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Low- and moderate-exploratory children with learning disabilities engaged in exploratory behavior independently and with an adult who communicated support in one of two nonintrusive ways. Consistent with a developmental motivation perspective, low- and moderate-exploratory children showed higher levels of exploration under both kinds of supportive conditions.
The effect of monosodium-L-glutamate (MSG) administration in the neonatal period on habituation of exploratory behavior related to gender differences was investigated. Rats of both sexes were intraperitoneally treated with MSG (4 mg/g) or hypertonic saline (10% NaCl) on postnatal days 2, 4, 6, 8, and 10. On postnatal day 65, the animals were tested in an open-field test during 4 consecutive days, once daily in 6-min sessions. The rapidity of habituation of exploratory behavior during repeated exposure to the open field (interrupted habituation) and over individual sessions (uninterrupted habituation) was evaluated by using the method of linear regression. Compared to intact controls, there were no significant differences found in interrupted habituation, neither in males nor in females. Uninterrupted habituation in neonatally treated males was slowed down in the first 2 days of testing. No differences in adult behavior between treated groups (MSG and hypertonic saline) were observed, i.e., there were no late effects specific for neonatal MSG administration. In females, uninterrupted habituation was not affected. Males proved to be more sensitive to neonatal stress associated with injections of MSG or hypertonic saline than females, and showed feminine-like habituation in the new environment.
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The effects of the octapeptide angiotensin II (AT II) and its possible interaction with catecholaminergic (mainly dopaminergic) neurotransmission on the exploratory behavior of male rats in open field were studied. AT II changed exploratory behavior in a nonlinear dose-effect manner. The stimulant effects of AT II were antagonized by the AT II receptor antagonist saralasin. The AT II effects were increased by the DAergic agonists apomorphine and nomifensine and were decreased by the DAergic antagonist haloperidol and by the inhibitor of catecholamine synthesis alpha-methyl-para-tyrosine. It is suggested that the effects of AT II on open field behavior are realized through specific AT II receptors and through interactions with catecholaminergic (mainly dopaminergic) neurotransmission in the brain.
The effects of the octapeptide angiotensin II (AT II) and its interactions with GABA (gamma-aminobutyric acid) on the exploratory behavior of male rats in open field were studied. AT II (0.1 and 0.5 microgram i.c.v.) increased the open field behavior, mainly ambulation and rearing. GABA (100 micrograms i.c.v.) significantly reduced the effects of AT II. This influence of GABA was potentiated by subconvulsive doses of bicuculline. Our results demonstrate that the GABAergic system exerts an inhibitory control on pathways mediating the stimulatory effects of AT II on exploratory behavior in open field. The data also suggest close interactions between GABA AT II receptors.
An elevated plus-maze was used to investigate the effects of repeated testing on the locomotor and exploratory behaviors of malnourished rats. Pup malnutrition was induced during the lactation period (0 to 21 days of age) by feeding the dams a protein-deficient diet (6% protein) and the animals were allowed to recover from weaning to 70 days of age by eating a commercial lab chow diet. Control animals were suckled by dams receiving a normal protein diet (16% protein) during the lactation period and were fed a commercial lab chow diet after weaning. At 70 days, malnourished and control animals were placed on the central platform of the elevated plus-maze facing an enclosed arm and allowed to explore for 5 min. This procedure was repeated at 24-h intervals for 6 days. The repeated testing in the elevated plus-maze did not change the total number of arm entries and attempts to enter open arms, but decreased the percentage of open arm entries, time spent in open arms, and total time spent on the central platform. These data suggest an increase in anxiety with repeated testing in the elevated plus-maze. In addition, the malnourished animals showed a larger number of both rearings and attempts to enter the open arms, suggesting a high level of exploration and/or high impulsiveness of these animals as compared to control. The elevated plus-maze proved to be a useful animal model to evaluate exploratory behaviors in early protein malnourished animals.
