School completion and progression to higher education in adolescents with social anxiety: a linkage between Young-HUNT3 and national educational data (2008-2019), Norway.

BACKGROUND: Social anxiety disorder (SAD) most commonly develops in adolescence-a period of life that includes a transition to upper secondary school. The aim of this study is to investigate the extent to which social anxiety in adolescence is associated with the completion of upper secondary school and progression to higher education. METHODS: This longitudinal study includes 8,192 adolescents aged 13-19 years who participated in the Norwegian Young-HUNT 3 population-based study. Social anxiety is measured employing (1) diagnostic interview screening questions (interview) and (2) a self-reported symptom index (questionnaire). Notably, we define the cohorts based on these two methods. Using national educational data (2008-2019), we follow educational attainment among the cohorts until they turn 25 years of age. RESULTS: We found that adolescents who screened positive (SP) for SAD had a predicted probability of upper secondary school completion at 21 years of age that was 14% points lower than those who screened negative (SN). Further, differences remained when looking at completion rates at age 25 years. Moreover, predicted probabilities for completion were inversely associated with increasing levels of self-reported social anxiety symptoms. Similarly, the proportion of the completers of an academic program in the SP group that were enrolled in higher education by 25 years of age, were lower than for the SN group (87 vs. 92%). CONCLUSION: Social anxiety in adolescence, both self-reported symptoms and diagnostic screening, has long-term negative impact on upper secondary school completion and to some extent enrollment to higher education.

Mitigating adolescent social anxiety symptoms: the effects of social support and social self-efficacy in findings from the Young-HUNT 3 study.

Adolescents' exposure to negative life events (NLEs) and potentially traumatic events is highly prevalent and increases their risk of developing psychological disorders considerably. NLE exposure has also been linked to the development of social anxiety disorder (SAD) among older children and young adolescents. Despite the relatively low treatment efficacy reported for children and adolescents suffering from SAD, few studies have addressed the extent to which resilience factors, such as social support and social self-efficacy, are associated with SAD symptoms. This study examined whether social support and social self-efficacy predict, and buffer against SAD symptoms using a large, population-based sample of adolescents, among whom a large proportion have experienced NLEs. The results reveal that NLEs are significantly associated with SAD symptoms, while social support and social self-efficacy are both negatively associated with SAD symptoms. Only the NLEs × social support interaction significantly predicted SAD symptoms, with social support attenuating the association between NLEs and SAD symptoms. Moreover, increases in both social self-efficacy and social support were associated with reduced SAD symptoms, over and above variance explained by social support alone. Our cumulative results suggest that interventions that can modify both social support and social self-efficacy may help reduce SAD symptoms in at-risk adolescents.

A randomized controlled trial of individual cognitive therapy, group cognitive behaviour therapy and attentional placebo for adolescent social phobia.

BACKGROUND: Very few studies have investigated the effects of individual disorder-specific treatment of social phobia (SP) in adolescents. The objective of this study was to compare the effects of individual cognitive therapy for SP, group cognitive behavioural therapy (CBTG) and attentional placebo (AP) among adolescents with a primary diagnosis of SP. METHODS: A randomized controlled design was used, and a total of 279 adolescents were assessed. Fifty-seven adolescents, between 13 and 16 years old, were allocated to individual cognitive therapy, CBTG or AP. The participants were assessed before treatment, at the end of treatment and at a 12-month follow-up using both self-report and a semi-structured interview. RESULTS: The individual cognitive therapy showed significant reductions in symptoms, impairment and diagnostic criteria both at the end of treatment and at the 12-month follow-up. Compared with CBTG and AP, the individual cognitive therapy group demonstrated significantly greater effects on both symptom reduction and impairment. There were no significant differences between CBTG and AP. CONCLUSIONS: In a direct comparison between the most commonly used treatments for adolescent SP, we found that individual therapy was the most effective, yielding better effects than both CBTG and AP.

Does emotion regulation mediate the effect of stressful life events on depressive symptoms in adolescents?

