Stress in Neonatal Rats with Different Maternal Care Backgrounds: Monoaminergic and Hormonal Responses

Abstract

The first 2 weeks of life in rats are known as the stress hyporesponsive period because stress responses in pups are diminished as compared to adult animals. However, it is considered a critical period in development in which infant rats are susceptible to environmental events, such as stressful stimuli and quality of maternal care received. These early life events have long-lasting effects, shaping a variety of outcomes, such as stress responsivity. This study investigated the effects of maternal care and sex differences on the response to an aversive stimulus in rat pups from high (HL) and low licking (LL) mothers. Plasma corticosterone, oxytocin (OT), and central monoaminergic activity in 13-day-old rats submitted to cold stress were analyzed. Stress increased plasma corticosterone and marginally decreased hypothalamic dihydroxyphenylacetic acid/dopamine ratio. HL pups showed higher levels of plasma OT than LL pups. The maternal effect was also detected in the hippocampus, in which 5-hydroxyindole-3-acetic acid/serotonin ratio was increased in HL pups, independently of the sex and stress. Investigating the early life events is useful not only into understand the neurobiological and hormonal mechanisms underlying maternal and stressful influences on infant development into a healthy or psychopathological adult phenotype, but also to unveil the immediate outcomes on infancy.

Early adverse experience and substance addiction: dopamine, oxytocin, and glucocorticoid pathways

“…Altered OT levels have been documented in rodents exposed to low levels of naturally occurring maternal care or experimentally induced early separation . These effects have been observed in specific OT‐innervated brain regions, such as the HYP or AMY, as well as in the plasma .…”

“…Altered OT levels have been documented in rodents exposed to low levels of naturally occurring maternal care or experimentally induced early separation . These effects have been observed in specific OT‐innervated brain regions, such as the HYP or AMY, as well as in the plasma . Observed changes are generally in the direction of blunted OT levels in those exposed to early adversity, although it has been proposed that prolonged exposure may lead to a rise in OT levels as a way of protecting the system from the deleterious effects of stress .…”

“…70 These effects have been observed in specific OT-innervated brain regions, such as the HYP or AMY, 70,71 as well as in the plasma. 69 Observed changes are generally in the direction of blunted OT levels in those exposed to early adversity, although it has been proposed that prolonged exposure may lead to a rise in OT levels as a way of protecting the system from the deleterious effects of stress. 72,73 While studies involving primates are more sparse, rhesus monkeys reared in nurseries show reduced levels of cerebrospinal fluid (CSF) OT compared with those reared by their mothers, 74 paralleling results from rodent models.…”

Early Social Environment Affects the Endogenous Oxytocin System: A Review and Future Directions

“…Additionally, quality of maternal behavior has been linked to differences in oxytocin concentrations and OXTR expression observed in animal models ( 9 , 36 ). For example, high levels of maternal licking resulted in increased plasma oxytocin concentrations in neonatal rats ( 37 ). Furthermore, Kojima and colleagues ( 38 ) found that maternal skin-to-skin contact stimulates rat pups’ central oxytocin concentrations.…”

Early life social stress induced changes in depression and anxiety associated neural pathways which are correlated with impaired maternal care

“…OXT, AVP, and PRL are primary mediators of maternal care and have been implicated in the etiology and symptomology of stress related affective disorders (Faron-Górecka et al, 2014; Insel and Young, 2001; Mann and Bridges, 2001; Nephew, 2012; Rilling and Young, 2014; Zamorano et al, 2014). Furthermore, OXT is a key mediator of the reciprocal nature of the mother-infant bond (Carter, 2003; Feldman et al, 2011; Feldman et al, 2007; Henriques et al, 2014; MacKinnon et al, 2014; Mogi et al, 2011). The current study investigated additional neural targets that may be involved in the adverse effects of ECSS on the F1 generation and represent novel preventative and/or treatment targets.…”