Individual Behavioral Responses Research Articles

Gender-related qualitative differences in baseline and post-stress anxiety responses are not reflected in the incidence of criterion-based PTSD-like behaviour patterns

Background. Most epidemiological studies report higher prevalence rates of stress-related disorders such as acute stress disorder, post-traumatic stress disorder (PTSD) and major depressive disorder in women than in men. Few animal models of PTSD have taken gender differences into account and have typically used male subjects. In order to explore gender-related PTSD-like stress-responses more thoroughly, we applied an animal model that focuses selectively on individual patterns of behavioural responses. Methods. Prevalence rates of individual behavioural response to a single exposure to predator scent stress (PSS) were assessed by both elevated plus-maze and startle response paradigms. Prevalence rates of extreme behavioural disruption (EBR) on both tests were assessed, correlated to corticosterone levels, and compared to global population response data. In addition, we assessed learning and memory in the Morris water-maze (MWM). Results. There were no significant differences between the behavioural responses related to oestrous cycle phase in terms of global data for the groups or in terms of prevalence rates of EBR. The overall patterns of response of males and females were affected, yet females demonstrated greater levels of baseline anxiety-like behaviour and lower peak levels of post-exposure anxiety-like behaviour than males. However, the prevalence rates of individual subjects who responded with PTSD-like behaviour were equal for female and male subjects. PSS-exposed female subjects demonstrated significantly compromised performance in the MWM compared to males. Conclusions. In this animal model, the results clarified that the assumption that females are more vulnerable is true for the magnitude of the response, but not for the prevalence of pathological response patterns in rat populations.

Habitat Selection and Movement of Pond‐Breeding Amphibians in Experimentally Fragmented Pine Forests

ABSTRACT Population‐level responses of amphibians to forest management regimes are partly dictated by individual behavioral responses to habitat alteration. We examined the short‐term (i.e., 24‐hr) habitat choices and movement patterns of 3 amphibian species—southern leopard frogs (Rana sphenocephala), marbled salamanders (Ambystoma opacum), and southern toads (Bufo terrestris)—released on edges between forest habitats and recent clear‐cuts in the Upper Coastal Plain of South Carolina, USA. We predicted that adult frogs and salamanders would preferentially select forest using environmental cues as indicators of habitat suitability. We also predicted that movement patterns would differ in clear‐cuts relative to forests, resulting in lower habitat permeability of clear‐cuts for some or all of the species. Using fluorescent powder tracking, we determined that marbled salamanders selected habitat at random, southern toads preferred clear‐cuts, and southern leopard frogs initially selected clear‐cuts but ultimately preferred forests. Frogs exhibited long‐distance, directional movement with few turns. In contrast, toads exhibited wandering behavior and salamanders moved relatively short distances before locating cover. Southern toads and southern leopard frogs moved farther in forests, and all 3 species made more turns in clear‐cuts than in forests. Habitat selection by southern toads did not vary according to body size, sex, or the environmental cues we measured. However, marbled salamanders were more likely to enter clear‐cuts when soil moisture was high, and southern leopard frogs were more likely to enter clear‐cuts when relative humidity and air temperature were higher in the clear‐cut than in adjacent forest. Although we found evidence of reduced habitat permeability of clear‐cuts for southern leopard frogs and southern toads, none of the species exhibited strong behavioral avoidance of the small (4‐ha) clear‐cuts in our study. Further studies of long‐term habitat use and the potential physiological and other costs to individuals in altered forests are needed to understand the effects of forest management on population persistence. To reduce potentially detrimental effects of clear‐cutting on amphibians in the Southeast, wildlife managers should consider the vagility and behavior of species of concern, especially in relation to the size of planned harvests adjacent to breeding sites.