INTRODUCTION: Adolescents' exposure to stressful life events (SLEs) is highly prevalent and increases their risk of developing depression considerably. A small number of studies have addressed the extent to which resilience factors, such as the ability to emotionally regulate, mediate the relationship between SLEs and depression. This study examined whether emotion regulation mediates and significantly attenuates the direct path between SLEs and depressive symptoms in a nonclinical sample of adolescents. METHOD: A sample of 235 first- and second-year high-school students completed the Depression Anxiety Stress Scale, the Risk Factor Questionnaire, and the Difficulties in Emotion Regulation Scale. Mean age was 16.9 (SD = 1.8) years, and 65 % (n = 152) of the participants were female. To assess for mediation, a regression-based path analysis approach was used. RESULTS: SLEs were significantly (t = 5.13, p < 0.001) associated with depressive symptoms, explaining 59.1 % of the total variance. Controlling for the mediation variable (emotion regulation), we found a reduced but statistically significant direct effect (t = 2.87, p = 0.005) between SLEs and depressive symptoms. A statistically significant indirect effect explaining 64.6 % of the total effect demonstrated partial mediation from stressful life events to depressive symptoms via emotion regulation. LIMITATIONS: Our analyses are based on correlational and cross-sectional data and thus exclude statistical examination of temporal causal relationships, and assessments of whether reported affects are stable over time. CONCLUSIONS: Our results indicate that interventions that can modify the ability to regulate emotions may help reduce depressive symptoms in at-risk adolescents.

Social anxiety disorder in adolescents: Prevalence and subtypes in the Young-HUNT3 study.

BACKGROUND: Few studies have examined the prevalence of social anxiety disorder (SAD) among adolescents and the associated sex-specific fears. No previous studies have reported variance in SAD prevalence among adolescents based on a stepwise diagnostic approach. METHODS: Using various diagnostic thresholds from the Anxiety Disorders Interview Schedule child version, and the diagnostic criteria from both the 4th and 5th editions of the Diagnostic and Statistical Manual of Mental Disorders (DSM), we explored the point prevalence of SAD among a population-based sample of 8216 adolescents aged 13-19 years. RESULTS: Overall, 2.6% of adolescents met the SAD diagnostic criteria. The prevalence varied from 2.0% to 5.7% depending on the criteria-set. Twice as many females met the overall SAD criteria. The DSM-IV generalized SAD subtype was assigned to 86.5% of the sample, while 3.5% met the DSM-5 performance-only subtype. Compared with males aged 16-19 years, significantly more of those aged 13-15 years met the SAD criteria; no significant age group differences were found among females. CONCLUSIONS: This is the first study to demonstrate variance in SAD prevalence among adolescents based on the diagnostic threshold method. Depending on the threshold applied, SAD prevalence among adolescents varied from 2.0% to 5.7%. Age and sex differences in social fear experiences highlight the importance of considering developmental heterogeneity in SAD, especially for adapting prevention and treatment interventions.

Variations in the relative age effect with age and sex, and over time-Elite-level data from international soccer world cups.

The relative age effect (RAE) is a statistical bias observed across sport contexts and consists of a systematic skewness in birth date distribution within an annual-age cohort. In soccer, January 1st is the common cut-off date when categorizing players in competitions according to their chronological age, which potentially disadvantages those within the cohort who were born later in the year. Thus, relatively older soccer players in their cohort can be favored in talent identification, selection, and development. The aim of the current study was to investigate the variations in RAE in male and female international youth world-cup tournaments (U17 and U20) in the period from 1997-2019 and in international senior world-cup-tournaments from 2006-2019. A total of 20,401 soccer players participating in 47 different tournaments were analyzed. The birthdate distributions were categorized into four quartiles (January-March, Q1; April-June, Q2; July-September, Q3; October-December, Q4) and compared to a uniform distribution using Chi-square analysis with Cramer's V (Vc) as a measure of effect size. Based on the existing data concerning RAE in elite junior and senior soccer, it was hypothesized that: (I) the RAE is present in youth soccer world cup tournaments but is stronger in male players than in female players; (II) the younger the soccer players, the stronger the RAE; and (III) the RAE in world cup soccer tournaments has strengthened over time. All these hypotheses were supported by the data; novel findings included that the effect has now entered women's soccer, and in men's soccer it persists into senior world cup tournaments. Thus, a strong RAE bias occurs in selection among elite soccer players competing in international world cup tournaments.

