Infantile (handling) stimulation and behavior in young Roman high- and low-avoidance rats

Father's Absence in the Mongolian gerbil (Meriones unguiculatus) is associated with alterations in paternal behavior, T, cort, presence of ERα, and AR in mPOA/ BNST

Testosterone (T), estrogen receptor alpha (ERα), and androgen receptor (AR) play a significant role in the regulation of paternal behavior. We determined the effects of deprivation of paternal care on alterations in paternal behavior, T concentrations in plasma, and the presence of ERα and AR in the medial preoptic area (mPOA), bed nucleus of the stria terminalis (BNST), medial amygdala (MeA), and olfactory bulb (OB), as well as the corticosterone (CORT) concentrations in plasma caused by deprivation of paternal care in the Mongolian gerbil (Meriones unguiculatus). Twenty pairs of gerbils were formed; the pups were deprived of paternal care (DPC) in 10 pairs. In another 10 pairs, the pups received paternal care (PC). Ten males raised in DPC condition and 10 males raised in PC conditions were mated with virgin females. When they became fathers, each DPC male and PC male was subjected to tests of paternal behavior on day three postpartum. Blood samples were obtained to quantify T and CORT concentrations, and the brains were removed for ERα and AR immunohistochemistry analyses. DPC males gave less care to their pups than PC males, and they had significantly lower T concentrations and levels of ERα and AR in the mPOA and BNST than PC males. DPC males also had higher CORT concentrations than PC males. These results suggest that in the Mongolian gerbil father's absence causes a decrease in paternal care in the offspring, which is associated with alterations in the neuroendocrine mechanisms that regulate it.

c-Fos expression after neonatal handling in social brain regions: Distinctive profile of RHA-rat schizophrenia model on a social preference test

Neonatal handling (NH) is an environmental manipulation that induces long-lasting changes in behavioural, neuroendocrine, and neuroanatomical processes in rodents. We have previously reported that NH treatment increases social interaction preference in an animal model of schizophrenia-relevant features, the Roman high-avoidance (RHA) rats. The present study was aimed at evaluating whether the increase of social behaviour/preference due to NH treatment in RHA rats is associated with differences in c-Fos expression levels in some of the brain areas that integrate the "social brain". To this aim, we evaluated the performance of adult male rats from both Roman rat strains (RHA vs. RLA -Roman low-avoidance- rats), either untreated (control) or treated with NH (administered during the first 21 days of life) in a social interaction task. For the analyses of c-Fos activation untreated and NH-treated animals were divided into three different experimental conditions: undisturbed home cage controls (HC); rats exposed to the testing set-up context (CTX); and rats exposed to a social interaction (SI) test. It was found that, compared with their RLA counterparts, NH treatment increased social behaviour in RHA rats, and also specifically enhanced c-Fos expression in RHA rats tested for SI in some brain areas related to social behaviour, i.e. the infralimbic cortex (IL) and the medial posterodorsal amygdala (MePD) regions.

Optimising Puppy Socialisation-Short- and Long-Term Effects of a Training Programme during the Early Socialisation Period

The socialisation period in dog puppies is one of the most important periods determining behavioural development in dogs. Here, we aimed to test the effect of providing stimulation (beyond mere exposure) early during the socialisation period (approx. 3-6 weeks) on puppies' behaviour. Each of 12 litters (83 puppies) of various breeds was divided into a treatment and a control group. Between 3-6 weeks, the treatment group received age-appropriate "challenge" exercises (carefully graded noise exposure, novel objects, and problem-solving tasks) four times per week (total 12 times). The control group spent the same time with the trainer, who cuddled or played with the puppies. In a behaviour test at 6-7 weeks, two of four principal components, "social-startle" and "response to novelty", differed significantly between the groups. Treatment puppies were bolder towards the novel object, showed a reduced startle reaction, and recovered more quickly after a loud noise. Furthermore, they accomplished the problem-solving task faster and were more persistent during problem-solving than the control group. The control group showed a higher interest in a friendly stranger. It is a possibility that increased handling experienced by the control group had beneficial effects on their sociability. No long-term effects of the treatment were found, as determined by a validated dog personality questionnaire, available for 67 dogs at the age of six months. Likely, a continuation of the treatment over a longer time period would be necessary to obtain lasting effects, since the training took place only during the first third of the socialisation period.

Neurobehavioral and neurodevelopmental profiles of a heuristic genetic model of differential schizophrenia- and addiction-relevant features: The RHA vs. RLA rats

The Roman High- (RHA) and Low-(RLA) avoidance rat lines/strains were generated through bidirectional selective breeding for rapid (RHA) vs. extremely poor (RLA) two-way active avoidance acquisition. Compared with RLAs and other rat strains/stocks, RHAs are characterized by increased impulsivity, deficits in social behavior, novelty-induced hyper-locomotion, impaired attentional/cognitive abilities, vulnerability to psychostimulant sensitization and drug addiction. RHA rats also exhibit decreased function of the prefrontal cortex (PFC) and hippocampus, increased functional activity of the mesolimbic dopamine system and a dramatic deficit of central metabotropic glutamate-2 (mGlu2) receptors (due to a stop codon mutation at cysteine 407 in Grm2 -cys407*-), along with increased density of 5-HT2A receptors in the PFC, alterations of several synaptic markers and increased density of pyramidal "thin" (immature) dendrític spines in the PFC. These characteristics suggest an immature brain of RHA rats, and are reminiscent of schizophrenia features like hypofrontality and disruption of the excitation/inhibition cortical balance. RHA rats represent a promising heuristic model of neurodevelopmental schizophrenia-relevant features and comorbidity with drug addiction vulnerability.

Decreased social interaction in the RHA rat model of schizophrenia-relevant features: Modulation by neonatal handling

The Roman-Low (RLA) and High-Avoidance (RHA) rat strains have been bidirectionally selected and bred, respectively, for extremely poor vs. rapid acquisition of the two-way active avoidance task. Over 50 years of selective breeding have led to two strains displaying many differential specific phenotypes. While RLAs display anxious-related behaviours, RHA rats show impulsivity, and schizophrenia-like positive and cognitive symptoms or phenotypes. Neonatal handling (NH) is an environmental treatment with long-lasting anxiolytic-like and anti-stress effects. NH also reduces symptoms related to schizophrenia, such as pre-pulse inhibition (PPI) impairment and latent inhibition (LI) deficits, and improves spatial working memory and cognitive flexibility. The present work was aimed at exploring whether RHAs also display negative schizophrenia-like symptoms (or phenotypes), such as lowered preference for social interaction (i.e. asociality), and whether NH would reduce these deficits. To this aim, we evaluated naïve inbred RHA and RLA rats in a social interaction (SI) test after either long- or short-term habituation to the testing set up (studies 1-2). In Study 3 we tested untreated and NH-treated RHA and RLA rats in novel object exploration (NOE) and SI tests. Compared with RHAs, RLA rats displayed increased anxiety-related behaviours in the NOE (i.e. higher behavioural inhibition, lesser exploration of the novel object) and SI (i.e. higher levels of self-grooming) tests which were dramatically reduced by NH treatment, thus supporting the long-lasting anxiolytic-like effect of NH. Remarkably, RHA rats showed decreased social preference in the SI test compared with RLAs, evidencing that RHAs would present a relative asociality, which is thought to model some negative symptomatology (i.e. social withdrawal) of schizophrenia. NH increased absolute levels of social behaviour in both strains, but with a more marked effect in RHA rats, especially in the first 5 min of the SI test. Thus, it is hypothesized that, apart from its effects on anxiety-related behaviours, NH might have long-lasting positive effects on behavioural and neurobiological processes that are impaired in schizophrenia.