The effects of the octapeptide angiotensin II (AT II) and its interaction with yohimbine, an alpha 2-adrenoceptor antagonist, on the exploratory behavior of male rats in open field were studied. AT II (0.1 and 0.5 microgram intracerebroventricularly, i.c.v) increased the open field behavior, mainly ambulation and rearing. Yohimbine (1 and 3 mg/kg) significantly reduced the stimulatory effects of AT II, mainly on ambulation. It is suggested that the augmented release of noradrenaline (NA) resulting from alpha 2-adrenoceptor blockade decreases the exploratory behavior effects of AT II. An interaction between AT II receptors and NA-ergic neurotransmission in the brain might be taken into consideration as an explanation of the influence of yohimbine on AT II effects in open field behavior.
The influence of imipramine treatment on apomorphine-induced behavior was studied. Imipramine was administered twice a day for 14 days at 10 mg/kg. The control group received a single dose of imipramine. Both groups were tested at 48 hours after imipramine administration, using open field; the number of line crossings and episodes of rearing and looking into holes were counted as part of the exploratory behavior. Repeated, but not single, administration of imipramine increased the exploratory activity induced by apomorphine injection an effect which was blocked by haloperidol pretreatment. The results indicate that repeated imipramine administration enhances the sensitivity of brain dopamine receptors related to exploratory behavior.
The effects of adafenoxate (Adf), meclofenoxate (Mf), piracetam (Pc), and citicholine (CCh) on scopolamine (Scop)--impaired memory and exploratory behavior (experiments on rats) and on physical capabilities (experiments on mice) were studied. In the experiments with scopolamine (2 mg/kg i.p.) we used the step-through passive avoidance method to determine the memory changes. In the case of single treatment with the drugs tested scopolamine was injected immediately after training and Adf, Mf, and CCh at doses of 20 and 100 mg/kg and Pc at a dose of 100 mg/kg were administered immediately after scopolamine. In the case of multiple administration the drugs were applied at the same doses for 7 days before training. Scopolamine was injected immediately after training. Retention tests were given 3 and 24 hours later. All the four drugs tested prevented to a large extent or completely the scopolamine-induced retrograde amnesia. However, significant quantitative differences in the antiamnestic effects of the drugs tested were observed. The effects of the four drugs on exploratory behavior were tested in the Opto Varimex apparatus. After 7-day treatment with the drugs at the doses utilized, the behavior of experimental animals was observed for 10 min, checking out the changes in the frequency of rearing, ambulation, and rotation. Only Adf at a dose of 50 mg/kg significantly decreased rearing and ambulation frequencies; this effect was considered to be an expression of accelerated habituation. The physical capabilities of mice were studied, using the method of treadmill (revolving drum activity cage) training. Before the experiment the mice received orally Adf, Mf, and Pc at a dose of 100 mg/kg or were injected intraperitoneally with CCh at doses of 50 and 100 mg/kg once daily for 7 days. The number of revolutions of the drum cages was counted for 4 hours. Only Pc significantly increased the physical capabilities of mice and much delayed the occurrence of fatigue.
The lateral habenula is a major station conveying information between the limbic forebrain and midbrain. Bilateral lesions of the lateral habenula were found to increase exploratory behavior, including locomotor activity, rearing and hole-poke responses in rats. These effects were not due to an augmentation of general motor function, since the animal's performance on the Rota-rod treadmill was not significantly changed by the same manipulation. Lateral habenular lesion was also found to potentiate the effects of footshock stress on exploratory behavior in an open field. It is suggested that the lateral habenula probably plays an inhibitory role in the expression of certain emotion-related behaviors under normal and stressful situations.
Rats with bilateral hippocampal lesions and controls with neocortical lesions were compared on the habituation of lick suppression and startle response. The animals with hippocampal lesions showed no consistent differences from controls on any measure within these two response systems. Importantly, the rats with hippocampal lesions showed significant retention of habituation over periods of 24 hr and 21 days. Experimental and control differences were not revealed when stimulation was presented on a 1-sec interstimulus interval. None of these results varied with the extent of the hippocampal lesions, which ranged from relatively small lesions restricted to the dorsal hippocampus to large lesions that damaged the hippocampus in its dorsal, posterior, and ventral aspects. In contrast to the startle response and lick suppression results, hippocampal lesions significantly disrupted Y-maze exploratory behavior, and the disruption was directly related to the extent of hippocampal damage. The data suggest that the hippocampus is not involved in any important way in the control of either short-term or long-term habituation of elicited, reflex-like behaviors but is importantly involved in the control of emitted, exploratory behaviors.
