The ontogeny of anxiety-like behavior in rats from adolescence to adulthood

In human beings, susceptibility to anxiety disorders can be relatively high during adolescence. Understanding the ontogeny of anxiety-like behavior in laboratory rodents has implications for developing anxiolytic drugs that are suitable for this age group. Given the dearth of information about adolescent rodents, this study examined the response of both male and female adolescent, late adolescent, young adult, and older adult rats to three tests of anxiety-like behavior: the emergence test (ET), open field (OF), and elevated plus-maze (EPM). The results showed that adolescent rats exhibited a higher anxiety-like response than adults on each test; the amount of locomotion in the OF and percentage of time spent on the open arms of the EPM increased across the age groups, while older adult rats made the fewest start box re-entries in the ET. These results support the hypothesis that adolescent rats have a more pronounced response to stressors than do adults.     

The ontogeny of exploratory behavior in male and female adolescent rats (Rattus norvegicus)

During adolescence, rats gain independence from their mothers and disperse from the natal burrow, with males typically dispersing further than females. We predicted that, if dispersal patterns are associated with responsiveness to novelty, exploratory behavior in novel environments would increase across adolescence, and males would explore more than females. Alternatively, females might explore more than males, if females are more motivated than males to learn about the immediate environment or if females have poorer spatial abilities than males. Twenty‐five male and 21 female rats were exposed to two novel environments (open field and elevated plus‐maze) during early, mid‐, or late adolescence. Total locomotion and amount of exploration directed towards aversive areas increased across adolescence, even when body weight was included as a covariate. Female adolescents locomoted more and spent more time exploring aversive areas than males. Developmental changes in neural function potentially underlie age and sex differences in exploratory behavior. © 2009 Wiley Periodicals, Inc. Dev Psychobiol 51: 513–520, 2009     

Social experience during adolescence in female rats increases 50 kHz ultrasonic vocalizations in adulthood,without affecting anxiety-like behavior

Adolescents are highly motivated to engage in social interactions, and researchers have hypothesized that positive social relationships during adolescence can have long term, beneficial effects on stress reactivity and mental well-being. Studies of laboratory rodents provide the opportunity to investigate the relationship between early social experiences and later behavioral and physiological responses to stressors. In this study, female Lister-hooded rats (N = 12 per group) were either (a) provided with short, daily encounters (10 min/day) with a novel partner during mid-adolescence (postnatal day 34–45; “social experience,” SE, subjects) or (b) underwent the same protocol with a familiar cagemate during mid-adolescence (“control experience,” CE, subjects), or (c) were left undisturbed in the home cage (non-handled “control,” C, subjects). When tested in adulthood, the groups did not differ in behavioral responses to novel environments (elevated plus maze, open field, and light-dark box) or in behavioral and physiological (urinary corticosterone) responses to novel social partners. However, SE females emitted significantly more 50 kHz ultrasonic vocalizations than control subjects both before and after social separation from a familiar social partner, which is consistent with previous findings in male rats. Thus, enhanced adolescent social experience appears to have long-term effects on vocal communication and could potentially modulate adult social relationships.     

Changes in hyporesponsiveness to acute amphetamine and age differences in tyrosine hydroxylase immunoreactivity in the brain over adolescence in male and female rats

We investigated hyposensitivity after amphetamine in early (postnatal Day 30; P30) and late (P45) adolescent rats compared to adults (P70) in experiment 1. Locomotor activity was measured for 1 hr after the first (acute) and second (24 hr later) injection of amphetamine (0.5 or 1.5 mg/kg). P30 and P45 rats were transiently hypoactive compared to adults, as indicated by reduced locomotor activity after acute amphetamine and enhanced activity after the second injection in adolescents only. In experiment 2, ovariectomy did not alter locomotor activity during habituation at any age compared to intact rats, and, as for intact adolescents, ovariectomized adolescents continued to be less active after amphetamine than adults, suggesting gonadal immaturity alone cannot account for age differences in experiment 1. However, ovariectomy attenuated the increase in activity after the second treatment. In experiment 3 involving untreated rats, tyrosine hydroxylase immunoreactivity was reduced in P30, P40, and P50 compared to P90 rats in the nucleus accumbens core and the medial prefrontal cortex. Thus, adolescents may have an increased threshold of behavioral activation that can be overcome with either a higher dose or with repeated amphetamine treatment, and may be related to changes in the dopamine system over development. © 2009 Wiley Periodicals, Inc. Dev Psychobiol 51: 417–428, 2009.     