An individual approach to modelling emergent structure in termite swarm systems

Social insects provide a unique example of emergence and self-organisation. Their ability to exploit environmental complexity to offset individual simplicity presents us with a novel and immensely powerful engineering methodology. In this work we present our 3D agent-based simulation model of the emergent construction behaviour of Macrotermes termites, focusing on construction of the queen's royal chamber and protective trail galleries using available biological evidence. Previous models have been somewhat lacking in modelling individual behavioural responses and in including factors intrinsic to the termite building process. We show how simple response-threshold functions can be combined with pheromone templates and stigmergic mechanisms to mirror experimental work and provide an explanation for poorly understood termite behavioural patterns. We also demonstrate the low-level disorder inherent in such a system and explain how such effects can add a layer of stochasticity to facilitate the self-organised building process.

Do battles lead to coexistence? Role of interference competition in structuring the insect community on fermented tree sap

Abstract 1. In insect communities on fermented tree sap, agonistic interactions occur frequently among the component species. This study examined the effects of such interference competition on community structure and species co‐occurrence on a spatio‐temporally small scale.2. Experimental removal of giant hornets (Vespa mandarinia), one of the most dominant species, showed no effect on either species richness or total abundance of the remaining insects. Significant increases in abundance were detected for five out of 19 taxa: V. ducalis, V. crabro, Lasius japonicus, Cryptarcha lewisi, and a group of micro sap beetles (Epuraea spp., Haptoncus spp., and Haptoncurina spp.).3. Behavioural observations indicated that interference did not alter the staying time at a patch (an exuding spot on a tree) for V. mandarinia, Rhomborrhina japonica, and Neope goschkevitschii. Interference‐mediated departure from a patch was less frequent than departure without interference for all nine species observed, except for R. japonica. These behavioural contexts varied yearly for several species.4. These results suggest that interference competition is a minor determinant of overall community structure, despite its conspicuousness. This weak effect of interference may be attributed to the short stay of dominant species and to individual behavioural responses, such as competitor avoidance. The variable influence of interference might be related to differences in species attributes, such as dominance hierarchies.

EVIDENCE FOR COEVOLUTION OF SOCIALITY AND RELATIVE BRAIN SIZE IN THREE ORDERS OF MAMMALS

As the brain is responsible for managing an individual's behavioral response to its environment, we should expect that large relative brain size is an evolutionary response to cognitively challenging behaviors. The "social brain hypothesis" argues that maintaining group cohesion is cognitively demanding as individuals living in groups need to be able to resolve conflicts that impact on their ability to meet resource requirements. If sociality does impose cognitive demands, we expect changes in relative brain size and sociality to be coupled over evolutionary time. In this study, we analyze data on sociality and relative brain size for 206 species of ungulates, carnivores, and primates and provide, for the first time, evidence that changes in sociality and relative brain size are closely correlated over evolutionary time for all three mammalian orders. This suggests a process of coevolution and provides support for the social brain theory. However, differences between taxonomic orders in the stability of the transition between small-brained/nonsocial and large-brained/social imply that, although sociality is cognitively demanding, sociality and relative brain size can become decoupled in some cases. Carnivores seem to have been especially prone to this.

A single high dose of cocaine induces differential sensitization to specific behaviors across adolescence

Adolescence is a critical period for drug addiction. Acute stimulant exposure elicits different behavioral responses in adolescent and adult rodents. The same biological differences that mediate age-specific behavioral responsiveness to stimulants in rodents could contribute to increased addiction vulnerability in adolescent humans. This study compared the ability of a single high dose of cocaine (40 mg/kg) to induce behavioral sensitization to a challenge dose of cocaine (10 mg/kg) 24 h later in young adolescent postnatal day 28 (PN 28), mid-adolescent (PN 42), and young adult (PN 65) male rats. Horizontal activity was resolved into ambulatory and non-ambulatory movements. An observational behavioral rating was obtained by recording specific behaviors. We examined if individual behavioral responses to novelty and cocaine correlate with sensitization in each age group. Single dose cocaine pretreatment induced behavioral sensitization to non-ambulatory horizontal activity, sniffing behaviors, and stereotypies in animals of all ages. Ambulatory sensitization was observed only in the youngest adolescents. Cocaine pretreatment caused greater increases in stereotypies in the young adolescents than in adults. The magnitude of the behavioral response to the initial cocaine treatment was positively correlated with the magnitude of sensitization in individual young adolescents. High levels of novelty-induced ambulatory activity only correlated with the magnitude of ambulatory sensitization in the youngest adolescents. We conclude that a single high dose of cocaine produces age-specific patterns of behavioral sensitization. Young adolescent rats appear to be more sensitive than adults to some of the behavioral alterations induced by a single high dose of cocaine.

