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Maternal Style Selectively Shapes Amygdalar Development and Social Behavior in Rats Genetically Prone to High Anxiety

ABSTRACT: The early-life environment critically influences neurodevelopment and later psychological health. To elucidate neural and environmental elements that shape emotional behavior, we developed a rat model of individual differences in temperament and environmental reactivity. We selectively bred rats for high versus low behavioral response to novelty and found that high-reactive (bred high-responder, bHR) rats displayed greater risk-taking, impulsivity and aggression relative to low-reactive (bred low-responder, bLR) rats, which showed high levels of anxiety/depression-like behavior and certain stress vulnerability. The bHR/bLR traits are heritable, but prior work revealed bHR/bLR maternal style differences, with bLR dams showing more maternal attention than bHRs. The present study implemented a cross-fostering paradigm to examine the contribution of maternal behavior to the brain development and emotional behavior of bLR offspring. bLR offspring were reared by biological bLR mothers or fostered to a bLR or bHR mother and then evaluated to determine the effects on the developmental gene expression in the hippocampus and amygdala. Genome-wide expression profiling showed that cross-fostering bLR rats to bHR mothers shifted developmental gene expression in the amygdala (but not hippocampus). All samples were generated from Sprague-Dawley male rats selectively bred for high novelty response (HRs), low novelty response (LRs) or LRs that were crossfostered to either a LR dame or HR dame.

ORGANISM(S): Rattus norvegicus

PROVIDER: GSE88874 | GEO | 2016/10/19

SECONDARY ACCESSION(S): PRJNA349006

REPOSITORIES: GEO

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Project description:Innate differences in human temperament strongly influence how individuals cope with stress and predispose for specific types of psychopathology. The present study examines the developing brain in an animal model of temperamental differences to understand how altered neurodevelopment may engender differences in emotional reactivity that are stable throughout the animal’s life. We utilize selectively-bred High Responder (bHR) and Low Responder (bLR) rats that exhibit dramatic emotional behavior differences, with bHRs exhibiting exaggerated novelty-exploration, aggression, impulsivity and drug self-administration, and bLRs showing marked behavioral inhibition, exaggerated anxiety- and depressive-like behavior. Using Affymetrix microarrays, we assessed bLR/bHR gene expression in the developing brain on postnatal days (P)7, 14, and 21, focusing on the hippocampus and nucleus accumbens, two regions related to emotionality and known to differ in adult bLR/bHR rats. We found dramatic bLR/bHR gene expression differences in the P7 and P14 hippocampus, with minimal differences in the nucleus accumbens. Some of the most profound differences involved genes critical for neurodevelopment and synaptogenesis. Stereological studies evaluated hippocampal structure in developing bHR/bLR pups, revealing enhanced hippocampal volume and cell proliferation in bLR animals. Finally, behavioral studies showed that the bHR/bLR behavioral phenotypes emerge very early in life, with exploratory differences apparent at P16 and anxiety differences present by P25. Together these data point to specific brain regions and critical periods when the bHR/bLR phenotypes begin to diverge, which may eventually allow us to test possible therapeutic interventions to normalize extreme phenotypes (e.g. the anxiety-prone nature of bLRs or drug addiction proclivity of bHRs). 2x2x3 factorial design with N=6 per group. Factors as follows: 1) Two selectively bred strains of rats (derived from an original Sprague Dawley population) termed High Responders (HR) and Low Responders (LR), 2) Two brain regions, Hippocampus (HPC) and Nucleus Accumbens (N.Acc), 3) Three developmental timepoints, specifically postnatal days 7 (P7), 14 (P14) and 21 (P21).

Project description:The strong pattern of comorbidity amongst psychiatric disorders is believed to be generated by a spectrum of latent liability, arising from a complex interplay of genetic risk and environmental factors, such as stress and childhood adversity. At one end of this spectrum are internalizing disorders, which are associated with neuroticism, anxiety, and depression. At the other end of the spectrum are externalizing disorders, which are associated with risk-taking and novelty-seeking, as seen in mania, substance abuse, and impulse-control disorders. We model the genetic contributions underlying both extremes of this spectrum by selectively breeding rats that react differently to a novel environment. “Bred high responder” (bHR) rats are highly exploratory with a disinhibited, novelty-seeking temperament, including hyperactivity, aggression, and drug-seeking. “Bred low responder” (bLR) rats are highly-inhibited, exhibiting reduced locomotor activity and anxious and depressive-like behavior. These behavioral propensities are robust and stable, beginning early in development similar to temperament in humans. This dataset was part of a larger RNA-Sequencing study examining gene expression in the bHR/bLR hippocampus, a region critical for emotional regulation. The original study compared repeated injections of either antidepressant medication (fluoxetine or desipramine) or vehicle (VEH=1:1 saline and water) solution in bHR and bLR rats (14 days of intraperitoneal injections - P78-P92, 1 per day) under either standard laboratory housing conditions or chronic variable stress. This upload includes only the data from the control subjects: generation F43 adult male bHR VEH rats and bLR VEH rats housed in standard conditions (n=5/group). Prior to sacrifice, at age P92, the rats underwent social interaction testing after 15 minutes of exposure to an anxiogenic environment (the elevated plus maze). The results from the social interaction testing are provided here along with the gene expression data.

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Maternal Style Selectively Shapes Amygdalar Development and Social Behavior in Rats Genetically Prone to High Anxiety

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