172 They could constitute the basis of a nongenetic mechanism for the transmission of individual differences in stress reactivity and coping styles across generations. In 1958, Levine reported that rats handled for the
first 21 days of life exhibit reduced fearfulness compared with nonhandled controls. Since then, several studies have shown the beneficial effects of neonatal handling and a progressive habituation to stress on adults’ stress responses and anxiety-related behaviors. Neonatal handling can even reverse the behavioral abnormalities induced by prenatal stress.173 These effects appear to be mediated essentially by the CRF/HPA axis system,174,175 although the serotonergic and catecholaminergic Inhibitors,research,lifescience,medical systems could be also Inhibitors,research,lifescience,medical involved.176,177 A study has shown that neonatal
handling increases the expression of the peripheral benzodiazepine receptor (PBR), which has been implicated in the synthesis of endogenous, natural anxiolytic agents such as the neurosteroids, in rat adrenals, kidney, and gonads.178 It is likely that increased adrenal production of naturally anxiolytic compounds such as allopregnanolone contributed to the decrease in anxiety reported in this study. Sex differences in the effects of neonatal handling have been recently reported: Inhibitors,research,lifescience,medical neonatal handling may provide males with a greater capacity to actively face chronic stressors.179 Recent data indicate that neonatal handling can also affect memory processes involved in contextual fear conditioning.180 In the Roman rat lines, neonatal handling has been shown Inhibitors,research,lifescience,medical to alter the behavioral phenotype of the more anxious RLA/Verh rats so that, in adulthood, they behave in the same way as their nonhandled, hypoemotional RHA/Verh counterparts. Females were found to be more sensitive than males to the positive influences of early stimulation.181 The effects of neonatal handling on RLA/Verh Inhibitors,research,lifescience,medical rats were not limited to behavioral stress responses and coping behaviors, but were accompanied
by a concomitant decrease in stress-induced ACTH, corticosterone, and prolactin release, indicating that the neurochemical substrates GSK2656157 underlying these responses were also permanently affected by early experience.182,183 This and other examples indicate that the developmental processes that determine individual sensitivity to stressors, Sodium butyrate or emotionality, and coping behaviors involve complex interactions between genetic and environmental factors, and that anxiety-related phenotypes cannot be predicted on the sole basis of a genetic predisposition or early adverse experience. Conclusions The biological bases of fear and anxiety are now recognized, and the major brain structures and neuronal circuits involved in emotional information processing and behavior are delineated. Emotional and cognitive processes cannot be dissociated, even when considering such a basic emotion as fear.
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