Fear-like behavioral responses in mice in different odorant environments: Trigeminal versus olfactory mediation under low doses

Odors can have repulsive effects on rodents based on two complementary adaptive behaviors: the avoidance of predator odors (potentially dangerous) and the avoidance of trigeminal stimulants (potentially noxious). The present study aimed to compare the behavioral effects on mice of odors according to their trigeminal properties and ecological significance. We used three different odors: 2,4,5-trimethylthiazoline (TMT: a fox feces odor frequently used to elicit fear-induced behaviors), toluene (a strong stimulant of the trigeminal system) and phenyl ethyl alcohol (PEA: a selective stimulant of the olfactory system). First, we checked preference and avoidance behaviors in mice with and without anosmia towards these odors to ensure their olfactory/trigeminal properties. Secondly, we used a standard test (open-field and elevated plus-maze) to assess the behaviors of mice when exposed to these odors. The results show that the anosmic and control mice both avoided TMT and toluene odors. In the open-field and the elevated plus-maze, mice exhibited "anxious" behaviors when exposed to TMT. Conversely, exposure to PEA induced "anxiolytic" effects confirmed by low blood corticosterone levels resulting from completion of the elevated plus-maze. Compared with TMT exposure, toluene exposure induced moderate "anxious" effects.     

Probabilistic Risk Assessment and Risk Mapping of Sediment Metals in Sydney Harbour Embayments

Sediment metal concentrations in embayments of Sydney Harbour, acquired from the literature and from samples collected for this study, were used to generate contaminant probability density distributions using AQUARISK. The sediment metal concentrations often exceeded Australia's interim sediment quality guidelines. Similarly, estuarine spiked sediment toxicity test literature provided adverse biotic effects concentration data to generate species sensitivity distributions using AQUARISK. Although the harbor is subject to other inorganic and organic contamination, we have used sediment metals to demonstrate an approach for ecological risk mapping and environmental management prioritization. Sufficient spiked sediment toxicity test data were found for only three metals—Cd, Cu, and Zn—and some tests were likely to overestimate toxicity. The estimates of the hazardous concentration to 5% of species (the 50th percentile of the 95% species protection level) were 5, 12, and 40 mg/kg DW of total sediment metal for Cd, Cu, and Zn, respectively. These values were generally low when compared with the interim sediment quality guidelines due to the overestimation of toxic effects in the literature data. The parameters for the species sensitivity distributions have been combined with the measured sediment metal concentrations in Homebush Bay to generate risk maps of the estimated species impact for each metal as well as for all three metals collectively assuming proportional additivity. This has demonstrated the utility of comparing contaminants on a consistent scale—ecological risk.     

Prenatal stress alters reproductive responses of rats in behavioral estrus and paced mating of hormone-primed rats

Adult female offspring of dams exposed to gestational stress (prenatal stress, PNS) may show altered reproductive behavior, exploration in novel environments, and/or social interactions than do their non-PNS counterparts. These behavioral differences may be more readily observed in a seminatural, paced mating paradigm, in which females have greater control of their sexual contacts, than in a standard mating situation. Adult offspring of dams exposed to restraint and lights for 45 min on Gestational Days 14-20 (PNS) were compared with those not subjected to stress (non-PNS, control condition). The motor, reproductive, and sociosexual behaviors of hormone-primed (Experiment 1) or cycling adult offspring in behavioral estrus (Experiment 2) were examined following 20 min of restraint stress under bright lights (postnatal stress). Hormone-primed PNS rats displayed less motor behavior in a novel arena than did non-PNS rats. In a standard mating test, hormone-primed PNS females tended to be more aggressive toward the male than were non-PNS rats. In a seminatural mating situation, hormone-primed PNS females showed increased avoidance behavior, such as longer latencies to the initial intromission, greater return latencies following mounts and intromissions, and more exiting subsequent to mounts and intromissions, than did non-PNS rats. PNS rats in behavioral estrus had decreased incidence and intensity of lordosis, and fewer solicitation behaviors, in both standard or paced mating situations, in which latency to and number of mounts were also increased. Thus, hormone-primed PNS rats exposed to restraint showed more avoidance behaviors in paced mating situations, while cycling PNS rats in behavioral estrus had greater disruption of reproductive responses in standard or paced mating paradigms than did non-PNS control rats.     