Attention deficit hyperactivity disorder symptoms predict nicotine dependence and progression to regular smoking from adolescence to young adulthood

OBJECTIVE: To examine the association between retrospectively reported attention deficit hyperactivity disorder (ADHD) symptoms and progression to smoking and the association with nicotine dependence. METHODS: Study sample consisted of a nationally representative cohort of U.S. adolescents (n = 13,494). Logistic regression was used to examine ADHD symptoms from both the inattentive (IN) and hyperactive-impulsive (HI) domains and smoking trajectories. Linear regression was used to examine nicotine dependence. RESULTS: HI symptoms were associated with progression from nonsmoking to regular smoking (OR = 1.14, 95% CI = 1.07-1.21), and with progression from experimentation to regular smoking (OR = 1.16, 95% CI = 1.08-1.26). IN and HI symptoms were associated with nicotine dependence among current smokers (IN: beta = 0.17, SE = 0.03, p < 0.0001; HI: beta = 0.10, SE = 0.04., p < .001). CONCLUSIONS: These results have important implications for the development of prevention and treatment modalities.     

Emergence of the exploratory motive in rats

As infant rats approach weaning, they must overcome their infantile attraction to the home nest and prepare to leave its safety to forage for food. Although nutritive needs may help to motivate pups to make this bold move, a newly emerging exploratory motive also may play a role. Three experiments are reported here which examine age-related changes in the exploratory motive. In the first experiment, preferences for a novel side over a familiar side of a two-sided testing chamber were examined in postnatal Days 15 (P15), 17 (P17), 19 (P19), and 21 (P21) rat pups. Subjects did not prefer to explore the novel side until P19. In the same test, no preference for a novel object was observed at any of the ages tested, suggesting that this preference, which is expressed in adulthood, does not emerge until a later age; however, additional studies are needed to verify this. In the second experiment, P15 subjects demonstrated their ability to discriminate the two sides of the testing chamber in a novelty-induced locomotion test. In the third experiment, the presence of a home-nest-associated object was shown to inhibit exploration of novel context in P15, but not P21, subjects. These data suggest that home nest egression may be more the consequence of the declining attractiveness of the home nest than of a growing exploratory motive.     

Ontogeny of Rat Recognition Memory measured by the novel object recognition task

Detection of novelty is an essential component of recognition memory, which develops throughout cerebral maturation. To better understand the developmental aspects of this memory system, the novel object recognition task (NOR) was used with the immature rat and ontogenically profiled. It was hypothesized that object recognition would vary across development and be inferior to adult performance. The NOR design was made age‐appropriate by downsizing the testing objects and arena. Weanling (P20–23), juvenile (P29–40), and adult (P50+) rats were tested after 0.25, 1, 24, and 48 hr delays. Weanlings exhibited novel object recognition at 0.25 and 1 hr, while older animals showed a preference for the novel object out to 24 hr. These findings are consistent with previous research performed in humans and monkeys, as well as to studies using the NOR after medial temporal lobe damage in adult rats. © 2009 Wiley Periodicals, Inc. Dev Psychobiol 51: 672–678, 2009     

Longitudinal associations of sleep problems with alcohol and cannabis use from adolescence to emerging adulthood