The Huntington's disease (HD) R6/1 transgenic mouse model, containing a human huntington gene exon-1 with approximately 115 CAG repeats, has multiple biochemical and neuroanatomical abnormalities. Overt neurological symptoms have a relatively late onset (15-21 weeks of age). In this paper, we report exploratory behavior abnormalities that appear well before the onset of obvious pathology. The first differences in exploratory behaviors were evident by 4 weeks of age, when R6/1 mice were hyperactive relative to wild-type controls. However, by 6-7 weeks of age, R6/1 mice were less active than controls. R6/1 mice traveled less in the activity monitor, engaged in fewer stereotypic movements, spent more time resting, and traveled less distance per movement than did wild-type controls. R6/1 mice also displayed intersession habituation abnormalities over the 3 days of testing. These behavioral abnormalities precede the earliest neurochemical and molecular changes reported in the literature to date, and thus indicate subtle early pathology that has not yet been documented. These behavioral abnormalities also occur prior to weight loss in the transgenic mice. Since we were able to detect an abnormal phenotype at an early age in R6/1 mice, this assay may be a useful tool for evaluating therapeutic agents.
The aim of this study was to assess in developing mice whether the neutralization of endogenous NGF following ICV administration of anti-NGF antibodies (50 micrograms/2 microliters) on postnatal days 3, 6, 9, and 12 affected locomotor activity, exploratory behavior, and response to the cholinergic blocker scopolamine. In Experiments 1 and 2 activity and age-typical scopolamine effects were evaluated on PND 13 or 17 in an automated apparatus. No significant main effect of anti-NGF treatment was found at either age. On day 13 scopolamine (0.2, 1, or 2 mg/kg) decreased locomotion in both anti-NGF and control animals. In Experiment 3, locomotion and exploratory behavior were analyzed in an open field arena or in a hole board apparatus on PND 16. No significant effects of anti-NGF treatment on general motor activity and investigation of a novel object in the open field was found, though anti-NGF animals tended to be less active than controls. In the hole board anti-NGF pups showed a different pattern of head dipping behavior from controls, exploring mainly the holes located in the periphery of the apparatus.
The effect of dietary restriction of n-3 fatty acids during development on brain phospholipid fatty acid composition and exploratory behavior has been studied in male Sprague Dawley rats. Female rats were fed semipurified diets containing either 5.5% safflower oil or 6% soybean oil for 6 wk prior to mating and throughout gestation and lactation. Control rats were maintained on laboratory chow. The male pups were weaned to the diets of the dams except for one group which was switched from safflower to soybean oil at weaning. Behavioral studies and brain phospholipid analyses were conducted at 16-18 wk of age. Rats fed safflower oil showed significantly lower levels of 22:6n-3 in phospholipids of synaptic membranes and myelin than rats fed soybean oil or chow. The decrease in 22:6n-3 was compensated for by an increase in 22:5n-6, the total content of polyunsaturated fatty acids remaining approximately constant. The brain phospholipid fatty acid composition of rats switched from safflower to soybean oil at weaning was similar to that of rats fed soybean oil throughout the experiment. There was no difference in spontaneous locomotor activity among the different dietary groups. However, rats raised on safflower oil displayed a significantly lower exploratory activity (horizontal movements and rearings) in a novel environment than rats fed soybean oil or chow. In contrast to the brain phospholipid fatty acid composition, there was no recovery of exploratory behavior in rats raised on safflower oil and switched to soybean oil at weaning suggesting a specific requirement of n-3 fatty acids during development.