A Unified Likelihood‐Based Approach for Estimating Population Size in Continuous‐Time Capture–Recapture Experiments with Frailty

A unified likelihood-based approach is proposed to estimate population size for a continuous-time closed capture-recapture experiment with frailty. The frailty model allows the capture intensity to vary with individual heterogeneity, time, and behavioral response. The individual heterogeneity effect is modeled as being gamma distributed. The first-capture and recapture intensities are assumed to be in constant proportion but may otherwise vary arbitrarily through time. The approach is also extended to capture-recapture experiments with possible random removals. Simulation studies are conducted to examine the performance of the proposed estimators. By asymptotic efficiency comparison and simulation studies, the proposed estimators have been shown to be superior to their discrete-time model counterparts in genuine continuous-time capture-recapture experiments.

Sex-specific behavioural responses of elk to spatial and temporal variation in the threat of wolf predation

We studied individual and herd level behavioural responses of elk to spatial and temporal variation in the risk of predation by wolves over three winters in the Upper Gallatin drainage, Montana, U.S.A. Within a given drainage, elk of both sexes moved into or closer to protective cover (timber) in response to wolf presence. Cow elk responded to elevated risk by increasing vigilance in exchange for foraging, and large mixed (cow, calf, spike) herds substantially decreased in size. In contrast, when wolves were present, bulls did not increase vigilance levels, or decrease feeding, and small bull-only groups slightly increased in size. As a consequence, small bull-only herds and large mixed-sex herds converged on a similar size when wolves were present. We think this response is a balancing of the benefits of risk dilution with increased detectability or attractiveness of larger herds to wolves. Based on proportions in the population, wolves overselected bulls and underselected cows as prey. Thus, bulls showed weaker antipredator responses than cows, despite facing a greater risk of predation. Using marrow fat content from elk killed by wolves as an indicator of body condition, bulls were in significantly worse body condition than cows throughout the winter, and condition deteriorated for both sexes as winter progressed. Overall, we conclude that antipredator behaviours carry substantial foraging costs, that bulls, because of their poorer body condition, are less able to pay these costs than cows, and that differences in ability to pay foraging costs probably explain sex-specific differences in antipredator behaviours.

Cognitive enrichment affects behavioural reactivity in domestic pigs

Cognitive challenges presented in connexion with the foraging behaviour of animals may have the potential to enrich the housing environment of captive animals, and thus can have beneficial effects on their behaviour and welfare. Therefore, we have developed a food-rewarded learning system based on a combination of classical and operant conditioning for groups of domestic pigs using acoustic cues (‘call-feeding station’). The present study investigated the characteristics of learning behaviour in seven experimental groups ( n = 8 individuals each) of growing pigs in postnatal weeks 7–20. The behavioural budget of each group was observed weekly within the housing environment and compared to seven conventionally fed control groups ( n = 8) which were supplied with an equal food amount. The alterations of individual behavioural responses after 6 and 12 weeks of cognitive enrichment were analysed in combined open-field/novel-object tests and compared to controls. All experimental pigs were able to discriminate reliably an individual tone that was associated with a locally changing feeding site. Generally, the animals were also willing to work for food (push a button with increasing fixed ratio, FR) but this motivation varied considerably between the groups ranging from FR 1 to 10. Sustained cognitive enrichment also affected other behavioural patterns within the housing environment as indicated by an increased locomotor behaviour and less belly nosing. Behavioural test responses were altered towards a greater reduction in open-field activity as well as a reduced excitement and fear behaviour compared to control pigs. Behavioural differences seem to be more pronounced the longer pigs were faced with the cognitive challenge. However, with equal food intake, the weight gain of the experimental pigs was not different compared to the controls. The present study suggests that, in domestic pigs, the presented cognitive enrichment may induce repeated positive appraisals in pigs by the association of successful coping with a demanding behavioural task rewarded by several small portions of food during the day. This appears to agree very well with pigs’ motivational needs and may also be applicable for animal welfare enhancing management of feeding.