Social Nesting, Animal Welfare, and Disease Monitoring

Simple Summary

Most standardized tools to evaluate welfare and disease progression in animals assess the individuals, while social behaviors are scarcely monitored, despite being useful to detecting acute illness and chronic and mental health problems. The main reason is that social behavior is complex and time-consuming. We are currently using the nests built by animals living together, a species-typical behavior naturally occurring in standard housing conditions, to monitor them. Here, we provide an example of its use to evaluate social deficits and the long-term effects of a neonatal tactile-proprioceptive sensorial treatment from postnatal day 1 to 21, in male and female adult mice modeling Alzheimer’s disease compared to mice with normal aging. Social nesting was worse in the mutants, mostly in males, since the number of days needed to build a perfect nest was longer or unsuccessful in a three-day test. Early life intervention was successful. Social nesting, easily included in housing routines, can be a useful tool to assess animal welfare, monitor disease progress, and evaluate potential risk factors and effects of preventive/therapeutical strategies. Other advantages, such as being a noninvasive, painless, simple, short, and low-cost, rend social nesting feasible to be implemented in most animal department settings.

Abstract

The assessment of welfare and disease progression in animal models is critical. Most tools rely on evaluating individual subjects, whereas social behaviors, also sensitive to acute illness, chronic diseases, or mental health, are scarcely monitored because they are complex and time-consuming. We propose the evaluation of social nesting, a species-typical behavior naturally occurring in standard housing conditions, for such behavioral monitoring. We provide an example of its use to evaluate social deficits and the long-term effects of neonatal tactile-proprioceptive sensorial stimulation from postnatal day 1 to 21, in male and female adult 3xTg-AD mice for Alzheimer’s disease compared to sex- and age-matched non-transgenic (NTg) counterparts with normal aging. Social nesting was sensitive to genotype (worse in 3xTg-AD mice), sex (worse in males), profile, and treatment (distinct time to observe the maximum score and incidence of the perfect nest). Since social nesting can be easily included in housing routines, this neuroethological approach can be useful for animal welfare, monitoring the disease’s progress, and evaluating potential risk factors and effects of preventive/therapeutical strategies. Finally, the noninvasive, painless, simple, short time, and low-cost features of this home-cage monitoring are advantages that make social nesting feasible to be successfully implemented in most animal department settings.

A Genetic Model of Impulsivity, Vulnerability to Drug Abuse and Schizophrenia-Relevant Symptoms With Translational Potential: The Roman High- vs. Low-Avoidance Rats

The bidirectional selective breeding of Roman high- (RHA) and low-avoidance (RLA) rats for respectively rapid vs. poor acquisition of active avoidant behavior has generated two lines/strains that differ markedly in terms of emotional reactivity, with RHA rats being less fearful than their RLA counterparts. Many other behavioral traits have been segregated along the selection procedure; thus, compared with their RLA counterparts, RHA rats behave as proactive copers in the face of aversive conditions, display a robust sensation/novelty seeking (SNS) profile, and show high impulsivity and an innate preference for natural and drug rewards. Impulsivity is a multifaceted behavioral trait and is generally defined as a tendency to express actions that are poorly conceived, premature, highly risky or inappropriate to the situation, that frequently lead to unpleasant consequences. High levels of impulsivity are associated with several neuropsychiatric conditions including attention-deficit hyperactivity disorder, obsessive-compulsive disorder, schizophrenia, and drug addiction. Herein, we review the behavioral and neurochemical differences between RHA and RLA rats and survey evidence that RHA rats represent a valid genetic model, with face, construct, and predictive validity, to investigate the neural underpinnings of behavioral disinhibition, novelty seeking, impulsivity, vulnerability to drug addiction as well as deficits in attentional processes, cognitive impairments and other schizophrenia-relevant traits.

Access to a high resource environment protects against accelerated maturation following early life stress: A translational animal model of high, medium and low security settings

Early life exposure to a low security setting, characterized by a scarcity of resources and limited food access, increases the risk for psychiatric illness and metabolic dysfunction. We utilized a translational rat model to mimic a low security environment and determined how this manipulation affected offspring behavior, metabolism, and puberty. Because food insecurity in humans is associated with reduced access to healthy food options the "low security" rat manipulation combined a Western diet with exposure to a limited bedding and nesting manipulation (WD-LB). In this setting, dams were provided with limited nesting materials during the pups' early life (P2-P10). This manipulation was contrasted with standard rodent caging (SD) and environmental enrichment (EE), to model "medium security" and "high security" environments, respectively. To determine if transitioning from a low to high security environment improved outcomes, some juvenile WD-LB offspring were exposed to EE. Maternal care was impacted by these environments such that EE dams engaged in high quality care when on the nest, but spent less time on the nest than SD dams. Although WD-LB dams excessively chased their tails, they were very attentive to their pups, perhaps to compensate for limited resources. Offspring exposed to WD-LB only displayed subtle changes in behavior. However, WD-LB exposure resulted in significant metabolic dysfunction characterized by increased body weight, precocious puberty and alterations in the hypothalamic kisspeptin system. These negative effects of WD-LB on puberty and weight regulation were mitigated by EE exposure. Collectively, these studies suggest that both compensatory maternal care and juvenile enrichment can reduce the impact of a low security environment. Moreover, they highlight how utilizing diverse models of resource (in)stability can reveal mechanisms that confer vulnerability and resilience to early life stress.

Severe Perinatal Hypoxic-Ischemic Brain Injury Induces Long-Term Sensorimotor Deficits, Anxiety-Like Behaviors and Cognitive Impairment in a Sex-, Age- and Task-Selective Manner in C57BL/6 Mice but Can Be Modulated by Neonatal Handling