Interacting Constraints and Relative Age Effect in Elite Cross-Country Skiers and Freeskiers.

Different characteristics of sports disciplines potentially lead to skewness in birth month distribution (relative age effect, RAE). These characteristics can be considered from a constraint-based approach with interacting environmental, task, and individual constraints as a theoretical framework with which to examine variations in RAE. The main aim of the present study was to examine the theoretical predictions of the constraint-based framework by investigating the birth month distribution in cross-country skiers and freeskiers at elite junior and senior levels. The sample was comprised of top ranked Norwegian U15-U19/20 cross-country skiers and junior-level freeskiers. Birth months of top ranked international senior-level skiers in cross-country and freeskiing were also collected. Results indicated an over-representation of skiers born in the first half versus the second half of the year at all junior ages in cross-country skiing. There was no significant difference in the distribution of birth months in freeskiing or in senior cross-country skiers or freeskiers. Based upon the interacting constraint framework, the skewness towards more early-born athletes in junior cross-country skiing could be due to strict age-grouped and results-oriented developmental programs beginning at an early age (environmental constraints) as well as high-demand for physical capabilities (task constraints) that favour more physically mature athletes (individual constraints). For freeskiing, the interacting environmental (less structured and more individualistic-oriented development), task (high technical/motor skill demands), and individual (no advantage of advanced physical maturation) constraints potentially operate in the opposite direction compared to cross-country skiing.

In Pursuit of a Comprehensive Understanding of Expertise Development: A Comparison between Paths to World-Class Performance in Complex Technical vs. Endurance Demanding Sports.

A comprehensive understanding of skill acquisition is important for different performance domains, and has practical implications for both sport sciences and public health. The study compared important constraints for expertise development in a physically demanding sport (cross-country skiing) versus a technically demanding sport (freeskiing). Eighteen world-class athletes reported the importance of different constraints for their developmental history subdivided into two age spans: (1) 7-15 years and (2) 16 years until present. The total amount of training did not differ between the groups, but from the age of 16, the cross-country skiers spend approximately 98% of their training specific to their main sport, compared to 75% for freeskiers. No differences were found between the distribution of organized versus non-organized training in main sport, but freeskiers reported a higher amount of unorganized training in other sports after the age of 16. No differences were found in perceived importance of facilities, enjoyment of performing their sport, or the need for early specialization of training. After the age of 16, the cross-country skiers reported a higher need for coach involvement compared to freeskiers. The two sports mainly share common paths to expertise but differ in the need for specific training and coach involvement.

Prevalence of depressive symptoms among older children and young adolescents: a longitudinal population-based study.

INTRODUCTION: This paper investigates levels of depressive symptoms among older children and young adolescents, 11-14 years of age. The population-based sample was assessed twice during a 12-month period. Point-prevalence, 12-month prevalence, and 12-month incidence were measured by a validated self-reported scale (SFMQ) and are presented in this paper. METHODS: A total of 2148 pupils were invited to participate in this study, and 1748 pupils and at least one parent/guardian provided informed consent. The population was assessed twice within one 12-month period resulting in 1439 participants at both data collection points. Depressive symptoms were measured by a validated self-reported scale, The Short Mood and Feelings Questionnaire (SMFQ). RESULTS: The results indicate that the point-prevalence was just under 10% in 6th to 10th grade with a 12-month prevalence at almost 3%. The results also indicate an incidence rate of 4.5% over 12-months. This study confirms that girls report a higher range of point prevalence, 12- month-prevalence, and 12-month incidence compared to boys. CONCLUSIONS: The results indicate that depressive symptoms among children and young adolescents is a serious health challenge. The results demonstrate substantial gender differences even at an early age (11-14 years), where girls report significantly higher point prevalence, 12-month-prevalence, and 12-month incidence compared to boys. Results from this study suggest that depressive symptoms are an important problem that young adolescents face, and the study underlines the need for more intervention tailored to gender at the middle-school level, especially with respect to those children and adolescents who experience persistent depressive symptoms.