The tachykinin NK 3 receptor antagonist SR142801 blocks the behavioral effects of cocaine in marmoset monkeys

Brain neuropeptide transmitters of the tachykinin family are involved in the organization of many behaviors. However, little is known about their contribution to the behavioral effects of drugs of abuse. Recently, the tachykinin NK 3 receptor, one of the three tachykinin receptors in the brain, was shown to attenuate the acute and chronic behavioral effects of cocaine in rats. In order to test if these findings can be generalized to primates we investigated the role of the tachykinin NK 3 receptor in the acute behavioral effects of cocaine in marmoset monkeys ( Callithrix penicillata) using a figure-eight maze procedure. Animals were pretreated with the tachykinin NK 3 receptor antagonist, ( R)-( N)-[1-[3-[1-benzoyl-3-(3,4-dichlorophenyl)piperidin-3-yl]propyl]-4-phenylpiperidin-4-yl]- N-methylacetamide (SR142801; 0, 0.02, 0.2, 2.0 mg/kg, i.p.), and received either a treatment with cocaine (10 mg/kg, i.p) or saline (i.p.). Cocaine increased locomotor activity and aerial glance behavior, but reduced exploratory and bodycare activities, scent marking and terrestrial scanning behavior. A sensitivity analysis revealed that two responder types can be differentiated in relation to the occurrence of a hyperlocomotor response to cocaine. SR142801 blocked the actions of cocaine on several behaviors dose-dependently for each responder type, respectively. There was no effect of SR142801 alone on any behavior measured. These data suggest that the tachykinin NK 3 receptor contributes to the individual behavioral response to cocaine in marmoset monkeys. Having no behavioral effects on its own, but blocking the cocaine effects, might suggest the tachykinin NK 3 receptor antagonist, SR142801, as a potential treatment of cocaine addiction in humans.

Influence of age, kinship, and large-scale habitat quality on local foraging choices of Siberian jays

The dynamics of natural populations may be influenced by a variety of factors, ranging from feeding interference and territoriality to the risk of predation and climatic effects. The relative influence of these factors may be contingent upon the quality of the habitat in which individuals reside. A factor that can largely affect population dynamics and that often covaries with habitat structure is predation risk. However, the combined effect of habitat and predation risk can vary according to the social context and intrinsic characteristics that affect individual behavioural responses. This thesis investigates the effects of habitat quality at the level of the population and the individual, and examines how it relates to the above factors in Siberian jays (Perisoreus infaustus), a territorial, group-living species in which the main cause of mortality is predation. The results demonstrate a strong effect of habitat on survival, reproduction and behaviour. Mortality was generally higher in open areas and managed forests and reproductive success decreased after forest management. Breeding females were more sensitive to environmental factors than males, possibly because of higher reproductive costs. Estimates of spatial demography suggested that there were more sinks than sources, and that they were located in open, managed forests. Behavioural decisions confirmed that open forests were associated with higher predation risks. However, decisions depended on social context; immigrants took highest risks and were the recipients of most aggression, largely an effect of social subordination. Also, parents provide their offspring with benefits that are withheld from immigrants. As a result, first-year survival was higher in retained offspring. Investigating the effects of multi-scale habitat quality on individual behaviour and population dynamics has generated an increased understanding of the effects of forest management on the dynamics of this population. This approach should facilitate development of an effective conservation management policy for this species.