Perinatal brain injury (PBI) leads to neurological disabilities throughout life, from motor deficits, cognitive limitations to severe cerebral palsy. Yet, perinatal brain damage has limited therapeutic outcomes. Besides, the immature brain of premature children is at increased risk of hypoxic/ischemic (HI) injury, with males being more susceptible to it and less responsive to protective/therapeutical interventions. Here, we model in male and female C57BL/6 mice, the impact of neonatal HI and the protective effects of neonatal handling (NH), an early life tactile and proprioceptive sensory stimulation. From postnatal day 1 (PND1, modeling pre-term) to PND21 randomized litters received either NH or left undisturbed. HI brain damage occurred by permanent left carotid occlusion followed by hypoxia at PND7 (modeling full-term) in half of the animals. The behavioral and functional screening of the pups at weaning (PND23) and their long-term outcomes (adulthood, PND70) were evaluated in a longitudinal study, as follows: somatic development (weight), sensorimotor functions (reflexes, rods and hanger tests), exploration [activity (ACT) and open-field (OF) test], emotional and anxiety-like behaviors [corner, open-field and dark-light box (DLB) tests], learning and memory [T-maze (TM) and Morris Water-Maze (MWM)]. HI induced similar brain damage in both sexes but affected motor development, sensorimotor functions, induced hyperactivity at weaning, and anxiety-like behaviors and cognitive deficits at adulthood, in a sex- and age-dependent manner. Thus, during ontogeny, HI affected equilibrium especially in females and prehensility in males, but only reflexes at adulthood. Hyperactivity of HI males was normalized at adulthood. HI increased neophobia and other anxiety-like behaviors in males but emotionality in females. Both sexes showed worse short/long-term learning, but memory was more affected in males. Striking neuroprotective effects of NH were found, with significantly lower injury scores, mostly in HI males. At the functional level, NH reversed the impaired reflex responses and improved memory performances in hippocampal-dependent spatial-learning tasks, especially in males. Finally, neuropathological correlates referred to atrophy, neuronal densities and cellularity in the affected areas [hippocampal-CA, caudate/putamen, thalamus, neocortex and corpus callosum (CC)] point out distinct neuronal substrates underlying the sex- and age- functional impacts of these risk/protection interventions on sensorimotor, behavioral and cognitive outcomes from ontogeny to adulthood.

Exploration of a novel object in late adolescence predicts novelty-seeking behavior in adulthood: Associations among behavioral responses in four novelty-seeking tests

The sensation/novelty seeking behavioral trait refers to the exploration/preference for a novel environment. Novelty seeking increases during late adolescence and it has been associated with several neurobehavioral disorders. In this experiment, we asked whether inbred Roman high- and low-avoidance (RHA-I, RLA-I) rats (1) differ in novelty seeking in late adolescence and (2) whether late adolescent novelty seeking predicts this trait in adulthood. Thirty six male RHA-I and 36 RLA-I rats were exposed to a novel object exploration (NOE) test during late adolescence (pnd: 52-59;

DEPENDENT VARIABLES

contact latency, contact time, contact frequency). Head-dipping (hole-board, HB), time and visits to a novel-arm (Y-maze), and latency-in and emergence latency (emergence test) were registered in adulthood (pnd: 83-105). The results showed strain differences in all these tests (RHA-I>RLA-I). Factor analysis (RHA-I+RLA-I) revealed two clusters. The first one grouped HB and emergence test measures. The second one grouped NOE and Y-maze variables. Time exploring a novel object (NOE) was a significant predictor of novel arm time (RHA-I+RLA, RHA-I); contact latency was a significant predictor of novel arm frequency (RLA-I). Present results show consistent behavioral associations across four novelty-seeking tests and suggest that late adolescent novelty seeking predicts this genetically-influenced temperamental trait in adult Roman rats.

Cognitive and emotional alterations in young Alzheimer's disease (3xTgAD) mice: effects of neonatal handling stimulation and sexual dimorphism

Alzheimer disease is the most common neurodegenerative disorder and cause of senile dementia. It is characterized by an accelerated memory loss, and alterations of mood, reason, judgment and language. The main neuropathological hallmarks of the disorder are β-amyloid (βA) plaques and neurofibrillary Tau tangles. The triple transgenic 3xTgAD mouse model develops βA and Tau pathologies in a progressive manner which mimicks the pattern that takes place in the human brain with AD, and showing cognitive alterations characteristic of the disease. The present study intended to examine whether 3xTgAD mice of both sexes present cognitive, emotional and other behavioral alterations at the early age of 4 months, an age in which only some intraneuronal amyloid accumulation is found. Neonatal handling (H) is an early-life treatment known to produce profound and long-lasting behavioral and neurobiological effects in rodents, as well as improvements in cognitive functions. Therefore, we also aimed at evaluating the effects of H on the behavioral/cognitive profile of 4-month-old male and female 3xTgAD mice. The results indicate that, (1) 3xTgAD mice present spatial learning/memory deficits and emotional alterations already at the early age of 4 months, (2) there exists sexual dimorphism effects on several behavioral variables at this age, (3) neonatal handling exerts a preventive effect on some cognitive (spatial learning) and emotional alterations appearing in 3xTgAD mice already at early ages, and 4) H treatment appears to produce stronger positive effects in females than in males in several spatial learning measures and in the open field test.

Natural variation in early parental care correlates with social behaviors in adolescent prairie voles (Microtus ochrogaster)

Natural variation in early parental care may contribute to long-term changes in behavior in the offspring. Here we investigate the role of variable early care in biparental prairie voles (Microtus ochrogaster). Total amounts of parental care were initially quantified for 24 breeder pairs and pairs were ranked in relation to one another based on total contact. Consistency in key components of care suggested a trait-like quality to parental care. Based on this ranking, breeder pairs from the top (high-contact) and bottom (low-contact) quartiles were selected to produce high- and low-contact offspring to investigate adolescent behavior after varying early care. Parental care of subject offspring was again observed postnatally. Offspring of high-contact parents spent more time passively nursing and received more paternal non-huddling contact while low-contact offspring spent more time actively nursing and received more paternal huddling and pseudohuddling in the first postnatal days (PNDs). Low-contact offspring also displayed faster rates of development on a number of physical markers. Post-weaning, offspring were evaluated on anxiety-like behavior, social behavior and pre-pulse inhibition (PPI) to a tactile and an acoustic startle. High-contact offspring spent more time sniffing a juvenile and less time autogrooming. With an infant, high-contact offspring spent more time in non-huddling contact and less time autogrooming and retrieving than did low-contact offspring. Considering sexes separately, high-contact females spent more time sniffing a novel juvenile than low-contact females. High-contact males spent more time in non-huddling contact with an infant than low-contact males; while low-contact females retrieved infants more than high-contact females. In both measures of social behavior, high-contact males spent less time autogrooming than low-contact males. These results suggest a relationship between early-life care and differences in social behavior in adolescence.

The biology of fear- and anxiety-related behaviors

Anxiety is a psychological, physiological, and behavioral state induced in animals and humans by a threat to well-being or survival, either actual or potential. It is characterized by increased arousal, expectancy, autonomic and neuroendocrine activation, and specific behavior patterns. The function of these changes is to facilitate coping with an adverse or unexpected situation. Pathological anxiety interferes with the ability to cope successfully with life challenges. Vulnerability to psychopathology appears to be a consequence of predisposing factors (or traits), which result from numerous gene-environment interactions during development (particularly during the perinatal period) and experience (life events), in this review, the biology of fear and anxiety will be examined from systemic (brain-behavior relationships, neuronal circuitry, and functional neuroanatomy) and cellular/molecular (neurotransmitters, hormones, and other biochemical factors) points of view, with particular reference to animal models. These models have been instrumental in establishing the biological correlates of fear and anxiety, although the recent development of noninvasive investigation methods in humans, such as the various neuroimaging techniques, certainly opens new avenues of research in this field. Our current knowledge of the biological bases of fear and anxiety is already impressive, and further progress toward models or theories integrating contributions from the medical, biological, and psychological sciences can be expected.