Linking phenotypic correlations from a diverse set of laboratory tests to field behaviors in the crayfish,Orconectes virilis

The presence of phenotypic behavioral correlations and their connection to fitness consequences of organisms have received considerable debate within the literature. Yet, little work has been carried out to connect any behavioral correlates found within a set of laboratory studies to natural behavior observed under complex environmental conditions. To help fill this gap, individual crayfish, collected from the same local population, completed five different behavioral assays in a laboratory setting in a random order. These data were used to reveal any possible correlations for behavioral scores across all of the laboratory tests. Subsequently, these same individuals were placed into the field and video recorded for 24 hr. A separate set of field behaviors, related to the laboratory assays, were quantified from the field videos. The normalized laboratory and field behaviors were used in three stepwise statistical analyses. First, normalized data were loaded into a PCA to generate a priori hypotheses on potential behavioral correlates. These hypotheses were subsequently tested using general multiple linear regression. Finally, structural equation modeling was performed to elucidate any behavioral modules from the laboratory assays that correlated with behavioral patterns present from the fieldwork. Three laboratory‐based behavioral modules were connected to three separate field assays: exploration–avoidance, bold–shy, and aggressiveness. Yet, some behaviors exhibited in the laboratory assays were uncorrelated with any behaviors found in the field and vice versa. Results from this study provide evidence that although many different behavioral correlates may exist within laboratory settings, these same modules may not translate directly into predicting behavior under natural settings.     

Progress of research on the toxicology of antibiotic pollution in aquatic organisms

Antibiotics are widely used to improve human and animal health and treat infections. Antibiotics are often used in livestock farms and fisheries to prevent diseases and promote growth. Recently, there has been increasing interest in the presence of antibiotics in aquatic environments. Low levels of antibiotic components are frequently detected in surface water, seawater, groundwater, and even drinking water. Antibiotics are consistently and continually discharged into the natural environment as parent molecules or metabolites, which are usually soluble and bioactive, and this results in a pseudo and persistent pollution. The effects of environmental antibiotic toxicity on non-target organisms, especially aquatic organisms, have become an increasing concern. Although antibiotics have been detected worldwide, their ecological and developmental effects have been poorly investigated, particularly in non-target organisms. This review describes the toxicity and underlying mechanism of antibiotic contamination in aquatic organisms, including the effects on vertebrate development. A considerable number of antibiotic effects on aquatic organisms have been investigated using acute toxicity assays, but only very little is known about the long-term effects. Aquatic photosynthetic autotrophs, such as Pseudokirchneriella subcapitata, Anabaena flos-aquae, and Lemna minor, were previously used for antibiotic toxicity tests because of low cost, simple operation, and high sensitivity. Certain antibiotics show a different degree of potency in algal toxicity tests on the basis of different test algae. Antibiotics inhibit protein synthesis, chloroplast development, and photosynthesis, ultimately leading to growth inhibition; some organisms exhibit growth stimulation at certain antibiotic concentrations. Daphnia magna and other aquatic invertebrates have also been used for checking the toxicity priority of antibiotics. When investigating the acute effect of antibiotics (e.g., growth inhibition), concentrations in standard laboratory organisms are usually about two or three orders of magnitude higher than the maximal concentrations in the aquatic environment, resulting in the underestimation of antibiotic hazards. Vertebrate organisms show a promising potential for chronic toxicity and potentially subtle effects of antibiotics, particularly on biochemical processes and molecular targets. The adverse developmental effects of macrolides, tetracyclines, sulfonamides, quinolones, and other antibiotic groups have been evaluated in aquatic vertebrates such as Danio rerio and Xenopus tropicalis. In acute toxicity tests, low levels of antibiotics have systematic teratogenic effects on fish. The effects of antibiotics on oxidative stress enzymes and cytochrome P450 have been investigated. Cytotoxicity, neurotoxicity, and genotoxicity have been observed for certain antibiotic amounts. However, there are no firm conclusions regarding the chronic toxicity of antibiotics at environmentally relevant levels because of the lack of long-term exposure studies. Herein, future perspectives and challenges of antibiotic toxicology were discussed. Researchers should pay more attention to the following points: chronic toxicity and potentially subtle effects of environmentally relevant antibiotics on vertebrates; effects of toxicity on biochemical processes and mode of action; combined toxicity of antibiotics and other antibiotics, metabolites, and heavy metals; and environmental factors such as temperature and pH.     

