Correlation between Changes in Stress-Induced Corticosterone Secretion and GR mRNA Levels

The current study was conducted to determine the potential relationship between stress-induced corticosterone secretion and corticosteroid receptor mRNA levels after 5 days of intermittent stress. In particular, we were interested in the rate at which animals terminate a stress response, and how this termination may be altered by repeated stress. Adult male Sprague-Dawley rats were subjected to either 5 days of restraint stress or 5 days of an unpredictable stress paradigm. Restraint-stress induced corticosterone secretion was measured on Days 1 and 5 in both groups, and animals were killed on Day 6. Glucocorticoid receptor (GR), and mineralocorticoid (MR) mRNA levels were determined using in-situ hybridization techniques. Five days of restraint stress caused an habituation of the plasma corticosterone response to stress measured 60 and 90 min post-stress initiation; this pattern of corticosterone secretion was not observed in the animals subjected to unpredictable stress. Five days of either stress paradigm did not alter MR mRNA levels measured within the hippocampus or GR mRNA levels within the hippocampus or the medial parvocellular division of the paraventricular nucleus of the hypothalamus (mpPVN). However, an individual's GR mRNA levels measured within the CA1/2 region of the hippocampus and the mpPVN were significantly correlated with the degree of habituation of the corticosterone response to stress measured on Day 5. This suggests that an increase in the rate of termination of the stress response and levels of GR within the hippocampus and mpPVN may be functionally related.     

The Association between Positive Parenting and Externalizing Behavior

The present study examined the role of positive parenting on externalizing behaviors in a longitudinal, genetically informative sample. It often is assumed that positive parenting prevents behavior problems in children via an environmentally mediated process. Alternatively, the association may be due to either an evocative gene-environment correlation, in which parents react to children's genetically-influenced behavior in a positive way, or a passive gene-environment correlation, where parents passively transmit a risk environment and the genetic risk factor for the behavioral outcome to their children. The present study estimated the contribution of these processes in the association between positive parenting and children's externalizing behavior. Positive parenting was assessed via observations at ages 7, 9, 14, 24, and 36 months and externalizing behaviors were assessed through parent report at ages 4, 5, 7, 9, 10, 11, and 12 years. The significant association between positive parenting and externalizing behavior was negative, with children of mothers who showed significantly more positive parenting during toddlerhood having lower levels of externalizing behavior in childhood; however, there was not adequate power to distinguish whether this covariation was due to genetic, shared environmental, or nonshared environmental influences.     

Structure and Etiology of Co-occurring Internalizing and Externalizing Disorders in Adolescents

Several studies suggest that a two-factor model positing internalizing and externalizing factors explains the interrelationships among psychiatric disorders. However, it is unclear whether the covariation between internalizing and externalizing disorders is due to common genetic or environmental influences. We examined whether a model positing two latent factors, internalizing and externalizing, explained the interrelationships among six psychiatric disorders (major depressive disorder, generalized anxiety disorder, separation anxiety disorder, attention-deficit/hyperactivity disorder, oppositional defiant disorder, and conduct disorder) in adolescents, and whether there are common genetic and environmental influences on internalizing and externalizing latent factors. Multivariate behavior genetic analyses of data from 1162 twin pairs and 426 siblings ascertained from the general population via the Colorado Center for Antisocial Drug Dependence (CADD) were conducted. We found support for a model positing two latent factors (internalizing and externalizing). These factors were moderately heritable and influenced by significant common genetic and nonshared environmental influences. These findings suggest that co-occurrence of internalizing and externalizing psychopathology in adolescents results from both genetic and environmental influences.