Long-term effects of neonatal handling on mu-opioid receptor levels in the brain of the offspring

Neonatal handling is an experimental paradigm of an early experience which permanently alters hypothalamic-pituitary-adrenal axis function resulting in increased ability to cope with stress, and decreased emotionality. In the present work we investigated the effect of neonatal handling on adult rat brain mu-opioid receptor levels, since the opioid system is known to play an important role in emotional processing, anxiety and stress responses. Neonatal handling resulted in increased levels of mu-opioid receptors in the basolateral and central amygdaloid nuclei, in the CA3 and CA4 hippocampal areas, in the ventral tegmental area, the nucleus accumbens and the prefrontal cortex. Handled animals of both sexes had lower anxiety as measured in the elevated plus maze. The increased mu receptor levels could participate in the molecular mechanisms underlying the well-documented decreased stress and anxiety responses of handled animals.

Fearfulness in a large N/Nih genetically heterogeneous rat stock: differential profiles of timidity and defensive flight in males and females

Anxiety-related behaviors were evaluated across various tests in a large sample (n=787, both sexes) of genetically heterogeneous (N/Nih-HS) rats, derived from an eight-way cross of inbred strains. These tests either evoke unlearned (black-white box, BWB-; novel-cage activity, NACT-; elevated "zero" maze, ZM-; baseline acoustic startle response, BAS-) or learned (fear-potentiated startle, FPS-; two-way active-shuttle box-avoidance acquisition, SHAV-) anxious/fearful responses. The results showed that, with the exception of fear-potentiated startle, almost all (unlearned and learned) behaviors assessed fit with a pattern of sex effects characterized by male rats as being more fearful than females. We applied factor analyses (oblique rotation) to each sex, with the final two-factor solution showing: (1) a first factor (labelled as "Timidity") comprising BWB, NACT and ZM variables in both sexes, plus SHAV responding in the case of males, and (2) a second factor (called "Defensive Flight") which grouped BAS, FPS, and SHAV responding in both sexes. An additional regression analysis showed significant influences of (unlearned) risk assessment (i.e. stretch-attendance) behavior on SHAV in males, while FPS was the main variable positively influencing SHAV (in the intermediate and advanced phases of acquisition) in females. This indicates, for the first time, that fear-potentiated startle may have a facilitating role in the rat's active responses (at least in females) to the cue in the intermediate to advanced phases (i.e. when the initial "passive avoidance/active avoidance" begins to fade) of shuttle box avoidance acquisition. The results of this first extensive behavioral evaluation of N/Nih-HS rats are discussed in terms of their potential usefulness for present and future neurobehavioral and genetic studies of fearfulness/anxiety.

The communicative functions of touch in humans, nonhuman primates, and rats: a review and synthesis of the empirical research

Although touch is one of the most neglected modalities of communication, several lines of research bear on the important communicative functions served by the modality. The authors highlighted the importance of touch by reviewing and synthesizing the literatures pertaining to the communicative functions served by touch among humans, nonhuman primates, and rats. In humans, the authors focused on the role that touch plays in emotional communication, attachment, bonding, compliance, power, intimacy, hedonics, and liking. In nonhuman primates, the authors examined the relations among touch and status, stress, reconciliation, sexual relations, and attachment. In rats, the authors focused on the role that touch plays in emotion, learning and memory, novelty seeking, stress, and attachment. The authors also highlighted the potential phylogenetic and ontogenetic continuities and discussed suggestions for future research.

Can knowledge of developmental processes illuminate the evolution of parental care?

There are two levels of investigation for elucidating the evolution of parental behavior. The macro level focuses on how parental behavior can evolve as an aspect of reproduction. The micro level focuses on how species variations in parental behavior evolve. Recently, modern evolutionary biology has turned to developmental biology as a source for information about how trait variability (the substrate upon which natural selection and other evolutionary mechanisms can operate) can emerge during development (called "evo-devo"). Application of this evo-devo approach to the phenomenon of parental behavior requires identification of those mechanisms that produce variations in developmental pathways leading to parental behavior. It is these variations that provide the phenotypes for the potential evolution of different parental behavior systems. Variations in rodent maternal behavior affect the development of the HPA and HPG axes in their offspring. These mechanisms are examined to reveal how such developmental variations could underlie the evolution of biparental behavior. Knowledge of the developmental mechanisms responsible for species variations in mammalian parental behavior systems may provide insight into those mechanisms that may have been involved in the evolution of parental behavior itself.

Effects of neonatal novelty exposure on sexual behavior, fear, and stress-response in adult rats

Environmental stimuli in early life may result in permanent behavioral and physiological changes. Present study evaluated the effects of exposing pups to a novel environment on behaviors (open-field test and sexual behavior) and prolactin stress-responses in adult male rats. Half of a litter was daily removed outside (OUT) from the nest and stimulated by handling for 3 min, while the other half remained inside (IN) the nest and was also handled for the same period during the first 10 days postpartum. Maternal behavior after all the pups were returned to the nest was not different between IN and OUT littermates. In adulthood, OUT males showed increased general and central locomotion activity in the open-field test, reduced sexual behavior, and attenuated prolactin secretion in response to restraint stress compared with the IN littermates. The repeated exposition of rat pups to a novel environment is a causal factor for the long-lasting behavioral and endocrine changes. The premature exposition of the pup to unfamiliar environments decreases fear and stress-response, and also reduces sexual behavior. We suggest that the absence of the odor of the mother may be crucial to explain the effects detected in adulthood.

Single, intense prenatal stress decreases emotionality and enhances learning performance in the adolescent rat offspring: interaction with a brief, daily maternal separation

Perinatal manipulations can lead to neurobehavioural changes in the progeny. In this study we investigated, in adolescent male rat offspring, the consequences of a single, intense prenatal stress induced by a 120 min-maternal immobilization at gestational day 16, and of a daily, brief maternal separation from postnatal day 2 until 21, on: unconditioned fear/anxiety-like behaviour in open field and in elevated plus-maze; learning performance in the "Can test", a non-aversive spatial and tactile/visual task; corticosterone plasma levels under basal and stress-induced conditions. Our results indicate that both prenatal stress and maternal separation procedures decrease emotionality and enhance learning performance. Maternal separation potentiates prenatal stress-induced effects in enhancing learning performance. Both basal and stress-induced corticosterone plasma levels are reduced following prenatal stress, maternal separation and the combination of two procedures. These findings suggest that a single, intense prenatal stress can enhance the adaptive stress-related responses in the progeny, probably due to the involvement of maternal factors. The synergistic effect of prenatal stress and maternal separation on learning performance may be due to a further damping of hypothalamic-pituitary-adrenal axis response in the progeny that better cope with the task administered.