Bilateral Interference in Motor Performance in Homologous vs. Non-homologous Proximal and Distal Effectors.

Performance of bimanual motor actions requires coordinated and integrated bilateral communication, but in some bimanual tasks, neural interactions and crosstalk might cause bilateral interference. The level of interference probably depends on the proportions of bilateral interneurons connecting homologous areas of the motor cortex in the two hemispheres. The neuromuscular system for proximal muscles has a higher number of bilateral interneurons connecting homologous areas of the motor cortex compared to distal muscles. Based on the differences in neurophysiological organization for proximal vs. distal effectors in the upper extremities, the purpose of the present experiment was to evaluate how the level of bilateral interference depends on whether the bilateral interference task is performed with homologous or non-homologous effectors as the primary task. Fourteen participants first performed a unilateral primary motor task with the dominant arm with (1) proximal and (2) distal controlled joysticks. Performance in the unilateral condition with the dominant arm was compared to the same effector's performance when two different bilateral interference tasks were performed simultaneously with the non-dominant arm. The two different bilateral interference tasks were subdivided into (1) homologous and (2) non-homologous effectors. The results showed a significant decrease in performance for both proximal and distal controlled joysticks, and this effect was independent of whether the bilateral interference tasks were introduced with homologous or non-homologous effectors. The overall performance decrease as a result of bilateral interference was larger for proximal compared to distal controlled joysticks. Furthermore, a proximal bilateral interference caused a larger performance decrement independent of whether the primary motor task was controlled by a proximal or distal joystick. A novel finding was that the distal joystick performance equally interfered with either homologous (distal bilateral interference) or non-homologous (proximal bilateral interference) interference tasks performed simultaneously. The results indicate that the proximal-distal distinction is an important organismic constraint on motor control and for understanding bilateral communication and interference in general and, in particular, how bilateral interference caused by homologous vs. non-homologous effectors impacts motor performance for proximal and distal effectors. The results seem to map neuroanatomical and neurophysiological differences for these effectors.

A Comparison of Motives by Gender and Age Categories for Training at Norwegian Fitness Centres.

Examining participatory motives clarifies what engages and keeps individuals participating in exercise. The popularity of training at fitness centres has greatly increased over the last two decades, but individual determinants for motivation remain uncertain. This study compared motives between gender and age categories in training and performing physical activity at Norwegian fitness centres. To compare motives, a survey utilising a standardised questionnaire (MPAM-R) was conducted at six different Norwegian fitness centres. It was hypothesised that the intrinsic motive socialisation and extrinsic motive fitness would be more important among the older age categories for both genders, while the extrinsic motive appearance and intrinsic motive enjoyment would be more important among younger age groups. A total response of 183 men and 150 women, aged 14-80 years, was divided into seven categories based on their age and included in the statistical analysis. The main findings after conducting a two-way analysis of variance (ANOVA) with repeated measures, were that the most important motive for training at fitness centres was increasing fitness, followed by enjoyment, competence, vitality and appearance. The social motive was rated the lowest. Women rated fitness and enjoyment higher compared to men, and men rated the motive for appearance higher than women, but this decreased with age in both genders. With increasing age, the importance of enjoyment and competence decreased in men, while women seemed to place increased importance on vitality with age. The importance of the social motive decreased first as age increased, but then increased again in the age group 41-50 years and older. It was concluded that the motives for participating in exercise at fitness centres was dependent on individual characteristics and that motives about training at fitness centres differed by gender and changed with age.

