Maternal separation affects expression of stress response genes and increases vulnerability to ethanol consumption

Abstract

IntroductionMaternal separation is an early life stress event associated with behavioral alterations and ethanol consumption. We aimed to expand the current understanding on the molecular mechanisms mediating the impact of postnatal stress on ethanol consumption.MethodsIn the first experiment (T1), some of the pups were separated from their mothers for 6 hr daily (Maternal Separation group ‐ MS), whereas the other pups remained in the cage with their respective mothers (Control group ‐ C). In the second experiment (T2), mice from both groups were subjected to the model of free‐choice between water and sucrose solution or between water and ethanol solution. Maternal behavior was assessed at the end of T1. At the end of both T1 and T2, pups were subjected to the light/dark box behavioral test and blood corticosterone concentrations were analyzed.ResultsOur maternal separation protocol led to intense maternal care and affected weight gain of the animals. The expression of stress response genes was altered with higher levels of Crh and Pomc being observed in the hypothalamus, and higher levels of Crhr1, Crhr2, Htr2a and lower levels of Nr3c1 and Htr1a being observed in the hippocampus after T1. At the end of T2, we observed higher levels of Avp and Pomc in the hypothalamus, and higher levels of Crhr1, Crhr2, Nr3c1, Slc6a4, Bdnf and lower levels of Htr1a in the hippocampus. Additionally, maternal separation increased vulnerability to ethanol consumption during adolescence and induced changes in anxiety/stress‐related behavior after T2. Furthermore, voluntary ethanol consumption attenuated stress response and modified expression of reward system genes: enhancing Drd1 and Drd2, and reducing Gabbr2 in the striatum.ConclusionMaternal separation induced behavioral changes and alterations in the expression of key genes involved in HPA axis and in the serotonergic and reward systems that are likely to increase vulnerability to ethanol consumption in adolescence. We demonstrated, for the first time, that ethanol consumption masked stress response by reducing the activity of the HPA axis and the serotonergic system, therefore, suggesting that adolescent mice from the MS group probably consumed ethanol for stress relieving purposes.

Effects of Early-Life Stress on the Brain and Behaviors: Implications of Early Maternal Separation in Rodents

“…Furthermore, ethanol consumption is affected by dopaminergic neurons in the VTA projecting to the NAc, which alters GABAergic transmission. Several studies have reported that MS increases pup vulnerability to ethanol during adolescence, inducing an increase in ethanol consumption [ 83 , 84 ]. These findings mirror the phenomena in humans who suffer child abuse and neglect in early life, showing higher morbidity of drug abuse and alcoholism.…”

An improved light dark box test by using a real-time video tracking system

“…Among reports it is evident that, while performing LDB test, light chamber parameters have been considered over the dark box parameters [6]. As a result, distance travelled in the dark chamber, total distance travelled in the apparatus, and other behaviors were not taken into consideration (in fact it remained unknown at least in some experiments) when this test was conducted manually [17,21,39,44]. Many a times, researchers have to perform additional tests to get an idea about animal locomotion even after conducting LDB test.…”

“…Sarwar et al [42] has conducted the test by videotaping the rat behavior in the apparatus, but rat's activity in the dark compartment has not been reported. Although these reports demonstrated the use of technology for conducting LBD test, in some of the very recent reports it can be observed that this test has been performed entirely manually [17,21,39,44]. These methodological variations make it difficult to replicate or compare the results different laboratories.…”

“…There is no consensus in the literature regarding the initial release of animal into light/dark chamber [23,28]. In some studies, it has been reported that the rat was placed initially into the light chamber [2,44] and in some others into the dark first [17,22]. Placing rat first in the dark chamber will enable the experimenter to record latency to enter the light, and this can be used as a measure of anxiety.…”

Neuroendocrine and immune pathways from pre- and perinatal stress to substance abuse

“…A rodent study on postnatal maternal separation found that offspring demonstrated increased vulnerability to ethanol consumption during adolescence with enhanced expression of key genes associated with HPA axis functioning ( de Almeida Magalhães, Correia, de Carvalho, Damasceno and Brunialti Godard, 2017 ). A separate rodent study found that maternally separated offspring demonstrated a strong preference for ethanol, elevations in ACTH and corticosterone during a lab stressor, and that the ethanol consumption was correlated with the stress response ( Huot et al, 2001 ).…”