Elevated corticosterone levels elicit non-calling mating tactics in male toads independently of changes in circulating androgens

Competition among males for a limited number of females may result in the expression of condition-dependent alternative mating tactics. In such cases, decision rules mediating mating tactic expression are likely to be influenced by a male's external as well as internal environment. For example, experimental studies with anuran amphibians (frogs and toads) indicate that changes in the social-acoustic environment alter the probability that an individual adopts a calling versus non-calling “satellite” mating tactic. However, there is considerable variation in the behavioral responses of individuals in such studies, suggesting that physiological differences among individuals play an important role in tactic expression. For instance, recent models predict that natural elevation in adrenal glucocorticoids during vocal production alters androgen production and/or neural activity to mediate transitions between reproductive tactic expression in anuran amphibians. Using corticosteroid injections, we show that elevation in circulating corticosterone levels significantly increase the probability that free-ranging male Great Plains toads ( Bufo cognatus) and Woodhouse's toads ( B. woodhousii) adopt a non-calling satellite tactic. Corticosterone-induced behavioral transitions occurred rapidly (<1 h) and independently of fluctuations in circulating androgen levels, suggesting a direct effect of glucocorticoids on brain centers controlling vocal production. We discuss our findings in the context of behavioral studies that alter the social-acoustic environment to examine its influence on tactic expression.

Non‐lethal control of wildlife: using chemical repellents as feeding deterrents for the European badger Meles meles

Summary Non‐lethal methods of controlling wildlife foraging damage may offer conservation, ethical, legal and efficacy advantages over lethal control. Chemical repellents present a potential non‐lethal approach, but have not been adequately researched in natural environments. Many previous studies have been poorly designed and a lack of data on individual behavioural responses has limited the practical development of repellents. We aimed to identify effective repellents for resolving feeding conflict with wild mammals, using European badgers Meles meles as models. We tested the relative efficacy of capsaicin, cinnamamide and ziram, in a multichoice paradigm, using remote video‐surveillance to obtain detailed behavioural observations of known free‐ranging individuals. Treatment nights were alternated with control nights over 56 nights. Badgers discriminated precisely between the four treatments, demonstrating a clear preference for untreated baits, followed by cinnamamide and capsaicin (in no particular order) and then ziram. All untreated baits, and baits treated with capsaicin or cinnamamide, were eaten throughout the trial. Ziram baits were fully consumed on treatment nights 1 and 2. Ziram consumption then declined to zero between treatment nights 3 and 9, this coinciding with a sharp rise in bait patch rejection. This ‘learning curve’ peaked at treatment night 7. We conclude that badgers developed conditioned taste aversion towards ziram‐treated baits at this point. Ziram bait consumption was practically zero over the last 20 treatment nights (40 trial nights) and individuals avoided ziram baits, without sampling, for the last 12–22 treatment nights (24–44 trial nights). Observed changes in badger behaviour suggested that avoidance at a distance was facilitated by odour cues. Synthesis and applications. This study provides proof of the concept that ziram has clear potential for reducing badger feeding damage through conditioned taste aversion to an odour. Our detailed observations allowed us to elucidate the behavioural mechanism involved, crucial for directing future development of this approach, thus demonstrating the importance of studying individual responses in wildlife management research. Second‐order conditioning, such as this, might be applicable to managing other wild mammals. The next step will be to develop a strategy for use in wildlife damage situations.

Pharmacokinetic considerations in the treatment of attention-deficit hyperactivity disorder with methylphenidate.