More Pronounced Bimanual Interference in Proximal Compared to Distal Effectors of the Upper Extremities.

Bimanual performance depends on effective and modular bilateral communication between the two bodysides. Bilateral neural interactions between the bodysides could cause bimanual interference, and the neuromuscular system for proximal and distal muscles is differently organized, where proximal muscles have more bilateral interneurons at both cortical and spinal level compared to distal muscles. These differences might increase the potential for bimanual interference between proximal arm muscles, because of greater proportions of bilateral interneurons to proximal muscles. The purpose of the present experiment was to evaluate potential differences in bimanual interference between proximal versus distal effectors in the upper extremities. 14 participants first performed a unilateral primary motor task with dominant arm with (1) a proximal and (2) distal controlled joysticks (condition A). Performance in condition A, was compared with the same effector's performance when a bimanual interference task was performed simultaneously with the non-dominant arm (condition B). The results showed a significant bimanual interference for both the proximal and distal controlled joysticks. Most interestingly, the bimanual interference was larger for the proximal joystick compared to the distal controlled joystick. The increase in spatial accuracy error was higher for the proximal controlled joystick, compared with the distal controlled joystick. These results indicate that the proximal-distal distinction is an important organismic constraint on motor control, and especially for bilateral communication. There seem to be an undesired bilateral interference for both proximal and distal muscles. The interference is higher in the case of proximal effectors compared distal effectors, and the results seem to map the neuroanatomical and neurophysiological differences for these effectors.

Player load in male elite soccer: Comparisons of patterns between matches and positions.

Our primary aim was to explore the development of player load throughout match time (i.e., the pattern) using moving 5-min windows in an elite soccer team and our secondary aim was to compare player load patterns between different positions within the same team. The dataset included domestic home matches (n = 34) over three seasons for a Norwegian Elite League team. Player movements (mean ± SD age 25.5 ± 4.2 years, height 183.6 ± 6.6 cm, body mass 78.9 ± 7.4 kg) were recorded at 20 Hz using body-worn sensors. Data for each variable (player load, player load per meter, total distance, accelerations, decelerations, sprint distance, high-intensity running distance) were averaged within positions in each match, converted to z-scores and averaged across all matches, yielding one time series for each variable for each position. Pattern similarity between positions was assessed with cross-correlations. Overall, we observed a distinct pattern in player load throughout match time, which also occurred in the majority of individual matches. The pattern shows peaks at regular intervals (~15 min), each followed by a period of lower load, declining until the next peak. The same pattern was evident in player load per meter. The cross-correlation analyses support the visual evidence, with correlations ranging 0.88-0.97 (p < .001) in all position pairs. In contrast, no specific patterns were discernible in total distance, accelerations, decelerations, sprint distance and high-intensity running distance, with cross-correlations ranging 0.65-0.89 (p < .001), 0.32-0.64 (p < .005), 0.18-0.65 (p < .005 in nine position pairs), 0.02-0.38 (p < .05 in three pairs) and 0.01-0.52 (p < .05 in three pairs), respectively. This study demonstrated similarity in player load patterns between both matches and positions in elite soccer competition, which could indicate a physical "pacing pattern" employed by the team.

The effects of depression and stressful life events on the development and maintenance of syndromal social anxiety: sex and age differences.

This study assessed age and sex differences in the prevalence and incidence rates of syndromal social anxiety (SSA), as well as the predictive role of depressive symptoms and stressful life events on the development and persistence of SSA. A sample of 1,439 young people, between 11 and 14 years of age, was assessed twice within a 12-month interval. No age differences were found. Girls had a significantly higher prevalence of SSA than boys, but there was no sex difference for incidence rate. Depressive symptoms did not play a significant role in either the development or the persistence of SSA, whereas SSA predicted the development of depression. Stressful life events played a significant role in SSA's development but not in its persistence.

