced hypoactivity. Morphine's direct effect on activity is believed to have a biphasic dose-response curve; therefore, the relation of dose to conditioning was also studied. Increases in activity were the only conditioned behaviors observed; they were present only at the higher doses (16, 4, and 1 vs. .25, .065, and 0 mg/kg), and they occurred whether or not the dose was associated with unconditioned hypoactivity. The discussion deals with the relation of conditioning and morphine tolerance, the question of whether the unconditioned stimulus of morphine conditioning is a compensatory or a direct effect of morphine, and the similarity of conditioned increases in activity produced by morphine and by other stimuli that are reinforcing.     

Effects of Limitations on the Use of Some Visual and Kinaesthetic Information in Spatial Mapping during Exploration in the Rat

The purpose of this experiment was to study the effects of limiting visual and/or locomotor access to a part of the environment in the building up of a spatial representation of the whole space. During five sessions, rats were allowed to explore separately and successively the two halves (subspaces) of a circular open field containing four objects. During exploration of each half, continuous or discontinuous locomotor and/or visual access to the other half was provided by using opaque or transparent partitions, with or without doors. Once habituation was complete, the partition was removed for some subjects but remained for others. The locomotor and exploratory reactions to this removal were recorded. Whatever their locomotor experience (continuous or discontinuous), rats that had a discontinuous visual experience between the subspaces displayed a renewal of exploratory activity, whereas the rats that had received a continuous visual experience did not re-explore the objects. This result suggests that continuous visual access to the whole space is necessary for the construction of an overall representation. Furthermore, continuous locomotor activity does not seem to compensate for the discontinuity of visual information.     

Behavioral studies in spontaneously hypertensive rats

In the present study we examined some behavioral patterns in spontaneously hypertensive (SHR) male rats as compared with Wistar (W) rats. The following methods were employed: open field test, two-way active avoidance, passive avoidance, shock-induced fighting, shock-induced suppression of drinking (conflict test), and dominant-subordinate behavior in rats competing for water. Spontaneously hypertensive rats showed higher level of locomotor activity, lower emotionality, lower anxiety level, increased acquisition of avoidance tasks, and enhanced dominance behavior. In addition, hypertensive rats were less aggressive in shock-induced fighting test. It is concluded, that spontaneously hypertensive rats seem to be hyperactive in terms of locomotor activity while their emotionality appears to be paradoxically reduced.     

Effects of 6-hydroxydopamine lesions of the nucleus accumbens septi and olfactory tubercle on feeding, locomotor activity, and amphetamine anorexia in the rat.

Bilateral 6-hydroxydopamine lesions of the nucleus accumbens septi (NAS) and olfactory tubercle (OT) caused enhanced intake of wet mash in 23-hr-food-deprived rats tested in photocell activity cages during restricted 30-min sessions. This mild hyperphagia was accompanied by a significant hypoactivity in the group with NAS/OT lesions. No hyperphagia was observed during a prolonged 120-min test session or in free-feeding tests conducted in the home cage. Anorexia induced by d-amphetamine (.5 and 1.5 mg/kg) was unaltered by the lesion, although the locomotor stimulant action of the drug was attenuated. A second experiment showed that the NAS/OT lesion also enhanced food intake in the photocell cages during 30-min sessions with dry food pellets but that food-associated drinking was concomitantly reduced. The results are consistent with the hypothesis that the behavioral changes caused by mesolimbic neuron destruction result in part from an inability to switch from one behavioral activity to another.     

The influence of competitive status (winner/loser) on the behavior of male rats in three models of anxiety

Studies indicate that features such as prior stressful experience, strain, gender, and age can influence the behavior of rats in animal models of anxiety. In the present study, we examined the possible influence of competitive status (winner/loser) in three such models: the elevated plus‐maze, the open field, and the social interaction test. One hundred to 135‐day‐old male Wistar rats were conditioned to traverse a straight runway tube to obtain food. Subsequently, two rats were placed at the same time in the runway tube and, being unable to pass each other, one of them pushed the other to the opposite end‐box. The rats were categorized as winners or losers in this competition. One week after the straight runway tube test, the rats were submitted to the anxiety models, where it was observed that winner rats showed greater locomotor activity than the losers in the three models studied. Furthermore, winner rats showed less immobility and higher central and total locomotor activity in the open field and a greater duration of social interaction in the social interaction test. These results suggest that competitive status has an influence on the locomotor activity of rats in animal models of anxiety. However, whether competitive status influences anxiety as assessed in these models is unclear, and further investigations are warranted. Aggr. Behav. 28:164–171, 2002. © 2002 Wiley‐Liss, Inc.     

Independence of blood pressure and locomotor hyperactivity in normotensive and genetically hypertensive rat

The spontaneously hypertensive rat (SHR) exhibits locomotor hyperactivity in comparison to its normotensive progenitor Wistar-Kyoto (WKY) strain. We asked whether the hyperactive behavior was a direct consequence of elevated blood pressure in the hypertensive rat. Three experimental protocols were used to chronically alter blood pressure. In the first protocol, a group of adult SHRs was given hydralazine (20 mg/kg/day) in their drinking water to lower blood pressure. These animals exhibited a significant decrease in blood pressure, but no change in locomotor activity. In the second protocol, young SHRs (4 weeks of age) were treated with the same dosage of hydralazine until 16 weeks of age. Blood pressure was significantly decreased in these animals with no change in locomotor activity. In the third protocol, normotensive WKY and Sprague-Dawley (SD) rats were made hypertensive with unilateral renal clips. The resulting increase in blood pressure in these animals did not alter locomotor activity. These results suggest that locomotor hyperactivity is an inherent property of the SHR and is independent of blood pressure.     