Methylphenidate is commonly used for the treatment of attention-deficit hyperactivity disorder (ADHD). Its efficacy in improving the core symptoms of ADHD, as well as some of the aggressive and oppositional behaviours, is well documented, based on a large volume of research. Methylphenidate has a wide margin of safety and relatively mild adverse effects, most commonly appetite suppression and insomnia. Methylphenidate is a rapidly absorbed medication that, in its d-isomer form, readily penetrates the CNS, particularly the striatum. It appears to function by blocking the reuptake of dopamine. Both the plasma concentrations and behavioural effects of methylphenidate demonstrate a time to maximum of between 1 and 3 hours, with the maximum behavioural effects occurring when the plasma concentrations are increasing. Because of the rapid onset of action, the effects of methylphenidate can be dramatic but usually last only about 4 hours with the immediate-release formulation. The behavioural responses of individuals are also highly variable, so that it is necessary to start treatment at a low dosage and increase up to a maximally effective dosage (usually starting at 10-15 mg/day with increases of 10-15mg at weekly intervals to a maximum dosage of 60 mg/day, irrespective of formulation). Because of the variability in behavioural responses, assessment of plasma concentrations is not clinically useful nor does weight help in deciding an appropriate dosage. The difficulties in administering methylphenidate multiple times a day, particularly during the school day, have been alleviated in the past few years by the development of extended-release preparations with varying behavioural effects lasting 8-12 hours. The 8-hour preparations (Metadate) CD and Ritalin) LA) utilise a microbead technology, while the 12-hour preparation (Concerta) utilises an osmotic pump system. All extended-release formulations effectively control the symptoms of ADHD. While pharmacokinetic differences appear to exist between some of these new formulations, there are currently no clinical data available to demonstrate clinical efficacy differences between them.

Management of insomnia in patients with chronic pain conditions.

The management of insomnia in patients experiencing chronic pain requires careful evaluation, good diagnostic skills, familiarity with cognitive-behavioural interventions and a sound knowledge of pharmacological treatments. Sleep disorders are characterised by a circular interrelationship with chronic pain such that pain leads to sleep disorders and sleep disorders increase the perception of pain. Sleep disorders in individuals with chronic pain remain under-reported, under-diagnosed and under-treated, which may lead--together with the individual's emotional, cognitive and behavioural maladaptive responses--to the frequent development of chronic sleep disorders. The moderately positive relationship between pain severity and sleep complaints, and the specificity of pain-related arousal and mediating variables such as depression, illustrate that insomnia in relation to chronic pain is multifaceted and poorly understood. This may explain the limited success of the available treatments. This article discusses the evaluation of patients with chronic pain and insomnia and the available pharmacological and nonpharmacological interventions to manage the sleep disorder. Non-pharmacological interventions should not be considered as single interventions, but in association with one another. Some non-pharmacological interventions especially the cognitive and behavioural approaches, can be easily implemented in general practice (e.g. stimulus control, sleep restriction, imagery training and progressive muscle relaxation). Hypnotics are routinely prescribed in the medically ill, regardless of their adverse effects; however, their long-term efficacy is not supported by robust evidence. Antidepressants provide an interesting alternative to hypnotics, since they can improve pain perception as well as sleep disorders in selected patients. Sedative antipsychotics can be considered for sleep disturbances in those patients exhibiting psychotic features, or for those with contraindications to benzodiazepines. Low doses of sedative antipsychotics may improve chronic insomnia in the elderly. However, no intervention is likely to be effective unless a good physician-patient relationship is developed.

The effects of combined aromatase inhibitor and anti-androgen on male territorial aggression in a tropical population of rufous-collared sparrows, Zonotrichia capensis

