Evolution proposes and ontogeny disposes

The Influence of Pre- and Postnatal Factors on Early Behavior Formation

The maternal impact on the early behavioral responses in pups was studied in cross-fostering experiments with the newborn Wistar rats (the primiparous females were fostering the pups born to the females parturiated for the second time and vise versa). The maternal experience had a significant influence on the function development in both pre- and postnatal periods. Specific features of prenatal ontogeny of pups born by experienced females resulted in further, more stable development of the early behavioral responses. In the postnatal period, the maternal experience determined synchronization of the behavioral responses, which promoted the formation of the functional systems important for the newborn survival.

[A new chapter in the field of memory: hippocampal neo-neurogenesis]

The dogma according to which "once the development of the central nervous system ended, generation of neurons was impossible" has been challenged by the discovery that new neurons are created in specific regions of the adult mammalian brain. This discovery has been one of the most controversial of modern neuroscience. One of these regions is the dentate gyrus of the hippocampal formation, a key structure in memory. Here we will review our current knowledge on the role of adult hippocampal neurogenesis in memory and in the pathophysiology of memory. In particular we will review evidence showing that adult-born neurons are required for learning and memory and that an alteration of their production rate leads to memory impairments. We also discuss how neurogenesis is finely shaped by learning for the purpose of mnemonic information processing.

Postnatal stimulation of the pups counteracts prenatal stress-induced deficits in hippocampal neurogenesis

BACKGROUND

Prenatal stress constitutes a developmental risk factor for later psychopathology. The behavioral disorders are sustained by neurobiological alterations including long-term reduction of hippocampal neurogenesis; its deregulation has been involved in cognitive impairments, mood disorders and addiction. A major goal is to define periods in development and strategies for intervening to prevent the effects of early stressful events. We investigated the ability of a postnatal infantile stimulation to prevent prenatal stress-induced alteration in hippocampal neurogenesis.

METHODS

The influence of postnatal handling on prenatal stress-induced changes in hippocampal neurogenesis was examined in 4 and 26 month-old male rats. Three distinct phases of the neurogenesis were studied: proliferation, survival and neuronal differentiation.

RESULTS

Prenatal stress reduced hippocampal cell proliferation all throughout life. Furthermore, the survival rate of newborn cells, the number of immature neurons and the number of differentiated new neurons were reduced in young and old prenatally-stressed rats. All those deleterious effects were counteracted by neonatal handling.

CONCLUSIONS

These data show that finer aspects of brain shaping can be rewired by environmental influences occurring at sensitive phase of development. They also suggest that infantile stimulation may reverse the appearance of behavioral disorders induced by early life stress.

Development and evolution of hidden regulators: Selective breeding for an infantile phenotype

Mother-infant separation in the rat has been used as an analytical tool to reveal biosocial processes underlying infant physiology and behavior. The same strategy has guided a project in which selective breeding for an infantile behavior has provided insights into how biological systems become recruited and integrated as expressions of temperamental affective responses. Two lines of rats (High and Low USV lines) were selectively bred based on rates of USV emission to maternal separation and isolation at postnatal day (P) 10. After many generations of breeding, the High and Low lines show widespread and distinctly different profiles of physiology and behavior in the first 3 weeks of life. Insights gained from longitudinal studies suggest that selection may work by reorganizing developmental processes, not just a given trait, over the postnatal period. As animal models, the lines have the potential to provide valuable tools for understanding developmental mechanisms underlying genetic and developmental risk for depression/anxiety syndromes in children and adults.

Life history and the early origins of health differentials

Current epidemiologic models concerning the fetal origins of later health risk are evaluated from the perspectives of evolutionary and developmental biology. Claims of adaptive value for and biological status of fetal programming are critically examined. Life history theory is applied to identify key trade-offs in adaptive strategies that constrain developmental design to use information from the environment to guide ontogeny and establish cost-benefit trade-offs that weigh early survival advantage against remote or unlikely future costs. Expectable environments of evolutionary adaptedness, particularly of gestation, are characterized and their impact on human adaptive design discussed. The roles of neuroendocrine mechanisms in scaffolding life course development, negotiating ongoing cost-benefit trade-offs, and mediating their long-term impacts on function and health are reviewed in detail. Overviews of gestational biology and the postnatal physiologic, cognitive-affective, and behavioral effects of gestational stress identify a shared central role for the hypothalamic-pituitary-adrenal (HPA) axis. Rather than merely mediating stress responses, the axis emerges an agent of resource allocation that draws a common thread among conditions of gestation, postnatal environments, and functional and health-related outcomes. The preponderance of evolutionary and developmental analysis identifies environments as agents on both sides of the health risk equation, by influencing vulnerabilities and capacities established in early and later life course development, and determining exposures and demands encountered over the life course.