Mysids in toxicity testing — a review

The use of mysid shrimp, particularly the genusMysidopsis, along with specific testing procedures, has become accepted in aquatic toxicology. Investigators have developed methodologies for both culture and testing of these organisms. Acute and chronic (life cycle) toxicity tests in addition to dredge spoil and effluent tests with mysids are now becoming common. Attempts have been made to use mysids as test organisms in behavioral, physiological, nutritional, and food-chain studies. In general,Mysidopsis spp. have been shown to be as sensitive or more sensitive to toxic substances than other marine species tested. The ease of handling and culture, relative sensitivity to toxicants, short life cycle, small size and direct larval development make these organisms desirable for research purposes. Continued research using mysid species will probably demonstrate even greater usefulness of these organisms in assessment of pollutant impacts on estuarine or marine communities.     

Review: ecotoxicity of organic and organo-metallic antifouling co-biocides and implications for environmental hazard and risk assessments in aquatic ecosystems

Hazard assessments of Irgarol 1051, diuron, 2-(thiocyanomethylthio)benzothiazole (TCMTB), dichloro-octylisothiazolin (DCOIT), chlorothalonil, dichlofluanid, thiram, zinc pyrithione, copper pyrithione, triphenylborane pyridine (TPBP), capsaicin, nonivamide, tralopyril and medetomidine were performed to establish robust environmental quality standards (EQS), based on predicted no effect concentrations (PNECs). Microalgae, zooplankton, fish and amphibians were the most sensitive ecological groups to all the antifoulants evaluated, especially in the early life stages. No differences were identified between freshwater and seawater species. The use of toxicity tests with non-standard species is encouraged because they increase the datasets, allowing EQS to be derived from probabilistic-based PNECs whilst reducing uncertainties. The global ban of tributyltin (TBT) has been heralded as a major environmental success; however, substitute antifoulants may also pose risks to aquatic ecosystems. Environmental risk assessments (ERAs) have driven decision-makings for regulating antifouling products, but in many countries there is still a lack of regulation of antifouling biocides which should be addressed.     

Behavior and neurobehavioral teratology using the ferret

A behavioral profile of the ferret is presented for those who would like to use this animal in behavioral teratology and toxicology, or other disciplines involving behavior. We have reviewed neurobehavioral teratology of lisencephalic ferrets and neuropsychology of ferrets sustaining frontal lesions, as well as most of the studies of "normal" ferret behavior that have appeared in the research literature. Emphasis is placed on discussion of the tests used and how ferrets behaved on them. The behaviors discussed include spatial (maze) learning, delayed response, visual discrimination learning, discrimination learning sets, schedule maintained behavior, shock avoidance learning and spontaneously occurring behaviors, such as ambulation in open field, spontaneous alternation and species specific behaviors. Although the use of the ferret in behavioral experiments is not yet extensive and large gaps exist in our knowledge about the basic functional capacities of this animal, the ferret is unquestionably well suited for behavioral studies.     

The Need for Multiple Lines of Evidence for Predicting Site-Specific Ecological Effects

The goal of this paper is to illustrate the value and importance of the “weight of evidence” approach (use of multiple lines of evidence from field and laboratory data) to assess the occurrence or absence of ecological impairment in the aquatic environment. Single species toxicity tests, microcosms, and community metric approaches such as the Index of Biotic Integrity (IBI) are discussed. Single species toxicity tests or other single lines of evidence are valuable first tier assessments that should be used as screening tools to identify potentially toxic conditions in a effluent or the ambient environment but these tests should not be used as the final quantitative indicator of absolute ecological impairment that may result in regulatory action. Both false positive and false negative predictions of ecological effects can occur due to the inherent variability of measurement endpoints such as survival, growth and reproduction used in single species toxicity tests. A comparison of single species ambient toxicity test results with field data showed that false positives are common and likely related to experimental variability or toxicity to selected test species without measureable effects on the ecosystem. Results from microcosm studies have consistently demonstrated that chemical exposures exceeding the acute or chronic toxicity concentrations for highly sensitive species may cause little or no ecologically significant damage to an aquatic ecosystem. Sources of uncertainty identified when extrapolating from single species tests to ecological effects were: variability in individual response to pesticide exposure; variation among species in sensitivity to pesticides; effects of time varying and repeated exposures; and extrapolation from individual to population-level endpoints. Data sets from the Chesapeake Bay area (Maryland) were used to show the importance of using “multiple lines of evidence” when assessing biological impact due to conflicting results reported from ambient water column and sediment toxicity tests and biological indices (benthic and fish IBIs). Results from water column and sediment toxicity tests with multiple species in tidal areas showed that no single species was consistently the most sensitive. There was also a high degree of disagreement between benthic and fish IBI data for the various stations. The lack of agreement for these biological community indices is not surprising due to the differences in exposure among habitats occupied by these different taxonomic assemblages. Data from a fish IBI, benthic IBI and Maryland Physical Habitat Index (MPHI) were compared for approximately 1100 first through third-order Maryland non-tidal streams to show the complexity of data interpretation and the incidence of conflicting lines of evidence. A key finding from this non-tidal data set was the need for using more than one biological indicator to increase the discriminatory power of identifying impaired streams and reduce the possibility of “false negative results”. Based on historical data, temporal variability associated with an IBI in undisturbed areas was reported to be lower than the variability associated with single species toxicity tests.     