Study ObjectivesThis study examined longitudinal associations of sleep problems with alcohol and cannabis use across six annual waves of data from adolescence to emerging adulthood.MethodsParticipants were 3,265 youth from California (ages 16–22 across waves). At each wave, past-month alcohol use and cannabis use, mental health, and several dimensions of sleep health (i.e. social jetlag, bedtimes, time in bed, trouble sleeping) were assessed via questionnaire. Parallel process latent growth models examined the association between sleep and alcohol or cannabis use trajectories and the role of mental health in contributing to such trajectories.ResultsSmaller declines in social jetlag (r = 0.11, p = 0.04), increases in trouble sleeping (r = 0.18, p < 0.01), and later weekday (r = 0.16, p < 0.01) and weekend bedtimes (r = 0.25, p < 0.01) were associated with increases in likelihood of alcohol use over time. Declines in weekend TIB (r = −0.13, p = 0.03), as well as increases in weekday TIB (r = 0.11, p = 0.04) and later weekday (r = 0.18, p < 0.01) and weekend bedtime (r = 0.24, p < 0.01), were associated with increases in likelihood of cannabis use over time. Most associations remained significant after controlling for time-varying mental health symptoms.ConclusionsTrajectories of sleep health were associated with trajectories of alcohol and cannabis use during late adolescence to emerging adulthood. Improving sleep is an important target for intervention efforts to reduce the risk of substance use during this critical developmental transition.     

Changes in muscle fibre type from adolescence to adulthood in women and men

Age-related changes in muscle fibre characteristics have been presented in cross-sectional studies previously. The aim of the present study was to investigate longitudinally whether the muscle fibre type composition and muscle fibre area change from adolescence to adulthood. Fifty-five men and 28 women were studied at the age of 16 and again at the age of 27. Biopsies were taken from the vastus lateralis muscle and analysed for fibre types (I, IIA, IIB, IIC) and fibre areas. Different development of fibre type composition with increased age were seen in women and men: the type I percentage tended to increase in the women (51 ± 9 to 55 ± 12) and decrease significantly in the men (55 ± 12 to 48 ± 13). The fibre areas remained unchanged in both sexes. It is suggested that there is a sex-related fibre adaptation to increased age.     

正常青年人脑电图光驱动反应性别差异的初步研究

目的 :研究正常青年脑电图光驱动反应的性别差异 ,探讨光刺激对视觉系统的影响。方法 :对年龄为 2 1～ 2 5岁的正常健康者男 35例 ,女 33例 ,记录安静状态下脑电图 ,并进行闪光刺激。闪光刺激的频率为 5、10和 15Hz。将安静状态和闪光刺激中的脑电图功率值变为波幅 ,对男女两组进行比较。结果 :安静状态下 ,在 β1和 β2 波带女性比男性有较高的波幅 (P <0 0 5 ) ;而在δ、θ、α1、α2 波带的差异无显著意义。闪光刺激中 ,15Hz光刺激相对应的β带域 (14 5～ 15 5Hz)的波幅差异更显著 ,在所有部位都有显著意义 (P <0 0 5 )。结论 :视觉系统存在性别差异 ,女性对光刺激比男性有更高的敏感性     

Neural responses to social and monetary reward in early adolescence and emerging adulthood

Reward processing is often considered to be a monolithic construct, with different incentive types eliciting equivalent neural and behavioral responses. The majority of the literature on reward processing has used monetary incentives to elicit reward‐related activity, yet social incentives may be particularly important due to their powerful ability to shape behavior. Findings from studies comparing social and monetary rewards have identified both overlapping and distinct responses. In order to explore whether reward processing is domain general or category specific (i.e., the same or different across reward types), the present study recorded ERPs from early adolescents (ages 12–13) and emerging adults (ages 18–25) while they completed social and monetary reward tasks. Temporospatial principal components analysis revealed morphologically similar reward positivities (RewPs) in the social and monetary reward tasks in each age group. In early adolescents, no significant difference was found between the magnitude of the RewP to social and monetary rewards. In emerging adults, however, the RewP to monetary rewards was significantly larger than the RewP to social rewards. Additionally, responses to feedback between the two tasks were not significantly correlated in either age group. These results suggest that both domain‐general and category‐specific processes underlie neural responses to rewards and that the relative incentive value of different types of rewards may change across development. Findings from this study have important implications for understanding the role that neural response to rewards plays in the development of psychopathology during adolescence.     