Environmentally induced long-term structural changes: cues for functional orientation and vulnerabilities

Environmental challenges profoundly modify phenotypes and disrupt inherent developmental programs both at functional and structural levels. As an example, we have studied the impact of these environmental influences on adult neurogenesis in the dentate gyrus. Neurogenesis results from an inherent program, participates to hippocampal network organization and, as a consequence, to the various functional abilities depending on this region, including memories. In preclinical studies of aging we have shown that phenotypes vulnerable to the development of spatial memory disorders are characterized by lower hippocampal neurogenesis. We have hypothesized that these interindividual variations in functional expression of neurogenesis in senescent subjects could be predicted early in life. Indeed, a behavioral response (novelty-induced locomotor reactivity) and a biological trait (hypothalamo-pituitary-adrenal axis activity), which are predictive of cognitive impairments later in life, are related to neurogenesis in young adult rats. This suggests that subjects starting off with an impaired neurogenesis, here rats that are high reactive to stress, are predisposed for the development of age-related cognitive disorders. We have further shown that these inter-individual differences result from early deleterious life events. Indeed, prenatal stress orients neurogenesis in pathological ways for the entire life, and precipitates age-related cognitive impairments. Altogether these data suggest first that hippocampal neurogenesis plays a pivotal role in environmentally-induced vulnerability to the development of pathological aging, and second that environmental challenges and life events orient structural developments, leading to different phenotypes.

Genetic basis of anxiety-like behaviour: a critical review

The way genetic and/or environmental factors influence psychiatric disorders is an enduring question in the field of human psychiatric diseases. Anxiety-related disorders provide a relevant example of how such an interaction is involved in the aetiology of a psychiatric disease. In this paper we review the literature on that subject, reporting data derived from human and rodent studies. We present in a critical way the animal models used in the studies aimed at investigating the genetic basis of anxiety, including inbred mice, selected lines, multiple marker strains, or knockout mice and review data reporting environmental components influencing anxiety-related behaviours. We conclude that anxiety is a complex behaviour, underlined not only by genetic or environmental factors but also by multiple interactions between these two factors.

The genetic basis of the pharmacological effects of anxiolytics: a review based on rodent models

Anxiolytic drugs exert their pharmacological actions by binding to molecular targets, such as benzodiazepine receptors or 5-hydroxytryptamine (5-HT) receptors. Specific genes encode these receptors, or the subunits of which they are formed. Therefore, genetic factors may influence strongly the ability of anti-anxiety agents to produce their behavioural effects. The literature on this subject is reviewed here, with emphasis on data derived from studies with rodents. We present in a critical way the animal models used in the studies aimed at investigating the genetic basis of the action of anxiolytic compounds, including inbred mice, selected lines, linkage strains or mice generated by targeted mutation. Data show that increased anxiety-like behaviour is not a predictive factor for increased sensitivity to anxiolytic treatment, and it is possible that gene deletion might not be isomorphic to pharmacological antagonism. It is suggested that the strain differences in anxiety-like behaviour may be used as a tool in assaying anxiolytic activity of new drugs.

Varying intertrial interval reveals temporally defined memory deficits and enhancements in NTAN1-deficient mice

The N-end rule is one ubiquitin-proteolytic pathway that relates the in vivo half-life of a protein to the identity of its N-terminal residue. NTAN1 deamidates N-terminal asparagine to aspartate, which is conjugated to arginine by ATE1. An N-terminal arginine-bearing substrate protein is recognized, ubiquitylated by UBR1/E3alpha, and subsequently degraded by 26S proteasomes. Previous research showed that NTAN1-deficient mice exhibited impaired long-term memory in the Lashley III maze. Therefore, a series of studies, designed to assess the role of NTAN1 in short- and intermediate-term memory processes, was undertaken. Two hundred sixty mice (126 -/-; 134 +/ +) received Lashley III maze training with intertrial intervals ranging from 2-180 min. Results indicated that inactivation of NTAN1 amidase differentially affects short-, intermediate-, and long-term memory.