Selection for contextual fear conditioning affects anxiety‐like behaviors and gene expression

Abstract

Conditioned fear and anxiety-like behaviors have many similarities at the neuroanatomical and pharmacological levels, but their genetic relationship is less well defined. We used short-term selection for contextual fear conditioning (FC) to produce outbred mouse lines with robust genetic differences in FC. The high and low selected lines showed differences in fear learning that were stable across various training parameters and were not secondary to differences in sensitivity to the unconditioned stimulus (foot shock). They also showed a divergence in fear potentiated startle, indicating that differences induced by selection generalized to another measure of fear learning. However, there were no differences in performance in a Pavlovian approach conditioning task or the Morris water maze, indicating no change in general learning ability. The high fear learning line showed greater anxiety-like behavior in the open field and zero maze, confirming a genetic relationship between FC and anxiety-like behavior. Gene expression analysis of the amygdala and hippocampus identified genes that were differentially expressed between the two lines. Quantitative trait locus (QTL) analysis identified several chromosomal regions that may underlie the behavioral response to selection; cis-acting expression QTL were identified in some of these regions, possibly identifying genes that underlie these behavioral QTL. These studies support the validity of a broad genetic construct that includes both learned fear and anxiety and provides a basis for further studies aimed at gene identification.

Rapid Selection Response for Contextual Fear Conditioning in a Cross Between C57BL/6J and A/J: Behavioral, QTL and Gene Expression Analysis

“…Fear conditioning procedures were identical to those described previously in Ponder et al (2007a). Fear conditioning chambers obtained from Med Associates (St. Albans, VT) had inside dimensions of 29 cm × 19 cm × 25 cm with metal walls on each side, clear plastic front and back walls and ceilings, and stainless steel bars on the floor.…”

“…Procedures for mass selection to create STSL are described in Ponder et al (2007a). The foundation population was an F 1 cross between C57BL/6J (B6) females and A/J (AJ) male mice obtained from The Jackson Laboratory (Bar Harbor, ME).…”

“…Two-thirds of the mice in this study were male and only one-third were female, this was a result of availability, this ratio was uniform across treatment groups and lines; none of our analyses detected main effects or interactions involving sex. The protocol and apparatus are similar to those that have been described previously (Ponder et al 2007a). On day 1 mice from each line (low or high) were randomly presented with one of three training sessions.…”

“…In particular, there is a positive relationship between fear learning as measured in a laboratory setting and anxiety in humans (Lissek et al 2005), suggesting that fear learning provides a means of probing the activity of brain circuits related to anxiety. In an effort to identify the genetic basis of emotionality in mice, a number of previous studies have examined fear learning (Caldarone et al 1997;Gershenfeld and Paul 1997;Owen et al 1997;Ponder et al 2007aPonder et al , 2007bRadcliffe et al 2000;Talbot et al 2003). …”

“…Short-term selected lines (STSL) are thus particularly well suited to assess correlated phenotypes and can be used to directly address questions about the nature of the selected phenotypic difference (Phillips et al 2002). We and others have previously used short-term selection to produce reliable differences in fear conditioning in a cross between C57BL/6J and DBA/2J (Ponder et al 2007a;Radcliffe et al 2000). In the present study we created an STSL for contextual fear conditioning based on an F 2 cross between C57BL/6J (B6) and A/J (AJ) mice.…”