Hippocampal RNA-Seq Data and Behavioral Data from an F2 intercross of Rats Selectively-Bred to Show High or Low Levels of Locomotor Activity in a Novel Environment (bred High Responders vs. bred Low Responders)
Using selective breeding, we have produced two rat lines with highly contrasting heritable behaviors: bred Low Responders (bLR) are extremely inhibited and anxious in a novel environment, whereas bred High Responders (bHR) are exploratory and sensation-seeking. These traits map onto temperamental extremes predictive of internalizing vs. externalizing psychiatric disorders in humans and can model two divergent paths to drug abuse. To elucidate gene expression underlying these behavioral extremes, bHRxbLR were bred to produce a F0-F1-F2 cross. We then measured exploratory locomotion, anxiety-like behavior, and sensitivity to reward cues (Pavlovian Conditioned Approach) and performed hippocampal RNA sequencing in both F0s (n=24, n=6/phenotype/sex) and F2s (n=250, n=125/sex).   The data included in this GEO upload is the data from the F2s from this experiment. Overall design: Selectively breeding rats for a high or low propensity to explore a novel environment produced the bHR and bLR lines, respectively, at the University of Michigan (Stead et al., 2006). After 37 generations, an initial set (“F0”) of bHRs and bLRs were chosen from 24 distinct families (12 bHR, 12 bLR) to cross-breed for creating 12 intercross families. Their “F1” offspring were screened for novelty-induced locomotion, and individuals with similarly high or low LocoScores were bred with each other to produce a re-emergence of diverse behavioral phenotypes in the “F2” generation. These 48 F2 litters generated 540 rats, 323 of which were phenotyped as young adults (2-4 months old). Our current study used a subset of these animals (F0: n=24, n=6/phenotype per sex; F2: n=250, n=125/sex).     Behavioral data analysis: All F0 and F2 rats were tested for locomotor activity in a novel environment (“LocoScore,” protocol: (Stead et al., 2006)). Exploratory and anxiety-related behaviors were measured on an Elevated Plus Maze (protocol: (Chitre et al., 2022)), including distance traveled (cm), time immobile (sec), and percent time in the open arms. A subset of F2s (n=209) was subsequently tested for Sign Tracking vs. Goal Tracking behavior during the last two days of a week-long Pavlovian Conditioned Approach task (protocol: (Meyer et al., 2012)) using a combined score (“PavCA Index”) summarizing behaviors indicating preference for the conditioned stimuli (lever) vs. unconditioned stimuli (food magazine).    Tissue dissection, RNA extraction, and sequencing: Adults (postnatal days 113-132) were decapitated without anesthesia and brains extracted within two minutes. For the F0s, whole HPC was immediately dissected and flash frozen. For the F2s, whole brains were flash frozen, and then later hole punches from the dorsal and ventral HPC were pooled from four hemisected coronal slabs (-2.12 to -6.04 mm Bregma; (Paxinos & Watson, 2013)) for each animal. RNA was extracted using the Qiagen RNeasy Plus Mini Kit. A NEB PolyA RNA-seq library was produced and then sequenced using a NovaSeq S4 101PE flowcell (targeting 25 million reads/sample).    The data included in this GEO upload is the data from the F2s from this experiment.