Chronic ethanol intake causes various types of neural damage and behavioral impairments, probably acting through oxidative stress and excitotoxicity, while dietary restriction is considered by some authors to protect the central nervous system from these kinds of damage. In the present study, a factorial experimental design was used to investigate the effects of chronic ethanol and dietary restriction treatments, associated or not, on Wistar rats' exploratory behavior, spatial memory aspects and cortical and hippocampal acetylcholinesterase (AChE) activity. Dietary restriction lasted for the whole experiment, while ethanol treatment lasted for only 3 weeks. Despite the short ethanol treatment duration, for two behavior categories assessed, moving and rearing, an interaction was observed between the effects of chronic ethanol and dietary restriction. There were no significant differences in AChE activities among the groups. Cerebellar neural nitric oxide synthase (nNOs) activity was measured as a first step to assess oxidative stress. Dietary restriction significantly reduced NO formation. The present results indicate that dietary restriction might exert a protective effect against chronic-ethanol-induced changes in exploratory behavior. It is hypothesized that the mechanisms underlying this protection can involve prevention of oxidative stress.
The effects of age on the habituation of exploratory behavior of 8-month- and 28-month-old male C57BL/NNia mice were examined under three different stimulus complexity conditions. Increases in the degree of stimulus complexity resulted in an attenuation of between-session habituation and an initial disruption of within-session habituation by 8-month-old mice. Although increases in stimulus complexity also resulted in an increase in the overall level of exploration by aged mice, stimulus complexity was not found to have a systematic effect on between- or within-session habituation by aged mice. No between-session habituation was observed in aged mice under any of the stimulus complexity conditions. Further, aged mice exhibited significant within-session increases, rather than decreases, in exploration under each stimulus complexity condition. This disruption of within-session habituation in aged mice was found to persist over four daily test sessions. In view of the specific patterns of exploration by aged mice, the disruption of within-session habituation was attributed to age-related differences in reactivity to the arousal-inducing properties of novel stimuli.
The effect of diazepam on exploratory behavior was investigated in two inbred strains of rats, Fischer 344 (F344) and Lewis (LEW). The total numbers of head-dips and head-dipping duration in the rat hole-board test, and the total number of rearing and locomotor activity in the open-field test were measured after diazepam administration. The numbers of head-dips and rearings, and head-dipping duration and locomotor activity in naive F344 were significantly greater than those in naive LEW (P less than 0.001), suggesting that LEW is more emotional than F344. Diazepam, 0.31 and 0.63 mg/kg for F344 and 0.31-1.25 mg/kg for LEW, increased head-dips, head-dipping duration and rearings. However, there were no strain differences in enhancing effect of diazepam on locomotor activity. On the contrary, higher doses of diazepam, 0.94-2.50 mg/kg for F344 and 2.50 mg/kg for LEW, decreased head-dips, head-dipping duration, and rearings. However, the effect of diazepam on rotarod performance in LEW was similar to that in F344. These results suggest that F344 is more sensitive to sedative effect of diazepam than LEW, and that the sensitivity to diazepam may be strongly influenced by genetic factors.
The neuropathological hallmark shared between Alzheimer's disease (AD) and familial frontotemporal dementia (FTDP-17) are neurofibrillary tangles (NFT) which are composed of filamentous aggregates of the microtubule-associated protein tau. Their formation has been reproduced in transgenic mice, which express the FTDP-17-associated mutation P301L of tau. In these mice, tau aggregates are found in many brain areas including the hippocampus and the amygdala, both of which are characterized by NFT formation in AD. Previous studies using an amygdala-specific test battery revealed an increase in exploratory behavior and an accelerated extinction of conditioned taste aversion in these mice. Here, we assessed P301L mice in behavioral tests known to depend on an intact hippocampus. Morris water maze and Y-maze revealed intact spatial working memory but impairment in spatial reference memory at 6 and 11 months of age. In addition, a modest disinhibition of exploratory behavior at 6 months of age was confirmed in the open field and the elevated O-maze and was more pronounced during aging.