Neonatal handling increases fear and aggression in lactating rats

Neonatal handling reduces fear in male and cycling female rats, but increases maternal aggressive behavior against intruders to the nest area. Present study aimed to analyze the effects of neonatal handling on the maternal aggressive behavior and the activity in the open field with a predator of lactating rats on the 8th and the 18th postpartum days (periods of high and low aggressiveness). As pups, animals were divided into two groups: nonhandled (no neonatal manipulation) and handled (handling for 1 min during the first 10 days after delivery). As adults, females of both groups were impregnated and tested against a male intruder for aggressive behavior and in the open field with a cat inside a wire-meshed cage. Results showed that on the 8th day frequency of aggressive behaviors of handled females was higher than that of the nonhandled ones, but on the 18th day, no significant difference was detected. Surprisingly, in the open field test, handled females showed decreased locomotion and increased freezing on the 8th day compared to the nonhandled ones. The opposite relationship between increased aggressiveness with reduced fear is observed in the nonhandled control females in early and late lactation periods. However, neonatal handling abolishes this relationship. Apparently, the increased aggressiveness in neonatal handled lactating females does not depend on a decrease in fear. Our findings support the hypothesis that long lasting effects of early life stimulation is a dynamic function depending on the behavioral system and the period of life analyzed. Moreover, they caution the relationship between aggressive behavior and fear.

Inter-individual vs line/strain differences in psychogenetically selected Roman High-(RHA) and Low-(RLA) Avoidance rats: neuroendocrine and behavioural aspects

Inter-individual differences in neuroendocrine and behavioural responses to environmental challenges will be considered within the context of psychogenetic selection, using the Roman High-(RHA) and Low-(RLA) Avoidance rat lines as an example. We assume that the selected genotypes, by interacting with environmental factors, determine specific 'biobehavioural profiles'. Practical and theoretical problems regarding the measurement of inter-individual vs line/strain differences, the definition of 'traits' vs experimental variables, and possible correlations between physiological and behavioural parameters will be discussed. We will argue that environmental influences are the main cause of inter-individual variability, and that the genotype only constitutes a 'blueprint' from which typical biobehavioural profiles are established, notably under the influence of early environmental factors. These biobehavioural profiles may correspond in part to human categories known as 'types', 'temperaments' or 'personality traits'. Within each category (including those which can be obtained by psychogenetic selection), more individual personality traits can evolve, notably as a result of social interactions and particular life events.

Further evidences that risk assessment and object exploration behaviours are useful to evaluate emotional reactivity in rodents

In this study, we tested the ability of risk assessment and exploration behaviours to emphasise PH effects. Indeed, postnatal handling (PH) decreases emotional reactivity in rats but inconsistent behavioural results can be observed and may be due to false negative (i.e. existing effects are not detected). Risk assessment behaviours were measured in the elevated plus maze, in the free exploration paradigm and in the open field. In addition, we measured object exploration behaviours towards familiar/new objects in the open field. PH increased general activity in the elevated plus maze and in the free exploration paradigm and risk assessment behaviours allowed demonstrating that these effects were specific to emotional reactivity. In the open field, PH increased object exploration as early as first exposition while general activity was unaffected. PH also decreased behavioural inhibition in response to the introduction of a novel object. On the whole, our results show that risk assessment and object exploration behaviours are valuable tools to measure more precisely emotional reactivity in rodents. This reinforces the idea that these behaviours should be used more frequently in order to avoid false negative when emotional reactivity changes are expected in unconditioned conflict tests.

The Roman high- and low-avoidance rats respond differently to novelty in a familiarized environment

The purpose of the present study was to investigate the response to novelty in Roman high- and low-avoidance rats under non-stressful conditions. To reduce fear, a procedure of repetitive placing in the experimental chamber consisting of start, screen, and tunnel zones was applied. Each animal was placed in the experimental chamber daily for a 6min period. The first 11 sessions were the habituation sessions. In the 12th session, the novelty was introduced into the screen and tunnel zones. The subsequent two sessions were conducted under novelty conditions. Behavioral activities such as walking, object contacts, time spent in given zones, and entering the tunnels were measured. All the comparisons were made for two 3-min intervals, using a three-factor MANOVA, involving 2(sex)x2(subline)x8(3-mininterval). All subjects increased time spent in the tunnel zone, but RHA/Verh rats responded to a greater extent, especially the males. All subjects spent shorter times in the screen zone, but the RHA/Verh rats responded to a much greater extent. RHA/Verh rats, especially males responded with a substantial increase of time spent inside the tunnels. All subjects responded with an increased amount of object contacts. In general the RHA/Verh subjects showed a more pronounced response to novelty, as evidenced by a significant shift toward the tunnel zone. They spent more time in this zone than their RLA/Verh counterparts. Among the RLA/Verh rats, males tended to behave similarly to RHA/Verh rats, especially during the second 3min interval of session "12." The differences between the rat lines obtained in this study may be attributed to mechanisms specific to exploration, making them promising subjects to study the relationships between reactivity, novelty detection, adaptation, and environmental information processing.

Effects of neonatal handling on basal and stress-induced monoamine levels in the male and female rat brain

Neonatal handling has pervasive effects on the rat brain leading to increased ability to cope with and adapt to stressful stimuli. We determined the effects of neonatal handling on the dopaminergic and serotonergic system, in the male and female rat brain, under basal conditions before and after puberty and after short- and long-term forced swimming stress. Exposure of animals to neonatal handling resulted in sex-dependent changes in the concentration and turnover of monoamines in the different brain areas. In the prepubertal brain, the effect of neonatal handling was manifested as an increase in dopamine turnover in the females, particularly in the hypothalamus, an increase in serotonin levels and a decrease in its turnover in all three brain regions examined of both males and females. Certain of the handling-induced effects observed in the prepubertal brain were reversed in the postpubertal animals. Thus, in the postpubertal brain, the handling-induced changes in serotonin levels and its turnover observed in both sexes before puberty were abolished. On the other hand, the handling-induced increase in hypothalamic dopamine turnover was maintained. After exposure to short-term stress, the effect of handling was manifested on one hand as decreased striatal dopamine levels in the females, and decreased dopamine turnover in the hypothalamus of both males and females, and on the other, as increased serotonin levels in the hypothalamus. After exposure to long-term stress, handled females had decreased dopamine turnover in the hypothalamus and the striatum, but there was no effect of handling on the serotonergic system. Our results provide some neurobiological evidence supporting the determinant role of the mother-infant relationship in the development of psychopathology. Neonatal handling, which modifies normal mother-pup interactions, results in alterations in brain dopaminergic and serotonergic systems, both of which are involved in the etiopathogenesis of major psychoses. Exposure to either short- or long-term stress in adult life results in sex-dependent changes in brain monoamines, which are affected by handling thus making coping more efficient and rendering the stressful stimulus less noxious.

The positive effects of postnatal handling on defensive burying are more obvious in a situation that enlarges the potential coping responses

A recent study reported few effects of postnatal handling in the defensive burying test. Since the importance of testing conditions has been emphasised in this paradigm, the lack of handling effects in this test could be attributed to the testing situation. Our experiment was carried out to test whether postnatal handling in DA/HAN strain rats have positive effects in two situations of the defensive burying test: a no-hide situation, in which avoidance of the probe was not possible, and a hide situation, in which animals were allowed to avoid the probe by sheltering in a hiding compartment. Our results showed no difference between control and handled rats defensive reactions in the no-hide situation. However, the general coping style of handled rats was different, mostly by a higher level of exploration of the apparatus and of the probe. In the hide situation, the time spent burying the probe was significantly lower in handled rats and they also spent less time in the hiding compartment. Those results, along with approach/avoidance behaviours directed towards the probe demonstrate that postnatal handling do have some positive effects in the defensive burying test. In addition, our results also point out that testing situations in which complex coping strategies are available are appropriate to test the effects of early stimulation such as handling.