Territorial aggression, exhibited by male vertebrates in a reproductive context, is generally thought to be mediated by elevated levels of the gonadal steroid hormone testosterone. Rufous-collared sparrows from Papallacta, Ecuador are only aggressive during the breeding season when plasma testosterone concentrations are elevated. However, previous experiments have determined that during the breeding season testosterone does not increase in response to territorial challenges and testosterone implants do not make males more aggressive. This relationship between testosterone and aggression is different from closely related northern latitude species. We conducted another experiment investigating the role of testosterone in mediating territorial aggression, during the breeding season, in male rufous-collared sparrows. We predicted that blocking the actions of the testosterone would suppress aggression in response to territorial challenges. During the early breeding season males were captured using a simulated territorial intrusion and there was no relationship between time to capture and plasma testosterone, dihydrotestosterone, and corticosterone concentrations. Individual males were then implanted with both the aromatase inhibitor ATD and the anti-androgen Flutamide or empty implants as a control. After one week, birds were challenged with a simulated territorial intrusion and the aggressive responses measured. There were no differences in individual behavioral responses (number of songs, flights, closest approach, or time within 5 m) or overall aggression between the two groups. Androgen levels were elevated, post-implant, in the experimental group suggesting that the treatment was successful by blocking the negative feedback system. We conclude that pharmacologically inhibiting testosterone during the breeding season does not affect territorial aggression in these birds.

A scalar analysis of landscape connectivity

Landscape connectivity is critical to the maintenance of spatially‐structured populations and consists of both a structural component, which describes the shape, size and location of landscape features; and a biological component, which consists of both the response of individuals to landscape features, and the patterns of gene flow that result from those individual responses. Traditional studies of landscape connectivity have attempted to discern individual behavioral responses to landscape features, but this methodology is intractable for many species. This paper is an attempt to relate the components of landscape connectivity through the explicit treatment of their spatial and temporal scales. Traditional measures of structural and biological components of connectivity are reviewed and more recently developed methods for the analysis of scale for each are introduced. I then present a framework for the comparison of scalar phenomena based on Watt's unit pattern, describe the potential outcomes of the comparison and discuss the implications of each. Several testable hypotheses emerge from the analysis that may serve as a useful framework for the investigation of landscape connectivity in the future.

Response to novelty as a predictor of cocaine sensitization and conditioning in rats: a correlational analysis.

An animal's response to novelty has been suggested to be a predictor of its response to drugs of abuse. The possible relationship between an individual's behavioral response to novelty and its subsequent behavioral response to cocaine has not been subjected to a detailed correlational analysis. To use a repeated cocaine treatment protocol to induce cocaine sensitization and conditioned cocaine locomotor stimulant effects and to assess the relationship of these effects to pre-cocaine locomotor behavior in a novel environment. In two separate experiments, rats were given a 20-min test in a novel open-field environment. Subsequently, the rats were given a series of additional tests in conjunction with either saline or cocaine (10 mg/kg) treatments to induce cocaine sensitization and conditioned effects. The repeated cocaine treatments induced cocaine behavioral sensitization and conditioned effects. Correlational analyses showed that the initial 20-min novel environment test proved to be a strong predictor of an animal's subsequent saline activity level but did not predict the rats' behavioral acute and sensitized response to cocaine. When change in activity was used as the dependent variable, initial activity level was reliably negatively correlated with activity changes on cocaine tests as well as cocaine conditioning tests. The negative correlation between initial activity in a novel environment and the change in activity induced by cocaine indicates that low responders to environmental novelty tend to have the strongest response to cocaine. These results appear consistent with the classic initial value and response rate dependent analyses of stimulant drug effects.