Defense behavior of fish against predators and parasites

This paper is a review of empirical and theoretical studies of the behavioral mechanisms and ecological consequences of the anti-predator and anti-parasite activities of teleost fishes. While the individual and cooperative behaviors used by fish to protect themselves from predators have received marked attention from researchers in the fields of ecology, ethology and applied fish biology, the behaviors by which fish protect themselves from parasites have been poorly investigated. Generally, free-swimming parasites, which are difficult to distinguish, do not elicit any marked behavioral response from fish prior to contact. We hypothesize that the behaviors by which fish avoid parasites are much more efficient for fish in groups than they are for solitary fish. Early avoidance of predators and parasites is compared with the behavioral tactics fish use when such enemies are in close proximity. Individual versus cooperative tactics, as well as the role of learning, are also analyzed. Learning is more important for behaviors which protect fish from predators than those which they use against parasites, especially at the level of individual fish. Finally, we briefly discuss the importance of coordination of anti-predator and anti-parasite activities, which present the most complicated tasks for fish and intriguing problems for researchers.     

Differences in spontaneously avoiding or approaching mice reflect differences in CB1-mediated signaling of dorsal striatal transmission

Approach or avoidance behaviors are accompanied by perceptual vigilance for, affective reactivity to and behavioral predisposition towards rewarding or punitive stimuli, respectively. We detected three subpopulations of C57BL/6J mice that responded with avoiding, balancing or approaching behaviors not induced by any experimental manipulation but spontaneously displayed in an approach/avoidance conflict task. Although the detailed neuronal mechanisms underlying the balancing between approach and avoidance are not fully clarified, there is growing evidence that endocannabinoid system (ECS) plays a critical role in the control of these balancing actions. The sensitivity of dorsal striatal synapses to the activation of cannabinoid CB1 receptors was investigated in the subpopulations of spontaneously avoiding, balancing or approaching mice. Avoiding animals displayed decreased control of CB1 receptors on GABAergic striatal transmission and in parallel increase of behavioral inhibition. Conversely, approaching animals exhibited increased control of CB1 receptors and in parallel increase of explorative behavior. Balancing animals reacted with balanced responses between approach and avoidance patterns. Treating avoiding animals with URB597 (fatty acid amide hydrolase inhibitor) or approaching animals with AM251 (CB1 receptor inverse agonist) reverted their respective behavioral and electrophysiological patterns. Therefore, enhanced or reduced CB1-mediated control on dorsal striatal transmission represents the synaptic hallmark of the approach or avoidance behavior, respectively. Thus, the opposite spontaneous responses to conflicting stimuli are modulated by a different involvement of endocannabinoid signaling of dorsal striatal neurons in the range of temperamental traits related to individual differences.     

利用综合评价方法和等级模型评价乐安江水体重金属污染

采用1992-1995年在江西乐安江所获得的野外调查数据。对化学、毒理学和生态学数据的性质进行分析比较,分析了不同类型评价参数的性质和综合利用时存在的问题。并提出了三者综合的评价方法和一个等级模型。来评价江西省乐安江河流重金属污染及潜在的生态影响。结果表明对于复杂的河流生态系统,采用多指标综合评价方法是描述污染和预测污染生态效应的一种有效途径。     