Longitudinal 1H MRS of rat forebrain from infancy to adulthood reveals adolescence as a distinctive phase of neurometabolite development

This study represents the first longitudinal, within‐subject ¹H MRS investigation of the developing rat brain spanning infancy, adolescence and early adulthood. We obtained neurometabolite profiles from a voxel located in a central location of the forebrain, centered on the striatum, with smaller contributions for the cortex, thalamus and hypothalamus, on postnatal days 7, 35 and 60. Water‐scaled metabolite signals were corrected for T₁ effects and quantified using the automated processing software LCModel, yielding molal concentrations. Our findings indicate age‐related concentration changes in N‐acetylaspartate + N‐acetylaspartylglutamate, myo‐inositol, glutamate + glutamine, taurine, creatine + phosphocreatine and glycerophosphocholine + phosphocholine. Using a repeated measures design and analysis, we identified significant neurodevelopment changes across all three developmental ages and identified adolescence as a distinctive phase in normative neurometabolic brain development. Between postnatal days 35 and 60, changes were observed in the concentrations of N‐acetylaspartate + N‐acetylaspartylglutamate, glutamate + glutamine and glycerophosphocholine + phosphocholine. Our data replicate past studies of early neurometabolite development and, for the first time, link maturational profiles in the same subjects across infancy, adolescence and adulthood. Copyright © 2013 John Wiley & Sons, Ltd.     

Effects of novelty on behavior in the adolescent and adult rat

Adolescence is a time of high-risk behavior and increased exploration. This developmental period is marked by a greater probability of initiating drug use and is associated with an increased risk to develop addiction and dependency in adulthood. Human adolescents are predisposed towards an increased likelihood of risk taking behaviors (Zuckerman, 1986), including drug use or initiation. The purpose of the study was to examine differences in developmental risk taking behaviors. Adolescent and adult animals were exposed to a novel stimulus in a familiar environment to assess impulsive behaviors, novelty preference, and exploratory behaviors. Adolescent animals had greater novelty-induced locomotor activity, greater novelty preference, and showed higher approach and exploratory behaviors compared to adult animals. These data support the notion that adolescents may be predisposed toward sensation seeking and consequently, are more likely to engage in risk-taking behaviors, such as drug use initiation.     

Effects of novelty on behavior in the adolescent and adult rat

Adolescence is a time of high‐risk behavior and increased exploration. This developmental period is marked by a greater probability of initiating drug use and is associated with an increased risk to develop addiction and dependency in adulthood. Human adolescents are predisposed towards an increased likelihood of risk taking behaviors (Zuckerman, 1986), including drug use or initiation. The purpose of the study was to examine differences in developmental risk taking behaviors. Adolescent and adult animals were exposed to a novel stimulus in a familiar environment to assess impulsive behaviors, novelty preference, and exploratory behaviors. Adolescent animals had greater novelty‐induced locomotor activity, greater novelty preference, and showed higher approach and exploratory behaviors compared to adult animals. These data support the notion that adolescents may be predisposed toward sensation seeking and consequently, are more likely to engage in risk‐taking behaviors, such as drug use initiation. © 2006 Wiley Periodicals, Inc. Dev Psyshobiol 48: 273, 2006.     

Familial transmission of cognitive abilities in offspring tested in adolescence and adulthood: A longitudinal study

As part of a follow-up study of now-adult offspring who originally participated in the Hawaii Family Study of Cognition (HFSC) from 1972 to 1976, 49 females and 46 males from 73 families of Caucasian ancestry and 63 females and 55 males from 92 families of Japanese ancestry were retested (average test-retest interval, 13 years) on the battery of cognitive abilities tests they took as adolescents. Age-corrected scale scores for verbal ability, spatial ability, perceptual speed, visual memory, and unrotated first principal component were calculated for the offspring's fathers and mothers, for their original HFSC testing, and for the retesting. Model-fitting procedures for a univariate model of familial transmission indicated significant differences in the parameters between the two racial/ethnic groups for all five cognitive abilities scales. These procedures also demonstrated no significant differences in familialities for offspring abilities in adolescence vs. mature adulthood across all five abilities scales and both racial/ethnic groups.