Early-life handling stimulation and environmental enrichment: are some of their effects mediated by similar neural mechanisms?

Neonatal (early) handling (EH) and environmental enrichment (EE) of laboratory rodents have been the two most commonly used methods of providing supplementary environmental stimulation in order to study behavioral and neurobiological plasticity. A large body of research has been generated since the 1950s, unequivocally showing that both treatments induce profound and long-lasting behavioral and neural consequences while also inducing plastic brain effects and being "protective" against some age-related deficits. The present work is aimed at reviewing the main neurobehavioral effects of both manipulations, with the final purpose of comparing them and trying to find out to what extent the effects of both treatments may share (or not) possible neural mechanisms.

The influence of handling and isolation postweaning on open field, exploratory and maternal behavior of female rats

Fifty-three black-hooded female rats, raised from the 28th to the 128th day of life under four types of environmental conditions differing in social and handling factors, had their behavioral performance evaluated in eight tests involving exploration of a complex environment (EX) in two open field (OF) tests and in three pup-retrieving tests. These tests were held before, during and after the period of lactation of their first brood. Females differed from (previously studied) males in that environmental raising conditions had a much smaller influence, especially during the lactation period. Nevertheless, females raised in isolation tended to remain for longer times inside a protected den in the exploration tests and to have greater locomotion in the open field. Previous handling allowed a greater exploration during the first contact with the novel complex environment as well as greater activity in the open field. The presence of small pups drastically reduced the exploratory motivation, but the presence of pups more than 20 days old tended to increase it. Maternal behavior evaluated in the pup retrieval test and in the test of time for the female to leave the nest side of the double box system was markedly refractory to previous environmental influences.

Sex differences in the effects of neonatal handling on the animal's response to stress and the vulnerability for depressive behaviour

Neonatal handling is known to affect the programming of the hypothalamic-pituitary-adrenal axis and, as a result, the ability of the organism to respond to stress. We determined the effect of neonatal handling on the animal's response in three animal models of depression, as well as to either (a) acute or (b) chronic forced swimming stress. Neonatal handling resulted in a significant increase in the immobility time in the Porsolt forced swimming test in both sexes, and in the 8-hydroxy-2-(di-n-propylamino) tetralin-induced hypothermia in the males. On the other hand, handling had sex-dependent effects when animals were exposed to a chronic stressor. After exposure to chronic restraint stress, statistically more handled than non-handled females failed to adapt, while no such difference was found in the males. In the chronic forced swimming stress, handled males had shorter immobility times, and higher plasma corticosterone levels, while the opposite held true in the females. Furthermore, neonatal handling significantly decreased basal plasma corticosterone levels in both pre- and post-pubertal animals. Thus, the early experience of handling provides males with a greater capacity to actively face chronic stressors, while in the females it increases their susceptibility to express 'depressive' behaviour since they are unable to cope and adopt a 'passive, despaired' behaviour.

Long-lasting effects of neonatal stimulation on the behavior of rats

The present study aimed to analyze the effects of neonatal stimulation on species-specific behaviors (defensive reactions to a predator and social interactions) in adult male and female rats. Handling and an unpredictable sequence of aversive stimuli were applied to male and female pups from the 1st to the 10th day after delivery; behavioral inhibition, aggression, and sexual behavior were evaluated in adulthood. Results showed that either neonatal handling or aversive stimulation decreased behavioral inhibition in a novel and potentially harmful situation (open field with a predator) in both male and female rats and increased maternal aggressive behavior. Sexual behavior in both males and females decreased, which could affect reproductive capability. The results could cast doubts on the generalization of beneficial effects of neonatal stimulation on the behavior of adult rats.

Different effects of acute neonatal stressors and long-term postnatal handling on stress-induced changes in behavior and in ornithine decarboxylase activity of adult rats

A transient increase in brain polyamine (PA) metabolism, termed the PA-stress-response (PSR), is a common response to stressful stimuli. Previous studies have implicated the PSR as a component of the adaptive and/or maladaptive brain response to stressful events. Ample evidence indicates that stressful experiences during early life can alter normal developmental processes and may result in pathophysiological and behavioral changes in the adult. The aim of the present study, therefore, was to determine whether strong acute neonatal stressors (3 mg/kg dexamethasone, or 2 h restraint stress at day 7), as compared to mild long-term intermittent maternal separation and handling (15 min, twice a day between postnatal days 2 and 25), would lead in adult Wistar rats to different PSR and behavioral reactivity to novelty stress. Changes in ornithine decarboxylase (ODC) activity and in tissue PA concentrations served as markers of the PSR, and behavioral alterations in an open-field arena indicated the reactivity to novelty stress. Animals subjected to acute neonatal stressors, showed reduced behavioral reactivity in the open-field test, indicative of increased emotional reactivity to novelty. In these animals, the increase in ODC activity after dexamethasone challenge was attenuated in the brain, but exaggerated in the liver. In the thymus and adrenal gland of these animals, the basal enzyme activity was significantly increased, but a similar reduction was observed after dexamethasone challenge. In contrast, long-term postnatal handling led in adults to novelty-induced changes indicative of reduced emotional behavior, yet the alterations in ODC activity after dexamethasone challenge in these animals were similar to those in animals after acute stressors. The concentrations of tissue polyamines in adults were not affected by any of the postnatal stressors. The results justify the following conclusions: (1) Strong acute neonatal stressors can lead to increased emotional behavior in adults, while mild long-term intermittent handling, may result in adaptation and reduced emotionality. (2) Attenuated stress-induced increase of ODC activity in the brain, but exaggerated increased activity in the liver, may be implicated in altered emotional behavior reactivity to stressors.

Preweaning experience as a modifier of prenatal drug effects in rats and mice--a review

The effects of preweaning experience in rats and mice on neuroendocrine and behavioral end points and their implications for prenatal drug effects are reviewed. The hypothalamo-pituitary-adrenal axis and the dopaminergic system were shown to be affected. Behavior related to hippocampal, adrenocortical functions and to the benzodiazepine receptor system was also modified. Other paradigms (nociception, conditioned taste aversion) exhibited susceptibility to such preweaning manipulations also. The effects of these early experiences seem to be mediated through complex factors including neuroendocrine responses of the pup to hypothermia and a permanent alteration of mother-infant interactions, with subsequent effects on neuroendocrine functions that are important for postnatal brain organization. Studies of interactions between prenatal drug effects and preweaning manipulations have been performed only with ethanol. When extending this work to other compounds, the systems and functions described above may provide some guidance in looking for possible interactions. In most cases the preweaning manipulations alleviated the effects of prenatal ethanol exposure. These findings may have important implications regarding the controversy about environmental influences affecting the outcome of exposure to neurobehavioral teratogens.