Temperature sensing and context-dependent thermal behavior in nematodes

As small ectotherms, whose temperature equilibrates almost instantly with that of their environment, free-living nematodes rely on their behavior for thermoregulation. Caenorhabditis elegans has been extensively used as a model to address the fundamental mechanisms involved in thermosensation and the production of temperature-dependent behaviors. Behavioral responses include avoidance of acute noxious heat or cold stimuli and thermotactic responses to innocuous temperatures to produce oriented navigation in spatial thermogradients. In order to produce these behaviors, C. elegans relies on its ability to detect thermal cues with exquisite sensitivity, orchestrate a set of specific behavioral responses and adapt these responses in specific contexts, including according to past sensory experience and current internal states. The present review focuses on recent advances in our understanding of the processes occurring at the molecular, cellular, and circuit levels that enable thermosensory information processing and plasticity.     

Toxicological Considerations of Contaminants in the Terrestrial Environment for Ecological Risk Assessment

The terrestrial environment acts as a “sink” for contaminants that have been purposely or accidentally released into the environment. Science and policy that support protective measures for terrestrial ecosystems have run behind those of aquatic toxicology and water quality concerns. As a result ecological risk assessment (ERA) involving terrestrial environments tends to be conducted at a simplistic level, relying on numeric targets (soil quality criteria) as a basis for decision-making. However, soil criteria for ecological receptors are somewhat deficient in terms of the numbers available and the data that supports these numbers. Direct toxicity assessments (DTA) for terrestrial environments, such as those used for water quality evaluations, can provide additional useful information about the toxicity and bioavailability of mixtures of contaminants present in soils. This article outlines the approaches used for assessing the toxicity of soil contaminants in terrestrial environments and critiques their advantages and pitfalls.     

Uncertainties in the Environmental Risk Assessment of Metals

As life has evolved in the presence of metals, the assessment of the potential adverse effects of metals on ecosystems requires a different approach than those presently used for man-made organic substances. This article provides a brief review of applications and limitations of current techniques and presents, based on recent research results, suggestions for improving the scientific relevance and accuracy of environmental risk assessments of metals. The importance of the following factors responsible for major uncertainties in current environmental risk assessments of metals are discussed: factors affecting metal bioavailability and toxicity, the potential importance of deficiency effects (for essential metals), and field extrapolation of laboratory toxicity data. Possible (regulatory) consequences of inaccurately assessing the natural background concentrations of metals and acclimatization/adaptation potential of laboratory organisms and resident communities are illustrated using examples of recent research, hypothesis development, and a probabilistic environmental risk assessment.     

Variations in the behaviors to novel objects among five inbred strains of mice

Novelty stimuli cause various behavioral responses, such as exploration and avoidance, and contextual variables may contribute to the behavioral outputs. Here, we tried to compare the behavioral responses to novel objects of five inbred strains of mice (C57BL/6J, 129/svJae, C3H/HeJ, BALB/cJ and DBA/2J) by using a modified novel object test where a small light-weight cube wrapped with paper was presented to mice in a home cage without beddings. In response to these objects, the C57BL/6J, 129/svJae and C3H/HeJ mice showed mild exploratory behaviors, such as approaching, sniffing or brief contact. In striking contrast, the BALB/cJ and DBA/2J mice, which have been known to show high avoidance/low exploration in other behavioral paradigms, exhibited play-like secondary reactions toward the objects after initial primary exploratory behaviors. Specifically, DBA/2J mice would move the object around in the cage, holding it with their mouths, and BALB/cJ mice would gnaw the object, eventually stripping off the wrapping paper. Such behaviors decreased when similar objects were presented repeatedly. The present results suggest that active manipulations of novel objects may be a relevant parameter for measuring novelty-induced behaviors in mice and appear to be strongly influenced by genetic factors.     

Sensitivity of bacterial vs. acute Daphnia magna toxicity tests to metals

The objectives of this study were to evaluate the sensitivity of two bacterial tests commonly used in metal toxicity screening — the Vibrio fischeri bioluminescence inhibition test and the Pseudomonas putida growth inhibition test — in comparison to the standard acute Daphnia magna test, and to estimate applicability of the selected methods to the toxicity testing of environmental samples. The D. magna acute test proved to be more sensitive to cadmium (Cd), zinc (Zn) and manganese (Mn) than the two bacterial assays, whereas P. putida seems to be the most sensitive species to lead (Pb). Manganese appears to be slightly toxic to D. magna and non-toxic to the two selected bacteria. This leads to the conclusion that even in regions with high background concentrations, manganese would not act as a confounding factor. Low sensitivity of V. fischeri to heavy metals questions its applicability as the first screening method in assessing various environmental samples. Therefore, it is not advisable to replace D. magna with bacterial species for metal screening tests. P. putida, V. fischeri and/or other bacterial tests should rather be applied in a complex battery of ecotoxicological tests, as their tolerance to heavy metals can unravel other potentially present toxic substances and mixtures, undetectable by metal-sensitive species.     

