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Neuroplasticity of the hypothalamic–pituitary–adrenal (HPA) axis early in life requires recurrent recruitment of stress-regulating brain regions

Department of Anatomy and Neurobiology, University of California, Irvine, Irvine, California, United States
The Journal of Neuroscience : The Official Journal of the Society for Neuroscience (Impact Factor: 6.75). 04/2006; 26(9):2434-42. DOI: 10.1523/JNEUROSCI.4080-05.2006
Source: PubMed

ABSTRACT An eloquent example of experience-induced neuroplasticity involves the enduring effects of daily "handling" of rat pups on the expression of genes regulating hormonal and behavioral responses to stress. Handling-evoked augmentation of maternal care of pups induces long-lasting reduction of hypothalamic corticotropin releasing hormone (CRH) expression and upregulates hippocampal glucocorticoid receptor levels. These changes promote a lifelong attenuation of hormonal stress responses. We have found previously that handling-evoked downregulation of CRH expression occurs already by postnatal day 9, implicating it as an early step in this experience-induced neuroplasticity. Here, we investigated the neuronal pathways and cellular mechanisms involved. CRH mRNA expression in hypothalamic paraventricular nucleus (PVN) diminished after daily handling but not after handling once only, indicating that "recurrent" handling was required for this effect. Return of handled pups to their cage provoked a burst of nurturing behavior in dams that, in turn, induced transient, coordinate Fos expression in selected regions of the pups' brains. These included central nucleus of the amygdala (ACe) and bed nucleus of the stria terminals (BnST), regions that are afferent to PVN and influence CRH expression there. Whereas handling once sufficed to evoke Fos expression within ACe and BnST, expression in thalamic paraventricular nucleus, a region involved in storing and processing stress-related experience, required recurrent handling. Fos induction in all three regions elicited reduced transcription factor phosphorylation, followed by attenuated activation of CRH gene transcription within the PVN. These studies provide a neurobiological foundation for the profound neuroplasticity of stress-related genes evoked by early-life experience.

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Available from: Yuncai Chen, Jun 05, 2015
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    • "The effects of neonatal handling on the HPA axis and the stress response have been widely described (Pryce & Feldon, 2003; Meerlo et al., 1999; Fenoglio et al., 2006; Panagiotaropoulos et al., 2004; Meaney et al., 1991; Severino et al., 2004). "
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    ABSTRACT: During the postnatal period, the nervous system is modified and shaped by experience, in order to adjust it to the particular environment in which the animal will live. This plasticity, one of the most remarkable characteristics of the nervous system, promotes adaptive changes, but it also makes brain more vulnerable to insults. This chapter will focus on the effects of interventions during the postnatal development in animal models of neonatal handling (usually up to 15 min of handling) and maternal separation (usually at least for 3 h). Sex-specific changes and effects of prepubertal stress such as social isolation later on in life were also considered. These interventions during development induce long-lasting traces in the pups' nervous system, which will be reflected in changes in neuroendocrine functions, including the hypothalamus-pituitary-adrenal and hypothalamus-pituitary-gonadal axes; anxiety and cognitive performance; and feeding, sexual, and social behavior. These enduring changes may be adaptive or maladaptive, depending on the environment in which the animal will live. The challenge researchers facing now is to determine how to reverse the deleterious effects that may result from early-life stress exposure.
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    • "It should be noted that, in Experiments 2 and 3, the drug injection procedure may potentially influence maternal behavior and thus the levels of synaptic proteins in the hippocampus . Although we limited the duration of injection to <15 min per litter, brief daily separation of the pups from the mother (early handling) has been shown to stimulate maternal care (Liu et al., 1997; Fenoglio et al., 2006b) and enhance hippocampal function of the offspring (Tang, 2001; Fenoglio et al., 2005). Because maternal behavior was not assessed in this study, the possibility that our manipulations affect maternal behavior, which in turn alters hippocampal synaptic protein levels, cannot be completely excluded. "
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    • "Experiments also explored the resulting changes (plasticity) of the hypothalamic CRF neuron. Because the CRF neuron is a component of a neuronal network activated by maternal care (Fenoglio et al., 2006a), we examined if its neuroplasticity consisted of altered excitatory and/or inhibitory synaptic input. These changes, in turn, may provoke repression of the crf gene. "
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    ABSTRACT: Stress is among the strongest signals promoting neuroplasticity: Stress signals, indicating real or perceived danger, lead to alterations of neuronal function and often structure, designed to adapt to the changed conditions and promote survival. Corticotropin releasing factor (CRF) is expressed and released in several types of neuronal populations that are involved in cognition, emotion and the regulation of autonomic and endocrine function. CRF expressing neurons undergo functional and structural plasticity during stress and, in addition, the peptide acts via specific receptors to promote plasticity of target neurons.
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