Effect of Instructions Emphasizing Velocity or Accuracy Given in a Random or Blocked Order on Performance Testing and Kinematics in Dart Throwing.

The aims of this study were to investigate the effects of throwing instruction (i.e., velocity and accuracy) and testing order (random or blocked) on dart throwing performance testing and on the movement strategies leading to this performance. Twelve physical education students (nine men and three women, age: 24 ± 7.5; mass: 77.7 ± 15.8, height: 1.77 ± 0.06 m) performed dart throws with four different instructions, varying in priority regarding velocity and accuracy, instructed in a blocked and random manner. The main findings were that dart velocity decreased when the priority of accuracy increased. However, when accuracy was the main priority, accuracy increased only when measured for consistency. Testing order influenced peak joint kinematics of wrist flexion in addition to finger extension and the time of occurrence of elbow extension. Instructions emphasizing velocity and/or accuracy showed a clear speed-accuracy trade-off in dart throwing and thereby followed Fitts' law. Testing order had a minor effect on the speed-accuracy trade-off. The blocked testing order appeared to increase performance outcomes that favored the priority set by the instruction in contrast to the random test order. These differences were based upon adjustments of joint movements, which were based upon the knowledge of the previous attempts. These adjustments were visible between the different instructions through changes in the execution timing of peak wrist flexion and elbow and finger extension.

Interpersonal and intrapersonal entrainment of self-paced tapping rate.

Entrainment is a ubiquitous property not only of interacting non-linear dynamical systems but also of human movements. In the study reported here, two premises of entrainment theory were investigated in a tapping task conducted in both interpersonal (i.e. between individuals) and intrapersonal (i.e. between effectors) conditions. Hypothesis 1 was that interacting oscillatory systems should demonstrate synchronisation, which was predicted to emerge as in-phase tapping behaviour in both inter- and intrapersonal conditions. Support for Hypothesis 1 was observed in the in-phase synchronisation of tapping in both individual bimanual trials and uni-manual and bimanual tapping in dyads. By contrast, Hypothesis 2 was that the oscillatory system with the faster initial rate would decelerate, whereas the one with the slower initial rate would accelerate, as manifest in increased self-paced tapping rates amongst participants with initially slower rates and decreased rates amongst ones who initially tapped at faster rates. However, that pattern predicted in Hypothesis 2 was not observed; on the contrary, all participants increased their tapping rates in interpersonal conditions, which occurred significantly amongst participants with the lowest preferred tapping rates. Such an outcome indicates a novel aspect of synchronised movement in humans that warrants further investigation.

The Validity of Functional Threshold Power and Maximal Oxygen Uptake for Cycling Performance in Moderately Trained Cyclists.

Cycling is a popular sport, and evaluation of the validity of tests to predict performance in competitions is important for athletes and coaches. Similarity between performance in sprints in mass-start bike races and in the laboratory is found, but, to our knowledge, no studies have investigated the relationship between laboratory measurements of maximal oxygen uptake (VO2max) and functional threshold power (FTP) with performance in official mass-start competitions. The purpose of this study was to evaluate the validity of a 20 min FTP test and VO2max as predictors for performance in an official mountain bike competition. Eleven moderately trained male cyclists at a local level participated in this study (age: 43 ± 5.1 years; height: 183.4 ± 5.4 m; weight: 84.4 ± 8.7 kg; body mass index: 25.1 ± 2.1). All subjects performed a 20 min FTP test in the laboratory to measure the mean power. In addition, the subjects completed an incremental test to exhaustion to determine VO2max. These two laboratory tests were analyzed together with the results from a 47 km mass-start mountain bike race, with a total elevation of 851 m. A significant relationship was found between the mean relative power (W/kg) for the 20 min FTP test and performance time in the race (r = -0.74, P < 0.01). No significant correlation was found between VO2max and cycling performance for these subjects (r = -0.37). These findings indicate that a 20 min FTP test is a more valid test for prediction of performance in mass-start bike races than a VO2max test for moderately trained cyclists.