Differential effects of support providers on adolescents' mental health

This prospective study examined the differential effects of parent, teacher, and peer social support on depression and self-esteem of 217 adolescents, ages 15 to 18. Results indicate that female adolescents perceived significantly more support from friends than male adolescents did, whereas male adolescents perceived significantly more support from fathers than female adolescents did. No gender differences were found in perceptions of support from mothers or teachers. Boys and girls perceived the least amount of support from fathers compared with other providers. Multisample structural equation models were invariant across female and male groups for the effects of support providers on each outcome. The joint effects of the support providers explained a significant amount of variance in time 2 depression and self-esteem, after controlling for both at time 1, suggesting that social support has important effects on symptoms. The separate effects of mothers, teachers, and friends had similarly sized, significant negative effects on time 2 depression. Self-esteem was significantly, positively affected by friend and teacher support. Key words: adolescence; depression! mental health; self-esteem; social support ********** Current theory and research suggest that not all social support is the same. Two important influences on the effectiveness of support are the characteristics of the provider and of the recipient (Antonucci, 1983). For example, alternate support providers such as parents and peers differentially affect adolescent outcomes such as mental health and academic achievement (Barone, Iscoe, Trickett, & Schmid, 1998; Garnefski & Diekstra, 1996; Richman, Rosenfeld, & Bowen, 1998; Wentzel, 1998). In terms of recipient characteristics, research has consistently found gender differences in the amount and kind of support that adolescents receive and from whom they receive it (Berndt, 1982; Cauce, Reid, Landesman, & Gonzales, 1990; Colarossi, 2001; Furman & Buhrmester, 1992; Levitt, Guacci-Franco, & Levitt, 1993). For example, girls receive more support from peers than boys do, whereas boys receive more support from family sources than girls do. If these supporters have different impacts on developmental outcomes, then balance and appropriate use are the challenges for adolescents as they begin to diversify their support networks. Unfortunately, there is a paucity of studies that simultaneously contrast the effects of multiple providers and recipients on specific adolescent outcomes. A descriptive study published recently in Social Work Research (Colarossi, 2001) related findings from a sample of adolescents that showed gender differences in the amount and satisfaction of support received by various providers. The prospective study presented here follows up the same sample to test the differential relation of support from three contexts (that is, family, school, and peers) on depression and self-esteem with adolescents over the course of one year. Multisample structural equation models were used to examine gender differences in the predictive models. THEORETICAL FOUNDATION This study builds on a foundation of theory and research describing developmental processes, gender differences in social support, and the effects of support on mental health. Kahn and Antonucci's (1980) Convoy Model of social support posits that social support develops over time from person-environment interaction that involves attachment processes, social role requirements, and characteristics of the social network composition and its support provisions. These interactions have aspects of both stability and change over the life course, in which social context is an important moderating factor in addition to an individual's personality style, role demands, and emotional and behavioral responses. This life-course perspective is important for several reasons. An individual's need for social support varies with age-related changes such as dependence on others, social roles related to occupational and social status (for example, student, parent, employee or employer, or friend or spouse), and changes in residence (for example, living with family, living on college campus, or living in different neighborhoods). …

Fractal analysis of Daphnia motion for acute toxicity bioassay.

To quantify individual behavioral responses to toxic chemicals, the swimming motion of individual Daphnia magna was continuously monitored using a motion analysis system. The fractal dimension was introduced to compare the straightness or complexity of the swimming trajectory before and after exposure to toxic chemicals. Analysis indicated that the swimming trajectory of individual Daphnia has a fractal structure. The basal fractal dimension in the control medium was 1.35+/-0.01 (n = 50 Daphnia). Exposure to CuSO(4) (10 microg/L), organophosphorus (Dichlorvos; 10 microg/L), and carbamate (Propoxur; 500 microg/L) pesticide caused a significant increase in the fractal dimension with a latency of 60 min, reaching a maximal level of 2.26+/-0.34, 2.43+/-0.19, and 2.51+/-0.21, respectively, after a 120-min exposure. The magnitude of the change in the fractal dimension was related to the toxic chemical concentration and the exposure time. Threshold concentrations determined at 60 min of exposure were 10 microg/L for CuSO(4), 5 microg/L for Dichlorvos, and 500 microg/L for Propoxur. The toxicity index (EC(50)) values after 120 min of exposure were 6.31 microg/L, 7.64 microg/L, and 466 microg/L for CuSO(4), Dichlorvos, and Propoxur, respectively. Thus, the fractal dimension seems useful for analyzing and comparing complex trails, such as swimming trajectories, which could be used as the endpoint for an acute bioassay.