Inbred Roman high- and low-avoidance rats: differences in anxiety, novelty-seeking, and shuttlebox behaviors

In the present study, male inbred animals (from the 10th generation of an inbreeding program that has been carried out in parallel to that of the outbred Roman high- and low-avoidance rat lines), were compared for emotionality in different testing situations, exploratory behavior in the holeboard and two-way, active-avoidance acquisition. Compared to the inbred Roman high-avoidance (RHA-I/Verh) rats, inbred Roman low-avoidance (RLA-I-Verh) rats showed higher emotionality in the open field (reduced distance travelled and number of rearings, and increased self-grooming behavior), in the elevated plus-maze test (increased number of total and open-arm entries, reduced distance travelled in the open arms, and increased self-grooming behavior), and during the habituation period in the shuttle box (decreased number of crossings, increased self-grooming behavior and defecations). Results from the hyponeophagia test were not conclusive, probably due to the test-dependent hyperactivity shown by RHA-I/Verh rats. In the holeboard apparatus, RHA-I/Verh rats explored more than RLA-I/Verh rats, especially when novel objects were located beneath the holes. Finally, RHA-I/Verh animals rapidly acquired active, two-way (shuttlebox) avoidance, whereas RLA-I/Verh animals required four 50-trial sessions to achieve an assymptotic level of 30-40% avoidance. Thus, the behavioral patterns of the Roman inbred strains were very similar to those previously reported for the RHA/Verh outbred lines. Differences in locomotor activity, exploratory, and self-grooming behavior were actually greater between the inbred strains than between the outbred lines. Differences in defecation, however, although still significant, were not so pronounced as those noted previously at this laboratory with the outbred lines.

Prenatal stress induces high anxiety and postnatal handling induces low anxiety in adult offspring: correlation with stress-induced corticosterone secretion

It is well known that the hypothalamo-pituitary-adrenal (HPA) axis is altered by early environmental experiences, particularly in the perinatal period. This may be one mechanism by which the environment changes the physiology of the animal such that individual differences in adult adaptative capabilities, such as behavioral reactivity and memory performance, are observable. To determine the origin of these behavioral individual differences, we have investigated whether the long-term influence of prenatal and postnatal experiences on emotional and cognitive behaviors in adult rats are correlated with changes in HPA activity. To this end, prenatal stress of rat dams during the last week of gestation and postnatal daily handling of rat pups during the first 3 weeks of life were used as two environmental manipulations. The behavioral reactivity of the adult offspring in response to novelty was evaluated using four different parameters: the number of visits to different arms in a Y-maze, the distance covered in an open field, the time spent in the corners of the open field, and the time spent in the open arms of an elevated plus-maze. Cognitive performance was assessed using a water maze and a two-trial memory test. Adult prenatally stressed rats showed high anxiety-like behavior, expressed as an escape behavior to novelty correlated with high secretion of corticosterone in response to stress, whereas adult handled rats exhibited low anxiety-like behavior, expressed as high exploratory behavior correlated with low secretion of corticosterone in response to stress. On the other hand, neither prenatal stress nor handling changed spatial learning or memory performance. Taken together, these results suggest that individual differences in adult emotional status may be governed by early environmental factors; however, perinatal experiences are not effective in influencing adult memory capacity.

Early postnatal stimulation influences passive avoidance behaviour of adult rats

In this study, the effects of stimulation on either postnatal days 1 to 7 or 21 to 27 on the passive avoidance reaction (PAR) of 3-month-old rats were examined. Animals received tactile or visual stimulation or tactile-visual stimulation for 10 min each day, and were trained at the beginning of the 4th month of life in a step-through apparatus using a footshock of 0.5 mA. Memory retention was measured 24, 48, 72, 96, and 120 h after the acquisition trial. Step-through latencies to enter the dark compartment and the total duration of stay in the illuminated compartment were recorded up to 200 s. Rats that received tactile or a combined tactile-visual stimulation during the 1st postnatal week displayed significantly longer PAR latencies and a longer duration of stay in the illuminated compartment compared to unstimulated control animals. Visual stimulation during the postnatal days 1 to 7 and 21 to 27 resulted in a longer duration of stay in the illuminated compartment. This effect, however, was more pronounced when stimulation was applied during the 1st postnatal week. Rats that received tactile stimulation during the 4th postnatal week showed decreased PAR performance for all measured parameters when compared to animals that received stimulation during the 1st postnatal week. Furthermore, combined tactile-visual stimulation during the 4th postnatal week led to a reduced duration of stay in the illuminated compartment when compared to the stimulation during the 1st postnatal week. These findings can be attributed to the higher degree of plasticity and to a heightened sensitivity to various stimuli in the 1st postnatal week. The results suggest that tactile, visual or combined tactile-visual stimulation have a long-lasting effect on the ability of adult rats to cope with stressful tasks.

Early development of synchronized walking on the rotorod in rats. Effects of training and handling

There is considerable improvement of motor coordination on the rotorod during the first 3 weeks of development in rats. The purpose of the present study was to determine some factors implicated in this improvement. From days 15-22 of age, rats were: (1) extensively trained on the rotorod; (2) minimally trained on the rotorod; (3) handled daily but not trained on the rotorod; and (4) neither handled nor trained. All animals were tested on the rotorod on day 23, with separate groups of the naive rats also being tested on days, 19, 20, 21 or 22. Latencies before falling and the percentage of time spent walking in time to the movement of the rotating rod were recorded. There was a close correspondence between these two scores during ontogeny. The percentage of time spent walking was similar among extensively trained, minimally trained, and handled rats and significantly higher than that measured in rats tested only on 1 day. These results indicate that the emergence of this postural sensorimotor skill is more dependent on the maturation of sensorimotor brain region than on previous training on the apparatus.

Neonatal handling reduces emotional reactivity and susceptibility to learned helplessness. Involvement of catecholaminergic systems

Environmental circumstances during the neonatal period are critical for the establishment of adult responses to stressful environmental situations. As these responses are underpinned by adaptations in the functioning of brain neurotransmitter systems, the present study was designed to assess the mediation of noradrenergic and dopaminergic systems in the long-lasting effects of neonatal handling on both emotionality and learned helplessness behaviour. Animals received either prazosin, propranolol, haloperidol or saline before infantile handling. When the animals were 2 months old, they were subjected first to an open field test and then to the learned helplessness paradigm. Non-treated handled animals exhibited lower emotional reactivity and reduced susceptibility to helplessness compared to non-treated non-handled rats. The results suggest that noradrenergic, but not D2-dopamine receptor systems mediate the influence of neonatal handling on the acquisition of learned helplessness in the adult. Only beta-adrenoceptors appear to play a role in emotional responsiveness.

Effects of electrolytic lesions of the medial prefrontal cortex or its subfields on 4-arm baited, 8-arm radial maze, two-way active avoidance and conditioned fear tasks in the rat

The present study tested the effects of electrolytic lesions in two mPFC subregions, the dorsal anterior cingulate area (dACA) and prelimbic cortex, as well as the effects of a larger medial prefrontal cortex (mPFC) lesion which included both subregions, on 4-arm baited, 4-arm unbaited, 8-arm radial maze task and its reversal (Experiments 1 and 4), two-way active avoidance (Experiments 2 and 5) and conditioned emotional response (Experiments 3 and 6). Rats with large or small lesions of the mPFC learned the location of the 4 baited arms in the training and reversal stages of the radial maze task similarly to sham rats, indicating that these lesions did not affect animals' capacity to process and remember spatial information. dACA and mPFC lesions produced a transient deficit in the acquisition of the radial maze task, suggestive of an involvement of these regions in mnemonic processes. However, in view of the normal performance of these groups by the end of training and during reversal, this deficit is better interpreted as stemming from a difficulty to learn the memory-based strategy used to solve the task. Only mPFC lesion led to better avoidance performance at the beginning of training and tended to increase response during the presentation of a stimulus previously paired with shock, compared to sham rats. Both effects can be taken as an indication of reduced emotionality following mPFC lesion. The results are discussed in relation to known behavioral functions of the mPFC and the suggested functional specialization within this region.