A Population Study of Relative Age Effects on National Tests in Reading Literacy.

We examined relative age effects (RAE) in national test results in reading literacy in Norway in 2013, in Grades 5, 8, and 9 students (n = 173,421) to estimate how month of birth is associated with mean scores and different achievement levels. The results confirm that there is an approximately linear decrease in test scores across months of birth for all grades and both genders. Consequently, students born early in the year are more likely to end up at higher achievement levels than students born later in the year. Possible explanations for this phenomenon are the greater maturity of older children and that they might be considered more gifted when compared with their younger peers. Further, we found increasing gap in test scores between girls and boys from grade 5 to 8 and 9. We suggest both maturity and motivational reasons for these differences.

Structural confirmation and occurrence of azaspiracids in Scandinavian brown crabs (Cancer pagurus).

In 2005 and 2006, azaspiracids were for the first time detected in brown crabs (Cancer pagurus) from the west coast of Sweden and the north and north-west coast of Norway. Azaspiracids are marine toxins that have been detected in blue mussels in Europe in recent years. On some occasions, they have been responsible for human intoxications with symptoms similar to those occurring by consumption of shellfish contaminated with okadaic acid group toxins. While the latter toxin group has been reported to accumulate in green crabs and brown crabs, azaspiracids have previously only been reported to occur in bivalve molluscs. LC-MS analysis of the hepatopancreas (HP) and roe of brown crabs revealed the presence of azaspiracid-1, -2 and -3, but only very low levels were detected in the white meat from the claws or the main shell. Mass spectral data were recorded using two different mass spectrometers, one with a triple-quadrupole mass analyzer and one with a linear ion-trap mass analyzer. The identities of the toxins were confirmed by comparing retention times and mass spectra of azaspiracid standards and the detected toxins. Levels detected ranged from 1.4 microg/kg tissue up to as much as 733 microg/kg tissue, although the majority of samples analyzed were below the suggested regulatory limit of 170 microg/kg HP. Higher levels were detected in HP compared with roe. Very little azaspiracids were detected in mussels from the same locations at the same time, and no proposed microalgal source of azaspiracids was reported in the water previous to or at the time of collection of the toxic crabs.

Effect of mouse strain and gender on LD(50) of yessotoxin.

The aim of the present study was to determine whether the intraperitoneal LD(50) for yessotoxin (YTX) in mice varies with strain or gender. Thirty-six male and 36 female mice, of body weight 16-20 g, from each of the strains ICR (CD-1), Swiss (CFW-1) and NMRI were employed. They were not fasted before YTX treatment. At each dose, nine mice were injected with YTX solutions at 1.0 mL/20 g body weight, and observed for 24h. Symptoms and time to death were recorded. Within each mouse strain and gender arm, the study was performed as a basic four level Response Surface Pathway designed trial with nine mice at each dose level. YTX was isolated from a culture of Protoceratium reticulatum. The LD(50) values for female and male mice, respectively, were estimated as 380 and 462 microg/kg for the ICR, 269 and 328 microg/kg for the Swiss, and 314 and 412 microg/kg for the NMRI strains. The increases in LD(50) from female to male mice were found to be 22% for ICR, 22% for Swiss and 31% for NMRI. The largest difference in LD(50) among mouse strains was detected between the ICR and Swiss strains, where the deviation was 41% in both females and males. The difference between mouse strains was found significant (p = 0.03). For all three strains, females were more susceptible than males, with a difference in LD(50) of 1.2-1.3-fold. The largest difference between the least- and most-susceptible strain was 1.4-fold for both females and males. The largest difference in LD(50), 1.7-fold, was observed between female Swiss and male ICR mice. The difference between genders was not significant (p = 0.12). These results indicate that other factors, like handling of the animals, and the source and handling of the toxin, may significantly influence the outcome of studies on acute toxicity since the reported differences in LD(50) vary by a factor of about seven.