Behavioral phenotyping of transgenic and knockout mice: practical concerns and potential pitfalls

New technologies in molecular genetics have dramatically increased the number of targeted gene mutations available to the biomedical research community. Many mutant mouse lines have been generated to provide animal models for human genetic disorders, offering insights into anatomical, neurochemical, and behavioral effects of aberrant gene expression. A variety of assays have been developed to identify and characterize phenotypic changes. In the behavioral domain, our phenotyping strategy involves a comprehensive standardized methodological approach that assesses general health, reflexes, sensory abilities, and motor functions. This assessment is followed by a series of complementary tasks in the specific behavioral domain(s) hypothesized to reveal the function(s) of the gene. Our multitiered approach minimizes intersubject variability by standardizing the experimental history for all animals, improves interlaboratory reliability by providing a clearly defined experimental protocol, and minimizes artifactual interpretations of behavioral data by careful preliminary assessments of basic behaviors, followed by multiple tests within the behavioral domain of interest. Despite meticulous attention to experimental protocol, attention to environmental factors is essential. Differences in noise, light, home cage environment, handling, and diet can dramatically alter behavior. Baseline differences in the behaviors of inbred strains used to generate targeted mutant mouse lines can directly influence the behavioral phenotype of the mutant line. Strategies aimed at minimizing environmental variability and contributions of background genes will enhance the robustness of mouse behavioral phenotyping assays.     

A direct solid‐phase assay specific for heavy‐metal toxicity. II. Assessment of heavy‐metal immobilization in soils and bioavailability to plants

We have used the solid‐phase MetPLA TE, an enzyme assay that is specific for heavy‐metal toxicity, to investigate metal toxicity of soils that have been amended with urban wastewater sludges or contaminated with dry deposition from metal‐plating industries. We have shown that soil toxicity, using MetPLA TE, ranged from 21 to 72.5% inhibition of enzyme activity. Evin soil, which displayed the highest toxicity, also had the highest concentrations of Pb and Zn. Metal uptake studies with ryegrass grown on Evin soil, showed Zn, Cd, and Pb accumulation in the plant that exceeds the standard levels reported for grasses

Solid‐phase MetPLA TE was also used as a tool to study the reduction of heavy‐metal toxicity following soil amendments to immobilize metals in soil and thus reduce their toxicity. It was found that the addition of 1% hydrated manganese oxide significantly reduced dissolved metals in soil, their accumulation by ryegrass, and soil toxicity as shown by MetPLA TE.     

Loss of Hippocampal Neurons after Kainate Treatment Correlates with Behavioral Deficits

Treating rats with kainic acid induces status epilepticus (SE) and leads to the development of behavioral deficits and spontaneous recurrent seizures later in life. However, in a subset of rats, kainic acid treatment does not induce overt behaviorally obvious acute SE. The goal of this study was to compare the neuroanatomical and behavioral changes induced by kainate in rats that developed convulsive SE to those who did not. Adult male Wistar rats were treated with kainic acid and tested behaviorally 5 months later. Rats that had experienced convulsive SE showed impaired performance on the spatial water maze and passive avoidance tasks, and on the context and tone retention tests following fear conditioning. In addition, they exhibited less anxiety-like behaviors than controls on the open-field and elevated plus-maze tests. Histologically, convulsive SE was associated with marked neuron loss in the hippocampal CA3 and CA1 fields, and in the dentate hilus. Rats that had not experienced convulsive SE after kainate treatment showed less severe, but significant impairments on the spatial water maze and passive avoidance tasks. These rats had fewer neurons than control rats in the dentate hilus, but not in the hippocampal CA3 and CA1 fields. Correlational analyses revealed significant relationships between spatial memory indices of rats and neuronal numbers in the dentate hilus and CA3 pyramidal field. These results show that a part of the animals that do not display intense behavioral seizures (convulsive SE) immediately after an epileptogenic treatment, later in life, they may still have noticeable structural and functional changes in the brain.