Effects of postnatal stimulation on the passive avoidance behaviour of young rats

We examined the effects of stimulation on either postnatal days 1-7 or 21-27 on passive avoidance reaction (PAR) of young rats. Animals received tactile or visual stimulation for 10 min each day, and were trained on postnatal day 28 in a step-through apparatus using a footshock of 0.75 mA for 2 s. Retention was tested on five consecutive days beginning on day 29. Memory retention was measured for each rat 24, 48, 72, 96 and 120 h after the acquisition trial. Step-through latencies to enter the dark compartment, time spent in the illuminated compartment and number of crossings of the light beam were recorded up to 200 s. Rats that received tactile or visual stimulation during the 4th postnatal week displayed significantly lower PAR latencies, a shorter stay in the illuminated compartment and a higher number of crossings of the light beam compared to rats treated during the 1st postnatal week. The untreated control group showed a rapid decline of PAR latencies. All experimental groups remained in the illuminated compartment longer and showed PAR latencies well above those of the control group. The differences became more pronounced when visual stimulation in the first postnatal week was used. The number of crossings of the light beam was significantly reduced by the treatment, with the exception of the experimental group stimulated visually in the 4th week. The behavioural changes induced by tactile or visual stimulation have a long-lasting effect in coping with a stressful task.

Effect of neonatal handling on learned helplessness model of depression

The present study was undertaken to investigate the effects of neonatal handling on learned helplessness (LH) model of depression in the rat. We also investigated the effect of neonatal handling on behavior in an open field test of emotionality. The handling procedure reduced helplessness behavior, with a decrease in the number of escape failures, an increase in the number of avoidance responses, and a decrease in the escape latency in the shuttle-box after induction of LH. In addition, handling during infancy decreased the number of boli in an open field test, which suggests that the level of emotivity in adulthood was reduced. It is suggested that handling in infancy improves behavioral adaptation to the environment, including enhanced adaptive response to stress.

Environmental enrichment and postnatal handling prevent spatial learning deficits in aged hypoemotional (Roman high-avoidance) and hyperemotional (Roman low-avoidance) rats

The present study investigated the enduring effects of postnatal handling (administered during the first 21 days of life), and environmental enrichment (for a period of 6 months starting 3 weeks after weaning) on spatial learning in 24-month-old hypoemotional (Roman high-avoidance, RHA/Verh) and hyperemotional (Roman low-avoidance, RLA/Verh) rats. Two groups of 5-month-old rats from both lines were also included in the experiment as young controls. The Roman lines performed differently in the Morris water maze: Path lengths of RLA/Verh rats were shorter and they swam at lower speed than RHA/Verh rats, showing quicker and more efficient learning overall. Postnatal handling improved learning mainly in RHA/Verh rats, whereas environmental enrichment was able to prevent the deficits shown by aged controls of both lines. Young, enriched, and handled plus enriched animals exhibited better performance than impaired aged controls, to the point that aged enriched and handled plus enriched animals did not differ from young controls. Thus, besides indicating that RLA/Verh rats are better learners than RHA/Verh rats in the Morris water maze, this study demonstrates that environmental enrichment prevents the cognitive loss associated with aging, over the long term. Finally, the positive effects obtained with postnatal handling were dependent on the rat line.

Evaluating activity and emotional reactivity in a hexagonal tunnel maze: correlational and factorial analysis from a study with the Roman/Verh rat lines

Two hundred forty 30-day-old Roman high- and low-avoidance (RHA/Verh and RLA/Verh) rats (divided equally by line and gender) which had received several peri- and/or postnatal treatments, forming two factorial [line x sex x treatment(s)] experimental designs, were tested in a hexagonal tunnel maze including a brightly illuminated central arena. The present study reports the results of correlational and factorial (principal-components) analyses performed on the data from those two experimental constituencies. The purpose of the study was to evaluate the validity of the hexagonal tunnel maze for testing emotionality, and therefore, the following measures were included in the analysis: entries into the central illuminated arena, total activity during testing, defecation during testing, and defecation during handling and weighing after testing. An overall pattern of negative correlations (or opposite loadings in the principal-components analyses) between defecation (especially during maze testing) and entries into the illuminated center and activity was found, thus giving support to the validity of entries into the illuminated center as being indicative of emotional reactivity.

Maturation of the behavioral and neuroendocrine differences between the Roman rat lines

The behavioral and/or neuroendocrine reactivity to psychological (open-field exposure) and physiological (CRF challenge) stimulations, as well as adrenal tyrosine hydroxylase (TH) and phenylethanolamine N-methyl transferase (PNMT) activities were measured, at different ages, in the Roman high avoidance (RHA) and Roman low avoidance (RLA) rat lines that have been genetically selected on the basis of their divergent active avoidance behavior. The highest locomotor activity in the open field, associated to blunted prolactin and renin reactivity to an emotional stress and lower specific TH and PNMT activities, characterized the RHA rats of all ages. HPA axis reactivity to psychological and/or physiological stimulations was identical in young animals (14 weeks old) of the two lines. Nevertheless, it displayed with age maturation processes, since the amplitude of postopen-field secretion peak for ACTH was larger in RLA rats from 20 weeks on, the response to CRF being not increased until 42 weeks. These maturation processes could result from genetically influenced changes related to environmental stimulations. Therefore, the Roman lines may be an excellent model to study the interactions between the genetic and developmental factors controlling the coupling between both behavioral and neuroendocrine functions.

Postnatal handling, perinatal flumazenil, and adult behavior of the Roman rat lines

The effect of infantile handling stimulation and/or perinatal flumazenil (Ro 15-1788; a benzodiazepine receptor antagonist; 3.7 mg/kg/day) administration on exploratory and emotional-related behavior was investigated using adult females from the Roman high- and low-avoidance (RHA/Verh and RLA/Verh) lines. When rats (6 months old) were exposed to a hexagonal tunnel maze including an illuminated central arena, it was found that RHA/Verh rats were more active, explored more maze area, showed more outward preference, and more frequently entered the illuminated center than RLA/Verh rats. In addition, postnatal stimulation decreased emotional-related behavior in both lines of rats, as expressed by increased entry into, and time spent in, the central arena. Perinatal flumazenil treatment decreased entry into the maze central arena in both rat lines but this effect was counteracted by postnatal (handling) stimulation. Thus, the present study extends to adult RHA/Verh and RLA/Verh rats the positive long-lasting effects of postnatal handling and shows postnatal handling x flumazenil interactions in some behavioral parameters related to the pattern of exploration and exploratory efficiency.