Age-related changes in working and reference memory performance and locomotor activity in the Wistar rat

Wistar rats of three age groups were tested in an automated tunnel-maze system of variable geometry to investigate whether changes in spontaneous locomotor activity and in learning and memory develop differentially or in a correlated fashion as a function of age. Senescent (30 months) as well as mature-adult (17 months) rats showed an age-correlated decline of locomotor activity as compared to the mature-young (5 months) group. Both working-memory (measured as within-trial arm discrimination performance) and reference-memory (measured as avoidance of "blind alley" visits) were severely affected in the senescent group, whereas the middle-aged animals suffered only from a working-memory deficit. The findings provide evidence that locomotor deficits do not necessarily interfere in the assessment of age-related changes in cognitive performance. Furthermore the results support the hypothesis that working and reference memory have different underlying physiological correlates and that these neuronal systems are differentially affected by the aging process.     

An infrared device for detecting locomotor activity

An electronic device for detecting locomotor activity in the home cage of small animals is described. The system involves a dense array of infrared (IR) beams designed to function as switches and capable of penetrating plastic walls of standard rodent cages without operational decrement. The device is reasonably inexpensive, is simple to calibrate, can be used with groups of animals, may be used for extended periods without maintenance, and is reliable with different cages.     

Arousal and activity level of rats with lesions in the dorsal hippocampus.

The effect on gross locomotor activity of irrelevant stimuli, prior exposure to these stimuli and two dosages of amphetamine were assessed on rats with lesions in the dorsal hippocampus. These animals were significantly more active post-operatively than sham-lesioned subjects. Prior exposure to the irrelevant stimuli increased post-operative differentiation between stimuli, whereas the introduction of amphetamine had the reverse effect. Changes in locomotor activity occurred at lower dosages of amphetamine than in previous studies, suggesting that the irrelevant stimuli have an arousal effect which acts additively with amphetamine and hippocampal impairment.     

Paradoxical sleep deprivation impairs acquisition, consolidation, and retrieval of a discriminative avoidance task in rats

The aim of the present study was to investigate the effects of paradoxical sleep deprivation (PSD) for 96 h on the learning/memory processes in rats submitted to the plus-maze discriminative avoidance task (PM-DAT), which simultaneously evaluates learning, memory, anxiety and motor function. Four experiments were performed in which rats were submitted to: (1) post-training and pre-test PSD; (2) post-training or pre-test PSD; (3) pre-training PSD or pre-training paradoxical sleep (PS) rebound (24 h) and (4) pre-test PSD rebound. Concerning Experiment I, post-training and pre-test PSD induced memory deficits, an anxiolytic-like behavior and an increase in locomotor activity. In Experiment II, both post-training PS-deprived and pre-test PS-deprived groups showed memory deficits per se. However, only the pre-test PS-deprived animals presented anxiolytic-like behavior and increased locomotor activity. In Experiment III, pre-training PS-deprived rats showed learning and memory deficits, anxiolytic-like behavior and increased locomotor activity. A 24h-sleep recovery period after the PSD abolished the learning and memory deficits but not anxiety and locomotor alterations. Finally, sleep rebound did not modify acquisition (Experiment III) and retrieval (Experiment IV). This study strengthened the critical role of paradoxical sleep (but not sleep rebound) in all the phases of learning and memory formation. In addition, it suggests that PSD effects on acquisition and consolidation do not seem to be related to other behavioral alterations induced by this procedure.     

A semiautomated Wisconsin General Test Apparatus

A modification of the WGTA is described. It retains those features of the original apparatus which make it efficient. In addition, it provides (1) precise and largely automatic control of trial pacing and stimulus presentation, (2) simultaneous acquisition of data on problem-solving and locomotor activity of the S, (3) rapid change to any one of a wide variety of behavioral situations, and (4) thorough but quick cleaning and disinfection of the monkey cage.     

吗啡行为及条件性行为敏感化效应及其个体差异

目的：考察吗啡处理下,大鼠行为敏感化及条件性行为敏感化效应及其个体差异性表现。方法：根据大鼠在初次抵达的新颖环境中水平活动量的高低,将大鼠划分为高反应大鼠（High responder, HR）和低反应大鼠（Low responder, LR）,应用自动监测大鼠活动箱,分别考察HR和LR大鼠在行为及条件性行为敏感化效应表达上的差异。结果：（1）连续5天吗啡给药,LR大鼠活动量显著升高,HR大鼠无此效应;（2）条件测试日（第6天）,给药与环境匹配大鼠,活动量较给药与环境非匹配组动物和对照组动物显著为高;此效应在HR和LR大鼠同时存在;（3）从给予吗啡到给予盐水,发现LR大鼠活动量显著下降,而HR大鼠活动量无显著改变。结论：在连续给药下,LR大鼠较HR大鼠,在行为敏感化效应的形成中,具有更为显著的效应,此效应为LR动物对吗啡更高的药物效应,而非条件效应所致,同时HR和LR大鼠都可以对吗啡条件性线索产生应答,产生条件性行为敏感化效应。